Browsing by Author "Cheng, Lanxia"
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Item Hydroquinone-ZnO Nano-Laminate Deposited by Molecular-Atomic Layer Deposition(American Institute of Physics Inc) Huang, Jie; Lucero, Antonio T.; Cheng, Lanxia; Hwang, Hyeon Jun; Ha, M. -W; Kim, Jiyoung; 70133685 (Kim, J)In this study, we have deposited organic-inorganic hybrid semiconducting hydroquinone (HQ)/zinc oxide (ZnO) superlattices using molecular-atomic layer deposition, which enables accurate control of film thickness, excellent uniformity, and sharp interfaces at a low deposition temperature (150 °C). Self-limiting growth of organic layers is observed for the HQ precursor on ZnO surface. Nano-laminates were prepared by varying the number of HQ to ZnO cycles in order to investigate the physical and electrical effects of different HQ to ZnO ratios. It is indicated that the addition of HQ layer results in enhanced mobility and reduced carrier concentration. The highest Hall mobility of approximately 2.3 cm²/V·s and the lowest n-type carrier concentration of approximately 1.0 × 10¹⁸/cm³ were achieved with the organic-inorganic superlattice deposited with a ratio of 10 ZnO cycles to 1 HQ cycle. This study offers an approach to tune the electrical transport characteristics of ALD ZnO matrix thin films using an organic dopant. Moreover, with organic embedment, this nano-laminate material may be useful for flexible electronics.Item Low Temperature Synthesis of Graphite on Ni Films Using Inductively Coupled Plasma Enhanced CVD(Royal Soc Chemistry) Cheng, Lanxia; Yun, Kayoung; Lucero, Antonio; Huang, Jie; Meng, Xin; Lian, Guoda; Nam, Ho-Seok; Wallace, Robert M.; Kim, Moon J.; Venugopal, Archana; Colombo, Luigi; Kim, Jiyoung; A-5283-2008 (Wallace, RM); A-2297-2010 (Kim, MJ); 70133685 (Kim, J)Controlled synthesis of graphite at low temperatures is a desirable process for a number of applications. Here, we present a study on the growth of thin graphite films on polycrystalline Ni films at low temperatures, about 380 ⁰C, using inductively coupled plasma enhanced chemical vapor deposition. Raman analysis shows that the grown graphite films are of good quality as determined by a low I-D/I-G ratio, ~0.43, for thicknesses ranging from a few layers of graphene to several nanometer thick graphitic films. The growth of graphite films was also studied as a function of time, precursor gas pressure, hydrogen concentration, substrate temperature and plasma power. We found that graphitic films can be synthesized on polycrystalline thin Ni films on SiO₂/Si substrates after only 10 seconds at a substrate temperature as low as 200 ⁰C. The amount of hydrogen radicals, adjusted by changing the hydrogen to methane gas ratio and pressure, was found to dramatically affect the quality of graphite films due to their dual role as a catalyst and an etchant. We also find that a plasma power of about 50 W is preferred in order to minimize plasma induced graphite degradation.Item Nucleation and Growth of WSe₂: Enabling Large Grain Transition Metal Dichalcogenides(IOP Publishing Ltd, 2017-09-22) Yue, Ruoyu; Nie, Yifan; Walsh, Lee A.; Addou, Rafik; Liang, Chaoping; Lu, Ning; Barton, Adam T.; Zhu, Hui; Che, Zifan; Barrera, Diego; Cheng, Lanxia; Cha, Pil-Ryung; Chabal, Yves J.; Hsu, Julia W. P.; Kim, Jiyoung; Kim, Moon J.; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae; Hinkle, Christopher L.; 0000-0002-2910-2938 (Liang, C); Yue, Ruoyu; Nie, Yifan; Walsh, Lee A.; Addou, Rafik; Liang, Chaoping; Lu, Ning; Barton, Adam T.; Zhu, Hui; Che, Zifan; Barrera, Diego; Cheng, Lanxia; Chabal, Yves J.; Hsu, Julia W. P.; Kim, Jiyoung; Kim, Moon J.; Wallace, Robert M.; Cho, Kyeongjae; Hinkle, Christopher L.The limited grain size (< 200 nm) for transition metal dichalcogenides (TMDs) grown by molecular beam epitaxy (MBE) reported in the literature thus far is unsuitable for high-performance device applications. In this work, the fundamental nucleation and growth behavior of WSe₂ is investigated through a detailed experimental design combined with on-lattice, diffusion-based first principles kinetic modeling to enable large area TMD growth. A three-stage adsorption-diffusion-attachment mechanism is identified and the adatom stage is revealed to play a significant role in the nucleation behavior. To limit the nucleation density and promote 2D layered growth, it is necessary to have a low metal flux in conjunction with an elevated substrate temperature. At the same time, providing a Se-rich environment further limits the formation of W-rich nuclei which suppresses vertical growth and promotes 2D growth. The fundamental understanding gained through this investigation has enabled an increase of over one order of magnitude in grain size for WSe₂ thus far, and provides valuable insight into improving the growth of other TMD compounds by MBE and other growth techniques such as chemical vapor deposition (CVD).Item Organic-Inorganic Hybrid Semiconductor Thin Films Deposited Using Molecular-Atomic Layer Deposition (MALD)(Royal Society of Chemistry) Huang, Jie; Zhang, Hengji; Lucero, Antonio; Cheng, Lanxia; KC, Santosh; Wang, Jian; Hsu, Julia W. P.; Cho, Kyeongjae; Kim, Jiyoung; 0000 0003 8600 0978 (Hsu, JWP); 0000-0003-2698-7774 (Cho, K); 0000-0003-2781-5149 (Kim, J); Huang, Jie; Zhang, Hengji; Lucero, Antonio; Cheng, Lanxia; KC, Santosh; Wang, Jian; Hsu, Julia W. P.; Cho, Kyeongjae; Kim, JiyoungMolecular-atomic layer deposition (MALD) is employed to fabricate hydroquinone (HQ)/diethyl zinc (DEZ) organic-inorganic hybrid semiconductor thin films with accurate thickness control, sharp interfaces, and low deposition temperature. Self-limiting growth is observed for both HQ and DEZ precursors. The growth rate remains constant at approximately 2.8 Å per cycle at 150°C. The hybrid materials exhibit n-type semiconducting behavior with a field effect mobility of approximately 5.7 cm² V⁻¹ s⁻¹ and an on/off ratio of over 103 following post annealing at 200°C in nitrogen. The resulting films are characterized using ellipsometry, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-Vis spectroscopy, transistor behavior, and Hall-effect measurements. Density functional theory (DFT) and many-body perturbation theory within the GW approximation are also performed to assist the explanation and understanding of the experimental results. This research offers n-channel materials as valuable candidates for efficient organic CMOS devices. © 2016.