Novel piezoelectric thin film impact sensor: application in non-destructive material discrimination

We report on the design, development, and performance study of a packaged piezoelectric thin film impact sensor, and its potential application in non-destructive material discrimination. The impact sensing element employed was a thin circular diaphragm of flexible Phynox alloy. Piezoelectric ZnO thin film as an impact sensing layer was deposited on to the Phynox alloy diaphragm by RF reactive magnetron sputtering. Deposited ZnO thin film was characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) techniques. The d(31) piezoelectric coefficient value of ZnO thin film was 4.7 pm V-1, as measured by 4-point bending method. ZnO film deposited diaphragm based sensing element was properly packaged in a suitable housing made of High Density Polyethylene (HDPE) material. Packaged impact sensor was used in an experimental set-up, which was designed and developed in-house for non-destructive material discrimination studies. Materials of different densities (iron, glass, wood, and plastic) were used as test specimens for material discrimination studies. The analysis of output voltage waveforms obtained reveals lots of valuable information about the impacted material. Impact sensor was able to discriminate the test materials on the basis of the difference in their densities. The output response of packaged impact sensor shows high linearity and repeatability. The packaged impact sensor discussed in this paper is highly sensitive, reliable, and cost-effective.

Role of substrate temperature on the properties of Na-doped ZnO thin film nanorods and performance of ammonia gas sensors using nebulizer spray pyrolysis technique

Sodium doped zinc oxide (Na:ZnO) thin films were deposited on glass substrates at substrate temperatures 300,400 and 500 degrees C by a novel nebulizer spray method. X-ray diffraction shows that all the films are polycrystalline in nature having hexagonal structure with high preferential orientation along (0 0 2) plane. High resolution SEM studies reveal the formation of Na-doped ZnO films having uniformly distributed nano-rods over the entire surface of the substrates at 400 degrees C. The complex impedance of the ZnO nano-rods shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 170 to 270 degrees C and thereafter slightly increased. (c) 2013 Elsevier B.V. All rights reserved.

Polyelectrolyte/silver nanocomposite multilayer films as multifunctional thin film platforms for remote activated protein and drug delivery

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50 +/- 20 nm, which increased to 80 +/- 20 nm when the AgNO3 concentration was increased from 25 to 50 mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Specroelectrochemical, Switching Kinetics, and Chronoamperometric Studies of Dibenzyl Derivative of Poly(3,4-propylenedioxythiophene) Thin-Film-Based Electrochromic Device

The dibenzyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT-Bz(2)) thin film is deposited onto ITO-coated glass substrate by electropolymerization technique. The electropolymerization of ProDOT-Bz(2) is carried out by a three-electrode electrochemical cell. The cyclic voltammogram shows the redox properties of electrochemically prepared films deposited at different scan rates. The thin films prepared were characterized for its morphological properties to study the homogeniety. Classic six-layer structure of PProDOT-Bz(2) electrochromic device using this material was fabricated and reported for the first and its characterizations such as spectroelectrochemical, switching kinetics, and chronoamperometric studies are performed. The color contrast of the thin film and the device achieved are 64 and 40%, respectively, at lambda(max) (628 nm). The switching time is recorded and the observed values are 5 s from the coloring state to the bleaching state and vice versa. The chronoamperometry shows that the device performed up to 400 cycles, and it is capable of working up to 35 cycles without any degradation. (C) 2014 Wiley Periodicals, Inc.

Influence of film thickness on the properties of sprayed ZnO thin films for gas sensor applications

Transparent conducting ZnO films were prepared at substrate temperature 400 degrees C with different film thicknesses by nebulizer spray pyrolysis method on glass substrates. XRD studies reveal that the films are polycrystalline in nature having hexagonal crystal structure with preferred grain orientations along (0 0 2) and (1 0 1) directions. The crystallite size increases along (0 0 2) plane with the thickness increase and attains a maximum 109 nm for 913 nm film thickness. Analysis of structural parameters indicates that the films having thickness 913 nm are found to have minimum dislocation density and strain values. The HRSEM measurements show that the surface morphology of the films also changes with film thickness. EDAX estimates the average atomic percentage ratio of Zn and O in the ZnO films. Optical studies reveal the band gap energy decrease from 3.27 to 3.14 eV with increase of film thickness. Room temperature PL spectra show the near-band-edge emission and deep-level emission due to the presence of defects in the ZnO thin films. Impedance spectroscopy analysis indicates that grain boundary resistance decreases with the increasing ammonia concentration up to 500 ppm and the maximum sensitivity is found to be 1.7 for 500 ppm of ammonia. (C) 2014 Elsevier Ltd. All rights reserved.

Effect of film thickness and annealing on optical properties of TiO2 thin films and electrical characterization of MOS capacitors

Titanium dioxide (TiO2) thin films were deposited on glass and silicon (100) substrates by the sol-gel method. The influence of film thickness and annealing temperature on optical transmittance/reflectance of TiO2 films was studied. TiO2 films were used to fabricate metal-oxide-semiconductor capacitors. The capacitance-voltage (C-V), dissipation-voltage (D-V) and current-voltage (I-V) characteristics were studied at different annealing temperatures and the dielectric constant, current density and resistivity were estimated. The loss tangent (dissipation) increased with increase of annealing temperature.

Semi-insulating layer for novel high voltage polysilicon thin film transistors

This work describes the deposition and characterisation of semi-insulating oxygen-doped silicon films for the development of high voltage polycrystalline silicon (poly-Si) circuitry on glass. The performance of a novel poly-Si High Voltage Thin Film Transistor (HVTFT) structure, incorporating a layer of semi-insulating material, has been investigated using a two dimensional device simulator. The semi-insulating layer increases the operating voltage of the HVTFT structure by linearising the potential distribution in the device offset region. A glass compatible semi-insulating layer, suitable for HVTFT applications, has been deposited by the Plasma Enhanced Chemical Vapour Deposition (PECVD) technique from silane (SiH4), nitrous oxide (N2O) and helium (He) gas mixtures. The as-deposited films are furnace annealed at 600°C which is the maximum process temperature. By varying the N2O/SiH4 ratio the conductivity of the annealed films can be accurately controlled up to a maximum of around 10-7 Ω-1cm-1. Helium dilution of the reactant gases improves both film uniformity and reproducibility. Raman analysis shows the as-deposited and annealed films to be completely amorphous. A model for the microstructure of these Semi-Insulating Amorphous Oxygen-Doped Silicon (SIAOS) films is proposed to explain the observed physical and electrical properties.

Size Dependent Nanoindentation of a Soft Film on a Hard Substrate

Nanoindentation experiments on Al/glass systems show that, as the indentation depth increases, the hardness decreases during a shallow indentation, and increases when the indenter tip approaches the film–substrate interface. We associate the rise in hardness during two stages with the strong strain gradient effects, the first stage is related with the small scale effects and the second stage with the strain gradient between the indenter and the hard substrate. Using the strain gradient theory proposed by Chen and Wang and the classical plasticity theory, the observed nanoindentation behavior is modeled and analyzed by means of the finite element method, and it is found that the classical plasticity cannot explain the experiment results but the strain gradient theory can describe the experiment data at both shallow and deep indentation depths very well. The results prove that both the strain gradient effects and substrate effects exist in the nanoindentation of the film–substrate system.

Thin film monitoring with silicon bulk acoustic resonators

Abstract-This paper reports a single-crystal silicon mass sensor based on a square-plate resonant structure excited in the wine glass bulk acoustic mode at a resonant frequency of 2.065 MHz and an impressive quality factor of 4 million at 12 mtorr pressure. Mass loading on the resonator results in a linear downshift in the resonant frequency of this device, wherein the measured sensitivity is found to be 175 Hz cm2/μg. The silicon resonator is embedded in an oscillator feedback loop, which has a short-term frequency stability of 3 mHz (approximately 1.5 ppb) at an operating pressure of 3.2 mtorr, corresponding to an equivalent mass noise floor of 17 pg/cm2. Possible applications of this device include thin film monitoring and gas sensing, with the potential added benefits of scalability and integration with CMOS technology. © 2008 IEEE.

Fractal Pattern Formation In Anodic Bonding Of Pyrex Glass/Al/Si

Anodic bonding of Pyrex glass/Al/Si is an important bonding technique in micro/nanoelectromechanical systems (MEMS/NEMS) industry. The anodic bonding of Pyrex 7740 glass/Aluminum film/Silicon is completed at the temperature from 300 degrees C to 375 degrees C with a bonding voltage between 150 V and 450 V. The fractal patterns are formed in the intermediate Al thin film. This pattern has the fractal dimension of the typical two-dimensional diffusion-limited aggregation (2D DLA) process, and the fractal dimension is around 1.7. The fractal patterns consist of Al and Si crystalline grains, and their occurrences are due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al layers. The formation of the fractal pattern is helpful to enhance the bonding strength between the Pyrex 7740 glass and the aluminum thin film coated on the crystal silicon substrates.

Nanoindentation of thin-film-substrate system: Determination of film hardness and Young's modulus

In the present paper, the hardness and Young's modulus of film-substrate systems are determined by means of nanoindentation experiments and modified models. Aluminum film and two kinds of substrates; i.e. glass and silicon, are studied. Nanoindentation XP II and continuous stiffness mode are used during the experiments. In order to avoid the influence of the Oliver and Pharr method used in the experiments, the experiment data are analyzed with the constant Young's modulus assumption and the equal hardness assumption. The volume fraction model (CZ model) proposed by Fabes et al. (1992) is used and modified to analyze the measured hardness. The method proposed by Doerner and Nix (DN formula) (1986) is modified to analyze the measured Young's modulus. Two kinds of modified empirical formula are used to predict the present experiment results and those in the literature, which include the results of two kinds of systems, i.e., a soft film on a hard substrate and a hard film on a soft substrate. In the modified CZ model, the indentation influence angle, phi, is considered as a relevant physical parameter, which embodies the effects of the indenter tip radius, pile-up or sink-in phenomena and deformation of film and substrate.

Small scale, grain size and substrate effects in nano-indentation experiment of film-substrate systems

The mechanical properties of film-substrate systems have been investigated through nano-indentation experiments in our former paper (Chen, S.H., Liu, L., Wang, T.C., 2005. Investigation of the mechanical properties of thin films by nano-indentation, considering the effects of thickness and different coating-substrate combinations. Surf. Coat. Technol., 191, 25-32), in which Al-Glass with three different film thicknesses are adopted and it is found that the relation between the hardness H and normalized indentation depth h/t, where t denotes the film thickness, exhibits three different regimes: (i) the hardness decreases obviously with increasing indentation depth; (ii) then, the hardness keeps an almost constant value in the range of 0.1-0.7 of the normalized indentation depth h/t; (iii) after that, the hardness increases with increasing indentation depth. In this paper, the indentation image is further investigated and finite element method is used to analyze the nano-indentation phenomena with both classical plasticity and strain gradient plasticity theories. Not only the case with an ideal sharp indenter tip but also that with a round one is considered in both theories. Finally, we find that the classical plasticity theory can not predict the experimental results, even considering the indenter tip curvature. However, the strain gradient plasticity theory can describe the experimental data very well not only at a shallow indentation depth but also at a deep depth. Strain gradient and substrate effects are proved to coexist in film-substrate nano-indentation experiments. (c) 2006 Elsevier Ltd. All rights reserved.

Femtosecond optical Kerr effect study of Ge(10)AS(40)S(30)Se(20) film

The results of the femtosecond optical heterodyne detection of optical Kerr effect at 805 nm with the 80 fs ultrafast pulses in amorphous Ge10As40S30Se20 film is reported in this paper. The film shows an optical non-linear response of: 200 fs under ultrafast 80 fs-pulse excitation and the values of real and imaginary parts of non-linear susceptibility chi((3)) were 9.0 X 10(-12) and -4.0 X 10(-12) esu, respectively. The large third-order non-linearity and ultrafast response are attributed to the ultrafast distortion of the electron orbits surrounding the average positions of the nucleus of Ge, As, S and Se atoms. This Ge10As40S30Se20 chalcogenide glass would be expected as a promising material for optical switching technique. (c) 2005 Elsevier Ltd. All rights reserved.

Ultrafast optical Kerr effect in amorphous Ge10As40S30Se20 film induced by ultrashort laser pulses

The results of the femtosecond optical heterodyne detection of optical Kerr effect at 805 am with the 80 fs ultrafast pulses in amorphous Ge10As40S30Se20 film is reported in this Letter. The film shows an optical nonlinear response of 200 fs under ultrafast 80 fs-pulse excitation, and the values of real and imaginary parts of nonlinear susceptibility chi((3)) were 9.0 x 10(-12) esu and -4.0 x 10(-12) esu respectively. The large third-order nonlinearity and ultrafast response are attributed to the ultrafast distortion of the electron orbits surrounding the average positions of the nucleus of Ge, As, S and Se atoms. This Ge10As40S30Se20 chalcogenide glass would be expected as a promising material for optical switching technique.

Determination and analysis of the optical constants of thin films of nickel(II) and copper(II) hydrazone complexes by spectroscopic ellipsometry

Thin films of four nickel(II) and copper(II) hydrazone complexes, which will hopefully be used as recording layers for the next-generation of high-density recordable disks, were prepared by using the spin-coating method. Absorption spectra of the thin films on K9 optical glass substrates in the 300-700 nm wavelength region were measured. Optical constants (complex refractive indices N) and thickness d of the thin films prepared on single-crystal silicon substrates in the 275-675 nm wavelength region were investigated on a rotating analyzer-polarizer scanning ellipsometer by fitting the measured ellipsometric angles (Psi(lambda) and Delta(lambda)) with a 3-layer model (Si/dye film/air). The dielectric functions epsilon and absorption coefficients alpha as a function of the wavelength were then calculated. Additionally, a design to achieve high reflectivity and optimum dye film thickness with an appropriate reflective layer was performed with the Film Wizard software using a multilayered model (PC substrate/reflective layer/dye film/air) at 405 nm wavelength.