An electric field-induced reversible structural distortion at room temperature is observed at an as-cut single-crystalline SrTiO3 [001] wafer. The structural changes have been characterised in situ by means of X-ray diffraction. It is concluded that the effect requires a distortion of the cubic crystal structure, as it was present only at the rough unpolished side of the wafer. The appearance of the phenomenon was found to depend on the direction of the electric field. Structural changes, depending on the electric field strength, were completely reversible. Regarding the possible electromechanical coupling phenomena, the piezoelectric and electrostrictive effects have to be considered. Cubic SrTiO3 belongs to the centrosymmetric point group \(m\overline{3}m\) ; hence, no piezoelectric effect is present, whereas second-order effects like electrostriction may occur. Peculiarities arising as a result of the special constraints are discussed.

To test nanosize surface patterning for application as implant material, a suitable titanium composition has to be found first. Therefore we investigated the effect of surface chemistry on attachment and differentiation of osteoblast-like cells on pure titanium prepared by pulsed laser deposition (TiPLD) and different Ti alloys (Ti6Al4V, TiNb30 and TiNb13Zr13). Early attachment (30 min) and alkaline phosphatase (ALP) activity (day 5) was found to be fastest and highest, respectively, in cells grown on TiPLD and Ti6Al4V. Osteoblasts seeded on TiPLD produced most osteopontin (day 10), whereas expression of this extracellular matrix protein was an order of magnitude lower on the TiNb30 surface. In contrast, expression of the corresponding receptor, CD44, was not influenced by surface chemistry. Thus, TiPLD was used for further experiments to explore the influence of surface nanostructures on osteoblast adhesion, differentiation and orientation. By laser-induced oxidation, we produced patterns of parallel Ti oxide lines with different widths (0.2–10 µm) and distances (2–20 and 1,000 µm), but a common height of only 12 nm. These structures did not influence ALP activity (days 5–9), but had a positive effect on cell alignment. Two days after plating, the majority of the focal contacts were placed on the oxide lines. The portion of larger focal adhesions bridging two lines was inversely related to the line distance (2–20 µm). In contrast, the portion of aligned cells did not depend on the line distance. On average, 43% of the cells orientated parallel towards the lines, whereas 34% orientated vertically. In the control pattern (1,000 µm line distance), cell distribution was completely at random. Because a significant surplus of the cells preferred a parallel alignment, the nanosize difference in height between Ti surface and oxide lines may be sufficient to orientate the cells by contact guiding. However, gradients in electrostatic potential and surface charge density at the Ti/Ti oxide interface may additionally influence focal contact formation and cell guidance.

Due to the non-equilibrium nature of deposition techniques, thin films can exhibit an energetic state far from thermodynamic equilibrium. Energy supply can stimulate a transition into other metastable states. Examples of metastable phase formation presented in this work are thermally stimulated solid state reactions in metallic nanometer Al/Co/Ni multilayers and phase formation and transition in metallic alloy films of the elemental materials system Fe-Cr. An interesting application illustrates the technical potential of metastable nanometer films.

Two different single-walled carbon nanotube (SWNT) growth modes (cap growth mode and circumference growth mode) are shown to exist. General SWNT diameter windows are derivable from catalyst particle size considerations. In addition, an almost complete picture of nanotube diameter dependencies for the cap growth mode is drawn from experiment. The nanotube diameter always scales linear with temperature, but the degree of dependence varies with the catalyst element. The nanotube diameter scales logarithmically with the gas pressure and catalyst composition. Very few or exactly one atom of a catalyst additive is sufficient to induce SWNT diameter changes. The experimental data allow the conclusion that the observed nanotube diameter is based on materials properties of sp(2)-bonded carbon/graphene sheets, on individual properties of the catalyst elements, and on additional kinetic components from temperature and pressure changes. Indications are found for a specific and maybe decisive role of adsorbate atoms at the surface of a catalyst particle on the nanotube diameter and therefore on the process of nanotube nucleation and growth.

Thermal evolution of the structure of Fe/Al multilayers (MLs) with nominal composition 5*(5 nm Al/5 nm Fe) prepared by crossed-beam pulsed laser deposition is studied by wide-angle X-ray scattering and X-ray reflectometry after different temperature-time procedures of thermal treatments under high-vacuum conditions. In comparison to direct thermal annealing at temperatures of 250 degreesC and 275 degreesC, respectively, which results in nearly complete mixing of the MLs and formation of the FeAl intermetallic compound, quite different behaviour was found after dedicated thermal pretreatment. Annealing at successive growing temperatures before final annealing at temperatures mentioned, resulted in conservation of pronounced multilayer structure. From the results it is generalised, that also in the case of ML systems, the tendency of mixing a dedicated tuning of interface characteristics by thermal treatment allows for formation of diffusionhindering interlayers.

This paper contributes to the studies of physical properties of metastable Fe‐Cr phases which have been discovered recently in the thin films deposited from the hyperthermal Fe and Cr particle beams. The electrical resistance and the magnetic remanence are correlated with the crystallographic parameters and phase composition of the samples. It is demonstrated that the focused ion‐beam induced phase transformation in the unusual metastable Fe‐Cr alloys can be used for the fabrication of ferromagnetic arrays. © 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

Metastable Fe–Cr alloy films of various composition prepared by cross-beam pulsed laser deposition using two different procedures are investigated by wide-angle X-ray scattering. Depending on the Fe–Cr composition of the samples in an extended range, a body-centered cubic (bcc) phase or metastable phases with body-centered tetragonal (bct), face-centered orthorhombic (fco) or primitive orthorhombic (po) and primitive cubic (pc) lattices are formed in the films prepared by simultaneous co-deposition of Fe and Cr. In the films produced by layer-by-layer deposition of thin separate Fe and Cr layers (thickness of about 1 nm), only bcc and bct Fe–Cr phases were observed. A long-time annealing (∼50 h) at a temperature of 425°C near the low-temperature existence limit of the σ-phase under equilibrium conditions followed by slow cooling (rate ∼0.5°C/min) has been performed and various phase transformations were observed. In addition to known equilibrium and metastable Fe–Cr crystalline phases (mainly bcc and bct phases in the films prepared by layer-by-layer technique and bcc, bct and σ-FeCr phases in co-deposited films), a new metastable Fe–Cr superstructure characterised by a primitive tetragonal lattice with parameters a and c of about 0.57 and 0.63 nm, respectively, has been identified. It is shown that the formation of α″-crystallites with preferred orientation in the metastable Fe–Cr alloy films during dedicated long-time annealing gives rise to a spatially periodic modulation of chemical composition resulting in the formation of multilayers with periods of one or a few atomic monolayers of individual Fe and Cr components.

Contrary to expectations to obtain a continuous series of supersaturated b.c.c. Fe-Cr solid solutions by co-deposition of both metals in cross-beam PLD, there form unusual for this materials system metastable intermetallic phases. The structure of alloys develops from a tetragonally distorted b.c.c. at low Cr-content through a face centered orthorhombic (f.c.o.) to a partly ordered primitive orthorhombic (p.o.) crystal structure of the A15-like type at nearly equiatomic composition. It seems to be the first observation of an ordering of restrictedly soluble components under the bombardment of hyperthermal species in PLD. Intriguing fact is that these metastable phases are initially paramagnetic (PM) at room temperature but become ferromagnetic (FM) after annealing in a temperature range 400-500 degreesC or under ion bombardment. The induced PM-FM transformation in the alloys is demonstrated to be useful for formation of stable lateral magnetic microstructures.

Double layers of Fe–Cr and Co–Cu, respectively, were prepared on oxidized Si substrates by pulsed laser deposition (PLD). The interfacial roughness structure was studied by synchrotron X-ray reflectivity measurements at the absorption K-edges using the contrast enhancement due to resonant scattering. The results are determined from simulations of the measured specular and diffuse scans. Whereas in Fe–Cr double layers the σrms-interface width for Fe deposition on Cr (σCr=0.70±0.1 nm) is not very different from that of Cr deposition on Fe (σFe=0.85±0.1 nm), in Co–Cu double layers, in contrast, for Cu deposition on Co, the width (σCo=0.65±0.1 nm) is much smaller than for Co deposition on Cu (σCu=1.5±0.15 nm). On the basis of the fractal model to describe the interface roughness morphology, from the off-specular scans the lateral roughness correlation length, ξ and the roughness exponent, h, were determined. For both types of double layers extremely high ξ-values (larger than 2 μm) were found. However, the flatness is accompanied by a high short-scale roughness (jaggedness), expressed by a small h-parameter (h=0.25±0.05). Both facts were found to be characteristic for the ‘as-deposited’ state of such metal/metal layers prepared by PLD.

Main processes which accompany the interaction of energetic particles with the substrate and the growing film in the pulsed laser deposition (PLD) in vacuum are considered. The subplantational film growth mode, which is inherent to PLD, results in the formation of diffuse transition layers (TLs) between the individual materials of the substrate and film. It is argued that thermodynamic forces do not play a significant role in formation of TLs at room temperature by PLD in vacuum, and the resulting concentration profile between the individual materials is determined almost purely by ballistic effects. Up to 10 nm thick TLs in Fe/Al and Ag/Co PLD-produced bilayers have been determined by numerical simulations, semiquantitative analysis and experimentally by means of a quartz thickness monitor. The latter technique has been proposed as an in situ method for determination of TLs between the individual materials with different sputtering yields. The concentration profiles of TLs are featured by a steep slope on the substrate side and an up to 10 nm long tail of the underlying material in the upper layer.

Crystal structure of sol-gel derived SrBi2Ta2O9 thin films (thickness < 100 nm) deposited on silicon substrates has been investigated as a function of annealing temperature and time by means of X-ray diffraction.P-type Si(100) substrates were treated in a diluted HF solution after chemical cleaning and subsequently a precursor solution for SrBi2Ta2O9 was deposited on the Si substrates by spin coating technique.After drying at 423 K in the atmosphere the samples were annealed in a furnace.At annealing temperatures of 823-973 K the crystallization from amorphous phase to a fluorite-type structure (space group: Fm3m) was confirmed, but a ferroelectric phase (space group: A21am) was not observed even after annealing for 10 hours.As annealing temperature was higher than 1003 K, at first diffraction only from the fluorite-type structure was observed, and then diffraction from A21am structure appears after a specific time t0; it depends on the annealing temperature.The diffraction intensities from the fluorite-type structure decreased and those from A21am structure increased with annealing time.Finally diffraction only from the A21am structure was observed.These results mean that crystal structure of the SrBi2Ta2O9 thin film was gradually transformed from fluorite into A21am structure with time.By atomic force microscope it was confirmed that grain growth occurred simultaneously with the structural transformation.Furthermore, X-ray reflectivity analysis indicated that an interfacial layer was formed during the crystallization and the thickness of the layer increased with annealing time.

Unusual phase formation in Fe–Cr alloys co-deposited by pulsed laser deposition (PLD) is reported. Contrary to expectations to obtain a continuous series of supersaturated body centered cubic (b.c.c.) solid solutions, the structure of alloys develops from a tetragonally distorted b.c.c. at low Cr-content to an ordered primitive orthorhombic crystal structure of the A15 type at nearly equiatomic composition. It seems to be the first observation of an ordering of restrictedly soluble components under the bombardment of hyperthermal species in PLD. The film formation in PLD can be described in the frames of subplantation model of Lifshitz et al. where the phase that forms is a product of kinetic factors like defect formation beneath the free surface and their disintegration rather than thermodynamic driving forces.

Unusual metastable paramagnetic phases have been observed in Fe–Cr thin films (thickness about 40 nm) fabricated by pulsed laser deposition. In the present article, x-ray diffraction and Mössbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation with a projected range positioned in the center of the films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (bcc) structure depends on the initial phase of the film and the ion mass. The initial body-centered tetragonal phase, which forms in the alloys with low Cr content (∼30 at. %), can be completely transformed to the bcc phase already by a dose of 5×1015 Cr/cm2, whereas the primitive orthorhombic phase of roughly equiatomic Fe–Cr alloys is about four times more resistant against ion bombardment. A five times higher Ne ion dose is required to induce the same transformation as by the Cr bombardment. The observed effects are discussed in view of radiation damage caused by the different ions and the grade of affinity of the initial phase to the bcc one.

Reasons are presented which suggest that the liquefaction of the catalytic particles is a decisive condition for formation of single wall carbon nanotubes (SWNTs) by physical synthesis techniques. It is argued that the SWNT growth mechanism is a kind of solid–liquid–solid graphitization of amorphous carbon or other imperfect carbon forms catalyzed by molten supersaturated carbon–metal nanoparticles. The assumption of low temperature melting of these nanoparticles in contact with amorphous carbon followed by its precipitation in the form of SWNTs allows to explain qualitatively the experimentally observed SWNT growth rates and temperature dependence of the SWNT yield. Guidelines for increasing SWNT yield are proposed.

Four rate-limiting processes for the formation of single-wall carbon nanotubes (SWCNT) could be identified by varying furnace temperature, gas type, and pressure in a pulsed-laser evaporation setup. One rate-limiting process accounts essentially for all relevant gas-pressure dependencies and can be quantitatively described using a single gas-specific constant. One thermally activated process is related to fullerene formation, whereas another process, following a T-2-law, is discussed in terms of the diffusion of carbon through molten catalyst nanoparticles. The data provide strong support for an "undercooled melt" mechanism of nanotube formation.

Fe100−xCrx (x=24.5–61.7, 100 at.%) alloy nanometer films prepared by crossed-beam pulsed laser deposition were examined by wide-angle X-ray scattering. On varying the Cr content, x, a change of phase content is observed starting from the known body-centered cubic phase at low Cr content. Indications for three new metastable Fe–Cr phases were found to form in body-centered tetragonal, face-centered orthorhombic and primitive orthorhombic lattice types, respectively.

It is argued that the growth mechanism of single-wall carbon nanotubes (SWNTs) is a kind of solid–liquid–solid (SLS) catalytic graphitization of non-graphitic forms of carbon (predominantly amorphous carbon, condensed at early stages of the carbon vapor relaxation) catalyzed by molten supersaturated carbon–metal nanoparticles. The liquefaction of nanoparticles of the catalytic metals in contact with the amorphous carbon below the equilibrium eutectic temperature of the corresponding metal–carbon alloys is considered as a decisive condition for the SWNT formation both at the nucleation and at the growth stages. It leads to a pronounced increment of carbon solubility (up to 50at.% C), which alters the character of the interaction of the precipitated graphitic form of carbon with the catalyst surface and presumably can result in the SWNT nucleation. Furthermore, it lowers the energy barrier between the initial amorphous and final graphitic carbon phases. The experimental dependencies of the SWNT abundance in the soot on the synthesis temperature, pressure, carrier gas flow velocity, and the initial catalyst content in the target support the idea of the a “catalyst particle size window” in which the supersaturated metal–carbon alloy may remain liquid below the equilibrium eutectic temperature.

Co/Cu multilayers were prepared by cross-beam pulsed laser deposition and characterised by high-angle X-ray diffraction as well as specular and off-specular reflection before and after annealing (500 °C, 2 h). Using synchrotron radiation at the K-edge energy of Co and Cu to enhance the scattering contrast, the study shows that annealing does not enlarge the interface roughness, σr.m.s., but strongly influences the interface morphology. In the fractal model of self-affine structures the latter is expressed by the drastic reduction of the extremely large lateral roughness correlation length parameter, ξ, from approximately 4 μm in the as-deposited state to approximately 20 nm after annealing. High-angle X-ray diffraction indicates that the reduction of ξ is caused by grain coarsening due to growth of crystallites and grain boundaries. Thermal treatment enhances the separation of Co and Cu at the interface, i.e. the initially very jagged (roughness exponent, h, between 0.15 and 0.3) structure is smoothed (h between 0.6 and 0.7).

A novel continuous high productive laser–powder method of carbon single-wall nanotube (SWNT) synthesis based on the laser ablation of mixed graphite and metallic catalysts (Ni/Co=1:1) powders by a 2-kW continuous wave CO2 laser in an argon or nitrogen stream has been proposed. Thermal conductive losses of the laser power introduced in micron-size particles were significantly decreased compared to laser heating of the bulk solid targets in known laser techniques. As a result, more effective utilization of the absorbed laser power for material evaporation was achieved. The carbon soot yield obtained was 5 g/h. Preliminary tests have revealed a SWNT abundance in the soot of 20–40% with a mean diameter of 1.2–1.3 nm as established by Raman spectroscopy and HRTEM. Approaches for the enrichment of the soot with nanotubes are considered.