• Energy Research

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

The sublimation-recondensation growth of titanium nitride crystals with N/Ti ratio of 0.99 on tungsten substrates is reported. The growth rate dependence on temperature and pressure was determined, and the calculated activation energy was 775.8 ± 29.8 kJ/mol. The lateral and vertical growth rates changed with the time of growth and the fraction of the tungsten substrate surface covered. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45° angle between TiN [100] and W [100], occurs not only for TiN crystals deposited on (001) textured tungsten but also for TiN crystals deposited on randomly orientated tungsten. This study demonstrates that this preferred orientational relationship minimizes the lattice mismatch between the TiN and tungsten.

The sublimation-recondensation growth of titanium nitride crystals with N/Ti ratio of 0.99 on tungsten substrates is reported. The growth rate dependence on temperature and pressure was determined, and the calculated activation energy was 775.8 ± 29.8 kJ/mol. The lateral and vertical growth rates changed with the time of growth and the fraction of the tungsten substrate surface covered. The orientation relationship of TiN (001) || W (001) with TiN [100] || W [110], a 45° angle between TiN [100] and W [100], occurs not only for TiN crystals deposited on (001) textured tungsten but also for TiN crystals deposited on randomly orientated tungsten. This study demonstrates that this preferred orientational relationship minimizes the lattice mismatch between the TiN and tungsten.

In this work, we report a detailed material study of ultrafast laser textured silicon surfaces to gain insight into the impact of ultrafast laser processing conditions on photovoltaic device properties. A comprehensive study of the ultrafast laser processed silicon is achieved by determination of crystal structure and elemental compositional changes using transmission electron microscopy, compositional mapping by energy dispersive X-ray spectroscopy and depth profiling compositional determination using X-ray photoelectron spectroscopy. We have observed material non-homogeneity, impurity incorporation and strained silicon, all limited to the surface. A combination of chemical etching and thermal annealing was used to remove the laser induced changes and the material was restored to its starting quality. Further, silicon solar cell devices on such defect-etched surfaces are fabricated. These devices are characterized through dark i–v analysis and Fourier transform deep level transient spectroscopy for defect analysis.

In this work, we report a detailed material study of ultrafast laser textured silicon surfaces to gain insight into the impact of ultrafast laser processing conditions on photovoltaic device properties. A comprehensive study of the ultrafast laser processed silicon is achieved by determination of crystal structure and elemental compositional changes using transmission electron microscopy, compositional mapping by energy dispersive X-ray spectroscopy and depth profiling compositional determination using X-ray photoelectron spectroscopy. We have observed material non-homogeneity, impurity incorporation and strained silicon, all limited to the surface. A combination of chemical etching and thermal annealing was used to remove the laser induced changes and the material was restored to its starting quality. Further, silicon solar cell devices on such defect-etched surfaces are fabricated. These devices are characterized through dark i–v analysis and Fourier transform deep level transient spectroscopy for defect analysis.