D. R. Lee

Roles of the first atomic layers in growth of SrTiO3 films on LaAlO3 substrates

Growth behaviors of SrTiO3/LaAlO3 films could be varied substantially by controlling terminating atomic layers of the substrates. In a film on the LaO-terminated substrate, strain-induced roughening was observed. In a film on the AlO2-terminated substrate, the first atomic layer of the interface seemed to have lots of defects. However, the stress became quickly relaxed, so a SrTiO3 film could be grown in a layer-by-layer mode after a few monolayers. All these observations could be explained in terms of chemical matching between the atomic layers at the interface.

Electrical properties of SrVO3/SrTiO3 superlattices grown by laser molecular beam epitaxy

Abstract SrVO 3 /SrTiO 3 superlattices were successfully grown on SrTiO 3 (001) substrates by laser molecular beam epitaxy. By varying thicknesses of metallic SrVO 3 and insulating SrTiO 3 sublayers, we could observe an interesting metal–insulator transition in the superlattices. The systematic study of electrical transport properties of the superlattices revealed interlayer coupling between SrVO 3 sublayers through two unit cells of SrTiO 3 sublayers. Although the dead layer was about 10 unit cells in SrVO 3 films, the superlattices with much thinner SrVO 3 sublayers could become metallic.

Effects of oxidation process on interface roughness of gate oxides on silicon: X-ray reflectivity study

We report on the effects of the wet and dry oxidation processes on the interfacial roughness and time dependent dielectric breakdown (TDDB) characteristics of the poly-Si/SiO2/Si(100) trilayer. The interface roughness of the oxide layers buried under a thick poly-Si electrode has been investigated using an x-ray reflectivity technique. Analysis of x-ray reflectivity data for the trilayer samples and for a bare oxide film shows that interface roughness of poly-Si electrode/SiO2 interfaces depends on oxidation process while oxide layers have smooth SiO2/Si-subtstrate interfaces. TDDB of the SiO2 layer has also been observed to depend on the oxidation process, indicating that the interface roughness is a crucial factor affecting the TDDB characteristics. The wet oxidized SiO2 film is more stable to dielectric breakdown and has smoother interfaces than the dry oxidized sample.

High-density transition layer in oxynitride interfaces on Si(100)

Nitrided SiO2 thin films on Si wafers were studied by x-ray reflectivity measurements and their electron-density profiles were evaluated. Interfacial layers of the oxides were found to have densities higher than that of either crystalline Si substrates or strained interfacial layers of thermal oxides. The high density probably results from nitrogen incorporation near the interfaces. The present results suggest that strongly retarded boron penetration through nitrided gate oxides is due to their high-density interfacial layers.

Diffuse X-Ray Reflectivity Study of Interface Roughness in Mo/Si Multilayers

Diffuse x-ray reflectivity intensities were measured to characterize interface morphologies of Mo/Si multilayers with and without interleaved carbon thin layers. Parameters related to the interface morphologies can be obtained by fitting the measured intensities within the distorted wave Born approximation in such a way that intermixing widths of graded interfaces, correlated interface roughness amplitudes and vertical correlation lengths are obtained. The interface parameters of Mo/Si and Mo/C/Si/C multilayers are compared for as-grown samples and annealed ones.

Influence of deposition conditions on the growth of micron-thick highly c-axis textured superconducting GdBa2Cu3O7-δ films on SrTiO3 (100)

A fundamental understanding of film processing conditions and its effect on the microstructure, crystallinity, and electrical properties of thick layers of a GdBa2Cu3O7-δ (GdBaCuO) superconductor is necessary to optimize material requirements for its applications. In this work, the authors investigated the surface microstructure, crystalline quality, and superconducting properties of GdBaCuO thick films on (100) SrTiO3 single crystal substrates prepared by pulsed laser deposition (PLD). To clarify the effect of PLD growth conditions the substrate temperature, oxygen partial pressure, and laser fluence were systematically varied, then their impact was correlated on the microstructure and superconducting properties of thick layers of GdBaCuO films. By optimizing these growth conditions, the authors successfully obtained preferentially c-axis textured and superconducting films with a uniform and homogeneous layer up to 3.8 μm thick. Based on these results, the authors provide a key guiding principle in achie...

Thickness driven spin reorientation transition of epitaxial LaCrO3 films

We grew fully strained epitaxial LaCrO3 (LCO) films on SrTiO3(001) under layer-by-layer control up to the film thickness of t = 130 nm using a pulsed laser deposition method. The spin axis of the antiferromagnetic LCO film was systematically examined as a function of t by using Cr L2,3-edge x-ray magnetic linear dichroism (XMLD). The XMLD results manifest a spin reorientation transition (SRT) across a transition thickness of tT ∼ 60 nm. This SRT is well explained in terms of two competing magnetic anisotropy energies of the surface/interface (KS) and the LCO film itself (KV).