2-amino-4,5-imidazoledicarbonitrile (AIDCN) is known as a promising material for organic nonvolatile memory application, and it has been reported that the performance of the AIDCN-based devices strongly depends on electrode metals. In the present study, we carried out photoemission spectroscopy (PES) measurements on the organic-on-metals (Ag and Al) and metals-on-organic model interfaces of an AIDCN-based memory device. The AIDCN overlayers on the Ag surface formed a sharp interface without apparent chemical interaction, while clear signs of a chemical reaction between the metal and AIDCN and formation of Al clusters in the AIDCN overlayers were revealed on the Al surface. Tendencies of the vacuum level shift and the highest occupied molecular orbital (HOMO) positions depending on the AIDCN coverage looked similar irrespective of the substrates. In the case of the metals-on-organic interfaces, in contrast, the shifting tendencies were opposite depending on the top-electrodes;the Ag-on-AIDCN interface showed upward band-bending with increasing the metal thickness, whereas downward bend-bending was observed for the Al-on-AIDCN interface. A possible origin of the band-bending is explained as intercalation of Ag or Al that behaves as acceptor- or donor-centers, respectively, into the AIDCN film.
We have investigated the thermal stability of TiN/HfSiON gate stack structures using synchrotron-radiation photoemission spectroscopy. Spectral intensities of the Si-oxide components in Si 2p core-level spectra systematically increase with annealing temperature, which strongly depends on thickness of the TiN metal gate layer. Changes brought by annealing procedures in in-depth profiles indicate segregation of Si atoms at the TiN surface. Furthermore, chemical-states-resolved in-depth analyses by angle-resolved photoemission spectroscopy suggest formation of TiSix and HfNy components, due to chemical bond breaking in the HfSiON layer during TiN film growth. This can be related to the degradation of thermal stability.
Shave-off depth profiling achieves depth information by reconstructing accurate elemental distributions even for a roughed surface and a hetero interface. In this paper, we will demonstrate two examples using shave-off depth profiling. One example is a memory chip on semiconductor, which is consisted of thousands of via-holes on the surface. Shave-off depth profiling reconstructed the sample as a manufacturing process. Useful yield on shave-off depth profiling was discussed on the same sample. The other example is focused on hetero interface, which might cause failure on circuit board. Shave-off depth profiling visualized the electro-chemical migration process ; diffusion from Cu anode to resign. We concluded that the shave-off depth profiling is powerful to samples with roughed surface and hetero interface.
Microscope having atomic resolution with chemical sensitivity is one of the ultimate microscopes for the material science. Scanning tunneling microscope (STM) assisted by the core-level excitation by synchrotron radiation (SR) may be a possible candidate of such an ultimate microscope. In this paper we will demonstrate that we can observe element specific images of surfaces in the spatial resolution of several tens of nanometer by measuring the photon induced current images taken with an STM tip detecting the secondary electrons produced by the electron-hole recombination after the core-level excitation. Importance of the chemical contrast-enhancement by dividing the SR-STM image taken at photon absorption edge top by that of at the edge bottom is demonstrated by the observation of transition metal micro patterns. Possibility of a nanometer scale chemical imaging such as C60 domain structure on Si(111)√3×√3-Ag surface with an assistance of high-brilliant light sources is also suggested.
We have been developing a low invasive cell manipulation technology using a nanoneedle of diameter 200 nm and length 10 μm. The nanoneedle insertion is performed by using an atomic force microscope (AFM) to sense a force response when inserting the needle into a living cell body. In this study, nanoneedles functionalized with FRET-based molecular probe have been developed to detect the intracellular mRNA or protein of a living cell. A molecular beacon which targets on human GAPDH mRNA or a FRET-sensor protein which contains substrate motif of caspase-3 was immobilized on a nanoneedle and each functionalized nanoneedle was inserted into a healthy HeLa cell or an apoptotic HeLa cell, respectively. FRET disruptions on the nanoneedles caused by hybridizing with mRNA or by digesting of the sensor protein with caspase-3 could be detected with a confocal scanning fluorescent microscopy.
Recently, SiC is focused as a next-generation semiconductor power device because of its excellent properties. However, SiC is hard to be figured due to the physical hardness and chemical inertness. Therefore, there exist many scratches, damaged layers, and polishing haze on the commercial SiC wafers, which deteriorate surface integrity. We have developed a novel damage-free ultraprecision figuring technique and obtain atomically-flat and damage-free SiC(0001) surfaces. Using the ultraprecision figured on-axis and 8o-off 4H-SiC(0001) surfaces as substrates, we demonstrated the formation of graphene layers upon them, and successfully produced atomically-flat monolayer-graphene with high-qualities, on entire ultraprecision figured SiC surfaces by annealing in ultra-high vacuum without any Si flux.
We have investigated the atomic-site resolved distribution of the excess electronic charge density created by the oxygen vacancies on the rutile TiO2(110) surface. Contrary to the conventional model where the excess charge is localized at the defect, scanning tunneling microscopy and density functional theory show that the charge is delocalized over more than 10 proximate unit cells. According to the theory, the lattice distortion and accompanying rehybridization between the Ti 3d and O 2p orbitals displace the charge from the defect site.
When electrons are confined to nanostructures, quantum interference takes place due to their wave-particle duality. Using spin-polarized scanning tunneling microscopy, we studied the influence of quantum interference of electrons on the spatial distribution of the spin polarization within a single magnetic nanostructure. We find changes in both the magnitude and sign of the spin polarization on a subnanometer scale. We compare our experimental results with ab initio calculations of the spin-resolved local density of states (LDOS). We find that the modulation of the spin-polarization at a given energy can be ascribed to the different magnitudes of spatially modulated majority states and non-modulated minority states contributing to the total LDOS.
A hard X-ray photoelectron spectroscopy (HXPS) instrument has been developed for laboratory use by combining a monochromatic Cr Kα focused X-ray source, a wide acceptance angle objective lens and a high energy electron analyzer. The Cr Kα X-rays excited by a micro focused electron beam at 20 kV beam voltage are diffracted by an ellipsoidal bent crystal monochromator and focused on the sample. A wide acceptance angle objective lens was integrated as the first section of an input lens of a hemispherical analyzer. A 9.9 μm diameter minimum X-ray spot size was achieved and the energy resolution of 0.56 eV was obtained by Au Fermi edge measurements. The maximum acceptance angle and angular resolution were 70o and 0.54o, respectively. The typical acquisition time is about 30 min for a wide energy survey spectrum and about 1 h for Si 1s angle resolved spectra obtained without tilting the sample. The application of this instrument for the analyses of overlayers and multilayer thin films is also discussed.
Electronic structure of a Ag(111) quantum film covered with a (√3×√3) R30o Bi/Ag ordered suface alloy, which shows Rashba spin-split surface states, is investigated with high-resolution spin- and angle-resolved photoemission spectroscopy. Quantum well states (QWS) of the Ag film are significantly modified by the interaction with the spin-split surface states (SS). The band dispersion of the QWS forms energy gaps at the crossing points with the SS bands when spins of the QWS and the SS are parallel, while it remains free-electron-like when those spins are anti-parallel. The present results give a direct evidence of breakdown of the spin-degeneracy in the quantum film of a non-magnetic metal by the surface Rashba effect.
It is proposed that an array of metallic nanorods works as a lens to resolve objects with nanospatial resolution. The fluorescence or scattered light from molecules is plasmonically transferred through the rod array to reproduce the electric field distribution of the object in the other side. The field distributions are simulated by finite-difference time-domain algorithm. The spatial resolution was achieved to 40 nm given by the rod diameter and the array distance. It is found that the stacked arrangement of metallic nanorods resonates in broadband. This broadband resonance enables to generate a magnified image in color. The magnification is achieved by using much larger spacing between nanorods at the image plane compared with the object plane. Such a metallic nanolens has a potential to be a powerful imaging tool for the observation of individual viruses and molecules in the far-field.