Search

The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSb islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates. [ABSTRACT FROM AUTHOR]

We examine the role of vicinal surface steps in the formation and propagation of twins during the growth of epitaxial III-V thin films (GaAs, InP, GaSb, AlSb) on silicon substrates. This is achieved through the combined use of two-dimensional X-ray diffraction and conventional transmission electron microscopy techniques, which allow for both a macro and nano/micro characterization of the material systems. Observed is a systematic suppression of twins formed opposite to the tilt direction of vicinal substrates through a process of step-flow overgrowth of nucleated twins, and an enhancement of twins toward the tilt direction when the fastest growth planes are aligned with the step-flow. These results indicate a probable path to the enhancement of the electronic mobility of lateral devices based on III-V semiconductors on silicon. [ABSTRACT FROM AUTHOR]

An investigation of the magnetocaloric effect for Ni-Mn-Ga films with a composition chosen to yield the highly advantageous magnetostructural phase transition between the paramagnetic austenitic and the ferromagnetic martensitic phases is presented. The observed effect is particularly strong at low magnetic fields, yielding a maximum negative entropy change of -1.4 J/kg K for a field change of only 0.5 T. It is also observed that the cooling process yields a 40% larger entropy change compared to the heating process. Temperature dependent magnetic, structural, and transport measurements indicate that the entropy peak difference between cooling and heating cycles is associated with a stronger overlap of the Curie transition of the austenitic phase with the magnetostructural phase transition upon cooling. The observed behavior is significant to micro-length-scale spot cooling applications utilizing thin films and large-scale magnetic refrigeration applications where low magnetic fields are favorable. [ABSTRACT FROM AUTHOR]

We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide (InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a ∼100 nm deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of ∼60 nm at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one (∼1730 nm) less than but close to the laser wavelength and one (∼470 nm) four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated with the LIPSS modulation. Finally, LIPSS formation is discussed in terms of the observed subsurface microstructures. [ABSTRACT FROM AUTHOR]

With few exceptions, YBa2Cu3O7-δ thin films have been shown to be heavily microtwinned. Conflicting reports of twin-free films, however, have been presented when using the (0 0 1) NdGaO3 substrate. In this report, we address this issue as well as investigate the epitaxial relationship between YBa2Cu3O7-δ and this substrate. We find no evidence that the films are twin-free, but instead provide corroborative support for other work showing that the films are preferentially twinned. This work also establishes the epitaxial relationship between the film and substrate; a relationship consistent with the formation of preferential twins. [ABSTRACT FROM AUTHOR]

Focuses on a study which reported the in situ growth of three distinct phases of lithium cobalt oxide[sub2] by laser ablation deposition on heated substrates in an oxygen background. Characterization of the films by x-ray diffraction; Investigation of crystal grain size using electron microscopy; Film morphology.