High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425oC, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 ?Omega cm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90percent. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm

High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425oC, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 ?Omega cm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90percent. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm

Plasma potential mapping of high power impulse magnetron sputtering discharges

Pulsed emissive probe techniques have been used to determine the plasma potential distribution of high power impulse magnetron sputtering (HiPIMS) discharges. An unbalanced magnetron with a niobium target in argon was investigated for pulse length of 100 μs at a pulse repetition rate of 100 Hz, giving a peak current of 170 A. The probe data were taken with a time resolution of 20 ns and a spatial resolution of 1 mm. It is shown that the local plasma potential varies greatly in space and time. The lowest potential was found over the target’s racetrack, gradually reaching anode potential (ground) several centimeters away from the target. The magnetic pre-sheath exhibits a funnel-shaped plasma potential resulting in an electric field which accelerates ions toward the racetrack. In certain regions and times, the potential exhibits weak local maxima which allow for ion acceleration to the substrate. Knowledge of the local E and static B fields lets us derive the electrons’ E×B drift velocity, which is about 105 m/s and shows structures in space and time

Near infrared electrochromism of doped colloidal nanocrystals

Electronically doped metal oxide nanocrystals, such as indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO) exhibit surface plasmon absorption in the near IR (NIR). In addn., chem. strategies have been developed for achieving conducting networks of nanocrystals that were initially passivated by insulating hydrocarbon ligands. Starting with well-controlled colloidal synthesis, we achieve nanoporous films with variable feature size and doping level. We are investigating these films' potential as electrochromic coatings that selectively modulate NIR transmittance while maintaining near unity transparency for visible light, which is of keen interest for energy efficient windows. Positioning a nanocrystal film as the working electrode in an electrochem. cell, the carrier population - and thus the NIR transmittance - responds dynamically to an applied bias. Work is underway to correlate the dynamic spectral response with doping and nanocrystal size variations and, eventually, to optimize the dynamic range of transmittance for solar NIR radiation

Understanding the Plasmon Resonance in Ensembles of Degenerately Doped Semiconductor Nanocrystals

Inevitable variations in size and composition within nanocrystal ensembles affect their optical absorbance as revealed by effective medium theory calculations. We critically analyzed the effects of such inhomogeneity and of the surface ligands on the localized surface plasmon resonance absorption of In₂O₃:Sn and Cu_2–<i>x</i>Se nanocrystal dispersions. Modeling the absorbance line shape readily provides valuable and quantitative insight into the structural, electrical, and optical properties of colloidal nanocrystals

Dynamically Modulating the Surface Plasmon Resonance of Doped Semiconductor Nanocrystals

Localized surface plasmon absorption features arise at high doping levels in semiconductor nanocrystals, appearing in the near-IR range. The surface plasmons of Sn-doped In oxide nanocrystal films can be dynamically and reversibly tuned by postsynthetic electrochem. modulation of the electron concn. Without ion intercalation and the assocd. material degrdn., a textgreater1200 nm shift in the plasmon wavelength and a factor of nearly 3 change in the carrier d. was induced

DEPOSITION OF NIOBIUM AND OTHER SUPERCONDUCTING MATERIALS WITH HIGH POWER IMPULSE MAGNETRON SPUTTERING: CONCEPT AND FIRST RESULTS

Niobium coatings on copper cavities have been considered as a cost-efficient replacement of bulk niobium RF cavities, however, coatings made by magnetron sputtering have not quite lived up to high expectations due to Q-slope and other issues. High power impulse magnetron sputtering (HIPIMS) is a promising emerging coatings technology which combines magnetron sputtering with a pulsed power approach. The magnetron is turned into a metal plasma source by using very high peak power density of ~ 1 kW/cm{sup 2}. In this contribution, the cavity coatings concept with HIPIMS is explained. A system with two cylindrical, movable magnetrons was set up with custom magnetrons small enough to be inserted into 1.3 GHz cavities. Preliminary data on niobium HIPIMS plasma and the resulting coatings are presented. The HIPIMS approach has the potential to be extended to film systems beyond niobium, including other superconducting materials and/or multilayer systems