Highly accurate depth profiling has been developed by combining angle-resolved photoelectron spectroscopy with high resolution Rutherford backscattering spectroscopy. In this review, the examples are given for the studies on gate insulator/Si interfacial transition layer and the atomic-oxygen-induced oxidation process of strained Si layer formed on SiGe at low temperature.
High-resolution Rutherford backscattering spectroscopy (HRBS) is an excellent technique for surface analysis, that allows quantitative and non-destructive analysis with a sub-nm depth resolution within a short measurement time without any special sample preparation. While HRBS becomes popular in various research fields and industries, especially in micro-electronics industry, there are several issues which should be carefully treated for precise analysis. Principles of HRBS are discussed with particular emphasis placed on the precision of HRBS analysis. The uncertainty in HRBS analysis caused by the scattering cross sections, stopping powers and charge state distributions are discussed in detail. The overall precision of HRBS is estimated to be better than several % in both depth and concentration.
We show that high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) can be applicable to quantitative examination of Hf chemical distribution at a HfO2/SiO2 interface in a ultra-thin gate dielectric of an advanced MOS-FET. We examined how the annealing at 1000oC changes the chemical composition distribution at the interface and analyzed the observed change in the chemical composition in terms of Hf diffusion in SiO2. The estimated diffusion coefficient of Hf in SiO2 was 2.5×10-18 cm2/s and the diffusion length was 1.6×10-2 nm for annealing at 1000oC for 1 s. These indicate that high-temperature annealing used to fabricate Si devices, such as conventional dopant activation process, hardly changes the chemical composition distribution at the interface.
The MOS technologies are making rapid progress in their performance and scale, and the EOT (Equivalent Oxide Thickness) will be needed to decrease to less than 1 nm at the 65 nm generation. Since silicon oxide gate dielectric materials that are extended with use of nitrization have nearly reached their leakage limits, the high-k gate dielectric material is now required. The series of materials consisting of hafnium are the most promising ones in high-k dielectric. It is well known that impurities in the high-k gate dielectric films influence the performance of the MOS devises. Therefore, it is very important to control the amount of impurities. Although SIMS is a very powerful tool for depth profiling, it is very difficult to do quantification for correct distribution of impurity in these materials because of their variable composition. We discuss the problems such as change in sensitivity and the sputtering rate due to the variation in the composition, and describe how we have made an effort for those challenges.
Formations of spatiotemporal patterns in nonlinear chemical reactions have attracted a lot of attentions from the viewpoint of dynamic self-organization in molecular systems. It is now widely known that such spatiotemporal patterns can also be observed in electrochemical systems. The electrochemical system has advantages for the study of the dynamic spatiotemporal patterns: (1) the distance from the equilibrium can be tuned continuously and reversibly by simply changing the electrode potential, (2) the diffusion processes can be flexibly controlled by tuning the structure of the electrochemical cell, and (3) the mode of the spatiotemporal patterns can be tuned easily by changing the geometrical arrangements of the electrodes and the applied potential or current. Here we review experimental and theoretical studies on the spatiotemporal patterns formed at electrode surfaces, by taking electrochemical oscillation during H2O2 reduction on Pt electrode as a representative example.
Stimuli-responsive polymers and their applications to sensors and actuators are widely studied. On the other hand, we have prepared the novel self-oscillating polymer and gels by utilizing the chemical energy of Belousov-Zhabotinsky (BZ) reaction. The polymer is composed of poly (N-isopropylacrylamide) in which Ru (bpy)3, a catalyst for the Belousov-Zhabotinsky (BZ) reaction, is covalently bonded to the polymer chain. Under the coexistence of the reactants (malonic acid, sodium bromate and nitric acid), the polymer undergoes spontaneous cyclic soluble-insoluble changes or swelling-deswelling changes (in the case of gel) without any on-off switching of external stimuli. In this review, the design of self-motive nano-conveyer by arraying the micro-gel beads on surface and novel fabrication method —double template polymerizaiton— were summarized.
Plasmodium of true slime mold, Physarum polycephalum, is an amoeba-like unicellular organism. It crawls in environment with oscillating the cell thickness. The oscillating parts of the plasmodium are connected through tube structures where the protoplasm (intracellular substance) streams. Thus the plasmodium can be modeled as a network consisting of oscillating nodes (or vertices) and links (or edges). In this paper, the network geometries in various environments were analyzed with considering the relation with the spatio-temporal oscillating pattern in the each network. We show the geometry of the networks depends on environmental condition:It forms lattice networks in pleasant environment, tree-graph networks in unpleasant environment, and intermixture of them in neutral environment. The relation between the morphology and the biological function of the plasmodia is discussed in the context of spatio-temporal structure.
Nanoscale manipulation of C60 molecules in a close-packed layer has been achieved by use of scanning tunneling microscope (STM). The evaporation of C60 molecules is performed at a single molecule precision by carrier injection through an application of electric field from STM tip into the close-packed layer, and the voids ascribed to the missing molecules can be freely moved by the carrier injection into the molecules adjacent to the voids. Furthermore, the polymer ring has been formed by the carrier injection from the STM tip into the close-packed layer, and the outer and inner diameters are expanded with an increase in the applied bias voltage. The mechanism for formation of polymer ring is fully discussed by a model based on carrier propagation through the bands of C60 molecules. The carrier propagation has been found to be disturbed by grain boundaries in the close-packed layer.
The atomic force microscope (AFM) has advantages in creating topographic images of the sample surface at high resolution even in a liquid environment, and has been expected to be used as a powerful tool for observing biological samples under the condition closer to the physiological state. However, in contrast with the advances in AFM imaging under ambient conditions, it is still difficult to obtain clear images of biological samples by AFM in liquid, because the samples are usually very soft and uneven, and easily deformed during AFM operation. In this article, based upon our experience, we showed some techniques suitable for imaging biological soft samples by AFM in a liquid environment. Special attention was paid to the dynamic mode AFM for biological studies in liquid. We also introduced a Q-control technique of dynamic mode AFM in liquid, which is helpful for increasing the image quality of soft biological sample.