Fraunhofer Center for Laser Applications

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Fraunhofer Center for Laser Applications

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Haubold L.,Fraunhofer Center for Laser Applications | Schuelke T.,Fraunhofer Center for Laser Applications | Becker M.,Fraunhofer Center for Laser Applications | Woodrough G.,Symmetry Medical
Diamond and Related Materials | Year: 2010

Hydrogen-free and predominantly tetrahedrally bonded amorphous carbon thin films (ta-C) are excellent coatings to protect surfaces from wear due to their low coefficient of friction and high hardness. Since these coatings may be several times harder than common engineering materials counterpart wear can be significant. Therefore the surface texture of the ta-C coating is critical to wear applications. While the surface roughness is an important factor, the paper shows that other surface texture parameters have to be considered as well to predict the wear performance of the coating. Wear data are compared of as deposited, polished and brushed ta-C coatings. The results show that typically referenced average values for the surface roughness such as Ra and Rz may prove insufficient to reliably predict the wear behavior of the coating. Additional parameters describing the surface texture such as the "Skewness" (Rsk) and "Kurtosis" (Rku) can provide relevant information. For example, a brushed ta-C surface with an average roughness of Ra = 31 nm showed a tenfold improved wear performance over a polished ta-C surface with an average roughness of Ra = 10 nm. This phenomenon is explained by analyzing the Rsk and Rku data, which prove to more closely capture the post-treatment specific changes to the surface texture of the coatings. © 2009 Elsevier B.V. All rights reserved.

Agency: National Science Foundation | Branch: | Program: STTR | Phase: Phase I | Award Amount: 149.99K | Year: 2009

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This Small Business Technology Transfer Phase I project will demonstrate the effectiveness of a new window insulation technology with thermal performance properties comparable to a well insulated wall. In the United States, buildings account for more than 40% of total energy consumption. Because windows are between 20-40% of the vertical surface area of an average building, they consume 30-60% of heating and cooling energy, representing an annual impact of more than 4.1 quadrillion BTU of primary energy, costing building owners over $40 billion/year. Our innovation is to use nanometer sized spherically shaped silica particles attached to glass fibers to create an insulation material with extremely small points of contact that can be used to make thin vacuum insulation panels. This Phase I project will determine the feasibility of incorporating these nanoparticle-modified fibers into innovative Multilayer Vacuum Insulation Panels to achieve target thermal insulation properties in a commercially viable, dynamic window covering. This technology will exceed the US DOE's target window insulation properties in a commercially viable product that will serve as a cost effective solution for net-zero energy new construction as well as a retrofit product to improve the energy efficiency of existing buildings. By facilitating the development and commercialization of a product that will substantially reduce unwanted heat transfer through fenestration, the research in this Phase I STTR project will contribute a partial solution to global energy and environmental challenges. The development of new core materials for vacuum insulation panels offers enormous opportunities for the improvement of the energy efficiency of buildings while also contributing a substantial financial savings over time. The educational impact of this research will be significant on two levels: 1) a substantial amount of the work will be performed by students under the direct supervision of recognized experts and 2) the research will significantly advance the state of the art in thermal insulation technology.

Schuelke T.,Fraunhofer Center for Laser Applications | Grotjohn T.A.,Michigan State University
Diamond and Related Materials | Year: 2013

The empirical know-how of single crystalline diamond polishing has been developed over centuries in the diamond gem cutting industry. Since the 1950s new and varied uses and potential applications for synthetically produced diamond have been consistently proposed and developed. This innovation process continues with the availability of ever better, more specialized and less costly single crystalline and polycrystalline diamond materials. Yet, the potential exploitation of this hardest of materials is still in its infancy. Polishing is a critical and limiting step for advancing diamond applications in terms of cost effective processing and the achievable material surface finish. The current state-of-the-art of polishing single crystalline and polycrystalline diamond materials is reviewed based on the published literature. The material removal process during traditional mechanical polishing using diamond grit and polishing wheels is strongly anisotropic and depends upon crystal planes and polishing directions. Wear debris analyses and molecular dynamic simulations led to the understanding that this anisotropy is primarily caused by a mechanically induced transition from diamond to an amorphous carbon phase rather than by microchipping as previously thought. Mechanical polishing also leads to subsurface damage and limits the achievable surface finish for single crystalline diamond. Advanced techniques are discussed to improve the polished crystal's surface quality. Mechanical polishing of polycrystalline diamond films and freestanding plates is particularly slow due to the intrinsic structure variations in such materials. To overcome these limitations faster polishing techniques have been developed and are reviewed and compared. These techniques introduce additional chemical and physical means of material removal extending the capabilities of mechanical polishing. There is no single method that can address all requirements, but the available variety affords the careful selection of an optimal process for a given task. Finally, while diamond polishing is a subject of interest since centuries, it still remains a very important research area required to unfold the promise of diamond as a technical material. © 2012 Elsevier B.V.

Lu J.,Michigan State University | Gu Y.,Michigan State University | Grotjohn T.A.,Michigan State University | Grotjohn T.A.,Fraunhofer Center for Laser Applications | And 3 more authors.
Diamond and Related Materials | Year: 2013

The detailed experimental behavior of a microwave plasma assisted chemical vapor deposition (MPACVD) reactor operating within the high, 180-300 torr, pressure regime is presented. An experimental methodology is described that first defines the reactor operating field map and then enables, while operating at these high pressures, the determination of the efficient, safe and discharge stable diamond synthesis process window. Within this operating window discharge absorbed power densities of 300-1000 W/cm3 are achieved and high quality, single crystal diamond (SCD) synthesis rates of 20-75 μm/h are demonstrated. The influence of several input experimental variables including pressure, N2 concentration, CH4 percentage and substrate temperature on SCD deposition is explored. At a constant pressure of 240 torr, a high quality, high growth rate SCD synthesis window versus substrate temperature is experimentally identified between 1030 and 1250 C. When the input nitrogen impurity level is reduced below 10 ppm in the gas phase the quality of the synthesized diamond is of type IIa or better. © 2013 Elsevier B.V.

Grotjohn T.A.,Michigan State University | Grotjohn T.A.,Fraunhofer Center for Laser Applications | Tran D.T.,Michigan State University | Yaran M.K.,Fraunhofer Center for Laser Applications | And 2 more authors.
Diamond and Related Materials | Year: 2014

Semiconducting n-type diamond can be fabricated using phosphorus as a substitutional donor dopant. The dopant activation energy level at 0.58 eV is deep. At high dopant concentrations of 1020 cm- 3 the activation energy reduces to less than 0.05 eV. Phosphorus doping at concentrations of 1020 cm- 3 or higher has been achieved with epitaxial growth on the (111) diamond crystallographic surface. In this work epitaxial growth of diamond with high phosphorus concentrations exceeding 1020 cm- 3 is performed using a microwave plasma-assisted chemical vapor deposition process with process conditions that include a pressure of 160 Torr. This pressure is higher than previous phosphorus doping reports of (111) surface diamond growth. The other growth conditions include a feedgas mixture of 0.25% methane and 500 ppm phosphine in hydrogen, and a substrate temperature of 950-1000 C. The measured growth rate was 1.25 μm/h. The room temperature resistivity of the heavily phosphorus doped diamond was 120-150 -cm and the activation energy was 0.027 eV. © 2014 Elsevier B.V. All rights reserved.

Patwa R.,Fraunhofer Center for Laser Applications | Herfurth H.,Fraunhofer Center for Laser Applications | Bratt C.,Fraunhofer Center for Laser Applications | Christophersen M.,U.S. Navy | Phlips B.F.,U.S. Navy
Journal of Laser Applications | Year: 2015

X ray collimator optics for space application require an array of high aspect ratio holes of 60:1 with a minimal tantalum (Ta) thickness of ≥2 mm and a very high open area fraction (hole versus wall fraction) of 70% to achieve high collimator efficiency. Each collimator with a drilled area of 110 mm × 70 mm contains several million holes and need a fast drilling process. Laser percussion drilling was performed using an IR pulsed disk laser in a 1 and 2 mm thick Ta plate. A tightly spaced hexagonal closed packed pattern was used to maximize open area fraction with hole-to-hole spacing as small as 80 μm. However, this resulted in a high concentration of debris and a thick recast layer on the remaining walls between the holes. Different process gases were investigated to minimize debris formation and reduce the recast layer thickness. Ramping of pulse energy during the drill cycle was investigated to minimize the adhesion between the substrate and recast layer. Chemical etching was used to remove the debris and recast from the top surface and the inside of the laser-drilled holes. Hole cross sections showed that a high aspect ratio was achieved with a hole diameter of about Ø50 μm in 2 mm thick Ta. To achieve the shortest drilling time of 200 ms per hole, the process parameters were optimized and a hybrid nozzle, with both horizontal and vertical gas flow, was developed and implemented. © 2015 Laser Institute of America.

Gu Y.,Michigan State University | Lu J.,Michigan State University | Grotjohn T.,Michigan State University | Grotjohn T.,Fraunhofer Center for Laser Applications | And 4 more authors.
Diamond and Related Materials | Year: 2012

The design and performance of an improved microwave plasma assisted chemical vapor deposition (MPACVD) reactor is described. This reactor operates with high power densities and at pressures up to 300 torr. Differences from earlier MPACVD reactor designs [4] include an increase in applicator and dome size and the excitation of the applicator with a new "hybrid "TM 0/TEM 001" mode. The reactor is experimentally evaluated by synthesizing single crystal diamond (SCD) at pressures from 180 to 300 torr with absorbed power densities between 400 and 1000 W/cm 3. Without N 2 addition SCD growth rates as high as 75 μm/h were observed. A SCD growth window between 950°C and 1300°C was identified and within this growth window growth rates were 1.2 to 2.5 times greater than the corresponding growth rates for earlier reactor designs. SCD characterization by micro-Raman spectroscopy, SIMS, and by IR-UV transmission spectroscopy indicated that the synthesized SCD quality is that of type IIa diamond. © 2012 Elsevier B.V. All rights reserved.

Hinuber C.,Fraunhofer Center for Laser Applications | Hinuber C.,TU Dresden | Kleemann C.,Fraunhofer Center for Laser Applications | Kleemann C.,TU Dresden | And 6 more authors.
Journal of Biomedical Materials Research - Part A | Year: 2010

Diamond-like carbon (DLC) films are favored for wear components because of diamond-like hardness, low friction, low wear, and high corrosion resistance (Schultz et al., Mat-wiss u Werkstofftech 2004;35:924-928; Lappalainen et al., J Biomed Mater Res B Appl Biomater 2003;66B:410-413; Tiainen, Diam Relat Mater 2001;10:153-160). Several studies have demonstrated their inertness, nontoxicity, and the biocompatibility, which has led to interest among manufacturers of surgical implants (Allen et al., J Biomed Mater Res B Appl Biomater 2001;58:319-328; Uzumaki et al., Diam Relat Mater 2006;15:982-988; Hauert, Diam Relat Mater 2003;12:583-589; Grill, Diam Relat Mater 2003;12:166-170). In this study, hydrogen-free amorphous, tetrahedrally bonded DLC films (ta-C) were deposited at low temperatures by physical vapor deposition on medical grade Co28Cr6Mo steel and the titanium alloy Ti6Al4V (Scheibe et al., Surf Coat Tech 1996;85:209-214). The mechanical performance of the ta-C was characterized by measuring its surface roughness, contact angle, adhesion, and wear behavior, whereas the biocompatibility was assessed by osteoblast (OB) attachment and cell viability via Live/Dead assay. There was no statistical difference found in the wettability as measured by contact angle measurements for the ta-C coated and the uncoated samples of either Co28Cr6Mo or Ti6Al4V. Rockwell C indentation and dynamic scratch testing on 2-10 Iμm thick ta-C films on Co28Cr6Mo substrates showed excellent adhesion with HF1 grade and up to 48 N for the critical load LC2 during scratch testing. The ta-C coating reduced the wear from 3.5 × 10-5 mm3/Nm for an uncoated control sample (uncoated Co28Cr6Mo against uncoated stainless steel) to 1.1 × 10-7 mm3/Nm (coated Co28Cr6Mo against uncoated stainless steel) in reciprocating pin-on-disk testing. The lowest wear factor of 3.9 × 10-10 mm3/Nm was measured using a ta-C coated steel ball running against a ta-C coated and polished Co28Cr6Mo disk. Student's t-test found that the ta-C coating had no statistically significant (p < 0.05) effect on OB attachment, when compared with the uncoated control samples. There was no significant difference (p < 0.05) in the Live/Dead assay results in cell death between the ta-C coated Co28Cr6Mo and Ti6Al4V samples and the uncoated controls. Therefore, these ta-C coatings show improved wear and corrosion (Dorner-Reisel et al., Diam Relat Mater 2003;11:823-827; Affato et al., J Biomed Mater Res B Appl Biomater 2000;53:221-226; Dorner-Reisel et al., Surf Coat Tech 2004;177-178:830-837; Kim et al., Diam Relat Mater 2004;14:35-41) performance and excellent in vitro cyto-compatibility, when compared with currently used uncoated Co28Cr6Mo and Ti6Al4V implant materials. © 2010 Wiley Periodicals, Inc.

Berkun I.,Michigan State University | Demlow S.N.,Michigan State University | Suwanmonkha N.,Michigan State University | Hogan T.P.,Michigan State University | And 2 more authors.
Materials Research Society Symposium Proceedings | Year: 2013

A temperature dependent Hall Effect measurement system with software based data acquisition and control was built and tested. Transport measurements are shown for boron-doped single crystal diamond (SCD) films deposited in a microwave plasma-assisted chemical vapor deposition (MPCVD) reactor. The influence of Ohmic contacts and temperature control accuracy are studied. For a temperature range of 300K-700K IV curves, Hall mobilities and carrier concentrations are presented. © 2013 Materials Research Society.

Tran D.T.,Michigan State University | Fansler C.,Michigan State University | Grotjohn T.A.,Michigan State University | Grotjohn T.A.,Fraunhofer Center for Laser Applications | And 4 more authors.
Diamond and Related Materials | Year: 2010

Diamond etching is characterized using a microwave ECR plasma reactor with regard to etch rate selectivity, surface morphology, and feature size. Etching is performed on diamond substrates using a variety of etch mask materials including aluminum, titanium, gold, silicon dioxide and silicon nitride. The etch feed gases are combinations of oxygen, sulfur hexafluoride and argon. Aluminum masks provided the highest selectivity ratio of diamond etch rate to mask etch rate, both with and without SF6 in the oxygen/argon feedgas. Selectivity was not found to be dependent on mask feature size. Gold masks produced the least degree of micromasking. © 2010 Elsevier B.V. All rights reserved.

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