Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N2: Nanoscale Crystals |
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Sponsoring Units: DCMP Chair: Dmitri Talapin, Lawrence Berkeley Laboratory Room: Baltimore Convention Center Ballroom III |
Wednesday, March 15, 2006 8:00AM - 8:36AM |
N2.00001: LeRoy Apker Award (2005): Tunable Nonlocal Spin Control in a Coupled Quantum Dot System Invited Speaker: The effective interaction between magnetic impurities in metals that can lead to various magnetic ground states often competes with a tendency for electrons near impurities to screen the local moment (known as the Kondo effect). The simplest system exhibiting the richness of this competition, the two-impurity Kondo system, was realized experimentally in the form of two quantum dots coupled through an open conducting region. We demonstrate nonlocal spin control by suppressing and splitting Kondo resonances in one quantum dot by changing the electron number and coupling of the other dot. The results suggest an approach to nonlocal spin control that may be relevant to quantum information processing. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 9:12AM |
N2.00002: Electrical Transport Through a Single Semiconductor Nanocrystal Tetrapod Invited Speaker: Semiconductor nanocrystal tetrapods represent a unique complex nanostructure of interest for multiterminal electrical and electromechanical studies. We demonstrate by single electron transport measurements the electronic coupling between the nanotetrapod core quantum dot and the four arm quantum rods. Either ionic or covalent bonding-type of coupling can exist when the interaction between quantum dot at the junction and arm rods is weak or strong. In addition, we demonstrate a new integrated single electron transistor scheme enabled by the unique coupled nanotetrapod systems: one arm can be used as a sensitive arm-gate to control the electrical transport through the whole system. The work here reveals that nanotetrapods and other branched colloidal nanocrystals represent a new class of chemically controlled ``artificial molecules'' of coupled quantum dots. [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:48AM |
N2.00003: Controlled assembly and electronics in semiconductor nanocrystal-based devices Invited Speaker: I will discuss the assembly of semiconductor nanocrystals (CdSe and PbSe) into electronic devices and the basic mechanisms of charge transport in nanocrystal arrays [1-4]. Spherical CdSe nanocrystals show robust memory effects that can be exploited for memory applications [1]. Nanocrystal memory can be erased electrically or optically and is rewritable. In PbSe nanocrystal arrays, as the interdot coupling is increased, the system evolves from an insulating regime dominated by Coulomb blockade to a semiconducting regime, where hopping conduction is the dominant transport mechanism [2]. Two-dimensional CdSe nanorod arrays show striking and anomalous transport properties, including strong and reproducible non-linearities and current oscillations with dc-voltage [4]. I will also discuss imaging of the charge transport in nanocrystal-based electronic devices. Nanocrystal arrays were investigated using electrostatic force microscopy (EFM) and transmission electron microscopy (TEM) [3]. Changes in lattice and transport properties upon annealing in vacuum were revealed. Local charge transport was directly imaged by EFM and correlated to nanopatterns observed with TEM. This work shows how charge transport in complex nanocrystal networks can be identified with nm resolution [3]. This work was supported by the ONR grant N000140410489, the NSF grants DMR-0449553 and MRSEC DMR00-79909, and the ACS PRF grant 41256-G10. \newline \newline References:\newline 1) Fischbein M. D. and Drndic M., ``CdSe nanocrystal quantum-dot memory,'' Applied Physics Letters, 86 (19), 193106, 2005.\newline 2) H. E. Romero and Drndic M., ``Coulomb blockade and hopping conduction in PbSe quantum dots,'' Physical Review Letters 95, 156801, 2005.\newline 3) Hu Z., Fischbein M. D. and Drndic M., ``Local charge transport in two-dimensional PbSe nanocrystal arrays studied by electrostatic force microscopy",'' Nano Letters 5 (7), 1463, 2005.\newline 4) Romero H.E., Calusine G. and Drndic M., ``Current oscillations, switching and hysteresis in CdSe nanorod superlattices,'' Physical Review B 72 (23), 2005. [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:24AM |
N2.00004: Localized charge of single CdSe quantum rods and the role of lattice imperfections Invited Speaker: The local electronic structure of colloidal semiconductor nanoparticles is of significant fundamental and technical interest. Electrostatic force microscopy was used to determine that single CdSe quantum rods (QRs) have a permanent polarization surface-charge density, an unexpected observation for supposedly well-shaped, neutral dielectric particles. To investigate the source of the surface charge, we performed electron nanodiffraction studies with a scanning transmission electron microscope (STEM). Electron nanodiffraction patterns suggest that rotations exist between various ``sections'' of individual QRs, and that the rotation axes may form substantial angles with the c-axis. Thus, the surface charge results from the slight angle between the QR sides and the direction of internal electric polarization. Despite the large dipole moment expected for CdSe QRs, none was observed. The unavoidable presence of permanently charged surfaces on CdSe QRs has the potential to impede the development of novel devices incorporating these materials. [Preview Abstract] |
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