Michael E. Graham

Bio: Michael E. Graham is an academic researcher from Northwestern University. The author has contributed to research in topics: Sputter deposition & Thin film. The author has an hindex of 16, co-authored 45 publications receiving 1108 citations. Previous affiliations of Michael E. Graham include Dana Corporation.

A comparison of mixed phase titania photocatalysts prepared by physical and chemical methods: The importance of the solid-solid interface

Abstract: Mixed phase titania photocatalysts, such as Degussa P25, typically show higher photocatalytic activity than pure phase titania, as reported by many researchers. Our previous experimental results indicate that the solid–solid interface is a key factor in enhancing the photocatalytic reactivity of mixed phase titania and may be the location of catalytic “hot spots”. In this study, titania photocatalysts consisting of varying amount of anatase and rutile phases are prepared by reactive dc magnetron sputtering and by a modified sol–gel method. These titania materials are characterized with a variety of techniques and are tested in the photocatalytic degradation of acetaldehyde. Mixed phase titania thin films prepared by magnetron sputtering have a high density of anatase–rutile interfaces and display the highest photocatalytic activity among the catalysts tested. Studies by electron paramagnetic resonance spectroscopy show a unique distribution of charge trapping sites which are characteristic of the sputtered films. The role of anatase–rutile interface to separate charge and improve the photoactivity of mixed phase materials is discussed.

The replacement of electroplating

Abstract: With the increasing concern over toxic wastes produced by conventional metal finishing operations there is a strong drive in the USA to replace “dirty” electroplating processes (especially chrome and cadmium) with “clean” technologies. While many companies and military agencies continue to think in terms of less polluting electroplates, others are turning away from bath technologies completely, in favor of the modern high performance dry coating methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD) and thermal spraying. Under funding from the US Defense Department's Advanced Research Projects Agency, various dry alternatives to electrolytic hard chrome, namely PVD, plasma nitriding, high velocity oxyfuel (HVOF), laser CVD and laser cladding, have been examined for use both in original equipment manufacture and in rebuilding worn components. In this paper hard chrome replacement is used to illustrate the requirements for replacement of electrolytic coatings in general. Hard chrome alternatives are being evaluated to ensure not only that their performance is at least comparable with the chrome they replace, but also that they fit with the way in which the coated components are produced, used, and refurbished. They must be reliable and cost-effective, and must fit the needs of the end user over the entire life cycle of the coated component. HVOF, PVD and duplex plasma-nitride PVD coatings show great promise as replacements in a variety of applications, from bearing surfaces and hydraulics to decorative finishes. The combination of performance data with cost analyses shows that these alternatives can be cost-effective chrome replacements. For example, HVOF coatings can provide more than twice the life in sliding wear at half the cost.

High rate reactive sputtering in an opposed cathode closed-field unbalanced magnetron sputtering system

Abstract: Attention is given to an opposed cathode sputtering system constructed with the ability to coat parts with a size up to 15 cm in diameter and 30 cm in length. Initial trials with this system revealed very low substrate bias currents. When the AlNiCo magnets in the two opposed cathodes were arranged in a mirrored configuration, the plasma density at the substrate was low, and the substrate bias current density was less than 1 mA/sq cm. If the magnets were arranged in a closed-field configuration where the field lines from one set of magnets were coupled with the other set, the substrate bias current density was as high as 5.7 mA/sq cm when NdFeB magnets were used. In the closed-field configuration, the substrate bias current density was related to the magnetic field strength between the two cathodes and to the sputtering pressure. Hard well-adhered TiN coatings were reactively sputtered in the opposed cathode system in the closed-field configuration, but the mirrored configuration produced films with poor adhesion because of etching problems and low plasma density at the substrate.

Method for sputtering compounds on a substrate

Abstract: A method and apparatus for monitoring and controlling deposition of metal, insulating compounds or other compounds on a substrate by sputtering techniques includes maintaining pulsed, constant, direct current power to the target, sensing the voltage of the target material used in the process, simultaneously rapidly sensing the partial pressure of the reactive gas, and simultaneously biasing the substrate to activate the reactive gas or otherwise energizing the reactive gas in the vicinity of the substrate. An apparatus for practicing the invention is also disclosed.

Review of the anatase to rutile phase transformation

Abstract: Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

Abstract: Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Titanium dioxide-based nanomaterials for photocatalytic fuel generations.

Abstract: Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,† †State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China ‡Department of Chemistry, College of Arts and Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, Missouri 64110, United States

Review on Modified TiO2 Photocatalysis under UV/Visible Light: Selected Results and Related Mechanisms on Interfacial Charge Carrier Transfer Dynamics

Abstract: Titania is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The former can be overcome by modifying the electronic band structure of titania including various strategies like coupling with a narrow band gap semiconductor, metal ion/nonmetal ion doping, codoping with two or more foreign ions, surface sensitization by organic dyes or metal complexes, and noble metal deposition. The latter can be corrected by changing the surface properties of titania by fluorination or sulfation or by the addition of suitable electron acceptors besides molecular oxygen in the reaction medium. This review encompasses several advancements made in these aspects, and also some of the new physical insights related to the charge transfer events like charge carrier generation, trapping, detrapping, and their transfer to surface are d...