Rolled-Up Nanotech: Illumination-Controlled Hydrofluoric Acid Etching of AlAs Sacrificial Layers

<p>Abstract</p> <p>The effect of illumination on the hydrofluoric acid etching of AlAs sacrificial layers with systematically varied thicknesses in order to release and roll up InGaAs/GaAs bilayers was studied. For thicknesses of AlAs below 10 nm, there were two etching regimes for the area under illumination: one at low illumination intensities, in which the etching and releasing proceeds as expected and one at higher intensities in which the etching and any releasing are completely suppressed. The &#8220;etch suppression&#8221; area is well defined by the illumination spot, a feature that can be used to create heterogeneously etched regions with a high degree of control, shown here on patterned samples. Together with the studied self-limitation effect, the technique offers a way to determine the position of rolled-up micro- and nanotubes independently from the predefined lithographic pattern.</p

Thermal Transport on the Nanometer Scale and the Effect of Microstructure and Interface Resistance

94 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.The aim of this research is to provide a better understanding of the physics of phonons involved in thermal transport on nanometer scale and to address the need for systematic information about the thermal properties of ultra-thin films. The present work includes data on thermal transport in dense and porous hydrogen silsesquioxane thin films and thin SiO2 films, across TiN/MgO(001), TiN/MgO(111) and TiN/Al2O3(0001), and in W/Al2O3, Re/Al2O3 and W/B multilayers. The thermal conductivities of low-k dielectric thin films were measured with the 3o method between 80 and 400 K. The strong temperature dependence is not reflected by the minimum thermal conductivity model for homogeneous materials. The differential effective medium model predicts a 1.5 power scaling of thermal conductivity with atomic density, in good agreement with experimental data. The thermal conductances G of TiN/MgO(001), TiN/MgO(111) and TiN/Al2O3(0001), interfaces, measured at temperatures between 79.4 and 294 K using time-domain thermoreflectance, are essentially identical and in good agreement with the predictions of lattice dynamics models and the diffuse mismatch model. Near room temperature G &ap; 700 MW m-2 K-1, &ap;5 times larger than the highest values reported previously for any individual interface. For W/Al2O3, multilayers deposited by atomic layer deposition with layers only a few nanometers thick, the high interface density produced a strong impediment to heat transfer, giving a thermal conductivity of &sim;0.6 W m-1 K-1. The thermal conductivities of magnetron sputtered multilayers of W/Al2O3, Re/Al 2O3 and W/B decrease with increasing number of layers and the dependence on temperature is similar to that predicted by the diffuse mismatch model. The conductivities of W/Al2O3, and Re/Al 2O3 multilayers were found to be similar, and as low as &sim;0.6 W m-1 K-1---suitable for ultra-low conductivity thermal barriers.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Structure, reactivity, electronic configuration and magnetism of samarium atomic layers deposited on Si(001) by molecular beam epitaxy

The surface structure, interface reactivity, electron configuration and magnetic properties of Sm layers deposited on Si(0 0 1) at various temperatures are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and magneto-optical Kerr effect (MOKE). It is found that metal Sm is present on samples prepared at low temperature, with an interface layer containing SmSi2 and Sm4Si3. When samples are prepared at high temperature, much less metal Sm is found, with an increasing amount of SmSi2. Room temperature ferromagnetism is observed for all prepared layers, with a decrease of the saturation magnetization when samples are prepared at high temperature. It is found that ferromagnetism implies mostly a compound with approximate stoichiometry Sm4Si3. Also, the decrease in the intensity of the XAS 2p3/2 → 3d white lines with the corresponding increasing amount of SmSi2 may be explained by assuming a higher occupancy of Sm 5d orbitals (5d2 configuration), most probably due to hybridation effects

Photocatalytic and Antibacterial Properties of Doped TiO₂ Nanopowders Synthesized by Sol−Gel Method

For environmental applications, nanosized TiO2-based materials are known as the most important photocatalyst and are intensively studied for their advantages such as their higher activity, lower price, and chemical and photoresist properties. Zn or Cu doped TiO2 nanoparticles with anatase crystalline structure were synthesized by sol−gel process. Titanium (IV) butoxide was used as a TiO2 precursor, with parental alcohol as a solvent, and a hydrolysing agent (ammonia-containing water) was added to obtain a solution with pH 10. The gels were characterized by TG/DTA analysis, SEM, and XPS. Based on TG/DTA results, the temperature of 500 °C was chosen for processing the powders in air. The structure of the samples thermally treated at 500 °C was analysed by XRD and the patterns show crystallization in a single phase of TiO2 (anatase). The surface of the samples and the oxidation states was investigated by XPS, confirming the presence of Ti, O, Zn and Cu. The antibacterial activity of the nanoparticle powder samples was verified using the gram−positive bacterium Staphylococcus aureus. The photocatalytic efficiency of the doped TiO2 nanopowders for degradation of methyl orange (MO) is here examined in order to evaluate the potential applications of these materials for environmental remediation

Antimicrobial Properties of TiO2 Microparticles Coated with Ca- and Cu-Based Composite Layers

The ability of TiO2 to generate reactive oxygen species under UV radiation makes it an efficient candidate in antimicrobial studies. In this context, the preparation of TiO2 microparticles coated with Ca- and Cu-based composite layers over which Cu(II), Cu(I), and Cu(0) species were identified is presented here. The obtained materials were characterized by a wide range of analytical methods, such as X-ray diffraction, electron microscopy (TEM, SEM), X-ray photoelectron (XPS), and UV-VIS spectroscopy. The antimicrobial efficiency was evaluated using qualitative and quantitative standard methods and standard clinical microbial strains. A significant aspect of this composite is that the antimicrobial properties were evidenced both in the presence and absence of the light, as result of competition between photo and electrical effects. However, the antibacterial effect was similar in darkness and light for all samples. Because no photocatalytic properties were found in the absence of copper, the results sustain the antibacterial effect of the electric field (generated by the electrostatic potential of the composite layer) both under the dark and in light conditions. In this way, the composite layers supported on the TiO2 microparticles&rsquo; surface can offer continuous antibacterial protection and do not require the presence of a permanent light source for activation. However, the antimicrobial effect in the dark is more significant and is considered to be the result of the electric field effect generated on the composite layer