Solution processed ZnO homogeneous quasisuperlattice materials

Heterogeneous multilayered oxide channel materials have enabled low temperature, high mobility thin film transistor technology by solution processing. The authors report the growth and characterization of solution-based, highly uniform and c-axis orientated zinc oxide (ZnO) single and multilayered thin films. Quasisuperlattice (QSL) metal oxide thin films are deposited by spin-coating and the structural, morphological, optical, electronic, and crystallographic properties are investigated. In this work, the authors show that uniform, coherent multilayers of ZnO can be produced from liquid precursors using an iterative coating-drying technique that shows epitaxial-like growth on SiO2, at a maximum temperature of 300 °C in air. As QSL films are grown with a greater number of constituent layers, the crystal growth direction changes from m-plane to c-plane, confirmed by x-ray and electron diffraction. The film surface is smooth for all QSLs with root mean square roughness <0.14 nm. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) of electronic defects in the QSL structure show a dependence of defect emission on the QSL thickness, and PL mapping demonstrates that the defect signature is consistent across the QSL film in each case. XPS and valence-band analysis shown a remarkably consistent surface composition and electronic structure during the annealing process developed here

Highly-ordered growth of solution-processable ZnO for thin film transistors

We demonstrate that crystalline, epitaxial-like and highly ordered ZnO thin films and quasi-superlattice structures can be achieved from a precursor liquid at relatively low temperature via spin-coating. The synthesised films are smooth, stoichiometric ZnO with controllable thickness. An iterative layer-by-layer coating schematic is employed to demonstrate the effects of film thickness on structure, morphology as well as the surface and internal defects. Characterisation of the crystallinity, morphology, O-vacancy formation, stoichiometry, surface roughness and thickness variation was determined through X-ray diffraction, scanning and transmission electron and atomic force microscopy, X-ray photoelectron and photoluminescence spectroscopy. We demonstrate that iterative spin-coating of deposited ZnO films results in a transition in crystal texture with increasing thickness (number of layers) from the [ ] m-plane to the [ ] c-plane. The films attain a c-axis preferential orientation, with no other crystalline peaks present. Results show that the film’s surface morphology was very smooth, with average rms roughness <0.15 nm. Examination of these films also shows the consistency of the surface composition and defect level while highlighting the effect of temperature and cumulative annealing condition on the internal defect concentration

Optical reflectivity of spin-coated multilayered ZnO and Al:ZnO Thin Films

Controlling growth, doping, crystallization, thickness of thin films of thin film transistor (TFT) channel materials is required in order to improve and control physical properties, primarily electronic conductivity and optical transparency. With the advent of flexible electronics and curved TFT-based display panels, low cost, solution-processed methods are important and provide scalable coating methods on a range of substrates. This work demonstrates the changes to the morphology, crystalline structure, optical reflectivity and electrical conductance of solution-processed ZnO thin films by the inclusion of an aluminium dopant during spin-coating. The measurements also determine the compositional chemical state of the Al:ZnO structures compared to ZnO using X-ray photoelectron spectroscopy in conjunction with detailed X-ray diffraction and transmission electron microscopy examination of the film morphology

Alkane and alkanethiol passivation of halogenated Ge nanowires

The ambient stability and surface coverage of halogen (Cl, Br, and I) passivated germanium nanowires were investigated by X-ray photoelectron and X-ray photoelectron emission spectroscopy. After exposure to air for 24 h, the stability of the halogen-terminated Ge nanowire surfaces toward reoxidation was found to improve with the increasing size of the halogen atoms, i.e., I > Br > Cl. Halogen termination was effective in removing the native Ge oxide (GeOx) and could also be utilized for further functionalization. Functionalization of the halogenated Ge nanowires was investigated using alkyl Grignard reagents and alkanethiols. The stability of the alkyl and alkanethiol passivation layers from the different halogen-terminated surfaces was investigated by X-ray photoelectron spectroscopy and attenuated total reflectance infrared spectroscopy. Alkanethiol functionalized nanowires showed greater resistance against reoxidation of the Ge surface compared to alkyl functionalization when exposed to ambient conditions for 1 week

Formation mechanism of metal–molecule–metal junctions: molecule-assisted migration on metal defects

Activation energies, Ea, measured from molecular exchange experiments are combined with atomic-scale calculations to describe the migration of bare Au atoms and Au–alkanethiolate species on gold nanoparticle surfaces during ligand exchange for the creation of metal–molecule–metal junctions. It is well-known that Au atoms and alkanethiol–Au species can diffuse on gold with sub-1 eV barriers, and surface restructuring is crucial for self-assembled monolayer (SAM) formation for interlinking nanoparticles and in contacting nanoparticles to electrodes. In the present work, computer simulations reveal that naturally occurring ridges and adlayers on Au(111) are etched and resculpted by migration of alkanethiolate–Au species toward high coordination kink sites at surface step edges. The calculated energy barrier, Eb, for diffusion via step edges is 0.4–0.7 eV, close to the experimentally measured Ea of 0.5–0.7 eV. By contrast, putative migration from isolated nine-coordinated terrace sites and complete Au unbinding from the surface incur significantly larger barriers of +1 and +3 eV, respectively. Molecular van der Waals packing energies are calculated to have negligible effect on migration barriers for typically used molecules (length < 2.5 nm), indicating that migration inside SAMs does not change the size of the migration barrier. We use the computational methodology to propose a means of creating Au nanoparticle arrays via selective replacement of citrate protector molecules by thiocyanate linker molecules on surface step sites. This work also outlines the possibility of using Au/Pt alloys as possible candidates for creation of contacts that are well-formed and long-lived because of the superior stability of Pt interfaces against atomic migration

Fully porous GaN p-n junctions fabricated by chemical vapor deposition.

Porous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increases the price of the final system. Also, the penetration depth of these etching techniques is limited, and affects not only the semiconductor but also the other elements constituting the LED when applied to the final device. In this paper, we present the fabrication of fully porous GaN p–n junctions directly during growth, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p–n junction. We characterized their diode behavior from room temperature to 673 K and demonstrated their ability as current rectifiers, thus proving the potential of these fully porous p–n junctions for diode and LEDs applications. The electrical and luminescence characterization confirm that high electronic quality porous structures can be obtained by this method, and we believe this investigation can be extended to other III–N materials for the development of white light LEDs, or to reduce reflection losses and narrowing the output light cone for improved LED external quantum efficiencies

The White Mountain Polarimeter Telescope and an Upper Limit on CMB Polarization

The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave telescope and receiver system for observing polarization of the Cosmic Microwave Background. WMPol is located at an altitude of 3880 meters on a plateau in the White Mountains of Eastern California, USA, at the Barcroft Facility of the University of California White Mountain Research Station. Presented here is a description of the instrument and the data collected during April through October 2004. We set an upper limit on $E$-mode polarization of 14 $\mu\mathrm{K}$ (95% confidence limit) in the multipole range $170<\ell<240$. This result was obtained with 422 hours of observations of a 3 $\mathrm{deg}^2$ sky area about the North Celestial Pole, using a 42 GHz polarimeter. This upper limit is consistent with $EE$ polarization predicted from a standard $\Lambda$-CDM concordance model.Comment: 35 pages. 12 figures. To appear in ApJ

Strong signature of natural selection within an FHIT intron implicated in prostate cancer risk

Previously, a candidate gene linkage approach on brother pairs affected with prostate cancer identified a locus of prostate cancer susceptibility at D3S1234 within the fragile histidine triad gene (FHIT), a tumor suppressor that induces apoptosis. Subsequent association tests on 16 SNPs spanning approximately 381 kb surrounding D3S1234 in Americans of European descent revealed significant evidence of association for a single SNP within intron 5 of FHIT. In the current study, resequencing and genotyping within a 28.5 kb region surrounding this SNP further delineated the association with prostate cancer risk to a 15 kb region. Multiple SNPs in sequences under evolutionary constraint within intron 5 of FHIT defined several related haplotypes with an increased risk of prostate cancer in European-Americans. Strong associations were detected for a risk haplotype defined by SNPs 138543, 142413, and 152494 in all cases (Pearson's χ2 = 12.34, df 1, P = 0.00045) and for the homozygous risk haplotype defined by SNPs 144716, 142413, and 148444 in cases that shared 2 alleles identical by descent with their affected brothers (Pearson's χ2 = 11.50, df 1, P = 0.00070). In addition to highly conserved sequences encompassing SNPs 148444 and 152413, population studies revealed strong signatures of natural selection for a 1 kb window covering the SNP 144716 in two human populations, the European American (π = 0.0072, Tajima's D= 3.31, 14 SNPs) and the Japanese (π = 0.0049, Fay & Wu's H = 8.05, 14 SNPs), as well as in chimpanzees (Fay & Wu's H = 8.62, 12 SNPs). These results strongly support the involvement of the FHIT intronic region in an increased risk of prostate cancer. © 2008 Ding et al

Data-Driven Identification of Unusual Prescribing Behavior: Analysis and Use of an Interactive Data Tool Using 6 Months of Primary Care Data From 6500 Practices in England.

BACKGROUND: Approaches to addressing unwarranted variation in health care service delivery have traditionally relied on the prospective identification of activities and outcomes, based on a hypothesis, with subsequent reporting against defined measures. Practice-level prescribing data in England are made publicly available by the National Health Service (NHS) Business Services Authority for all general practices. There is an opportunity to adopt a more data-driven approach to capture variability and identify outliers by applying hypothesis-free, data-driven algorithms to national data sets. OBJECTIVE: This study aimed to develop and apply a hypothesis-free algorithm to identify unusual prescribing behavior in primary care data at multiple administrative levels in the NHS in England and to visualize these results using organization-specific interactive dashboards, thereby demonstrating proof of concept for prioritization approaches. METHODS: Here we report a new data-driven approach to quantify how "unusual" the prescribing rates of a particular chemical within an organization are as compared to peer organizations, over a period of 6 months (June-December 2021). This is followed by a ranking to identify which chemicals are the most notable outliers in each organization. These outlying chemicals are calculated for all practices, primary care networks, clinical commissioning groups, and sustainability and transformation partnerships in England. Our results are presented via organization-specific interactive dashboards, the iterative development of which has been informed by user feedback. RESULTS: We developed interactive dashboards for every practice (n=6476) in England, highlighting the unusual prescribing of 2369 chemicals (dashboards are also provided for 42 sustainability and transformation partnerships, 106 clinical commissioning groups, and 1257 primary care networks). User feedback and internal review of case studies demonstrate that our methodology identifies prescribing behavior that sometimes warrants further investigation or is a known issue. CONCLUSIONS: Data-driven approaches have the potential to overcome existing biases with regard to the planning and execution of audits, interventions, and policy making within NHS organizations, potentially revealing new targets for improved health care service delivery. We present our dashboards as a proof of concept for generating candidate lists to aid expert users in their interpretation of prescribing data and prioritize further investigations and qualitative research in terms of potential targets for improved performance