Spontaneous Organization of Single CdTe Nanoparticles into Luminescent Nanowires (original) (raw)
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Electrochemical formation of quantum-conductance Cu-metal nanobridges
Russian Journal of Electrochemistry, 2008
The electrodeposition of copper with formation of narrow nanobridge contacts was investigated. Stable quantum nanobridges (QNB) with ballistic conductance have been obtained by pulsed Cu deposition/electroetching on Cr interdigitated microelectrodes nanolithographed on a quartz wafer. The minimum quantum conductance associated with monatomic-wide constriction in the nanobridge was observed. Stepped differential conductance G = ng 0 (where g 0 is the minimum quantum conductance and n = 1, 2, 3, …) was generally observed although fractional multiples of g o were also found, likely due to the deviations of the nanowire junction geometry from linear configuration and reflection losses. In the layer-by-layer Cu deposition/etching technique employed for junction formation, the current amplification associated with interdigitated electrode pattern was utilized, which allowed us for easy electrochemical control with no need for special instrumentation. Quantum mechanical calculations of the electronic structure of Cu-QNB have been carried out using small-cluster approach with configuration 14m -14 , where m denotes the number of Cu atoms in the monatomic-wide bridge, and the base electrodes are simulated by clusters with 14 Cu atoms each. The calculations performed for m = 1 to 4, indicate that corrugations of electron density along the conductance channel virtually disappear for m = 3, whereas for even number of Cu atoms in the bridge, a distinct, very narrow constriction is formed in the center of the bridge. These results corroborate earlier findings for alkali metals, for which considerable differences between odd and even number of atoms in a monatomic-wide conductance channel have been reported.
Spectroscopy of the local density of states in nanowires using integrated quantum dots
Physical Review B
In quantum dot (QD) electron transport experiments, additional features can appear in the differential conductance dI/dV that do not originate from discrete states in the QD, but rather from a modulation of the density of states (DOS) in the leads. These features are particularly pronounced when the leads are strongly confined low-dimensional systems, such as in a nanowire (NW) where transport is one dimensional and quasi-zero-dimensional lead states can emerge. We study such lead states in InAs NWs. We use a QD integrated directly into the NW during the epitaxial growth as an energetically and spatially well-defined tunnel probe to perform dI/dV spectroscopy of discrete bound states in the "left" and "right" NW lead segments. By tuning a sidegate in close proximity of one lead segment, we can distinguish transport features related to the modulation in the lead DOS and to excited states in the QD. We implement a noninteracting capacitance model and derive expressions for the slopes of QD and lead resonances that appear in two-dimensional plots of dI/dV as a function of source-drain bias and gate voltage in terms of the different lever arms determined by the capacitive couplings. We discuss how the interplay between the lever arms affects the slopes. We verify our model by numerically calculating the dI/dV using a resonant tunneling model with three noninteracting quantum dots in series. Finally, we use the model to describe the measured dI/dV spectra and quantitatively extract the tunnel couplings of the lead segments. Our results constitute an important step towards a quantitative understanding of normal and superconducting subgap states in hybrid NW devices.
Indication of Unusual Pentagonal Structures in Atomic-Size Cu Nanowires
Physical Review Letters, 2004
We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of 0:45 nm and 4:5 conductance quanta.
Evidence for spin injection in a single metallic nanoparticle: A step towards nanospintronics
Applied Physics Letters, 2006
We have fabricated nanometer sized magnetic tunnel junctions using a new nanoindentation technique in order to study the transport properties of a single metallic nanoparticle. Coulomb blockade effects show clear evidence for single electron tunneling through a single 2.5 nm Au cluster. The observed magnetoresistance is the signature of spin conservation during the transport process through a non magnetic cluster. Spintronics debuted with the discovery of giant magnetoresistance[1] effect in magnetic multilayers in which a single dimension was reduced to the nanometer range. This field was then extended to structures with two reduced dimensions like nanowires[2] and nanopillars or nanotubes . Today, a challenge for spintronics is the study of spin transport properties in structures based on 0D elements in which the three dimensions have been reduced. In particular, we have in mind systems in which the reduction of the size leads to both Coulomb blockade and spin accumulation effects . Transport studies on systems including mesoscopic islands[9, 10, 11] or granular films have paved the way to understanding the effect of confinement on charge and spin transport properties in metallic nano-objects. However, so far, very few techniques allow to contact a single isolated nanometer sized object to study the effect of confinement on spin transport.
INTERNATIONAL JOURNAL OF NANOTECHNOLOGY, 2008
This paper gives an overview over the fundamental research in nanosciences at the Institute of Electronics, Microelectronics and Nanotechnology (IEMN). We present some highlights from the numerical simulation of the electronic structure of nanowires and nanotubes, the charge G. Allan et al. spectroscopy of Si nanoparticles and C nanotubes, the scanning tunnelling spectroscopy of semiconductor quantum dots, to research in surface science for bio-screening.
Lead Chalcogenides quantum dots are ideal for fundamental studies of strongly quantum confined systems with possible technological applications. Tunable electronic transitions at near-infrared wavelengths can be obtained with these quantum dots. Applications of lead chalcogenides encompass quite a good number of important fields viz. the fields of telecommunications, medical electronics, optoelectronics etc. Very recently, it has been proposed that 'memristor' (Memory resistor) can be realized in nanoscale systems with coupled ionic and electronic transports. The hystersis characteristics of 'memristor' are observed in many nanoscale electronic devices including semiconductor quantum dot devices. This paper reports synthesis of lead Sulphide quantum dots embedded in Poly Vinyl alcohol matrix by chemical route. The fabricated samples are characterized by UV-visible Spectroscopy, Photoluminescence Spectroscopy, X-ray diffraction, Energy Dispersive X-ray Spectroscopy, High Resolution Transmission Electron Microscopy, Selected Area Electron Diffraction. Observed characteristics confirm nano formation. The as-fabricated Poly Vinyl Alcohol/lead Sulphide quantum dot devices exhibit hysteresis behaviour of memristor. For the application as memory unit/device, capacitance-voltage and conductance-voltage, frequency-dependent measurements are to be done.
Evidence for Spontaneous Spin-Polarized Transport in Magnetic Nanowires
Physical Review Letters, 2003
The exploitation of the spin in charge-based systems is opening revolutionary opportunities for device architecture. Surprisingly, room temperature electrical transport through magnetic nanowires is still an unresolved issue. Here, we show that ferromagnetic (Co) suspended atom chains spontaneously display an electron transport of half a conductance quantum, as expected for a fully polarized conduction channel. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results suggest that the nanowire low dimensionality reinforces or induces magnetic behavior, lifting off spin degeneracy even at room temperature and zero external magnetic field.