Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L01: Materials Synthesis |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Zhifeng Ren, Univ of Houston Room: LACC 150A |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L01.00001: Topochemical Reduction of BaZrO3 Thin Films Thom Orvis, Yang Liu, Shanyuan Niu, Jayakanth Ravichandran Doping-induced electronic and ionic transport in perovskites have been of interest for numerous electronic and energy applications. Specifically, BaZrO3 has been studied widely as a proton conducting material. Electronic conduction in BaZrO3 is hard to achieve due to the low electron affinity of this material, though low electron affinity conductors find notable applications. Recent advances in the use of strong solid state reducing agents to induce topochemical reduction offers the possibility to achieve electron conduction in BaZrO3. Here, we report our study on CaH2 based reduction of BaZrO3 epitaxial thin films. We report the structural characterization and electrical properties of these films before and after reduction. Our studies show that hydride based reduction is a viable method to induce electron doping in BaZrO3, and we discuss the stability and properties of the reduced films using time-dependent property measurements. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L01.00002: A bottom up approach for producing highly effective electrical contacts to nanofin-based light emitting diodes Robin Hansen, Babak Nikoobakht Semiconducting nanowires have been examined for many different applications including nanophotonics, optoelectronics, and on-chip light sources which can be integrated into semiconducting manufacturing. ZnO nanowires and nanofins are materials suitable for use in the construction of high quantum efficiency nanolasers. Presented here is a bottom up technique for producing scalable electrical contacts on highly controlled ZnO nanofins grown laterally across p-type GaN through VLS growth. This produces a heterojunction between ZnO and GaN which provides for ideal nanoscale light emitters within the semiconducting material. Growth conditions are optimized for tall nanofins with a straight epitaxial growth. Nanofin structures are ideal for the anisotropic depositions of insulative oxides and metal contacts designed for a highly efficient electrical injection into the ZnO sidewalls. We will present results on how the thickness of the profile of the nanofins impacts thickness of the oxide and ways it can be adjusted via controlling its angle of deposition and thickness via reactive ion etching. The developed methods enable interfacing a massive number of nano-LEDs with metal electrodes which can be incorporated into more complex device designs. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L01.00003: Conditioning of III-Nitride nanowire Light Emitting Diodes (LEDs) Camelia Selcu, Brelon May, A T M Golam Sarwar, Roberto Myers Nanowire-based III-Nitride LEDs are attractive because they cover a wide range of band gap regions from deep UV to near IR, have a low defect density and can be grown on a variety of inexpensive substrates. However, the inhomogeneities of the nanowire ensemble result in a local variation of the current distribution and subsequently the LED efficiency. We used short-time overload (STO) voltages as a method to burn-out electrical shorts in order to homogenize the current flow. Using conductive atomic force microscopy (cAFM), by acquiring current maps at nanoscale, we show the existence and elimination of such nano-shorts due to STO. In macroscopic devices, these nano-shorts can be destroyed under a reverse bias. As a result, the threshold voltage and electroluminescence (EL) will increase. For UV nanowire LEDs, STO conditioning improved EL intensity by more than 200%. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L01.00004: Water Promotion on Chemical Vapor Deposited Large Area 2D MoS2 Yan Jiang, Usha Philipose, Jingbiao Cui, Yuankun Lin High quality and large area growth of mono-layered MoS2 is desired with good experimental repeatability and reproducibility. However, this is still a challenge to experimentalists. In this talk, I will present results of 2D MoS2 growth by chemical vapor deposition (CVD) using water as a promoter. It was found that water droplets have a promotion and stabilization effect on the growth of triangle-shape-flakes of 2-D MoS2 and continuous films of monolayer and multilayer. By varying the quantity and distribution of water on the growth substrate, it was possible to tune the size and number of layers of MoS2, the areal coverage of MoS2, and the distribution area to stacking direction. The results showed good experimental repeatability and reproducibility. Raman microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the layer number, island size, distribution and crystallinity based on optical images from optical microscopy. This study demonstrates the controllability on 2D MoS2 growth with a simple setup of water assistance and paves a new way for synthesizing large areas of 2D MoS2 through a simplified growth process that improves controllability and experimental repeatability and reproducibility. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L01.00005: Toward single photon emission in naturally contacted CVD grown WSe2 devices Thushan Wickramasinghe, Shrouq Aleithan, Sudiksha Khadka, Ruhi Thorat, Eric Stinaff Among two dimensional materials is the class of transition metal dichalcogenides (TMDs) which, in their single layer form, are found to be direct bandgap semiconductors, making them ideal of optoelectronic devices. While several groups have successfully demonstrated single photon emission from exfoliated monolayers, few layer boundaries, and defect boundaries in WSe2, there have been only a few reports in materials produced using CVD techniques. Our group has recently demonstrated success in growing naturally contacted TMDs such as MoS2 and WS2 using chemical vapor deposition (CVD) with finely tuned parameters to develop complex device structures. We are currently working to develop WSe2 devices by growing on predetermined structures that could potentially generate electrically driven single photons on demand. We will present our work to date on the development of WSe2 using both CVD and exfoliation techniques to create monolayers that exhibit single photon emission properties. Our ultimate goal is to employ techniques, such as a Hanburry-Brown and Twiss setup, to study these structures and their quantum emission properties. |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L01.00006: Two-dimensional N-type Doping in Silicon with Antimony April Jewell, Alexander Carver, Shouleh Nikzad, Michael Hoenk JPL-invented delta-doped and superlattice-doped ("2D-doped") silicon detectors offer high durability and high sensitivity to wavelengths spanning soft X-rays to near IR. Importantly, 2D-doped detectors offer a vast improvement in stability against damaging radiation. Device passivation by 2D-doping requires high dopant concentrations (~1014 cm-2) with dopant layers confined to within a few nanometers of the surface. P-type doping with B from an effusion cell is relatively straightforward; B evaporates as an atomic beam, and the small boron atoms incorporate with the silicon crystal lattice. Conversely, n-type doping of silicon using Sb presents challenges, arising primarily from the tendency of antimony to segregate to the surface. However, at sufficiently low Si deposition rates epitaxial growth is achieved for finite thicknesses even at low temperatures. We previously reported on the low-temperature growth of Sb delta-doped silicon, demonstrating activated dose concentrations as high as 2×1014 cm-2 and sharp dopant profiles (~35 Å FWHM). We have extended our capabilities to n-type superlattices. Electrical characterization and preliminary device measurements will be included. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L01.00007: Crystal growth, and high thermal conductivity in cubic zinc-blende BAs and BP Sheng Li, Xiaoyuan Liu, Qiye Zheng, Bai Song, Gang Chen, David Cahill, Bing Lv The zinc blende cubic BAs and BP, due to their potential ultra-high thermal conductivity (k) calculated through first principle approach, have attracted significant research efforts in the past few years. In order to experimentally verify the predicted high k values, high quality defect-free single crystal growth is needed to eliminate phonon scattering caused by defects such as deficiency, anti-site defects, voids, impurities, twin/grain boundaries. Herein, we have carried out systematical studies to: 1) find out the suitable crystal growth techniques for BAs and BP despite many challenges; 2) investigate the growth mechanism to optimize the crystal growth; and 3) grow large size of BAs and BP crystals up to 1.5 mm size where a high k up to 600 W/m/K is obtained in BP crystals from time-domain thermoreflectance (TDTR) measurements. The obtained k value is much higher than that of well-known AlN (~400 W/m/K), and is only smaller than that of C-based diamond and nanotube/graphene |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L01.00008: Seeded Growth and Characterization of Boron Arsenide Single Crystals with High Thermal Conductivity Fei Tian, Bai Song, Bing Lv, Jingying Sun, Shuyuan Huyan, Qi Wu, Jun Mao, Yizhou Ni, Zhiwei Ding, Samuel Huberman, Te-Huan Liu, Gang Chen, Shuo Chen, Paul Chu, Zhifeng Ren With the rapid miniaturization of modern microelectronic devices, the need for materials with high thermal conductivity for passive cooling is continuously growing. Recently, zinc-blende boron arsenide (BAs) has emerged with a surprisingly high lattice thermal conductivity of over 2000 W m-1 K-1 at room temperature as predicted by first-principles calculations, which makes it a potential competitor for diamond that holds the highest thermal conductivity to date. However, due to the extremely challenging difficulties in the preparation of high quality single crystals, experimental demonstration has not been obtained. Here, we report synthesis of BAs crystals (0.4 ~ 0.6 mm) via a seeded chemical vapor transport method. The measured thermal conductivity, at least 341 W m-1 K-1 at room temperature, is not as high as predicted, but is highest among reported values and comparable to that of popular high thermal conductivity materials like copper and aluminum nitride. Further improvement seems very possible along this direction. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L01.00009: Molecular dynamics simulations of faceting of silicon carbide nanoparticles Henrik Sveinsson, Anders Hafreager, Priya Vashishta, Anders Malthe-Sørenssen, Rajiv Kalia Equilibrium shapes of crystals can be calculated using Wulff construction. However, kinetic barriers can prevent a system from realizing its equilibrium shape. On the basis of a simple model, Mullins predicted that nanoparticles can be kinetically immobilized so that normal motion of facets does not happen, prohibiting the nanoparticle from realising its equilibrium shape. Using molecular dynamics simulations, we obtain the equilibrium shape of silicon carbide nanocrystals (n-SiC) from an initially spherical shape. During a 300 nanoseconds simulation at 2200 K, an 8 nm particle of SiC-3C transforms from its initial spherical shape to a rhombic dodecahedron. Furthermore, by performing multiple simulations – a total of 40 µs – of initially cylindrical SiC nanoparticles, we identify energy barriers to facet growth normal to facet planes. We find that the energy barrier to normal growth of facets on n-SiC is higher than in Mullins’ model, but we still observe normal motion of the facets. The final shapes of SiC nanoparticles are independent of the initial configuration when the temperature is sufficiently high to overcome the facet growth barrier. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L01.00010: Nucleation versus instability race in strained films. Jean Noel Aqua, Kailang Liu, Peter Voorhees, Isabelle Berbezier, Luc Favre, Antoine Ronda, Abbarchi Marco, Thomas David Under the generic term Stranski-Krastanov are grouped two different growth mechanisms of SiGe quantum dots. They result from the self-organized Asaro-Tiller-Grinfel'd (ATG) instability at low strain, while at high strain, from a stochastic nucleation. While these regimes are well known, we elucidate the origin of the transition between these two pathways thanks to a joint theoretical and experimental work. Nucleation is described within the master equation framework. By comparing the time scales for ATG instability development and three-dimensional (3D) nucleation onset, we demonstrate that the transition between these two regimes is simply explained by the crossover between their divergent evolutions. Nucleation exhibits a strong exponential deviation at low strain while ATG behaves only algebraically. Consequently, at high (low) strain, nucleation (instability) occurs faster and inhibits the alternate evolution. The crossover between nucleation and ATG instability is found to occur both experimentally and theoretically at a Ge composition around 50%. |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L01.00011: Effect of Vanadium doping on dielectric properties of TiO2 Nasima Khatun, Somaditya Sen The V doped TiO2 samples are prepared by the modified sol-gel process and sintered at 1400 °C. The phase formation is confirmed by XRD. The lattice parameters are decreased due to V doping. The V content in the samples is confirmed by EDX analysis. The grain sizes of all the samples are between 20-30 mm observed by SEM study. The dense nature of pellet surface is also revealed from SEM studies. The dielectric measurement is carried out in the frequency range from 1 Hz to 1 MHz. The dielectric constant increases in V doped TiO2 samples. The dielectric loss on the other hand, also increases with increasing doping concentration due to the presence of donor levels in the bandgap. The electrons in these donor levels can hop freely at room temperature. The high dielectric loss is a result of high conductivity which is arising out of these free hopping electrons. |
Wednesday, March 7, 2018 1:27PM - 1:39PM |
L01.00012: Mechanistic Insight into the Chemical Exfoliation and Functionalization of Ti3C2 MXene Avanish Mishra, Pooja Srivastava, Hiroshi MIZUSEKI, Kwang-Ryeol Lee, Abhishek Singh MXenes are chemically exfoliated from the bulk MAX phase using HF, however, mechanistic understanding of exfoliation and subsequent functionalization of these technologically important materials is still lacking. To emphasize the presence of the functional group, MXene is often presented as Mn+1CnTx, where T=F, OH, O. Using density-functional theory we show that exfoliation of Ti3C2 MXene proceeds via HF insertion through edges of Ti3AlC2 MAX phase. Spontaneous dissociation of HF and subsequent termination of edge Ti atoms by H/F weakens Al−MXene bonds. The consequent opening of interlayer gap allows further insertion of HF that leads to the formation of AlF3 and H2, which eventually come out of the MAX. Analysis of the calculated Gibbs free energy (△G) shows fully fluorinated MXene to be lowest in energy, whereas the formation of pristine MXene is thermodynamically least favorable. The△G for the mixed functionalized MXenes are close, indicating the non-uniform functionalization of MXene. The microscopic understanding gained here unveils the challenges in exfoliation of MXene. |
Wednesday, March 7, 2018 1:39PM - 1:51PM |
L01.00013: Hollow microstructures fabricated by combination of nonlinear laser lithography and wet etching deep inside silicon Petro Deminskyi, Ahmet Turnali, Mona Borra, Tahir Çolakoğlu, Alpan Bek, Rasit Turan, Fatih Ilday, Onur Tokel Silicon is the most widely used material in microelectronics and integrated photonics. Despite the different methods available, they generally do not allow the fabrication of 3D microstructures deep inside silicon. We have recently demonstrated laser-based two-step fabrication of complex 3D structures deep inside silicon (Tokel et al., Nat. Photon., 2017). Laser modification of desired points is based on permanent disruption of the crystalline structure as a result of the laser beam collapsing and momentarily creating conditions far from thermal equilibrium, leading to heat- and pressure-induced stresses. This disruption causes the Si-Si bonding to be much weakened in comparison to conventional crystalline Si, and the weakened structure can be chemically etched with high selectivity using an optimized HF, HNO3, CH3COOH, Cu(NO3)2, H2O. While the laser-induced disruption can be limited to a region with a diameter of ~1 µm, limited by the laser wavelength and can be induced at any point within the Si chip, the etched structures have minimal features sizes in the range of 5-10 µm. Here, we report a systematic study on this two-step process, including minimum achievable feature size after etching, optimization of the surface quality and complexity of the 3D structures. |
Wednesday, March 7, 2018 1:51PM - 2:03PM |
L01.00014: Subsurface processing of GaAs by nanosecond pulses Ahmet Turnali, Petro Deminsky, Serim Ilday, Fatih Ilday, Onur Tokel Gallium Arsenide (GaAs) has unique properties owing to its direct band-gap, offering significant optical and electrical device opportunities, including mid-infrared photonic applications. However, due to limitations in fabrication, GaAs-based devices are essentially constrained to the wafer surface. Here, we present the first laser-induced subsurface modifications formed deep inside GaAs wafers, without damaging the crystal above or below. By exploiting various nonlinear laser interactions, we have recently demonstrated arbitrary 3D fabrication inside silicon wafers, with ~1-µm resolution [1]. Here, using a similar approach, we demonstrate formation of deeply buried laser-induced modifications in GaAs. To the best of our knowledge, this is the first “in-chip” modification of this material. The observed disruptions are in the form of nanogratings, similar in nature to nanogratings observed in various materials [2]. Such modifications can be exploited for fabricating various micro-devices using optical index changes or potentially be used for functional components such as lenses and holograms for mid-infrared applications [1]. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700