analysis, the region formed by dark lumps is nickel- and silicon-rich, namely most likely a nickel silicide layer. Along with the dark lumps there are some small bright dots, which were found to be carbon-rich. These carbon clusters were commonly found before inside 4H- and 6H-SiC silicide [117,118] and were considered to increase the interfacial net carriers, helping to reduce the contact resistivity. With the annealing temperature further increased to 1000 ◦ C (Figure 4.15b), the Ti interlayer became less noticeable and a series of void (highlighted by red dotted circles) emerged along it. These vacancies are caused by silicon diﬀusion into the nickel (Kirkendall Eﬀect) and will not have an impact on the contact resistivity, although they are harmful in terms of contacts reliability . The small carbon clusters spotted previously are shown to expand in Figure 4.15b, which can be explained by the further reaction of Si with Ni. This further increases the interfacial carrier concentration, leading to a resistivity drop from 900 ◦ C to 1000 ◦ C. At 1100 ◦ C, even more severe carbon clustering is observed (Figure 4.15c) with large carbon crystallites formed. It is hypothesised that the extra active donors generated could be high enough that Coulomb scattering eﬀects start to dominate and increase the contact resistance.
post oxidation annealing successfully shifted the inherent negative threshold of 3C-SiC MOS devices to more positive values, however, accompanied with a degradation of the peak channel mobility: 14.3% lower than the dry oxidised sample and 33.3% comparing to the nitrided sample. It was revealed by the XPS analysis that, the high temperature wet oxidation led to the formation of Si suboxide, which may have acted as extra interface traps, even though the more conventional traps caused by C-C bonds are greatly reduced.
It is difficult to create a device model to meet all the rules above. In the literature several device models have been presented for SiC MOSFETs and Schottky diodes. They can be divided in two major groups: 1) analytical models based on the finite element solution of drift-diffusion carrier transport in two or three dimensions [ 14 ] - [ 16 ]; and 2) circuit-oriented models which employ equation-based description of device behavior. Analytical models provide very high accuracy but require long simulation time and detailed information about device fabrication, while circuit-based models require much less time for simulation with acceptably accurate results using model parameters that can be extracted from experimental measurements. An additional advantage of physics-based circuit-oriented models is that they are compatible with circuit simulators and can be used to simulate an entire switching converter. New physics-based circuit-oriented SiC MOSFET and Schottky diode models will be developed in this dissertation.
Tissue engineered constructs which contain cells derived from the patient’s body that are suitable for vascular replacement procedures is a goal in medical research . Various approaches have been developed to fabricate blood vessels [13, 14, 15]. These include the use of tubular scaffolds manufactured from natural and synthetic biomaterials that are subsequently seeded with vascular cells to create living prostheses [16, 17]. An alternative approach that would facilitate cell-based fabrication of conduits comprised of vascular cells and extracellular matrix (ECM) constituents was developed by collaborators at the Medical University of South Carolina (MUSC) . In this study, the mechanical responses of such constructs were tested both at multiple culture times and multiple culture conditions.
ODS alloys are typically made from elemental or pre-alloyed metal powders mechanically alloyed with oxide powders in a high-energy attributor mill filled with argon gas, and then consolidated by either hot isostatic pressing or hot extrusion , though other fabrication techniques are also being proposed and tested. This process causes the production of nanometer scale oxide and carbide particles within the alloy matrix; these are typically 2-3 nm in size, though the observed range varies almost up to a micrometer in diameter . Crystalline properties such as creep strength, ductility, corrosion resistance, tensile strength, swelling resistance, and resistance to embrittlement are all observed to be improved by the presence of nanoparticles in the matrix, however the science behind these experimental observations is yet to be fully understood, and is crucial to further improvement of reactor materials currently under scrutiny.
As the demand for smaller and smaller electronic devices grows, the need for one- dimensional electronically active materials also expands. The macrocyclic columnar structures such as arylene ethynylene macrocycles (AEMs) from Moore’s group (Figure 9b) are potentially simple building blocks for controlled one-dimensional assembly. These systems can be cyclized in high yield through an alkyne metathesis process. 180 Casting of AEMs with linear alkyl side chains on carbon films afforded entangled nanofibrils via aryl stacking interactions and side chain interdigitation. 181 These fibrils showed polarized emission parallel to the aryl-stacking of the cycles, which indicated an intermolecular delocalization of the π clouds. The delocalization led to long range fluorescence quenching. This together with the electron donating capability of the AEM and the porous structure of the nanofibrils deposited on a surface enabled the detection of oxidative molecules (such as TNT) at the part-per-trillion scale. 186
While many advances were made in lighting technology over time, the continued production of solid-state lighting materials containing rare earths is in jeopardy. It is projected that rare-earth oxide demand will surpass the supply of rare-earth oxide materials. Furthermore, China controls approximately 97% of the global market. The export of these materials will also decrease due to China’s own growing demand. This supply and demand situation for rare-earth materials may eventually cause lighting research to focus more and more on the development of rare-earth free lighting materials and/or organic light emitting devices (OLEDs) 6 . A 2011 report by Philips Lighting Company, showed the critical need for rare-earths oxides to sustain the global demand for lighting materials. The main rare earth ions needed for phosphor materials are