Orientational disorder and other aspects of C70 and C60-C70 films deposited on single-crystal substrates

C-70 films deposited on highly oriented pyrolytic graphite (HOPG), Ag(110), Ag(111) and Pt(110) substrates have been investigated by scanning tunnelling microscopy. Interesting observations on novel molecular arrangements, as well as orientational disorder, are presented. Solid solutions of C-60 and C-70 show interesting packing of these molecules when deposited on HOPG.

Microwave ECR Plasma Assisted MOCVD of Y(2)O(3) Thin Films Using Y(tod)(3) Precursor and Their Characterization

Yttrium oxide (Y(2)O(3)) thin films were deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process using indigenously developed metal organic precursors Yttrium 2,7,7-trimethyl-3,5-octanedionates, commonly known as Y(tod)(3) which were synthesized by an ultrasound method. A series of thin films were deposited by varying the oxygen flow rate from 1-9 sccm, keeping all other parameters constant. The deposited coatings were characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and roughness for the films were measured by stylus profilometry. Optical properties of the coatings were studied by the spectroscopic ellipsometry. Hardness and elastic modulus of the films were measured by nanoindentation technique. Being that microwave ECR CVD process is operating-pressure-sensitive, optimum oxygen activity is very essential for a fixed flow rate of precursor, in order to get a single phase cubic yttrium oxide in the films. To the best of our knowledge, this is the first effort that describes the use of Y(tod)(3) precursor for deposition of Y(2)O(3) films using plasma assisted CVD process.

Bioactivity and mechanical properties of nickel-incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a-C : H) and nickel-incorporated hydrogenated carbon (Ni/a-C : H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni3C) only. The presence of Ni3C has increased the sp(2) carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a-C : H films shows very low friction coefficient with higher scratch-resistance behavior than that of pure a-C : H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone-like apatite layer on Ni/a-C : H films. Thus, the results have indicated the suitability of the films for bone-related implant coating applications. Copyright (C) 2011 John Wiley & Sons, Ltd.

Structural and mechanical properties of room temperature sputter deposited CrN coatings

Chromium nitride (CrN) thin films were deposited at room temperature on silicon and glass substrates using DC reactive magnetron sputtering in Ar + N-2 plasma. Structure and mechanical properties of these films were examined by using XRD, FESEM and nanoindentation techniques. XRD studies revealed that films are of mixed phase at lower nitrogen partial pressure (P-N2) and single phase at higher (P-N2). Microscopy results show that the films were composed of non-equiaxed columns with nanocrystallite morphology. The hardness and elastic modulus of the films increase with increasing nitrogen partial pressure (P-N2). A maximum hardness of similar to 29 GPa and elastic modulus of 341 GPa were obtained, which make these films useful for several potential applications. (C) 2012 Elsevier Ltd. All rights reserved.

Inorganic Analogues of Graphene

The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two-dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene-like MoS2 and WS2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO2.

Observation of asymmetry in U�I characteristics of contacts of the form metal 1�superconductor�metal 2

During experiments carried out to find out a suitable contact metal for electronic components based on high-T(c) superconductor films (Y-Ba-Cu-O), it is observed that there is an asymmetry in the U-I characteristics if the two contacts are made of different metals. The asymmetry is more pronounced if one of the contact metals is aluminium. The asymmetry is lowest if one of the contact metals is silver and the other gold.

Hydrothermal synthesis of Gd2O3:Eu3+ nanophosphors: Effect of surfactant on structural and luminescence properties

Various morphologies of Eu3+ activated gadolinium oxide have been prepared by hydrothermal method using hexadecylamine (HDA) as surfactant at different experimental conditions. The powder X-ray diffraction studies reveal as-formed product is hexagonal Gd(OH)(3):Eu3+ phase and subsequent heat treatment at 350 and 600 degrees C transforms to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+ phases respectively. SEM pictures of without surfactant show irregular shaped rods along with flakes. However, in the presence of HDA surfactant, the particles are converted into rods of various sizes. The temperature dependent morphological evolution of Gd2O3:Eu3+ without and with HDA surfactant is studied. TEM micrographs of Gd(OH)(3):Eu3+ sample with HDA confirms smooth nanorods with various diameters in the range 20-100 nm. FTIR studies reveal that HDA surfactant plays an important role in conversion of cubic to hexagonal phases. Among these three phases, cubic phase Gd2O3:Eu3+ (lambda(ex) = 254 nm) show red emission at 612 nm corresponding to D-5(0)-> F-7(2) and is more efficient host than the monoclinic counterpart. The band gap for hexagonal Gd(OH)(3):Eu3+ is more when compared to monoclinic GdOOH:Eu3+ and cubic Gd2O3:Eu3+. (C) 2013 Elsevier B. V. All rights reserved.

Fermi-Edge Transmission Resonance in Graphene Driven by a Single Coulomb Impurity

The interaction between the Fermi sea of conduction electrons and a nonadiabatic attractive impurity potential can lead to a power-law divergence in the tunneling probability of charge through the impurity. The resulting effect, known as the Fermi edge singularity (FES), constitutes one of the most fundamental many-body phenomena in quantum solid state physics. Here we report the first observation of FES for Dirac fermions in graphene driven by isolated Coulomb impurities in the conduction channel. In high-mobility graphene devices on hexagonal boron nitride substrates, the FES manifests in abrupt changes in conductance with a large magnitude approximate to e(2)/h at resonance, indicating total many-body screening of a local Coulomb impurity with fluctuating charge occupancy. Furthermore, we exploit the extreme sensitivity of graphene to individual Coulomb impurities and demonstrate a new defect-spectroscopy tool to investigate strongly correlated phases in graphene in the quantum Hall regime.

Investigation on two magnon scattering processes in pulsed laser deposited epitaxial nickel zinc ferrite thin film

Ferromagnetic resonance (FMR) measurements are employed to evaluate the presence of the two magnon scattering contribution in the magnetic relaxation processes of the epitaxial nickel zinc ferrite thin films deposited using pulsed laser deposition (PLD) on the (0 0 1) MgAl2O4 substrate. Furthermore, the reciprocal space mapping reveals the presence of microstructural defects which acts as an origin for the two magnon scattering process in this thin film. The relevance of this scattering process is further discussed for understanding the higher FMR linewidth in the in-plane configuration compared to the out-of-plane configuration. FMR measurements also reveal the presence of competing uniaxial and cubic anisotropy in the studied films.

Tunability of 1/f Noise at Multiple Dirac Cones in hBN Encapsulated Graphene Devices

The emergence of multiple Dirac cones in hexagonal boron nitride (hBN)-graphene heterostructures is particularly attractive because it offers potentially better landscape for higher and versatile transport properties than the primary Dirac cone. However, the transport coefficients of the cloned Dirac cones is yet not fully characterized and many open questions, including the evolution of charge dynamics and impurity scattering responsible for them, have remained unexplored. Noise measurements, having the potential to address these questions, have not been performed to date in dual-gated hBN graphene hBN devices. Here, we present the low frequency 1/f noise measurements at multiple Dirac cones in hBN encapsulated single and bilayer graphene in dual-gated geometry. Our results reveal that the low-frequency noise in graphene can be tuned by more than two-orders of magnitude by changing carrier concentration as well as by modifying the band structure in bilayer graphene. We find that the noise is surprisingly suppressed at the cloned Dirac cone compared to the primary Dirac cone in single layer graphene device, while it is strongly enhanced for the bilayer graphene with band gap opening. The results are explained with the calculation of dielectric function using tight-binding model. Our results also indicate that the 1/f noise indeed follows the Hooge's empirical formula in hBN-protected devices in dual-gated geometry. We also present for the first time the noise data in bipolar regime of a graphene device.

Emergent photophenomena in three dimensional van der Waals heterostructures

We report on the fabrication and observation of emergent opto-electronic phenomena in three dimensional, micron-sized van der Waals heterostructures self-assembled from atomic layers of graphene and hexagonal boron nitride in varying ratios.

Probing disorder in cubic pyrochlore Bi-1 Zn-5(1) Nb-0(1) O-5(7) (BZN) thin films

The dielectric response of pulsed laser ablated Bi-1 Zn-5(1) Nb-0(1) O-5(7) (BZN) thin films are investigated within the temperature range of 300-660 K and frequency range of 100 Hz-100 kHz Thin film exhibited a strong dielectric relaxation behavior A sharp rise in dielectric constant of BZN thin film at high temperatures is related to disorder in canon and anion lattices Observed dielectric relaxation implies a redistribution of charges within the unit cell This phenomenon suggests that the large change in dielectric constant is due to a dynamical rise of dipolar fluctuations in the unit cell XPS spectra of BZN (A(2)B(2)O(6)O') cubic pyrochlore confirm that the relaxation corresponds to the ionic hopping among the A and O' positions of several local potential minima Barrier height for hopping is distributed between 0 and 0 94 eV The O is spectrum confirms presence of two types of oxygen in BZN thin film The disorder in charge neutralized thin film is correlated with XPS spectra (C) 2010 Elsevier Ltd All rights reserved

Nitride synthesis using ammonia and hydrazine - a thermodynamic panorama

Because of the wide variety of projected applications of ultrapure nitrides in advanced technologies, there is interest in developing new cost-effective methods of synthesis. Explored in this study is the use of ammonia and hydrazine for the synthesis of nitrides from oxides, sulfides and chlorides. Even when the standard Gibbs energy change for the nitridation reactions involved are moderately positive, the reaction can be made to proceed by lowering the partial pressure of the product gas below its equilibrium value. Use of a metastable form of precursor in the nanometric size range is an alternative method to facilitate nitridation. Ellingham-Richardson-Jeffes diagrams are used for a panoramic presentation of the driving force for each set of reactions as a function of temperature. Oxides are the least promising precursors for nitride synthesis; sulfides offer a larger synthetic window for many useful nitrides such as BN, AlN, InN, VN, TiN, ThN and Si3N4. The standard Gibbs free energy changes for reactions involving chlorides with either ammonia or hydrazine are much more negative. Hydrazine is a more powerful nitriding agent than ammonia. The metastability of hydrazine requires that it be introduced into a reactor through a water-cooled lance. The use of volatile halides with ammonia or hydrazine offers the potential for synthesis of pure and doped nanocrystalline nitrides. Nitride thin films can also be prepared by suitable adaptations of the chloride route. (C) 2002 Kluwer Academic Publishers.

Reactive pulsed laser deposition and characterization of niobium nitride thin films

We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be similar to 30 GPa at the deposition pressure of 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

Reactive Pulsed Laser Deposition of titanium nitride thin film: Optimization of process parameters using Secondary Ion Mass Spectrometry

Reactive Pulsed Laser Deposition is a single step process wherein the ablated elemental metal reacts with a low pressure ambient gas to form a compound. We report here a Secondary Ion Mass Spectrometry based analytical methodology to conduct minimum number of experiments to arrive at optimal process parameters to obtain high quality TiN thin film. Quality of these films was confirmed by electron microscopic analysis. This methodology can be extended for optimization of other process parameters and materials. (C) 2009 Elsevier B.V. All rights reserved.