The Metastable, Glasslike Solid‐State Phase of HAlO and Its Transformation to Al/Al2O3 Using a CO2 Laser

Veith, Michael; Andres, Kathrin; Faber, S.R.; Blin, Joël; Zimmer, Michael; Wolf, Yan; Schnöckel, Hansgeorg; Köppe, Ralf; Masi, R.; Hüfner, S.

doi:10.1002/ejic.200300485

Cited by 23 publications

(26 citation statements)

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“…[37] Thus, the existence of the Al n nanoparticles that are oxidized at the exterior and which have been discussed recently [38] also becomes plausible. In addition, a hypothesis for the surface reaction of metals which we established recently on the basis of experimentally determined structures of metalloid clusters is confirmed [Eq.…”

Section: àmentioning

confidence: 99%

From Icosahedral Boron Subhalides to Octahedral Metalloid Aluminum and Gallium Analogues: Quo vadis, Wade's Rules?

2007

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The synthesis and characterization of polyhedral boron hydrides [1] and boron subhalides, [2] originally regarded as curios, at a second glance have proved to be a lucky chance for progress in chemistry, as on this basis new concepts of chemical bonding were developed, e. g. the Wade-Mingos rules. [3][4][5][6][7] Two milestones in aluminum-organic chemistry with a polyhedral {Al n }-lattice are [Al 12 R 12 ] 2À (1 2À ) [8] and [Al 4 Cp* 4 ] (2; Cp* = C 5 Me 5 ) [9][10][11] (Figure 1). The polyhedral closo-cluster 1 2À is an exception compared to the common low-valent aluminum and gallium clusters which tend to be so-called metalloid clusters.[12] These are clusters mainly characterized by the fact that the topology of the "naked", that is, non-ligand bearing cluster atoms in the cluster core, in many cases reflects the topology of the atoms found in metals and elements, respectively. [13][14][15] Prior to presenting the results of quantum chemical calculations for some [M 12 X 12 ] and [M 13 X 12 ] (M = B, Al, Ga; X = halide) model compounds, we describe our most recent experimental findings which prompted us to start these investigations: [16] Mass spectrometric examinations of the structurally known metalloid-cluster anion [Ga 13 (GaR À (3 À ). [16][17][18] This anion formed during the stepwise reaction of chlorine in the gas phase and as a result of the cleavage of six GaCl moieties [Eq (1)]. The isomer 3 À , when generated from density functional theory (DFT) calculations is, with its octahedral {Ga 6 } core, 30 kJ mol À1 more stable than the icosahedral molecule with a {Ga 12 } core and 12 terminally bound ligands that would be expected according to Wades rules. Based on these surprising results [16, 19] we have performed DFT calculations to elaborate some fundamental differences between typical Wade clusters in boron chemistry and metalloid clusters in aluminum and gallium chemistry.We have examined neutral and dianionic compounds of the structure [M 12 Cl 12 ] 0,2À (M = B, Al, Ga) to determine which of the two structural patterns (icosahedral M 12 -units or clusters with an M 6 -core) is energetically favored for the particular element. For each species we calculated the isomer with an icosahedral structure and terminally bound ligands (ico) and the isomer with an octahedral core of "naked" metal atoms (hence the term "metalloid" (m)). For the metalloid clusters (m), a protecting shell results consisting of doubly oxidized MX 2 units; the bridging (M-X-M) unit contributes to the stabilization of the cluster. The energetic relations between all isomers are shown in Figure 2. Selected structural parameters of [B 12 Cl 12 ] (4), [B 12 The energy diagram (Figure 2) depicts the differences between boron-, aluminum-, and gallium clusters: The icosahedral species 4 (ico) and 4 2À (ico) are energetically favored by 600 kJ mol À1 and 918 kJ mol À1 , respectively, over the metalloid isomers 4 (m) and 4 2À (m). On the other hand, the neutral metalloid Al and Ga clusters 5 (m) and 6 (m) are,

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Section: àmentioning

confidence: 99%

From Icosahedral Boron Subhalides to Octahedral Metalloid Aluminum and Gallium Analogues: Quo vadis, Wade's Rules?

2007

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“…Veith et al [189] investigated CVD grown HAlO compounds which are transparent, non-crystalline, glass-like material and in which oxygen as well as hydrogen are directly bound to aluminium [190]. The HAlO growth at 310 • C led to microhill like topography and showed high human dermal fibroblast cell adhesion and proliferation comparable to single-crystalline silicon surfaces.…”

Section: Other Ceramic Based Compound Filmsmentioning

confidence: 99%

Inorganic PVD and CVD Coatings in Medicine — A Review of Protein and Cell Adhesion on Coated Surfaces

Lackner

Waldhauser

2010

Journal of Adhesion Science and Technology

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The functionalization of biomaterials for implants becomes increasingly important for designing bioinert and bioactive surfaces to reduce the impact of implantation to human body (inflammation, encapsulation) and extend the lifetime of implants. Even pharmacological effects can be triggered by nanomaterials like thin films and nanoparticles in medical treatment. However, the systematic knowledge of the interactions between cells and artificial, inorganic materials is poor yet. Finding the decisive influences for high hemocompatibility or osseointegration is very difficult. Surface chemistry including wetting behaviour, surface charge, homogeneity and functional groups as well as surface topography are some of the fundamental surface parameters defining the cell-surface interaction. Focusing on physical and chemical vapour deposited thin films and coatings, this review will provide for a better understanding of biocompatible coating materials like titanium-and carbon-based compounds and calcium phosphates. of the main goals of biomaterials research [3,4]. However, the precise mechanisms involved in this cell-surface and protein-surface interactions are still unknown.Generally, surfaces of synthetic biomaterials (e.g., polymers, metals and ceramics) are not bioactive themselves. Rather, surface bioactivity is provided by the proteins that adsorb to the biomaterial surface following exposure of the surface to biological fluids. The first molecules are water molecules reaching the surface in a biological milieu containing cells. When cells arrive at the surface, they 'see' a protein-covered surface whose bioactive protein layer has properties that were initially determined by the pre-formed water shells. To control cellular response, it is important to first understand how surface chemistry, surface topography and mechanical forces influence the formation of the adsorbed protein layer and the bioactive sites presented by this layer. Besides water, proteins and cells, biological model systems for biointerfaces (or surfaces) must contain amino acids, nucleic acids and lipids, peptides and DNA (segments), and tissue to describe the sequences occurring in the human body [5]. The recognition of these molecular-scale features is programmed into the molecules through the combination of their 3-D topographic architecture, the superimposed chemical architecture, and the dynamic properties [5]. Although the fundamental interactions occur on the molecular scale, there is an interesting and unique synergistic connection between the nanometer and the micrometer length scales [6-8], when cells are present.Recent advances in topographical surface modification techniques such as electron beam lithography [9], photolithography [10], colloidal lithography [11,12], laser ablation [13] and polymer demixing [14] have allowed the fabrication of surfaces with nano-sized features. In addition, the modification of the surface chemistry by coating with biomaterials or biomolecules of 'higher biocompatibility' helps to separate between bulk pr...

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“…At temperatures over 230 C on the surface of the substrate, the molecular precursor loses simultaneously hydrogen and isobutene forming a transparent layer of HAlO. [8] When this HAlO layer is heated up to higher temperatures (400-550 C), one can observe the evolution of dihydrogen in an on-line mass spectrometer and also a steady change of the color to grey or black, depending on the conditions (time of heating, thickness of the HAlO layer). Elemental analysis (volumetric titration of the metal ions and EDX) of the obtained layer reveals a 1:1 molar ratio of aluminum and oxygen and no hydrogen due to CHN-analysis.…”

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confidence: 99%

“…2 and 3). [8] In this study we report about the formation of l-meter structures on a HAlO layer using laser interference metallurgy. The formation of Al/Al 2 O 3 composite by this laser technique may be interesting as it is known that the chemical properties of Al/Al 2 O 3 cermets can be changed by laser irradiation.…”

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confidence: 99%

“…The situation is very much comparable to our findings using a CO 2 laser and writing motifs on the HAlO film. [8] In Figure 2 the pattern obtained with the three beam interference set-up under analogous conditions is visualized by optical microscopy. The spots are equally displaced with a distance of approximately 4 lm and their pattern approaches hexagonal symmetry.…”

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Periodical Micro‐Structuring of Hydride Containing Metastable Aluminumoxide using Laser Interference Metallurgy

et al. 2005

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Interference of coherent laser beams may be used to structure different types of materials ranging from metals [1] over semiconductors [2,3] to organic polymers. [4] In this process coherent laser beams interfere with one and another to create perfect line-like or dot-like periodic patterns with a very high long range order. During this process the periodic energy distribution is used to be transformed by three effects according to Bäuerle: [5] In the case of polymers with a low amount of free' electrons to interact with the electrical field vector of the electromagnetic wave, primarily a non-thermal photochemical bond-breaking and resulting ablation of material gives the possibilty for a topographical structuring. In the case of semiconductors and ceramics both thermal and nonthermal effects are in an equilibrium and a photo-physical periodical ablation and periodical heat treatment with effects such as melting, re-crystallization and phase transformation, etc., are the results. In the case of metals with a large amount of free' electrons, the non-thermal wave energy is instantanaously transformed into heat and gives the possibility for a periodical heat treatment. Periodical heat treatment of ceramics and metals opens the path to periodical micro-metallurgy. [1] Recently, we have shown that a HAlO layer, which has been produced using the molecular precursor ([tBu-O-AlH 2 ] 2 ) [6,7] in a CVD (chemical vapor deposition) process, can be transformed through thermal treatment into an Al/Al 2 O 3 composite. The chemical processes in these transformations are assembled in the Reactions 1 to 3.These reactions can be explained as follows: In a first step the HAlO layer is deposited on metallic (Cu, Ni, Fe) or semiconducting (Si) substrates, when a gas flow of [(H 3 C) 3 C-OAlH 2 ] 2 at reduced pressure is oriented on the heated substrate. At temperatures over 230 C on the surface of the substrate, the molecular precursor loses simultaneously hydrogen and isobutene forming a transparent layer of HAlO. [8] When this HAlO layer is heated up to higher temperatures (400-550 C), one can observe the evolution of dihydrogen in an on-line mass spectrometer and also a steady change of the color to grey or black, depending on the conditions (time of heating, thickness of the HAlO layer). Elemental analysis (volumetric titration of the metal ions and EDX) of the obtained layer reveals a 1:1 molar ratio of aluminum and oxygen and no hydrogen due to CHN-analysis. In the X-ray diffractogram of the layer (scratched and grinded to a powder) only the diffraction lines of aluminum appear, whereas after heating in a vacuum additional lines of a second phase evolute, which can be attributed to c-Al 2 O 3 . From these findings it can be deduced that the ceramic HAlO layer has been transformed to a composite of metallic aluminum in an amorphous Al 2 O 3 matrix. 27 Al solid state NMR in the MAS mode as well as XPS spectroscopy of this composite reflect the composite nature of the product as well as of its phases. We assume that the mechanism ...

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The Metastable, Glasslike Solid‐State Phase of HAlO and Its Transformation to Al/Al₂O₃ Using a CO₂ Laser

Cited by 23 publications

References 22 publications

From Icosahedral Boron Subhalides to Octahedral Metalloid Aluminum and Gallium Analogues: Quo vadis, Wade's Rules?

From Icosahedral Boron Subhalides to Octahedral Metalloid Aluminum and Gallium Analogues: Quo vadis, Wade's Rules?

Inorganic PVD and CVD Coatings in Medicine — A Review of Protein and Cell Adhesion on Coated Surfaces

Periodical Micro‐Structuring of Hydride Containing Metastable Aluminumoxide using Laser Interference Metallurgy

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