Thermal stability analysis of thin film Ni-NiOx-Cr tunnel junctions

This research reports on the thermal stability of Ni-NiO_x-Cr based Metal-Insulator-Metal (MIM) junction. Effect of annealing (250 to 400 °C) on the electrical and physical transport properties of this MIM stack was understood to determine the thermal budget allowable when using these diodes. MIM tunnel junctions were fabricated by sputtering and the NiO_x was formed through reactive sputtering. The performance of the tunnel junctions after exposure to elevated temperatures was investigated using current-voltage measurements. This was correlated to the structural properties of the interfaces at different temperatures, characterized by Atomic Force Microscopy, X-ray Diffraction and Transmission Electron Microscopy (TEM). MIM tunnel junctions annealed up to 350 °C demonstrated satisfactory current-voltage characteristics and sensitivity. MIM junctions exhibited improved electrical performance as they were heated to 250 °C (sensitivity of 42 V^− 1 and a zero-bias resistance of ~300 Ω) due to improved crystallization of the layers within the stack. At temperatures over 350 °C, TEM and Energy Dispersive Spectra confirmed a breakdown of the MIM structure due to interdiffusion.     

Carrier induced magnetism in dilute Fe doped Ge1−xSbx thin films

Thin films of Fe_0.01Ge_1−xSb_x (x = 0.01, 0.05, 0.10) alloys were prepared by thermal evaporation technique. Characterization of these thin films was done using High Resolution X-Ray Diffraction (HRXRD), Two Probe Resistivity measurement, Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM) respectively. The resistivity results show that activation energy increases with increase in Sb concentration. The low temperature conduction is explained by Variable Range-Hopping mechanism, which fits very well for the whole temperature range. The Arrhenius plot reveals semiconducting behavior. The AFM images of alloys show almost uniform particle size distribution with average particle size varying from 35 to 60 nm with increase in Sb concentration. The MFM images corresponding to the AFM images show the films exhibiting ferromagnetic interactions at room temperature. The average magnetic domain sizes were observed to increase from 43 to 68 nm with increase in Sb concentration from x = 0.01 to x = 0.10.     

Crystallization kinetics in as-synthesis high yield of a-Se100−xTex nanorods

The paper reports the synthesis of high yield of a-Se_100−xTe_x (x = 3, 6, 9 and 12) nanorods using one of the simplest approaches i.e. melt quenching technique. The morphology and microstructure of as-prepared alloys is studied using scanning Electron Microscopy (SEM) and transmission electron microscopy (TEM). From SEM investigation, it is observed that these powder samples of a-Se_xTe_100−x contain high yield of nanorods and their diameter is of the order of several hundred nanometers. The XRD patterns of these samples suggest that these nanorods are amorphous in nature. Crystallization kinetics in these nanorods of amorphous Se_xTe_100−x glasses are studied at different heating rates (5, 10, 15 and 20 K min⁻¹) under non-isothermal condition using differential scanning calorimetry. It is observed that the value of glass transition temperature and crystallization temperature varies with the composition and heating rate. From the heating rate dependence of glass transition temperature and crystallization temperature, the activation energy for structural relaxation (ΔE_t), the activation energy of crystallization (ΔE_c) and the order parameter (n) have been calculated. The composition dependence of the activation energy for thermal relaxation and activation energy for crystallization is discussed in terms of the structure of Se–Te glassy system.     

Characterization of nanostructures of ZnO and ZnMnO films deposited by successive ionic layer adsorption and reaction method

ZnO and ZnMnO thin films were obtained by the successive ionic layer adsorption and reaction (SILAR) method. All thin films were deposited on glass microscope slide. A precursor solution of 0.1 M of ZnCl₂ complexed with ammonium hydroxide and water close to boiling point (92 °C) as a second solution was used for the ZnO films. An uncomplexed bath comprised of 0.1 M ZnCl₂, 0.1 M MnCl_2, and a second solution of 0.1 ml of NH₄OH with water close to boiling point was used for the ZnMnO films. The film samples were deposited by the SILAR method and annealed at 200 °C for 15 min. These samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (EDS), and Atomic Force Microscope. Atomic absorption was used to determine quantitatively the amount of Mn incorporated into the films. According to the XRD patterns these films were polycrystalline with wurtzite hexagonal structure. The morphology of the ZnO films constituted by rice-like and flower-like structures changed significantly to nanosheet structures with the Mn incorporation. The Mn inclusion in a ZnO structure was less than 4% according to the results from EDS, XRD, and atomic absorption.     

Study of the chemical and morphological evolution of InSb(001) surface under low energy ion bombardment

InSb(001) surfaces were subjected to 4 keV Ar⁺ bombardment at oblique angles of incidence with ion fluences in the range of 9.0 × 10¹³-6.2 × 10¹⁷ ions/cm². The evolution of bombardment induced surface structures and their chemical composition were studied with Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) in UHV, and “ex situ” with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). Various morphological features, such as small dots, wires and for very high ion fluence ripple-like structures were observed. It was found that both the initial surface crystallographic structure and the ion beam direction influence the developing anisotropic nanostructures on the irradiated surface. It was also found that the time evolution of the nanostructured surface in terms of surface roughness σ, follows a power law σ ∼ t^β. The surface nanostructures (dots and wires), at every stage of their development, are found to have different work functions in comparison to the surrounding InSb substrate. The results indicate that the nanostructures developed on the irradiated InSb surfaces consist of indium.     

Microwave-assisted synthesis and investigation of SnO2 nanoparticles

Microwave technique was adopted for preparation of tin dioxide nanoparticles with particles size ranging from 10 to 11 nm within 10 min. The formation of monocrystalline SnO₂ nanoparticles was confirmed by the XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy) as well as with SAED (Selected Area Electron Diffraction) analysis. The structure of the SnO₂ crystal was found to be Cassiterite type tetragonal structure. The FT-IR results further supported the formation of tin dioxide from tin hydroxyl group without any post annealing. The samples were further characterized by thermo gravimetric analysis (TGA), electrical resistance measurements and photoluminescence spectrum.     

Significance of Al on the morphological and optical properties of Ti1−xAlxN thin films

TiN and Ti_1−xAl_xN thin films with different aluminum concentrations (x = 0.35, 0.40, 0.55, 0.64 and 0.81) were synthesized by reactive magnetron co-sputtering technique. The structure, surface morphology and optical properties were examined using Grazing Incidence X-ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry, respectively. The structure of the films were found to be of rocksalt type (NaCl) for x = 0.0–0.64 and X-ray amorphous for x = 0.81. AFM topographies show continuous mound like structure for the films of x between 0.0 and 0.64, whereas the film with x = 0.81 showed smooth surface with fine grains. Micro-Raman spectroscopic studies indicate structural phase separation of AlN from TiAlN matrix for x > 0.40. Ti_1−xAl_xN has the tendency for decomposition with the increase of Al concentration whereas c-TiN and hcp-AlN are stable mostly. The optical studies carried out by spectroscopic ellipsometry measurements showed a change from metallic to insulating behavior with the increase in x. These films are found to be an insulator beyond x = 0.81.     

Fabrication and characterization of Cu2ZnSnS4 thin films deposited by spray pyrolysis technique

We have investigated synthesis conditions and some properties of sprayed Cu₂ZnSnS₄ (CZTS) thin films in order to determine the best preparation conditions for the realization of CZTS based photovoltaic solar cells. The thin films are made by means of spraying of aqueous solutions containing copper chloride, zinc chloride, tin chloride and thiourea on heated glass substrates at various temperatures. In order to optimize the synthesis conditions of the CZTS films, two series of experiments are performed. In the first series the sprayed duration was fixed at 30 min and in the second it is fixed at 60 min. In each series, the substrate temperature was changed from 553°K to 633°K. The X-ray diffraction shows, on one hand, that the best crystallinity was obtained for 613°K as substrate temperature and 60 min as sprayed duration. On the other hand, these CZTS films exhibit the kesterite structure with preferential orientation along the [112] direction. Atomical Force Microscopy was used to determine the grain sizes and the roughness of these CZTS thin film. After the annealing treatment, we estimated the optical band-gap energy of the CZTS thin film exhibiting the best crystallinity as 1.5 eV which is quite close to the optimum value for a solar cell.     

Raman study of Ni and Ni silicide contacts on 4H- and 6H-SiC

Ni₂Si, NiSi and NiSi₂ contacts were prepared on n-type 4H- and 6H-SiC(0001) by deposition of Ni and Si multilayers in the respective stoichiometry after high-temperature annealing, as well as pure Ni contacts. After annealing, the individual contacts were analyzed by Raman spectroscopy and electrical property measurements. Contact structures were then etched-off and subsequently observed by means of AFM (Atomic Force Microscopy). Ni reacted with SiC, forming Ni₂Si and carbon. At Ni_xSi_y/SiC contact structures the respective silicides were already formed at low annealing temperatures, when only Schottky behavior of the structures was observed. The intended silicides, once formed, did not change any further with increasing annealing temperature. All contact structures provided good ohmic behavior after being annealed at 960 °C. By means of combined AFM and Raman analysis of the etched-off contacts we found that the silicide contact structures very probably did not react with SiC which is in accordance with the thermodynamic assumptions. After annealing the silicide contact structures at such temperature, when Schottky behavior changed to ohmic, a certain form of interaction between the SiC substrate and the silicide contact structures must have occurred.     

Study of manganese oxide thin films grown by pulsed laser deposition

In this paper, we report on the growth of manganese oxides thin films by Pulsed Laser Deposition using an MnO target at various oxygen pressures and substrate temperatures ranging from 550 to 800 °C. Grazing Incidence X-Ray Diffraction measurements on the grown films revealed that, at low deposition temperature, the dominant phase is Mn₂O₃, but as the deposition temperature was raised above 700 °C, a phase transformation occurred leading to the formation of Mn₃O₄. In a qualitative comparison, in the temperature range of 500-850 °C, and at a pressure below 13 Pa, the phase diagram of bulk manganese oxides and our grown films show a fair correlation. The films grown near the transition temperature (T = 700 °C) were found to be very thin compared to those grown at lower or higher temperatures, but the surface roughness was found to increase with temperature, as determined by Atomic Force Microscopy.     

Influence of nitrogen flow rate on the physical properties of ZrOxN1−x coatings produced by magnetron sputtering

In this work we produce ZrO_xN_1−x thin coatings and ZrYO_xN_1−x by DC reactive magnetron sputtering. In order to study the effect of nitrogen flow rates on physical and mechanical properties, the N₂/O₂ relation was changed between 0.025 and 0.2. The addition of nitrogen to the ZrO₂ and ZrO₂Y₂O₃ systems was performed to study the influence on the stabilization of the high temperature tetragonal or cubic phases of ZrO₂. X-ray diffraction (XRD) measurements were used to characterize the coating structures and to study the influence of nitrogen addition on the high temperature stabilized phases. The residual stresses were also determined by measuring the radius of curvature of the thin-coated substrates. The surface microtopography was analyzed by Atomic Force Microscopy (AFM) and the roughness was evaluated. Energy Dispersive X-ray (EDX) Spectroscopy was used to assess the thin film composition. Scanning Electron Microscopy (SEM) was used to measure the film thickness, to observe microstructure of the film cross-section and to analyze the surface morphology.     

Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of Ni_xCo₁–_xFe₂O₄, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (T_c) for all samples was noted from resistivity data. The activation energy below and above T_c was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline Ni_xCo₁–_xFe₂O₄ at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline Ni_xCo₁–_xFe₂O₄ samples.     

Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation

Ti_1 − xSi_xC_yN_1 − y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH₄ and N₂ gas gave films with 0 ≤ x ≤ 0.13 and 0 ≤ y ≤ 0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32-40 GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35-44 GPa when isothermally annealed up to 900 °C. The temperature threshold for over-ageing was decreased to 700 °C with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.     

In situ observation of the change in domain structure due to phase transformation in a perovskite La2MnGaO6

The microstructure of a perovskite, La₂MnGaO₆, was studied by Transmission Electron Microscopy (TEM). An idiomorphic grain exhibited a domain structure at ambient temperature, and each domain possessed a common b-axis and axial relation, [1 0 0]//[0 0 1]. When the grain was heated by a convergent electron beam, the domains vanished after the orthorhombic to rhombohedral phase transformation taking place at 423 K. The domains reappeared when cooled, although domain boundaries moved and the domains rotated by 90° with respect to the b-axis.     

Synthesis of SrSnO3 thin films by pulsed laser deposition: Influence of substrate and deposition temperature

SrSnO₃ thin films were prepared by pulsed laser deposition on amorphous silica and single crystal substrates of R-sapphire, (100)LaAlO₃ and (100)SrTiO₃. High quality epitaxial (100) oriented films were obtained on LaAlO₃ and SrTiO₃ while a texture was revealed for films on sapphire deposited at the same deposition temperature of 700 °C. Amorphous films were obtained on silica but a post annealing at 800 °C induced crystallization with a random orientation. The screening of deposition temperature showed epitaxial features on SrTiO₃ from 650 °C while no crystallization was observed at 600 °C. The influence of substrate and deposition temperature was confirmed by Scanning Electron Microscopy and Atomic Force Microscopy observations.     

Mechanical, microstructural and oxidation properties of reactively sputtered thin CrN coatings on steel

Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N₂ flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr₂N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N₂. Also intrinsic coating hardness is influenced by both N₂ flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.     

A one-step hydrothermal way for the synthesis of vanadium oxide nanotubes containing the phenylpropylamine as template obtained via non-alkoxide route

Vanadium oxide nanotubes (VO_x-NTs) with high crystallinity were synthesized by using the crystalline V₂O₅ as precursor for the first time with 3-phenylpropylamine as structure-directing template via one-step hydrothermal way. Structure and morphology of the nanotubes were investigated by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray powder diffraction, Thermal analysis and Infrared. The inner and the outer of the obtained nanotubes vary respectively between 15 to 25 nm and 70 to 100 nm with a length up to 4 μm.     

The effect of Au and Pt nanoclusters on the structural and hydrogen sensing properties of SnO2 thin films

Au and Pt nanoparticle modified SnO₂ thin films were prepared by the sol-gel method on glass substrates targeting sensing applications. Structural and morphological properties of these films were studied using X-ray Diffraction and Scanning Electron Microscopy. It was proved that the films crystallized in tetragonal rutile SnO₂ crystalline structure. Scanning Electron Microscopy observations showed that the metallic clusters' dimensions and geometry depend on the kind of the metal (Au or Pt) while SnO₂ films surface remains almost the same: nanostructured granular very smooth. Optical properties of the films were studied using UV-visible spectroscopy. The modified SnO₂ films were tested as hydrogen sensors. The response of SnO₂, SnO₂-Au and SnO₂-Pt thin films against hydrogen was investigated at different operating temperatures and for different gas concentrations. The addition of metal nanoparticles was found to decrease the detection limit and the operating temperature (from 180 °C to 85 °C), while increasing the sensing response signal.     

Titanium and zirconium hard coatings on glass substrates prepared by the sol-gel method

In this work innovative antiscratch sol-gel coating films deposited on a soda-lime glass substrate are examined. Sol-gel coatings of different composition (TiO₂, TiO₂/B₂O₃, ZrO₂ and ZrO₂/B₂O₃) were prepared starting from Titanium, Zirconium and Boron alkoxides and from boron oxide. Coatings were obtained at room temperature and at atmospheric pressure by dip-coating using common soda lime silicate glass slides as substrates. Densification was carried out at 550 °C for 2 h in air. The morphology of the coatings has been studied by Atomic Force Microscopy, Scanning Electron Microscopy, and with a profilometer. Roughness grows with thickness and with boron addition. The mechanical properties of the films were evaluated by micro scratch at fixed and variable load. The scratch hardness numbers of ZrO₂ and ZrO₂/B₂O₃ coatings reach 6 GPa (glass value = 1.9 GPa), whereas the best value for the critical load is 16.7 N (glass value = 9 N).     

Formation of nanoparticles and nanorods in a N2-C2H4-H2 atmospheric pressure dielectric barrier Townsend discharge

In the present publication, the effect of the addition of H₂ in an atmospheric pressure Townsend Dielectric Barrier Discharge in an atmosphere of N₂-C₂H₄ is examined with an emphasis put on the evaluation of the surface chemistry and growth mechanisms. Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and Fourier Transform Infrared Spectroscopy were used to characterize the coatings. For all H₂ concentrations, films obtained present high N/C ratio (∼ 0.8) with high NH_x and nitrile content. However, when H₂ is added in the discharge, nanoparticles/nanorods are formed imbedded in a smooth film. The average size of the nanorods is 100-200 nm in diameter with length from 1 to 10 μm. A growth mechanism is proposed to explain the formation of the nanorods on the surface of the coating in the presence of H₂.