Papers

ICMCTF2004 Session F4: Microstructural, Microanalytical and Imaging Characterization

Monday, April 19, 2004 10:30 AM in Room Sunrise

Monday Morning

Start	Invited?	Item
10:30 AM		F4-1 Colossal Supersaturation - A New Concept for Surface Engineering F. Ernst (Case Western Reserve University) We have obtained fundamental insight into the micromechanism and the thermodynamic and kinetic foundations of a novel, low-temperature gas-phase carburization process that vastly improves the surface properties of Fe-Cr-Ni austenitic stainless steels. X-ray diffractometry and X-ray photoelectron spectrometry revealed that the process yields homogeneous, carbide-free solid solutions with > 10 at% interstitially dissolved carbon - more than 600 times the equilibrium solubility at the carburization temperature (743 K). Such "colossal" supersaturation introduces enormous biaxial compressive stresses (2 GPa) and provides exceptional hardness (1200 HV25). Only after prolonged carburization times does the precipitation of carbide particles occur. Transmission electron microscopy determined that most of these particles are Hägg carbide (M₅C₂), a very uncommon carbide in austenitic stainless steels. Thermodynamic and kinetic considerations will be presented to explain the phenomenon of colossal supersaturation. Our results suggest that colossal supersaturation with interstitial solutes can be applied to a variety of alloy families and should therefore lead to a new generation of materials with markedly improved surface properties.
11:10 AM		F4-3 Production of AlN on Aluminum Substrates: Ion Nitriding versus PVD Coating U. Figueroa, O. Salas, J. Oseguera (ITESM-CEM, Mexico) The properties of AlN render this material very attractive for optical, electronic and tribological applications, thus a great interest exists for the production of thin AlN films on a variety of substrates. Many methods have been developed for this purpose where 2 processes outstand: ion nitriding and PVD coating. In the present paper, we compare the processing advantages and disadvantages of both methods in terms of the characteristics of the layers formed. AlN production by ion nitriding is very sensitive to pre-sputtering cleaning and working pressure, but layers several microns thick can be produced in a few hours. However, the surface morphology of the layers is rather rough. On the other hand, PVD coating by DC reactive magnetron sputtering results in macroscopically smoother AlN films although thinner than the ion nitrided layers for the same processing times. The characteristics of these films, in particular their adhesive strength and deposition rate seem to be closely related to the partial pressure of the reactive gas and the applied voltage.
11:30 AM		F4-4 Interface Structure and Reactivity in the Fe/GaAs Epitaxial System A. Trampert, X. Kong, J. Herfort, L. Daeweritz, K.H. Ploog (Paul-Drude Institute for Solid State Electronics, Germany) The integration of magnetism into microelectronics is widely accepted as one of the big challenges for the next decade. An important component of this effort is the successful growth of high-quality epitaxial ferromagnetic films on semiconductor substrate s. A promising candidate is the Fe/GaAs system because of the excellent lattice constant match of the bulk materials. However, it is reported that As diffusion takes place into the Fe layer at the applied growth temperature resulting in Fe-As complexes quenching the magnetism near the interface and thus suppress a spin transfer. At present, there is still a discussion about the formation mechanism of this interfacial reaction layer as well as about its structure and composition. On the other hand, informa tion about the atomic structure of the ideal Fe/GaAs interface is scarcely known as well that would be important in understanding the magnetic anisotropy of the bcc Fe. In this contribution, we present our results about interface of various Fe/GaAs heterostructures investigated by transmission electron microscopy (TEM). The samples were grown by molecular beam epitaxy under different growth temperatures in order to study the reaction mechanism and to identify the conditions for reaching perfect bounda ries. Consequently, the atomic arrangement across the ideal interface is determined by high-resolution TEM imaging that is quantitatively analyzed by comparing the interference contrast with computer simulations. The results of the translation state are discussed in connection with interface models based on ab-initio calculations (taken from literature). The structure and morphology of the extended reaction layers at the interfaces are determined by nano-beam diffraction and HRTEM imaging, the chemical composition of these FeGaAs alloys is analyzed by electron energy loss spectrometry.
11:50 AM		F4-5 Microstructure and Characterization of Amorphous Silicon Films by PECVD C.K. Chung (National Chung Kung University, Taiwan, R.O.C.); P.H. Tsai (Industrial Technology Research Institute, Taiwan, R.O.C.) High quality of amorphous silicon film without island structure has been obtained at low temperature of 300°C by plasma enhanced chemical vapor deposition (PECVD) technology. In comparison with conventional sputtering deposition techniques, PECVD deposited amorphous silicon film has better adhesion to silicon or oxide substrate without cracking and peeling. The film quality is quite related to the process condition such as RF power, frequency mode and substrate temperature, and substrate material. Amorphous silicon film without island structure is achieved on the 1k oxide/Si(100) substrate while some islands occur in amorphous silicon as deposited on the crystalline Si(100) substrate. The morphology and microstructure of amorphous silicon are examined by optical microscopy, electron microscopy and X-ray diffraction. Such amorphous silicon can be applied to many MEMS devices e.g. as high selectivity of etching mask of thick oxide layers in waveguide, the sacrificial/strucure layer in surface micromachined micro relay or CMOS-MEMS integrated display. The released microstructure and thick oxide etching of 12mm using such silicon films as sacrificial layer and etching mask respectively are demonstrated.
12:10 PM		F4-6 Synthesis and Characterization of Novel Polyaniline Nanocomposite Films A. Hopkins, R.M.H. Villahermosa, R.A. Lipeles, D.D. Sawall (The Aerospace Corporation) In this work, we report a simple three-step process for the direct synthesis of electrically conducting polyaniline nano-sized fibers directly to the surface of an Au substrate. An interfacial polymerization technique was used to form a two-dimensional mesh of polyaniline (PANI) fibers which was patterned on the Au surface by a self-assembled thio monolayer of 4-aminothiophenol (4-ATP). Scanning electron microscopy (SEM) images captured the growth of these nanofibers on Au in increments of 1, 3, 5 min and after 24 hr of polymerization. The nature of fiber formation in the presence of the surface-confined 4-ATP monolayer is not completely understood; however, the nature of the interaction seems to be covalent bonding between the developing nanofiber and the Au.