Tariq Manzur

Site selectivity in Fe doped β phase NiAl

We have investigated site selectivity in iron doped β phase ternary alloys of the composition NixFeyAl(100−x−y), where the Ni concentration is within a few at. % of stoichiometry. Experimental techniques used include extended x‐ray absorption edge fine structure and Mossbauer measurements. The transition metal atoms in excess of 50 at. %, which occupy sites with transition metal nearest neighbors, are not chosen randomly among Ni and Fe, but are exclusively Fe, to within the accuracy of the measurements. This result requires a re‐analysis of previous magnetic susceptibility measurements on this system, which as re‐analyzed here imply more reasonable moment values for the Fe dopants. Our findings regarding Fe site selectivity are of significance in regards to recent studies showing a ductilization effect of Fe dopants microalloyed into Ni50Al50.

Potential role of high-power laser diode in manufacturing

We present examples of manufacturing applications like solid freeform fabrication by sintering metal/ceramic powders, and drilling using semiconductor laser diodes. From the stand point of energy requirements, these demonstration indicates that many other laser manufacturing functions like cutting, soldering, marking, printing, etc. can be carried out by currently available commercial laser diodes. Most of these applications are currently being done by the inefficient and bulky lasers like CO2, Nd:YAG and Excimer. These are 30 years matured technologies and still costs over

Optical response of laser-doped silicon carbide for an uncooled midwave infrared detector.

DOL150/Watt. We believe the price of semiconductor laser diode chips, like computer chips, will come down rapidly, as volume market opens up, from

Nitrogen location in R2Fe17 compounds: an NMR study

DOL300/Watts today to less than

Active layer design and power calculation of nitride-based THz quantum cascade lasers

DOL10/Watt in 5 years. The paper begins with some market survey indicating economic opportunities for high power diode companies.

Active layer design of THz GaN quantum cascade lasers

An uncooled mid-wave infrared (MWIR) detector is developed by doping an n-type 4H-SiC with Ga using a laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide and a wide bandgap semiconductor. The dopant creates an energy level of 0.30  eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21  μm. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refractive index, and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam, such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless detector. The variation of refractive index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refractive index of the doped sample, indicating that the detector is suitable for applications at the 4.21  μm wavelength.

NMR study of Y2Fe17 nitrides

Abstract 14 N, 89 Y and 1 H spin-echo NMR experiments have been carried out in order to study the nitrogen location in the R 2 Fe 17 lattice with R = Gd, Lu and Y. The observed 14 N spectrum for the Gd-compound indicates that essentially all of the N atoms occupy the octahedral interstitial sites. However, the ‘two-peak’ 14 N spectra for the Y-compounds and, to a lesser degree the Lu-compound, indicate that some of the N atoms enter the tetrahedral interstitial sites in addition to the octahedral sites. A consideration of both 14 N and 89 Y spectra indicates that the probability for a N atom to enter a tetrahedral site in the Y 2 Fe 17 lattice is much smaller than that for octahedral site occupation. This study reveals that the local structure of Y 2 Fe 17 N x may change with the nitrogenation conditions.

Near-marine boundary layer atmospheric and turbulence measurement and modeling

Room temperature III-nitride QCL THz is reported. With increasing carrier concentration, the peak in optical shifts towards higher energies. Peak in the optical gain increases with carrier concentration demonstrating a blue shift correlated to quantum confinement. THz power increases linearly with current demonstrating an output power of 0.4448 μW at 6THz. A higher THz power is obtained in AlxGa1-xN/GaN/AlxGa1-x heterostructures as compared to heterostructures incorporating In. An increase in the Al-mole fraction results in higher THz power.

Microstructure of Nb/sub 3/ (AlSiB) supercondcuting tapes with extremely high critical current densities

The structural, material and field dependence of the THz lasing frequency is reported for a QCL based upon GaN/AlGaN heterostructures. The inter-subband transition initiated generation of THz followed by the LO-phonon assisted fast depopulation takes into account the appropriate energy band alignments. Valence and conduction band alignments incorporating spin-orbit and crystal field splitting as well as bi-axial strain are used to determine the conduction band offset as a function of Al-mole fraction. Determination of eigen states takes into account the spontaneous and piezoelectric polarization induced modification in the conduction band profile. A lower THz generation frequency is predicted for Ga-face GaN/AlGaN-based QCLs using the revised energy band alignments.

Continuous Al5 Nb3Ge superconducting tapes via the amorphous state

14 N, 57 Fe and 89 Y spin-echo NMR experiments have been carried out in Y 2 Fe 17 N x , 0 < x < 2.8. It is found that the N distribution in the octahedral sites is not random, and a preferred nitrided (with Y-2N configuration)/unnitrided configuration is present. The change in the Fe hyperfine field distribution with N content provides evidence that lattice expansion plays a major role in the Fe moment enhancement upon nitrogenation