CdS and Mn-doped CdS capped with TOPO (tri-n-octylphosphineoxide) have been prepared by a single source route using bis(methylhexyldithiocarbamato)cadmium(II) and manganese dichloride as precursors. The nanoparticles obtained show quantum size effects in their optical spectra with the CdS nanoparticles exhibiting near band-edge luminescence. The PL spectrum of the doped CdS nanoparticles have an emission maximum at 585 nm attributed to the 4T1-6A1 electronic transition of Mn in a tetrahedral site. However the PL spectrum changes over time (weeks) and gave a deep trap emission. The Selected Area Electron Diffraction (SAED) and X-ray diffraction (XRD) pattern show both CdS and the Mn doped CdS particles to be of the hexagonal phase. Transmission Electron Microscopy (TEM) and High Resolution TEM show well-defined images of nanosize particles with clear lattice fringes. ESR spectra and ICP results confirm the presence of Mn in the CdS nanoparticles.

We present a synthesis of colloidal CdTe nanocrystals whose absolute room temperature quantum yields are routinely above 60%. The preparation is based on the trioctylphosphine oxide (TOPO) method reported by Murray, with a more stalbe tellurium precursor now used as the chalcogenide source. The photoluminescence is continuously tunable over the range 590-760 nm and is as narrow as 135 meV (45 nm) FWHM. No deep trap luminescence is detected for the diameter range 4-11 nm. CdTe nanocrystals are characterized by UV/vis absorption, photoluminescence emission, transmission electron microscopy, and powder X-ray diffraction.

Electrochemical atomic-layer epitaxy (EC-ALE) is an approach to electrodepositing thin-films of compound semiconductors. It takes advantage of underpotential deposition (UPD), deposition of a surface limited amount (a monolayer or less) of an element at a potential less negative than bulk deposition, to form a thin-film of a compound--one atomic layer at a time. Ideally, the 2-D growth mode should promote epitaxial deposition.

Many II-VI and a few III-V compounds have been formed by EC-ALE. TI-VI films such as CdSe, CdS, and CdTe have been successfully formed. In addition, deposition of III-V compounds of InAs and InSb are being explored, along with initial studies of GaAs deposition. Depositions of the I-VI systems are better understood so this report will focus on the III-V's, particularly InAs and InSb.

Building compounds an atomic layer at a time lends electrochemical-ALE to nanoscale technology. Deposited thickness ranged from a few nanometers to a few hundred. The films are typically characterized by atomic-force microscopy (AFM), X-ray diffraction (XRD), electron microprobe analysis (EPMA) and ellipsometry. InAs deposits are also characterized by infrared reflection absorption.

We present the synthesis and characterization of nanocrystalline II-VI semiconductors of mixed composition (CdSe/ZnSe, CdS) grown in fatty acid Langmuir-Schaefer multi-layer templates. The controlled production of i) homogeneous nanocrystalline CdxZn1−xSe alloys and ii) heterogeneous mixtures of different pure composition II-VI semiconductors such as CdSe and ZnSe provides, in addition to the size control, the parameter of the chemical composition for the fine tuning of the electronic properties. The samples are characterized bty optical and quasi-resonance micro-Raman spectroscopy.

Nano-sized dispersions have been employed as precursor inks for the spray deposition of contacts to both Si and CdTe materials. In the case of Si, nano-sized Al particles (nano-Al) were dispersed and spray deposited onto p-type Si. Annealing above the eutectic temperature causes alloy formation yielding a p+ layer with p ∼ 10−4 Ω•cm. For CdTe, nano-sized Te particles (nano-Te) were dispersed and sprayed onto CdTe/CdS/SnO2/glass heterostructures. Contact to the CdTe layer occurred during a 30 min anneal in He (T = 215 to 255 °C). These solar cells were finished by spin-coating the Te layer with Ag paint and subsequently annealing in air (100 °C / 1 h). This approach produces solar cells with open circuit voltages (Voc) from 720 to 800 mV, short circuit current densities (Jsc) from 18 to 20 mA/cm2 and efficiencies up to 10.3%. The performance of these cells was similar to those produced using the standard NREL contact.

We have fabricated Ge nanostructures buried in AlN and Al2O3 matrices grown on Si(111) and sapphire substrates by pulsed laser deposition. Our approach involved three-dimensional island growth of low band-gap material followed by a layer of wide band-gap material. The nanodots were uniformly distributed in between alternating layers of AlN or Al2O3. It was observed that these nanodots exhibit crystalline structure when grown at 300-500 °C. The average size of Ge islands was determined to be ∼5-15 nm, which could be varied by controlling laser deposition and substrate parameters. The Raman spectrum showed a peak of the Ge-Ge vibrational mode downward shifted upto 295 cm− which is caused by quantum confinement of phonons in the Ge-dots. The photoluminescence of the Ge dots (size ∼15nm) was blue shifted by ∼0.266 eV from the bulk Ge value of 0.73 eV at 77 K, resulting in a distinct peak at ∼1.0 eV. The spectral positions of both E1 and E2 transitions in the absorption spectra at room temperature and 77K shift toward higher energy as the Ge dot size decreases. The interpretation of these behaviors in terms of quantum confinement is discussed in this work, and the importance of pulsed laser deposition in fabricating novel nanostructures is emphasized

In this communication we report the preliminary results of in-situ functionalisation, of Q-CdSe and Q-GaAs using thiols, (HSC12H25), dithiols, (HSC9H18SH), pyridine derivatives (4-ethylpyridine, 4-butylpyridine) and carboxylic acids (mercaptopropionic acid).

The functionalisation of the capping group provides a potential route to the assembly of 2D arrays and supperlattices. Anchorage of the nanocrystals to surfaces for use in devices, such as solar cells and Grätzel type cells is also discussed.

In this paper we report the synthesis of metal sulfide nanocrystals, (CdS and ZnS), from the thermolysis, between 150 – 300 °C, in a dynamic vacuum, of the novel long chain asymmetric metal dithiocarbamates, bis(N-methyloctadecyldithiocarbamato) cadmium(II) or zinc(lI), [M {S2CN(C18H37)(CH3)}2].

These nanoparticles ‘self-cap’ during preparation. Different size nanocrystals were synthesised, at different temperatures and there was a change in phase from cubic to hexagonal CdS at a decomposition temperature greater than 300 °C.

Application of negative heavy ions, alleviating surface charging on insulators, enables us to conduct low-energy and high-flux implantation, and leads to a well-defined tool to fabricate near-surface nanostructures. Negative Cu ions of 60 keV, at high doses, have generated nanocrystals in amorphous(a-)SiO2 with a size (∼10 nm) suitable for nonlinear optical devices. The kinetic processes, inside the solid and at the surface, are studied by cross-sectional TEM and tapping AFM, respectively. In a-SiO2, nanoparticles spontaneously grow with dose rate, being controlled by the surface tension and radiation-induced diffusion. Furthermore, the nanospheres give rise to a two-dimensional (2D) arrangement around a given dose rate. The 2D-distribution occurs in coincidence with enhanced sputtering where a considerable Cu fraction sublimates from the surface. The dose-rate dependence of nanoparticles indicates that the surface-sputtering process influences the intra-solid process and contributes to the 2D-distribution. A self-assembling mechanism for 2D-arrangement of nanospheres is discussed taking into account contribution of the surface sputtering.

The crystallization behavior (ordering) of undoped and boron-doped Si0.5Ge0.5 films, deposited on SiO2/Si(001) substrate by molecular beam epitaxy in hish vacuum at room temperature, were studied by XRD, HRTEM and in situ by Doppler broadening spectroscopy using monoenergetic positrons. Some decomposition features of SiGe solid solutions were demonstrated via splitting the XRD peaks at high temperatures. The SiGe decomposition was detected in the precrystalline state of the SiGe undoped and doped films in the temperature range from 450 to 600 K by compaering S- and W-parameters of SiGe with that of amorphous silicon and germanium. In conclusion, we discuss model of internim ordering states before crystallization.

Tungsten carbide (WC) coatings were prepared using supersonic impaction of nanoparticles produced by pulsed laser ablation of microparticle aerosols. The influence of experimental parameters such as, carrier gas type and impaction velocity on the structure, composition and physical properties of the resultant particles and films were studied. It was found that stoichiometric, crystalline films could be grown. These films pass both the adhesive lift off and scratch tests. TEM investigations indicate that the laser ablation forms individual particles with mean size of 7 ± 3 nm. At the highest aersol pressures small aggregates were also observed, and adjustment of the gas pressure in the laser interaction cell was found to control the degree of aggregation. Upon impaction, the separate particles form dense, self sintering nanocrystalline films, with helium forming the most dense as determined from SEM images.

For poly-Si films prepared by a plasma-enhanced chemical vapor deposition, we examined the changes in the local structure caused by adding H2 and/or SiF4 in the SiH4 feed gases and by changing supplied rf power values. The conditions of low rf power supply, low H2 addition, and SiF4 addition allow formation of films with microcrystalline or nanocrystalline structures. In addition, the H2 or SiF4 addition was found to be effective in promotive growth of <111> or <110> grains, respectively. In such low crystallized films, it was suggested that high-angle boundary would be formed, leading to a decrease in the density of SiH2 and Si dangling bonds, and to an increase in g values.

Nanocrystalline β-SiC particulates with a grain size range of 5-20 nm were prepared by heating a pre-pyrolyzed, chlorine-containing polysilane/polycarbosilane (PS/PCS) to 1600°C. The transformation from the pre-pyrolyzed PS/PCS to nanocrystalline SiC was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), mass-spectrometry and infrared spectroscopy. The results indicated that the nanocrystalline P-SiC was formed by the crystallization of the PS/PCS random network, and crosslinking of Si-Si, Si-Cl, and Si-CH2-Si bonds. The TEM observation showed that SiC particulates consist of equiaxed, randomly oriented, ultrafine grains.

Arrays of nanowires have attracted considerable recent attention due to their unique electronic and optical properties. While much effort has been directed at fabricating arrays and measuring their properties, much less has been done to characterize these materials. Understanding the structure and composition of the constituents in these arrays is crucial in order to control their properties. In this work, arrays with wire diameters from 35-90nm were fabricated by pressure injecting liquid bismuth into porous alumina templates. Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) were used to characterize the arrays.

Dimensionality can play an important role in determining the properties of materials. In the case of thermoelectric materials, it has been proposed that one-dimensional quantum wires, or nanowires, and two-dimensional superlattices could exhibit substantially higher efficiencies compared to the corresponding bulk, three-dimensional solids. To explore such predictions we have initiated a program directed towards the controlled growth of nanowires, and herein, we report the synthesis of single crystal Bi2Te3 and PbTe nanowires by a pulsed laser ablation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Bi2Te3 wires 80 nm to 200 nm in diameter and lengths exceeding 10 microns, and PbTe wires 25 nm to 60 nm in diameter and lengths to 2 microns can be readily produced by the laser ablation method. High-resolution TEM and electron diffraction show that Bi2Te3 nanowires are single crystals with wire axes along the <110> crystal direction. TEM and electron diffraction measurements also show that the PbTe nanowires are single crystals with a <100> growth axis. The transport properties of these new nanowire materials will be discussed.

Amorphous silicon nanowires (a-SiNW's) with average diameter around 20 nm were synthesized at about 950° C under an Ar/H2 atmosphere on large area of a (11) Si substrate without supplying any gaseous or liquid Si sources. The Si substrate, deposited with a layer of Ni of about 40 nm thick, served itself as a silicon source for the growth of the a-SiNWs. Different from the well-known vapor-liquid-solid (VLS) for conventional whisker growth, it was found that growth of the a-SiNWs was controlled by a solid-liquid-solid mechanism, which is analogous to the VLS model.

Highly oriented silicon nanowires were grown on Si (111) substrate via a solid-liquid-solid (SLS) mechanism. Unlike the well known vapor-liquid-solid (VLS) mechanism of whisker growth, no gaseous or liquid Si source was supplied during growth. Ni was used as the liquid forming agent and mixture of H2 and Ar was introduced in the experiment. Oriented silicon nanowires grew at 950°C and the ambient pressure kept at about 200 Torr. The oriented silicon nanowires have a length around I il m and uniform diameter about 25nm. Selected area electron diffraction showed that silicon nanowires are completely amorphous. The approach used here is simple and controllable, and may be useful in large-scale synthesis of various nanowires.

Composite nanowires with typical diameters of 30-100nm, which consisted of Si, β-SiC, amorphous carbon were converted from Si nanowires by ion beam deposition. The Si nanorods were exposed to broad low energy ion beams. The low energy hydrocarbon, argon and hydrogen ions, generated in a Kaufman ion source, reacted with Si nanowires and formed the composite nanowires. It has been assumed that the reaction pathway to form the composite nanowires were driven by both thermal diffusion and kinetic energic of interacting particles.

Monoclinic gallium oxide (β-Ga2O3) nanowires were catalytically synthesized by electric arc discharge of GaN powders mixed with a small amount (less than 5 %) of transition metals under a pressure of 500 Torr (80 %-Ar + 20 %-O2). Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images showed that the average diameter of the wires were about 30 nm and their lengths were as long as up to one hundred micrometer, resulting in extremely large aspect ratio. Fourier diffractogram was indicative of single crystalline nature of the β-Ga2O3 wire. HRTEM image also showed β-Ga2O3 with twin defects at the center of the wire which might play as nucleation seeds. Both X-ray diffraction (XRD) patterns and FT-Raman spectra of the wires identified the observed nanowires as monoclinic crystalline gallium oxides.

The room temperature structural, magnetization and magnetoresistive properties of Ni-nanowires of diameters 18, 30 and 78 nm and various lengths, fabricated by electrochemical deposition of Ni in the nanopores of anodic alumina, are investigated. The crystallographic orientation depends on the diameter of nanowires. Nanowires show perpendicular magnetic anisotropy and enhanced coercivity (Hc) and remanent magnetization (Mr) values of up to 500 Oe and 50% respectively. An electrodeposited Ni-layer (5 μm) on copper substrate shows in plane magnetic anisotropy and the Hc and Mr values are 97 Oe and 37%. Ni-nanowires and Ni-layer show an anisotropic magnetoresistive behaviour.