Change In Film Resistance Research Articles

Poly(phthalidylidenarylene)s: new effects — new horizons of application

Recently, new nonconjugated polymers of a poly(phthalidylidenarylene)s class were synthesized. They consist of functional units sensible to a number of external influences, such as temperature, pressure, electric field, PH-medium, etc. These influences cause the insulator-metal transition in the polymer film. As a result, the film resistance changes by 10–12 orders of magnitude. In addition, the films display electroluminescence. These phenomena open broad prospects for the application of these polymers in a variety of industrial products.

Solid‐State Hydrogen Sensors Using Palladium‐Nickel Alloys: Effect of Alloy Composition on Sensor Response

Thin film alloys of Pd and Ni make good sensors for hydrogen partial pressures over a very wide range: from . For from 1 to 700 Torr the atomic percent of Ni in the alloy has a strong effect on the change in film resistance which is used as the sensing property. The phase transition from the α‐ to the hydride β‐phase must be avoided to maintain a reversible sensor. The characteristics of alloys with Ni of 3, 5.3, 8, and 15% are reported. The phase transition was found in the 5.3% alloy at about 250 Torr, but alloys of showed no phase change behavior up to 630 Torr (pure) at ambient temperatures. Other characteristics of the Pd/Ni alloy sensors are also reported, including the effect of temperature, oxygen, and relative humidity, and the speed of response to step changes in .

Manipulation of the Ti/Si reaction paths by introducing an amorphous Ge interlayer

Evolution of the Ti/a-Ge/Si trilayer reactions has been investigated using transmission electron microscopy and Auger electron spectroscopy. Instead of amorphous phase formation, as usually observed in the Ti/Si bilayer reaction, the crystalline Ti6Ge5 is the first phase observed during the reaction. Preceding the equilibrium C54-Ti(Si,Ge)2, a substitutional solid solution type C49-Ti(Si,Ge)2 forms upon annealing at 550–600 °C, regardless of the replacement of amorphous phase by the crystalline phase. The C49-to-C54 polymorphic transformation occurs at ∼650 °C. The reaction path is also correlated with the change in film resistance obtained from a four-point sheet resistance measurement.

The oxidation and resistance of tantalum-nitride thin films

The oxidation of reactively-sputtered, tantalum—nitride thin films has been studied between 473 and 773 K in air. Films with thicknesses that correspond to sheet resistances of 43, 75, and 150 Ω/□ were evaluated in this study. X-ray diffraction revealed that the films and the oxidation products were amorphous. The oxidation products were characterized with AES and XPS. The oxidation process was monitored by measuring the change in sheet resistance with time. Sheet resistance measurements were performed with a four-point probe. The oxidation kinetics can be represented by the equation ΔR/R n =k′t. ΔR/R is sheet resistance change in %, t is time, and k′ is the rate constant. The oxidation kinetics, for the thickest film, were parabolic above about 598 K, and approximately quartic below this temperature. The 75 Ω/□ films deviated from parabolic kinetics below 603 K, and approached approximate cubic kinetics at 498 K. However, the data were forced to fit parabolic kinetics with good correlation. For the thinnest film, no deviation from parabolic kinetics was observed. The rate constants obeyed the Arrhenius relation. An activation energy of 147 kJ/mole (1.52eV) was calculated, for the thickest film, during parabolic kinetics. This value is approximately equal to the activation energy obtained during quartic kinetics. A model that explains the deviation from parabolic to quartic oxidation kinetics at lower temperatures is presented. In this model, the change in resistance as a function of time was due to simultaneous change in film resistivity, as a result of oxygen dissolution into the film, and oxide-scale growth. The temperature at which this deviation occurs should be a function of film thickness.

Effect of film history on the change in its properties under irradiation

The pattern of change in material properties under irradiation depends both on the conditions of irradiation and on the films' initial state. In the present paper the effect of low energy ( E = 4 keV) ion bombardment on the electrical properties of CrSiNi films, having different histories, is considered. The films were fabricated with the use of flash thermal evaporation under residual pressures of 2 × 10 −3 and 9 × 10 −3 Pa and evaporation times of 40–50 and 140–160 s. Some of the films before irradiation were annealed at a temperature of 623 K for 2 h. After annealing, the temperature coefficient of resistance (TCR) of the films shifts to the region of positive values, and the resistance weakly decreased or increased. After irradiation, the resistance of both type of initial film decreased, but the character of the resistance change of films annealed and irradiated after annealing depended on the conditions of deposition. The TCR of annealed films after irradiation shifted to the region of negative values. After storage, the resistivity of the films increased and the absolute value of the TCR decreased. A qualitative explanation of results is proposed.

Properties and microstructure of tungsten films deposited by ion-assisted evaporation

The modification of film properties in evaporated tungsten was studied as a function of deposition environment. Using concurrent argon ion bombardment of the growing film, the stress varied in the same manner at all ion energies and substrate temperatures. Initial increases in tensile stress are followed by a monotonic trend toward compressive stress, for all sets of films. On the other hand, the qualitative changes in film resistivity with concurrent bombardment were dependent on the ion energy and substrate temperature, showing increases at high temperature and energy and decreases at low temperature and energy. Changes in the microstructure and impurity content in deposited films were found to be strongly linked to stress and resistivity changes. The trend toward compressive stress induced by high levels of ion bombardment is primarily reflected in an increase in (110) orientation. Increased resistivity is related to decreased grain size, increased (110) texture, and increased levels of film argon and oxygen content. By choice of deposition conditions, both the resistivity and stress can be minimized.

A simple high-temperature superconducting thin-film optical bolometer

The authors have demonstrated the operation of a simple optical bolometer by irradiating a constriction in a Y1Ba2Cu3O7- delta thin film with chopped laser light at lambda =633 nm. The change in film resistivity was measured by lock-in detection of the AC component in the current-biased mode. Operating optimally near 77 K, the bolometer shows detectivity of 5 mV W-1 and NEP of 10-6 W Hz-12/. The authors discuss the possibility of methods to improve these figures by at least three orders of magnitude.

Heats of adsorption of hydrogen on polycrystalline iron films

A calorimetric method has been used to measure the heat of adsorption of hydrogen at 273 K and 77 K on iron films prepared under UHV conditions. The initial heat of adsorption was 98 ± 3 kJ mol -1 at 273 K and 88 ± 3 kJ mol -1 at 77 K. Film resistance changes were simultaneously measured and a comparison of changes in the two parameters allowed the coverage region to be divided into three distinct parts. A tentative explanation is made of the causes of these changes in terms of the state of the adsorbed species. Data for deuterium showed a zero- point energy effect on the adsorption heat, this being initially 104 ± 3 kJ mol -1 at 273 K.

Behavior of Ultrathin Zirconium Films upon Exposure to Oxygen

Discontinuous films of zirconium, having surface resistivities between 104 and 106 Ω sq−1, were deposited on glass substrates in ultrahigh vacuum and then exposed to oxygen pressures in the range of 5×10−7 to 4×10−8 Torr at temperatures of 25° and −196°C. The change in film resistance with time was monitored and a plot of logR vs logt was constructed. This graph was initially concave upwards, but became linear after a time which was characteristic of monolayer formation. An interpretation of the film behavior was based on the transport of electrons by tunneling through gaps separating the metal islands. The initial change in film resistance was caused by an increase in the zirconium work function. This increase was due to oxygen monolayer formation. The subsequent linear log-log behavior was caused by an increase in the tunneling distance which resulted from oxidation of the metal islands. Values for both the interisland spacing and the room-temperature oxidation rate constant have been calculated from the experimental data. Both impurities and the heat of adsorption interfered with determining a value for the interisland spacing, but when these interferences were eliminated, a distance of 6.9 Å was found for a 104 Ω sq−1 film. The oxidation rate constant for a comparable film at 25°C was 4×10−9 cm with an activation energy of 0.3 kcal mole−1. Pumping speeds also were determined. Zirconium initially pumped oxygen at ≈1500 ml·sec−1·cm−2. The sticking coefficient for oxygen on a partially oxygen covered zirconium surface was approximately 0.05.

Calorimetric determination of the heat of adsorption of oxygen on evaporated films of germanium and silicon

The heats of adsorption of oxygen on evaporated films of germanium and of silicon have been determined to an absolute accuracy of ± 5 per cent by means of a Beeck type calorimeter. The variation of the heat of adsorption with surface coverage has been studied, together with the simultaneous change in film resistance. The significance of the results is discussed.