The Synthesis and Crystal Structure of Hg3TeI4

The structure of cubic Hg₃TeI₄ was determined from powder data. The four positions of the cubic closestpacking of the anions are statistically occupied by 0.8 Te-atoms and 3.2 I-atoms. The two types of tetrahedral holes are occupied to the extent of 2/4 and 0.4/4, respectively, by Hg-atoms. With an ordered model of lower symmetry, the stoichiometric composition can be explained and a homogeneous charge distribution can be achieved. The ordered model contains regions of the structure of red HgI₂, which are connected by fragments of the SiS₂-type.     

Study of liquid crystal space groups using controlled tilting with cryogenic transmission electron microscopy

We developed a method that enables differentiation between liquid crystalline-phase particles corresponding to different space groups. It consists of controlled tilting of the specimen to observe different orientations of the same particle using cryogenic transmission electron microscopy. This leads to the visualization of lattice planes (or reflections) that are present for a given structure and absent for the other one(s) and that give information on liquid crystalline structures and their space groups. In particular, we show that we can unambiguously distinguish among particles having the inverted micellar cubic (space group Fd(3)m, 227), the inverted bicontinuous gyroid (space group Ia(3)d, 230), the inverted bicontinuous diamond (space group Pn(3)m, 224), and the inverted bicontinuous primitive cubic structure (space group Im(3)m, 229).     

Methanol – die Basischemikalie

Today methanol is produced from synthesis gas derived from coal and natural gas. However carbon dioxide and hydrogen obtained from water electrolysis with renewable energy have the potential to play a leading role as fuel, energy raw material and chemical feedstock. As a liquid energy storage system it can be used to easily transport electric power conserved in chemical bonds with unparalleled efficiency. Homologisation making use of the Mobil zeolite processes (MTG, MTO, MTA) for instance, or via the methanol derived platform chemicals methyl formate and dimethyl ether, the majority of organic chemicals established in chemical industry is available. Through its diverse of applications methanol has the potential to substitute crude oil and natural gas as the leading feedstock for organic chemicals.     

Transient behavior of Hg1−xCdxTe film growth on 3° off-(100) CdTe substrates by chemical vapor transport

The effects of substrate misorientation on Hg_1−xCd_xTe films, deposited on 3° off-(100) CdTe substrates by chemical vapor transport (CVT), have been studied for the first time using a transient growth technique. The morphological evolution of Hg_1−xCd_xTe films deposited on the vicinal CdTe substrates at 545°C shows a transition from three-dimensional islands to two-dimensional layer growth. The time and thickness required for the above morphological transition is about 0.75 h and 7 μm, respectively, under present experimental conditions. The pronounced long-range-terrace surface morphology of the Hg_1−xCd_xTe films illustrates the strong effects of the misorientation of the CdTe substrates and of the growth kinetics on the CVT growth of this hetero-epitaxial system. The transient behavior of the surface morphology, of the surface composition, and of the growth rate all reveal the influences of the 3° misorientation of the (100) CdTe substrates on the Hg_1−xCd_xTe epitaxy. The experimental mass flux results of the Hg_1−xCd_xTe-HgI₂ CVT system under transient and steady-state conditions can be related to the surface kinetics and to the thermodynamic properties of the system. The combined results show that the interface kinetics are not fixed in the transient regime and that they are coupled to the vapor mass transport.     

Electron properties in GaAs for the design of MM-wave IMPATTs

A very staightforward method has been developed to apply space-charge resistance measurements for determining the high-field drift velocity of electrons in GaAs. The breakdown voltages of the single-drift flat-profile IMPATT diodes used in these measurements justify the validity of well known ionization rates for still higher electric fields.     

Phase studies of the Cd-Fe-Se system in the Cd-rich region

The cadmium-rich region of the semi-magnetic semiconductor Cd-Fe-Se phase diagram has been partially determined, for the first time, by x-ray diffraction techniques and by metallurgical microscopy. The maximum solid solubility of iron in CdSe, employing annealing techniques, has been found in this work to be about 19 at. % at 925°C, while the solid solubility limit is generally discussed to be about 12 at %. The CdFeSe system appears to be a pseudo-binary one. Further considerations about the structure of this system are discussed.     

Fast growth of Cd1−xZnxTe single crystals by physical vapor transport

Good quality single crystals of Cd_1−xZn_xTe (x=0.04, 0.08, and 0.115) were obtained by the very fast vapor growth technique developed in this laboratory. The abundance of lamellar twins seems to be less than that in CdTe grown under the same conditions. Chemical etching results indicate a similar quality of the vapor grown crystals to those obtained from melt growth. The overall compositions of the crystals are uniform and approach those of the initial source material with increasing amount transported.