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Copper oxide (CuO) nanoflowers were synthesized by a reproducible and inexpensive wet chemical method. The synthesized CuO nanoflowers were characterized by x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. For an optimized operating temperature of 240°C, the sensor characteristics of the gas sensing device were measured using acetone as a volatile gas. The synthesized CuO nanoflower-based gas sensor responded very strongly for acetone gas concentrations in the range of 250–2250 ppm, and the recorded response for concentrations of 250 ppm and 2250 ppm was 2.7 and 7.2, respectively. The stability of the synthesized sensor was checked by repeating the measurements over a period of 1 month, and a very small change of 3.3% in the response of the sensor was observed.

We describe a two step vertical growth of silicon nanowires (SiNWs) and the lateral growth of a bridging network of carbon nanotubes (CNTs) across the SiNWs. SiNWs were formed by an electro-less chemical bath deposition technique using silver nano particles as a virtual mask. Subsequently, the silver nano particles present on the side walls of SiNWs were used as a catalyst in the growth of CNTs by atmospheric chemical vapor deposition technique, forming “nano bridges”. A reduced reflectance of 65 % for the “nano bridge” samples compared to the SiNW samples was obtained suggesting a potential use in anti-reflection coatings.

ZnO nanorods have been synthesized over etch-patterned Si (110) wafer using annealed silver thin film as growth catalyst. The growth of ZnO nanorods were performed by a two-step process. Initially, the deposition of Zn thin film was done on the annealed silver catalyst film over etch-patterned Si (110) substrate by thermal evaporation, and then annealed at 800°C in air. The etching of the patterned Si (110) wafers was carried out by 50% aqueous KOH solution. The samples were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy and room temperature photoluminescence spectroscopy. ‘V’ shaped grooves with no undercut were formed after etching due to the anisotropic nature of the KOH etchant. The etch-patterned wafer was used to provide larger surface area for ZnO growth by forming ‘V’-grooves. This ZnO film may be predicted as a very good material for gas sensor.

Sword-like (diameter ranging from 40 nm to 300 nm) and needle-like zinc oxide (ZnO) nanostructures (average tip diameter ∼40 nm) were synthesized on annealed silver template over silicon substrate and directly on silicon wafer, respectively via thermal evaporation of metallic zinc followed by a thermal annealing in air. The surface morphology, microstructure, chemical analysis and optical properties of the grown samples were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, room temperature photoluminescence and Raman spectroscopy. The sword-like ZnO nanostructures grown on annealed silver template are of high optical quality compared to needle-like ZnO nanorods for UV emission and show enhanced Raman scattering.

Thin Mn films were deposited on GaAs(100) surfaces at room temperature by a thermal evaporation system followed by annealing at 500 °C for times ranging from 2 to 8 h in nitrogen atmosphere. X-ray diffraction shows that for samples annealed at 500 °C, the interfacial reaction results in the formation of different phases such as Mn2As, MnAs and Mn3Ga. Rutherford Backscattering Spectrometry indicates a diffused layer of Mn–Ga–As system along with some minor oxygen content. Magnetization study done at 10 K shows M–H curve comprising a ferromagnetic and antiferromagnetic part and M–T measurement done from 10 to 300 K shows a transition around 45 K which may be related to the presence of GaMnAs alloy along with the presence of the above binary phases.

Many studies have been done on low energy (1–200 keV) and high dose (1016–1017) implantation of Mn in GaAs. This study is an attempt to incorporate Mn ions in GaAs through implantation of 1 MeV Mn+1 ions in semi-insulating GaAs substrates at doses of 3×1015/cm2 and subsequent annealing. This was done to find out if any alloy of Mn–Ga–As, or binary compounds of Mn–Ga or Mn–As form due to annealing of Mn+1 ions implanted in GaAs substrates. High Resolution XRD (HRXRD) performed before annealing shows a possibility of Ga–Mn–As alloy formation, and after annealing at 800°C, except for GaAs main peaks no other phase peaks were detected. Scanning electron microscopy (SEM) shows nanostructures of various dimensions which are thought to be formed due to the defects generated due to implantation. Fourier Transform Infrared (FTIR) study shows the shift in bandgap due to Mn doping. Raman spectroscopy shows the red shift in LO and TO peak positions of GaAs after annealing, which indicates the presence of disorder and damage due to implantation. Resistivity measurement shows a thermally activated semiconductor character of charge conduction with an activation energy of 51 meV and this activation may have occurred through the transitions from impurity band to valence band. Large positive (∼25%) magnetoresistance and a mixture of ferromagnetic and paramagnetic behavior obtained in the magnetization measurement indicate the presence of ferromagnetic MnAs nanoclusters embedded in paramagnetic GaAs:Mn matrix.

Needle-like nanorods and micron-scale flower-like structures of ZnO were synthesized by thermal evaporation of metallic zinc films with different thicknesses, followed by thermal annealing. Needle-like nanorods of ZnO were found through out the sample surface after annealing of the 1.3 μm thick Zn film. Three-dimensional crystalline nanorod-based flower-like structures of ZnO were also observed after annealing of the relatively thick (3.3 μm) Zn film. Thermal annealing of the Zn films was done at 800 °C in air for different time durations (30, 45, and 90 min). The flower size and number increase with increase in film thickness for the same annealing temperature and time. The X-ray diffraction results show that both the needle-like nanorods and flower-like structures are hexagonal wurtzite structure of ZnO. The room temperature PL spectrum shows a strong defect related violet emission peak centered at 441 nm for both the structures. The possible growth process based on root growth technique is proposed.

Several different cleaning procedures for GaAs (100) substrates are compared using X-ray photoelectron spectroscopy and optical microscopy. This work emphasizes the effect of the last etching step: using either HCl, HF-ethanol (5%) or static deionized water after HCl cleaning. All the procedures except HCl solution (1:1) produce an As-rich surface. Also, none of the etchants except HF-ethanol solution produce Ga or As-rich (oxide free) surfaces. Optical microscopic study shows different etch pits produced due to etching in different solutions.

Crystalline cubic silicon carbide (3C-SiC) nanopowders were synthesized using hexamethyldisilane (HMDS) in a resistance heated chemical vapour deposition (CVD) reactor. The effects of different diluent gases on the synthesis of the SiC powder were also studied. The deposited powder was characterized using high-resolution X-ray diffraction (HRXRD) analysis, transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and BET surface area measurements. The crystallite size was estimated to be in the range of nanometer (10–20 nm) from XRD data and the particle size (∼10–30 nm) was obtained by TEM, HRTEM and BET. The growth condition was optimized in terms of crystallinity, chemical composition and deposition rate by varying different parameters such as the diluent gas (H2/Ar ratio) and temperature.

Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.

Cubic silicon carbide (3C-SiC) thin films were grown on (100) and (111) Si substrates by CVD technique using hexamethyldisilane (HMDS) as the source material in a resistance heated furnace. HMDS was used as the single source for both Si and C though propane was available for the preliminary carbonization. For selective epitaxial growth, patterned Si (100) substrates were used. The effect of different growth parameters such as substrate orientation, growth temperature, precursor concentration, etc on growth was examined to improve the film quality. The surface morphology, microstructure and crystallinity of grown films were studied using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS).

A complete NMR study involving both 1D and 2D 13C-{103Rh} and 31P-{103Rh} HMQC measurements, on [Rh6C(CO)14(PPh3)]2- are reported and discussed, together with the multiple Rh quantum effects found for resonances associated with edge- and face-bridging CO's. As found in [Rh6C(CO)15]2-, the carbonyl ligands in [Rh6C(CO)14(PPh3)]2- undergo CO-intermolecular exchange with 13CO at different rates; for the edge-bridging CO's, the lower the value of 1J(Rh–CO), the faster the rate of intermolecular exchange with 13CO.

This article reports the formation of Schottky nanocontacts on single crystalline ZnO nanorods (NR) using atomic force microscopy (AFM) with a PtIr-coated Si cantilever in a contact mode. ZnO NRs were synthesized by thermal evaporation of metallic zinc thin film followed by annealing. The NRs are [11 $$ \overline{2} $$ 0] directed (i.e., along a-axis) which is quite unusual for wurtzite ZnO. The appearance of an intense visible emission band in room-temperature photoluminescence indicates the presence of a high density of intrinsic defects confirming n-type ZnO. The PtIr tip/ZnO Schottky nanocontacts with an ultra fine effective contact radius ~0.5 nm on horizontally dispersed NRs show an ideality factor of ~7, turn on voltage of ~1.0 V, Schottky barrier height of ~0.65 eV, breakdown voltage of ~−4.7 V, and ON to OFF current ratio of ~500 at ±2 V. The junction corresponds to a nanoscale Schottky contact with satisfactory properties which is comparable to the other PtIr/ZnO or Pt/ZnO reports at higher loading forces. Single crystallinity and contact on the side faces of the horizontally dispersed NRs are primarily thought to be the key factors for higher device performances.

Sensor response characteristics of Ru/3C-SiC (epitaxial layer of SiC on Si substrates) Schottky junctions were studied at different temperatures (200 – 400 °C) in presence of varying concentrations of hydrogen from 5000 – 20000 ppm. The output signal of the sensor, the response time and the reversibility were investigated from the transient response characteristics of the sensors. The sensor parameters improved with higher operating temperature, up to 400 °C. The sensitivity of the sensors was found to be a function of applied bias across the Schottky junction. As compared with the Pd/3C-SiC junctions, the Ru/3C-SiC Schottky sensors showed higher resolution and better reversibility in the hydrogen concentration range 10000 to 20000 ppm. The SIMS (Secondary Ion Mass Spectrometry), RBS (Rutherford Backscattering Spectrometry) and GIXRD (Glancing Incidence X-ray Diffraction) studies indicated that up to 400 °C there was no formation of ruthenium silicide at the Ru/3C-SiC interface.

Single crystalline 3C-SiC films have been grown on Si(111) substrate at 1200°C by conventional CVD process using HMDS (Hexamethyldisilane). Before columnar growth of SiC, columnar Si was made by depositing Au on Si(111) substrate as a solvent of VLS mechanism. Si growth was carried out by disproportional reaction in halide transport method. The columnar Si was produced on the patterned substrates. The columnar Si was covered by SiC. Needle like columns of SiC can be used for MEMS application such as micro-heat exchanger.

Epitaxial growth of 3C-SiC on Si substrates has been studied for many years, however an important issue is how to reduce the high density of interfacial defects. Channel epitaxy is the growth of a film on small channeled windows and is related to selective growth. Channel epitaxy of 3C-SiC grown on the seed 3C-SiC previously deposited on patterned Si substrates was achieved via CVD using hexamethyldisilane (HMDS). The proper selection of mask materials was also key to achieve channel epitaxy. Thermal oxide, silicon nitride and thin SiC masks were tried. Thin SiC was an effective mask to achieve selective growth at 1350°C. Smooth surface morphology was observed on both the channel regions and the mask regions at the growth temperature of 1350°C. Scanning electron microscopy revealed coalescence of the laterally grown regions via channel epitaxial growth of 3C-SiC.

We have grown epitaxial layer introducing buffer layer using N2 doping on 6H-SiC (1120) and (1100) substrate. The improvement of morphology could be obtained for (1120) and (1100) epilayers. Morphologies of (1120) epilayers were independent on off-orientations, Morphologies of (1100) epilayers were very sensitive to the off-orientations. The quality of epilayer, and impurity incorporation for a-plane were very influenced by the surface treatment before CVD growth compared to (0001) epilayers.

High quality SiC and AlN films allow the fabrication of metal/AlN/SiC MIS structures and SiC/AlN heterostructures that require a low lattice mismatch and excellent thermal stability. Epitaxial SiC on AlN/sapphire was grown using hexamethyldisilane (HMDS) by MOVPE. 2HAlN is epitaxially grown on sapphire by MOCVD, and subsequently SiC is deposited on it. The growth of high quality SiC was achieved in a one step process without any nucleation step using dilute hydrogen in argon (12% H2 + Ar) as the carrier gas, which is less explosive than pure H2. The effect of growth temperature and thickness of AlN on the SiC crystal quality and the surface smoothness were studied. All films were analyzed using reflection high energy electron diffraction (RHEED), Nomarski differential interference contrast microscopy (NDIC), X-ray diffraction (XRD), and atomic force microscopy (AFM). Optimum temperature for SiC growth was between 1300°C and 1350°C. At these temperatures, the grown films show strong epitaxial relationship with AlN and very smooth surfaces (RMS ∼ 0.1- 0.75 nm). At temperatures below 1300°C, the film becomes polycrystalline. At 1400°C, the films show highly textured features, observed by XRD. In the RHEED, however, weak rings appear superimposed on the spot pattern, which implies the grown films are polycrystalline but highly textured. In order to evaluate the effect of underlying AlN thickness on the SiC film, layers with various thicknesses (50, 200, 400 nm) have been used at 1350°C. The SiC film on a 50 nm thick AlN layer shows a very smooth surface (RMS ∼ 0.1 nm) compared to the SiC film on a 400 nm (RMS ∼ 0.7 nm) AlN layer. This seems to be caused by the increasing roughness of the underlying AlN, as it becomes thicker. However, all the films show highly epitaxial growth features, which implies that 50 nm is sufficient to relieve the mismatch strain of the underlying AlN/sapphire.

To reduce the defect density inherent in conventional heteroepitaxial growth of SiC on Si, selective epitaxy followed by lateral epitaxial growth was performed in a conventional atmospheric pressure chemical vapor deposition (APCVD) system. The source gas was primarily hexamethyldisilane (HMDS). Hydrogen was used as the carrier gas and small amounts of hydrogen chloride (HCl) were added to improve the selectivity. Si(001) wafers, with an oxide layer (∼ 700 nm thick) as a mask, were used as substrates. The grown films were analyzed using optical microscopy and scanning electron microscopy (SEM). In earlier work, we had demonstrated the problems associated with the application of this technique – viz., oxide degradation and high growth temperature. Using HMDS, the growth temperature has been considerably reduced allowing the continued use of an oxide mask. Selective growth was demonstrated in films grown at 1250° and below.

Together with sapphire, SiC is the most common substrate material for GaN epitaxial growth. In fact, SiC has advantages over sapphire because of its better thermal conductivity and lower film substrate lattice mismatch (∼3.5%). However, nucleation of GaN on SiC is rather difficult because of the low surface energy of SiC and the sensitivity of substrate preparation. This latter point makes it essential to use a very careful cleaning step, and also to pre-treat the substrate surface by growing a thick buffer layer of AlN at a relatively high temperature. In this study, several pre-treatment steps of SiC for GaN deposition were tested including (a) nitration with NH3 for 0.5-20 minutes, (b) pre-adsorption of trimethyl gallium (TMG) or trimethyl aluminum (TMA) for 0.5-5 minutes, and (c) deposition of an AlN buffer layer at ∼1150°C. After each pre-treatment, GaN was deposited by MOCVD using dilute H2(Ar+12%H2), NH3 and TMG. All the films were characterized by XRD and cross-sectional TEM. After nitration of SiC, the deposited GaN film was found to be polycrystalline. In case of pre-adsorption of TMG, epitaxial but island-like GaN formed on the substrate. In the third case, with an ultra-thin (∼1.5nm) coverage of AlN on SiC (by pre-adsorption of TMA or by 50 seconds deposition of AlN), GaN epilayers were successfully deposited on SiC. However, when AlN was deposited for longer than 3 minutes (up to 10 minutes), only polycrystalline GaN was obtained. With this technique of covering the surface with an ultra-thin layer of AlN, epitaxial GaN has been successfully deposited on 6H-SiC (0001), on 4H-SiC(0001), and on 3C-SiC/Si(111) substrates. The effect of the different pre-treatments of SiC on the quality of the deposited GaN films will be discussed and compared, and the optimal conditions for GaN deposition for each substrate will be presented.