Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W17: Nanostructures: Electrical, Optical and Structural Properties |
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Sponsoring Units: DCMP Chair: Stefan Badescu, Naval Research Laboratory Room: LACC 404B |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W17.00001: Coherent X-ray diffraction to image Silver Nanocrystals Mengning Liang, Yugang Sun, Ross Harder, Ian Robinson, Younan Xia Coherent x-ray diffraction is a method of imaging a crystalline object embedded inside a medium in a non-invasive way. When a coherent source is incident upon a crystal, the resulting diffraction pattern is the intensity of the 3D Fourier transform of the object. Were the phase information also known, an inverse Fourier transform could be performed to get an image of the original structure. It has been shown theoretically that the phase information can be recovered by oversampling the diffraction pattern and applying iterative algorithms. Silver nanocubes approximately 170nm in size were chemically synthesized and deposited on silica and silicon substrates using a variety of methods. Diffraction from a monochromatic, coherent x-ray beam was imaged on a CCD camera at the Advanced Photon Source at Argonne National Lab. The resultant diffraction pattern is a 2D slice through the 3D Fourier transform of a cube. Using various inversion algorithms, slices through the center are inverted into real 2D projections of the object while off center slices are shown to add a phase factor to the projection. [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W17.00002: Templated Nanowires for Electrical and Electro-Optic Applications Yun Peng, Chris LaFratta, Daniel Lim, J.T. Fourkas, M.J. Naughton We have prepared multi-metal nanowires via electrodeposition in AAO template membranes. The wires are 100 nm nominal diameter, and 5 to 20 $\mu$m in length. Most nanowires are composed of varying lengths of Ag and Au, including sections of submicron length. The wires have been characterized by SEM (including backscattered detection), TEM and AFM. We have made electrical contact to the nanowires by a direct laser writing technique, and have made electrical measurements in the presence and absence of pulsed laser illumination. In this talk, we will discuss the preparation and above characterizations, including with regard to electro-optic applications. [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W17.00003: Atomically-Flat Nanosurface Arrays for STM and Photonic Studies D.H. Dahanayaka, X.J. Wang, J.C. Keay, S. Hosain, W.D. Tennyson, T.G. Easley, G.D. Lian, M.B. Johnson, L.A. Bumm Flat gold nanoparticles (FGNPs) can be used as atomically-flat gold substrates for STM studies. When supported on ITO coated glass the FGNPs can also be used as atomically-flat photonic substrates. Transmission electron microscopy (TEM) shows that FGNP's can be prepared 100--500 nm across with shapes that range from triangular to hexagonal with thicknesses of 15-25 nm. Dark-field optical microscopy is a convenient method for evaluating the FGNP arrays because the FGNPs and spherical gold nanoparticles are distinguished easily. STM and AFM reveal atomically flat terraces on the large {\{}111{\}} FGNP facets. An optimized method for growing the FGNPs and for depositing them on ITO coated glass with a high particle density is presented.\textbf{ } [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W17.00004: Assembly of nanoclusters for application as a variable capacitor Nathalie Lidgi, P. Seneor, J. Carrey, D. Veautier, G. Viau, F. Nguyen Van Dau, A. Friederich, A. Fert, A. Vaures Variable capacitors are widely used electronic devices; we propose a new concept based on a 2D-assembly of clusters. We are investigating the synthesis, structural and transport properties of assemblies of metallic clusters in structures such as Metal / Dielectric / 2D assembly of clusters / Dielectric / Metal. Due to the Coulomb blockade phenomenon, a minimum voltage has to be applied between the two electrodes in order to measure a current. It is, thus, possible to control the charge on the assembly of cluster and consequently, the differential capacitance of the junction. The amplitude of the capacitance variation is directly linked to the clusters assembly properties (size distribution and density). We have studied samples with different assembly: junctions entirely made by sputtering present, at low temperatures, a behavior comparable to the current ``varicaps.'' Junctions made part by sputtering (electrodes and dielectric), part by chemistry (assembly of nanoparticles), demonstrate the importance of the cluster density. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W17.00005: Quantum Size Effects on Growth of Cylindrical Gold Nanoclusters on Surface Yong Han, Feng Liu We use a cylindrical hard wall model to investigate the stability of cylindrical gold nanoclusters (nanomesas) containing hundreds to millions of atoms. The model shows an oscillating pattern of size dependence of preferred growth direction of mesa height vs. mesa radius, which leads to selected mesa height and radius in different range of mesa sizes. We will discuss our theoretical results in comparison with experimental growth of gold mesas on graphite surface. *This work is supported by NSF. [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W17.00006: Charge Transport Studies of Dielectrophoretic Interconnects Composed of Gold Nanoparticles Birol Ozturk, Charles Blackledge, Daniel Grischkowsky, Bret N. Flanders Dielectrophoresis was used to assemble individual, sub-micron interconnects from suspensions of gold nanoparticles and to interface them with targeted points in a circuit, all in one step. The high degree of precision associated with the photo-lithographic electrodes facilitates the determination of key electrical properties of these nanostructured interconnects. By fabricating a range of interconnects with diameters as low as 500 nm and lengths as low as 20 $\mu $m, current-voltage studies were carried out to determine the charge transport properties of these nanoparticulate structures. This work sheds light on the sources of electrical resistance in these interconnects. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W17.00007: Transport Properties of Granular Metals Igor Beloborodov, Konstantin Efetov, Andrei Lopatin, Valerii Vinokur I will talk about electron transport in granular metallic systems at different ranges of temperatures. In particular I demonstrate that at low temperatures, T $<$ g$_t$ $\delta$, where g$_t$ is the tunneling conductance and $\delta$ is the mean level spacing in a single grain, the conductivity of granular metals strongly depends on the dimensionality of the granular array, while for high-temperature (T $>$ g$_t$ $\delta$) the conductivity is independent of the dimensionality of the array and logarithmically depends on temperature. The logarithmic behavior of the conductivity at large tunneling conductance's obtained in our model can explain numerous experiments on systems with a granular structure including some high - T$_c$ materials. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W17.00008: Transport conductivity calculation of atomic-scale nanostructures of Au and Co Liqin Ke, Mark van Schilfgaarde Ballistic transport conductivity calculations on infinite zigzag chains of Co, Au and small-dimension Au nanowires were computed using the Landauer-Buttiker formalism within the full-potential method of muffin-tin orbitals. In the case of infinite zigzag Cobalt chains, one of the two spin channels has quantized transport conductivity. But because of the close spacing of the $d$ levels, the majority channel does not show quantized conductance. In contrast, Au (which are calculated to be not spin polarized) does show well-behaved transport conductivity quantization in the case of infinite zigzag chain. By increasing the dimension of the cross section of the Au Chain, we gradually lose the transport quantization. This is analyzed in terms of a simple model. [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W17.00009: Energetics and equation of state of passivated nanocluster assemblies W.D. Luedtke, Uzi Landman Molecular dynamics simulations are used to explore several principal issues pertaining to the energetics of formation of superlattices made through the assembly of passivated nanoclusters and the interactions that underlie the cohesion of such superlattices [1]. The entropic contribution to the formation free energy of the superlattice assembly is found to be large and of similar magnitude as the potential energy component of the free energy. The major contribution to the cohesive potential energy of the superlattice is shown to originate from van der Waals interactions between molecules that passivate neighboring nanoclusters. Additionally, we have found that a passivated nanocluster assembly can undergo pressure induced structural transformations and we discuss the equation of state of such superlattice assemblies. [1] U. Landman and W. D. Luedtke, Faraday Discussions 125, 1 (2004). [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W17.00010: The Directed-Assembly of CdS Interconnects between Targeted Points in a Circuit Bret N. Flanders, Birol Ozturk, Ishan Talukdar A central goal in device-assembly is the development of methodology for fabricating targeted structures from nanoscopic building blocks, in a manner that embraces directed-assembly. Here we demonstrate the one-step dielectrophoretic assembly and interfacing of individual interconnects from populations of 3.7 nm CdS nanoparticles between targeted points in a circuit, shedding light on the most probable mechanism by which this occurs. We further show that the nanoparticles fuse into bulk CdS during the fabrication process. This finding is significant because it establishes a preliminary basis for the fabrication of structurally continuous semiconducting interconnects from nanoscopic building blocks. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W17.00011: Epitaxial growth of quantum-well photovoltaic structures on silicon substrates using beryllium chalcogenide interlayers Kevin Clark, Eduardo Maldonado, R.T. Bate, W.P. Kirk Epitaxial integration of wide-bandgap p-n junctions on silicon forms an approach for high-performance multijunction space power solar cells. Heteroepitaxy on silicon has materials incompatibilities associated with stacking faults from lattice and thermal mismatch, polar-on-nonpolar growth, cross diffusion etc. Beryllium telluride (BeTe) is a II-VI semiconductor nearly lattice-matched to gallium arsenide and has good growth characteristics on silicon, with planar two-dimensional growth and high stacking fault energy. We have grown AlGaAs p-i-n structures incorporating GaAs quantum wells on BeTe interlayers on arsenic-passivated silicon substrates by molecular beam epitaxy. We report growth characteristics, current-voltage characteristics, and photocurrent results for the structures. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W17.00012: Growth of ZnSe/BeTe double-barrier quantum-well heterostructure on vicinal Si (100) surfaces by Molecular Beam Epitaxy Eduardo Maldonado, Kevin Clark, Shweta Bhandaru, Wiley Kirk Growth of ZnSe/BeTe on arsenic passivated vicinal Si (100) substrates is reported with the intention to realize a double-barrier quantum-well structure. Such structures grown on GaAs have been reported by other research groups $^{1}$ and showed resonant tunneling at room temperature. In our case, the ZnSe/BeTe structure is grown on silicon via a Zn $_{0.06}$ Be $_{0.94}$ Te buffer layer that is lattice matched to GaAs. The silicon does not play an active role in the RTD behavior; it simply serves as a support layer for the entire structure. Reflection High Energy Electron Diffraction (RHEED) showed an epitaxial growth regime. $^{1}$ U.Lunz, M. Keim, G. Reuscher, F. Fischer, K. Schull, A. Waag, and G. Landwehr, J. Appl. Phys. \textbf{80}, 6329 (1996) [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W17.00013: Microstructure of Delta-Doped ZnSe:(Te, N) Grown by Migration Enhanced Epitaxy Y. Gong, I.L. Kuskovsky, H. Yan, Y. Gu, G.F. Neumark, I.C. Noyan, M.C. Tamargo It has been difficult to obtain good p-type ZnSe. A delta-doping technique, with N as an acceptor and Te as a ``codopant'' (ZnTe is easily doped p-type), was employed to obtain a net acceptor concentration $\sim $ 6$\times $10$^{18}$cm$^{-3 }$using small amounts of Te. To understand the doping mechanism, we performed HRXRD with synchrotron radiation (NSLS) complemented by optical absorption (OA) and reflection. Two samples grown on GaAs substrates without (A) and with (B) a ZnSe buffer layer were studied. Sample A is composed of 244 periods of delta-layers separated by 9ML spacers (nominally undoped ZnSe), whereas sample B contains 200 periods of delta-layers separated by 10ML spacers. The (004) $\omega $-2$\theta $ scans show a narrow high-intensity peak due to substrate and a series of satellite peaks. The best fitting was obtained with $\delta $-layer thickness $\sim $0.25ML for both samples. The average Te contents in spacers and delta-layers are 5{\%} and 50{\%} (A), and 3{\%} and 60{\%} (B). Finally, combining results of the reflection and OA, we estimated the optical band gap of samples A and B to be 2.75eV and 2.77eV, respectively. These correspond to Te compositions of $\sim $4.5{\%} and $\sim $3.0{\%}, which are in good agreement with results of the x-ray measurements. 1. W. Lin, et al. Appl. Phys. Lett. \textbf{76}, 2205 (2000) [Preview Abstract] |
Thursday, March 24, 2005 5:06PM - 5:18PM |
W17.00014: Realization and Characterization of a Curved Two-dimensional Electron Gas Nakul Shaji, Hua Qin, Ryan Toonen, Robert Blick, Christoph Deneke, Oliver Schmidt Using the built-in strain from lattice mismatch between Al$_{0.33}$Ga$_{0.67}$As and In$_{0.2}$Ga$_{0.8}$As as a bending force, a strip of two-dimensional electron gas (2DEG) in an Al$_{x}$Ga$_{1-x}$As/GaAs/Al$_{x}$Ga$_{1-x}$As heterostructure is curved into a tube when released from the substrate by wet etching. A variety of mesoscopic quantum devices can be defined in such curved 2DEG structures. This technology opens the door for investigating geometry-dependent electron transport under non-uniform magnetic fields. We have defined Hall bar patterns from a sheet of 2DEG using both optical and electron-beam lithography. The sample characterization under an external magnetic field will be discussed. [Preview Abstract] |
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W17.00015: Tailoring size and density of Au clusters grown by sputtering Nathalie Lidgi, P. Seneor, J. Carrey, F. Nguyen Van Dau, A. Friederich, A. Fert, C. Deranlot, A. Vaures We have investigated the growth of Au clustesr on amorphous Al203. On such a surface the growth mode is govern by nucleation on defects. It has been shown [1] that during the growth, the larger clusters can trap off from a defect and diffuse on the surface. This mechanism promotes the clusters enlargement at the first stage of growth. In order to control the distribution of defects and thus, the cluster size, we have etched the alumina surface with Ar+ plasma. Finding the good parameters allows to control the cluster size distribution and the cluster density. Thanks to this technique, we have reduced the dispersity of the cluster size distribution by 50{\%}. In a second part, this assembly has been integrated in a tunnel junction. The sample exhibits Coulomb blockade behavior at near room temperature. We will discuss the growth mechanisms that lead to a control of the dispersity and we will show how these nanostructures can be used as a novel concept of variable capacitor [2]. [1] J. Carrey et al., PRL 86, 4600 ( 2001) [2] P. Seneor et al., EPL 65, 699 (2004) [Preview Abstract] |
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