E. Silberman

A study of the homogeneity and deviations from stoichiometry in mercuric iodide

We have been able to determine the deviations from stoichiometry of mercuric iodide (HgI 2 ) by using differential scanning calorimetry (DSC). Mercury excess or iodine deficiency in mercuric iodide can be evaluated from the eutectic melting of α-Hgl 2 -Hg 2 I 2 at 235 °C, which appears as an additional peak in DSC thermograms. I 2 excess can be found from the existence of the I 2 -α-HgI 2 eutectic melting at 103°C. An additional DSC peak appears in some samples around 112°C, that could be explained by the presence of iodine inclusions. Using resonance fluorescence spectroscopy (RFS) we have been able to determine the presence of free I 2 that is released by samples during the heating at 120 °C (crystal growth temperature), thus giving additional support to the above DSC results.

Atomic force microscopy of lead iodide crystal surfaces

Abstract Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

Photoluminescence of vapor and solution grown ZnTe single crystals

Abstract ZnTe single crystals grown by horizontal physical vapor transport (PVT) and by vertical traveling heater method (THM) from a Te solution were characterized by photoluminescence (PL) at 10.6 K and by atomic force microscopy (AFM). Copper was identified by PL as a major impurity existing in both crystals, forming a substitutional acceptor, Cu Zn . The THM ZnTe crystals were found to contain more Cu impurity than the PVT ZnTe crystals. The formation of Cu Zn -V Te complexes and the effects of annealing, oxygen contamination and intentional Cu doping were also studied. Finally, the surface morphology analyzed by AFM was correlated to the PL results.

A review of recent measurements of optical and thermal properties of α-mercuric iodide

Abstract The band gap energy of α-mercuric iodide was measured recently at elevated temperatures using optical absorption and reflection methods. In addition, reflection spectral measurements indicate that the temperature dependence of the exciton peak can provide a means of measuring, in a nondisturbing and remote manner, the local surface temperature of an α-mercuric iodide crystal during its growth from the vapor. Recent measurements of the thermal diffusivity and thermal expansion tensors have confirmed the anisotropy of this material and have implications for growth morphology and the generation of lattice defects.

The possible crossover effects of NaNO3 confined in porous media: From bulk to clusters

Differential scanning calorimetry (DSC) and Raman spectra are reported for NaNO3 bulk and for NaNO3 confined in porous silica with pore radii, rp=2.5, 5, 10, 20 nm. Raman spectra are also given for a 6 M solution of NaNO3. The melting transition for the confined NaNO3 exhibits a 1/rp dependence where rp is the pore radius for rp≳5 nm. No melting transition is observed for NaNO3 confined in 2.5 nm pores. Above this pore size, their appears to be a deviation in the melting transition dependence on rp. The internal modes observed in the Raman spectra for the confined material are in agreement with those of the bulk solid except for a feature observed on the low frequency side of the ν1 band. The external TO mode observed at 100 cm−1 and the librational mode at 175 cm−1 for NaNO3 both decrease in intensity and broaden as rp decreases and both bands disappear at rp=2.5 nm. An additional peak at 70 cm−1 not observed in the solution or bulk NaNO3 spectra appears in the spectra of confined NaNO3 and increases in ...

Thermal diffusivity of α‐mercuric iodide

The thermal diffusivity and its anisotropy have been measured for α‐HgI2 single crystals using the flash pulse method. The results show that α[100]=3.70×10−3 cm2s−1±3% and α[001] =1.03×10−3 cm2s−1±10%. The analysis contains the necessary corrections for heat losses and finite pulse duration.

Surface morphology study on CdZnTe single crystals by atomic force microscopy

The study of the crystal surface morphology of CdZnTe is important for the understanding of the fundamentals of crystal growth in order to improve the crystal quality which is essential in applications such as substrates for epitaxy or performance of devices, i.e., room temperature nuclear spectrometers. We present here a first atomic force microscopy study on CdZnTe. Cleaved (110) surfaces were imaged in the ambient and an atomic layer step structure was revealed. The effects of thermal annealing on the atomic steps together with Te precipitation along these steps are discussed in terms of deformation due to stress relief and the diffusion of tellurium precipitates.

Micromorphology study of mercuric iodide crystals by atomic force microscopy

Atomic force microscopy was used to study the surfaces of mercuric iodide crystals at ambient. Various surface conditions were examined, including as‐grown (001), (110), and (013) faces, and cleaved, chemically etched, vacuum etched, and aged (001) surfaces. As‐grown (001) faces show a terraced structure and are smoother than as‐grown (110) faces. Freshly cleaved surfaces exhibit a terraced structure, with riser heights corresponding to multiples of the c‐lattice constant. All surfaces become progressively pitted and rougher by vacuum treatment or chemical etching. Defects identified as pits or hillocks with dimensions of the order of 100 nanometers were also observed, and surface roughness values were obtained for quantitative characterization of the various treatments.

Symmetry lowering due to site-occupation disorder in vibrational spectra of gehlenite, Ca2(AlSi)AlO7

Abstract Raman scattering and i.r. reflectance spectra of a gehlenite crystal, Ca 2 (AlSi)AlO 7 , have been measured. The data clearly indicate a lowering of the crystal symmetry from D 2d to S 4 due to occupation disorder in one of the C 3 sites, which statistically accommodates either a Si or an Al ion. Forty out of the 51 theoretically expected Raman active bonds, and 21 out of 35 expected i.r. bands have been resolved and assigned.

Purification of selenium by zone refining

We studied the purification of Se using zone refining, with emphasis on the efficiency of this technique in removing the Cu impurity, which is known to be related to a trapping center in CdSe. After 78 passes it was found that Cu accumulates at one end section of the ingot, while at the opposite end the level was below the detection limit of the atomic absorption spectroscopic analysis employed. Infrared spectroscopic data, differential solubility and differential scanning calorimetry measurements also indicate that the effective distribution coefficient, k, for the Cu solute, is less than 1. A model for the various phases present during zone melting is presented and the possibility of segregating impurities having k>1 is discussed.