H. Reichert

Interfacial roughness of partially correlated metallic multilayers studied by non-specular X-ray reflectivity

Abstract Using a two-dimensional image plate detector we measured the non-specular X-ray reflectivity from (Ni 0.81 Fe 0.19 )/Au metallic multilayers. The image plate pattern consists of periodic diffuse sheets which arise from the coherence of the roughness between different interfaces, and are strongest at the position of the Bragg peaks. We analyze the expression for the diffuse scattering cross-section derived from the distorted-wave Born approximation and separate the coherent and incoherent contributions. This allows us to determine the interface roughness parameters, assuming it to be self-affine. From the line shape of the diffuse sheets we determine the partial replication of the roughness for different length scales.

METASTABLE SURFACE ORDERING IN STRAIN RELAXED SI0.5GE0.5 EPITAXIAL LAYERS GROWN AT HIGH TEMPERATURE

We have studied compositional ordering in the near surface region of 3500 A thick unstrained Si0.5Ge0.5(001) samples grown by chemical vapor deposition. Measuring asymptotic Bragg scattering along integer and half-integer truncation rods, we found a type of metastable ordering at this surface which is characterized by integer/half-integer reflections along the integer order truncation rods. We show unambiguously that those scattering features originate from a thin layer at the surface. Annealing at 750 °C extinguished these reflections irreversibly, while the reflections of the RS3 bulk structure were not affected. Anomalous scattering at the Ge K edge also confirmed the existence of a new structure in the near surface region.

Surface induced changes in the critical behavior of the β1—β2 phase transition in V2H

Abstract The influence of the surface on the β1—β2 phase transition of V2H was studied using bulk and grazing incidence (GID) X-ray diffraction. This second-order transition is characterized by the change of the interstitial occupancy of the hydrogen atoms from ordered to random between (101) planes, which can be determined from the hydrogen-induced distortions of the host lattice. An effective bulk critical exponent β was determined to be β = 0.34 ± 0.04 at the specific concentration of 49% (H/V), whereas at a slightly higher concentration prior data [1] yielded β = 0.17. The present crystal traverses a two-phase region which in turn may complicate the study of the critical behavior. Our GID results indicate an increase of β in the near-surface region of the crystal and an ordered phase persisting up to 8 K above the bulk critical temperature, as opposed to a bulk ordered phase that persists 1.0 K above the phase boundary. Preliminary data on the ordering kinetics indicate a somewhat sluggish behavior at the surface which is driven by a more rapid bulk ordering.