Adsorption behavior of conjugated {C}3-oligomers on Si(100) and HOPG surfaces

A pi-conjugated {C}3h-oligomer involving three dithienylethylene branches bridged at the meta positions of a central benzenic core has been synthesized and deposited either on the Si(100) surface or on the HOPG surface. On the silicon surface, scanning tunneling microscopy allows the observation of isolated molecules. Conversely, by substituting the thiophene rings of the oligomers with alkyl chains, a spontaneous ordered film is observed on the HOPG surface. As the interaction of the oligomers is different with both surfaces, the utility of the Si(100) surface to characterize individual oligomers prior to their use into a 2D layer is discussed

Synthesis of long group IV semiconductor nanowires by molecular beam epitaxy

We report the growth of Si and Ge nanowires (NWs) on a Si(111) surface by molecular beam epitaxy. While Si NWs grow perpendicular to the surface, two types of growth axes are found for the Ge NWs. Structural studies of both types of NWs performed with electron microscopies reveal a marked difference between the roughnesses of their respective sidewalls. As the investigation of their length dependence on their diameter indicates that the growth of the NWs predominantly proceeds through the diffusion of adatoms from the substrate up along the sidewalls, difference in the sidewall roughness qualitatively explains the length variation measured between both types of NWs. The formation of atomically flat {111} sidewalls on the <110>-oriented Ge NWs accounts for a larger diffusion length

Electrical detection of plasmon-induced isomerization in molecule-nanoparticle network devices

We use a network of molecularly linked gold nanoparticles (NPSAN: nanoparticles self-assembled network) to demonstrate the electrical detection (conductance variation) of a plasmon-induced isomerization (PII) of azobenzene derivatives (azobenzene bithiophene : AzBT). We show that PII is more efficient in a 3D-like (cluster-NPSAN) than in a purely two-dimensional NPSAN (i.e., a monolayer of AzBT functionalized Au NPs). By comparison with usual optical (UV-visible light) isomerization of AzBT, the PII shows a faster (a factor about 10) isomerization kinetics. Possible PII mechanisms are discussed: electric field-induced isomerization, two-phonon process, plasmon-induced resonant energy transfer (PIRET), the latter being the most likely.Comment: Final manuscript with supporting informatio

Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

From electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and decay kinetics on photo-excitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. A large enhancement in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to a higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition

Atomic scale investigation of silicon nanowires and nanoclusters

In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers

Electric force microscopy of individually charged semiconductor nanoparticles

Charge injection experiments by electrostatic force microscopy are performed on single semiconductor nanoparticles. Different methods of detecting the stored charge are used. Although the amount of charge stored in particles of realistic shape can be determined quantitatively, we present here a qualitative comparison between Q (V ) hysteresis curves observed on silicon and GaN quantum dots, in dry nitrogen and in ultra high vacuum. For silicon dots in dry atmosphere, we find a hysteresis behavior entirely different from the one observed on GaN dots in ultra high vacuum. The contribution of interface states to hysteresis is discusse

Electric force microscopy of individually charged semiconductor nanoparticles

Charge injection experiments by electrostatic force microscopy are performed on single semiconductor nanoparticles. Different methods of detecting the stored charge are used. Although the amount of charge stored in particles of realistic shape can be determined quantitatively, we present here a qualitative comparison between Q (V ) hysteresis curves observed on silicon and GaN quantum dots, in dry nitrogen and in ultra high vacuum. For silicon dots in dry atmosphere, we find a hysteresis behavior entirely different from the one observed on GaN dots in ultra high vacuum. The contribution of interface states to hysteresis is discusse