Ultrafast Carrier Relaxation in InN Nanowires Grown by Reactive Vapor Transport

We have studied femtosecond carrier dynamics in InN nanowires grown by reactive vapor transport. Transient differential absorption measurements have been employed to investigate the relaxation dynamics of photogenerated carriers near and above the optical absorption edge of InN NWs where an interplay of state filling, photoinduced absorption, and band-gap renormalization have been observed. The interface between states filled by free carriers intrinsic to the InN NWs and empty states has been determined to be at 1.35 eV using CW optical transmission measurements. Transient absorption measurements determined the absorption edge at higher energy due to the additional injected photogenerated carriers following femtosecond pulse excitation. The non-degenerate white light pump-probe measurements revealed that relaxation of the photogenerated carriers occurs on a single picosecond timescale which appears to be carrier density dependent. This fast relaxation is attributed to the capture of the photogenerated carriers by defect/surface related states. Furthermore, intensity dependent measurements revealed fast energy transfer from the hot photogenerated carriers to the lattice with the onset of increased temperature occurring at approximately 2 ps after pulse excitation

Preparation of TiO2 Anatase Nanocrystals by TiCl4 Hydrolysis with Additive H2SO4

A new methodology was developed to synthesize uniform titania anatase nanocrystals by the hydrolysis of titanium chloride in sulfuric acid aqueous solutions at 0–90°C. The samples were characterized by Raman spectroscopy, UV-visible spectroscopy, transmission electron microscopy (TEM), electron diffraction (ED), and an Energy dispersive X-ray spectroscopy (EDS). The effects of the reaction temperature, mole ratio of SO42− to Ti4+, and the calcinations temperature on the particle size and crystal phase were investigated. Depending on the acidity, the hydrolysis temperature, and the calcination temperature, rhombic anatase nanocrystals sizes in the range of 10 nm to 50 nm were obtained. In the additive of sulfuric acid, Raman spectra and electron diffraction confirmed that the nanoparticles are composed of anatase TiO2. No other titania phases, such as rutile or brookite, were detected

Microwave-Assisted Synthesis of Titania Nanocubes, Nanospheres and Nanorods for Photocatalytic Dye Degradation

TiO2nanostructures with fascinating morphologies like cubes, spheres, and rods were synthesized by a simple microwave irradiation technique. Tuning of different morphologies was achieved by changing the pH and the nature of the medium or the precipitating agent. As-synthesized titania nanostructures were characterized by X-ray diffraction (XRD), UV–visible spectroscopy, infrared spectroscopy (IR), BET surface area, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. Photocatalytic dye degradation studies were conducted using methylene blue under ultraviolet light irradiation. Dye degradation ability for nanocubes was found to be superior to the spheres and the rods and can be attributed to the observed high surface area of nanocubes. As-synthesized titania nanostructures have shown higher photocatalytic activity than the commercial photocatalyst Degussa P25 TiO2

Synthesis of GaN particles in porous matrices by chemical vapor infiltration of single molecule precursors

The filling of porous materials like molecular sieves by semiconducting materials is explored as a concept to fabricate novel mesoscopic systems such as quantum wires, quantum dots for possible optoelectronic and photonic applications. The dimension and arrangement of the incorporated material is dictated by the shape, size and order of crystallinity of the pores of the template that is being used. GaN is one such interesting semiconducting material whose fabrication in thin film form is well developed. However GaN in the form of nanoparticles has not been explored with much success and there are very few reports so far. This work represents a single source precursor approach for the synthesis of GaN nanoparticles by chemical vapour infiltration (CVI). The formation of GaN using MCM-41 as a porous host template and the characterisation of the nanoparticles by N2 sorption studies (BET), XRD, TEM, EDX, 71 GaNMR, elemental analysis will be addressed in this paper

Growth of InN whiskers from single source precursor

The group-III nitrides GaN, InN, AIN and their alloys InxGa1-xN, AlxGa1-xN have recently acquired technological importance for LED and laser applications. However, InN has a low decomposition temperature and the growth of crystalline InN material at low temperatures is difficult. One of the approaches is to design single source precursors that decompose at low temperatures. Single source precursors of the type N3In[(CH2)3NMe2]2 were developed and the growth of crystalline InN films with preferred orientation was achieved using this compound. However employing specific CVD process parameters we were able to grow InN whiskers consistently by CVD using a cold wall CVD reactor on sapphire substrates at 500°C. These whiskers were characterised by XRD, SEM, EDX and TEM measurements

Organometallic Synthesis of β\beta-CoAl Nanoparticles and β\beta-CoAl/Al Nanoparticles and Their Behaviour upon Air Exposure

Nanocolloids of the intermetallic beta-CoAl phase were prepared by a soft organometallic route. They were fully characterized by (HR)TEM, EDX, WAXS, XAS and SQUID magnetometry. Their exposure to air led to an increased saturation magnetization in agreement with Co/Al segregation and the formation of Co/Al(2)O(3) nanocomposite. Furthermore, the beta-CoAl nanoparticles could be used as seeds to grow an aluminum overlayer, which passivated the alloyed core against oxidation. These nanoparticles yielded stable colloidal solutions in aromatic solvents

Lanthanide Oxide Thin Films by Metalorganic Chemical Vapor Deposition Employing Volatile Guanidinate Precursors

The application of two novel metalorganic complexes, namely the isostructural tris(N,N\u2019- diisopropyl-2-dimethlyamido-guanidinato)gadolinium(III) (1) and tris(N,N\u2019-diisopropyl-2-dimethlyamido- guanidinato)dysprosium(III) (2) as precursors for metalorganic chemical vapor deposition (MOCVD) of Gd2O3 and Dy2O3 is discussed. On the basis of the detailed thermal gravimetric analysis (TGA) and isothermal TGA studies, both the precursors are very volatile and able to deliver continuous mass transport into the gas phase. The extraordinary thermal stability of the precursors was revealed by nulcear magnetic resonance (NMR) decomposition studies. Depositions were carried out in the presence of oxygen at reduced pressure and varying the substrate temperature in the range 300-700 \ub0C. Uniform films with reproducible quality were deposited on Si(100) and Al2O3(0001) substrates over the entire temperature range. Employing a multitechnique approach (XRD, SEM, AFM, EDX, XPS, RBS, SNMS, C-V), variations of the growth characteristics and film properties with deposition temperature are studied in terms of crystallinity, structure, surface roughness, composition, and electrical properties