The Si(111)-7×7 reconstructed surface and fullerene (C60) molecules deposited on Si(111)-7×7 reconstructed surface were investigated by using a new technique called non-contact scanning nonlinear dielectric microscopy (NC-SNDM) under ultra-high vacuum conditions. A local atomic electric dipole moment distribution of Si atoms on Si(111)-7×7 reconstructed surface was resolved. This is the first successful demonstration of direct atomic dipole moment observation achieved in the field of capacitance measurement. Furthermore, both topography and induced electric dipole moment of individual C60 molecules as well as internal structure of the C60 molecule were successfully resolved with atomic-scale resolution. The NC-SNDM technique can yield the internal structure of the C60 molecule and the position where the charge transfer of the C60 molecules occurs on the Si(111)-7×7 reconstructed surface.
Heterodyne laser Doppler interferometry was used to implement a high frequency atomic force microscope (AFM) that can accommodate a cantilever with a natural frequency of up to 200 MHz. Since Doppler interferometry measures velocity, the signal level increases proportionally with frequency for a given amplitude of oscillation, or the noise floor in terms of displacement decreases with 1/f. A noise level of 0.5 fm/√Hz was attained around 2 MHz, giving a large signal to noise margin for high frequency cantilevers and higher vibration mode detection. We have so far confirmed the following: (i) atomic resolution of Si(111) 7×7 with an amplitude of drive as low as 0.03 nm at 1.6 MHz, (ii) true atomic resolution dynamic lateral force microscopy, (iii) lateral force gradient detection at the atomic level, (iv) manipulation of Si atoms at room temperature, (v) vibration measurement of Si nanowires, tungsten oxide whiskers and graphene cantilevers above 100 MHz, (vi) atomic resolution imaging with the 2nd and 3rd mode of deflection and (v) true atomic resolution imaging in water using deflection or torsion with a few 10 pm amplitude of drive.
The atomic force microscope (AFM) is unique in its capability to capture high-resolution images of biological samples in liquids. This capability becomes more valuable to biological sciences if AFM additionally acquires an ability of high-speed imaging. “Direct and real-time visualization” is a straightforward and powerful means of understanding biomolecular processes. With conventional AFM, it takes more than a minute to capture an image, while biomolecular processes generally occur on a millisecond timescale. In order to fill this large gap,various efforts have been carried out in the past decade. Here, we review these past efforts, describe the current state of the capability and limitations of our high-speed AFM, and discuss possibilities that may break the limitations, leading to an innovative high-speed bioAFM.
Noncontact atomic force microscopy (NC-AFM) using frequency modulation detection method has been widely used to investigate the various surfaces with atomic resolution. In this paper, we introduce the measurement technique of NC-AFM operating at low temperatures (LTs). First, we theoretically discuss the enhancement of the force sensitivity in NC-AFM operating at LTs. Then, we present the design and performance of LT-NC-AFM using fiber optic interferometer with quick sample and cantilever exchange mechanism. We also show the present status of the LT-NC-AFM imaging. In detail, we show the experimental results to investigate the influence of the surface stress around an SA step of Si(001) surface onto the buckled dimer at 5 K. We demonstrate that the LT-NC-AFM has a capability to detect the surface stress with atomic resolution.
Scanning tunneling microscope (STM) light emission spectroscopy provides a powerful tool for characterization of individual nanometer scale structures on solid surfaces. However, the light to be detected is usually very weak. It is desirable to improve the intensity level for measurements with good signal-to-noise ratio. For this purpose the role that the STM tip-sample gap plays in the light emission is analyzed by the dielectric theory of STM light emission. Based on the theoretical predictions, we discuss how one can obtain strong STM light emission and problems associated with the enhancement of emission.
Due to the size reduction in structures, the difference in the electronic properties, for example, caused by the structural nonuniformity in each element, has an ever more crucial influence on macroscopic functions of semiconductor devices. And the direct observation of the characteristics, which provides us with the basis for the macroscopic analysis of the results, is of great importance. Thus, for further advances, a method for exploring the transient dynamics of the local quantum functions in organized small structures is eagerly desired. However, it is extremely difficult to obtain spatial and temporal resolutions simultaneously on this scale, which requires a new method; namely, new microscopy. In this paper, we introduce the shaken-pulse-pair-excited scanning tunneling microscopy (SPPX-STM), which we have developed these years. SPPX-STM enables us to observe the dynamics of electronic structures with the ultimate spatial and temporal resolutions.
Aiming at the basic understanding of weakly ionized plasma for dry etching process, N2 and H2 plasmas have been analyzed by means of both computer simulations and experimental diagnostics. Basic plasma parameters such as electron temperature (Te) and electron density (Ne) were measured by probe and number density of electrically neutral radicals such as atomic hydrogen in H2 plasma and atomic nitrogen in N2 plasma were measured by vacuum ultraviolet absorption spectroscopy (VUVAS). These results are compared with two set of commercial plasma simulator with identical reaction models. Though Te and Ne were not so affected by the reaction model assumed for the simulation, number densities of radicals depend strongly on the reaction model. The experimentally measured values have been simulated successfully by reexamining the reaction paths and using precise value of surface reaction rate. These results show that careful examination on the set of reaction paths and substantial expansion of basic studies on surface reaction are indispensable in order to understand plasma process.