@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={["1521-4095"]}, DOI={10.1002/adma.202006801}, abstractNote={Light-emitting diodes (LEDs) with directional and polarized light emission have many photonic applications, and beam shaping of these devices is fundamentally challenging because they are Lambertian light sources. In this work, using organic and perovskite LEDs (PeLEDs) for demonstrations, by selectively diffracting the transverse electric (TE) waveguide mode while suppressing other optical modes in a nanostructured LED, the authors first demonstrate highly directional light emission from a full-area organic LED with a small divergence angle less than 3° and a TE to transverse magnetic (TM) polarization extinction ratio of 13. The highly selective diffraction of only the TE waveguide mode is possible due to the planarization of the device stack by thermal evaporation and solution processing. Using this strategy, directional and polarized emission from a perovskite LED having a current efficiency 2.6 times compared to the reference planar device is further demonstrated. This large enhancement in efficiency in the PeLED is attributed to a larger contribution from the TE waveguide mode resulting from the high refractive index in perovskite materials.}, number={9}, journal={ADVANCED MATERIALS}, 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={Mar} }
 @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={Quasi-2D Ruddlesden–Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA)2(FA)3Pb4Br13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carrier dynamics. These data show that highly oriented 2D crystal films have a faster energy transfer from the high-bandgap domains to the low-bandgap domains (<0.5 ps) compared to the randomly oriented films. High-performance light-emitting diodes can be realized with these highly oriented 2D films. Finally, amplified spontaneous emission with a low threshold 4.16 µJ cm−2 is achieved and distributed feedback lasers are also demonstrated. These results show that it is important to control the morphology of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for light-emitting devices.}, 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 that determine the propagation of photons. By incorporating PhCs into organic light-emitting diodes (OLEDs), the device efficiency and emission spectra can be modified, which can be explained and predicted by the mode dispersion. In this work, we experimentally measure the mode dispersion of 1-D and 2-D PhC OLEDs at different azimuthal angles with angle-resolved electroluminescence spectra. The results are explained using an intuitive geometry approach, which shifts and slices the cone-shaped optical modes to obtain the mode dispersion of PhC OLEDs. We note that the weak cavity mode and a narrow photonic band gap are visible only after eliminating the intrinsic emitter spectrum in the air mode dispersion. In the end, we discuss the implication of mode dispersion on the OLED light extraction.}, 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{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.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...}, 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{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}, 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{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} }