Alvin J. Drehman

Large pyroelectric response from reactively sputtered aluminum nitride thin films

We report the pyroelectric response of c-axis oriented, undoped, wurtzite, aluminum nitride reactively sputtered onto polished silicon wafers. The voltage between a metallic contact on the AlN surface and the n + -doped silicon substrate was monitored during pulsed infrared, radiant heating. From analysis of the data, a pyroelectric voltage coefficient, P v , in excess of 0.5 × 10 6 V/m/K was extracted for films in the 600 to 2500 A thickness range.

Optically driven microelectromechanical-system deformable mirror under high-frequency AC bias

A new, optically addressed deformable mirror device is demonstrated. The device consists of a pixellated metalized polymeric membrane mirror supported above an optically addressed photoconductive substrate. A conductive transparent ZnO layer is deposited on the back side of the substrate. A very high-frequency AC bias is applied between the membrane and the back electrode of the device. The membrane is deformed when the back of the device is illuminated because of impedance and bias redistribution between two cascaded impedances. We fabricated, demonstrated, and modeled the operation of this device.

Negative index metamaterial for selective angular separation of microwaves by polarization

Materials with simultaneously negative electric permittivity and magnetic permeability are referred to as left handed, and are also called backward wave and double negative media. The first experimental demonstration of such a metamaterial combined metallic split ring resonators with posts etched on opposite sides of dielectric boards. The boards are usually stacked in parallel planes with insulating spacers to form highly anisotropic prisms. We have demonstrated that this anisotropic. prism exhibits both positive and negative refractive indices and can split an incident beam into two components. The positive and negative indices are accessible by the choice of polarization of the electric field. Using an electric field parallel to the posts, negative refraction is observed. Rotating the electric fields 90/spl deg/ yields a positively refracted signal. Intermediate angles of polarization can achieve refraction in both negative and positive directions simultaneously, or the receiver polarization can be chosen to select either signal separately, The values of the positive and negative index and the wedge angle of the prism determine the separation angle of the output beams. This effect has potential application for a unique type of angular beam splitter.

Investigation Of Nucleation And Initial Stage Of Gan Growth By Atomic Force Microscopy And X-Ray Diffraction

The nucleation and initial stage of GaN growth on sapphire was investigated by atomic force microscopy, X-ray diffraction and photoluminescence. A 15 to 30 nm thick GaN buffer layer deposited at proper conditions was extremely smooth and nearly amorphous. Proper post deposition annealing resulted in the buffer crystallized. The buffer layer deposition temperature, thickness and annealing time and temperature must be coordinated. Low deposition temperature and/or insufficient annealing of the buffer results in a GaN wafer which has fine spiking surface morphology with an RMS of 3.4 nm for 1.4 μm wafer, strong yellow luminescence and wide xray rocking curve FWHM. High deposition temperature, longer crystallization time, and a low growth rate results in a wafer which exhibits strong band edge luminescence without noticeable yellow luminescence, and a narrow (002) diffraction rocking curve. However, the surface morphology exhibits well developed hexagonal feature with RMS roughness of 14.3 nm for a 570 nm thick layer. X-ray rocking curve analysis revealed buffer crystallization, domain coalescence and alignment process. The FWHM of the ω–scan of GaN (101) diffraction was 1700–2000 arc seconds for 200–1400 nm wafers which indicates that the twist of the domains is not changing much with the growth.

Heating of large-area substrates for in situ deposition of YBCO

We have developed a radiant technique for substrate heating which we found particularly useful for the in situ deposition of high temperature superconducting films. Using this technique, large area YBa/sub 2/Cu/sub 3/O/sub x/ films were deposited, using off-axis sputter deposition, onto lanthanum aluminate and sapphire substrates, the latter using an yttria-stabilized zirconia buffer layer. For both types of substrates we were able to obtain c-axis oriented films. The DC and microwave properties of the films deposited on lanthanum aluminate are presented along with the DC measurements of the films deposited on sapphire. The motivation for employing this method of heating are discussed, along with our current plans for scaling up the process to produce even larger area films.<<ETX>>

High throughput, large scale, broadband, plasmonic nanostructure fabrication for optical sensors

Plasmonics have the potential to enhance the performance of detectors. A thermal metal dewetting process was developed which can be easily scaled for high throughput production. Through this process, plasmonic nanostructures were fabricated providing broadband plasmon resonance tunable over a 1000 nm wavelength range. The plasmonic media and their integration into fluorescence-based sensors will be described.

Measured Polarization Response of Negative Index Metamaterial

Free space microwave measurements are reported of a split ring and post type metamaterial that exhibits negative index of refraction in a frequency band near 13.5 GHz. Varying azimuthal angles and magnitudes are achieved by changing the polarization of the transmitter and receiver relative to each other and to the anisotropic material. The amplitude of the cross-polarized transmission has been measured at 50% of the co-polarization level. This polarization conversion is a significant loss mechanism

Surface etching of YBCO films by xenon difluoride

We have demonstrated that xenon difluoride (XeF2) etches thin films of YBa2Cu3O7−x, the superconducting form of yttrium–barium–copper–oxide (YBCO), during dry etch processing. Both c-axis and mixed a∕c-axis YBCO films show evidence of such etching with a axis being more reactive. Profiles of YBCO films examined by ESCA show that the surfaces of both etched and unetched films are barium rich at the expense of yttrium. After XeF2 etching, fluorine was found to be present to a depth of at least 40nm. Despite the etching and the presence of fluorine in the YBCO films, the superconducting transition temperature, Tc, was unaffected by the XeF2 treatment.

Photoconductive optically driven deformable membrane for spatial light modulator applications utilizing GaAs and InP substrates

The fabrication and characterization of an optically addressable deformable mirror for spatial light modulator is described. Device operation utilizes an electrostatically driven pixellated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5-μm thick grid of patterned photoresist supports the 2-μm thick aluminized Mylar membrane. A conductive ZnO layer is placed on the backside of the GaAs wafer. Similar devices were also fabricated with InP. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage and frequency. A simplified analysis of device operation is also presented.

Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering

Using radio frequency (RF) diode sputtering of sintered stoichiometric (Eu,Y) 2 O 3 :7Ta 2 O5 ceramic targets, thin films (0.2–0.6 m) of Eu- and Y-polytantalates, and their solid solution Eu x Y 1-x Ta7O19 were deposited on fused silica, Si (100) and sapphire (001) substrates under various sputtering conditions. As-grown films were amorphous, and were crystallized by post-annealing in oxygen at 900 to 1000 °C. The influences of deposition gases (Ar and O 2 -partial pressure) substrate material, deposition time, substrate temperature, and post-annealing time and temperature on the structural, morphological and photo-luminescence (PL) properties of Eu 3+ -ions in the films have been studied and compared to properties of sintered (Eu,Y)Ta 7 O 19 ceramic and EuTa 7 O 19 single crystals.