Thin films of TiO2 have been deposited on silicon wafers from titanium tetrakis-isopropoxide (TTIP) and TTIP/H2O using low pressure metalorganic chemical vapor deposition. The films have been characterized by Rutherford backscattering spectrometry, forward recoil spectrometry, x-ray diffraction, and electrical techniques. Dielectric constants of approximately 30 were measured by high frequency C–V. Metal–oxide–semiconductor capacitors were fabricated using sputtered platinum as the upper electrode material. Films deposited in the presence of water vapor had a much lower quality interface with the silicon substrate. Normal thermionic emission was observed when the gate electrode was positively biased and barrier heights were extracted. Dramatically reduced leakage currents and increased barrier heights were seen after 750 °C anneals in dry oxygen. Using a ramped voltage test, capacitors were found to break down at applied fields of 3.0 MV/cm.
Scanning force microscopy (SFM) is used to investigate novel perturbation/response phenomena in a soft polymer network. Topics addressed include (i) the volume of film affected by tip−sample contact and (ii) the time-evolving residual signature of this contact. An outward deformation of nanometer-scale, soft, hydrated gelatin films is induced by the close proximity of the SFM tip. A domelike defect is created, centered at the site of approach and exceeding the tip−sample contact zone in diameter by as much as 3 orders of magnitude. The stretching of the film changes the stiffness of the polymer network and its frictional character. A precise correspondence of height and frictional force is quantified in histograms of the number of image pixels versus height or frictional force, and as a function of lateral distance from the center of approach. Relaxation of the dome is observed on a time scale of minutes with stretched exponential time dependence, consistent with a distribution of relaxation times. Film age also affects the size of the doming region: an increase to a maximum volume is observed, followed by a decrease to nanometer scale dimensions with age. This apparently reflects competing increases of long and short-range order that determine film cohesion. Five stages of gelatin film aggregation are experimentally distinguishable, differing in the extent of cohesion generated by progressive intermolecular coordination (e.g., crystallinity).
The overall energy conversion efficiency of photovoltaic cells depends on the combined efficiencies of light absorption, charge separation and charge transport. Dye-sensitized solar cells are photovoltaic devices in which a molecular dye absorbs light and uses this energy to initiate charge separation. The most efficient dye-sensitized solar cells (DSSCs) use nanocrystal titanium dioxide films to which are attached ruthenium complexes. Numerous studies have provided valuable insight into the dynamics of these and analogous photosystems, but the lack of site homogeneity in binding dye molecules to metal oxide films and nanocrystals (NCs) is a significant impediment to extracting fundamental details about the electron transfer across the interface. Although zinc oxide is emerging as a potential semiconducting component in DSSCs, there is less known about the factors controlling charge separation across the dye/ZnO interface. Zinc oxide crystallizes in the wurtzite lattice and has a band gap of 3.37 eV. One of the features that makes ZnO especially attractive is the remarkable ability to control the morphology of the films. Using solution deposition processes, one can prepare NCs, nanorods and nanowires having a variety of shapes and dimensions. This project solved problems associated with film heterogeneity through the use of dispersible sensitizer/ZnO NC ensembles. The overarching goal of this research was to study the relationship between structure, energetics and dynamics in a set of synthetically controlled donor-acceptor dyads and triads. These studies provided access to unprecedented understanding of the light absorption and charge transfer steps that lie at the heart of DSSCs, thus enabling significant future advances in cell efficiencies. The approach began with the construction of well-defined dye-NC dyads that were sufficiently dispersible to allow the use of state of the art pulsed laser spectroscopic and kinetic methods to understand the charge transfer events at a fundamental level. This was combined with the synthesis of a broad range of sensitizers that provide systematic variation of the energetics, excited state dynamics, structure and interfacial bonding. The key is that the monodisperse nature and high dispersibility of the ZnO NCs made these experiments reproducible; in essence, the measurements were on discrete molecular species rather than on the complicated mixtures that resulted from the typical fabrication of functional photovoltaic cells. The monodispersed nature of the NCs also allowed the use of quantum confinement to investigate the role of donor/acceptor energetic alignment in chemically identical systems. The results added significantly to our basic understanding of energy and charge transfer events at molecule-semiconductor interfaces and will help the R&D community realize zinc oxide's full potential in solar cell applications.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclotrigallazane, [H2GaNH2]3. Its preparation, structure, and conversion to cubic gallium nitride at 150.degree.CJen Wei Hwang, Scott A. Hanson, Doyle Britton, John F. Evans, Klavs F. Jensen, and Wayne L. GladfelterCite this: Chem. Mater. 1990, 2, 4, 342–343Publication Date (Print):July 1, 1990Publication History Published online1 May 2002Published inissue 1 July 1990https://pubs.acs.org/doi/10.1021/cm00010a004https://doi.org/10.1021/cm00010a004research-articleACS PublicationsRequest reuse permissionsArticle Views184Altmetric-Citations53LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
Metal films are used as diffusion barriers, anticorrosion surfaces, interconnects and resistors in microelectronics, reflective surfaces, antifriction and wear surfaces and decorative applications. They can be deposited by dip and powder coating methods, electrochemical and electroless depositions f...
The response of thin glassy films of polystyrene and poly(vinyl acetate) to a raster-scanned, sliding SFM tip was investigated. Several of the previously proposed mechanisms of the familiar scan-induced patterns are discussed. Increases in film volume and frictional response are quantified, and suggest that the observed tip-induced plastic deformation may relate to a second-order phase transition (glass-to-rubber) beneath the sliding tip. Analysis of the scan-induced patterns suggests a crazing mechanism for the observed plastic deformation. The susceptibility of the film to plastic deformation was examined as a function of scan geometry, applied load, and the gain of the feedback loop that maintains a constant applied load. An empirical quantity called the roughening susceptibility is defined and shown to be linear with respect to variations in the scan conditions. The roughening susceptibility is highly robust in quantifying the dependences on scan history and load. This finding will be further exploited in the second paper of the series, analyzing rate and temperature dependences and their relationship to the glass transition.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTopochemical Control in the Solid-State Conversion of Cyclotrigallazane into Nanocrystalline Gallium NitrideJen-Wei Hwang, John P. Campbell, Jan Kozubowski, Scott A. Hanson, John F. Evans, and Wayne L. GladfelterCite this: Chem. Mater. 1995, 7, 3, 517–525Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://doi.org/10.1021/cm00051a012RIGHTS & PERMISSIONSArticle Views337Altmetric-Citations110LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
