Anodization of sputtered metallic films: The microstructural connection

A simple microstructural rationale for successful anodization of metallic films into ordered oxide nanostructures has been identified. It applies to three of the most commonly studied systems, Zr, Ti and Al films and can be extended to other such oxides. A dense Zone T or II microstructure, in sputtered films, is the most critical ingredient. While T-substrate > 0.3T(melting) Ching is the simplest route, pressure and plasma heating can also be exploited. Such microstructures are also associated with a unique growth stress signature. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effects of Patterned Substrate on Thin Films Simulated by Family Model

Patterned substrate growth has been a subject of much interest. In this work, characteristics of some statistical properties of a film grown on triangular and vicinal substrates using the Family model are studied. Substrate size and tilt angle are varied. It is found that the interface width and the correlation function increase as the roughness of the pattern is increased. The new scaling exponents are calculated and anomalous scaling is obtained. The transient persistence probability does not show a power law relation when the initial surface is sufficiently rough. The initial rough surface also causes multifractal behavior in the model.

Metal-insulator transition characteristics of vanadium dioxide thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture

We report the synthesis of high quality vanadium dioxide (VO2) thin films by a novel spray pyrolysis technique, namely ultrasonic nebulized spray pyrolysis of aqueous combustion mixture (UNSPACM). This simple and cost effective two step process involves synthesis of a V2O5 film on an LaAlO3 substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (p21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal-insulator transition (MIT) was observed at 61 degrees C, where the resistivity changes by four orders of magnitude. Activation energies for the low conduction phase and the high conduction phase were obtained from temperature variable resistance measurements. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 mu m. This indicates the suitability of the films for optical switching applications at infrared frequencies.

Studies on RF Magnetron Sputtered HfO2 Thin Films for Microelectronic Applications

We investigated the effect of oxygen flow rate during the reactive magnetron sputtering on the compositional, structural, optical and electrical properties of HfO2 films. We also studied the influence of annealing temperature on the structural and electrical properties of optimized HfO2 films of 25 to 30 nm thick. X-ray photoelectron study reveals that the films deposited at 15 SCCM of oxygen flow rate are stoichiometric and have an optical band gap of 5.86 eV. X-ray diffraction indicates that films without oxygen flow are amorphous, and beyond an oxygen flow rate of 5 SCCM exhibit polycrystalline monoclinic structure. At an annealing temperature of 600 degrees C, tetragonal phase was observed besides the monoclinic phase. The dielectric constant of 11 and low leakage currents of 1 x 10(-7) A/cm(2) were achieved for the stoichiometric films. As-deposited films show significant frequency dispersion due to the presence of defect states at the HfO2/Si interface, and it reduces after annealing.

Effect of laser irradiation on the optical properties of As40Sb15Se45 chalcogenide thin films

The exposure with band gap light of thermally evaporated As40Sb15Se45 amorphous film of 800 nm thickness, were found to be accompanied by optical changes. The as-prepared and illuminated thin films were studied by X-ray diffraction, Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy and Raman spectroscopy. The optical band gap was reduced due to photo induced effects along with the increase in disorder. These optical properties changes are due to the change of homopolar bond densities. The core level peak shifting in XPS spectra and Raman shift supports the optical changes happening in the film due to light exposure.

Single-step synthesis of carbon nanotubes/iron/iron oxide composite films through inert-ambient CVD using ferric acetylacetonate as a precursor

We have developed a unique single-step chemical vapor deposition (CVD) route for the synthesis of composite thin films containing carbon nanotubes (CNTs). CVD was carried out in an inert ambient using only iron(III) acetylacetonate as the precursor. Depositions were conducted at 700 degrees C on stainless steel substrates in argon ambient in the absence of any reactive gases (such as oxygen, hydrogen). By changing the deposition parameters, especially the pressure in the CVD reactor, the form of carbon deposited could be changed from amorphous to carbon nanotubes, the latter resulting in Fe-Fe3O4-CNT films. X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy together confirm the formation of the three-component composite and illustrate the nanoscale mixing of the components. Elemental iron formed in this process was protected from oxidation by the co-deposited carbon surrounding it. Irrespective of the substrate used, a composite coating with CNTs was formed under optimum conditions, as verified by analyses of the film formed on polycrystalline alumina and silicon substrates.

Hydrogen-induced mechanical properties of amorphous silicon thin films

Mechanical properties of thin films such as residual stress and hardness are of paramount importance from the device fabrication point of view. Intrinsic stress in sputtered films can be tensile or compressive as decided by the number density and the energy of the plasma species striking the growing film. In the presence of hydrogen we analyzed the applicability of idealized stress reversal curve for amorphous silicon thin films deposited by DC, pulsed DC (PDC) and RF sputtering. We are successfully able to correlate the microstructure with the stress reversal and hardness. We observed a stress reversal from compressive to tensile with hydrogen incorporation. It was found that unlike in idealized stress reversal curve case, though the energy of plasma species is less in DC plasma, DC deposited films exhibit more compressive stress, followed by PDC and RF deposited films. A tendency towards tensile stress from compressive stress was observed at similar to 13, 18 and 23 at%H for DC, PDC and RF deposited films respectively, which is in exact agreement with the vacancy to void transition in the films. Regardless of the sputtering power mode, the hardness of a-Si:H films is found to be maximum at C-H similar to 10 at%H. Enhancement in hardness with C-H (up to C-H similar to 10 at%H) is attributed to increase of Si-H bonds. Beyond C-H similar to 10 at%H, hardness starts falling. (C) 2015 Elsevier Ltd. All rights reserved.

Growth of TiO2 Films by RF Magnetron Sputtering for MOS Gate Dielectrics: Influence of Substrate Temperature

Titanium dioxide thin films were deposited by RF reactive magnetron sputtering technique on p-type silicon(100) substrates held at temperatures in the range 303-673 K. The influence of substrate temperature on the core level binding energies, chemical bonding configuration, crystallographic structure and dielectric properties was investigated. X-ray photoelectron spectroscopy studies and Fourier transform infrared transmittance data confirmed the formation of stoichiometric films with anatase phase at a substrate temperature of 673 K. The films formed at 303 K were nanocrystalline with amorphous matrix while those deposited at 673 K were transformed in to crystalline phase and growth of grains in pyramidal like structure as confirmed by X-ray diffraction and atomic force microscopy respectively. Metal-oxide-semiconductor capacitors were fabricated with the configuration of Al/TiO2/Si structures. The current voltage, capacitance voltage and conductance voltage characteristics were studied to understand the electrical conduction and dielectric properties of the MOS devices. The leakage current density (at gate voltage of 2 V) decreased from 2.2 x 10(-6) to 1.7 x 10(-7) A/cm(2), the interface trap density decreased from 1.2 x 10(13) to 2.1 x 10(12) cm(-2) eV(-1) and the dielectric constant increased from 14 to 36 with increase of substrate temperature from 303 to 673 K.

Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto-enol equilibrium of a chiral salicylideneaniline

A new chiral amphiphilic salicylideneaniline bearing a terminal pyridine was synthesized. It formed reverse vesicles in toluene. The addition of Ag+, however, reversibly transforms these reverse vesicles into left-handed nanohelices accompanied by spontaneous gel formation at room temperature.

Influence of deposition time on the properties of electrodeposited Cu(In,Al)Se-2 thin films

Cu(In,Al)Se-2 films are grown using single step electrodeposition technique. The film properties are studied by varying the deposition time from 500 to 2000 s. Peaks corresponding to elemental Se and Cu2Se phase started appearing from 1200 s of deposition. The composition is changed significantly after 1500 S. Se concentration increased from 57 to 68% with the increase in the deposition time. The Cu2Se phase is dominant in the films deposited for a duration of 2000 s and the grain size increased from 1.12 to 2.15 mu m in this film. Raman analysis confirmed the presence of Se and Cu2Se phase in C1200. In C1500 and C2000 the spectra showed prominent mode corresponding to Cu2Se. The thickness of the film increased from 0.85 to 2.3 mu m with the increase in the deposition time. All the films showed p-type conductivity and resistivity reduced with increased thickness. (C) 2015 Elsevier Ltd. All rights reserved.

Structural diversities in Cu(I) and Ag(I) sulfonate coordination polymers and their anion exchange properties

Two new Cu(I) compounds, namely Cu-2(bds)(bpy)(2)]center dot 2H(2)O (1) and Cu-4(bds)(2)(azpy)(4)]center dot 6H(2)O (3) (where bds = benzene-1,3-disulfonate, bpy = 4,4'-bipyridine and azpy = 4,4'-azopyridine), and four Ag(I) compounds, namely Ag-2(bds)(bpy)(2)]center dot 2H(2)O (2), Ag-2(bds)(azpy)(2)]center dot 4H(2)O (4), Ag(bds)(1/2)(bpe)]center dot 3H(2)O (5), and Ag-4(bds)(2)(tmdp)(4)]center dot 9H(2)O (6) (where bpe = 1,2-di(4-pyridyl) ethylene and tmdp = 4,4'trimethylenedipyridine), have been synthesized, and their structures were determined and characterized by elemental analysis, IR, UV-vis and thermal studies. The structure of the compounds changed from 1D (1 and 2) to 2D (3-5) and interpenetrated 3D (6). In the case of 5, a solid-state 2 + 2] photochemical cycloaddition reaction has been performed. Compound 2 exhibits a reversible anion exchange for perchlorate and permanganate, whereas the other compounds (1, 3-6) exhibit an irreversible anion exchange behaviour for perchlorate. Catalytic studies on 2 indicate Lewis acidity.

Investigation of Annealing Induced Yttria Segregation in Sputtered Yttria-Stabilized Zirconia Thin Films

8mol% yttria-stabilized zirconia (8YSZ) is an extensively studied solid electrolyte. But there is no consistency in the reported ionic conductivity values of 8YSZ thin films. Interfacial segregation in YSZ thin films can affect its ionic conductivity by locally altering the surface chemistry. This article presents the effects of annealing temperature and film thickness on free surface yttria segregation behavior in 8YSZ thin film by Angle Resolved XPS and its influence on the ionic conductivity of sputtered 8YSZ thin films. Surface yttria concentration of about 32, 20, and 9mol% have been found in 40nm 8YSZ films annealed at 1273, 1173, and 1073K, respectively. Yttria segregation is found to increase with increase in annealing temperature and film thickness. Ionic conductivities of 0.23, 0.16, and 0.08Scm(-1) are observed at 923K for 40nm 8YSZ films annealed at 1073, 1173, and 1273K, respectively. The decrease in conductivity with increase in annealing temperature is attributed to the increased yttria segregation with annealing. Neither segregation nor film thickness is found to affect the activation energy of oxygen ion conduction. Target purity is found to play a key role in determining free surface yttria segregation in 8YSZ thin films.

Ag-doped hydroxyapatite as efficient adsorbent for removal of Congo red dye from aqueous solution: Synthesis, kinetic and equilibrium adsorption isotherm analysis

In the present study a versatile and efficient adsorbent with high adsorption capacity for adsorption of Congo red dye in aqueous solution at ambient temperature without adjusting any pH is presented over the Ag modified calcium hydroxyapatite (CaHAp). CaHAp and Ag-doped CaHAp materials were synthesized using facile aqueous precipitation method. The physico-chemical properties of the materials were determined by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM), UV-Visible spectroscopy, N-2 physisorption and acidity was determined by n-butylamine titration and pyridine adsorption methods. XRD analysis confirmed all adsorbents exhibit hexagonal CaHAp structure with P6(3)/m space group. TEM analysis confirms the rod like morphology of the adsorbents and the average length of the rods were in the range of 40-45 nm. Pyridine adsorption results indicate increase in number of Lewis acid sites with Ag doping in CaHAp. Adsorption capacity of CaHAp was found increased with Ag content in the adsorbents. Ag (10): CaHAp adsorbent showed superior adsorption performance among all the adsorbents for various concentrations of Congo red (CR) dye in aqueous solutions. The amount of CR dye adsorbed on Ag (10): CaHAp was found to be 49.89-267.81 mg g(-1) for 50-300 ppm in aqueous solution. A good correlation between adsorption capacity and acidity of the adsorbents was observed. The adsorption kinetic data of adsorbents fitted well with pseudo second-order kinetic model with correlation coefficients ranged from 0.998 to 0.999. The equilibrium adsorption data was found to best fit to the Langmuir adsorption isotherm model. (C) 2015 Elsevier Inc. All rights reserved.

Role of thermal annealing on SiGe thin films fabricated by PECVD

Amorphous Silicon Germanium (a-SiGe) thin films of 500 nm thickness are deposited on silicon substrates using Plasma Enhanced Chemical Vapour Deposition (PECVD). To obtain polycrystalline nature of films, thermal annealing is done at various temperature (450-600 degrees C) and time (1-10 h). The surface morphology of the pre- and post-annealed films is investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystallographic structure of the film is obtained by X-ray diffraction method. Raman spectroscopy is carried out to quantify the Ge concentration and the degree of strain relaxation in the film. Nano-indentation is performed to obtain the mechanical properties of the film. It is found that annealing reduces the surface roughness of the film and increases the Ge concentration in the film. The grain size of the film increases with increase in annealing temperature. The grain size is found to decrease with increase in annealing time up to 5 h and then increased. The results show that 550 degrees C for 5 h is the critical annealing condition for variation of structural and mechanical properties of the film. Recrystallization starts at this condition and results in finer grains. An increase in hardness value of 7-8 GPa has been observed. Grain growth occurs above this critical annealing condition and degrades the mechanical properties of the film. The strain in the film is only relaxed to about 55% even for 10 h of annealing at 600 degrees C. Transmission Electron Microscopy (TEM) observations show that the strain relaxation occurs by forming misfit dislocations and these dislocations are confined to the SiGe/Si interface. (C) 2015 Elsevier Ltd. All rights reserved.

Spotting 2D atomic layers on aluminum nitride thin films

Substrates for 2D materials are important for tailoring their fundamental properties and realizing device applications. Aluminum nitride (AIN) films on silicon are promising large-area substrates for such devices in view of their high surface phonon energies and reasonably large dielectric constants. In this paper epitaxial layers of AlN on 2 `' Si wafers have been investigated as a necessary first step to realize devices from exfoliated or transferred atomic layers. Significant thickness dependent contrast enhancements are both predicted and observed for monolayers of graphene and MoS2 on AlN films as compared to the conventional SiO2 films on silicon, with calculated contrast values approaching 100% for graphene on AlN as compared to 8% for SiO2 at normal incidences. Quantitative estimates of experimentally measured contrast using reflectance spectroscopy show very good agreement with calculated values. Transistors of monolayer graphene on AlN films are demonstrated, indicating the feasibility of complete device fabrication on the identified layers.