The formation of macrostep during high-temperature phase of barium meta-borate (^-BaB204) single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy (AFM). T...The formation of macrostep during high-temperature phase of barium meta-borate (^-BaB204) single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy (AFM). The in- si$u observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 ~m and 620 ~m for {1010} and (T010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm^200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.展开更多
This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on ...This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on the AI:Ti composition with no more than 50 at.% Al. The specific contact resistance (SCR) is obtained to be as low as 2.6 × 10-6Ωcm2 for the bilayered Ti(100 nm)/Al(100 nm) contact treated with 3 rain rapid thermal annealing (RTA) at 1000 ℃. The microstructure analyses examined by physical and chemical characterization techniques reveal an alloy-assisted ohmic contact formation mechanism, i.e., a high degree of alloying plays a decisive role in forming the interfacial ternary Ti3SiC2 dominating the ohmic behavior of the Ti/Al based contact. Furthermore, a globally covered Ti3 SiC2 layer with (0001)-oriented texture can be formed, regardless of the surface step bunching as well as its structural evolution during the metallization annealing.展开更多
Bunching of elementary steps by solution flow is still not yet clarified for protein crystals. Hence, in this study, we observed elementary steps on crystal surfaces of model protein hen egg-white lysozyme (HEWL) un...Bunching of elementary steps by solution flow is still not yet clarified for protein crystals. Hence, in this study, we observed elementary steps on crystal surfaces of model protein hen egg-white lysozyme (HEWL) under forced flow conditions, by our advanced optical microscopy. We found that in the case of a HEWL solution of 99.99% purity, forced flow changed bunched steps into elementary ones (debunching) on tetragonal HEWL crystals. In contrast, in the case of a HEWL solution of 98.5% purity, forced flow significantly induced bunching of elementary steps. These results indicate that in the case of HEWL crystals, the mass transfer of impurities is more significantly enhanced by forced solution flow than that of solute HEWL molecules. We also showed that forced flow induced the incorporation of microcrystals into a mother crystal and the subsequent formation of screw dislocations and spiral growth hillocks.展开更多
Micropipe and step structures on 6H-SiC (0001) surface were investigated by an atomic force microscopy (AFM). On the facet,all micropipes examined are the origins of spiral steps,indicating that dislocations inter...Micropipe and step structures on 6H-SiC (0001) surface were investigated by an atomic force microscopy (AFM). On the facet,all micropipes examined are the origins of spiral steps,indicating that dislocations intersect the surface at these points. Micropipes are empty-core super-dislocations as originally described by Frank. The micropipe radius increases with the square of the dislocation Burgers vector. From the center to the periphery,step structures change with different surface inclinations. Regular step is observed within the central faceted area. Step bunching and atomically rough surfaces are observed within the peripheral convex area. If the inclination with respect to the (0001) plane is large enough,step bunching of 15R-SiC can be observed.展开更多
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 50802105)
文摘The formation of macrostep during high-temperature phase of barium meta-borate (^-BaB204) single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy (AFM). The in- si$u observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 ~m and 620 ~m for {1010} and (T010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm^200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.
基金supported by the Key Specific Projects of Ministry of Education of China(Grant No.625010101)the National Natural Science Foundation of China(Grant No.61234006)+2 种基金the Natural Science Foundation of Shaan Xi Province,China(Grant No.2013JQ8012)the Doctoral Fund of Ministry of Education of China(Grant No.20130203120017)the Specific Project of the Core Devices,China(Grant No.2013ZX0100100-004)
文摘This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on the AI:Ti composition with no more than 50 at.% Al. The specific contact resistance (SCR) is obtained to be as low as 2.6 × 10-6Ωcm2 for the bilayered Ti(100 nm)/Al(100 nm) contact treated with 3 rain rapid thermal annealing (RTA) at 1000 ℃. The microstructure analyses examined by physical and chemical characterization techniques reveal an alloy-assisted ohmic contact formation mechanism, i.e., a high degree of alloying plays a decisive role in forming the interfacial ternary Ti3SiC2 dominating the ohmic behavior of the Ti/Al based contact. Furthermore, a globally covered Ti3 SiC2 layer with (0001)-oriented texture can be formed, regardless of the surface step bunching as well as its structural evolution during the metallization annealing.
基金Chinese Academy of Sciences visiting professorship for senior international scientists(2013T2J0060)
文摘Bunching of elementary steps by solution flow is still not yet clarified for protein crystals. Hence, in this study, we observed elementary steps on crystal surfaces of model protein hen egg-white lysozyme (HEWL) under forced flow conditions, by our advanced optical microscopy. We found that in the case of a HEWL solution of 99.99% purity, forced flow changed bunched steps into elementary ones (debunching) on tetragonal HEWL crystals. In contrast, in the case of a HEWL solution of 98.5% purity, forced flow significantly induced bunching of elementary steps. These results indicate that in the case of HEWL crystals, the mass transfer of impurities is more significantly enhanced by forced solution flow than that of solute HEWL molecules. We also showed that forced flow induced the incorporation of microcrystals into a mother crystal and the subsequent formation of screw dislocations and spiral growth hillocks.
基金National High-Technology Research and Development Program of China (No2004AA31G030)
文摘Micropipe and step structures on 6H-SiC (0001) surface were investigated by an atomic force microscopy (AFM). On the facet,all micropipes examined are the origins of spiral steps,indicating that dislocations intersect the surface at these points. Micropipes are empty-core super-dislocations as originally described by Frank. The micropipe radius increases with the square of the dislocation Burgers vector. From the center to the periphery,step structures change with different surface inclinations. Regular step is observed within the central faceted area. Step bunching and atomically rough surfaces are observed within the peripheral convex area. If the inclination with respect to the (0001) plane is large enough,step bunching of 15R-SiC can be observed.