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

Abstract

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 ...

Biomimetic structures for mechanical applications by interfering laser beams: More than solely holographic gratings

“…4). [11][12][13] The system can be in the form of a coating or thin film on a bulk material as well as a thin structure. In both cases, the system consists of the bulk material and the coating and is therefore a composite material by itself.…”

The Rahman-Nat diffraction on a thin laser-induced grating of the refractive index in semiconductors

“…Up o recent years, to form laser-induced surface structures in solids, interference of two or more laser beams has been used [4][5][6][7][8][9][10]. In practice, a system of the interference beams can be formed by both one source with a light divider and a proper system of mirrors or slits and by a bunch (a grating) of the identical lasers [13].…”

“…Let us consider a condensed matter (semiconductor), an outer surface of which is irradiated by two coherent light beams (CLBs) with an equal frequency that satisfies the inequality, g       (  is the carrier average energy and ε g is the bandgap of this semiconductor). These CLBs, as known [2][3][4][5][6][7][8][9][10], form an interference pattern on a condensed matter surface an interference pattern (Fig. 1).…”

“…The special interest is caused by the laser-induced spatially periodic surface structures. As a rule, they are created at interference of a few laser beams on solid surface [2][3][4][5][6][7][8][9][10]. This technology has already found practical application, in particular, during melting metals [6], and making printing plates [11].…”

Bio‐mimetic scaling of mechanical behavior of thin films, coatings, and surfaces by Laser Interference Metallurgy

“…[5,6] Such heating with specified threshold energies leads to both a direct structuring of the surface by topography effects [4,7] and phase-microstructure effects such as re-solidification, re-crystallization, [7] and phase transformation. [3,8,9] Therefore, the technique is called Laser Interference Metallurgy. It can produce periodically new phases or controlled defect structures to realize a bio-mimetic composite effect with much more reticulated interfaces than common structures.…”