The surface molecular conformation of poly(ethylene terephthalate) (PET) and the interface between alumina and PET has been investigated by sum-frequency generation (SFG). A considerable improvement in adhesion strength between AlOx and PET was achieved by short time Ar plasma modification. The increase in adhesion strength shows good correlation with the increase in SFG peak strength. By depositing AlOx, increase of SFG intensities and appearance of a new peak at 1,685 cm-1 are observed, indicating the formation of a C=O···Al bond at the interface. Adhesion improvement by the Ar plasma treatment is not due to the increase in the C=O···Al chemical species at the interface, but due to the increase in the surface energy followed by the increase in the area of the homogeneous amorphous region of the PET and the creation of the surface hydroxyl groups induced by the plasma pretreatment.
A compact type angular-resolved secondary ion mass spectrometry was newly developed. The angular distribution (AD) of secondary ions ejected by oblique Ar+ sputtering at 62 degree from the normal to the surface was measured by a simple tilt operation of the sample stage under a special geometry of an ion gun, a sample stage and a detector. Using this system, AD of sputtered ions was measured for a HfN film sample. Ion intensities of Hf+, N+ and HfN+ decreased monotonously with an increase in the ejection angle. AD of Hf+ was identical with that of N+, implying that preferential sputtering attributed to the difference in mass and surface binding energy played a dominant role in Ar+ sputtering of HfN. Since the yield of HfN+ dimer ions was almost independent of that of Hf+ and N+ monomer ions, it was concluded that the HfN+ ions originated from a direct ejection process of clusters.
Single molecular layers of avidin are fabricated on SiO2 surfaces, and characterized by atomic force microscopy (AFM) and infrared reflection absorption spectroscopy. Immobilization of avidin on the SiO2 surface is performed by; i) ester-group-modification of the surface using silane-coupling reagent, ii) carboxylation of the surface by hydrolyzation in HCl, and iii) amide bonding between the surface COOH and the-NH2 of the avidin. It is confirmed from the AFM observation that the immobilized avidin is dispersed and adsorbed as single molecules, not in aggregated state. Function-recognizing-AFM-observation shows that the binding ability of the avidin to biotin molecules is remained even after the covalent immobilization. Formation of tethered lipid bilayer membranes on the avidin single molecular layer bridged by avidin-biotin binding is also described.
An upright configuration SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope) has been introduced in SPring-8 in the framework of the nanotechnology support project of Ministry of Education, Culture, Sport, Science and Technology (MEXT), Japan. SPELEEM combines microscopy, spectroscopy and diffraction in one system, which allows a comprehensive characterization of the specimen. The combination of SPELEEM and polarized (circularly or linearly) soft X-rays in SPring-8 is expected to realize the highest performance. The characteristics of SPELEEM and typical results, for example nano-XANES (X-ray absorption near edge structure) of Fe oxide on Fe(100) surface, nano-XPS (X-ray photoemission spectroscopy) of indium (In) on Si(111) and antiferro-magnetic domain structure images of NiO(001) single crystal, are reported.
Au/Si(111) surface superstructures exhibit a two-dimensional glass-crystal transition between the β-√3×√3 (glass) and the 6×6 (crystal) phases, in a monatomic layer just by controlling thermal treatment. We have performed electrical resistance measurements at this transition by a microscopic 4-point probe method at various temperatures ranging from room temperature to 120 K, and succeeded in detecting a clear difference in resistance between the two phases. The 6×6 phase has a lower resistance than the β-√3×√3 phase at all temperatures. The resistance of each phase decrease with temperature increase, showing a semiconducting character. By comparing with photoemission spectroscopy data, the electrical conduction mechanism in high temperature region (above ∼175 K) is band conduction of thermally excited electrons with an activation energy ΔE∼100 meV for both phases. The mechanism for low temperature region (below ∼175 K) is hopping conduction with an activation energy ΔE∼3 meV and 8 meV for the 6×6 and the β-√3×√3 phases, respectively. The widths of localization areas are consistent with STM images.
The adsorption states of ethylene on Si(100)c(4×2) were studied by means of high-resolution electron energy loss spectroscopy at low temperatures. We found that some of ethylene molecules are weakly bonded to the surface as a π-complex type at low temperatures (∼50 K). This species is converted to di-σ bonded ethylene by heating. Thus, we conclude that the π-complex species is a stable intrinsic precursor for the cycloaddition reaction (the di-σ bond formation) of ethylene on Si(100)c(4×2). The activation energy from the π-complex precursor to the di-σ chemisorption state is experimentally estimated to be 0.20 eV.
We found that electron beam (EB) irradiation induces structural modification Si(001)-c(4×2) surfaces below ∼40 K. At 24 K, we observed a clear c(4×2) low energy electron diffraction (LEED) pattern immediately after opening the observation, while quarter-order diffraction spots became dim and streaky during the subsequent observation. The results indicate that the c(4×2) arrangement of asymmetric dimers is the most stable structure in the Si(001) surface even below 40 K. The proposed phase transition at 40 K [Matsumoto et al.: Phys. Rev. Lett. 90, 106103 (2003)] is improbable. We quantitatively investigated the current density, beam energy, and substrate temperature dependences of the EB induced decrease in intensity of the quarter-order spots to reveal the origin of the EB effect. Results obtained indicate that electronic excitation and the drop in the carrier concentration at low temperatures cause the EB effect.
We have investigated the atomic structure and electrostatic potential distribution of Ge(105)-(1×2) surfaces formed on Si(105) substrates by high-resolution atomic force microscopy (AFM) with Kelvin probe method. By detecting the force between the tip and samples, AFM makes images without being affected by the electronic states unlike scanning tunneling microscopy (STM). In our AFM study, we have succeeded in visualizing all eight atoms having a dangling bond in the (1×2) unit cell, which were not resolved with STM. The atomic positions are consistent with a structural model called rebonded step model, which was predicted in a previous study with STM and first principles calculation. Furthermore, we have directly observed charge transfer between dangling bond states of the surface atoms by measuring the electrostatic potential in atomic resolution using Kelvin probe method. These results demonstrate that atomically resolved non-contact AFM is an ideal tool for analysis of atomic structures and electronic properties of the surfaces.
A new method for silanol analysis by derivatization XPS has been presented. The feature of this method is to use tridecafluoro-1,1,2,2-tetrahydrooctyl dimethylchlorosilane (FOCS) for the derivatization reagent. We have applied this method to the surface analysis of silicon containing diamond like carbon (DLC-Si) coatings and found that silanol groups on the surface of DLC-Si coatings reduce the friction coefficient.