[A triple system water-urea-L-alpha-alanine. Thermodynamic properties and intermolecular interactions].

The heat of the dissolving of L-alpha-alanine at 293, 298, 306, and 318K in aqueous solutions of urea in the concentration range 0-7 mol urea/kg water has been determined by the microcalorimetric method. It was found that the heat of the dissolving of the amino acid linearly depends on the square root of the molality of the urea solution. It was shown that the enthalpy and entropy of the transfer of L-alpha-alanine from water into an aqueous solution of urea do not depend on temperature, and the heat capacity of transfer is equal to zero. An almost complete enthalpy-entropy compensation was noted. It was shown that the parameter characterizing the changes in the effective Gibbs energy of the dissolving of L-alpha-alanine in water and aqueous urea solutions has negative values due to the dominant entropy component. The system water-urea-L-alpha-alanine becomes less structured with increasing temperature and more structured as the urea concentration increases.

[Effects of hydrophilic and hydrophobic hydration in tetramethylbisurea and N,N'-dimethylpropyleneurea solutions].

The thermal effects of dissolving tetramethylbisurea in water at 298-318 K and N,N'-dimethylpropyleneurea at 293-313 K have been measured. It was shown that the standard heat of dissolution of tetramethylbisurea at 298 K was 3.58 +/- 0.04 kJ/mol, and that of N,N'-dimethylpropyleneurea was 22.8 +/- 0.01 kJ/mol. The standard heat capacities of urea derivatives at 298 K differed insignificantly: 167 +/- 10 J/(mol x K) and 149 +/- 5 J/(mol x K) for tetramethylbisurea and N,N'-dimethylpropyleneurea, respectively, indicating the moderately hydrophobic character of hydration of these compounds. It was found that, at temperatures close to the temperature of maximum density of water (277 K), the temperature dependence of Gibbs energy for tetramethylbisurea goes through the maximum.

Novel method of flat cold cathode formation from carbon-nitrogen nanofibers.

A novel method of high-efficiency cold cathode formation is developed. The technique is based on the growth of nitrogenated carbon nanofibers in a high-pressure apparatus on a graphite substrate. An average nitrogen concentration up to 13% was achieved. The turn-on and threshold fields for such cathodes are substantially lower than those for cathodes based on other carbon materials. A special method of substrate preparation provides strong adhesion of carbon-nitrogen nanomaterial and its durability during long-term cathode operation. It is shown that due to high uniformity, emission efficiency and time reliability, the field emission cathodes based on carbon-nitrogen nanofibers (CNNs) are very promising for high-brightness flat indicators and displays.

Synthesis of carbon-nitrogen nanostructures by hot isostatic pressure apparatus and their field emission properties.

Carbon-nitrogen (CN) nanofibers were synthesized in argon-nitrogen gas mixture at 75 MPa by high isostatic pressure (HIP) apparatus using a graphite resistive heater. The CN nanofibers were grown in random with the diameter of about 200 nm and the length over 5 microm. The structures obtained can be divided bamboo-like, spring-like, and bead necklace-like CN nanofibers. The nitrogen content of up to 8.4% was found in CN nanofibers by EELS analysis. Field emission results showed that the density of field emitters and the field enhancement factors changed by surface treatments and that CN nanofibers contained glass frit. The screen-printed CN nanofiber had a turn-on field of 2 V/microm.

3D spectrum imaging of multi-wall carbon nanotube coupled pi-surface modes utilising electron energy-loss spectra acquired using a STEM/Enfina system.

Numerous studies have utilised electron energy-loss (EEL) spectra acquired in the plasmon (2-10 eV) regime in order to probe delocalised pi-electronic states of multi-wall carbon nanotubes (MWCNTs). Interpretation of electron energy loss (EEL) spectra of MWCNTs in the 2-10 eV regime. Carbon (accepted for publication); Blank et al. J. Appl. Phys. 91 (2002) 1657). In the present contribution, EEL spectra were acquired from a 2D raster defined on a bottle-shaped MWCNT, using a Gatan UHV Enfina system attached to a dedicated scanning transmission electron microscope (STEM). The technique utilised to isolate and sequentially filter each of the volume and surface resonances is described in detail. Utilising a scale for the intensity of a filtered mode enables one to 'see' the distribution of each resonance in the raster. This enables striking 3D resonance-filtered spectrum images (SIs) of pi-collective modes to be observed. Red-shift of the lower energy split pi-surface resonance provides explicit evidence of pi-surface mode coupling predicted for thin graphitic films (Lucas et al. Phys. Rev. B 49 (1994) 2888). Resonance-filtered SIs are also compared to non-filtered SIs with suppressed surface contributions, acquired utilising a displaced collector aperture. The present filtering technique is seen to isolate surface contributions more effectively, and without the significant loss of statistics, associated with the displaced collector aperture mode. Isolation of collective modes utilising 3D resonance-filtered spectrum imaging, demonstrates a valuable method for 'pinpointing' the location of discrete modes in irregularly shaped nanostructures.