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Quantum Size Effects on the Chemical Sensing Performance of Two-Dimensional Semiconductors
Nah, Junghyo,Kumar, S. Bala,Fang, Hui,Chen, Yu-Ze,Plis, Elena,Chueh, Yu-Lun,Krishna, Sanjay,Guo, Jing,Javey, Ali American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.17
<P>We investigate the role of quantum confinement on the performance of gas sensors based on two-dimensional InAs membranes. Pd-decorated InAs membranes configured as H<SUB>2</SUB> sensors are shown to exhibit strong thickness dependence, with ∼100× enhancement in the sensor response as the thickness is reduced from 48 to 8 nm. Through detailed experiments and modeling, the thickness scaling trend is attributed to the quantization of electrons which favorably alters both the position and the transport properties of charge carriers; thus making them more susceptible to surface phenomena.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-17/jp300446z/production/images/medium/jp-2012-00446z_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp300446z'>ACS Electronic Supporting Info</A></P>
In situ doping control and electrical transport investigation of single and arrayed CdS nanopillars
Gu, Leilei,Liu, Xi,Kwon, Kyungmook,La, Chih-Chung,Lee, Min Hyung,Yu, Kyoungsik,Chueh, Yu-Lun,Fan, Zhiyong The Royal Society of Chemistry 2013 Nanoscale Vol.5 No.16
<P>Highly aligned intrinsic and indium doped CdS nanopillar arrays were fabricated via a template assisted Solid Source Chemical Vapor Deposition method (SSCVD). The prepared nanopillar arrays were well aligned, dense and uniform in diameter and length. Their geometry can be well defined by the design of the templates. These unique properties make them promising candidates for future photonic and optoelectronic devices. The structure of the prepared nanopillars has been studied by high resolution transmission electron microscopy and their different growth orientation as compared to those grown in free space has been observed and interpreted by the template induced change of the liquid-solid interfacial energy and the surface tension at the edge of the circular interface. To investigate electrical property of CdS nanopillars, vertical nanopillar array devices and horizontal individual nanopillar field-effect transistors have been fabricated and characterized. The measurements showed that the location of the indium doping source significantly affected carrier concentration, conductivity and field-effect mobility of the prepared CdS nanopillars. Particularly, it was found that conductivity could be improved by 4 orders of magnitude and field-effect mobility could be enhanced up to 50 cm(2) V(-1) s(-1) via proper doping control. These results enable further applications of CdS nanopillars in nano-optoelectronic applications such as photodetection and photovoltaics in the future.</P>
p‐Type InP Nanopillar Photocathodes for Efficient Solar‐Driven Hydrogen Production
Lee, Min Hyung,Takei, Kuniharu,Zhang, Junjun,Kapadia, Rehan,Zheng, Maxwell,Chen, Yu‐,Ze,Nah, Junghyo,Matthews, Tyler S.,Chueh, Yu‐,Lun,Ager, Joel W.,Javey, Ali WILEY‐VCH Verlag 2012 Angewandte Chemie Vol.124 No.43
<P><B>Perfekte Textur</B>: Der Einfluss der Oberflächen‐Nanotexturierung, der TiO<SUB>2</SUB>‐Passivierung und des Ru‐Cokatalysators auf die photoelektrochemische Wasserstoffentwicklung durch p‐InP‐Photokathoden wurde untersucht. Höhere Stromdichten und günstigere Onset‐Potentiale werden nach Oberflächen‐Nanotexturierung beobachtet. NHE=Normalwasserstoffelektrode.</P>
Ordered Arrays of Dual-Diameter Nanopillars for Maximized Optical Absorption
Fan, Zhiyong,Kapadia, Rehan,Leu, Paul W.,Zhang, Xiaobo,Chueh, Yu-Lun,Takei, Kuniharu,Yu, Kyoungsik,Jamshidi, Arash,Rathore, Asghar A.,Ruebusch, Daniel J.,Wu, Ming,Javey, Ali American Chemical Society 2010 Nano letters Vol.10 No.10
<P>Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the optimal absorption efficiency. Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance, with the absorbance showing a strong diameter dependency. To enhance the broad band optical absorption efficiency, a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient. The enabled single-crystalline absorber material with a thickness of only 2 μm exhibits an impressive absorbance of ∼99% over wavelengths, λ = 300−900 nm. These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-10/nl1010788/production/images/medium/nl-2010-010788_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl1010788'>ACS Electronic Supporting Info</A></P>
Manikandan, Arumugam,Ilango, P. Robert,Chen, Chia-Wei,Wang, Yi-Chung,Shih, Yu-Chuan,Lee, Ling,Wang, Zhiming M.,Ko, Hyunhyub,Chueh, Yu-Lun The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.31
<P>Here, we demonstrate the successful synthesis of (1T/2H) MoS2/α-MoO3 heterostructured nanoflowers at a low temperature of 200 °C by a one-step hydrothermal method. By tuning the reaction time under the influence of thiourea and hydrazine hydrate, we established a complete phase-engineered MoS2 with 1T and 2H phases on the surface of α-MoO3. Active sites associated with the phase-engineered (1T/2H) MoS2/α-MoO3 hybrid nanoflowers enable them to exhibit dual roles as a superior dye adsorbent and an electrocatalyst towards the hydrogen evolution reaction. The 2H-rich (1T/2H) MoS2/α-MoO3 hybrid heterostructured nanoflowers prepared at 16 h achieved a high surface area of 37.97 m<SUP>2</SUP> g<SUP>−1</SUP>, and 97% of the RhB dye with an initial concentration of 47.9 mg L<SUP>−1</SUP> was removed within 10 min through the adsorption process, which is the highest known removal efficiency reported in the literature. As a hydrogen evolution reaction (HER) electrocatalyst in acidic solution, the 1T-rich (1T/2H) MoS2/α-MoO3 hybrid heterostructured nanoflowers prepared at 12 h exhibited a highly efficient catalytic activity by achieving a low overpotential of 232 mV at a current density of 10 mA cm<SUP>−2</SUP>, which is comparable to those of previously reported HER catalysts based on MoS2. Moreover, this sample reached a low Tafel slope of 81 mV dec<SUP>−1</SUP> and was stable when operated for more than 1000 cycles.</P>
Um, Doo-Seung,Lee, Youngsu,Lim, Seongdong,Park, Jonghwa,Yen, Wen-Chun,Chueh, Yu-Lun,Kim, Hyung-jun,Ko, Hyunhyub American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.39
<P>Development of broadband photodetectors is of great importance for applications in high-capacity optical communication, night vision, and biomedical imaging systems. While heterostructured photodetectors can expand light detection range, fabrication of heterostructures via epitaxial growth or wafer bonding still faces significant challenges because of problems such as lattice and thermal mismatches. Here, a transfer printing technique is used for the heterogeneous integration of InGaAs nanomembranes on silicon semiconductors and thus the formation of van der Waals heterojunction photodiodes, which can enhance the spectral response and photoresponsivity of Si photodiodes. Transfer-printed InGaAs nanomembrane/Si heterojunction photodiode exhibits a high rectification ratio (7.73 x 10(4) at +/- 3 V) and low leakage current (7.44 X 10(-5) A/cm(2) at(-3) V) in a dark state. In particular, the photodiode shows high photoresponsivities (7.52 and 2.2 A W-1 at a reverse bias of -3 V and zero bias, respectively) in the broadband spectral range (400-1250 nm) and fast rise-fall response times (13-16 ms), demonstrating broadband and fast photodetection capabilities. The suggested III-V/Si van der Waals heterostructures can be a robust platform for the fabrication of high-performance on-chip photodetectors compatible with Si integrated optical chips.</P>
Quantum Confinement Effects in Nanoscale-Thickness InAs Membranes
Takei, Kuniharu,Fang, Hui,Kumar, S. Bala,Kapadia, Rehan,Gao, Qun,Madsen, Morten,Kim, Ha Sul,Liu, Chin-Hung,Chueh, Yu-Lun,Plis, Elena,Krishna, Sanjay,Bechtel, Hans A.,Guo, Jing,Javey, Ali American Chemical Society 2011 NANO LETTERS Vol.11 No.11
<P>Nanoscale size effects drastically alter the fundamental properties of semiconductors. Here, we investigate the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nanomembranes with varied thicknesses of 5–50 nm. First, optical absorption studies are performed by transferring InAs “quantum membranes” (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized. These sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Finally, the effective electron mobility of InAs QMs is shown to exhibit anomalous field and thickness dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The results provide an important advance toward establishing the fundamental device physics of two-dimensional semiconductors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-11/nl2030322/production/images/medium/nl-2011-030322_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl2030322'>ACS Electronic Supporting Info</A></P>
Gate-Tunable and Programmable n-InGaAs/Black Phosphorus Heterojunction Diodes
Lee, Youngsu,Um, Doo-Seung,Lim, Seongdong,Lee, Hochan,Kim, Minsoo P.,Yang, Tzu-Yi,Chueh, Yu-Lun,Kim, Hyung-jun,Ko, Hyunhyub American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.26
<P>Semiconductor heterostructures have enabled numerous applications in diodes, photodetectors, junction field-effect transistors, and memory devices. Two-dimensional (2D) materials and III-V compound semiconductors are two representative materials providing excellent heterojunction platforms for the fabrication of heterostructure devices. The marriage between these semiconductors with completely different crystal structures may enable a new heterojunction with unprecedented physical properties. In this study, we demonstrate a multifunctional heterostructure device based on 2D black phosphorus and n-InGaAs nanomembrane semiconductors that exhibit gate-tunable, photoresponsive, and programmable diode characteristics. The device exhibits clear rectification with a large gate-tunable forward current, which displays rectification and switching with a maximum rectification ratio of 4600 and an on/off ratio exceeding 10<SUP>5</SUP>, respectively. The device also offers nonvolatile memory properties, including large hysteresis and stable retention of storage charges. By combining the memory and gate-tunable rectifying properties, the rectification ratio of the device can be controlled and memorized from 0.06 to 400. Moreover, the device can generate three different electrical signals by combining a photoresponsivity of 0.704 A/W with the gate-tunable property, offering potential applications, for example, multiple logic operator. This work presents a heterostructure design based on 2D and III-V compound semiconductors, showing unique physical properties for the development of multifunctional heterostructure devices.</P> [FIG OMISSION]</BR>