J. L. Peña

CDTE OXIDE FILMS GROWN BY RADIO FREQUENCY SPUTTERING UTILIZING ARGON-NITROUS OXIDE PLASMA

Cadmium telluride oxide films (CdTe:O) were grown by a radio frequency sputtering technique using a controlled plasma (Ar–N2O) on glass slide substrates. The films were studied by Auger electron spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction. We demonstrate that with N2O the oxidation process occurs in a narrow range of partial pressures of nitrous oxide. We find that the films are amorphous and the amount of oxygen incorporated in the films depends on the N2O partial pressure and saturates at about 55 at. % oxygen. As the amount of oxygen increases the number of Te–O and Cd–O bonds increases. The compounds formed depend on the partial pressure of the N2O and are of the form CdxTeyOz. When saturation of oxygen is obtained the compound formed is probably CdTe2O5.

Auger electron spectroscopy analysis of oxidation states of Te in amorphous CdTe oxide thin films

Amorphous CdTe oxide (a-CdTe:O) thin films with different concentrations of oxygen were grown by rf sputtering and analyzed by Auger electron spectroscopy. A slight change of shape in the Cd MNN peak as a function of oxygen content in a-CdTe:O is observed. This peak resembles the Cd MNN peak of CdTe, at one extreme, and that of CdTeO3, at the other. The Te MNN and the O KLL peaks have similar shapes and lower intensities for a-CdTe:O oxygen saturated films than those in CdTeO3. On the other hand, there is a large and gradual difference in shape, intensity, and energy observed in the Te MNN peak among a-CdTe:O with low, intermediate, and high concentration of oxygen. Different Te oxidation states, as Te−2 and Te+4, contribute to this change as evidenced by a simulation with combinations of CdTe and of CdTeO3 spectra, or by combinations of a-CdTe:O spectra with low and high oxygen content.

Vibration isolation analysis for a scanning tunneling microscope

We analyze the efficiency of a vibration isolation system (VIS) for a scanning tunneling microscope as a function of the different parameters involved. The VIS consists of a stack of several metallic plates, separated by rubber elements with known properties. We show three‐dimensional graphs obtained for different values of parameters such as rigidity (spring) constant (K), damping constant (C), mass (M), and the number of stages (n). Analyzing the K dependence of the position of the main peaks, we find a parabolic behavior when the damping constant is small, with a slight deviation for larger values.

Effects of working pressure on physical properties of tungsten-oxide thin films sputtered from oxide target

Tungsten-oxide films were deposited on glass substrates from a metal-oxide target by nonreactive radio-frequency sputtering. The authors have studied the effect that changing Ar gas pressure has on the electrical, optical, and chemical composition in the thin films. Resistivity of WO3 changed ten orders of magnitude with working gas pressure values from 20 to 80 mTorr. Thin films deposited at 20 mTorr of Ar sputtering pressure showed lower resistivity and optical transmittance. X-ray photoelectron spectroscopy (XPS) measurements revealed similar chemical composition for all samples irrespective of Ar pressure used. However, XPS analyses of the evolution of W 4f and O 1s peaks indicated a mixture of oxides dependent on the Ar pressure used during deposition.

Influence of the sputtering variables in the ion bombardment during off-axis deposition of YBa2Cu3Ox films

YBa2Cu3Ox thin films were grown on SrTiO3 substrates using an off-axis-sputtering configuration. Using a target with 100 h of sputtering runs, only medium quality films were obtained. However, a fresh target allowed us to obtain, at the same sputtering conditions, high quality films. The different film properties obtained as a function of the target age, gas pressure, and substrate position were discussed in the framework of a previous model of the angular distribution of oxygen ions which bombard and affect the growing film.

Pressure and temperature influence on CdTe thin‐film deposit by close‐spaced vapor transport technique

CdTe thin films were grown by the close‐spaced vapor transport (CSVT) technique, and the sublimation rate had a transition as ambient pressure was changed. The transition is discussed in terms of diffusion and free sublimation processes. The interpretation of these results is given based on an argument on the mean free path of gas molecules. A transition in the activation energy is reported.

Behavior of superconducting samples levitated in a static magnetic field: Study in a non-vertical configuration

Abstract The mechanical response of superconducting samples in a static magnetic field was investigated. Levitation of superconducting YBa 2 Cu 3 O x samples was performed in an unusual configuration. Undamped oscillations were observed; most of the samples oscillated for times as long as 2 min, but a few of them showed a highly damped behavior. Volume magnetization of samples was estimated from the levitation; the magnetic stiffness was also measured, and we found a dependence on the density. The samples levitated rigidly after oscillating; a discussion in terms of flux pinning is given.

Influence of preparation conditions on characteristics of the YBa2Cu3O7−δ compound

Synthesis of ceramic YBa2Cu3O7−δ by solid-state reaction was performed under different conditions. Different values of cooling rate and oxygen flow were used, and no significant influence on superconducting characteristics of the samples was observed. A major influence on their mechanical properties was found.