Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications

The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3–4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromi...

Size vs surface: tuning the photoluminescence of freestanding silicon nanocrystals across the visible spectrum via surface groups.

This critical review discusses specific preparation and characterization methods applied to hybrid materials consisting of π-conjugated polymers (or oligomers) and semiconductor nanocrystals. These materials are of great importance in the quickly growing field of hybrid organic/inorganic electronics since they can serve as active components of photovoltaic cells, light emitting diodes, photodetectors and other devices. The electronic energy levels of the organic and inorganic components of the hybrid can be tuned individually and thin hybrid films can be processed using low cost solution based techniques. However, the interface between the hybrid components and the morphology of the hybrid directly influences the generation, separation and transport of charge carriers and those parameters are not easy to control. Therefore a large variety of different approaches for assembling the building blocks—conjugated polymers and semiconductor nanocrystals—has been developed. They range from their simple blending through various grafting procedures to methods exploiting specific non-covalent interactions between both components, induced by their tailor-made functionalization. In the first part of this review, we discuss the preparation of the building blocks (nanocrystals and polymers) and the strategies for their assembly into hybrid materials' thin films. In the second part, we focus on the charge carriers' generation and their transport within the hybrids. Finally, we summarize the performances of solar cells using conjugated polymer/semiconductor nanocrystals hybrids and give perspectives for future developments.

Conjugated polymers/semiconductor nanocrystals hybrid materials— preparation, electrical transport properties and applications

By including trap-limited recombination in a time-domain drift-diffusion model of a P3HT:PCBM solar cell, experimental transient photocurrent (TPC) measurements across the current–voltage (J–V) curve in both the light and the dark can be reproduced. Using the same set of model parameters, the steady-state current–voltage curves and charge-extraction data are also reproduced. The model is validated by predicting the recombination rate at open circuit and comparing results with the rate as measured by the transient photovoltage (TPV) measurement technique. It is demonstrated that the model, which incorporates transport, carrier trapping, carrier de-trapping, and recombination, is able to reproduce device dynamics correctly. The fit of the model to the experimental results is improved by varying the shape of the electron and hole density of state (DoS) functions. By discretizing the DoS in energy space and allowing its shape to vary, the TPC transients can be closely fitted and the form of the tails of the electron and hole DoS extracted. It is found that the DoS of trapped carriers can be represented by a series of Gaussians offset in energy. This is tentatively attributed to electronic disorder introduced by molecular packing of the molecules.

Extracting Microscopic Device Parameters from Transient Photocurrent Measurements of P3HT:PCBM Solar Cells

Silicon is the most important element of modern semiconductor industry. As a thermoelectric converter material, it would be able to promote applications dramatically since device integration and scaling of the fabrication processes could be borrowed from existing technology. Though the thermoelectric performance of single crystalline silicon is only poor, silicon nanostructures have demonstrated a competitive figure of merit. To make use of these nanostructures, novel device architectures are necessary. This review provides an overview over the physical background of silicon as thermoelectric converter material as well as different nanostructures like nanowires, porous nanomeshes, and nanocrystalline bulk and their thermoelectric properties, focusing mostly on experimental data. Further, different thermoelectric converter device concepts including nanowire device concepts, pn junction thermoelectric generators and integrated spot coolers are discussed and their realization with silicon nanostructures briefly sketched. 



(a) Nanowires, porous nanomeshes and nanocrystalline bulk with promising thermoelectric material's figure of merit. (b) Innovative device concepts using nanowires or large area pn junctions for thermoelectric heat-to-electricity conversion.

Silicon nanostructures for thermoelectric devices: A review of the current state of the art

The structural and electrical properties before and after laser annealing of spin-coated films of doped silicon nanocrystals (ncs) produced from the gas phase are presented. While the as-deposited films form a porous network of ncs and show only weak electrical conductivity independent of the doping level, a laser annealing step leads to sintering and melting of the particles and tremendously increases the lateral conductivity. By controlled doping of the initial particles, the conductivity can be further enhanced by seven orders of magnitude reaching values of up to 5 Ω−1 cm−1. The conductivity is found to increase with the doping concentration for highly doped samples while it is independent of the doping level below a critical concentration of 1019 cm−3. The results are discussed within a compensational model taking into account the defect concentration from electron paramagnetic resonance measurements and the activation energies of the electrical conductivity. Surface segregation of phosphorus during ...

Electronic properties of doped silicon nanocrystal films

Charge transfer between silicon nanocrystals (Si-nc) and organic semiconductors has been investigated via light-induced electron spin resonance (LESR). Composites of Si-nc with the hole conductor poly(3-hexylthiophene) (P3HT) and with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been investigated. The LESR measurements allow one to quantify light-induced charge transfer between Si-nc and P3HT, which results in positive P3HT polarons. PCBM, in contrast, acts as an electron acceptor in composites with Si-nc, and after illumination, negative PCBM radicals are created. These results are discussed in terms of light-induced generation and separation of charge carriers in the hybrid composites.

Light-induced charge transfer in hybrid composites of organic semiconductors and silicon nanocrystals

The invention relates to a method for producing higher hydridosilane wherein at least one lower hydridosilane and at least one heterogeneous catalyst are brought to reaction, wherein the at least one catalyst comprises Cu, Ni, Cr and/or Co applied to a carrier and/or oxide of Cu, Ni, Cr and/or Co applied to a carrier, the hydridosilane that can be produced according to said method and use thereof.

Process for preparing higher hydridosilanes

The present invention relates to a process for purifying low molecular weight hydridosilane solutions, in which a solution to be purified comprising a) at least one low molecular weight hydridosilane, b) at least one solvent and c) at least one impurity selected from the group of the compounds having at least 20 silicon atoms and/or the group of the homogeneous catalyst systems is subjected to a crossflow membrane process with at least one membrane separation step using a permeation membrane.

Process for purifying low molecular weight hydridosilanes

Die
vorliegende Erfindung betrifft ein Verfahren zur Herstellung thermoelektrischer
Bauelemente oder Peltier-Elemente sowie diese Bauelemente aus gedruckten
Siliciumschichten, hergestellt aus Dispersionen von zumindest teilweise
dotierten, halbleitenden Partikeln, insbesondere aus Silicium, Germanium
oder Silicium-Germanium-Legierungen.

Thermokraftelement oder Peltier-Elemente aus gesinterten Nanokristallen aus Silicium, Germanium oder Silicium-Germanium Legierungen

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