The negative temperature coefficient of resistivity (TCR) displayed by p-Ta, which has thus far not been satisfactorily explained, has been examined by measuring the variation of electrical resistivity with temperature, from -2S300 OK, and by measuring the Hall coefficients, at room temperature and a t 77 OK, of films containing up to -60 at.% oxygen. The Hall measurements indicate carrier concentrations of -loz2 ~m -~ and mobilities of -1 cm2/V s. The analysis of the results has considered the granular structure of the films and has subsequently compared these results with an 'activated tunneling' model of conduction. Theoretical calculations which assume the film to be comprised of cubic grains separated by T a 2 0 5 agree well with the experimental measurements.Metallic conduction still appears to be contributing to the film properties even at the highest oxygen concentrations of the present investigation.Le coefficient negatif de variation de resistivite en fonction de la temperature (TCR) du p-Ta, qui n'a pas encore ete expliquk de f a~o n satisfaisante, a etC examine en mesurant la resistivite Clectrique en fonction de la temperature de 20 a 300 "K et en mesurant, a temperature ambiante et a 77 OK, les coefficients de Hall de films contenant jusqu'a 60% d'oxygene atomique. Les mesures d'effet Hall indiquent des concentrations de porteurs de cm-3 et des mobilites de -1 cm2/V s. Lors de I'analyse des resultats on a tenu compte de la structure granulaire des films et on a subsequemment compare ces resultats avec un modele "d'effet tunnel active" de la conduction. Des calculs theoriques, faits en supposant que le film est compose de grains cubiques sCparCs par Ta205, concordent tres bien avec les mesures expirimentales.La conduction metallique contribue aux proprietes du film mCme avec les plus fortes concentrations en oxygene utilisees au cours de cette investigation.
The structural and electrical properties of oxygen-doped tantalum films, sputtered in a triode system, have been investigated. X-ray diffraction traces from films with a low oxygen content indicate the presence of bcc Ta with a strained lattice. The intensity of the (110) bcc Ta diffraction peak decreases with increasing oxygen content and is interpreted as a decrease in the amount of bcc Ta phase present. Over this same range the appearance and rise in intensity of the β-Ta (200) peak indicates the formation of β-Ta. As the oxygen content is further increased, the structural data indicate a reorientation of the tetragonal β-Ta (200) to the (202) planes with respect to the film surface, an effect which has been previously observed in diode-sputtered tantalum; further increase in oxygen content produces a stretching of the β-Ta lattice by as much as 10% of the value reported by Read and Altman. The room-temperature resistivity increases with increasing oxygen content until a ``plateau'' region is reached at ∼ 210 μΩ cm corresponding to 12 at. % oxygen, and together with the x-ray data the electrical measurements indicate a change of phase from bcc to β-Ta. Above approximately 40 at. % oxygen the resistivity increases rapidly suggesting the formation of tantalum oxide.
Specific heat measurements were made between 0.4 and 3.0 °K on the disordered and two ordered phases of the equiatomic alloy CuAu, and also on CuAu3 in the disordered and partially ordered condition. The two samples of the disordered equiatomic alloy measured were found to be unstable, the specific heat on successive measurements slowly changing towards the values obtained for the ordered phase CuAu II. This is a remarkable result because all previous work has shown that the ordered phase formed below 385 °C is CuAu I. The first sample of CuAu I measured showed a distinct 'bump', with the maximum at about 0.7 °K, superimposed on the normal specific heat. A second sample did not show this 'bump' but the specific heat remained slightly anomalous. The nuclear specific heats of the ordered phases CuAu I and CuAu II and the partially ordered CuAu3 are higher than those of the respective disordered phases, supporting the hypothesis that the nuclear term is a quadrupole effect. Taking the present results in conjunction with those of Martin on Cu3Au, it is found that the electronic specific heats of the disordered alloys are fitted reasonably well by Stern's 'charging' theory. Ordering reduces the electronic specific heat by a few percent except for CuAu I where it is increased. The low-temperature limiting Debye temperature is increased by a few percent on ordering except for CuAu I where it is decreased. The Debye temperature changes are consistent with room-temperature Young's modulus measurements on copper–gold alloys. Otherwise it will be noted that the behavior of CuAu I is rather singular.
The dependence of the structural and electrical properties of sputtered tantalum films on the rate at which oxygen is leaked into the system has been investigated. The films were deposited on glass and polycrystalline alumina substrates and both structural and electrical measurements were made on the same samples. While some films deposited in argon contained both the body-centered-cubic and tetragonal β phases of tantalum, those deposited in the presence of oxygen consisted of the β phase. Increasing oxygen content of the films caused an expansion of the tetragonal lattice and changed the preferred grain orientation from (200) to (202). Increases in the oxygen content from 10 to 50 at.% decreased the film density by 2 g/cm3, increased the resistivity ρ from 200 to 5000 μΩ cm, and decreased Δρ/ΔT from 0 to −3.5 μΩ cm/°C. While the activation energy for conduction was small, it increased with the changing orientation of the β-Ta. This may indicate that ρ is due to the semiconducting nature of β-Ta and that the band structure of β-Ta is anisotropic.
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