Characterization of carbon structures produced by graphene self-assembly

Reflection high energy electron diffraction (RHEED) was used to investigate surface roughening during low temperature Si(100) homoepitaxy. The use of RHEED allowed in situ real-time collection of structural information from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roughness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED analyses were quantified by calibrating against cross-section transmission electron microscopy (TEM) analyses of surface roughening. Both the RHEED and TEM analyses revealed similar scaling of surface roughness with deposited thickness, with RHEED analyses resulting in roughness values a factor of ∼2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si(100) homoepitaxial growth in a range of temperatures, 200–275 °C. Initially, surface roughness increased linearly with deposited thickness at a roughening rate that decreased with increasing growth temperature. At each growth temperature, near the crystalline/amorphous Si phase transition, the rate of surface roughening decreased. This decrease coincided with the formation of facets and twins along Si{111} planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature Eact∼0.31±0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, Eact∼0.35 eV, and suggests that limited thickness epitaxy is characterized by this saturation roughness. Once the saturation roughness was reached, no significant changes in surface roughness were detected. In addition, the decay of average in-plane coherence lengths was also temperature dependent. Values of average coherence lengths, at the crystalline/amorphous Si phase transition, also increased with growth temperature. All of these data are consistent with a model that links surface roughening to the formation of critically sized Si{100} facets and the eventual breakdown in crystalline growth.

I n situ real space images and reflection high energy electron diffraction (RHEED) data for the initial stages of molecular beam epitaxy growth of highly strained InxGa1−xAs (0.3≤x≤0.6) on GaAs(100) are reported. RHEED patterns, specular intensity oscillations, and surface lattice constant data are recorded simultaneously during growth. From the RHEED analysis we divide the film evolution into two stages, corresponding to a largely unrelaxed and relaxed surface lattice constant. Scanning tunneling microscopy images of the surface of the film as it appeared during growth reveal that the initial phase has a rippled morphology. With further growth the film evolves to a distinctive three-dimensional island microstructure. Both of these characteristic morphologies are interpreted as manifestations of strain in the growing film.

Surface morphology evolution of epitaxially grown CeO2(110) layers on Si(100) substrates is studied using atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED). The surface has a faceted structure; a stripe-appearance and triangular-shape in plan- and cross-sectional views, respectively. AFM measurements clarify that as the layer thickness increases, the cross-sectional shape changes from a gable roof shape toward trapezoidal, which is consistent with RHEED analyses. The width of the facet monotonically increases with the layer thickness, while its height saturates at ∼5 nm above 600 nm in thickness, which means that the surface approaches smooth morphology. Ion channeling analyses indicate that the thicker the layer, the better the crystalline quality at the surface.

Epitaxial growth of anatase TiO 2 thin films on LaAlO 3(100) prepared using pulsed laser deposition

Epitaxial BaTiO3 (BTO) thin films were deposited by molecular beam epitaxy on (001) silicon using an approximately 5 ML thick SrTiO3 (STO) as an intermediate buffer layer. In situ reflection high-energy electron diffraction (RHEED) was employed to quantitatively determine strain relaxation from the change in the in-plane lattice spacing. The crystalline quality, composition, and surface morphology of the BTO thin films were characterized by a combination of x-ray diffraction (XRD), atomic force microscopy, and x-ray photoelectron spectroscopy. RHEED analysis indicates that the initial growth of BTO was pseudomorphic. Strain relaxation occurred when the thickness reached a critical value of 10 MLs or 4nm. The lattice spacing approached the bulk BTO value for films with 30nm thickness. The BTO layer grows via a two dimensional growth mode. XRD measurement indicates a rocking curving width of the BTO (002) peak on Si as low as 0.9° has been achieved. Strain relaxation of the BTO films grown on different substrates including MgO, MgO/STO buffered Si, and STO buffered Si are compared.

The surface condition of substrate tape is an important factor to obtain epitaxial buffer layer on biaxially textured Ni tape for YBa2Cu3O7-x coated conductors. We prepare ceria films on Ni single crystal, biaxially textured Ni tape and sulfured Ni substrates by direct current magnetron sputtering. The results show that the ceria films prepared on Ni single crystal and sulfured Ni substrates each have a poor-textured grain structure. However, the ceria film fabricated on rolling assisted biaxially textured substrate (RABiTS) exhibits a good c-axis texture and desirable surface morphology. Reflection high-energy electron diffraction analysis indicates that the c(22) superstructure on the RABiTS Ni surface has a dramatic effect on the heteroepitaxial growth of oxide buffer layer.

Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Au/CuInSe2 interface. Au overlayers were deposited in steps on single-crystal p and n-type CuInSe2 at ambient temperature. Reflection high-energy electron diffraction analysis before and during growth of the Au overlayers indicated that the Au overlayer was amorphous. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the Au/CuInSe2 Schottky barrier height.

Single crystalline ZnO films were successfully grown on R-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Epitaxial relationship between the ZnO film and the R-plane sapphire was determined to be <TEX>$[-1101]Al_2O_3{\parallel}[0001]ZnO,\;[11-20]Al_2O_2{\parallel}[-1100]ZnO$</TEX> based on the in-situ reflection high-energy electron diffraction analysis and confirmed again by high-resolution X-ray diffraction measurements. Grown (11-20) ZnO films surface showed mound-like morphology along the <0001>ZnO direction and the RMS roughness was about 4 nm for <TEX>$2{\mu}m{\times}2{\mu}m$</TEX> area.

Epitaxial growth of indium nitride

Dy/Yb superlattices with atomicscale periodicity were fabricated by the molecular beam epitaxy method. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction analyses revealed that the fcc Yb layers grew epitaxially on a cleaved NaCl substrate, while Dy layers were found to have the hep structure with a [102] and/or [110] orientation. Thermal hysteresis resulting from different cooling conditions was observed in Dy/Yb superlattices. The magnetic spins of zero-field-cooled superlattices reoriented from the magnetic-frozen states to ferromagnetic states when heated from 4.2K to a specified temperature and then cooled back to 4.2K under a magnetic field.

We performed growth of body-centered-cubic Nb thin films using an electron cyclotron resonance (ECR) technique on {100} Si substrates. We deposited Nb films using both Ar and Xe plasmas. Reflection high-energy electron diffraction and atomic force microscopy analyses have been performed in order to observe the surface topography. We found that the surface roughness of films deposited by ECR is 4–5 times smoother than films deposited by magnetron sputtering systems. We obtained this result even at room temperature deposition conditions.

The solid-phase epitaxial growth of perovskite-type SrTiO3 films on Sr-deposited Si(001) substrates has been studied. Sr deposition on the Si oxide substrate reduces the thickness of the oxide layer and leads to the formation of a Si(001)-Sr(2×1) reconstructed surface. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) analyses, and atomic force microscopy (AFM) show that the SrTiO3 film grown at 80°C is amorphous and after postgrowth annealing at an elevated temperature the SrTiO3 film changes to a crystalline phase and has a smooth surface.

The reaction of CH4 on a Si(111)-7×7 surface is investigated by reflection high-energy electron diffraction (RHEED) analysis, quadrupole mass spectroscopy (QMS) and scanning electron microscopy/energy dispersive analysis of X-ray (SEM/EDAX). The RHEED patterns during CH4 exposure indicate the evolution of structures such as δ-7×7, 1×1, √3×√3 and SiC for various exposures at temperatures from room temperature (RT) up to approximately 800 °C. A mass spectrum shows that CH4 decomposition products are primarily CH3, CH4, and H2 at a tungsten filament temperature of 1500 °C. A SEM image of the SiC formed at 825 °C and 7920 L shows that the surface is rugged and consisted of hills and valleys. On the basis of the EDAX measurements, it is determined that the SiC layers are C-rich at the hill and Si-rich at the valley. It is found that the SiC layer is generated only after the formation of the √3×√3 structure.

The properties of phosphorus incorporation for n-type doping of diamond are discussed and summarized. Doping of (0 0 1)-oriented diamond is introduced and compared with results achieved on (1 1 1) diamond. This review describes detailed procedures and conditions of plasma-enhanced chemical vapour deposition (CVD) growth and characteristics of electrical properties of phosphorus-doped diamond. The phosphorus incorporation was characterized by SIMS analysis including mapping. n-type conductivity is evaluated by Hall-effect measurements over a temperature regime of 300–1000 K. The crystal perfection of (0 0 1)-oriented n-type diamond is also evaluated by x-ray diffraction, Raman spectroscopy, reflection high-energy electron diffraction and cathodoluminescence analyses. The results show that phosphorus atoms are incorporated into the diamond network during (0 0 1) CVD diamond growth and that phosphorus acts as a donor as in (1 1 1)-oriented diamond. This result eliminates the restriction on substrate orientation, which had previously created a bottleneck in the development of diamond electronic devices.

The correlation between the magnetic properties and micro-structure of electroless-plated CoNiP perpendicular magnetic recording media was investigated. By adjusting the plating bath factors, the perpendicular coercivity, H c? , of the film can be controlled to up to 1500 Oe without changing the saturation magnetization M s and the shapes of the M-H loops. Reflection high-energy electron diffraction (RHEED) analysis showed that these films consist of mixtures of ≪002≫ perpendicularly oriented hep structure regions, and fcc regions without an obvious crystal orientation. The increase in the proportion of the ≪002≫ oriented hep region in such films results in higher H c values; film with the maximum H c of 1500 Oe consisted almost entirely of ≪002≫ oriented hep crystal region. Transmission electron microscope observations revealed that the grain size increases to about 0.03 ?m with an increase in H c? , up to 1500 Oe. It was also clarified that in the initial growth stage, these films show a low H c , and consist of fine crystallites with low crystal orientation.