Search

When measuring the thickness of ultrathin overlayer films using X‐ray photoelectron spectroscopy (XPS), accurate values of the reference intensity ratio (R0) and the effective attenuation length (L) are essential. By definition, R0 is the peak intensity ratio for an overlayer and the substrate in "bulk" phases. Two issues need to be addressed in experimental determining R0 for ultrathin films: (i) How might a contamination layer on the sample used for measuring peak intensities impact R0? And (ii) do differences in the structure or chemistry of an ultrathin film make it inappropriate to determine R0 using bulk forms of the overlayer? In this study, we demonstrate the experimental determination of the R0 for an ultrathin HfO2 film on a Si(100) substrate with a 2 nm SiO2 layer. The values of R0 were determined using (i) the bulk materials of the HfO2 film and substrate and (ii) the ultrathin HfO2 films after different cleaning treatments. The results show that the R0 determined by the ultrathin films is higher than that determined by the bulk materials. Also, keeping the same level of carbonaceous contamination on the sample surface by cleaning as much as possible is essential for an accurate experimental determination of R0. In addition, the effective attenuation length was obtained using samples with known thicknesses measured by X‐ray reflectometry. The thicknesses and uncertainty budget of the ultrathin HfO2 films were then evaluated. [ABSTRACT FROM AUTHOR]

The synthesis of phosphoramidite monomers having a benzyl or ethyl ester in the side chain is described. These compounds were used in the facile and selective functionalization of nucleotides. Attachment of different amino compounds into the specific sites in oligonucleotides was accomplished by aminolysis of the esters. Analysis showed that the conjugates, in which oligoamines were interposed between two oligonucleotides, hydrolyzed RNA substrates at exactly the target sites.

Modifications of GaAs/air interface under x-ray exposure have been investigated by means of x-ray reflectometry (XRR). For this purpose a GaAs/AlAs multilayer system was continuously monitored for 90 h while acquiring XRR profiles. Three different starting models for the oxide/contaminants layer were tested for the analysis of XRR data and discussed. The main effect of x-ray exposure, revealed by the three different approaches, is an increase in the thickness of the gallium and arsenic oxides until a saturation value (about 3.0 nm) is reached after about 50 h. Total reflection x-ray fluorescence analysis performed on a couple of twin samples, either irradiated and nonirradiated, confirms that the oxidation process is promoted by x-ray exposure and indicates the presence of a richer As oxide phase at the surface of the x-ray irradiated samples. [ABSTRACT FROM AUTHOR]

The effects of contamination overlayer and density as well as surface and interface roughnesses on the x-ray reflectivity of a SiO2 ultrathin film are discussed from viewpoints of experiment and theory. Grazing incidence x-ray reflectivity (GIXRR) is used to accurately measure physical structures of SiO2 ultrathin films grown on Si substrate by effectively resolving deviations caused by a contamination overlayer (i.e., H2O and carbonaceous compounds). GIXRR results indicate that only the thickness accuracy of a SiO2 film is largely affected by the overlayer. The thickness of a SiO2 film obtained from GIXRR peak extrema and theoretical fitting reveals that if a SiO2 film with the thickness of 2.64 nm is considered as a single layer, the H2O overlayer with a thickness of 0.55 nm makes the thickness of the SiO2 film increase to 3.09 nm, and the deviation is about 17% from its corrected thickness. By evaluating the GIXRR results of three repeating measurements of a nominal 4-nm SiO2 film, its density, thickness, and surface and interface roughnesses are 2.43±0.01 g/cm3, 3.99±0.03 nm, and 0.40±0.02 nm and 0.25±0.02 nm, respectively. [ABSTRACT FROM AUTHOR]

The system In-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] on MoS[sub 2], prepared by the sequential evaporation of PTCDA and In on a cleaved MoS[sub 2] surface, was studied by low energy electron diffraction. The result indicates that reaction products form an ordered structure on the MoS[sub 2] surface. From the analysis of the diffraction pattern, the presence of six symmetry-equivalent domains of an oblique unit cell of In-PTCDA species results with the dimensions of 9.5 Å, 16.3 Å, and an enclosed angle of 80.2°. In addition, splitting in two domains by a mirror plane exists with the rotation angle R=±10.8° with respect to each of the three equivalent surface crystal axes of the MoS[sub 2] substrate. The new structure is explained by assuming that four In atoms are chemically bonded to the four carbonyl groups of the PTCDA molecules. Furthermore, it is concluded that the In[sub 4]PTCDA species become tilted after a chemical reaction between the PTCDA molecules and the In atoms, which is in agreement with results previously obtained by angle-resolved ultraviolet photoemission experiments. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which measured the indium-[perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] system using angle-resolved ultraviolet photoelectron spectroscopy. Background on the organic semiconductor, PTCDA; Experimental details; Results and discussion; Conclusions.

The effects of contamination overlayer and density as well as surface and interface roughnesses on the x-ray reflectivity of a SiO2 ultrathin film are discussed. The experimental and theoretical grazing incidence x-ray reflectivity (GIXRR) have demonstrated that the oscillation shape and extreme of the x-ray reflectivity spectrum of SiO2 ultrathin films are strongly related to its thickness and surface roughness.

The result of low energy electron diffraction (LEED) are measured and showed that an ordered In-PTCDA (perylene-3, 4,9,10-tetracarboxylic dianhydried) system can be formed on MoS2 surface by annealing. The LEED analysis shows that the In-PTCDA species lie titled on the MoS2 surface.

In the determination of the Avogadro constant using the X-ray crystal density method with a 28Si-enriched crystal prepared by the International Avogadro Coordination (IAC) project, the volume measurement and surface analysis of 28Si spheres play a crucial role. For accurate volume determination, an optical interferometer has been improved taking account of the geometrical shape of the optical components. Furthermore, a new spectroscopic ellipsometer with a sphere rotation system has been developed for accurate surface analysis. The optical interferometer and the ellipsometer have been used for the volume determination and surface analysis of the 28Si spheres repolished by the IAC, respectively. On the basis of the preliminary uncertainty estimation, the relative standard uncertainty of the apparent volume measurement has been reduced from 4.4 \times 10^-8 to 2.7 \times 10^-8 by the improvement of the interferometer. The number of ellipsometric measurement points on the sphere surface has been increased from 20 to 7782 by the installation of the new ellipsometer, yielding more reliable information on the sphere surface. Details of the improvements and the preliminary results of the measurements of the 28Si spheres are given. [ABSTRACT FROM PUBLISHER]

To reduce the uncertainty of the Avogadro constant for the new definition of the kilogram, the surface analysis of the Si sphere produced for the accurate determination of the Avogadro constant is indispensable. In this paper, we conducted the surface quantitative analyses to find out the metallic contaminations on a 1-kg natural Si sphere by X-ray fluorescence analysis. The X-ray photoelectron spectroscopy investigations were also carried out to estimate the thickness of the oxide layer and clarify the chemical binding state of the carbonaceous contamination layer on the surface of a dummy Si sphere. [ABSTRACT FROM PUBLISHER]