Engineering topics

Jones, E. W.

Publications and source records attributed to Jones, E. W..

25 records · Page 2

NASA NTRS1992

Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

Lin, T. L.↗

NASA NTRS1991

Second harmonic conversion in cubic silicon carbide at 1.06 micron

This letter describes second harmonic conversion in cubic silicon carbide (beta-SiC) at a wavelength of 1.06 micron. Epitaxial layers of beta-SiC formed by vapor phase growth on silicon are indeed birefringent, and thus phase matchable. Phase-matched films of beta-SiC have respectable conversion efficiencies even in the presence of adsorption at 532 nm. The measured value of the effective second order nonlinear susceptibility for beta-SiC is chi super (2) eff = 1.05 +/- 0.3 x 10 exp -9 esu.

Harris, G. L.↗

NASA NTRS1991

Advanced Si IR detectors using molecular beam epitaxy

SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

Lin, T. L.↗

NASA NTRS1981

The design of a mechanical referencing system for the rear drum of the Longwall Shearer Coal Miner

The design of two systems which reference the position of a longwall shearer coal miner to the mine roof of the present cut and of the last cut are presented. This system is part of an automation system that will guide the rear cutting drum in such a manner that the total depth of cut remains constant even though the front drum may be following an undulating roof profile. The rear drum referencing mechanism continually monitors the distance from the mine roof to the floor for the present cut. This system provides a signal to control a constant depth of cut. The last cut follower mechanism continually monitors the distance from the mine roof of the prior cut to the cutting drum. This latter system provides a signal to minimize the step height in the roof between cuts. The dynamic response of this hydraulic-pneumatic and mechanical system is analyzed to determine accumulator size and precharge pressure.

Jones, E. W.↗

NASA NTRS1979

Coal-rock interface detector

A coal-rock interface detector is presented which employs a radioactive source and radiation sensor. The source and sensor are separately and independently suspended and positioned against a mine surface of hydraulic pistons, which are biased from an air cushioned source of pressurized hydraulic fluid.

Rose, S. D.↗

NASA NTRS1979

Improved nucleonic coal-thickness monitor

Design for coal-thickness-sensing instrument features independent hydropneumatic suspension of radiation source and detector. Monitor uses source and detector which are independently mounted, to follow contour of coal surface more closely and to eliminate errors caused by variations in airgap along radiation path. Device may help to bring fully-automated coal mining closer to reality.

Crouch, C. E.↗

NASA NTRS1977

Nucleonic coal detector with independent, hydropneumatic suspension

The design of a nucleonic, coal interface detector which measures the depth of coal on the roof and floor of a coal mine is presented. The nucleonic source and the nucleonic detector are on independent hydropneumatic suspensions to reduce the measurement errors due to air gap.

Jones, E. W.↗