Search Results - (Author, Cooperation:M. T. Reiten)

2013-05-21

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

We present studies using a dc magnetron in an on-axis configuration to sputter Bi-Sr-Ca-Cu-O films from a composite target. These studies show that bismuth can be preferentially resputtered. The influence of ozone, molecular oxygen, and total pressure on the resputtering of bismuth is investigated and discussed. Ozone, in low concentrations, can dramatically affect the degree of resputtering. By comparing the effects of molecular oxygen and ozone, some insight is gained regarding the possible mechanisms of negative ion formation in the magnetron environment. Based on our results we suggest that molecular oxygen can bring about resputtering primarily by forming O+2, which collides with the target to produce energetic negative oxygen ions. In contrast, ozone may form negative ions by electron impact in the dark space above the target, giving rise to lower-energy negative ions, which can traverse the plasma unneutralized and can be stopped with an applied bias on the sample block. With no added oxidant, negative oxygen ions from the target oxygen may dominate the background resputtering. Similarity is found between our results and those for similar studies on Y-Ba-Cu-O by other workers. Bismuth in Bi-Sr-Ca-Cu-O behaves as barium in Y-Ba-Cu-O with regards to preferential resputtering; furthermore, the response of strontium, calcium, and copper to oxygen in sputtered Bi-Sr-Ca-Cu-O is similar to what is observed for copper in Y-Ba-Cu-O.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A bistatic terahertz impulse ranging system has permitted the full isolation and direct measurements of the surface wave loss and dispersion for terahertz frequencies on a dielectric cylinder. This system permits ranging investigations with variable bistatic angles between the source and detector. Direct, frequency dependent comparisons of surface wave loss and propagation velocity are compared to Mie theory and previous measurements of surface wave propagation over a 1 THz bandwidth. The observed radiation from the surface waves is seen to depend on the path of the radiation in and along the scatterer. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Using a well characterized terahertz (THz) impulse ranging system we demonstrate broad bandwidth imaging at THz frequencies using an inverse synthetic aperture deconvolution technique. The system demonstrates millimeter and submillimeter resolutions along the cross range and range axes, respectively. The range resolution, determined by the THz pulse bandwidth is 0.12 mm, while the cross range resolution is 1.2 mm; both resolutions agree well with theoretical predictions. Through imaging of cylindrical targets we demonstrate quantitative measurement of target position in the image plane within the experimental error of 0.2 mm. Imaging of geometrically scaled complex targets is demonstrated for a 1:2400 scale model ship (1 mm=24 m) corresponding to a full scale frequency bandwidth of 83–625 MHz at a distance of 840 m. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

An interferometer for broadband single-cycle THz pulses is developed based on the Michelson configuration. Total internal reflection of THz pulses in high-resistivity silicon prisms provides a nearly 180° phase shift of one arm relative to the other to achieve destructive interference. We show that due to automatic compensation for laser fluctuations by the interferometer, it is possible to measure the index and absorption of thin-film samples with more accuracy than is achievable with standard THz time-domain spectroscopy. We demonstrate characterization of the complex index of refraction of 2 μm thick Mylar (polyester) films. By measuring the signal amplitude directly in the time domain, the interferometer can be used for rapid measurements of film thickness with a resolution of better than 1 μm. © 2001 American Institute of Physics.

Electronic Resource