Work function of doped zinc oxide films deposited by ALD

Al-doped ZnO (AZO) is a promising earth-abundant alternative to Sn-doped In2O3 (ITO) as an n-type transparent conductor for electronic and photovoltaic devices. We have deposited AZO films with resistivities as low as 1.1 × 10-3 ω·cm by atomic layer deposition (ALD) using trimethylaluminum (TMA), diethylzinc (DEZ), and water at 200 °C. The work functions of the films were measured using a scanning Kelvin probe (sKP) to investigate the role of aluminum concentration. The work function of AZO films prepared by two different ALD recipes were compared: a "Al-terminated" recipe and a "ZnO-terminated" recipe. As aluminum doping increases, the Al-terminated recipe produces films with a consistently higher work function than the ZnO-terminated recipe. The resistivity of the Al-terminated recipe films shows a minimum at a 1:16 Al:Zn atomic ratio and using a ZnO-terminated recipe, minimum resistivity was seen at 1:19. The film thicknesses were characterized by ellipsometry, chemical composition by EDX, and resistivity by a four-point probe

Quantitative radiolabeled biomolecule detection using a functionalized CMOS sensor

For the first time a CMOS imager has been used to detect the presence of radiolabeled target biomolecules captured on a functionalized surface. Using aptamer functionalization the system successfully detected 32P labeled adenosine triphosphate (ATP) at concentrations well below those typically associated with fluorescence-based sensor architectures. The system has also demonstrated its amenability to multiplexed biomolecule detection. Geant4, a Monte Carlo toolkit for simulating the passage of radiation through matter, was used to analyze the detector. Radiolabel detection offers the potential for direct quantitative measurement of bound biomolecules which is advantageous compared to the use of fluorescent tags. \ua9 2012 IEEE.Peer reviewed: YesNRC publication: Ye

The impact of processing on the cytotoxicity of graphene oxide

In-house prepared graphene oxide (GO) was processed via base washing, sonication, cleaning and combinations of these processing techniques to evaluate the impact on the flake morphology, composition and cytotoxicity of the material. The flakes of unprocessed GO were relatively planar, but upon base washing, the flakes became textured exhibiting many folds and creases observed by AFM. In addition to the pronounced effect on the topography, base washing increased the C/O ratio and increased the cytotoxicity of GO on all four cell lines studied determined via the WST-8 assay. Sonicating the unprocessed and base washed samples resulted in smaller flakes with a similar topography; the base washed flakes lost the texture previously observed upon sonication. The sonicated samples were more toxic than the unprocessed sample, attributed to the smaller flake size, but were interestingly less toxic than the base washed, unsonicated sample despite the base washed unsonicated sample having a larger flake size. This unexpected finding was confirmed by a second analyst using the same, and a different source of GO and resulted in the conclusion that the morphology of GO greatly impacts the cytotoxicity. Cleaning the GO reduced the amount of nitrogen and sulfur impurities in the sample but had no significan