LaB6 is one of the fascinating cathode materials I to obtain the electron beam with high brightness. In this article, brief reviews are given on the recent development in the study of the surfaces of LaB6 single crystal. Thermionic emission properties are discussed based on the electronic structure of bulk. and its surface structure. The values of work function of borides are much correlated with its electron density as similar to the case of metalic element and is explained in view of the theory proposed by Lang and Kohn. The change of surfaces due to ion bombardment and oxygen chemisorption are also discussed and it is pointed out that the three dimentional frame work of boron at LaB6 surface is important for stabilities of the surface and the configuration of La atoms at the surface for the emission properties and anisotropy of work function.
The development of the excellent emitter materials has been very interested in the establishment of the so-called super LSI technique and the research of surface, physics. In this article, the preparation of transition metal carbides emitter e.g. TiC, ZrC, TaC, etc., including the crystal growing technique and the electron-emission characteristics of these materials are described. Furthermore, the results of the foundamental study of their surface character by Auger electron spectroscopy, X-ray photon spectroscopy, field-emission microscopy etc. and the experimental data on work function are discussed relating to emission character-istics.
The polymer sulphur nitride has been the subject of current interest as a possible one dimensional conductor. In the first part of this article, observed electronic properties of (SN)x are reviewed. The measurements of conductivity and specific heat indicate that (SN)x is metallic at all temperatures, and even becomes superconducting at Tc=0.3K, in contrast to other one dimensional systems such as (TTF) (TCNQ) and KCP. The conductivity and optical reflectivity exhibit highly anisotropic behaviour. In the latter part, band structures of (SN)x are reviewd. The band structures reported so far are classified into two types: The first type is that a three dimensional band yields semimetallic Fermi surfaces while the second type has the feature of overlapping conduction bands and its three dimensional Fermi surfaces consist of warped plane-like sheets. Both types are unstable against Peierls distortions. The interchain interaction is suggested as a possible metallic origin of (SN)x.
Using the detection efficiencies of a 3"φ×3" NaI (Tl) scintillator calculated by Monte Carlo methods, the relative variations of the minimum detectable specific activity (MDSA) have been estimated for samples of soil (ρ=1_??_3g/cm3) and Al2O3 (ρ=1.3g/cm3) with different thickness and radii. To optimize the geometry of samples with low level specific activity for gamma-ray measurements, a figure of merit (FOM), which is defined as the reciprocal of MDSA, is proposed. The geometrical conditions of samples under which FOM is maximum are found for both the normal mode and the coincidence mode measurement.
Pre-breakdown characteristics in thin films of amorphous semiconductor of As30-Te48-Ge10-Si12 (atomic %) system are inverstigated. Thin film samples of sandwich type structure are used as metal electrodes. Two types of transition current I with applied voltage V are observed by the difference of metal used as the electrode. When Au or Ni is chosen as electrode, I-V characteristics are found to vary as I∝V1.5-2 after following Ohm's law, and when Al is chosen as electrode, current varies as VL+1 where L is a constant. Possibility of conduction mechanisms for the I∝V1.5-2 relation are qualitatively discussed. The I∝VL+1 relation based on the theory of space charge limited current dominated by exponential distribution of traps are also discussed. In the discussion, values used for concentration of traps and electron mobility are _??_1015-16cm-3 and _??_10-4 cm2 V-1 sec-1, respectively. These values are applicable for amorphous materials.