Frank Hipler

Investigations on InN whiskers grown by chemical vapour deposition

Abstract Nanostructures of compound semiconductors of group-III nitrides are ideal building blocks for nanoscale optoelectronic devices. InN has a low decomposition temperature and the growth of nanoscale crystalline InN material at low temperatures is difficult. One of the approaches is to design single molecule precursors that decompose at low temperatures. Single molecule precursors of the type N 3 In[(CH 2 ) 3 NMe 2 ] 2 were developed and the growth of dense crystalline InN layers with preferred orientation was achieved using this compound. However, employing specific CVD process parameters we were able to grow InN whiskers consistently by CVD using a cold wall CVD reactor on bare sapphire substrates at a growth temperature of 500°C. These whiskers were characterised by XRD, SEM, EDX, XPS, RBS, TEM and SAED measurements.

A Study of Bisazido(dimethylamino‐propyl)gallium as a Precursor for the OMVPE of Gallium Nitride Thin Films in a Cold‐Wall Reactor System under Reduced Pressure

The use of alternative nitrogen sources for growing GaN materials by organometallic vapor phase epitaxy (OMVPE) is being continuously investigated in the hope of achieving device-quality films under moderate conditions, in comparison to conventional methods. Employing the single molecule precursor (N 3 ) 2 Ga[(CH 2 ) 3 NMe 2 ], and using a cold-wall CVD reactor, epitaxial films of GaN, transparent in appearance and stoichiometric in composition, were deposited on c-plane sapphire, in the absence of ammonia, above 1073 K, under low pressures (between 0.080 and 100.0 mbar). Dense, amorphous, and very smooth films were grown at temperatures as low as 773 K. The influence of substrate temperature, reactor pressure, and the effect of small quantities of additional ammonia, on the growth rate and the film properties, were studied in some detail. The films were characterized by high-resolution X-ray diffraction (XRD) (e.g., full width at half maximum (FWHM) of the 0002 GaN rocking curve of 130 arcsec), X-ray reflectometry, scanning electron microscopy (SEM), atomic force microscopy (AFM) (root mean square roughness of 1.9 nm), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Rutherford backscattering (RBS) (Ga/N = 1:1 ± 0.05), and photoluminescence (PL) measurements (band edge luminescence at 3.45 eV and FWHM of 0.22 eV at 300 K).

Examining thermolysis reactions and tautomerism of 2-mercapto-5-methyl-1,3,4-thiadiazole and 2,5-dimercapto-1,3,4-thiadiazole

A series of high-vacuum thermolysis experiments with 2,5-dimercapto-1,3,4-thiadiazole and 2-mercapto-5-methyl-1,3,4-thiadiazole was performed between ambient temperature and 800 °C. The thermolysis products were trapped by matrix-isolation techniques and characterised by IR spectroscopy. Thermolysis of 2,5-dimercapto-1,3,4-thiadiazole gave HNCS, CS2 and HCN, whereas 2-mercapto-5-methyl-1,3,4-thiadiazole shows a more complex fragmentation pattern forming HNCS, CH3NCS, HCN and CS2. Formation of CH3CN was not observed. The molecular structures of different isomers of both mercaptothiadiazoles were studied by ab initio and DFT computations.

Chemie gegen Reibung und Verschleiß: Untersuchung molekularer Wirkungsmechanismen von Schmierstoffadditiven

Although greases and oils are able to reduce friction without other substances being added, blending with additives is essential for todays high-performance lubricants. Only these synthetic additives yield the desired characteristics of the final product, which is often designed specially for a particular application. In most cases, however, the underlying chemical mechanism is not exactly understood. For anti-wear additives it will be shown how modem surface chemistry can help to understand the effectiveness of those substances and thus contribute to a systematic additive optimization.

Matrix-isolation pyrolysis investigation of mercapto-functionalized 1,3,4-thiadiazoles: thermal stability of thiadiazole lubricant additives

A series of high-vacuum thermolysis experiments with alkyldithio thiadiazoles was performed between ambient temperature and 900 degrees C to investigate the thermal stability of thiadiazole type lubricant additives. The thermolysis products were trapped by matrix-isolation techniques and characterized by IR spectroscopy. Thermolysis of 2-(tert-butyldithio)-5-methyl-,3,4-thiadiazole (TB1) gave 2-methylpropene, isothiocyanic acid (HNCS), 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT), hydrogen cyanide (HCN), carbon disulfide (CS2), acetonitrile (CH3CN), and elemental sulfur S(x) [x = (2), 4, 6, 8]. A decomposition mechanism is discussed explaining the temperature-dependent composition of product mixtures, and a general precursor concept for organosulfur type anti-wear additives is presented.

Preparation, spectroscopic properties and impedance characteristics of a novel ion conducting polymer

Preparation and characterization of a novel ion conducting polymeric material (2) is described. The backbone consists of alternating alkenylidene and sulfanylidene units with adjacent hydroxy groups. The material was characterized by elemental analysis, solid state MAS-NMR, IR, UV-VIS and XPS spectroscopy as well as by SEM, dynamic light scattering and complex impedance measurements. Fitting of the experimental data of the impedance measurements in a Bode plot reveals a conductivity of 6.6*10 m 2 S/cm and a capacitance of 2.2*10 m 5 F at room temperature. The deuterated derivative of 2 shows a significantly lower conductivity, which suggests that the latter can be attributed to proton migration.