Carsten Baehtz

Phase transition in stoichiometric GaSb thin films: Anomalous density change and phase segregation

The crystallization of stoichiometric GaSb thin films was studied by combined in situ synchrotron techniques and static laser testing. It is demonstrated that upon crystallization, GaSb thin films exhibit an unusual behaviour with increasing thickness and concomitant decreasing mass density while its electrical resistance drops as commonly observed in phase change materials. Furthermore, beyond GaSb amorphous-to-crystalline phase transition, an elemental segregation and a separate crystallization of a pure Sb phase is evidenced.

Nanoscale precipitation patterns in carbon―nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle

Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed ...

Ge-doped GaSb thin films with zero mass density change upon crystallization for applications in phase change memories

In order to optimize materials for phase change random access memories (PCRAM), the effect of Ge doping on Ga-Sb alloy crystallization was studied using combined in situ synchrotron x-ray techniques, electrical measurements, and static laser testing. The present data emphasize that the crystallization temperature can be increased up to 390u2009°C with subsequent higher thermal stability of the amorphous phase; phase segregation is evidenced with GaSb, Sb, and Ge phases that crystallize in a two-step crystallization process. The Ge-doped GaSb films exhibit a larger electrical contrast as compared to undoped GaSb alloy (up to ×100). The optical contrast measured by laser testing is shown to follow the mass density change variations upon crystallization, with a negative contrast (higher value in amorphous state) whatever Ge-doping levels. In situ x-ray reflectivity measurements show that zero mass density change can be achieved by low Ge-doping. Ge-doped GaSb alloys look promising since a phase change material w...

Unusual crystallization behavior in Ga-Sb phase change alloys

Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

Memory effect of Mn5Ge3 nanomagnets embedded inside a Mn-diluted Ge matrix

Crystalline Mn5Ge3 nanomagnets are formed inside a Mn-diluted Ge matrix using Mn ion implantation. A temperature-dependent memory effect and slow magnetic relaxation are observed below the superparamagnetic blocking temperature of Mn5Ge3. Our findings corroborate that the observed spin-glass-like features are caused by the size distribution of Mn5Ge3 nanomagnets, rather than by the interparticle interaction through the Mn-diluted Ge matrix.

The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti-Al-N thin films

Ternary Ti–Al–N films were deposited onto Al2O3 (0001) substrates by reactive cosputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy, and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675u2009°C result in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675u2009°C and above, however, yield domain growth of TiN and Ti2AlN due to Al loss to the vacuum. Depositions at a lower temperature of 600u2009°C yield films with correct 4:1:3 stoichiometry, but Ti4AlN3 formation is prevented, supposedly by insufficient adatom mobility. Instead, an incoherent Tin+1AlNn structure with random twinned stacking sequences n is obtained that exhibits both basal plane orientations parallel and nearly perpendicular to the substrate interface. X-ra...

Density change upon crystallization of Ga-Sb films

Besides crystallization time and temperature, the mass density change upon crystallization is a key parameter governing the reliability of phase change random access memory. Indeed, few percentages density change induces considerable mechanical stress in memory cells, leading to film delamination with subsequent electrical failures. This letter presents an extensive study of density change upon crystallization in a series of Ga-Sb thin films with various antimony contents. The mass density of the films is precisely determined by x-ray reflectivity in both their amorphous and crystalline states. The variations of the density in crystalline and amorphous films according to the Sb content found to cross with a zero-density change for 70 at. % Sb. The peculiar behavior of Ga-Sb thin films upon crystallization may be linked to their stress state and mechanical properties.

Tilting of carbon encapsulated metallic nanocolumns in carbon-nickel nanocomposite films by ion beam assisted deposition

The influence of assisting low-energy (∼50-100u2009eV) ion irradiation effects on the morphology of C:Ni (∼15 at. %) nanocomposite films during ion beam assisted deposition (IBAD) is investigated. It is shown that IBAD promotes the columnar growth of carbon encapsulated metallic nanoparticles. The momentum transfer from assisting ions results in tilting of the columns in relation to the growing film surface. Complex secondary structures are obtained, in which a significant part of the columns grows under local epitaxy via the junction of sequentially deposited thin film fractions. The influence of such anisotropic film morphology on the optical properties is highlighted.