@article{chen_poblete_bagal_zhu_chang_2022, title={Anelasticity in thin-shell nanolattices}, volume={119}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2201589119}, abstractNote={Significance In this work, the time-dependent deformation and recovery of the nanolattices is measured by a nanoindentation system. The Finite element analysis (FEA) with a defect diffusion model is employed to numerically predict the anelastic behavior of the nanolattices and the results agree reasonably well with the experiments. FEA reveals the role of point defect diffusion induced anelasticity in the time-dependent deformation and recovery in nanolattice structures. The indentation induces bending of the tubular structures, which results in a stress gradient that drives the point defect diffusion within the shells. FEA further shows that the geometric profile of the nanolattices has a dominant influence on the stress gradient and hence the anelastic behavior.}, number={38}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Chen, I-Te and Poblete, Felipe Robles and Bagal, Abhijeet and Zhu, Yong and Chang, Chih-Hao}, year={2022}, month={Sep} }
 @article{dong_fu_seyitliyev_darabi_mendes_lei_chen_chang_amassian_gundogdu_et al._2022, title={Cavity Engineering of Perovskite Distributed Feedback Lasers}, volume={9}, ISSN={2330-4022 2330-4022}, url={http://dx.doi.org/10.1021/acsphotonics.2c00917}, DOI={10.1021/acsphotonics.2c00917}, number={9}, journal={ACS Photonics}, publisher={American Chemical Society (ACS)}, author={Dong, Qi and Fu, Xiangyu and Seyitliyev, Dovletgeldi and Darabi, Kasra and Mendes, Juliana and Lei, Lei and Chen, Yi-An and Chang, Chih-Hao and Amassian, Aram and Gundogdu, Kenan and et al.}, year={2022}, month={Aug}, pages={3124–3133} }
 @article{fu_mehta_chen_lei_zhu_barange_dong_yin_mendes_he_et al._2021, title={Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes}, volume={33}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202006801}, DOI={10.1002/adma.202006801}, abstractNote={Abstract}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Fu, Xiangyu and Mehta, Yash and Chen, Yi‐An and Lei, Lei and Zhu, Liping and Barange, Nilesh and Dong, Qi and Yin, Shichen and Mendes, Juliana and He, Siliang and et al.}, year={2021}, month={Jan}, pages={2006801} }
 @article{luo_zhang_evans_chang_2020, title={Active Periodic Magnetic Nanostructures with High Aspect Ratio and Ultrahigh Pillar Density}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b18423}, abstractNote={Magnetically actuated micro/nanoscale pillars have attracted significant research interest recently due to their dynamic properties. These structures can be used for various applications, such as dry adhesion, cell manipulation, and sensors or actuators in microfluidics. Magnetically actuated structures can be fabricated by mixing magnetic particles and polymers to yield a favorable combination of magnetic permeability and mechanical compliance. However, the pillar density of demonstrated structures is relatively low, which limits the potential applications in active surface manipulation of microscale objects. Here we demonstrate active periodic nanostructures with pillar density of 0.25 pillar/μm^2, which is the highest density for magnetically actuated pillars so far. Having structure period of 2 μm, diameter of 600 nm, and high aspect ratio of up to 11, this structure can be magnetically actuated with displacement of up to 200 nm. The behaviors of the pillars under various cyclic actuation modes have been characterized, demonstrating that the actuation can be well controlled. This work can find potential applications in particle manipulation and tunable photonic elements. KEYWORDS Dynamic materials, active nanostructures, nanofabrication, magnetic nanoparticles, high aspect ratio.}, number={9}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Luo, Zhiren and Zhang, Xu A. and Evans, Benjamin Aaron and Chang, Chih-Hao}, year={2020}, month={Mar}, pages={11135–11143} }
 @article{lei_seyitliyev_stuard_mendes_dong_fu_chen_he_yi_zhu_et al._2020, title={Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing}, volume={32}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201906571}, abstractNote={Abstract}, number={16}, journal={ADVANCED MATERIALS}, author={Lei, Lei and Seyitliyev, Dovletgeldi and Stuard, Samuel and Mendes, Juliana and Dong, Qi and Fu, Xiangyu and Chen, Yi-An and He, Siliang and Yi, Xueping and Zhu, Liping and et al.}, year={2020}, month={Apr} }
 @article{fu_peng_samal_barange_chen_shin_mehta_rozelle_chang_so_2020, title={Mode Dispersion in Photonic Crystal Organic Light-Emitting Diodes}, volume={2}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00326}, abstractNote={Similar to an electronic lattice determining the motion of electrons in solids, photonic crystals (PhCs) are periodic photonic nanostructures which determine the propagation of photons. By incorpor...}, number={6}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={Fu, Xiangyu and Peng, Cheng and Samal, Monica and Barange, Nilesh and Chen, Yi-An and Shin, Dong-Hun and Mehta, Yash and Rozelle, Adam and Chang, Chih-Hao and So, Franky}, year={2020}, month={Jun}, pages={1759–1767} }
 @article{luo_chang_gao_chang_li_viehland_tian_jiang_2020, title={Multi-layered domain morphology in relaxor single crystals with nano-patterned composite electrode}, volume={182}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2019.10.017}, abstractNote={(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystals, especially with compositions near its morphotropic phase boundary (MPB), have been employed for a broad range of applications such as ultrasound transducers, sensors, and actuators. To further enhance the properties of PMN-PT, electrode patterning, as a method of domain engineering, was proved to be an effective approach. In our previous report, a 200 nm grating pattern electrode (Ti/Au–MnOx) (nano-electrode) was prepared on one surface of PMN-PT crystal, exhibiting 30% d33 enhancement. In this work, the multi-layered domain morphology and the domain engineering from nano-electrode were characterized using piezoresponse force microscopy (PFM). A hypothetical domain engineering model for nano-electrodes is established to explain the experimental results as well as the property enhancement from the nano-electrode. The electrode patterning proves that the nano-scale modification can tune the macro-scale piezoelectric properties of the bulk material.}, journal={ACTA MATERIALIA}, author={Luo, Chengtao and Chang, Wei-Yi and Gao, Min and Chang, Chih-Hao and Li, Jiefang and Viehland, Dwight and Tian, Jian and Jiang, Xiaoning}, year={2020}, month={Jan}, pages={10–17} }
 @article{fu_chen_shin_mehta_chen_barange_zhu_amoah_chang_so_2020, title={Recovering cavity effects in corrugated organic light emitting diodes}, volume={28}, ISSN={["1094-4087"]}, DOI={10.1364/OE.404412}, abstractNote={Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.}, number={21}, journal={OPTICS EXPRESS}, author={Fu, Xiangyu and Chen, Yi-An and Shin, Dong-Hun and Mehta, Yash and Chen, I-Te and Barange, Nilesh and Zhu, Liping and Amoah, Stephen and Chang, Chih-Hao and So, Franky}, year={2020}, month={Oct}, pages={32214–32225} }
 @article{chen_naidu_luo_chang_2019, title={Enhancing optical transmission of multilayer composites using interfacial nanostructures}, volume={126}, ISSN={["1089-7550"]}, DOI={10.1063/1.5097832}, abstractNote={We demonstrate the suppression of light reflections at solid-solid interfaces in multilayer thin and thick films using interfacial nanostructures. The embedded nanostructures have subwavelength features and function as a gradient-index medium to eliminate Fresnel losses induced by refractive index mismatch between dissimilar materials. Suppressing the interfacial reflection can reduce interference effects in thin films, and the transmittance measurement of a polymer on a silica substrate demonstrates a two-fold decrease in interference fringe contrast. A thick multilayer composite consisting of three fused silica and two polymer layers has also been fabricated and demonstrates the enhancement of optical transmission up to 30% at high incident angles. The effects of the interfacial structure geometry are examined by theoretical models based on rigorous coupled-wave analysis methods. The experimental results agree well with simulation models, which predicts that further improvements can be achieved using the optimized tapered profile. This work indicates that interfacial nanostructures can improve the broadband and wide-angle response of multilayers and can find applications in thin-film optics, optoelectronic devices, and composite windows.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Chen, Yi-An and Naidu, Sharan V and Luo, Zhiren and Chang, Chih-Hao}, year={2019}, month={Aug} }
 @article{chen_chen_chang_2019, title={Increasing etching depth of sapphire nanostructures using multilayer etching mask}, volume={37}, ISSN={["2166-2754"]}, DOI={10.1116/1.5119388}, abstractNote={In this study, the etching of sapphire nanostructures in inductively coupled plasma reactive ion etching using a multilayer etch mask is studied. The goals are to increase the etching depth and enable the fabrication of higher aspect ratio nanostructures in sapphire, which is traditionally difficult to micromachine. The etching rates and chemistry of different masking materials are examined for better understanding of the etching process. The etching of sapphire nanostructures is then studied using single and multilayer masks with Cl2-based chemistry. The fabrication results show that using the multilayer mask is an effective method for sapphire nanostructure fabrication, increasing the maximum etching depth from 25 to 230 nm for a ninefold improvement. To further validate the optical properties of fabricated sapphire nanostructures, the antireflection effects have been characterized. This work indicates that applying the multilayer mask can increase the etching depth of sapphire nanostructures, which can find applications in thin-film optics, optoelectronic devices, and composite windows.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Chen, Yi-An and Chen, I-Te and Chang, Chih-Hao}, year={2019}, month={Nov} }
 @article{luo_evans_chang_2019, title={Magnetically Actuated Dynamic Iridescence Inspired by the Neon Tetra}, volume={13}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.9b00822}, abstractNote={Inspired by the tropical fish neon tetra, we report a mechanism to achieve dynamic iridescence that can be magnetically tuned. This approach is based on the tilting of periodic photonic nanostructures, as opposed to the more common strain-induced color tuning. In this method, a periodic array of magnetic nanopillars serves as a template to guide the assembly of iron oxide nanoparticles when magnetized in a liquid environment. The periodic local fields induced by the magnetic template anchor the assembled particle columns, allowing the structure to tilt about the base when the angle of the applied field is changed. This effect emulates a microscopic "Venetian blind" and results in dynamic optical properties through structural coloration that is tunable in real time. The fabricated prototype demonstrates tunable reflectance spectra with peak wavelength shift from 528 to 720 nm. The magnetic actuation mechanism is reversible and has a fast response time around 0.3 s. This structure can be implemented on an arbitrary surface as dynamic camouflage, iridescent display, and tunable photonic elements, as well as in other applications such as active fluidic devices and particle manipulation.}, number={4}, journal={ACS NANO}, author={Luo, Zhiren and Evans, Benjamin Aaron and Chang, Chih-Hao}, year={2019}, month={Apr}, pages={4657–4666} }
 @misc{zhang_chen_chang_2019, title={Recent progress in near-field nanolithography using light interactions with colloidal particles: from nanospheres to three-dimensional nanostructures}, volume={30}, ISSN={["1361-6528"]}, DOI={10.1088/1361-6528/ab2282}, abstractNote={The advance of nanotechnology is firmly rooted in the development of cost-effective, versatile, and easily accessible nanofabrication techniques. The ability to pattern complex two-dimensional and three-dimensional nanostructured materials are particularly desirable, since they can have novel physical properties that are not found in bulk materials. This review article will report recent progress in utilizing self-assembly of colloidal particles for nanolithography. In these techniques, the near-field interactions of light and colloids are the sole mechanisms employed to generate the intensity distributions for patterning. Based on both ‘bottom-up’ self-assembly and ‘top-down’ lithography approaches, these processes are highly versatile and can take advantage of a number of optical effects, allowing the complex 3D nanostructures to be patterned using single exposures. There are several key advantages including low equipment cost, facile structure design, and patterning scalability, which will be discussed in detail. We will outline the underlying optical effects, review the geometries that can be fabricated, discuss key limitations, and highlight potential applications in nanophotonics, optoelectronic devices, and nanoarchitectured materials.}, number={35}, journal={NANOTECHNOLOGY}, author={Zhang, Xu A. and Chen, I-Te and Chang, Chih-Hao}, year={2019}, month={Aug} }
 @article{min_chen_chen_sun_lee_li_zhu_o'connor_parsons_chang_2018, title={Atomic Layer Deposition: Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors (Adv. Mater. Interfaces 22/2018)}, volume={5}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/ADMI.201870109}, DOI={10.1002/ADMI.201870109}, abstractNote={Physical vapor deposition of thin films on nanostructure topography is typically limited by line-of-sight transfer. This study demonstrates that by introducing an oxide interlayer using atomic layer deposition, the film uniformity and electrical properties can be improved. Enabling conformal coating at low cost, this method can find applications in manufacturing of integrated circuit and stretchable electronics. More details can be found in article number 1801379 by Joong-Hee Min, Chih-Hao Chang, and co-workers.}, number={22}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Min, Joong‐Hee and Chen, Yi‐An and Chen, I‐Te and Sun, Tianlei and Lee, Dennis T. and Li, Chengjun and Zhu, Yong and O'Connor, Brendan T. and Parsons, Gregory N. and Chang, Chih‐Hao}, year={2018}, month={Nov}, pages={1870109} }
 @article{min_chen_chen_sun_lee_li_zhu_brendan t. o'connor_parsons_chang_2018, title={Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors}, volume={5}, ISSN={["2196-7350"]}, DOI={10.1002/admi.201801379}, abstractNote={Abstract}, number={22}, journal={ADVANCED MATERIALS INTERFACES}, author={Min, Joong-Hee and Chen, Yi-An and Chen, I-Te and Sun, Tianlei and Lee, Dennis T. and Li, Chengjun and Zhu, Yong and Brendan T. O'Connor and Parsons, Gregory N. and Chang, Chih-Hao}, year={2018}, month={Nov} }
 @article{chang_zhang_kim_huang_bagal_chang_fang_wu_jiang_2018, title={Evaluation of Photoacoustic Transduction Efficiency of Candle Soot Nanocomposite Transmitters}, volume={17}, ISSN={["1941-0085"]}, url={https://doi.org/10.1109/TNANO.2018.2845703}, DOI={10.1109/TNANO.2018.2845703}, abstractNote={Candle soot nanoparticles (CSNP) and polydimethyl-siloxane (PDMS) composite has shown the highly efficient photoacoustic transduction owing to their high light absorption coefficient and low interfacial thermal resistance. In this study, we report the effect of candle soot structure and thickness on the photoacoustic transduction efficiency. Optical properties of the CSNP/PDMS nanocomposites were characterized through both experimental measurements and finite difference time domain analysis in the visible wavelength range, indicating that the carbon volume fraction and thickness of CS/PDMS composite are highly relevant with light absorption. With a low laser energy input ( <inline-formula><tex-math notation="LaTeX">$< {\text{1 mJ/pulse}}$</tex-math></inline-formula>), the CS/PDMS composite with 2.15 <italic>μ</italic>m thickness exerts an output pressure of 3.78 MPa and a conversion efficiency of <inline-formula><tex-math notation="LaTeX">${\text{9.69}}\,\times \,{\text{10}}^{- 3}$</tex-math> </inline-formula>, which is two orders of magnitude higher than previously reported results.}, number={5}, journal={IEEE TRANSACTIONS ON NANOTECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Chang, Wei-Yi and Zhang, Xu A. and Kim, Jinwook and Huang, Wenbin and Bagal, Abhijeet and Chang, Chih-Hao and Fang, Tiegang and Wu, Hanchang Felix and Jiang, Xiaoning}, year={2018}, month={Sep}, pages={985–993} }
 @article{chang_chung_yuan_chang_tian_viehland_li_jones_jiang_2018, title={Patterned nano-domains in PMN-PT single crystals}, volume={143}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2017.10.016}, abstractNote={The domain structure, dielectric, and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals with nanocomposite electrode, which includes MnOx semiconductor nanogratings and a Ti/Au conductive layer, were studied in this paper. These artificial MnOx nanogratings can alter the electric field distribution and then enhance the domain density. PMN-PT crystals with Ti/Au-MnOx nanocomposite electrodes showed high piezoelectric constant of 2250 p.m./V and dielectric constant of 5400 at 1 kHz, respectively. Compared to ones with conventional planar electrodes, the piezoelectric and dielectric constants of the samples with nanocomposite electrodes were increased 36.7% and 38.3%, respectively. Piezoresponse force microscopy (PFM) images revealed the domain pattern near the electrode/single crystal interface. A linear domain structure induced by the MnOx nanocomposite electrode was found in the samples with thickness less than 200 μm. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) results showed the diffusion of Mn about 300 nm in depth in PMNPT crystal after heat treatment during MnOx nanocomposite electrode. It is believed that the localized high electric fields induced by fringe effects caused by the nanocomposite electrode can enhance nucleation of new domains, and that diffusion from the patterned Mn layer may also lead to an enhancement in domain wall mobility. Our findings open up a new domain engineering technique for tailoring the dielectric and piezoelectric properties of PMN-PT single crystals.}, journal={Acta Materialia}, author={Chang, W.-Y. and Chung, C.-C. and Yuan, Z. and Chang, C.-H. and Tian, J. and Viehland, D. and Li, J.-F. and Jones, J.L. and Jiang, X.}, year={2018}, month={Jan}, pages={166–173} }
 @article{poteet_zhang_nagai_chang_2018, title={Twin photonic nanojets generated from coherent illumination of microscale sphere and cylinder}, volume={29}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/1361-6528/aaa35d}, DOI={10.1088/1361-6528/aaa35d}, abstractNote={Photonic nanojets, highly focused beams of light created by planar illumination of a microsphere, have been shown to produce narrow subwavelength beams over distances of several wavelengths in the near field. In this work, we investigate the generation of twin photonic nanojets through the illumination of a microsphere or cylinder from two coherent sources with relative phase shift. Under these conditions, symmetric twin nanojets separated by an intensity null can be generated. Compared to a photonic nanojet, the twin nanojets can achieve an even smaller subwavelength beam, and have the added advantage of having more complex intensity profiles that can be controlled by multiple parameters. Using both finite-difference time-domain and Mie theory models, the width, length, and intensity enhancement factor of the nanojet geometry are found to be functions of the phase, angle offsets, and particle geometry. Such twin photonic nanojets can find applications in optical trapping, manipulation, nanolithography, and enhancement of nonlinear optical properties.}, number={7}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Poteet, Austen and Zhang, Xu A and Nagai, Hironori and Chang, Chih-Hao}, year={2018}, month={Jan}, pages={075204} }
 @article{zhang_chen_bagal_chang_2017, title={Enhanced total internal reflection using low-index nanolattice materials}, volume={42}, ISSN={["1539-4794"]}, DOI={10.1364/ol.42.004123}, abstractNote={Low-index materials are key components in integrated photonics and can enhance index contrast and improve performance. Such materials can be constructed from porous materials, which generally lack mechanical strength and are difficult to integrate. Here we demonstrate enhanced total internal reflection (TIR) induced by integrating robust nanolattice materials with periodic architectures between high-index media. The transmission measurement from the multilayer stack illustrates a cutoff at about a 60° incidence angle, indicating an enhanced light trapping effect through TIR. Light propagation in the nanolattice material is simulated using rigorous coupled-wave analysis and transfer matrix methods, which agrees well with experimental data. The demonstration of the TIR effect in this Letter serves as a first step towards the realization of multilayer devices with nanolattice materials as robust low-index components. These nanolattice materials can find applications in integrated photonics, antireflection coatings, photonic crystals, and low-k dielectric.}, number={20}, journal={OPTICS LETTERS}, author={Zhang, Xu A. and Chen, Yi-An and Bagal, Abhijeet and Chang, Chih-Hao}, year={2017}, month={Oct}, pages={4123–4126} }
 @article{bagal_zhang_shahrin_dandley_zhao_poblete_oldham_zhu_parsons_bobko_et al._2017, title={Large-Area Nanolattice Film with Enhanced Modulus, Hardness, and Energy Dissipation}, volume={7}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/S41598-017-09521-6}, DOI={10.1038/S41598-017-09521-6}, abstractNote={Abstract}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Bagal, Abhijeet and Zhang, Xu A. and Shahrin, Rahnuma and Dandley, Erinn C. and Zhao, Junjie and Poblete, Felipe R. and Oldham, Christopher J. and Zhu, Yong and Parsons, Gregory N. and Bobko, Christopher and et al.}, year={2017}, month={Aug} }
 @article{tippens_bagal_zhang_chang_2017, title={Nanostructured antireflective in-plane solar harvester}, volume={25}, ISSN={["1094-4087"]}, DOI={10.1364/oe.25.00a840}, abstractNote={In this work, we demonstrate a two-dimensional nano-hole array that can reduce reflection losses while passively trapping and harvesting incident light. The surface structure is designed to scavenge a small portion of incident light that would typically be lost due to Fresnel reflection, while the majority of light transmits unobstructed like a regular window. The trapping mechanism is dependent on angle and wavelength, and can be designed to selectively trap narrow wavelength bands using the constructed theoretical models. We demonstrate that structures with periods of 275 nm and 325 nm can trap different wavelength range within the visible spectrum, while simultaneously suppressing reflection losses. The trapping effect can be observed visually, and can be converted to a current output using a photovoltaic (PV) cell on the glass edge. The fabrication of such materials employs a simple replication process, and can be readily scaled up for large-scale manufacturing. The demonstrated solar harvester can be potentially be widely deployed in residential and commercial buildings as multifunctional windows for solar energy harvesting, scavenging, spectra splitting, and anti-glare properties.}, number={16}, journal={OPTICS EXPRESS}, author={Tippens, Jared and Bagal, Abhijeet and Zhang, Xu A. and Chang, Chih-Hao}, year={2017}, month={Aug}, pages={A840–A850} }
 @article{nagai_poteet_zhang_chang_2017, title={Three-dimensional colloidal interference lithography}, volume={28}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/1361-6528/aa5e3f}, DOI={10.1088/1361-6528/aa5e3f}, abstractNote={Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle–light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd’s mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.}, number={12}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Nagai, Hironori and Poteet, Austen and Zhang, Xu A and Chang, Chih-Hao}, year={2017}, month={Feb}, pages={125302} }
 @article{min_zhang_chang_2016, title={Designing unit cell in three-dimensional periodic nanostructures using colloidal lithography}, volume={24}, ISSN={["1094-4087"]}, DOI={10.1364/oe.24.00a276}, abstractNote={Colloidal phase-shift lithography, the illumination of a two-dimensional (2D) ordered array of self-assembled colloidal nanospheres, is an effective method for the fabrication of periodic three-dimensional (3D) nanostructures. In this work, we investigate the design and control of the unit-cell geometry by examining the relative ratio of the illumination wavelength and colloidal nanosphere diameter. Using analytical and finite-difference time-domain (FDTD) modeling, we examine the effect of the wavelength-diameter ratio on intensity pattern, lattice constants, and unit-cell geometry. These models were validated by experimental fabrication for various combination of wavelength and colloid diameter. The developed models and fabrication tools can facilitate the design and engineering of 3D periodic nanostructure for photonic crystals, volumetric electrodes, and porous materials.}, number={2}, journal={OPTICS EXPRESS}, author={Min, Joong-Hee and Zhang, Xu A. and Chang, Chih-Hao}, year={2016}, month={Jan}, pages={A276–A284} }
 @article{min_bagal_mundy_oldham_wu_parsons_chang_2016, title={Fabrication and design of metal nano-accordion structures using atomic layer deposition and interference lithography}, volume={8}, ISSN={["2040-3372"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000371479000021&KeyUID=WOS:000371479000021}, DOI={10.1039/c5nr08566g}, abstractNote={Fabricated free-standing platinum nano-accordion structures with a wide variety of cross-sectional profiles using a combination of ALD and IL.}, number={9}, journal={NANOSCALE}, author={Min, J. -H. and Bagal, A. and Mundy, J. Z. and Oldham, C. J. and Wu, B. -I. and Parsons, G. N. and Chang, C. -H.}, year={2016}, pages={4984–4990} }
 @article{alden_guo_kirste_kaess_bryan_troha_bagal_reddy_hernandez-balderrama_franke_et al._2016, title={Fabrication and structural properties of AlN submicron periodic lateral polar structures and waveguides for UV-C applications}, volume={108}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/1.4955033}, DOI={10.1063/1.4955033}, abstractNote={Periodically poled AlN thin films with submicron domain widths were fabricated for nonlinear applications in the UV-VIS region. A procedure utilizing metalorganic chemical vapor deposition growth of AlN in combination with laser interference lithography was developed for making a nanoscale lateral polarity structure (LPS) with domain size down to 600 nm. The Al-polar and N-polar domains were identified by wet etching the periodic LPS in a potassium hydroxide solution and subsequent scanning electron microscopy (SEM) characterization. Fully coalesced and well-defined vertical interfaces between the adjacent domains were established by cross-sectional SEM. AlN LPSs were mechanically polished and surface roughness with a root mean square value of ∼10 nm over a 90 μm × 90 μm area was achieved. 3.8 μm wide and 650 nm thick AlN LPS waveguides were fabricated. The achieved domain sizes, surface roughness, and waveguides are suitable for second harmonic generation in the UVC spectrum.}, number={26}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Alden, D. and Guo, W. and Kirste, R. and Kaess, F. and Bryan, I. and Troha, T. and Bagal, A. and Reddy, P. and Hernandez-Balderrama, Luis H. and Franke, A. and et al.}, year={2016}, month={Jun} }
 @article{wang_zhao_bagal_dandley_oldham_fang_parsons_chang_2016, title={Wicking Enhancement in Three-Dimensional Hierarchical Nanostructures}, volume={32}, ISSN={["0743-7463"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84982307197&partnerID=MN8TOARS}, DOI={10.1021/acs.langmuir.6b01864}, abstractNote={Wicking, the absorption of liquid into narrow spaces without the assistance of external forces, has drawn much attention due to its potential applications in many engineering fields. Increasing surface roughness using micro/nanostructures can improve capillary action to enhance wicking. However, reducing the structure length scale can also result in significant viscous forces to impede wicking. In this work, we demonstrate enhanced wicking dynamics by using nanostructures with three-dimensional (3D) hierarchical features to increase the surface area while mitigating the obstruction of liquid flow. The proposed structures were engineered using a combination of interference lithography and hydrothermal synthesis of ZnO nanowires, where structures at two length scales were independently designed to control wicking behavior. The fabricated hierarchical 3D structures were tested for water and ethanol wicking properties, demonstrating improved wicking dynamics with intermediate nanowire lengths. The experimental data agree with the derived fluid model based on the balance of capillary and vicious forces. The hierarchical wicking structures can be potentially used in applications in water harvesting surfaces, microfluidics, and integrated heat exchangers.}, number={32}, journal={LANGMUIR}, author={Wang, Zhiting and Zhao, Junjie and Bagal, Abhijeet and Dandley, Erinn C. and Oldham, Christopher J. and Fang, Tiegang and Parsons, Gregory N. and Chang, Chih-Hao}, year={2016}, month={Aug}, pages={8029–8033} }
 @article{zhang_dai_xu_chang_2015, title={3D Nanostructures: Sculpting Asymmetric, Hollow-Core, Three-Dimensional Nanostructures Using Colloidal Particles (Small 11/2015)}, volume={11}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/SMLL.201570060}, DOI={10.1002/SMLL.201570060}, abstractNote={A 3D nanolithography technique exploiting particle–light interactions for the low-cost and controllable fabrication of asymmetric hollow-core nanostructures is described by C.-H. Chang and co-workers on page 1285. Multiple oblique illuminations on single particles generate unique complex intensity patterns, which are recorded by underlying photosensitive polymers. The cover depicts nanostructures generated from single, double, triple, and quadruple illuminations. The background image illustrates a non-close-packed polystyrene particle assembly used to fabricate asymmetric nanostructure arrays.}, number={11}, journal={Small}, publisher={Wiley}, author={Zhang, Xu A. and Dai, Bin and Xu, Zhiyuan and Chang, Chih-Hao}, year={2015}, month={Mar}, pages={1226–1226} }
 @article{elek_zhang_dai_xu_chang_2015, title={Fabrication of three-dimensional hierarchical nanostructures using template-directed colloidal assembly}, volume={7}, ISSN={["2040-3372"]}, DOI={10.1039/c4nr06840h}, abstractNote={Optical effects in template-directed colloidal assembly are explored to fabricate microscale patterns with integrated three-dimensional (3D) nanostructures.}, number={10}, journal={NANOSCALE}, author={Elek, J. E. and Zhang, X. A. and Dai, B. and Xu, Z. and Chang, C. -H.}, year={2015}, pages={4406–4410} }
 @article{bagal_dandley_zhao_zhang_oldham_parsons_chang_2015, title={Multifunctional nano-accordion structures for stretchable transparent conductors}, volume={2}, ISSN={["2051-6355"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000359586600003&KeyUID=WOS:000359586600003}, DOI={10.1039/c5mh00070j}, abstractNote={Nano-accordion structures allow brittle materials to stretch, enabling transparent conductors that are stretchable and flexible.}, number={5}, journal={MATERIALS HORIZONS}, author={Bagal, Abhijeet and Dandley, Erinn C. and Zhao, Junjie and Zhang, Xu A. and Oldham, Christopher J. and Parsons, Gregory N. and Chang, Chih-Hao}, year={2015}, month={Sep}, pages={486–494} }
 @article{zhang_bagal_dandley_zhao_oldham_wu_parsons_chang_2015, title={Ordered 3D Thin-Shell Nanolattice Materials with Near-Unity Refractive Indices}, volume={25}, ISSN={["1616-3028"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000365532100009&KeyUID=WOS:000365532100009}, DOI={10.1002/adfm.201502854}, abstractNote={The refractive indices of naturally occurring materials are limited, and there exists an index gap between indices of air and available solid materials. With many photonics and electronics applications, there has been considerable effort in creating artificial materials with optical and dielectric properties similar to air while simultaneously being mechanically stable to bear load. Here, a class of ordered nanolattice materials consisting of periodic thin‐shell structures with near‐unity refractive index and high stiffness is demonstrated. Using a combination of 3D nanolithography and atomic layer deposition, these ordered nanostructured materials have reduced optical scattering and improved mechanical stability compared to existing randomly porous materials. Using ZnO and Al2O3 as the building materials, refractive indices from 1.3 down to 1.025 are achieved. The experimental data can be accurately described by Maxwell Garnett effective media theory, which can provide a guide for index design. The demonstrated low‐index, low‐scattering, and high‐stiffness materials can serve as high‐quality optical films in multilayer photonic structures, waveguides, resonators, and ultra‐low‐k dielectrics.}, number={42}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Zhang, Xu A. and Bagal, Abhijeet and Dandley, Erinn C. and Zhao, Junjie and Oldham, Christopher J. and Wu, Bae-Ian and Parsons, Gregory N. and Chang, Chih-Hao}, year={2015}, month={Nov}, pages={6644–6649} }
 @article{zhang_dai_xu_chang_2015, title={Sculpting Asymmetric, Hollow-Core, Three-Dimensional Nanostructures Using Colloidal Particles}, volume={11}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201402750}, abstractNote={Colloidal elements have historically played a key role in “bottom‐up” self‐assembly processes for nanofabrication. However, these elementary components can also interact with light to generate complex intensity distributions and facilitate “top‐down” lithography. Here, a nanolithography technique is demonstrated based on oblique illuminations of colloidal particles to fabricate hollow‐core 3D nanostructures with complex symmetry. The light–particle interaction generates an angular light distribution as governed by Mie scattering, which can be compounded by multiple illuminations to sculpt novel 3D structures in the underlying photoresist. The fabricated geometry can be controlled by the particle parameters and illumination configurations, enabling the fabrication of a large variety of asymmetric hollow nanostructures. The proposed technique has high pattern versatility, is low cost and high throughput, and can find potential application in nanoneedles, nanonozzles, and materials with anisotropic properties.}, number={11}, journal={SMALL}, author={Zhang, Xu A. and Dai, Bin and Xu, Zhiyuan and Chang, Chih-Hao}, year={2015}, month={Mar}, pages={1285–1292} }
 @article{yang_zhang_bagal_guo_chang_2013, title={Antireflection effects at nanostructured material interfaces and the suppression of thin-film interference}, volume={24}, ISSN={["1361-6528"]}, DOI={10.1088/0957-4484/24/23/235202}, abstractNote={Thin-film interference is a well-known effect, and it is commonly observed in the colored appearance of many natural phenomena. Caused by the interference of light reflected from the interfaces of thin material layers, such interference effects can lead to wavelength and angle-selective behavior in thin-film devices. In this work, we describe the use of interfacial nanostructures to eliminate interference effects in thin films. Using the same principle inspired by moth-eye structures, this approach creates an effective medium where the index is gradually varying between the neighboring materials. We present the fabrication process for such nanostructures at a polymer–silicon interface, and experimentally demonstrate its effectiveness in suppressing thin-film interference. The principle demonstrated in this work can lead to enhanced efficiency and reduce wavelength/angle sensitivity in multilayer optoelectronic devices.}, number={23}, journal={NANOTECHNOLOGY}, author={Yang, Qiaoyin and Zhang, Xu A. and Bagal, Abhijeet and Guo, Wei and Chang, Chih-Hao}, year={2013}, month={Jun} }
 @article{bagal_chang_2013, title={Fabrication of subwavelength periodic nanostructures using liquid immersion Lloyd's mirror interference lithography}, volume={38}, ISSN={["0146-9592"]}, DOI={10.1364/ol.38.002531}, abstractNote={We have developed a liquid immersion Lloyd's mirror interference lithography system to fabricate subwavelength periodic nanostructures. In this approach, we construct the Lloyd's mirror interferometer within a liquid medium to increase the ambient index. The light wavelength is scaled by the refractive index of the immersion fluid, reducing the minimum interference pattern period and increasing the spatial resolution. The all-liquid system ensures continuous fluid contact with the sample without an external mechanism, allows rapid adjustment of pattern period with subwavelength resolution, and retains the passive vibration-correction capability of Lloyd's mirror interferometers. Using this approach, we have successfully fabricated a grating structure with 112 nm period using a laser with 325 nm wavelength, attaining a numerical aperture of 1.45. The proposed immersion strategy can be adapted to improve pattern resolution of more complex interference lithography systems.}, number={14}, journal={OPTICS LETTERS}, author={Bagal, Abhijeet and Chang, Chih-Hao}, year={2013}, month={Jul}, pages={2531–2534} }
 @article{chang_huang_bagal_chang_tian_han_jiang_2013, title={Study on dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O-3-0.3 PbTiO3 single crystal with nano-patterned composite electrode}, volume={114}, ISSN={["1089-7550"]}, DOI={10.1063/1.4821517}, abstractNote={Effect of nano-patterned composite electrode and backswitching poling technique on dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3 PbTiO3 was studied in this paper. Composite electrode consists of Mn nano-patterns with pitch size of 200 nm, and a blanket layer of Ti/Au was fabricated using a nanolithography based lift-off process, heat treatment, and metal film sputtering. Composite electrode and backswitching poling resulted in 27% increase of d33 and 25% increase of dielectric constant, and we believe that this is attributed to regularly defined nano-domains and irreversible rhombohedral to monoclinic phase transition in crystal. The results indicate that nano-patterned composite electrode and backswitching poling has a great potential in domain engineering of relaxor single crystals for advanced devices.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Chang, Wei-Yi and Huang, Wenbin and Bagal, Abhijeet and Chang, Chih-Hao and Tian, Jian and Han, Pengdi and Jiang, Xiaoning}, year={2013}, month={Sep} }
 @article{zhang_elek_chang_2013, title={Three-Dimensional Nanolithography Using Light Scattering from Colloidal Particles}, volume={7}, ISSN={["1936-086X"]}, DOI={10.1021/nn402637a}, abstractNote={The interaction between light and colloidal elements can result in a wealth of interesting near-field optical patterns. By examining the optical and colloidal properties, the intensity distribution can be tailored and harnessed for three-dimensional nanolithography. Here, we examine the use of light scattering from colloidal particles to fabricate complex hollow nanostructures. In this approach, a single colloidal sphere is illuminated to create a scattering pattern, which is captured by a photoresist in close proximity. No external optical elements are required, and the colloidal elements alone provide the modulation of the optical intensity pattern. The fabricated nanostructures can be designed to have multiple shells, confined volumes, and single top openings, resembling "nano-volcanoes." The geometry of such structures is dependent on the scattered light distribution and can be accurately modeled by examining the light-particle interaction. The hollow nanostructures can be used to trap nanomaterial, and we demonstrate their ability to trap 50 nm silica nanoparticles. These well-defined surface hollow structures can be further functionalized for applications in controlled drug delivery and biotrapping. Colloidal elements with different geometries and material compositions can also be incorporated to examine other light-colloid interactions.}, number={7}, journal={ACS NANO}, author={Zhang, Xu A. and Elek, Jonathan and Chang, Chih-Hao}, year={2013}, month={Jul}, pages={6212–6218} }
 @article{park_choi_chang_cohen_mckinley_barbastathis_2012, title={Nanotextured Silica Surfaces with Robust Superhydrophobicity and Omnidirectional Broadband Supertransmissivity}, volume={6}, ISSN={["1936-086X"]}, DOI={10.1021/nn301112t}, abstractNote={Designing multifunctional surfaces that have user-specified interactions with impacting liquids and with incident light is a topic of both fundamental and practical significance. Taking cues from nature, we use tapered conical nanotextures to fabricate the multifunctional surfaces; the slender conical features result in large topographic roughness, while the axial gradient in the effective refractive index minimizes reflection through adiabatic index-matching between air and the substrate. Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimizing the multifunctionality of the textured surface, but at the same time, these demands pose the toughest fabrication challenges. Here we report a systematic approach to concurrent design of optimal structures in the fluidic and optical domains and a fabrication procedure that achieves the desired aspect ratios and periodicities with few defects and large pattern area. Our fabricated nanostructures demonstrate structural superhydrophilicity or, in combination with a suitable chemical coating, robust superhydrophobicity. Enhanced polarization-independent optical transmission exceeding 98% has also been achieved over a broad range of bandwidth and incident angles. These nanotextured surfaces are also robustly antifogging or self-cleaning, offering potential benefits for applications such as photovoltaic solar cells.}, number={5}, journal={ACS NANO}, author={Park, Kyoo-Chul and Choi, Hyungryul J. and Chang, Chih-Hao and Cohen, Robert E. and McKinley, Gareth H. and Barbastathis, George}, year={2012}, month={May}, pages={3789–3799} }
 @article{heilmann_ahn_bruccoleri_chang_gullikson_mukherjee_schattenburg_2011, title={Diffraction efficiency of 200-nm-period critical-angle transmission gratings in the soft x-ray and extreme ultraviolet wavelength bands}, volume={50}, ISSN={0003-6935 1539-4522}, url={http://dx.doi.org/10.1364/ao.50.001364}, DOI={10.1364/ao.50.001364}, abstractNote={We report on measurements of the diffraction efficiency of 200-nm-period freestanding blazed transmission gratings for wavelengths in the 0.96 to 19.4 nm range. These critical-angle transmission (CAT) gratings achieve highly efficient blazing over a broad band via total external reflection off the sidewalls of smooth, tens of nanometer thin ultrahigh aspect-ratio silicon grating bars and thus combine the advantages of blazed x-ray reflection gratings with those of more conventional x-ray transmission gratings. Prototype gratings with maximum depths of 3.2 and 6 μm were investigated at two different blaze angles. In these initial CAT gratings the grating bars are monolithically connected to a cross support mesh that only leaves less than half of the grating area unobstructed. Because of our initial fabrication approach, the support mesh bars feature a strongly trapezoidal cross section that leads to varying CAT grating depths and partial absorption of diffracted orders. While theory predicts broadband absolute diffraction efficiencies as high as 60% for ideal CAT gratings without a support mesh, experimental results show efficiencies in the range of ∼50-100% of theoretical predictions when taking the effects of the support mesh into account. Future minimization of the support mesh therefore promises broadband CAT grating absolute diffraction efficiencies of 50% or higher.}, number={10}, journal={Applied Optics}, publisher={The Optical Society}, author={Heilmann, Ralf K. and Ahn, Minseung and Bruccoleri, Alex and Chang, Chih-Hao and Gullikson, Eric M. and Mukherjee, Pran and Schattenburg, Mark L.}, year={2011}, month={Mar}, pages={1364} }
 @article{chang_tian_hesse_gao_choi_kim_siddiqui_barbastathis_2011, title={From Two-Dimensional Colloidal Self-Assembly to Three-Dimensional Nanolithography}, volume={11}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl2011824}, DOI={10.1021/nl2011824}, abstractNote={A number of "top-down" lithographic and "bottom-up" self-assembly methods have been developed to fabricate three-dimensional (3D) nanostructures to support the recent advances in nanotechnology. But they are limited by a number of factors such as fabrication cost, pattern resolution, and/or flexibility of geometry. Here we present a 3D nanolithography process that utilizes self-assembled nanospheres to create a periodic array of focal spots, which are then replicated across multiple depth in a transparent medium according to the Talbot effect. The Talbot field then exposes a pattern onto the underlying photoresist, recording the 3D intensity distribution. We have demonstrated designable complex 3D periodic structures with 80 nm minimum feature size, roughly one-fourth of the operating wavelength. This approach combines 2D colloidal self-assembly and 3D phase lithography, is robust, cost-effective, and widely applicable to nanoscale research and manufacturing.}, number={6}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Chang, C.-H. and Tian, L. and Hesse, W. R. and Gao, H. and Choi, H. J. and Kim, J.-G. and Siddiqui, M. and Barbastathis, G.}, year={2011}, month={Jun}, pages={2533–2537} }
 @article{chang_dominguez-caballero_choi_barbastathis_2011, title={Nanostructured gradient-index antireflection diffractive optics}, volume={36}, ISSN={0146-9592 1539-4794}, url={http://dx.doi.org/10.1364/ol.36.002354}, DOI={10.1364/ol.36.002354}, abstractNote={We describe the fabrication and characterization of a nanostructured diffractive element with near-zero reflection losses. In this element, subwavelength nanostructures emulating adiabatic index matching are integrated on the surface of a diffractive microstructure to suppress reflected diffraction orders. The fabricated silicon grating exhibits reflected efficiencies that are suppressed by 2 orders of magnitude over broad wavelength bands and wide incident angles. Theoretical models of the fabricated structure based on rigorous coupled-wave analysis and effective medium theory are in agreement with the experimental data. The proposed principles can be applied to improve the performance of any diffractive structures, potentially leading to more efficient Fresnel lenses, holographic elements, and integrated optical systems.}, number={12}, journal={Optics Letters}, publisher={The Optical Society}, author={Chang, Chih-Hao and Dominguez-Caballero, Jose A. and Choi, Hyungryul J. and Barbastathis, George}, year={2011}, month={Jun}, pages={2354} }
 @article{chang_in_takahashi_deterre_choi_gotrik_barbastathis_2010, title={Assembling nanoparticle catalysts with nanospheres for periodic carbon nanotube structure growth}, volume={22}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/0957-4484/22/3/035301}, DOI={10.1088/0957-4484/22/3/035301}, abstractNote={We have developed a novel method to grow carbon nanotubes in a periodic structure using a simple one-step self-assembly process. In this approach, monodispersed nanospheres are utilized to assemble smaller nanoparticle catalysts into an ordered periodic pattern. Using this process, we have grown carbon nanotube bundles into a honeycomb structure. The proposed method eliminates the need for lithography and material deposition, greatly reducing the fabrication complexity and cost.}, number={3}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Chang, Chih-Hao and In, Hyun Jin and Takahashi, Satoshi and Deterre, Martin and Choi, Hyungryul Johnny and Gotrik, Kevin W and Barbastathis, George}, year={2010}, month={Dec}, pages={035301} }
 @article{chang_waller_barbastathis_2010, title={Design and optimization of broadband wide-angle antireflection structures for binary diffractive optics}, volume={35}, ISSN={0146-9592 1539-4794}, url={http://dx.doi.org/10.1364/ol.35.000907}, DOI={10.1364/ol.35.000907}, abstractNote={We propose a class of antireflecting structures that can effectively suppress reflections for binary diffractive optics. In this structure, multiple periodic thin films with gradually varying refractive indices are used to shift all reflected diffraction to the transmitted orders. The structure is optimized to operate over broad bands and wide angles using rigorous coupled-wave analysis and genetic algorithms. We validated the structure numerically using finite-difference time-domain methods. The proposed structure may lead to more efficient diffractive devices for applications in thin-film photovoltaic, waveguide coupler, and holographic optical elements.}, number={7}, journal={Optics Letters}, publisher={The Optical Society}, author={Chang, Chih-Hao and Waller, Laura and Barbastathis, George}, year={2010}, month={Mar}, pages={907} }
 @article{voronov_ahn_anderson_cambie_chang_gullikson_heilmann_salmassi_schattenburg_warwick_et al._2010, title={High-efficiency 5000 lines/mm multilayer-coated blazed grating for extreme ultraviolet wavelengths}, volume={35}, ISSN={0146-9592 1539-4794}, url={http://dx.doi.org/10.1364/ol.35.002615}, DOI={10.1364/ol.35.002615}, abstractNote={Volume x-ray gratings consisting of a multilayer coating deposited on a blazed substrate can diffract with very high efficiency, even in high orders if diffraction conditions in-plane (grating) and out-of-plane (Bragg multilayer) are met simultaneously. This remarkable property, however, depends critically on the ability to create a structure with near atomic perfection. In this Letter we report on a method to produce these structures. We report measurements that show, for a 5000l/mm grating diffracting in the third order, a diffraction efficiency of 37.6% at a wavelength of 13.6nm. This work now shows a direct route to achieving high diffraction efficiency in high order at wavelengths throughout the soft x-ray energy range.}, number={15}, journal={Optics Letters}, publisher={The Optical Society}, author={Voronov, Dmitriy L. and Ahn, Minseung and Anderson, Erik H. and Cambie, Rossana and Chang, Chih-Hao and Gullikson, Eric M. and Heilmann, Ralf K. and Salmassi, Farhad and Schattenburg, Mark L. and Warwick, Tony and et al.}, year={2010}, month={Jul}, pages={2615} }
 @inproceedings{voronov_cambie_ahn_anderson_chang_gullikson_heilmann_salmassi_schattenburg_yashchuk_et al._2010, title={Ultra-high Resolution Optics for EUV and Soft X-ray Inelastic Scattering}, url={http://dx.doi.org/10.1063/1.3463360}, DOI={10.1063/1.3463360}, abstractNote={We describe a revolutionary new approach to high spectral resolution soft x-ray optics. Conventionally in the soft x-ray energy range, high spectral resolution is obtained by use of a relatively low line density grating operated in 1st order with small slits. This severely limits throughput. This limitation can be removed by use of a grating either in very high order, or with very high line density, if one can maintain high diffraction efficiency. We have developed a new technology for achieving both of these goals which should allow high throughput spectroscopy, at resolving powers of up to 106 at 1 keV. Such optics should provide a revolutionary advance for high resolution lifetime free spectroscopy, such as RIXS, and for pulse compression of chirped beams. We report recent developmental fabrication and characterization of a prototype grating optimized for 14.2 nm EUV light. The prototype grating with a 200 nm period of the blazed grating substrate coated with 20 Mo/Si bilayers with a period of 7.1 nm demonstrates good dispersion in the third order (effective groove density of 15,000 lines per mm) with a diffraction efficiency of more than 33percent.}, publisher={AIP}, author={Voronov, D. L. and Cambie, R. and Ahn, M. and Anderson, E. H. and Chang, C. H. and Gullikson, E. M. and Heilmann, R. K. and Salmassi, F. and Schattenburg, M. L. and Yashchuk, V. V. and et al.}, year={2010} }
 @article{chang_tan_miao_barbastathis_2009, title={Self-assembled ferrofluid lithography: patterning micro and nanostructures by controlling magnetic nanoparticles}, volume={20}, ISSN={0957-4484 1361-6528}, url={http://dx.doi.org/10.1088/0957-4484/20/49/495301}, DOI={10.1088/0957-4484/20/49/495301}, abstractNote={We have developed an alternative self-assembly process to pattern different geometries with user-defined tunability across the micro and nanoscale. In this approach, field-induced assembly of colloidal magnetic nanoparticles within a microfluidic channel is used as a tunable mask for near-field lithography. We have fabricated dot arrays with controllable spacing and micro-ring patterns with 250 nm feature sizes. The proposed process is versatile, cost-effective, and scalable, presenting itself as a promising nanomanufacturing tool.}, number={49}, journal={Nanotechnology}, publisher={IOP Publishing}, author={Chang, Chih-Hao and Tan, Chee-Wee and Miao, Jianmin and Barbastathis, George}, year={2009}, month={Nov}, pages={495301} }
 @article{chang_heilmann_schattenburg_glenn_2008, title={Design of a double-pass shear mode acousto-optic modulator}, volume={79}, ISSN={0034-6748 1089-7623}, url={http://dx.doi.org/10.1063/1.2894210}, DOI={10.1063/1.2894210}, abstractNote={The design of a compact double-pass shear mode acousto-optic modulator for high power operation in the UV is presented. Using a spherical mirror retroreflector in the second pass to correct for beam deflection, changes in beam position and angle during frequency tuning can be eliminated. The use of the shear mode acousto-optic interaction offers several key advantages, but the strain-induced birefringence creates significant levels of spectral leakage in the system. These effects and the polarization of the beams are analyzed to minimize leakage. Using a heterodyne interferometry scheme, two double-pass acousto-optic modulators with offset acoustic frequency inputs are set up to measure the leakage intensity. The designed double-pass shear mode acousto-optic modulator was tested with λ=351.1nm and demonstrated a peak double-pass efficiency of 42.6% and a bandwidth of 28MHz. Over this bandwidth the spectral leakage was reduced to ∼0.01%–0.04% relative intensity.}, number={3}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Chang, Chih-Hao and Heilmann, R. K. and Schattenburg, M. L. and Glenn, P.}, year={2008}, month={Mar}, pages={033104} }
 @article{chang_zhao_heilmann_schattenburg_2008, title={Fabrication of 50 nm period gratings with multilevel interference lithography}, volume={33}, ISSN={0146-9592 1539-4794}, url={http://dx.doi.org/10.1364/ol.33.001572}, DOI={10.1364/ol.33.001572}, abstractNote={We have developed a multilevel interference lithography process to fabricate 50 nm period gratings using light with a 351.1 nm wavelength. In this process multiple grating levels patterned by interference lithography are overlaid and spatial-phase aligned to a common reference grating using interferometry. Each grating level is patterned with offset phase shifts and etched into a single layer to achieve spatial-frequency multiplication. The effect of the multilayer periodic structure on interference lithography is examined to optimize the fabrication process. This process presents a general scheme for overlaying periodic structures and can be used to fabricate more complex periodic structures.}, number={14}, journal={Optics Letters}, publisher={The Optical Society}, author={Chang, Chih-Hao and Zhao, Y. and Heilmann, R. K. and Schattenburg, M. L.}, year={2008}, month={Jul}, pages={1572} }
 @article{chang_zhao_heilmann_schattenburg_2008, title={Spatial-frequency multiplication with multilevel interference lithography}, volume={26}, ISSN={1071-1023 1520-8567}, url={http://dx.doi.org/10.1116/1.2976604}, DOI={10.1116/1.2976604}, abstractNote={The authors present a large-area spatial-frequency multiplication fabrication process for patterning one-dimensional periodic structures using multilevel interference lithography. In this process, multiple grating levels with different phase offsets are overlaid by aligning to a reference grating. Each grating level is pattern transfered into a single hard mask layer, effectively reducing the grating period. The linewidth of the grating lines is controlled with nanometer repeatability by plasma etching and an image-reversal process. The authors demonstrate overlay accuracy of 0.6±1.9nm over 16×12mm2 for two levels of 200nm period gratings. Using this process, a subdiffraction-limited resolution grating with 100nm period is fabricated using light with λ=351.1nm. This process can also be used to fabricate more complex periodic geometries.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Chang, Chih-Hao and Zhao, Y. and Heilmann, R. K. and Schattenburg, M. L.}, year={2008}, month={Nov}, pages={2135–2138} }
 @article{zhao_chang_heilmann_schattenburg_2007, title={Phase control in multiexposure spatial frequency multiplication}, volume={25}, ISSN={1071-1023}, url={http://dx.doi.org/10.1116/1.2794318}, DOI={10.1116/1.2794318}, abstractNote={Multiexposure spatial frequency multiplication is a technique that allows the spatial frequency of grating patterns to be increased by integer factors 2,3,4,… by applying a nonlinear development process between patterning steps. One of the main technical issues with this technique is how to accurately place subsequent patterns on a substrate with respect to previously established patterns, which is referred to as phase control of the overlay. The authors report a technique that achieves accurate phase control over large areas during spatial frequency multiplication by utilizing a surrounding alignment grating. Three key factors—the angle, period, and phase of the alignment grating—have been accurately measured and utilized to position subsequent patterns with respect to previous patterns. Some factors that can dramatically diminish the accuracy of phase control, such as particle-induced substrate distortion and nonlinear distortion of the alignment grating, have also been considered and minimized in order to improve the accuracy of phase control. For spatial frequency doubling with a 574 nm principal pitch, the authors achieved overlay phase errors with a mean of −1.0 nm±2.8 nm(1σ) between level 1 and level 2 grating patterns over a 25×32.5 mm2 area.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Zhao, Yong and Chang, Chih-Hao and Heilmann, Ralf K. and Schattenburg, Mark L.}, year={2007}, pages={2439} }
 @article{chang_akilian_schattenburg_2006, title={Describing isotropic and anisotropic out-of-plane deformations in thin cubic materials by use of Zernike polynomials}, volume={45}, ISSN={0003-6935 1539-4522}, url={http://dx.doi.org/10.1364/ao.45.000432}, DOI={10.1364/ao.45.000432}, abstractNote={Isotropic and anisotropic out-of-plane deformations induced by thin-film residual stress on thin cubic materials are studied. By transforming the compliance tensor, an analytical expression can be derived for the biaxial stiffness modulus for all directions in any given cubic crystal plane. A modified Stoney's equation, including both isotropic and anisotropic terms, can be formulated to predict the anisotropic out-of-plane deformation. The isotropic and anisotropic deformations are then described using the Zernike polynomials U21 and U22, respectively. Experimental results from (100) and (110) silicon wafers confirm the model by quantitatively comparing the changes in Z21 and Z22 coefficients due to thin-film stress.}, number={3}, journal={Applied Optics}, publisher={The Optical Society}, author={Chang, Chih-Hao and Akilian, Mireille and Schattenburg, Mark L.}, year={2006}, month={Jan}, pages={432} }
 @article{seely_goray_kjornrattanawanich_laming_holland_flanagan_heilmann_chang_schattenburg_rasmussen_2006, title={Efficiency of a grazing-incidence off-plane grating in the soft-x-ray region}, volume={45}, ISSN={0003-6935 1539-4522}, url={http://dx.doi.org/10.1364/ao.45.001680}, DOI={10.1364/ao.45.001680}, abstractNote={Efficiency measurements of a grazing-incidence diffraction grating in the off-plane mount were performed using polarized synchrotron radiation. The grating had 5000 grooves/mm, an effective blaze angle of 14 degrees, and was gold coated. The efficiencies in the two polarization orientations (TM and TE) were measured in the 1.5-5.0 nm wavelength range and were compared with the efficiencies calculated using the PCGrate-SX code. The TM and TE efficiencies differ, offering the possibility of performing unique science studies of astrophysical, solar, and laboratory sources by exploiting the polarization sensitivity of the off-plane grating.}, number={8}, journal={Applied Optics}, publisher={The Optical Society}, author={Seely, J. F. and Goray, L. I. and Kjornrattanawanich, Benjawan and Laming, J. M. and Holland, G. E. and Flanagan, K. A. and Heilmann, R. K. and Chang, C.-H. and Schattenburg, M. L. and Rasmussen, A. P.}, year={2006}, month={Mar}, pages={1680} }
 @article{kowalski_heilmann_schattenburg_chang_berendse_hunter_2006, title={Near-normal-incidence extreme-ultraviolet efficiency of a flat crystalline anisotropically etched blazed grating}, volume={45}, ISSN={0003-6935 1539-4522}, url={http://dx.doi.org/10.1364/ao.45.001676}, DOI={10.1364/ao.45.001676}, abstractNote={We have measured the extreme-ultraviolet (EUV) efficiency at an angle of incidence of 10 degrees of a flat crystalline anisotropically etched blazed grating. The measured efficiencies are high for uncoated gratings and agree well with a calculated model derived from a reasonable estimate of the groove profile. The highest groove efficiencies derived from the measurements are 48.8% at 19.07 nm and 64.1% at 16.53 nm for the -2 and -3 orders, respectively, which are comparable to the best values obtained yet from a holographic ion-etched blazed grating. This presents opportunities to instrument designs for high-resolution EUV spectroscopy in astrophysics where high efficiency in high orders is desirable.}, number={8}, journal={Applied Optics}, publisher={The Optical Society}, author={Kowalski, Michael P. and Heilmann, Ralf K. and Schattenburg, Mark L. and Chang, Chih-Hao and Berendse, Frederick B. and Hunter, William R.}, year={2006}, month={Mar}, pages={1676} }
 @article{montoya_chang_heilmann_schattenburg_2005, title={Doppler writing and linewidth control for scanning beam interference lithography}, volume={23}, ISSN={0734-211X}, url={http://dx.doi.org/10.1116/1.2127938}, DOI={10.1116/1.2127938}, abstractNote={Scanning beam interference lithography (SBIL) is a technique which is used to create large-area periodic patterns with high phase accuracy. This is accomplished by combining interference lithography and an X-Y scanning stage. We previously reported parallel scan mode in which the stage scans in a direction parallel to the interference fringes. Here we present a method called Doppler scanning. In this mode, the stage is scanned perpendicular to the interference fringes. In order to obtain high-contrast latent gratings in the exposed photoresist, several parameters must be controlled. These parameters include vibration, fringe period error, time delay (for Doppler writing), dose, beam overlap, and polarization. In this article we present results of how the time delay, fringe period error, and exposure dose effect the contrast and linewidth of our latent grating images. Furthermore, SBIL has a unique ability to read gratings in a metrology mode configuration. This article also describes how Doppler metrology mode allows us to measure the time delay of our system.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Montoya, Juan C. and Chang, Chih-Hao and Heilmann, Ralf K. and Schattenburg, Mark L.}, year={2005}, pages={2640} }
 @article{chang_montoya_akilian_lapsa_heilmann_schattenburg_li_flanagan_rasmussen_seely_et al._2004, title={High fidelity blazed grating replication using nanoimprint lithography}, volume={22}, ISSN={0734-211X}, url={http://dx.doi.org/10.1116/1.1809614}, DOI={10.1116/1.1809614}, abstractNote={We report progress in using nanoimprint lithography to fabricate high fidelity blazed diffraction gratings. Anisotropically etched silicon gratings with 200nm period and 7.5° blaze angle were successfully replicated onto 100mm diameter wafers with subnanometer roughness and excellent profile conformity. Out-of-plane distortion induced by residual stress from polymer films was also analyzed and found to be extremely low. The replicated blazed gratings were tested and demonstrated high x-ray diffraction efficiencies. This process was developed for fabricating blazed diffraction gratings for the NASA Constellation-X x-ray telescope.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Chang, Chih-Hao and Montoya, J. C. and Akilian, M. and Lapsa, A. and Heilmann, R. K. and Schattenburg, M. L. and Li, M. and Flanagan, K. A. and Rasmussen, A. P. and Seely, J. F. and et al.}, year={2004}, pages={3260} }
 @article{chang_heilmann_fleming_carter_murphy_schattenburg_bailey_ekerdt_frankel_voisin_2003, title={Fabrication of sawtooth diffraction gratings using nanoimprint lithography}, volume={21}, ISSN={0734-211X}, url={http://dx.doi.org/10.1116/1.1627814}, DOI={10.1116/1.1627814}, abstractNote={We report a process which integrates interference lithography, nanoimprint lithography, and anisotropic etching to fabricate replicated diffraction gratings with sawtooth profiles. This new process greatly reduces grating fabrication time and cost, while preserving the groove shape and smoothness. Relief gratings with 400 nm period inverted triangular profiles and 200 nm period gratings with 7° blaze angle were replicated from silicon masters with surface roughness of less than 1 nm. This process was developed for fabricating the off-plane blazed diffraction gratings for the NASA Constellation-X x-ray telescope.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Chang, Chih-Hao and Heilmann, R. K. and Fleming, R. C. and Carter, J. and Murphy, E. and Schattenburg, M. L. and Bailey, T. C. and Ekerdt, J. G. and Frankel, R. D. and Voisin, R.}, year={2003}, pages={2755} }
 @article{konkola_chen_heilmann_joo_montoya_chang_schattenburg_2003, title={Nanometer-level repeatable metrology using the Nanoruler}, volume={21}, ISSN={0734-211X}, url={http://dx.doi.org/10.1116/1.1610003}, DOI={10.1116/1.1610003}, abstractNote={We report on the measurement of the fringe-to-substrate phase error in our Nanoruler system. This system utilizes scanning beam interference lithography to pattern and measure large-area, nanometer-accuracy gratings that are appropriate for semiconductor and integrated opto-electronic metrology. We present the Nanonruler’s metrology system that is based on digital frequency synthesizers, acousto-optics, and heterodyne phase sensing. It is used to assess the fringe-to-substrate placement stability and the accuracy of the feedback signals. The metrology system can perform measurements in real time, on the fly, and at arbitrary locations on the substrate. Experimental measurements are presented that demonstrate the nanometer-level repeatability of the system. Dominant error sources are highlighted.}, number={6}, journal={Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures}, publisher={American Vacuum Society}, author={Konkola, Paul T. and Chen, Carl G. and Heilmann, Ralf K. and Joo, Chulmin and Montoya, Juan C. and Chang, Chih-Hao and Schattenburg, Mark L.}, year={2003}, pages={3097} }