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Cheng, Lanxia,Lee, Jaebeom,Zhu, Hui,Ravichandran, Arul Vigneswar,Wang, Qingxiao,Lucero, Antonio T.,Kim, Moon J.,Wallace, Robert M.,Colombo, Luigi,Kim, Jiyoung American Chemical Society 2017 ACS NANO Vol.11 No.10
<P>The successful realization of high-performance 2D-materials-based nanoelectronics requires integration of high-quality dielectric films as a gate insulator. In this work, we explore the integration of organic and inorganic hybrid dielectrics on MoS<SUB>2</SUB> and study the chemical and electrical properties of these hybrid films. Our atomic force microscopy, X-ray photoelectron spectroscopy (XPS), Raman, and photoluminescence results show that, aside from the excellent film uniformity and thickness scalability down to 2.5 nm, the molecular layer deposition of octenyltrichlorosilane (OTS) and Al<SUB>2</SUB>O<SUB>3</SUB> hybrid films preserves the chemical and structural integrity of the MoS<SUB>2</SUB> surface. The XPS band alignment analysis and electrical characterization reveal that through the inclusion of an organic layer in the dielectric film, the band gap and dielectric constant can be tuned from ∼7.00 to 6.09 eV and ∼9.0 to 4.5, respectively. Furthermore, the hybrid films show promising dielectric properties, including a high breakdown field of ∼7.8 MV/cm, a low leakage current density of ∼1 × 10<SUP>–6</SUP> A/cm<SUP>2</SUP> at 1 MV/cm, a small hysteresis of ∼50 mV, and a top-gate subthreshold voltage swing of ∼79 mV/dec. Our experimental findings provide a facile way of fabricating scalable hybrid gate dielectrics on transition metal dichalcogenides for 2D-material-based flexible electronics applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2017/ancac3.2017.11.issue-10/acsnano.7b04813/production/images/medium/nn-2017-048138_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn7b04813'>ACS Electronic Supporting Info</A></P>
Low temperature synthesis of graphite on Ni films using inductively coupled plasma enhanced CVD
Cheng, Lanxia,Yun, Kayoung,Lucero, Antonio,Huang, Jie,Meng, Xin,Lian, Guoda,Nam, Ho-Seok,Wallace, Robert M.,Kim, Moon,Venugopal, Archana,Colombo, Luigi,Kim, Jiyoung The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.20
<▼1><P>Synthesis of good quality graphite on Ni using IC-PECVD at a low temperature of 380 °C in a hydrogen free environment.</P></▼1><▼2><P>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 °C, 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>I</I>D/<I>I</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 °C. 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.</P></▼2>
Solution synthesis of few-layer 2H MX<sub>2</sub> (M = Mo, W; X = S, Se)
Barrera, Diego,Wang, Qingxiao,Lee, Yun-Ju,Cheng, Lanxia,Kim, Moon J.,Kim, Jiyoung,Hsu, Julia W. P. The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.11
<P>Two-dimensional transition metal dichalcogenides (TMDs) exhibit a wide range of properties depending on the chemistry of the transition metal element and the chalcogen, making them promising candidates for electronic applications. Current TMD thin films are either derived from bulk minerals, hence limited by the impurities, defects, and the availability of raw materials, or deposited using high vacuum or high reaction temperature processes. Here, we describe a versatile method to directly synthesize few-layer 2H MoS2, MoSe2, WS2, and WSe2 flakes from thermolysis of organometallic precursors in the presence of a chalcogen element using microwave-assisted heating. We study how the concentration of a reducing agent, 1,2-hexadecanediol, affects the chemical composition of TMDs using X-ray photoelectron spectroscopy (XPS). The crystalline phase of these materials is determined as trigonal prismatic (2H) using Raman spectroscopy and scanning transmission electron microscopy (STEM). Both STEM and atomic force microscopy (AFM) indicate that these flakes are a few layers thick (∼2 nm) with a relatively large lateral size (∼2 μm).</P>
Huang, Jie,Zhang, Hengji,Lucero, Antonio,Cheng, Lanxia,KC, Santosh,Wang, Jian,Hsu, Julia,Cho, Kyeongjae,Kim, Jiyoung The Royal Society of Chemistry 2016 Journal of Materials Chemistry C Vol.4 No.12
<▼1><P>Molecular-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.</P></▼1><▼2><P>Molecular-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 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and an on/off ratio of over 10<SUP>3</SUP> 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.</P></▼2>
Kim, Harrison Sejoon,Meng, Xin,Kim, Si Joon,Lucero, Antonio T.,Cheng, Lanxia,Byun, Young-Chul,Lee, Joy S.,Hwang, Su Min,Kondusamy, Aswin L. N.,Wallace, Robert M.,Goodman, Gary,Wan, Alan S.,Telgenhoff, American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.51
<P>Correlations between physical properties linking film quality with wet etch rate (WER), one of the leading figures of merit, in plasma-enhanced atomic layer deposition (PEALD) grown silicon nitride (SiN<SUB><I>x</I></SUB>) films remain largely unresearched. Achieving a low WER of a SiN<SUB><I>x</I></SUB> film is especially significant in its use as an etch stopper for technology beyond 7 nm node semiconductor processing. Herein, we explore the correlation between the hydrogen concentration, hydrogen bonding states, bulk film density, residual impurity concentration, and the WERs of PEALD SiN<SUB><I>x</I></SUB> using Fourier transform infrared spectrometry, X-ray reflectivity, and spectroscopic ellipsometry, etc. PEALD SiN<SUB><I>x</I></SUB> films for this study were deposited using hexachlorodisilane and hollow cathode plasma source under a range of process temperatures (270-360 °C) and plasma gas compositions (N<SUB>2</SUB>/NH<SUB>3</SUB> or Ar/NH<SUB>3</SUB>) to understand the influence of hydrogen concentration, hydrogen bonding states, bulk film density, and residual impurity concentration on the WER. Varying hydrogen concentration and differences in the hydrogen bonding states resulted in different bulk film densities and, accordingly, a variation in WER. We observe a linear relationship between hydrogen bonding concentration and WER as well as a reciprocal relationship between bulk film density and WER. Analogous to the PECVD SiN<SUB><I>x</I></SUB> processes, a reduction in hydrogen bonding concentration arises from either (1) thermal activation or (2) plasma excited species. However, unlike the case with silane (SiH<SUB>4</SUB>)-based PECVD SiN<SUB><I>x</I></SUB>, PEALD SiN<SUB><I>x</I></SUB> WERs are affected by residual impurities of Si precursors (i.e., chlorine impurity). Thus, possible wet etching mechanisms in HF in which the WER is affected by hydrogen bonding states or residual impurities are proposed. The shifts of amine basicity in SiN<SUB><I>x</I></SUB> due to different hydrogen bonding states and the changes in Si electrophilicity due to Cl impurity content are suggested as the main mechanisms that influence WER in the PEALD processes.</P> [FIG OMISSION]</BR>
Lucero, Antonio T.,Byun, Young-Chul,Qin, Xiaoye,Cheng, Lanxia,Kim, Hyoungsub,Wallace, Robert M.,Kim, Jiyoung Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol. No.
<P>Atomic layer deposition is used to convert an (NH4)(2)S cleaned p-In0.53Ga0.47As with diethylzinc (DEZ) and water, resulting in the formation of a ZnO/ZnS interfacial passivation layer (IPL). The process is studied using in-situ X-ray photoelectron spectroscopy. DEZ reacts with sulfur and oxygen present on the surface, chemically reducing arsenic 3+ and gallium 3+ to lower oxidation states. The sulfur concentration remains constant during the deposition process while the oxygen concentration on the surface remains small, confirming that the IPL is composed of both ZnO and ZnS. Measurements of metal-oxide-semiconductor capacitors with HfO2 for the dielectric show that the ZnO/ZnS IPL can nearly eliminate frequency dispersion (<1% per frequency decade) in accumulation and results in small hysteresis (<60 mV) with a Dit in the 10(11) eV(-1) cm(-2) range in the midgap. Frequency dispersion is observed in the depletion region and is attributed to minority carrier generation from the ZnO present in the IPL. (C) 2016 The Japan Society of Applied Physics</P>
플라즈마 화학기상증착법을 이용한다층 그래핀의 저온합성과 성장 메커니즘
윤가영 ( Kayoung Yun ),정다솔 ( Dasol Cheang ),현지연 ( Jiyeon Hyun ),노애란 ( Aeran Roh ),허선 ( Sun Heo ),( Lanxia Cheng ),( Jiyong Kim ),차필령 ( Pil Ryung Cha ),이재갑 ( Jagab Lee ),남호석 ( Ho Seok Nam ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.11
Multi-layer graphene is considered to be a potential replacement of copper wiring for LSI (large-scale integration). PECVD (plasma enhanced chemical vapor deposition) is one of the most reliable synthesis techniques to manufacture high-quality, large-scale graphene at low temperature. Compared with thermal CVD graphene, the relatively lower quality of PECVD graphene is its main drawback. In order to suggest a solution for this problem, we studied the growth mechanism of multi-layer graphene deposited onto nickel by PECVD at 400 ℃. We found that both segregation and solution-precipitation models affect the growth behavior of multi-layer graphene. To support this, we analyzed the influences of Ni-film thickness, cooling rate, and plasma energy on multi-layer graphene growth. The results from this study would be useful for optimizing graphene growth conditions for many applications.