Kelvin force microscopy (KFM) as one of the AFMs is very useful for corrosion study, because it provides the surface morphology and potential distribution with high accuracy. The mechanism of initial atmospheric corrosion of steels accelerated by sea salt particles is not well known. In-situ observations of the corrosion initiated with small droplets of artificial sea water and dilute MgCl2 solution were made under low relative humidity condition by using KFM and super Kelvin force microscopy (SKFM) which we have developed recently. At the same time, EDX analysis and optical microscope observation were made. The results show that the morphology of corrosion can be classified into 3 types. The potential of corroding part is more negative than those of other parts. Iron chloride is formed at the corroding part and water is supplied by the deliquescence of iron chloride.
The contact potential difference (CPD) imaging of Ag- and Au-deposited Si(111) 7×7 surfaces and the effect of CPD distribution on NC-AFM data are discussed. Scanning Kelvin probe force microscopy (SKPM) based on the measurement of electrostatic force gradient was applied under an ultrahigh vacuum (UHV) to acquire the data. The CPD images of Ag- and Au-deposited Si(111) 7×7 surfaces are virtually identical, irrespective of the deposited metals. Detailed analysis has revealed that the CPD images showing the atomically resolved potential difference, does not represent the intrinsic work function of the materials but reflects the local electron density on the surface. On the other hand, the average potential that corresponds to the DC level of the CPD image is considered to reflect the work function on the surface.
Surface potential measurements of Si nano-structures by KFM (Kelvin probe force microscopy) are reviewed from a viewpoint of device research. For the development of sub-0.1 µm MOSFETs and future novel devices like dot-based single-electron tunneling transistors, it is most important to know the internal potential distribution of devices. In this review, first, the most fundamental structure of p-n junction formed on Si surface is described. It is noted that an unexpectedly small potential difference across the p-n junction was detected. The surface band bending due to the trapped charge would probably be responsible for almost flat profiles. Next, the potential distribution in the surface channel region of MOSFET-like structure on SOI (silicon-on-insulator) substrates is shown under several device-bias conditions. Finally, it is shown that Si quantum dot is recognized in KFM images after charge-injection process by generation of a small but significant potential difference at the dot site. These results indicate that KFM is undoubtedly useful in detecting potential distributions of device surfaces with or without device-driving voltage sources.
Using Kelvin probe force microscopy (KFM), we have measured the surface potential of InAs thin films grown on flat or vicinal surfaces of GaAs(110) substrates. We found that the observed potential distribution corresponded to the surface corrugation of the InAs films and that the evaluated surface Fermi level position of the thick InAs was slightly closer to the vacuum level than that of the thin InAs. It was also found that the removal of the water-related contamination from both surfaces of the tip and the sample was very effective in order to improve the reliability of the potential measurements by KFM.
When a diameter of doped semiconductor phosphor goes down to less than Bohr diameter, its quantum efficiency of luminescence becomes larger than that of a conventional bulk material. This issue has been comprehensively studied since Bhargava's report appeared in 1994. Nanosizing enhances interaction between a host and a dopant to induce effective energy transfer. Surface modification of nanosize phosphors plays significant roles in capping of surface luminescent killers and the confinement of electron-hole pairs inside a nanoparticle. We have studied the photoluminescence properties of Mn2+-doped ZnS (ZnS:Mn) nanocrystal phosphors modified by organic compounds with functional groups, such as carboxyl and phosphoric groups. Since functional groups are simultaneously excited with ZnS, we focus on energy transfer from functional groups to Mn2+ ions as well as the above-mentioned effects. Electron paramagnetic resonance spectroscopy reveals a near-surface Mn2+ site with a lower symmetry, which is characteristic of nanocrystal. This lower symmetry explains the higher probability of d-d transition of Mn2+ ions as well as stronger interaction between Mn2+ and ZnS and between Mn2+ and functional groups, as compared to an inside Mn2+ site. Here I introduce our recent works on organic/inorganic hybrid ZnS:Mn nanocrystal phosphors.
In order to inspect quality of the silicon wafer surface region where devices are to be fabricated, an instrument named Optical Shallow Defect Analyzer (OSDA) was developed. The OSDA can estimate the size and depth of the defect by measuring scattered light from each defect at two wavelengths having different penetration depths in Si. The principle of OSDA measurement is based on the Beer-Lambert law. In this review, the validity, the limitation and applications of the OSDA measurement are described. The validity were checked by TEM observation of the defects detected with OSDA. The applications include measurements of grown-in defects in various Czochralski (CZ) Si wafers and epitaxial wafer, and discrimination between inner defects and surface pits, e.g. crystal originated particles (COPs) induced by thermal oxidation.
Electron probe microanalysis (EPMA) is a useful method for element mapping analysis. However, the samples to be subjected are restricted to heat-stable materials, such as metals and ceramics, because irradiation of focused electron beam generates intense heat. In order to apply EPMA to tissues, we sliced the samples off to sections of appropriate thicknesses by use of polished carbon block as a support, such sections were very stable against the intense electron beam. Thus the mapping analysis by EPMA has been applied to tissue sections for histopathologic diagnosis. The principal advantage of this method is high detection sensitivity that is about 1×106 at./µm2 in case of copper. This was confirmed by analyzing thin standard films containing the element. In addition, exact linear relationship between the amount of copper atoms and the characteristic X-ray intensity was established in the range up to 15×106 at./µm2. The usefulness of this method for histopathologic diagnosis, such as Wilson's disease, was confirmed by mapping analysis of many section samples.