Donald H Galvan | Universidad Nacional Autónoma de México (original) (raw)

Papers by Donald H Galvan

Applied Surface Science, May 1, 2004

Chemical Physics Letters, 2008

Fuller Nanotub Carbon Nanostr, 2001

In this work, we report the production of NbSe2 (niobium diselenide) nanotubes formed by irradiat... more In this work, we report the production of NbSe2 (niobium diselenide) nanotubes formed by irradiating NbSe2 with high doses of electron irradiation. The apparatus used for the irradiation was a 2 MeV Van de Graaff accelerator at the following conditions: voltage 1.3 MeV, current 5 μA, dose rate 25 kGy/min, and total dosage 1000 kGy. These conditions were maintained fixed while irradiation dosage was changed between 100, 250 and 500 Mrad. We observed enormous and very well defined nanotubes with a length of several nm and width of a few nm, which are hollow and capped at one end. As the level of irradiation is increased to 500 Mrad, onion-like structures were observed.

Physica C, 2003

Magnetization measurements on NbSe 2 samples subjected to 100, 250, and 500 Mrad of electron irra... more Magnetization measurements on NbSe 2 samples subjected to 100, 250, and 500 Mrad of electron irradiation revealed an enhancement in the critical current density J c with radiation dosage. This enhancement attained a maximum value with almost double the J c of the unirradiated material at 500 Mrad. The measured superconducting transition temperature T c of all the samples did not change as a result of the irradiation.

Adsorption, 2000

Adsorption-desorption cycles were measured for methane on non-irradiated WS 2 , and on irradiated... more Adsorption-desorption cycles were measured for methane on non-irradiated WS 2 , and on irradiated WS 2 (which contained, in part, WS 2 fullerenes and nanotubes). Both types of samples were further subdivided into three sets: one set received no further treatment, another set was heated under vacuum, and the last set was acid-treated and heated. The specific surface area was determined for each set; so was the presence or absence of a hysteresis loop in the adsorption-desorption cycles. The results of these two groups of measurements were correlated with the space available for adsorption. The implications of the results for the experimental determination of the dimensionality of gas adsorbed at the interior of nanotubes are discussed.

Structural and electronic properties of graphene with one gold atom at top were calculated using ... more Structural and electronic properties of graphene with one gold atom at top were calculated using the Full-Potential Augmented Plane Waves with Local Orbitals Method and the local density approximation (LDA), within the Density Functional Theory. For the calculations, we use a ...

Superconductor Science and Technology

We have investigated the damage induced by irradiation in Y 1 Ba 2 Cu 3 O 7−x silver added sample... more We have investigated the damage induced by irradiation in Y 1 Ba 2 Cu 3 O 7−x silver added samples. The samples were prepared with 0 and 6.5 wt% of silver and irradiated by high-energy γ irradiation (50-150 Mrad). The roles of silver and dosage irradiation are discussed in terms of their effects on microstructure, crystallinity, critical temperature (T c) and zero-resistance temperature (T 0). After irradiation, T c decreased while the room-temperature electrical resistance increased by a factor of 8 for some of the samples. The difference in T 0 between irradiated and non-irradiated YBCO samples was of the order of 10 K. We have found that the difference is bigger for silver-added samples. We have also observed several changes in diffraction patterns of YBCO and YBCO-silver samples. SEM images, EDS and XPS analysis showed that silver resided inside the grains as single atoms and as metallic clusters. The relative concentrations of the elements in samples were quantified by Auger electron spectroscopy. The J c values showed a gradual increase for radiation doses ranging between 0 and 100 Mrad. For doses up to 100 Mrad, J c decreased because of the weak-link breakage induced by high doses of γ rays.

In a recent paper, Bauer et al. [1] synthesized CePt3Si, a heavy fermion material with both trans... more In a recent paper, Bauer et al. [1] synthesized CePt3Si, a heavy fermion material with both transitions magnetic and superconducting, without inversion center in the crystal structure. This compound is very interesting from many points of view. In the present work, we report the analysis of the electronic structure of the CePt3Si in normal state. The calculation was performed with

MRS Proceedings, 1987

AbstactHydrogenated amorphous silicon (a-Si:H) is well known by its applications for solar energy... more AbstactHydrogenated amorphous silicon (a-Si:H) is well known by its applications for solar energy conversion devices in a large scale. Hydrogen has the capability of terminating the dangling bonds in the amorphous silicon structure and improves the optical properties for effective utilization of the solar spectrum. With this, the quantification of the hydrogen content in a-Si:H is an important task in its characterization.Auger electron spectroscopy induced by Ar+ ion bombardment (IAES) has been shown to be sensitive to the presence of hydrogen in a-Si:H [1,2]. The Si-L 2VV peak has a distinctively new shape as compared to electron- xcited. Auger were only some slight differences can be observed [3]. contribution to the IAES to that particular peak coming from de-excitations inside and outside the solid can be identified [4].In this work, IEAS of the Si-L23VV peak were obtained for a-Si:H prepared by glow discharge, grystalline silicon, and crystalline silicon implanted with silicon...

Superconductor Science and Technology, 1999

Thick polycrystalline films of silver doped YBCO were produced by the standard screen printing me... more Thick polycrystalline films of silver doped YBCO were produced by the standard screen printing method and irradiated with a source of electrons at 1000 kGy. The critical temperature 0953-2048/12/5/005/img8, the zero resistance temperature 0953-2048/12/5/005/img9, the broadening of the superconductor transition and normal resistance, measured at 298 K, changed substantially in the irradiated sample when compared to the non-irradiated specimen. A

International Journal of Modern Physics B, 2009

A set of AlN thin films was prepared by reactive magnetron sputtering at room temperature. The ef... more A set of AlN thin films was prepared by reactive magnetron sputtering at room temperature. The effect of oxygen impurities on the structural and optical properties of AlN films is discussed. The structural and optical properties were characterized using X-ray diffraction (XRD) and spectroscopic ellipsometry, respectively. Depending on the deposition conditions, films can grow hexagonal (würzite, P 63 m 3) or cubic (zinc-blende, Fm3m) in microstructure. From the optical measurements, the ellipsometric parameters (ψ, Δ) and the real refractive index as a function of energy were obtained. From the ellipsometric measurements, a model of Lorentz single-oscillator was employed to estimate the optical band gap, Eg. In the theoretical part, a calculation of density of states (DOS) and band structure was performed to be compared with the experimental results.

Journal of Superconductivity, 1999

We investigated the flux pinning behavior induced by gamma irradiation in Y1Ba2Cu3O(7-x) silver-a... more We investigated the flux pinning behavior induced by gamma irradiation in Y1Ba2Cu3O(7-x) silver-added samples. The superconductors were prepared through solid-state route and added with silver in amounts of 0-, 6.5-, and 20-wt%, following which the samples were irradiated by high-energy gamma irradiation (?) at doses of 0, 500, and 1500 kGy at the dosage rate of 8.2 kGy/h. We performed

Design and Applications of Nanomaterials for Sensors, 2014

Physical Review B, 2003

Calculation of the band structure, total and projected density of states, crystal orbital populat... more Calculation of the band structure, total and projected density of states, crystal orbital population analysis ͑COOP͒, and Mulliken population analysis were performed for the filled skutterudites YbFe 4 Sb 12 , UFe 4 P 12 , and ThFe 4 P 12. The calculated energy bands depict a semimetal behavior for YbFe 4 Sb 12 and UFe 4 P 12 , and metallic behavior for ThFe 4 P 12. Furthermore, the contributions from each orbital to the total DOS for each compound corroborate these findings. The bonding strength was derived from the COOP analysis between different pairs of atoms, considering nearest neighbor distances between 3.40 and 6.47 Å for YbFe 4 Sb 12 , 2.91 and 6.47 Å for UFe 4 P 12 , and 2.48 and 5.51 Å for ThFe 4 P 12. Mulliken population analysis suggests ionic behavior for these compounds.

Thin Solid Films, 1997

... Rev. B., 28 (1983) 116i. [8] C. Natarajan, PB Abel andR.W. Hoffman, Z Vac. Sci. Technol. A, 3... more ... Rev. B., 28 (1983) 116i. [8] C. Natarajan, PB Abel andR.W. Hoffman, Z Vac. Sci. Technol. A, 3 (1985) 1309. ... Sci., 331-333 (1995) 1050. [13]A. Duarte-Moller, L. Cota-Araiza, GA Hirata, L. Morales de la Garza, DH Galv~n and M. Avalos-Borja, AppI. Surf. ...