Atom probe thin films

We consider a model of a two-probe molecular device which is schematically shown in Fig. 1 where a Ceo molecule is contacted by two semi-infinite gold electrodes [35,36]. One can replace the Ceo by other molecules, atomic clusters, thin films, semiconductors, and other materials. 

Other excellent methods of phase identification include TEM and electron diffraction. These may be more useful for low-Z materials, ultrathin films, and for characterizing small areas, including individual grains. For multiphase films with incomplete texture, these methods and XRD are complementary, since in commonly used geometries, they probe atomic planes perpendicular and parallel to the thin film surface, respectively. 

Thin film technology is becoming one of the important technologies today. While there are infinite varieties of thin film fabrication methods, most amorphous thin films seem to exhibit fractal-like atomic structures. Depending on the fabrication conditions, a thin film grows on the substrate into columnar structures with many voids interdispersed in the thin film.80 These structures can be seen in the field ion microscope, and compositional variation can be analyzed with the atom-probe. In addition, formation of atomic clusters inside the thin film can be substantiated with the observation of a large fraction of cluster ions in field evaporation by the atom-probe. 

FTM and atom-probe studies of thin films of Ni, Au, Pt, a-Ge H, a-Si H and WO3, etc., on various substrates were reported by Krishna-swamy et a/.81 First, field ion tips each with a field evaporated surface were prepared. They are placed in an MRC model 8502 r.f. sputtering system. Tips were mounted on a recessed and shielded structure behind the sputtering surface which is bored with small holes about 1 to 2 mm in diameter. The very end of the tips came out of the holes to approximately the same level of the sputtering surface. Films were sputtered at about 20 mTorr Ar at an r.f. power of about 50 W. Thickness of a deposited thin film was controlled by both the r.f. power and the deposition time. Film thickness in the range of a few hundred to a few thousand A were studied. These tips were then imaged with Ne in the field ion microscope, or analyzed in the flight-time-focused ToF atom-probe. 

Ge(OH)+, Ge(OH)2+, Ge(OH)3+ and Ge202+, etc. It is clear from these observations that atoms tends to form clusters in thin films. Thin films also tend to react with water in the atmosphere. In field evaporation, water molecules are desorbed in the form of hydride, oxide or hydroxide ions with the substrate atoms and atomic clusters. From the above discussions, it is clear that the FIM and atom-probe can now be applied to study a wide variety of problems for a wide variety of materials. Field ion microscopy is no longer confined to studying refractory metals, as many scientists still erroneously perceive. 

Basic information needed to understand the physical and chemical properties of solid surfaces and thin solid films include the atomic structures and the compositional variations across the surface and interface layers. The atomic structures can be studied with microscopies and with surface sensitive diffraction and particle scattering techniques. Compositions of surfaces and thin films can be studied with the atom-probe FIM. In general, however, compositional analyses are mostly done with surface sensitive macroscopic techniques, such as auger electron... 

The angle 0h is the angle between the X-ray polarization direction, s, and the direction to the atom h in the j shell. For isotropic materials, like powders, the sum becomes N/3. For thin films like heteroepitaxial metallic films [19], there is often an intrinsic asymmetry leading to different in-plane and out-of-plane bonds. Otherwise, the polarization dependence of EXAFS can be also an important tool for studying texturized films providing an alternative probe to the long range order technique such as diffraction when XRD diffraction is dominated by that from the substrate. 

Recently, Pcs organized on surface have been used as molecular probes for the determination of quantum confined effects [207], CoPc molecules form ordered self-assembled monolayers (SAM) on the top of Pb(lll) thin films grown on a Si( 111) substrate with the Pc units lying flat on the surface, as revealed by atomically resolved STM. A close analysis of the STM data revealed that the Pc molecules adsorb and self-assemble on the surface following a thickness-dependent adsorption pattern, which is ultimately related to the quantum size effects of the metal surface. 

Research on nano- and micro-fabrications based on anodizing treatments combined with chemical/mechanical processes such as laser irradiation, atomic force micro-probe processing and thin film deposition techniques... 

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