Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T12: Focus Session: Non-Oxide Nanostructures and Artificially Structured Materials and Related Phenomena |
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Sponsoring Units: DMP Chair: Pratibha Dev, Naval Research Laboratory Room: 007C |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T12.00001: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T12.00002: Artificially-Engineered III-Nitride Digital Alloy for Solar Energy Harvesting Wei Sun, Chee-Keong Tan, Nelson Tansu The pursuit of III-Nitride based solar cell has been primarily driven by the attribute of broad solar spectrum coverage through the use of InGaN material. However, the phase separation in high In-content InGaN alloy has been one of the largest barrier in the pursuit of nitride-based solar cells. Thus, a new approach in extending the bandgap coverage in nitride-based alloy needs to be pursued. In this work, we propose a novel artificially engineered III-Nitride based digital alloy structure to overcome the limitation presented by the epitaxy of phase-separated InGaN material with high In-content. The InGaN digital alloy structure is a short period superlattice that is formed by GaN and InN thin film layers alternately in which the thickness of each layer is represented by a number of monolayer (ML). By adjusting the thickness of GaN layer (m MLs) and InN layer (n MLs), the In-content and the band structure of InGaN digital alloy can be engineered correspondingly. The use of this digital alloys demonstrated suitability of this method in extending the bandgap coverage in nitride-based semiconductors. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T12.00003: Simulation of Epitaxial Growth of DNA-nanoparticle Superlattices on Pre-patterned Substrates Saijie Pan, Ting Li, Monica Olvera de la Cruz DNA self-assembly is a well-developed approach towards the construction of a great variety of nanoarchitectures. E-beam lithography is widely used for high-resolution nanoscale patterning. Recently, a new technique combining the two methods was developed to epitaxially grow DNA-mediated nanoparticle superlattices on a pre-patterned surface[1]. Here we use multi-scale simulations to study and predict the formation and defects of the absorbed superlattice monolayer. We demonstrate that the epitaxial growth is enthalpy driven and show that the anisotropy of the DNA-mediated substrates leads to structure defects. We develop design rules to dramatically reduce defects of the attached layer. Ultimately, with the assist of our simulation, this technique will open the door for the construction of well-ordered, three-dimensional novel metamaterials. [1] H. Atwater, et al. Nano Lett. 2013, 13, 6084. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T12.00004: Theory of Energy Level Tuning in Quantum Dots by Surfactants Danylo Zherebetskyy, Lin-Wang Wang Besides quantum confinement that provides control of the quantum dot (QD) band gap, surface ligands allow control of the absolute energy levels. We theoretically investigate energy level tuning in PbS QD by surfactant exchange. We perform direct calculations of real-size QD with various surfactants within the frame of the density functional theory and explicitly analyze the influence of the surfactants on the electronic properties of the QD. This work provides a hint for predictable control of the absolute energy levels and their fine tuning within 3 eV range by modification of big and small surfactants that simultaneously passivate the QD surface. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T12.00005: Crystalline (Al$_{1-x}$B$_{x})$PSi$_{3}$ and~(Al$_{1-x}$B$_{x})$AsSi$_{3}$ tetrahedral phases via reaction of Al(BH$_{4})_{3}$ and M(SiH$_{3})_{3}$ (M$=$P, As) Patrick Sims, Andrew White, Toshihiro Aoki, Jose Menendez, John Kouvetakis Crystalline (Al$_{1-x}$B$_{x})$PSi$_{3}$ alloys ($x =$ 0.04-0.06) are grown lattice-matched on Si(100) by reactions of P(SiH3)3 and Al(BH4)3 using low-pressure CVD. The materials have been characterized by ellipsometry, XRD, XTEM, EELS and EDS, indicating the formation of single-phase monocrystalline layers with tetrahedral structures based on AlPSi$_{3}$. The latter comprises interlinked AlPSi$_{3}$ tetrahedra in which Al-P pairs are isolated within a Si matrix. Raman scattering of Al$_{1-x}$B$_{x}$PSi$_{3}$ films support the presence of substitutional B in place of Al and provides evidence that B is bonded to P. The substitution of B atoms is desirable for promoting lattice matching, as required for Si-based solar cell designs. Analogous reactions of As(SiH3)3 with Al(BH4)3 produce (Al$_{1-x}$B$_{x})$AsSi$_{3}$ in which the B incorporation is limited to doping concentrations at 10$^{20}$ cm$^{-3}$. In both cases the Al(BH4)3 efficiently delivers Al to create crystalline group IV-III-V materials comprising light, earth abundant elements with possible application in photovoltaics and light element refractory solids. [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T12.00006: Optical trends in InP polytypic superlattices Guilherme Sipahi, Tiago de Campos, Paulo Eduardo de Faria Junior Recent advances in growth techniques have allowed the fabrication of semiconductor nanostructures with mixed wurtzite/zinc-blende crystal phases. Although the optical characterization of these polytypic structures is well reported in the literature, a deeper theoretical understanding of how crystal phase mixing and quantum confinement change the output linear light polarization is still needed. Here, we theoretically investigate the effects of these polytypic homojunctions on the interband absorption of an InP superlattice [1]. Using a single 8x8 k.p Hamiltonian that describes both crystal phases [1,2] together with the effects of quantum and optical confinement we where able to explain the recent optical exeperimental results carried on polytypic InP [3]. In summary, we have shown how the interplay of crystal phase mixing and quantum confinement can be used for light polarization engineering in polytypic homojunctions. \\[4pt] [1] P. E. Faria Junior, T. Campos and G. M. Sipahi, J. Appl. Phys. 2014 in press, arXiv:1409.6836.\\[0pt] [2] P. E. Faria Junior and G. M. Sipahi, J. Appl. Phys. 112, 103716 (2012).\\[0pt] [3] E. G. Gadret, et al., Phys. Rev. B 82, 125327 (2010). [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T12.00007: Erbium doped Aluminum Nitride Nanoparticles for Nano-Thermometer Applications Sneha G. Pandya, Martin E. Kordesch We have synthesized Nanoparticles (NPs) of Aluminum Nitride (AlN) doped \textit{in} situ with Erbium (Er) using the inert gas condensation technique. These NPs have optical properties that make them good candidates for nanoscale temperature sensors. The Photoluminescence (PL) spectrum of Er$^{3+}$ in these NPs shows two emission peaks in the green region at around 540 nm and 560 nm. The ratio of the intensities of these luminescence peaks is related to temperature. Using Boltzmann's distribution, the temperature of the NP and its surrounding can be calculated. The NPs were directly deposited on (111) p-type Silicon wafers, TEM grids and glass cover slips. XRD and HRTEM study indicates that most of the NPs have crystalline hexagonal AlN structure. An enhancement of the luminescence from these NPs was observed after heating in-air at 770 K for 3 hours. The sample was then heated in air using a scanning optical microscope laser. The corresponding change in PL peak intensities of the NPs was recorded for laser powers ranging from 0.2-15.1 mW. Temperature calculated using the Boltzmann's distribution was in the range of 320-470 K. This temperature range is of interest for semiconductor device heating and for thermal treatment of cancerous cells, for example. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T12.00008: Controlled formation of GeSi nanostructures on pillar-patterned Si substrate Tong Zhou, Ceng Zeng, Yongliang Fan, Zuimin Jiang, Jinsong Xia, Zhenyang Zhong GeSi quantum nanostructures (QNs) have potential applications in optoelectronic devices due to their unique properties and compatibility with the sophisticated Si technology. However, the disadvantages of poor quantum efficiency of the GeSi QNs on flat Si (001) substrates hinder their optoelectronic applications. Today, numerous growth strategies have been proposed to control the formation of GeSi QNs in hope of improving the optoelectronic performances. One of the ways is to fabricate GeSi QNs on patterned substrates, where the GeSi QNs can be greatly manipulated in aspects of size, shape, composition, orientation and arrangement. Here, self-assembled GeSi QNs on periodic Si (001) sub-micro pillars (SPMs) are systematically studied. By controlling the growth conditions and the diameters of the SPMs, different GeSi QNs, including circularly arranged quantum dots (QDs), quantum rings (QRs), and quantum dot molecules (QDMs), are realized at the top edge of SMPs. Meanwhile, fourfold symmetric GeSi QDMs can be also obtained at the base edges of the SPMs. The promising features of self-assembled GeSi QNs are explained in terms of the surface chemical potential, which disclose the critical effect of surface morphology on the diffusion and the aggregation of Ge adatoms. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T12.00009: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T12.00010: Utilizing Ballistic Electron Emission Microscopy to Study Sidewall Scattering of Electrons Westly Nolting, Chris Durcan, Robert Balsano, Vincent LaBella Sidewall scattering of electrons in aggressively scaled integrated devices dramatically increases the resistance since the dimensions are approaching the mean free path of electrons in a metal $\sim$ 40 nm. Ballistic Electron Emission Microscopy (BEEM) can be utilized to study hot electron scattering in metal films. In this presentation BEEM is performed on a lithographically patterned interface between a metal and a semiconductor to determine its potential at measure sidewall scattering. This is accomplished by acquiring spectra on a regularly spaced grid and then fitting the spectra to determine both the Schottky barrier height and the slope of the spectra. The position dependent maps of these two parameters are then related to the scattering at the interface due to the underlying pattern. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T12.00011: Novel size effects on magneto-optics in the spherical quantum dots M. Kushwaha We embark on investigating the magneto-optical absorption in {\em spherical} quantum dots {\em completely} confined by a harmonic potential and exposed to an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines' RPA that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. Intensifying the confinement or magnetic field and reducing the dot-size yields a blue-shift in the absorption peaks. However, the size effects are seen to be predominant in this role. The magnetic field tends to maximize the localization of the particle, but leaves the peak position of the radial distribution intact. The intra-Landau level transitions are forbidden. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T12.00012: Silicene, germanene and tinene: Modeling of IR absorbance and topological states Friedhelm Bechstedt, Lars Matthes, Olivia Pulci, Paola Gori The graphene-like but Si-, Ge- or Sn-derived group-IV honeycomb crystals [1] have attracted much attention due to their unique properties and their recent realization in experiments [2]. We study their electronic and optical properties by means of ab initio electronic-structure calculations. Conical valence and conduction bands and a vanishing electronic band gap have enormous consequences. Independent of the group-IV element and the degree of hybridization a universal absorbance ruled by the Sommerfeld finestructure constant appears [3,4]. This result is however influenced by spin-orbit coupling, which also plays an important role for germanene and tinene nanoribbons. Topological metallic edge states appear, if the edges are non-magnetic [5]. \\[4pt] [1] L. Matthes et al., J. Phys. CM 25, 395305 (2013)\\[0pt] [2] P. Vogt et al., PRL 108, 155501 (2012)\\[0pt] [3] F. Bechstedt et al., APL 100, 261906 (2012)\\[0pt] [4] L. Matthes et al., PRB 87, 035438 (2013); New J. Phys. 16, 105007 (2014)\\[0pt] [5] L. Matthes, F. Bechstedt, PRB 90, 165431 (2014) [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T12.00013: Internal Strain in Nano-Diamond and Boron Nitride William Mattson, Donald Johnson Nanodiamond surfaces undergo reconstruction imposing stress on nanoparticle (NP) core and possibly storing strain energy. The unique way in which these NPs store energy may lead to useful applications, but a greater understanding of strain energy storage/release is needed. In the current work, density functional theory methods are employed to predict structural properties and energetics of C (diamond) and cubic-BN NPs. The goal is to quantify NP core stress and its relationship to surface rearrangement, particle size, and material composition. Initial results suggest different chemical factors drive surface rearrangement, leading to compressive stress in C and tensile stress in BN. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T12.00014: Plasmon Enhanced Raman Scattering in Ag-CdTe Core-Shell Nanostructures Sheng Wang, Dexiong Liu, Jiang Zeng, Hua Zhang, Deliang Wang, Zhenyu Zhang Surface-enhanced Raman scattering (SERS) has been a powerful technique in investigating the properties of semiconductors. For semiconductor thin films, plasmon resonance and photoluminence (PL) are two important factors in determining the signal of SERS. Here we carry out a combined experimental and theoretical study of the optical properties of metal-semiconductor hybrid nanosystemes using SERS. First, we fabricate Ag-CdTe core-shell nanostructures by depositing CdTe on Ag nanoparticle arrays. By varying the thickness of the CdTe shell, one peak of plasmon is tuned to the wavelength of the incident light for resonant absorption, which is further verified by our finite-difference time-domain simulations. The coupling between the plasmons and excitons at the interface quenches the radiative PL process, while the non-radiative Raman scattering process is unaffected. Furthermore, the importance of multi-phonon resonance Raman scattering in these systems is investigated. [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T12.00015: Band Gaps in InN/GaN Superlattices: Polar and Nonpolar Growth Directions Niels Christensen, Izabela Gorczyca, Kamila Skrobas, Tadeusz Suski, Axel Svane The electronic structures of short-period superlattices (SLs) consisting of $m$InN/$n$GaN unit cells with composition ($m$,$n)$ have been calculated within the density-functional theory including corrections for the ``LDA gap error''. The variation of the gaps with SL composition and the dependence on the growth direction, the \textit{polar} (c) and \textit{nonpolar} (a,m) directions in the wurtzite structure, are compared. The band gaps calculated for the polar SLs are much smaller than those found for non-polar SLs due to the electric polarization fields in the (c) SLs. For the (\textit{1,m}) class of polar samples photoluminescence measurements yield energy-gap values, which are much larger than the calculated values. The reason for this is that the structure of the samples differs from the assumed ideal composition. Transmission electron microscopy studies of the assumed polar \textit{1}InN/$n$GaN SLs show that the real structure is 1In$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/GaN with In-content x$=$0.33. New calculations for such SLs are in perfect agreement with photoluminescence experiments. [Preview Abstract] |
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