@article{saare_xie_parsons_2023, title={Comparison of BCl3, TiCl4, and SOCl2 chlorinating agents for atomic layer etching of TiO2 and ZrO2 using tungsten hexafluoride}, volume={41}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0002708}, DOI={10.1116/6.0002708}, abstractNote={Recent advances in the semiconductor industry have created an exigency for processes that allow to deposit and etch material in conformal matter in three-dimensional devices. While conformal deposition is achieved using atomic layer deposition (ALD), conformal etching can be accomplished by thermal atomic layer etching (ALE) which, like ALD, proceeds via a binary sequence of self-limiting reactions. This study explores ALE of TiO2 and ZrO2 using WF6 as a fluorinating agent, and BCl3, TiCl4, or SOCl2 as a co-reactant. The effect of co-reactant chemistry was studied using atomic force microscopy, in situ ellipsometry, and in vacuo Auger electron spectroscopy measurements along with thermodynamic modeling. All three co-reactants exhibited saturation and etch rates increasing with temperature. At 170 °C, TiO2 can be etched using WF6 with BCl3, TiCl4, or SOCl2, and the etching proceeds at 0.24, 0.18, and 0.20 nm/cycle, respectively. At 325 °C, ZrO2 ALE can occur using these same reactants, proceeding at 0.96, 0.74, and 0.13 nm/cycle, respectively. A higher temperature is needed for ZrO2 ALE versus TiO2 because the ZrCl4 product is less volatile than the corresponding TiCl4. During ZrO2 and TiO2 etching using BCl3 or TiCl4, boron oxide or titanium oxide intermediate layers, respectively, were formed on the surface, and they were subsequently removed by WF6. In contrast, for ALE of TiO2 using SOCl2, a similar intermediate layer is not observed. This study broadens the understanding of co-etchants role during thermal ALE and expands the range of reactants that can be used for vapor etching of metal oxides.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Saare, Holger and Xie, Wenyi and Parsons, Gregory N.}, year={2023}, month={Jul} }
 @article{wang_pirzada_xie_barbieri_hossain_opperman_pal_wei_parsons_khan_2022, title={Creating hierarchically porous banana paper-metal organic framework (MOF) composites with multifunctionality}, volume={28}, ISSN={["2352-9407"]}, url={https://doi.org/10.1016/j.apmt.2022.101517}, DOI={10.1016/j.apmt.2022.101517}, abstractNote={We report a robust approach to integrate metal-organic frameworks (MOF) via vapor phase synthesis on a cost-effective and mechanically durable fibrous banana paper (BP) substrate developed from lignocellulosic biomass. The unique hollow fibrous structure of BP combined with the methodology used produces MOF-fiber composites with uniform MOF distribution and enhanced functionalities, with minimal use of organic solvents. The BP-MOF composites demonstrate a high surface area of 552 m2/g and uniform surface growth of MOF on them. Mechanical strength and bending flexibility of the substrate is well retained after the MOF growth, while the hollow tubular nature and hierarchical porosity of the BP facilitate gas diffusion. The BP-MOF composites demonstrate strong antibacterial activity with 99.2% of E.coli destroyed within the first hour of incubation. Preliminary studies with smartphone-based volatile organic compound (VOC) sensor show enhanced 1-octen-3-ol vapor absorption on BP-MOF, indicating its potential for VOC capture and sensing. We believe that the sustainable nature and flexibility of the lignocellulosic BP substrate taken together with uniform growth of MOF on the hierarchically porous BP impart impressive attributes to these composites, which can be explored in diverse applications.}, journal={APPLIED MATERIALS TODAY}, publisher={Elsevier BV}, author={Wang, Siyao and Pirzada, Tahira and Xie, Wenyi and Barbieri, Eduardo and Hossain, Oindrila and Opperman, Charles H. and Pal, Lokendra and Wei, Qingshan and Parsons, Gregory N. and Khan, Saad A.}, year={2022}, month={Aug} }
 @article{dai_pradeep_zhu_xie_barton_si_ding_yu_parsons_2021, title={Freestanding Metal Organic Framework-Based Multifunctional Membranes Fabricated via Pseudomorphic Replication toward Liquid- and Gas-Hazards Abatement}, volume={10}, ISSN={["2196-7350"]}, url={https://doi.org/10.1002/admi.202101178}, DOI={10.1002/admi.202101178}, abstractNote={Abstract}, journal={ADVANCED MATERIALS INTERFACES}, publisher={Wiley}, author={Dai, Zijian and Pradeep, Shravan and Zhu, Jie and Xie, Wenyi and Barton, Heather F. and Si, Yang and Ding, Bin and Yu, Jianyong and Parsons, Gregory N.}, year={2021}, month={Oct} }
 @article{xie_parsons_2020, title={Thermal atomic layer etching of metallic tungsten via oxidation and etch reaction mechanism using O-2 or O-3 for oxidation and WCl6 as the chlorinating etchant}, volume={38}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/1.5134430}, DOI={10.1116/1.5134430}, abstractNote={Atomic layer etching (ALE), offering highly controlled removal of thin film materials, is considered as an enabling process technology for future development of transistor devices. The authors previously reported a thermal tungsten (W) ALE process using WF6 and O2 for temperatures ≥275 °C, and they recently discovered the opportunity for low-temperature W etching using WCl6 as the etchant instead of WF6. This article demonstrates a two-step, thermal W ALE process viable for temperatures ≥200 °C, consisting of an oxidation half-reaction with O2 or O3 and an etch half-reaction using WCl6 as the chlorinating etchant. In situ quartz crystal microbalance (QCM) analysis reveals that W ALE using O2 and WCl6 is self-limiting and proceeds at an etch rate of ∼7.3–8.2 Å/cycle for temperatures between 205 and 235 °C. QCM analysis further reveals a surface dependence in the etch rate of the O2/WCl6 process, where the etch rate is the largest during the first cycle and decreases to a smaller value in later cycles. In addition, the authors show that O3 is a more effective oxidant than O2 for W ALE at lower temperatures; saturation is achieved with a much shorter exposure. Etching of W films on silicon substrates was confirmed using ex situ techniques. Overall, this study increases the understanding of surface reactions in thermal ALE and expands the range of etchants and coreactants that are useful for thermal etching of metallic thin films.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Xie, Wenyi and Parsons, Gregory N.}, year={2020}, month={Mar} }
 @article{xie_khan_rojas_parsons_2018, title={Control of Micro- and Mesopores in Carbon Nanofibers and Hollow Carbon Nanofibers Derived from Cellulose Diacetate via Vapor Phase Infiltration of Diethyl Zinc}, volume={6}, ISSN={["2168-0485"]}, url={https://doi.org/10.1021/acssuschemeng.8b02014}, DOI={10.1021/acssuschemeng.8b02014}, abstractNote={Common thermoplastic polymers, such as poly(vinyl alcohol) and cellulose derivatives are abundant and inexpensive precursors for preparing carbon nanofibers. These polymers are soluble in common solvents and can be readily processed to prepare nanofibers with high external surface area. However, thermoplastic polymers undergo a melting transition upon heating, resulting in loss of initial morphology and low carbon yield. In this study, vapor infiltration of diethyl zinc (DEZ) is applied to modify electrospun cellulose diacetate (CDA) nanofibers before carbonization, resulting in excellent retention of the original fiber structure while maintaining a high surface area and pore size distribution. Our goal is to investigate the effect of inorganic modification on the morphology and structural properties of the carbon product from the CDA nanofibers. We found that the CDA nanofiber structure was preserved after incorporation of ∼10 wt % Zn by vapor infiltration of DEZ. In addition, we found the pore volume di...}, number={11}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, publisher={American Chemical Society (ACS)}, author={Xie, Wenyi and Khan, Saad and Rojas, Orlando J. and Parsons, Gregory N.}, year={2018}, month={Nov}, pages={13844–13853} }
 @article{xie_lemaire_parsons_2018, title={Thermally Driven Self-Limiting Atomic Layer Etching of Metallic Tungsten Using WF6 and O-2}, volume={10}, ISSN={["1944-8244"]}, url={https://doi.org/10.1021/acsami.7b19024}, DOI={10.1021/acsami.7b19024}, abstractNote={The semiconductor industry faces a tremendous challenge in the development of a transistor device with sub-10 nm complex features. Self-limiting atomic layer etching (ALE) is essential for enabling the manufacturing of complex transistor structures. In this study, we demonstrated a thermally driven ALE process for tungsten (W) using sequential exposures of O2 and WF6. Based on the insight gained from the previous study on TiO2 thermal ALE, we proposed that etching of W could proceed in two sequential reaction steps at 300 °C: (1) oxidation of metallic tungsten using O2 or O3 to form WO3(s) and (2) formation and removal of volatile WO2F2(g) during the reaction between WO3(s) and WF6(g). The O2/WF6 etch process was experimentally studied using a quartz crystal microbalance (QCM). We find that both the O2 and WF6 ALE half reactions are self-limiting, with an estimated steady-state etch rate of ∼6.3 Å/cycle at 300 °C. We also find that etching of W proceeds readily at 300 °C, but not at temperatures lower than 275 °C. Thermodynamic modeling reveals that the observed temperature dependence is likely due to the limited volatility of WO2F2. The use of WF6 with O3 in place of O2 also allows W etching, where the stronger oxidant leads to a larger mass removal rate per cycle. However, we find O2 to be more controllable for precise metal removal per cycle. In addition, etched W films were examined with ex situ analytical tools. Using spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM), we confirm etching of tungsten film on silicon substrates. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed a minimal fluorine content on the W film after partial etching and on the silicon surface after full etching. This suggests that W ALE does not significantly alter the chemical composition of W films. This work serves to increase the understanding of ALE reactions and expand the base of available ALE processes for advanced material processing.}, number={10}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Xie, Wenyi and Lemaire, Paul C. and Parsons, Gregory N.}, year={2018}, month={Mar}, pages={9147–9154} }
 @article{li_xie_wilt_willoughby_rojas_2018, title={Thermally Stable and Tough Coatings and Films Using Vinyl Silylated Lignin}, volume={6}, ISSN={["2168-0485"]}, DOI={10.1021/acssuschemeng.7b03387}, abstractNote={We modified lignin, a renewable biomacromolecule with high carbon density, with silicon-containing vinyl groups via a highly efficient silylation reaction that achieved ∼30% substitution of lignin’s hydroxyl units. This exothermic process was carried out in the melt state, in situ, in a reactive extruder. 1H, 13C, and 31P NMR and FTIR confirmed the success of the silylation and were used to access the reactivity of the vinyl silylated lignin for copolymerization with polyacrylonitrile (PAN). Copolymers of the unmodified lignin and PAN were also produced as a reference. Importantly, the rheological behaviors of the copolymers of lignin and PAN were suitable for application in surface coating and films that were not possible if lignin or physical mixtures of lignin and PAN were used. Glass surfaces were treated via solution casting followed by oven drying, yielding films that were evaluated regarding their morphology (SEM) and thermal properties (TGA and DSC). The films produced with copolymers based on vin...}, number={2}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, author={Li, Shuai and Xie, Wenyi and Wilt, Meghan and Willoughby, Julie A. and Rojas, Orlando J.}, year={2018}, month={Feb}, pages={1988–1998} }