We have investigated thermal stability and adsorption structure of adipic acid (HOOC-(CH2)4-COOH) on Cu(110) surfaces as a function of sample temperature using temperature programmed desorption (TPD), low energy electron diffraction (LEED) and fourier transform infrared adsorption spectroscopy (FT-IRAS). From 350 to 400 K, adipic acid adsorbed as monoadipiate (HOOC-(CH2)4-COO−) forms corresponding structure of c(2×2). As the temperature increases until about 600 K, monoadipiate changes to biadipiate (−OOC-(CH2)4-COO−) corresponding structure of p(1×2) or p(6×2). Biadipiate structure is stable until 600 K and then desorption occurred.
Understanding the SiO2/Si interface on atomic level is an important subject for fabricating silicon based superior devices. However, despite of many studies on the SiO2/Si interface, the interfacial electronic states have been evaluated as the average, but not specifically with individual states. In the present study, we successfully observed the electronic states of particular atoms at the SiO2/Si interface for the first time, using soft X-ray absorption and emission spectroscopy. The interfacial states are noticeably different from those of the bulk SiO2 and strongly depend on the intermediate oxidation states at the interface. Furthermore, comparing the experimental results to theoretical calculations reveals the local interfacial structures.
We have investigated selective growth of carbon nanotubes, such as single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs) and carbon nanocoils, using alcohol CVD through a combination of the metal catalysts and growth temperature. In the case of Fe and Co catalysts, SWNTs were grown at 900oC, and MWNTs at 700oC. Using a Ni catalyst, on the other hand, carbon nanocoils with a variety of helical structures were grown at 900oC. We believe that these findings will contribute to progress in the applications of carbon nanotubes to electronic devices.
We have been developing photoemission electron microscopy (PEEM) using both soft and hard X-rays at SPring-8 beamline BL 15 XU, in order to realize two-dimensional chemical analysis for commercial materials. In order to clarify the sub-surface of specimens, high kinetic energy photoelectrons are appropriate owing to their longer inelastic mean free path. Low kinetic energy photoelectrons, such as secondary electrons, have a high electron yield so that one can easily adjust the PEEM lens condition in real-time with a high spatial resolution image and obtain the bulk sensitive information. Therefore, detecting both high energy photoelectrons and low energy secondary electrons is highly desirable for the practical PEEM system. Our PEEM can also observe several materials including thick insulators and rugged specimens. Using our PEEM, we realized a wide energy scan, and successfully observed the energy filtered image using photoelectrons emitted from deep inner shell for the first time. In this paper, we present the performance of our XPEEM and a finding of the micro-area X-ray absorption near-edge structure (μ-XANES) of DVD+RW for a practical material.
We have studied an indirect observation for surface plasmons on a variety of nano-structured surfaces by means of surface-enhanced Raman scattering (SERS). In this report, we find the ultrahigh Raman enhancement for carbon films on the silver dendrite structures, fabricated by electroplating. Bright spots were observed in the Raman intensity image of the sputtered carbon film on silver dendrites. In order to estimate Raman enhancement on some topographic features, (A) smooth quartz substrates without silver film, (B) smooth quartz substrates with silver film of 300 nm in thickness, (C) silver protrusions of 50 nm in the tip diameter, and (D) silver dendrites were prepared. The maximum Raman intensity of G-band and D-band for the case (D) is 88,000 times larger than that on the flat glass substrates (case(A)). The relative enhancement is 5 times for the case (B) and 400 times for the case (C). In the case (D), some strong Raman scattering points, so called “hot spots” were observed at around the region of 500 nm in the dendrite structures, where the electric field intensity can be enhanced by local plasmons.
A method is described for the detection of DNA hybridization on porous Si thin film, based upon the pairing of oligonucleotide chemistry and the silicon nano-technologies. A porous Si thin film with a pore diameter of approximately 25 nm was synthesized by anodizing a highly doped, n-type Si crystal in a dilute hydrofluoric acid (HF) solution. The surface of pores in the porous Si film was converted to the DNA-modified surface, on which single-stranded DNA molecules are covalently attached. Infrared spectromicroscopy was employed to monitor the hybridization of DNA immobilized on the pore surface with its complementary DNA. In our method, labeling of target DNA with fluorophore probes is not necessary. We demonstrate that DNA hybridization on porous Si thin film can be detected with high sensitivity by analyzing IRAS spectral profiles, suggesting potential utility of our method in DNA sensing chips.
In order to produce nano-scaled ultra-fine patterns into diamond films, a nano-crystalline diamond film with very flat surface has been synthesized. The fabrication process for a nano-scaled patterning in the nano-crystalline diamond film has also been developed. The nano-crystalline diamond film was grown on a silicon wafer by the microwave plasma-enhanced chemical vapor deposition with 1.0 % nitrogen addition in the gas phase. The grown diamond film consisted of nanometer-sized crystals has a smaller surface roughness of Rms=18 nm compared to nitrogen-undoped polycrystalline diamond films. The nano-crystalline diamond film was fabricated into ultra-fine patterns by the e-beam lithography and the reactiveion etching technique. In these processes, one of the key factors for the ultra-fine patterning was a selection of the mask material. The amorphous silicon nitride thin-film was revealed to be appropriate for the etching mask. As the nano-crystalline diamond film etching gas, a mixture of oxygen and a small amount of tetrafluorocarbon was effective for obtaining a higher aspect ratio pattern with little residue at the etched surfaces. We have succeeded in producing nano-scaled ultra-fine patterns into nano-crystalline diamond films with a minimum line-width of 100 nm.
In order to clarify the relation between the diamond surface chemical structures and their surface potentials, we measured the surface work function change varied with the chemisorbed structures of the chemical vapor deposited diamond surfaces. The chemical vapor deposition of homoepitaxial diamond thin films yielded an atomically flat diamond surfaces appropriate for studying a diamond surface chemistry. The surface chemisorbed structure varied with increasing of the oxidized temperature in the range from R.T. to 500oC. According to the surface chemisorbed structure, the surface potential change was observed. The oxidation temperature below 300oC, little chemisorbed hydrogen on the diamond surface was abstracted and replaced to chemisorbed oxygen. In the temperature range, a slight decrease of surface potential was observed. The oxidized temperature in the range between 300∼420oC, a hydrogen terminated diamond surface turned into an oxygen terminated one such as an ether and a ketone structure with increasing of the temperature. A drastic decrease of surface potential was observed with the surface structure variation.
We have observed in-situ the hybridization (double helix formation) and denaturation (separation of double helix at elevated temperatures) of DNA in aqueous solution using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. We demonstrated that conformational changes of DNA strands due to hybridization and denaturation are reflected in the infrared absorption spectra of the bases of DNA. Comparing with the results of ab-initio cluster calculation, we found that hybridization produces the specific C=O stretching vibration modes in the hydrogen-bonded bases, and also that the C=O stretching vibration modes of the bases of a single strand may be greatly influenced by its surrounding water molecules that interact with the bases.
A simple and easy method to prepare super-hydrophobic surface was proposed. Sol-gel films were prepared by hydrolysis and condensation of alkoxysilane compounds. The roughness and free energy at the film surface were controlled by changing the amounts of colloidal silica particles and fluoroalkylsilane, respectively. When both amounts were optimized in a sol-gel film, the surface exhibited an excellent repellency to not only water but also oil. The sol-gel film obtained could be coated onto any solid substrate by a single process. The durability and transparency of the coated layers were sufficient to be applied for practical uses.