Electronic transport and carrier concentration in conductive ZnO:Ga thin films

Transparent and conductive Ga-doped ZnO (ZnO:Ga) films were post-annealed after sputter deposition, and their structural and electrical properties were investigated. Post-annealing led to an improvement of crystallinity along the [001] direction, but did not change lateral grain size. Therefore, carrier concentration and electron mobility of films were analyzed as a function of crystallinity. The electrical parameters were obtained with both optical reflectance based on the Drude free-electron model and the Hall method, and similar tendencies were observed within the two methods. Even though the lowest resistivity was demonstrated by the film annealed at 550 °C, the optimum values for carrier concentration and mobility were observed in films with different post-annealing temperatures.     

Laser reflectance relaxation spectroscopy: Determination of thermal diffusivity in thin films of gold

The technique of thermal modulation is applied to the study of transient thermal properties of thin films of Au. Relaxation spectra as seen in the reflected laser light give a value for the thermal diffusivity of Au as κ ? 1.2 cm²/sec, comparable to previous data for the bulk metal. Versatility and potentials of the laser reflectance relaxation spectroscopy are discussed.     

Two-color approach for determination of thickness and dielectric constant of thin films using surface plasmon resonance spectroscopy

We report a real time, in situ non-perturbative all-optical approach for determining both the average thickness and the average dielectric constant of transparent thin films using surface plasmon resonance spectroscopy. While it is impossible to obtain both of these parameters from a single surface plasmon resonance spectroscopy experiment, we show both theoretically and experimentally that a two-color experiment allows unambiguous determination of both parameters. The approach is tested for organic thin films at the gold/solution interface which have thickness of a single monolayer.     

Alkyl chain effects in thin films of substituted phthalocyanines studied using infrared spectroscopy

Thin films (2-50 nm) of unsubstituted and 1,4-octa-alkyl substituted zinc phthalocyanines were investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, whereas the alkyl chains are C₄H₇, C₇H₁₃, C₁₀H₁₉. The absorption bands in the whole spectral range are discussed. We observe distinct differences in the spectra between the alkyl substituted Phthalocyanine (Pc) compounds. In contrast to PcZn and (but)₈PcZn, the spectra of (hep)₈PcZn and (dec)₈PcZn show two additional features in the spectral range between 3700 and 3000 cm⁻¹, which are discussed in detail.     

Stabilization of silicon-based devices in ion-containing media using thin Al2O3 platelets and MoS2 oriented thin films

A simplified analogue to an Ion-Sensitive Field-Effect Transistor (ISFET) was tested in the presence of ions. The gate electrode in an ISFET is an aqueous solution, unlike in a Metal-Oxide Field-Effect Transistor (MOSFET) where the gate is a metal. A problem with the ISFET is that the insulating oxide between the silicon and the solution is slowly penetrated by various ions such as OH^– or Na⁺ causing a change in the characteristics of the device.The application of thin alumina platelets and thin MoS₂ films as a protective insulating layer, when deposited over the insulating silicon oxide, was tested against the penetration of ions. It is shown that there is a significant decrease in the ion penetration through to the silicon oxide layer, depending on the applied bias, when the oxide is covered with thin alumina or MoS2 layers. The effect of different ions and ion concentrations are presented. Suggestions for further improvement are made.     

近红外漫反射光谱快速测定复合肥料各养分及石粉含量的研究

提出了一种近红外漫反射光谱法同时测定复合肥料各养分及石粉含量的新方法,其中复合肥料由尿素、磷酸一铵、氯化钾和石粉组成,各养分含量分别用总氮(N)含量、有效五氧化二磷(P)含量、氧化钾(K)含量表示.文中建立了N,P和石粉含量的PLS模型,其SEP值分别为0.8,0.8和1.4.其中,石粉含量模型是借助于石粉中结晶水的光...     

Small signal admittance spectroscopy applied for extraction of charge carrier mobility in thin organic layers

The work presents new way of extraction of charge carrier mobility from small signal spectra of admittance. It can be a useful method for thin organic layers in a sandwich arrangement. It is better than the version of small signal admittance currently applied for getting charge carrier mobility, since the final result is not charged with uncertainty of geometric capacitance and the upper limit of measurable charge carrier mobility is higher.     

Real-time study of phase transformations in Cu-In chalcogenide thin films using in situ Raman spectroscopy and XRD

The growth of polycrystalline CuInSe₂ and CuInS₂ thin films from metallic precursor layers is investigated using two complementary in situ methods which give bulk sensitive (XRD) and surface sensitive (Raman) information. From the time evolution of the XRD and Raman peak intensities the phase transformation sequences and the reaction kinetics can be derived. In both cases the chalcogenization of the Cu-In precursors proceeds at the top surface. Thus, the process is at least limited by cation diffusion through the metallic precursor. However, the growth kinetics of CuInSe₂ and CuInS₂ films differ. While the CuInSe₂ growth is limited by the reaction of binary phases, CuInS₂ growth is controlled by fast diffusion which is solely restricted to the period of raising temperature during the process.     

High resolution hard X-ray photoemission using synchrotron radiation as an essential tool for characterization of thin solid films

Recently, we have shown that hard X-ray photoemission spectroscopy using undulator X-rays at SPring-8 is quite feasible with both high resolution and high throughput. Here we report an application of hard X-ray photoemission spectroscopy to the characterization of electronic and chemical states of thin solid films, for which conventional PES is not applicable. As a typical example, we focus on the problem of the scatter in the reported band-gap values for InN. We show that oxygen incorporation into the InN film strongly modifies the valence and plays a crucial role in the band gap problem. The present results demonstrate the powerful applicability of high resolution photoemission spectroscopy with hard X-rays from a synchrotron source.     

A numerical model for the leakage characteristics in ferroelectric thin films under ionizing radiation

A numerical model is developed to describe the leakage characteristics in ferroelectric thin films under ionizing radiation. The trap-controlled space-charge-limited conduction mechanism is modified by considering radiation-induced charge carriers and changes in the relative dielectric constant. The effect of dose rate is related to the changes in the carrier mobility. Numerical simulation using this model reveals a radiation hardness of 10 Mrad(Si) for barium strontium titanate (BST) thin films at a constant dose rate of 10 Krad(Si)/s. Differences in the leakage behavior under radiation for different conduction regions are also discussed. This model provides a useful tool in predicting the leakage behavior under ionizing radiation and estimating the radiation hardness for ferroelectric materials.     

Method for determining the tritium concentration using the effects of dissociation of molecular beams of hydrogen isotopes on thin carbon films

Physical foundations of a new method for mass-spectrometric determination of tritium concentration in hydrogen-containing media, which is based on the effect of dissociation of molecular ions of hydrogen isotopes passing through thin carbon films, are formulated. The effects accompanying the interaction of particles with a solid (angular scattering, change in the charge state, energy losses in protons, deuterons, and tritons) are analyzed. The corresponding theoretical and experimental data indicate that the proposed technology can be implemented in practice for a comparatively low particle energy of ∼10 keV/nucleus.     

A live fringe technique for stress measurements in reflecting thin films, using holography

A simple technique is given for measuring stresses in reflecting thin films, using real-time holography. The technique gives clear real fringes with good visibility which can be easily monitored and photographed. No substrate profile measurement is needed. Thermal stress of 0.49 × 10⁹ dynes cm^-2 is observed for a 200.0 nm thick Ag film in the temperature range of 30 to 55°C. This is in good agreement with reported values.     

Effective barrier height and work function of Mg:Ag thin films with a low Mg concentration acting as cathodes in high-efficiency organic light emitting devices

Organic molecular-beam deposition (OMBD) of Mg:Ag thin films with a low Mg concentration on tris(8-hydroxyquinolino) aluminum (Alq₃) layers at room temperature was performed to investigate the feasibility of using Mg:Ag thin films as cathode electrodes in organic light-emitting devices (OLEDs). The effective barrier height of the Mg:Ag (5:95) thin films grown on the Alq₃ layers, determined from the current-voltage measurements, was as low as 0.22 eV. The work function of the Mg:Ag (5:95) thin film, determined from the secondary electron emission coefficients obtained by using focused ion beam, was 4.12 eV. These results indicate that Mg:Ag (5:95) thin films with a low Mg concentration grown by using the OMBD method hold promise for potential applications as cathode electrodes in high-efficiency OLEDs.     

Choosing the ranges for measuring the reflectivity of a prism coupler in the waveguide spectroscopy of thin films

A criterion for selecting the best ranges for measuring the reflectivity of a prism coupler, based on minimizing the error in reconstructing the parameters of thin films using the least-square method, is proposed. The effectiveness of the criterion is demonstrated by solving the inverse optical problem for a SiO_x film deposited on a silicon substrate as an example.     

On the new procedure for the determination of surface conditions in thin films with internal layer inhomogeneity

A method for determining the surface conditions on both surfaces of the film, based in the thickness dependence of localized states is proposed.     

Preparation of thin films using the tape-casting process for use in the solid oxide fuel cell

Solid oxide fuel cells (SOFCs) produce electricity by electrochemically combining hydrogen and oxygen to give water. They operate at high temperatures (typically 1000 °C) allowing natural gas (hydrogen source) to be reformed in the cell rather than in an external reformer, reducing cost. Comparison with current electrical power generation systems, show SOFCs to have increased efficiencies, reduced NO_x and SO_x emissions and improved reliability promising a viable future alternative for electricity production. Thin ceramic films to less than 200 μm are necessary for reduced all resistance. Tape casting is one method for production of thin ceramic (or metallic) films. In this paper, tape casting was used to produce both dense and porous thin films of 8-mol% Yttria stabilised Zirconia (YSZ). The films were fired both separately and together in a monolithic multi-layered block in order to determine the feasibility of using this method for the production of all components of the SOFC. The effects of organic content, addition of pore-forming agents and firing temperature on the microstructure of the films were investigated. Each individual layer produced was between 40–60 μum thick, with the highest density being>97% and the highest porosity obtained at 30% (produced by addition of a pore former). No de-lamination was observed upon heating the multi-layers. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Nanoscale observations of the operational failure for phase-change-type nonvolatile memory devices using Ge2Sb2Te5 chalcogenide thin films

In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge₂Sb₂Te₅ (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5 m. After the programming signals of more than 2×10⁶ cycles were repeatedly applied to the device, the high-resistance memory state (reset) could not be rewritten and the cell resistance was fixed at the low-resistance state (set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than 1×10¹⁰ cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming.