Growth and characterization of low temperature silicon selective epitaxy

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990.Includes bibliographical references (leaves 204-210).by Tri-Rung Yew.Ph.D

Method of manufacturing shallow trench isolation

[[abstract]]A method of manufacturing shallow trench isolation structures. The method includes the steps of depositing insulating material into the trench of a substrate to form an insulation layer. The substrate has a plurality of active regions, each occupying a different area and having different sizes. In addition, there is a silicon nitride layer on top of each active region. Thereafter, a photoresist layer is then deposited over the insulation layer. Next, a portion of the photoresist layer is etched back to expose a portion of the oxide layer so that the remaining photoresist material forms a cap layer over the recessed area of the insulation layer. Subsequently, using the photoresist cap layer as a mask, the insulation layer is etched to remove a portion of the exposed oxide layer, thereby forming trenches within the oxide layer. After that, the photoresist cap layer is removed. Finally, a chemical-mechanical polishing operation is carried out to polish the insulation layer until the silicon nitride layer is exposed.[[fileno]]2020309060025[[department]]材料科學工程學

Dual damascene process

[[abstract]]A dual damascene process forms a two level metal interconnect structure by first providing a interlayer oxide over a device structure and covering the interlevel oxide layer with an etch stop layer. The etch stop layer is patterned to form openings corresponding to the pattern of the interconnects that are to be formed in the first level of the two level interconnect structure. After the etch stop layer is patterned, an intermetal oxide layer is provided over the etch stop layer. Because the etch stop layer is relatively thin, the topography formed on the surface of the intermetal oxide layer is relatively small. A photoresist mask is then provided over the intermetal oxide layer with openings in the mask exposing portions of the intermetal oxide layer in the pattern of the wiring lines to be provided in the second level of the interconnect structure. The intermetal oxide layer is etched and the etching process continues to form openings in the interlayer oxide where the interlayer oxide is exposed by the openings in the etch stop layer. Thus, in a single etching step, the openings for both the second level wiring lines and the first level interconnects are defined. Metal is then deposited over the structure and excess metal is removed by chemical mechanical polishing to define the two level interconnect structure.[[fileno]]2020309060078[[department]]材料科學工程學

Structural and Mechanical Properties of Klebsiella pneumoniae Type 3 Fimbriae▿ §

This study investigated the structural and mechanical properties of Klebsiella pneumoniae type 3 fimbriae, which constitute a known virulence factor for the bacterium. Transmission electron microscopy and optical tweezers were used to understand the ability of the bacterium to survive flushes. An individual K. pneumoniae type 3 fimbria exhibited a helix-like structure with a pitch of 4.1 nm and a three-phase force-extension curve. The fimbria was first nonlinearly stretched with increasing force. Then, it started to uncoil and extended several micrometers at a fixed force of 66 ± 4 pN (n = 22). Finally, the extension of the fimbria shifted to the third phase, with a characteristic force of 102 ± 9 pN (n = 14) at the inflection point. Compared with the P fimbriae and type 1 fimbriae of uropathogenic Escherichia coli, K. pneumoniae type 3 fimbriae have a larger pitch in the helix-like structure and stronger uncoiling and characteristic forces

Identification of Protein Domains on Major Pilin MrkA That Affects the Mechanical Properties of <i>Klebsiella pneumoniae</i> Type 3 Fimbriae

The <i>Klebsiella pneumoniae</i> type 3 fimbriae are mainly composed of MrkA pilins that assemble into a helixlike filament. This study determined the biomechanical properties of the fimbriae and analyzed 11 site-directed MrkA mutants to identify domains that are critical for the properties. <i>Escherichia coli</i> strains expressing type 3 fimbriae with an Ala substitution at either F34, V45, C87, G189, T196, or Y197 resulted in a significant reduction in biofilm formation. The <i>E</i>. <i>coli</i> strain expressing MrkAG189A remained capable of producing a normal number of fimbriae. Although F34A, V45A, T196A, and Y197A substitutions expressed on <i>E</i>. <i>coli</i> strains produced sparse quantities of fimbriae, no fimbriae were observed on the cells expressing MrkAC87A. Further investigations of the mechanical properties of the MrkAG189A fimbriae with optical tweezers revealed that, unlike the wild-type fimbriae, the uncoiling force for MrkAG189A fimbriae was not constant. The MrkAG189A fimbriae also exhibited a lower enthalpy in the differential scanning calorimetry analysis. Together, these findings indicate that the mutant fimbriae are less stable than the wild-type. This study has demonstrated that the C-terminal β strands of MrkA are required for the assembly and structural stability of fimbriae