Surface structure investigations using noncontact atomic force microscopy

Surfaces of several A_IIIB_V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination.     

The influence of temperature on superplasticity of Zn-Al-Cd alloy

Experimental results of the study of superplastic behaviour in Zn-0·35 wt. % Al-0·25 wt. % Cd alloy are presented. The attention has been paid to the influence of temperature on stress-strain curves, ductility, strain rate sensitivy parameterm and activation energy of superplastic flow. The best superplastic properties have been established at temperatures T370 K (0·53 T_m): ductilityA=600% and parameterm=0·56. A fast grain growth observed at temperaturesT 380 K has been suggested to be responsible both for the decrease in ductility and parameterm values and for the origin of an anomaly in the decreasing temperature dependence of flow stress. The measurements of activation energy have shown an expected decrease in activation energy at the transition from the non-superplastic region at lower temperatures to the superplastic region at higher temperatures. Significant transient effects after strain rate changes have been observed. The experimental results obtained in the Zn-Al-Cd alloy have been compared with those obtained in binary Zn-1·1 wt. % Al alloy and discussed from the point of view of possible models of structural superplasticity.     

Quantification of copper and zinc species fractions in legume seeds extracts by SEC/ICP-MS: validation and uncertainty estimation

Fractions of Cu and Zn species in legume samples (common white bean, pea, chick pea and lentil seeds and defatted soybean flour) were analysed by on-line hyphenation of size exclusion chromatography and inductively coupled plasma-mass spectrometry. Samples were extracted by 0.02 mol l⁻¹ Tris–HCl buffer solution, pH 7.5. The extraction efficiency lay in the region 60–90 and 60–80% for Cu and Zn, respectively. Quantification of elements in the individual chromatographic fractions was carried out by isotope dilution (ID) and external calibration (EC) techniques. For ID analysis the chromatographic effluent was mixed with the flow of ⁶⁵Cu and ⁶⁸Zn isotope enriched solution and the isotope ratio values ⁶³Cu/⁶⁵Cu and (⁶⁴Zn+⁶⁶Zn)/⁶⁸Zn were measured. In the case of EC technique calibration solutions of elements were injected to the flow of mobile phase by the second injector. Prior entering detector the effluent was mixed with the flow of internal standard solution (In, 50 μg l⁻¹). Both methods have similar precision, however the behaviour of both studied elements was not the same. The chromatographic analysis itself was the main source of variability in the case of Cu. For Zn species analysis, the extraction process and the manipulation with the extract, played the significant role too. It was probably caused by lower stability of the present zinc chelates. The total amounts of Zn found in all chromatographic fractions represented 85–95% of Zn in sampled extract whereas those of Cu approached 100%. In case of small peaks the results of ID and EC were not the same. The EC results were lower then ID results. The great deal of results uncertainty accounts for the precision.     

Comparison of zirconia- and silica-based reversed stationary phases for separation of enkephalins

In this study, the separation of biologically active peptides on two zirconia-based phases, polybutadiene (PBD)-ZrO2 and polystyrene (PS)-ZrO2, and a silica-based phase C18 was compared. Basic differences in interactions on both types of phases led to quite different selectivity. The retention characteristics were investigated in detail using a variety of organic modifiers, buffers, and temperatures. These parameters affected retention, separation efficiency, resolution and symmetry of peaks. Separation systems consisting of Discovery PBD-Zr column and mobile phase composed of a mixture of acetonitrile and phosphate buffer, pH 2.0 (45:55, v/v) at 70 degrees C and Discovery PS-Zr with acetonitrile and phosphate buffer, pH 3.5 in the same (v/v) ratio at 40 degrees C were suitable for a good resolution of enkephalin related peptides. Mobile phase composed of acetonitrile and phosphate buffer, pH 5.0 (22:78, v/v) was appropriate for separation of enkephalins on Supelcosil C18 stationary phase.     

ICP-MS determination of heavy metals in submerged cultures of wood-rotting fungi

Accumulation of five heavy metal ions by five species of wood-rotting basidiomycetes during a 9-day cultivation was studied. Contents of Cd, Cu, Pb, and Zn were measured using ICP-MS; the amount of mercury was determined directly in solid samples using the Advanced Mercury Analyser. A standard operation procedure for the sample preparation and determination of metal content was developed and validated. Presence of Cd, Cu, Hg, and Pb decreased the accumulation of zinc by the fungi. The basidiomycete Pycnoporus cinnabarinus exhibited the highest metal binding capacity of all fungi tested.     

Thermal properties of hydrated lanthanum and yttrium polyvanadates

The study of thermal properties of La(HV₆O₁₆)₃.19.5H₂O and Y(HV₆O₁₆)₃.22H₂O showed, that the dehydration of both compounds is discontinuous. After release of last water amount, the parent structure is destabilized and products of thermal decomposition, V₂O₅ and corresponding orthovanadates, start to be formed. The decomposition of La(HV₆O₁₆)₃.19.5H₂O results in formation of V₂O₅ and LaVO₄, the temperatures of crystallization of which differ. The decomposition products of yttrium salt crystallize simultaneously. All compounds formed melt at 685°C. By crystallization of the melt, the mixtures V₂O₅-LaVO₄ and V₂O₅-YVO₄, respectively, are formed which are stable up to 1000°C.     

Preparation and dilute solution properties of model gemini nonionic surfactants

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (Cn-2H2n-3CHCH2O(CH2CH2O)mH)2(CH2)6 (or GemnEm), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n = 12, 14, and 20 and m = 5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100 degrees C. Surfactants with small m (i.e., n = 12, 14, m = 5 and n = 20, m = 10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10(-7) to 10(-6) M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.     

A study of the relative reactivity of maleic anhydride and some maleimides in free radical copolymerization and terpolymerization

Composition data for the free radical copolymerization of maleic anhydride with N-phenylmaleimide in toluene at 60°C have been obtained. Relative reactivity ratios in terminal and penultimate models using nonlinear least-squares optimization routine have been determined. The standard error was found to be somewhat smaller in the penultimate model, but is still larger than the uncertainty estimated for the copolymer composition. Terpolymers of maleic anhydride and styrene with maleimide, N-butylmaleimide, N-phenylmaleimide, and N-carbamylmaleimide were obtained. On the basis of analysis of the product composition at various monomer feeds the relative reactivity of maleic anhydride and maleimides in these reactions is compared and the influence of the structure of thesemonomers on the rate of some chain growth reactions is discussed.     

Low temperature InSb(0 0 1) surface structure studied by scanning tunneling microscopy

InSb(0 0 1) surface prepared by ion sputtering and thermal annealing has been studied in the temperature range from 77 K up to 300 K using scanning tunneling microscopy (STM). At 300 K the surface is c(8 × 2) reconstructed as indicated by low energy electron diffraction and STM images, and its structure appears to be consistent with the “ζ-model” recently proposed for this surface. Upon lowering of the temperature below 180 K a new phase appears on the surface. This phase is characterized by the surface structure period doubling along [1 1 0], lowering the surface symmetry from c2mm to p2, and appearance of structural domains. Possible origins of the new phase are discussed.