Metal properties and thin film oxidation

The dependence of thin film oxidation rates on the metal properties is discussed in terms of a surface state charge at the metal-oxide interface and a space charge layer in the growing oxide. The properties considered are the magnetic change at the Curie temperature, allotropic transformation and crystal orientation of the metal substrate. Experimental data on the direct logarithmic oxidation of iron, nickel, cobalt and copper forming p-type semiconducting oxides are analysed.     

A photoluminescence study of film structure in CdTe nanoparticle thin films

The layer-by-layer deposition of thin films of CdTe nanoparticles and three different polyelectrolytes has been investigated. Photoluminescence spectra were used to monitor the energy transfer properties within the films. As the number of bilayers in a thin film was increased a decrease in the energy of the light emitted was observed. The wavelength change is a two-stage process. Deposition of the first one to two bi-layers of a thin film produced a sharp energy change (626 nm to 637 nm with the addition of a single bi-layer) whereas deposition of subsequent bi-layers produced a more gradual energy change (642 nm-646 nm with the addition of 5 bi-layers). A space-filling mechanism is suggested to account for these changes; smaller nanoparticles penetrate the earlier levels of a thin film and increase the inter-particle energy transfer opportunities within the layers.     

Organic field-effect transistors containing a SiO2 nanoparticle thin film as the gate dielectric

In this article, we report the fabrication of organic field-effect transistors using self-assembled SiO2 as a gate dielectric material and pentacene as a semiconductor. The dielectric layer was self-assembled with 10 layers of SiO2 nanoparticles 45 nm in diameter, and its breakdown field was larger than 0.57 MV/cm. Being a low-cost and low-temperature process, the layer-by-layer self-assembly is particularly suitable for organic field-effect transistor fabrication. The pentacene was thermally evaporated on the substrate under high vacuum at the room temperature. The fabricated transistor has a threshold voltage of 0.3 V, field-effect mobility of 0.05 cm2/Vs, and slope of 1.4 V/decade.     

A silver nanoparticle thin film modified glass substrate as a colourimetric sensor for hydrogen peroxide

In this work, a silver nanoparticle (AgNP) coated glass slide was developed as a device for sensing hydrogen peroxide. AgNPs were synthesised using borohydride reduction with a citrate stabiliser, resulting in a negatively charged stabilised particle surface. The particles were attached to the glass surface using the layer-by-layer (LbL) technique. Poly (diallyldimethylammonium chloride) and poly (styrene sulphonate) were used as cationic and anionic polyelectrolyte layers, respectively. The glass slide was modified with polyelectrolytes leaving a cationic layer on the top surface. The AgNPs were subsequently deposited on the slide via electrostatic interaction. As a result, a dark yellow film of AgNPs was obtained with maximum absorption at 410 nm. Film fabrication based on LbL assembly provided acceptable reproducibility (relative standard deviation = 6.5%). The fabricated film had long-term stability (>6 weeks). A very small quantity of AgNPs was used in this method. Fabrication was performed under ambient conditions. Therefore this fabrication was considered as a green method. The AgNP modified slide was developed to sense hydrogen peroxide. Detection is based upon oxidation of AgNPs by hydrogen peroxide. This results in a change in colour of the film from dark yellow to colourless. Linear calibration was obtained over the range of 1.0--100.0 mM of hydrogen peroxide. The device was successfully used for measuring hydrogen peroxide in urine.     

Magnetization spreading in a thin film memory

The hard axis magnetic field distribution within the uniaxial magnetic film element of a thin film memory device is calculated. In the memory device considered, the driving stripline and magnetic film are located between a magnetic keeper and a conducting ground plane. The difficulty encountered in the keeper-ground plane problem arises from the requirement of satisfying boundary conditions at the keeper and ground plane surfaces simultaneously, or in other words, from considering an infinite set of film and stripline images. A method of solution using Fourier transforms proves satisfactory. The dependence of the magnetic field distribution on the relative position of the elements and on variations in material properties is assessed.     

Magnetization switching in a garnet thin film

An improved technique for observing subnanosecond magnetization changes in thin films has been used to study the underdamped oscillatory behavior in a (Y2.5Gd0.5) (Fe4Ga1)O12sample. The measurement setup uses a version of the alternate sampling technique in which the sensitivity has been upgraded by the use of a lock-in amplifier. By using a shorted stripline of appropriate length to apply to the film two properly timed magnetic field steps, the precession of the magnetization can be quelled, and the magnetization can be switched between initial and final directions in a half-cycle of the resonant frequency.     

Ultrasonic spray coating and flash lamp annealing of silicon nanoparticle dispersions for silicon thin film formation

Ultrasonic spray coating is reported as a deposition method for thin silicon films using a mixture of silicon nanoparticles and organosilicon compounds. The as-deposited films were treated by flash lamp annealing (FLA) using xenon light in order to obtain polycrystalline silicon. The nanoparticles were characterized by diffuse reflection infrared Fourier transform spectroscopy, transmission electron microscopy, and powder X-ray diffraction prior to deposition and film formation. The effect of FLA on the morphology of silicon films obtained from these silicon nanoparticles is investigated. Thin polycrystalline films up to 4 µm with a silicon content up to 95 % were prepared by combining the use of ultrasonic spray coating and FLA.     

Time dependent conductive behavior of the layer-by-layer self-assembled SnO2 nanoparticle thin film

The understanding of the electrical conductivity properties of polyion/nanoparticle thin film assemblies has long-term impact for exploring the unique electrical properties in applications such as sensor, actuator and conductive coating. This paper reports on the observations of the time dependent conducting behavior of the SnO₂ thin film produced by layer-by-layer self-assembly. The thin film consists of 5 layers of polyion matrix and 12 nm SnO₂ nanoparticles that are adsorbed in an alternating sequence. The electrical current flowing through such thin film is not stabilized immediately, but instead increases with time until saturation. We further find a threshold current that is required to trigger the current self-enhancing process. It is hypothesized that the self-heating of the semiconductive nanoparticle explains this phenomenon. Based on this hypothesis, a hybrid channel is designed to completely eliminate this effect. This fundamental study may find applications in different gas and biomedical sensors and transparent electronics.     

Performance of a three-element thin film detector

A nuclear charged particle detector has been designed and fabricated at the University of Florida for use in identifying the nuclear charge Z and mass number A of low energy (1 MeV/amu) heavy mass ions. The detector consists of a stack of three sequential thin film detectors (made from NE-102A plastic scintillator) for three successive measurements of the specific luminescence ΔL/Δx and velocity of a transiting ion and a terminal surface barrier detector for measuring the ion residual energy. This detector assembly was tested by measuring its response to various isotopes of germanium and selenium ions accelerated to selected energies between 53 and 169 MeV and then scattered from a thin gold target foil. The tests were performed to obtain quantitative information on the ability of the detector system to identify the nuclear Z of an impinging ion and to test the 0810 1076 V 3 advantage of having three successive measurements of ΔL/Δx from three sequential and independent thin film detectors. It was determined that below 2 MeV/amu the detector response was dependent on particle velocity but independent of particle mass and below about 0.9 MeV/amu the detector was not able to distinguish between ions having two units difference in Z, probably due to similarities in ionic charge state distributions. It was also determined that the use of three detectors reduced the FWHM of the TFD response by 54%.     

Anomalously high conductivity in a thin polyphthalidylidene biphenylene film

An anomalously high conductivity was observed for the first time in a thin film of polyphthalidylidene biphenylene inserted between two metal electrodes with no electric field applied but exposed to the action of a small uniaxial mechanical pressure. Pis’ma Zh. Tekh. Fiz. 24, 89–94 (July 12, 1998)     

Simulations of nanoindentation in a thin amorphous metal film

Nanoindentation was simulated in a two dimensional model metallic glass thin film using molecular dynamics. Strain localization was observed in simulations where the system was sufficiently structurally relaxed prior to deformation. Indentation simulations utilized an atomic indenter that adhered to the surface or a frictionless indenter. Boundary conditions were varied to constrain the film or allow the film to relax in-plane to examine the effect on shear band formation. The most constrained system, i.e. that with the atomic indenter and the constrained boundaries exhibited the highest hardness.     

Weakly nonlinear stationary waves in a thin fluid film

Stationary periodic wave flow regimes of thin films of a viscous fluid on an inclined plane are considered.     

Behavior of TiO2 thin film in a nanocapacitor

Gold and platinum nanocapacitors have been fabricated using a magnetron sputtering technique. TiO2 is used as a dielectric material to separate the metal layers which act as the parallel plates for the capacitors. The thickness for metal films and TiO2 layer is 80 nm and 400 nm, respectively. Capacitance of the nanocapacitors has been measured and dielectric constant of TiO2 calculated. Both capacitance and dielectric constant are observed to have strong frequency dependence.     

Distance-dependent plasmon resonant coupling between a gold nanoparticle and gold film

We present an experimental analysis of the plasmonic scattering properties of gold nanoparticles controllably placed nanometers away from a gold metal film. We show that the spectral response of this system results from the interplay between the localized plasmon resonance of the nanoparticle and the surface plasmon polaritons of the gold film, as previously predicted by theoretical studies. In addition, we report that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field. Both the spectral response and the polarization effects are highly sensitive to the nanoparticle-film separation distance. Such a system shows promise in potential biometrology and diagnostic devices.     

Oxidation of a thin samarium film on iridium

Thermal desorption spectroscopy has been used to study the interaction of oxygen with a thin (<1 nm) samarium film deposited onto a textured iridium ribbon. Desorption of Sm atoms from Ir surface takes place from various states (chemisorbed, condensed, from compound with iridium, and oxide). The formation of samarium oxide is observed already at room temperature. As the temperature increases to T = 1100 K, a compound of samarium with iridium is formed at the first stage and then oxygen interacts with Sm atoms from this compound and “slow” (compared to the first process) growth of samarium oxide takes place.     

Fabrication of a novel organic polymer thin film

Fabrication of organic polymer thin films and organic semiconductors are critical for the development of sophisticated organic thin film based devices. Radio Frequency plasma polymerisation is a well developed and widely used fabrication technique for polymer thin films. This paper describes the fabrication of an organic polymer thin film from a monomer based on Lavandula angustifolia. Several polymer thin films were manufactured with thicknesses ranging from 200 nm to 2400 nm. The energy gap of the polymer thin film was measured to be 2.93 eV. The refractive index and extinction coefficient was determined to be 1.565 (at 500 nm) and 0.01 (at 500 nm) respectively. The organic polymer thin film demonstrates the possibility of an environmentally friendly, cost effective organic semiconductor.