Substrate Normal Direction Research Articles

Structural and electro-optic properties of pulsed laser deposited Bi4Ti3O12 thin films on MgO

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X-ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro-optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.

Texture of obliquely sputtered ZnO thin films

A series of ZnO polycrystalline thin films were prepared on Si(100)/SiO 2/TiN substrates by radio frequency (RF) sputtering at various angles between the sputter direction and the substrate normal. The X-ray diffraction θ/2 θ scans confirmed the expected c-orientation of the films, depending at some extent on the angle of sputtering. The limited pole figures, obtained by rocking-curve measurement, show a slight deviation of the texture axis from the substrate normal direction, which increase with the sputtering angle. The texture axis is inclined not toward the sputtering direction, as was expected, but quite opposite.

Liquid phase epitaxy of cubic FeSi2 on (111) Si induced by pulsed laser irradiation

Epitaxial βFeSi2 layers thermally grown on (111) Si substrates have been irradiated by 25 ns ruby laser pulses in the energy density range 0.3–0.7 J/cm2. Rutherford backscattering analyses in combination with the channeling effect have shown that the silicide stoichiometry does not change for irradiations up to an energy density of 0.5 J/cm2, while alignment of the irradiated silicide along the [111] substrate normal direction is observed. Transmission electron diffraction in the plan view configuration showed that this silicide phase has a cubic symmetry with a lattice parameter very similar to that of Si. Diffraction patterns taken along different poles of the substrate indicated that the epitaxial phase is 180° rotated about the [111] normal direction like the B type NiSi2 and CoSi2 silicides.

Photon drag detection of 10 μm radiation in Bi thin-films evaporated on amorphous substrates

We have observed IR detection signals with ns response in irradiated Bi thin films, which were evaporated at large angles with the substrate normal direction. At 10 μm radiation, these detectors show a voltage response with reversed sign compared to the visible-light response which is generated by a well-known thermoelectric effect. Other thin-film metallic detectors as Cr films operating with this effect do not show this sign inversion at 10 μm. We attribute the sign-reversed fast signal in bismuth to a transversal photon drag effect related to the interband transition induced by the 10 μm radiation.

Origin of Grown-in Dislocations in III-V Compound Semiconductor Epitaxial Layers

ABSTRACTA transmission electron microscope was used to study the origin of grown-in dislocations observed in quaternary InGaAsP layers grown by vapor phase epitaxy on (001) InP substrates. Many of the grown-in dislocations were found to exist as dislocation dipoles and were connected to particles formed at the lnGaAsP/lnP interface. X-ray micro-analysis has indicated that the particles are quaternary alloys having chemical compositions slightly richer in both Ga and P than that of the lattice-matched InGaAsP layer. In some cases, this compositional deviation led to a significant lattice mismatch. As the particle grows larger, a strain relaxation occurs by generating misfit dislocations around the particle in the form of a dislocation half loop. If these dislocation half loops do not develop into a complete loop by totally surrounding the particle, they leave two unclosed dislocation segments (a dislocation dipole), which are replicated by the quaternary overlayer along the substrate normal direction, i.e., [001]. These dislocations eventually become a source for grown-in dislocations.

Extracting physical structure information from thin organic films with reflection absorption infrared spectroscopy

A RATIO method has been developed to extract physical structure information from anisotropic thin organic films on metal substrates using reflection absorption infrared spectroscopy (RAIR). The physical structure information referred to are the Euler angles, θ and ψ, specifying the molecular orientation relative to the surface normal and f, the fraction of material oriented in that manner. Such films are viewed as consisting of polycrystalline domains which have a natural tendency to orient preferentially with respect to the substrate normal direction. Two equations are developed involving these three physical structure parameters and two measured quantities obtained from the thin-film RAIR spectra. These measured quantities are derived from the ratios of band absorbances, the transition moments of which belong to different symmetry groups. The method is tested by applying it to vacuum-deposited metal-free phthalocyanine (H2Pc) films on air-oxidized aluminum. The molecular orientation derived in the α-H2Pc crystallites is in very good agreement with the stacking configurations published in the literature for the isomeric phthalocyanine derivatives, predicting a ‘‘standing b-axis’’ orientation with the normal to the molecular planes inclined 26.5° with respect to the b-axis. In addition, spectroscopic evidence is presented for the first time of the existence of more than one metastable α polymorph of H2Pc. The less stable α polymorph is thermally converted by vacuum annealing to the more stable α polymorph and the first order rate kinetics measured. The resulting activation enthalpy and entropy are very close to those reported by Sharp and Miller for the higher temperature α to β-H2Pc transition.