Lothar Spieß

Growth of cubic InN on r-plane sapphire

InN has been grown directly on r-plane sapphire substrates by plasma-enhanced molecular-beam epitaxy. X-ray diffraction investigations have shown that the InN layers consist of a predominant zinc blende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase which content increases with proceeding growth. The lattice constant for zinc blende InN was found to be a=4.986 A. For this unusual growth of a metastable cubic phase on a noncubic substrate an epitaxial relationship was proposed where the metastable zinc blende phase grows directly on the r-plane sapphire while the wurtzite phase arises as the special case of twinning in the cubic structure.

Preparation of single phase tungsten carbide by annealing of sputtered tungsten-carbon layers

Abstract Tungsten carbide layers were prepared by sputtering from a stoichiometric WC target and subsequent annealing. Carbide formation was found at temperatures above 800°C. Annealing in pure hydrogen ambient results in a carbon depletion in the layers and the formation of a dominant W 2 C phase. We demonstrate that propane added to the annealing ambient stimulates a transformation of the tungsten-carbon layers to a stoichiometric WC phase. The variation of the propane concentration allows a continuously alteration of the layer structure between single phase WC and a mixed layer with dominant W 2 C and the adjustment of different values of the electrical resistance and the optical constants.

Spectroscopic ellipsometry of wurtzite ZnO and GaN: Examination of a special case

We examine the special case of spectroscopic ellipsometry measurements in the vicinity of the fundamental absorption edge of wurtzite ZnO and GaN when the optic axis is perpendicular to the sample surface. It is demonstrated, both by calculations and direct experimental data, that the isotropic dielectric function (DF) derived by means of the isotropic model does not lie between the ordinary and extraordinary DFs and is not their mixture. In general, the isotropic DF also cannot be considered as being approximately identical to the ordinary DF. We observe that their difference may become significant and, in addition, shows a complicated spectral behavior, especially in a range of excitonic absorption. The discrepancy between the isotropic and ordinary DFs of ZnO exceeds 15% at room temperature. For GaN, this effect is considerably smaller. However, the discrepancy might not be neglected if the temperature is sufficiently low.

High-Resolution XRD Investigations of the Strain Reduction in 3C-SiC Thin Films Grown on Si (111) Substrates

In this work the biaxial stress of 3C-SiC thin films epitaxia lly grown on Si(111) substrates has been investigated by using x-ray diffraction methods. The influence of the resulting strain on the electrical properties of SiC/Si heterojunctions was an lyzed. Different methods to prepare the surface prior to the SiC deposition were compared: (i) ex situ carbonization, (ii) interface modification by deposition of Ge prior to epitaxial growth and (iii) annealing of the silicon surface. The x-ray measurements revealed the lowest strain in ex situ carbonized samples, showing a transition from tensile to compressive strain when off-axis substrates were used. The highest strain appeared in SiC layers grown on a thin Ge intermediate layer whi ch was deposited prior to SiC growth without an additional annealing step of the substrate. The strai n in the SiC layer is directly correlated with the reverse current through the heterojunction. Introduction Epitaxially grown mismatched semiconductor heterostructures are of increasing importance for microand optoelectronic devices or circuits. Lattice mismatched layers can be elastically strained by pseudomorphic growth on the substrate. Alternatively the strain can be relieved by relaxation of the epilayer due to formation of misfit dislocations resulting in a n in-plane lattice parameter of the epitaxial film close to that of the bulk material. If epitaxia l l yers of 3C-SiC are grown on Si substrates the large mismatch in the lattice constants and the thermal expansion coefficients lead to a substantial residual tensile strain. A significant part of the 20% mismatch in lattice constants can be released by the formation of a dislocation network. However, the mis match in thermal expansion coefficients of SiC and Si introduces an additional strain into the s yst m during the cooling down process after growth. This strain results in a strong degradation of the layer properties and a wafer warpage, limiting the use of SiC/Si hetrostructures for device a pplications and as pseudo substrate for the deposition of group III-nitrides. In this work we analyze the e ffect of different techniques to minimize the residual strain of the SiC layers and to improve the structural and electrical properties of the grown heterostructures. Experimental The 3C-SiC thin films (thickness ~120 nm) were grown by solid-source mol cular-beam epitaxy (MBE) on (111)-oriented onand off-axis Si crystal wafers at a substrate temperature of 1000°C with a growth rate around 1 nm/min. Prior to epitaxial growth the Si( 111) substrates were prepared by different methods. The first method uses an ex vacuo carbonization process at 1280°C in a propane-hydrogen atmosphere inside a rapid thermal processing (RTP) sy stem [1]. The MBE Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 233-236 doi:10.4028/www.scientific.net/MSF.433-436.233

Komplexe Materialprüfung und Schadensanalyse

Kurzfassung Die Schadensanalyse an Bauteilen und Werkstoffen erfordert immer ein Zusammenspiel von verschiedenen und meist komplementären Werkstoffuntersuchungen, die in der Schadensanalyse als instrumentelle Analysen bezeichnet werden. An einigen ausgewählten Praxisbeispielen aus dem Ofenbau-, Beschichtungs- und Automobilbereich wird gezeigt, wie Metallographie, Elektronenmikroskopie, Röntgenbeugung und Glimmentladungsspektroskopie in Kombination sehr vorteilhaft für komplexe Schadensfälle eingesetzt werden können. Hierdurch lassen sich abgesicherte Hypothesen für die Schadensfälle aufstellen und unter günstigen Umständen auch weitere Informationen über den Hergang ermitteln.

Untersuchungen an dünnen Schichten

Bei der Untersuchung von dunnen Schichten liegt weniger kristallines Material vor als bei der ublichen Pulverdiffraktometrie. So ubersteigt die Eindringtiefe der Rontgenstrahlung bei dunnen Schichten deren Schichtdicke um ein Vielfaches. Damit ist das »Angebot an beugungsfahigen Kornern« stark eingeschrankt. Je nach Schichtart, d. h. amorph, polykristallin, einkristallin oder epitaktisch sind jeweils andere Betonungen auf die Untersuchungsanordnung und Messstrategie des Beugungsexperimentes zu legen. Eine Sammlung von Anwendungen und Darstellungen fur Schichten sind in [207] zusammengefasst.

Growth of 3C-(Si1-xC1-y)Gex+y Layers on 4H-SiC by Molecular Beam Epitaxy

In the present work cubic 3C-(Si1-xC1-y)Gex+y solid solutions were grown at different^temperatures by molecular beam epitaxy on on-axis 4H-SiC (0001) substrates. Two different growth methods are compared in order to explore the optimal growth conditions for the incorporation of Ge into the SiC lattice during the low temperature epitaxy. For this reason simultaneous growth and migration enhanced epitaxy were used. The chemical composition of the grown layers were analyzed by energy dispersive x-ray methods during transmission electron microscopy investigations. It was found that the migration enhanced epitaxy is a more suitable technique for the formation of high quality (Si1-xC1-y)Gex+y solid solutions. Additionally, polytypes transition from 4H-SiC to 3C-SiC occurs during the growth independent of the applied growth technique.

Beugung von Röntgenstrahlung

Neben den mikroskopischen Arbeitsverfahren und der thermischen Analyse haben besonders die Rontgenfeinstrukturuntersuchungsmethoden bei der Beschreibung von Werkstoffen ein weites Anwendungsfeld gefunden. Wahrend die Metallmikroskopie den Gefugeaufbau der Legierungen erschliest, untersucht man mit Hilfe der Rontgenstrahlen den atomaren Feinbau der einzelnen Gefugebestandteile.

Ionenimplantierte Titanoberflächen für den Hartgewebeersatz

Titanium and its alloys are the most commonly used implant materials for hard tissue replacements. Implant surfaces are coated with hydroxyl apatite or calcium phosphate layers using plasma spraying, CVD or electroplating to increase the bioactivity and the long term stability. Despite the fact that such coatings induce often a better and faster osseointegration revisions of implants are still necessary due to the limited stability of the interface between the implant and the surrounding biological tissue. Surface modification using ion implantation of calcium, phosphorus or sodium ions represents an alternative approach to improve the osseointegration. The surface topography, concentration profiles of the observed elements as well as their chemical state and their crystallographic structure have been characterized before and after the ion implantation using different analytical techniques such as Atomic Force Microscope (AFM), X-ray Diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), and Auger Electron Spectroscopy (AES). It could be shown that the implantation of different ions into titanium sample changes the surface properties significantly. However, the ion implanted titanium samples show a different precipitation capacity in simulated body fluid added with albumin. Considering the topographical and physico-chemical results as well as the findings from the precipitation experiments a changed positive cell response of the ion modified titanium samples can be expected. Danksagung Die Autoren bedanken sich bei Dr. W. Glien und J. Rahm (Mathys Orthopädie GmbH) für die großzügige Bereitstellung der notwendigen Titanproben. Dieses Forschungsthema wurde vom Thüringer Kultusministerium unter dem Förderkennzeichen B 478-02001 gefördert. Literatur [1] Kirkpatrick, C.; Bittinger, F.; Wagner, M., Köhler, H.; van Kooten, T.G.; Klein, C.; Otto, M.: Current trends in biocompatibility testing: Review Paper. Proc. Instn. Mech. Engrs. (212): 75-84, 1998. [2] Tirelli, M.; Kokkoli, E.; Biesalski, M.: The role of surface science in bioengineered materials. Surface Science (500): 6183, 2002. [3] Lausmaa, J.; Höfgren, P.; Kasemo, B.: Adsorption and coadsorption of water and glycine on TiO2. J. Biomed. Mater. Res. (44): 227-242, 1999. [4] Vogler, E.A.: Structure and reactivity of water at biomaterial surfaces. Adv. Coll. Int. Sci. (74): 69-75, 1998. [5] Scharnweber, D.: Verbesserung der Biokompatibilität und –funktionalität von Titan und Titan-Basislegierungen für Implantatanwendungen durch Bio Surface-Engineering. Habilitationsschrift an der Fakultät Maschinenwesen der TU Dresden: 1-371, 2005. [6] Brunette, D.M.; Tengvall, P.; Textor, M.; Thomsen, P.: Titanium in Medicine. Springer, Berlin, Heidelberg. 2001. [7] Zhu, X.; Chen, J.; Scheideler, L.; Altebaeumer, T.; GeisGerstorfer, J.; Kern, D.: Cellular reaction of osteoblasts to micronand submicron-scale porous structure of titanium surfaces. Cells Tissues Organs (178): 13-22, 2004. [8] Brauker, J.H.; Carr-Bendel, V.E.; Martinson, L.A.; Crudele, J.; Johnston, W.D.; Johnson, R.C.: Neovascularisation of synARBEITEN ORIGINAL Claudia Blank: Ionenimplantierte Titanoberflächen für den Hartgewebeersatz Dipl.-Ing. Claudia Blank Korrespondenzanschrift: HSG-IMIT e.V., Mikrotechnologie, Wilhelm-Schickard-Straße 10 D-78052 VillingenSchwenningen Claudia.Blank@hsg-imit.de Akademischer Lebenslauf: Dezember 2005 Abschluss des Studiums als Diplomingenieur für Biomechatronik Seit Mai 2006 wissenschaftl. Mitarbeiter am HSG-IMIT im Bereich Wafertechnologie/Flexible Mikrosysteme

Methoden der Röntgenbeugung

Fuhrt man ein Beugungsexperiment aus, dann ist damit immer das Ziel verbunden, mehr fiber die Feinstruktur der Probe zu erfahren. Aus dem Beugungsexperiment kann man die im Bild 5.1 aufgezeigten Zusammenhange und Informationen erhalten. Es ist damit ersichtlich, dass mit einer Untersuchung nicht alle Ergebnisse gleichzeitig, mit hochster Genauigkeit und dazu noch produktiv, d.h. sehr schnell vorliegen. Aus dem Kapitel 4.5.5 ist schon bekannt, dass Genauigkeit und Zeit sich oft diametral gegenuber stehen. Es ist also auserst wichtig und notwendig, erst abzuklaren, welche Informationen gewunscht werden und danach sowohl die Messanordnung als auch die Messstrategie auszuwahlen.