R. H. Hopkins's research while affiliated with Northrop Grumman and other places

... Recently some progress has been made in sulfides, selenides and oxides which are very useful in optical, electronic and energy storage industries. Some progress has been made in chalcogenides and chalcopyrites [1][2] which have shown applications in laser developments and hyperspectral imagers and multinary oxides [3][4][5] for dielectric energy storage and insulation layers. With evolution of nano scale structures, some of the materials properties have evolved which are dependent on morphologies. ...

... The maximum attainable resistivity in undoped Sic crystals is limited principally by residual nitrogen and boron in the growth environment. Reduction of boron content in Sic is particularly difficult since it exhibits a transfer coefficient of near unity [38]. The extent to which these impurities dominate the electrical behavior of the undoped Sic crystals grown by PVT is largely a function of the purity of the source materials and the cleanliness of the growth system. ...

... Systematic observations of screw dislocation (micropipe) formation processes using a variety of techniques thus suggest, in agreement with earlier reports [85,89,[115][116][117], that a possible mechanism for nucleation of micropipes in SiC involves the incorporation of inclusions into the crystal lattice. In the case of small isolated inclusions, it is found that the screw dislocations (micropipes) nucleate in pairs. ...

... In this technique, growth proceeds (usually along the c-axis) by vapor transport of C-and Si-bearing species from the source or carbon species from the graphite walls. For a typical 6H-and 4H-SiC bulk sublimation growth process, the SiC source temperature is 2100-2400°C ( Barrett et al. 1992), growth pressure is less than 20 Torr, and the temperature gradient between source and seed ranges from 20-35°C/cm. Typical growth rates for the bulk growth of SiC are in the range of 0.5-5 mm/hr. ...

... According to previous studies, defects in semiconductors can cause an increase in the surface electric field and tunneling electric field, which leads to the enhancement of the tunneling effect and barrier-lowering effect and finally causes an increase in the tunneling current [23,[26][27][28][29][30][31]. However, the increase in the leakage current is small after proton irradiation, especially in the high-voltage region, which may be due to the small change in the barrier height derived from the experimental results and the injection annealing effect of the proton irradiation of SiC [32,33]. The change of the on-resistance could be caused by the change in the carrier concentration. ...

... The Burgers vector in the micropipe was found to have a height of at least four to 12 unit cells (18 nm) to stabilize a hollow core dislocation. 14,16 More recent work on the growth of ZnO nanotubes likewise demonstrated the role of screw dislocations, but the measured effective Burgers vectors were three to four times higher than the magnitude of c-vectors. 17 There is another interesting consequence associated with the presence of screw dislocations during crystal growth. ...

... We bring our interest on a recently synthesized class of crystals for having superior properties in AO devices. The mercurous halide crystals [21][22][23][24][25][26] , such as Hg2Cl2 (i.e. Calomel), Hg2Br2 and Hg2I2 are highly anisotropic with a high AO figure of merit thanks to a high photoelastic constant and slow acoustic velocity. ...

... Lan et al. [21][22][23] developed a transparent furnace for crystal growth and flow visualization of sodium nitrate. Later, Batur et al. [24,25] implemented control schemes that relied upon the direct observation of the melt-crystal interface with a video camera and real-time imaging software. Since then, transparent furnaces have been employed in many studies [26][27][28][29][30]. Advances, including resistively heated, gold-coated quartz liners surrounded by a vacuum-insulated outer shell, have pushed the upper limit of transparent furnaces to approximately 1,200°C [31,32], which is high enough for the growth of some scintillator crystals [33][34][35]. ...

... The IMC molecules are useful for solvation dynamics [11], nonlinear optical properties [12], laser applications [13] as well as for fluorescence probes [14,15]. Beside these, the binary organic intermolecular compounds are known for their promising properties such as light emitting diodes of variable colors including white light, nonlinear optical (NLO), optoelectronics and conducting materials [16][17][18]. ...

... The proper choice of the SiC powder source during PVT growth is a prerequisite to achieve a high crystalline quality in the final SiC boule. In the literature, a number of factors that impact the growth process, like stoichiometry, purity, polytype, size distribution and related packaging density, have been discussed [2][3][4][5][6][7][8]. In principle, the ideal SiC source undergoes a minor morphological change during growth. ...