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Aluminium substituted mesoporous KIT-6 materials were directly synthesized by hydrothermal method with different silica to aluminium ratios (Si/Al = 25, 50, 75, 100). These materials were obtained by using Pluronic P123 and n-butanol as a structure-directing agent and co-solvent respectively, under high acidic conditions. The prepared catalysts were characterized by small-angle XRD, ICP-AES, nitrogen sorption analysis, TGA, SEM, TEM, and XPS techniques. The characterization revealed that aluminium is mainly incorporated into the framework of KIT-6. The XRD patterns and TEM images of materials showed a highly ordered cubic Ia3d mesostructure. The incorporation of the aluminium was clearly evident from XPS and ICP-AES techniques. Further, the synthesized Al-KIT-6 catalysts were tested in the acylation of isobutylbenzene (IBB) with acetic anhydride (AA). The results revealed that Al-KIT-6 (25) was a prominent active catalyst due to silica to aluminium ratio than others. The catalytic reaction conditions were tuned to obtain a high selectivity of 4-isobutyl acetophenone (4-IBA) with high conversion of isobutylbenzene. Al-KIT-6 (25) showed a high conversion (72%) of isobutylbenzene and 94% selectivity of 4-isobutyl acetophenone.

Praseodymium incorporated AlPO-5 was synthesized hydrothermally in fluoride medium using triethylamine as template. PrAlPO-5 could be bi-functional in nature since the isolated praseodymium sites acted both as redox and acid sites. The framework incorporation of praseodymium in AlPO-5, and the absence of separate praseodymium oxide phase were confirmed by laser Raman and fluorescence studies. The chemisorbed oxygen on praseodymium sites were identified by ESR. The ex-situ pyridine adsorbed IR spectrum confirmed the presence of Lewis acid sites. The catalytic activity of PrAlPO-5 was evaluated in the synthesis of campholenic aldehyde from α-pinene. The epoxidation of α-pinene through chemisorbed oxygen followed by isomerisation of α-pinene oxide over Lewis acid sites on PrAlPO-5 yielded campholenic aldehyde selectively. PrAlPO-5 was proved to be an active, selective and reusable catalyst.

SnO 2 thin films were obtained by ex-situ oxidation of Sn metal film deposited by thermal evaporation. The oxidation of the Sn film was carried out at 600, 700 and 900 °C for 2 h in a controlled oxygen atmosphere. GIXRD confirmed the tetragonal rutile phase of SnO 2 which was further confirmed by Raman spectroscopy. The RBS measurements provided the thickness and chemical information of the film. Thickness of the film was in the range of 6⿿12 nm and the presence of Sn and oxygen in the films are shown. Scanning electron microscopy revealed spherical particles of different sizes for films annealed at different temperatures. The SnO 2 thin film oxidized at 900 °C was tested for methane gas sensing. A sensing response of 78.46% for 100 ppm of methane at an operating temperature of 100 °C which is one of lowest reported was obtained.

Resonant Rutherford backscattering spectrometry (RRBS) technique can be used for analysis and quantification of carbon in few layer graphene and graphene oxide films. The carbon concentration estimated using RRBS measurements satisfactorily agreed with the theoretically reported value. Our experimental studies evidenced that RRBS technique can be used for the analysis of carbon in graphene based material, particularly, RRBS with glancing incident angle with its high sensitivity can be effectively used for thickness and estimation of carbon concentration.

Room temperature deposition of molybdenum-copper thin films have been performed by ion beam sputtering and characterized by x-ray diffraction, x-ray reflectivity, & Rutherford backscattering spectrometry studies. Electrical resistivity measurements were performed up to milli-Kelvin temperatures and residual resistivity ratio values have been calculated to figure out a correlation with copper thickness.Room temperature deposition of molybdenum-copper thin films have been performed by ion beam sputtering and characterized by x-ray diffraction, x-ray reflectivity, & Rutherford backscattering spectrometry studies. Electrical resistivity measurements were performed up to milli-Kelvin temperatures and residual resistivity ratio values have been calculated to figure out a correlation with copper thickness.

A novel magnetic Fe3O4 core-shell nanorods (MCSNs) were synthesized by crosslinking amine functionalized Fe3O4@SiO2 core-shell nanoparticles with 1,2-bromochloroethane. These nanorods were then protonated with dilute HCl. The MCSNs nanorods were characterized using FT-IR, N2 adsorption, VSM, SEM and TEM. The surface area of MCSNs nanorods was found to be 335 m2/g, which is higher than bare iron oxide and amine functionalized Fe3O4@SiO2. These nanorods were used simultaneously as ion-exchanger and adsorbent for the removal of arsenic from aqueous solution. It exhibited high adsorption capacity for arsenic. The kinetic study revealed that adsorption equilibrium attained within five min. The adsorbed arsenic on the nanorods were removed by magnetic separation and regenerated by acid treatment. The percentage removal of arsenic was more than 99%. Such nanorods can be used to remove not only arsenic but also other anions from potable water.

It was reported that non-amorphizing implantation by hydrogen has a potential in improving silicon machining. Post-implantation high-temperature treatment will affect implantation-induced damage, which can have impact on silicon machining. In this article, a relation of a thermal annealing of hydrogen implanted in silicon to micro-cutting experiment is investigated. Hydrogen ions were implanted into 4″ silicon wafers with 175 keV, 150 keV, 125 keV and doses of 2 × 1016 cm−2, 2 × 1016 cm−2 and 3 × 1016 cm−2, respectively. In this way, low hydrogen atom–low defect concentration was created in the region less than ~0.8 μm deep and high hydrogen atom–high defect concentration was obtained at silicon depth of ~0.8–1.5 μm. The post-implantation annealing was carried out at 300 and 400 °C in nitrogen for 1 h. Physical and electrical properties of implanted and annealed samples were characterized by secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD), Rutherford backscattering (RBS) and nanoindentation. Plunge cutting experiment was carried out in and silicon crystal direction. The critical depth of cut and cutting force were monitored and found to be influenced by the annealing. The limits of hydrogen implantation annealing contribution to the cutting characteristics of silicon are discussed in light of implantation process and redistribution of hydrogen and defects generation during annealing process.

Nano-crystalline diamond coatings were deposited on the silicon substrate using Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD). Experiments were performed by varying the H2 content in CH4/H2 plasma during synthesis. Raman spectral analysis revealed that with decrease in hydrogen content in the CH4 plasma, the ID/IG ratio decreases with the formation of smaller crystallites. Such a film possesses a large grain boundary fraction containing hydrogenated amorphous carbon (a-C:H). During tribological test, sufficient amount of hydrogen present in the grain boundary passivates the dangling σ-bond causing ultra-low friction and extremely low wear evident by improvement in microstructure.

International audience; We have prepared germanium nanoparticles embedded in SiO2 matrix by atom beam co-sputtering (ABS) of Ge+SiO2 on Si substrate. The as-deposited films were annealed at various temperatures in Ar+H2 atmosphere and irradiated with various energies with fixed fluence. The pristine and irradiated samples were characterized by Raman, X-ray diffraction and atomic force microscopy (AFM). Rutherford back scattering (RBS) was used to quantify the concentration of Ge in the SiO2 matrix and the film thickness. Raman studies of the films indicate the formation of Ge crystallites as a result of swift heavy ion (SHI) irradiation. Moreover, the crystalline nature of Ge improves with an increase in energy. Glancing angle X-ray diffraction and Raman results also confirm the presence of Ge crystallites in the irradiated samples. Similarly, 400keV Ge+ ions implanted into silicon substrate at higher fluence at 573K have been irradiated with 100MeV Au8+ions at RT. These irradiated implanted samples were subsequently characterized by XRD and Raman to understand the crystallization behavior. We also studied the surface morphology of a high-energy irradiated sample by AFM. The irradiation results were compared with those obtained by thermal annealing in ABS. The basic mechanism for crystallization induced by SHI in these films has been investigated.

Germanium atomic (Ge1) and molecular ions (Ge2) of equivalent energy are implanted in silicon at an elevated temperature. The ion induced damage has been characterized by RBS channeling (RBS/C) and positron annihilation spectroscopy. The RBS/C studies indicate that the molecular ion implantation has produced more defects in the near surface regions compared to the atomic ion implantation. This paper reports a first time observation of an enhanced production of vacancy related defects in silicon implanted with molecular ions.

Recently, interesting differences for ion – uniform film and ion – nanostructure interaction phenomena, particularly relating to ion beam mixing effects have been reported. Upon irradiation with 1.5 MeV Au 2+ ions on isolated Au nanostructures on silicon substrate, a higher probability of crater formation, larger sputtered particle size and its coverage and enhanced sputtering yield compared to the continuous films of Au on Si substrate were observed. Ion bombardment at high flux (≈6.3 × 10 12 ions cm −2 s −1 ) showed a dramatic mass transport from nanostructures extending up to a distance of about 60 nm into the substrate, much beyond their size. In this paper, RBS/Channeling results would be presented to elucidate on the arrangement of re-distributed gold atoms location in silicon and silicide matrix. Scanning transmission electron microscopy (STEM, with high angle annular dark field imaging) was used to complement the RBS results in determining the unusual mass transport and under ion–nanostructure interaction. The amorphous nature of the silicon matrix, that is deduced from both the RBS/Channeling and from TEM measurements, is an important factor in enhanced diffusion process resulting in dramatic mass flow.

Nanoscale cobalt clusters have been synthesized in an amorphous silica matrix by implanting high energy cobalt ions (2 MeV, Co 2+ ) with various doses. Surface acoustic radial vibration (phonons) modes confined to these cobalt nanoclusters have been detected using the low-frequency Raman scattering spectroscopy. Postannealing the ion implanted silica samples in a high vacuum atmosphere has led to significant growth of the cobalt nanoclusters in the silica glass matrix. Using suitable mechanism for the growth of the nanoclusters, activation energy for the diffusion of cobalt atoms in the silica matrix is calculated to be about 0.20 eV. Diffusion of the implanted cobalt atoms in the silica matrix during postannealing is further examined from the Rutherford backscattering measurements.

Zinc selenide thin films were deposited onto well-cleaned glass and silicon substrates using the vacuum evaporation technique under a vacuum of 3 × 10−5 Torr. These films were implanted with mass-analysed 75 keV N+ ions at different doses ranging from 1014 to 1016 ions cm−2. The composition, microstructure, surface roughness, optical bandgap and electrical properties of the as-deposited and nitrogen-implanted films were studied by Rutherford backscattering (RBS), grazing incidence x-ray diffraction (GIXRD), atomic force microscopy (AFM), Raman scattering, optical transmittance and I–V measurements. The RBS analysis indicates that the composition of the as-deposited and nitrogen-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and nitrogen-implanted thin films is cubic. In the AFM analysis, the surface roughness is found to increase with an increasing dose of nitrogen ions. In the optical studies, the optical bandgap value decreases with increase of the N+ dose. The prepared device exhibits a very good response in the visible region.

Application of SOI in high-power integrated circuit is limited by the self-heating effect, caused by the poor thermal conductivity of the buried SiO 2 layers. It is important to investigate new buried insulator with good thermal conductivity. We simulated the self-heating effects of AlN and SiO 2 thin films caused by power consumption of SOI devices with the help of ANSYS v6.1. Then prepared AlN thin films through ion beam enhanced deposition (IBED) system. The microstructure and dielectric properties were characterized through AFM, XPS, C – V , I – V and SRP. Our results show that the AlN thin films we prepared have excellent insulating properties and better thermal conductivity compared with SiO 2 films.

Kinetic Monte Carlo simulations for growth on substrates of three-fold symmetry predict the growth of islands of various shapes depending on the growth temperature [Phys. Rev. Lett. 71 (1993) 2967]. On Br–Si(1 1 1) substrates growth of epitaxial gold silicide islands of equilateral triangular and trapezoidal shapes have earlier been observed by annealing at the Au–Si eutectic temperature,363 � C [Phys. Rev. B 51 (1995) 14330]. We carried out annealing with temperature variation within a small window––(363 ± 30) � C. This has led to island growth of additional shapes like regular hexagon,elongated hexagon,walled hexagon and dendrite. Some of the observed island shapes have not been predicted.

A small indium flux was used as a surfactant during the growth of gallium nitride by rf-plasma assisted molecular beam epitaxy. The effects of the In surfactant on the optical and structural properties of undoped GaN were studied by photoluminescence (PL), X-ray diffraction, atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). PL studies show that the use of In surfactant is beneficial to the reduction of deep-level defects. The X-ray rocking curves demonstrate a 20% decrease in the full width at half maximum value for the films grown with In surfactant. AFM studies show that the root mean squared surface roughness for films grown with and without In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. The improved surface morphology is attributed to the enhanced 2-dimensional growth promoted by the application of In surfactant. RBS studies show that the χ min values along [0 0 0 1] direction are 2.06% and 2.16% for the samples grown with and without In surfactant respectively. Off-normal ion channeling studies were performed to further investigate the effects of In surfactant on the crystallinity. It is found that the number density of stacking faults is smaller for the sample grown with In surfactant compared to the one grown without In surfactant. However, defect analysis shows that dislocations are found in the sample grown with In surfactant in contrary to the one grown without In surfactant. We speculate that there is a thickness limit of GaN grown with In surfactant and the thickness of our samples exceed this limit, leading to the presence of dislocation.

We have deposited relatively thick (∼60 nm) Ge layers on Br-passivated Si(111) substrates by thermal evaporation under high vacuum conditions at room temperature. Ge has grown in a layer-plus-island mode although it is different from the Stranski-Krastanov growth mode observed in epitaxial growth. Both the islands and the layer are nanocrystalline. This appears to be a consequence of reduction of surface free energy of the Si(111) substrate by Br-passivation. The size distribution of the Ge nanoislands has been determined. The Br-Si(111) substrates were prepared by a liquid treatment, which may not produce exactly reproducible surfaces. Nevertheless, some basic features of the nanostructural island growth are reasonably reproducible, while there are variations in the details of the island size distribution.

La0.67Ca0.33MnO3 films are known to release oxygen upon vacuum annealing due to lattice expansion caused by change of valence state of Mn from Mn4+ to Mn3+. RBS measurements using O(α,α) resonance reaction at 3.043 MeV show that oxygen concentration decreases from 60% to 57% in 450 °C-vacuum annealed samples. There is also oxygen loss from the SrTiO3 substrate upto a certain depth. The measure of crystalline quality χmin degrades from 5.9% to 10%. A 45° in-plane orientation is observed which is due to the dominant presence of [1 1 0]0 texture in the epilayer. The measured channeling half width ψ1/2 decreases upon vacuum annealing. In the samples annealed in oxygen at high pressure at 700 °C, there is no measurable change in oxygen concentration and χmin improved to 4.4%. ψ1/2 increases upon high pressure oxygen annealing. Our measurements directly show that there is lattice disorder upon vacuum annealing and ordering upon high pressure oxygen annealing and it is the largest for the oxygen lattice sites.

A comparative study of Ti and TiN IBAD films as diffusion barriers for Cu has been done. It is found that amorphous Ti (a-Ti) and TiN (a-TiN) films show better thermal stability than (010) oriented Ti (c-Ti) and (111) oriented TiN (c-TiN) films. Such thermal stability can be attributed to their microstructure lacking grains that are fast diffusion paths compared to the imperfect preferentially oriented films prepared by IBAD. The absence of excess impurities in the c-TiN film also impedes the ‘stuffing effect’ and deteriorates its thermal stability. The 600 A c-Ti/a-TiN multilayer shows inferior thermal stability compared to 300 A a-TiN while the improvement resulting from the 600 A a-Ti/a-TiN multilayer is observed. The detrimental effect of the c-Ti layer inserted between the surface Cu and a-TiN can be attributed to the presence of its grain boundaries, making the interdiffusion between Cu and a-TiN much easier than at the interface of Cu/a-TiN.

Fe ions were implanted into Ge (110) using a metal vapor vacuum arc ion source. The samples were characterized by Rutherford backscattering spectrometry (RBS), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and superconducting quantum interference device magnetometry. The crystalline quality of the implanted layer was identified by RBS random/channeling measurements. The depth profile of the implanted Fe ions was obtained by AES. Low dose implantation causes formation of Fe–Ge precipitates whereas high dose implantation causes formation of Fe precipitates in the implanted layer as confirmed by TEM and XPS measurements. Magnetic measurements show the superparamagnetism of the Fe and Fe–Ge clusters at high temperatures.

Single-site CeAlPO-5 with Al/Ce ratios 25, 50, 75, 100 and 125 were synthesized hydrothermally in fluoride medium. The XRD patterns of CeAlPO-5 exhibited characteristic reflections of AlPO-5. 27Al MAS-NMR of CeAIPO-5(25) showed two unusual peaks at -20.78 and -71.35 ppm due to delocalization of cerium unpaired electron. However, 31P MAS-NMR exhibited the usual characteristic peak similar to that of AlPO-5. Vapour phase oxidation of toluene in air over CeAlPO-5 yielded benzaldehyde with high toluene conversion. The time on stream study established the stability of the catalyst. This catalyst can also be used for the selective oxidation of other alkyl aromatics.

Rutherford backscattering spectrometry (RBS) has been successfully applied to characterize compositionally graded BaxSr1-xTiO3 thin films fabricated by the sol-gel method. BaxSr1-xTiO3 compositionally graded films from × = 0.7 to 1 (upgraded) and × = 1 to 0.7 (downgraded) were fabricated on silicon substrates as well as on Pt/Ti/SiO2/Si substrates. For both upgraded and downgraded films, the measured Ba and Sr compositional gradients along the depth are consistent with the nominal values tailored during fabrication. XRD patterns demonstrate the existence of a perovskite structure. Thicknesses determined from cross-sectional SEM micrographs are consistent with the RBS results.

100 keV hydrogen ion implantation has been carried out on undoped semi-insulating 〈1 0 0〉 gallium arsenide single crystals for various ion doses at room temperature. The structural properties due to high dose, low energy hydrogen ion implantation has been investigated using X-ray double crystal diffractometry (DCD) analysis, Rutherford backscattering spectrometry and channeling (RBS/C) experiments and transmission electron microscopy (TEM) analysis. By using DCD analysis, the value of elastic lattice strain for the ion doses of 1 × 10 16 , 1 × 10 18 ions/cm 2 has been estimated to be 2.1 × 10 −3 and 3.2 × 10 -3 , respectively. The RBS spectra in the channeling mode for the high dose implantations (10 17 and 10 18 ions/cm 2 ) show a high yield indicating a highly damaged region near the range of the implanted hydrogen ions. Particularly, for the dose 10 18 ions/cm 2 , a heavily damaged region at the surface can be observed. The TEM results evidenced that no amorphisation occurred for the dose 10 18 ions/cm 2 . From TEM characterisation, it is also observed that there are no hydrogen bubbles present in the implanted region. But small dislocation loops have been identified. The projected range of implanted hydrogen ions and the thickness of the implanted layer obtained by RBS and TEM analysis are compared with the TRIM calculations.

PrAlPO-5 with (Al + P)/Pr ratios of 25, 50, 75 and 100 molecular sieves were successfully synthesized by hydrothermal method. These molecular sieves were characterised using XPS, TPD-NH3, ex-situ pyridine adsorbed IR, TPR, TGA, 27Al and 31P MAS-NMR and ESR studies. The incorporation of praseodymium in the framework of AlPO-5 was confirmed by XRD, DRS UV-vis and 27Al and 31P MAS-NMR analysis. ESR spectrum showed the presence of adsorbed oxygen. The nature and strength of acid sites were identified by ex-situ pyridine adsorbed IR and TPD-NH3. The BET surface area was found to be in the range of 238-272 m2 g(-1). The catalytic activity of the molecular sieves was tested for the liquid phase aerobic oxidation of ethylbenzene. Acetophenone was found to be the major product with more than 90% ethylbenzene conversion. ICP-OES analysis revealed the presence of praseodymium intact in the framework of AlPO-5 up to five cycles.

We study the effect of the indium or carbon buffer layer on the photoluminescence (PL) property of ZnO ultrathin films deposited on a Si(100) substrate. The surface morphology of the films obtained using scanning tunnelling microscopy shows spherical shaped ZnO nanoparticles of size ∼8 nm in ZnO/C/Si and ∼22 nm in ZnO/Si samples, while the ZnO/In/Si sample shows elliptical shaped ZnO particles. Further, the ZnO/C/Si sample shows densely packed ZnO nanoparticles in comparison with other samples. Strong band edge emission has been observed in the presence of In or C buffer layer, whereas the ZnO/Si sample exhibits poor PL emission. The influence of C and In buffer layers on the PL behaviour of ZnO films is studied in detail using temperature dependent PL measurements in the range of 4 K–300 K. The ZnO/C/Si sample exhibits a multi-fold enhancement in the PL emission intensity with well-resolved free and bound exciton emission lines. Our experimental results imply that the ZnO films deposited on the C buffer ...

Photosensitization of TiO2 with other transition metal oxides can extend its light absorption property in the visible region. Such materials could emerge as excellent catalysts for solar photocatalytic degradation. In the present study mesoporous Fe2O3/TiO2 (10, 30, 50, 70 and 90 wt% Fe2O3) photocatalysts were synthesized by sol-gel process and characterized using different techniques. The XRD patterns exhibited the presence of mesoporous structure and isomorphic substitution of Fe(3+) in TiO2 at low Fe(3+) loading and Ti(4+) in Fe2O3 at high Fe(3+) loading. The XPS results revealed the presence of Ti(4+) and Fe(3+) in Fe2O3/TiO2 materials. The DRS UV-vis spectra showed a shift in the band gap excitation of TiO2 to longer wavelength, thus illustrating incorporation of Fe(3+) in TiO2. In addition, free TiO2 and Fe2O3 particles were also present. Their photocatalytic activity was tested for the degradation of 4-chlorophenol in aqueous medium using sunlight. The activity of the catalysts followed the order: meso-30 wt% Fe2O3/TiO2>meso-10 wt% Fe2O3/TiO2>meso-50 wt% Fe2O3/TiO2>meso-70 Fe2O3/TiO2>meso-90 wt% Fe2O3/TiO2>meso-Fe2O3>meso-TiO2. This order concluded that mesoporous Fe2O3/TiO2 could be an active catalyst for pollutant degradation, as TiO2 with framework Fe(3+) and photosensitization with free Fe2O3 were involved in the activity.

The application of a silicon-on-insulator substrate in a high-power integrated circuit is limited by the self-heating effect, caused by the poor thermal conductivity of the buried SiO2. We introduce tetrahedral amorphous-carbon thin films, formed by the filtered arc deposition method, as an alteration. We investigated the surface morphology, microstructure, and electrical properties of these films. The films deposited under a substrate bias of −200 V displayed outstanding surface topography (low surface roughness with the Rrms value under 0.5 nm) and excellent electrical property (breakdown field of 4.7 MV/cm). The film has a high content of sp3 bonds of carbon (87%) and low content of oxygen (

Enhanced diffusion of gold atoms into silicon substrate has been studied in Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12 ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution transmission electron microscopy measurements showed the presence of gold silicide formation for the above-mentioned systems at fluence greater than equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and 27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively. Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick film, gold atoms from the film transported to a maximum depth of 265 nm in the substrate. The substrate silicon is found to be amorphous at the above fluence values where unusually large mass transport occurred. Enhanced diffusion has been explained on the basis of ion beam induced, flux dependent amorphous nature of the substrate, and transient beam induced temperature effects. This work confirms the absence of confinement effects that arise from spatially confined structures and existence of thermal and chemical reactions during ion irradiation., 15 pages, 3 figures

Gallium nitride films were grown by rf-plasma assisted molecular beam epitaxy. A small indium flux was used as surfactant during the growth. The optical and electrical properties of the films grown with and without In surfactant were characterized by investigating the photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and low-frequency noise power spectra. The sample grown in the presence of In surfactant showed a suppressed yellow luminescence (YL) compared to the one grown without In surfactant. Significant reduction in the full width at half maximum of the GaN (0002) x-ray diffraction peak, indicating a better film quality, was obtained when In surfactant was used during growth. Atomic force microscopy studies show that the root mean squared surface roughness for films grown with and without the In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. This is attributed to the enhanced 2-dimensional growth by In surfactant. A smaller Hooge parameter was obtained from the low-frequency noise measurement for the sample grown with In surfactant indicating that application of In surfactant led to significant reduction in the trap density of the material.

Nanoscale cobalt clusters are synthesized in a silica glass matrix through implantation of high energy cobalt ions. Surface acoustic symmetrical vibrational modes of cobalt nanoclusters are detected using Raman spectroscopy. Mode intensity is found to depend strongly on excitation wavelengths. X-ray diffraction studies reveal face-centered-cubic phase of cobalt nanoclusters in postannealed samples. Postannealing in vacuum has led to significant growth of the cobalt nanoclusters in the matrix.

Ferromagnetic ordering is reported in the post-annealed samples of Co doped n-GaN formed by Co+ implantation. A maximum Curie temperature ~ 250K is recorded for the sample with 8 atomic percent Co. Particle induced x-ray emission-channeling study confirmed the substitutional Co in Ga lattice site. Local atomic arrangement around magnetic impurities is also analyzed using Raman study. A disordered model with carrier mediated coupling of localized magnetic moments is made responsible for the observed ferromagnetic ordering., 11 pages, 3 figures, Journal

Self-assembled Ge nanoparticles have been grown on polymer-coated Si substrates by thermal evaporation under high vacuum utilizing the nonwetting condition given by the surface free-energy relation σGe≫σpolymer. The nanostructures have been characterized by Raman spectroscopy, atomic-force microscopy (AFM), and optical microscopy. Raman spectrum shows a prominent Ge–Ge vibration peak at 302 cm−1. AFM and optical microscopy show the formation of isolated Ge islands (≲100 nm base, ≲25 nm height), nanowires (160 nm base, 25 nm height), and islands in linear chains. The possibility of embedding such nanostructures in waveguide structures are discussed.

Thin Au films (∼45 nm) deposited by thermal evaporation under high vacuum on bromine-passivated Si(110) substrates, upon annealing showed the formation of long gold silicide wire-like islands on top of a thin uniform layer of gold silicide in a self-assembled Stranski–Krastanov growth process. Optical micrographs showed long, straight and narrow islands with aspect ratios as large as 200:1. Scanning electron microscopy images revealed the presence of facets. The islands are aligned along the [110] direction on the Si(110) surface. Rutherford backscattering spectrometry measurements with an ion microbeam identified the islands to possess varying thickness across a single island as one would expect for islands having facets and also showed the uniform silicide layer over the Si substrate to be very thin (∼1.5 nm). The observed alignment of the gold silicide islands on the Si(110) surface has been explained in terms of the lattice mismatch between gold–silicide and silicon and invoking the theory of shape t...