Hisazo Kawakatsu

Experiment on the Electron Phase Microscope

A method of electron phase microscopic observation is described which offers greater image contrasts for specimens possessing small phase differences than is possible with conventional methods of electron microscopic observation.It is shown that observation by dark contrast image using a phase plate, consisting of many holes in a carbon membrane, is very suitable for microtome section specimens as well as for thin crystal specimens, without a decrease in resolving power.

Mechanical Aberrations of a Magnetic Quadrupole Quadruplet Lens

The mechanical aberrations of a system of two or more magnetic quadrupoles have been studied. Displacement, rotation, and tilting of one quadrupole, and the effects of radial and rotational errors in alignment of one pole are considered as well as the inhomogeneity of the material used in the system. The changes in field distribution introduced by these errors are calculated and the corresponding aberration formulas are derived.As a particular case, the mechanical aberrations of a quadruplet projector, are computed. The construction tolerances are estimated for an allowable image defect (magnification error) of 3% in the radial and rotatinoal directions. The calculations indicate that the projector system can be used in an electron microscope without excessive image defects. The image is most sensitive to rotational misalignment with a required tolerance of ±2×10−3 rad.

Gel Formation in Negative Electron Resists

Exposure characteristics of negative electron resists are described on the basis of Charlesbys theory on gel formation by a chain reaction. By use of the theory, the important resist parameters, contrast and sensitivity, can be related to the chemical properties of the resist materials. Applicability of the theory to exposure curves of Kodak thin film resist (KTFR), polymethylvinylsiloxane (PMVS), and epoxidized polybutadiene (EPB) is experimentally verified. The radiation yield for the reaction initiated directly by the electron irradiation and that for the over-all reaction propagated via radicals is separately estimated. It is found that the sensitivity of styrene-butadiene copolymers (SB) is increased by an introduction of ..cap alpha..-phenylmaleimide. This increase in sensitivity is also explained by the theory. The observed lowering in contrast associating the improvement in sensitivity by ..cap alpha..-phenylmaleimidation in SB, by epoxidation in polybutadiene, and by introduction of vinyl groups in polysiloxanes is in good agreement with the theoretical results. It is concluded that if a resist with higher contrast than 1.0 is required, the chain reaction must be inhibited so that the inhibition factor is larger than about 0.5.

Contamination layers formed by argon ion bombardment

Contamination layers formed on an aluminium substrate by 5-35 keV argon ion bombardment have been studied at various ion bombarding times, current densities, ion energies and substrate temperatures. The results are compared with a simple theory which takes sputtering into account and good qualitative agreement is obtained. According to this theory, the higher contamination growth by ion bombardment than by electron bombardment can be explained by the large cross section for polymerization of organic molecules adsorbed on the surface. Furthermore, it is ascertained that heating the substrate or using a cold trap surrounding the substrate can effectively reduce the contamination growth.

Field‐emission liquid‐metal ion source and triode ion gun

A pointed‐filament‐type field‐emission liquid‐metal ion source is designed and employed as a gold ion source. By adding a crossbar across a hairpin bend, the amount of the gold adhering on the filament is increased. The lifetime is estimated to be over 200 h at 10‐μA emission current. The emission current increases with increasing extraction voltage up to a saturation value which is ascribed to a limitation of the supply of liquid gold to the needle apex. The value of current density per unit solid angle is 30 μA/sr at a total current of 30 μA, which is of the same order as that obtained from a gallium ion source previously reported. Emission current fluctuations of a few tens of percent of the dc component are observed. In order to regulate the emission current and suppress current fluctuations, a bias electrode in addition to a counterelectrode is placed close to the needle apex. With such a triode structure, the emission current is regulated by a bias voltage of several hundred volts and stabilized to ...

Molecular‐weight dependence of developed contours in poly‐ (methyl methacrylate) electron resists

In order to study effects of initial molecular weight, developed profiles in poly‐ (methyl methacrylate) (PMMA) films are simulated by use of the Monte Carlo method coupled with a time‐dependent solubility model. The solubility rate measured in PMMA with molecular weights of up to 1.6×107 is used. The induction period observed before the beginning of dissolution is taken into consideration at the surface layer of the resist film. With increase in the initial molecular weight, the minimum usable dose can be lowered while the required development time is increased. The influence of the molecular weight becomes considerably slight in the region of molecular weight higher than about 1×105. The minimum linewidth obtainable at high dose is determined by the electron scattering and is almost independent of the initial molecular weight. The long development time required at the low‐dose region, causing the significant thickness loss and lateral spread of the profile, is mainly due to the decrease in the solubility rate in the deeper part of the resist film. By decreasing the initial molecular weight with the film depth, the decrease in the solubility rate of the deeper portion can be compensated for and consequently the usable exposure dose is lowered without loss of resolution.

Electron‐Optical Properties of a Quadrupole Quadruplet Projector Lens

A magnetic quadrupole quadruplet projector system has been designed, built, and studied, which has excellent characteristics for high‐resolution and high‐energy electron microscopes. The focal length is continuously variable from 0.7 mm to 3.6 mm by adjusting two current supplies. The third‐order distortion aberrations and first‐order chromatic aberration were calculated using measured field distributions. These aberrations change very little over the whole range of focal lengths and are always lower than these aberrations in the best set of rotationally symmetric lenses designed to cover this range of focal lengths.

Superconducting objective lens utilizing field trapping in Nb3Sn disks

A high‐quality superconducting objective lens has been designed, and the optical characteristics have been tested in a conventional electron microscope. The lens uses Nb3Sn disks held in the gap of a ferromagnetic container. The magnetic field is trapped in the disks using an excitation coil that is then deenergized leaving a persistent field that has a Gaussian distribution. Using a stack of 20 disks in a gap of 2.5 mm with a bore diameter of 3 mm, a peak field of 22 kG and a half‐width of 1.76 mm is produced. The spherical and chromatic aberration coefficients given by this field have been calculated. The lens was tested in an experimental cryostat mounted in the column of an Hitachi HU‐11A. The images obtained showed reasonable quality with the resolution limit of 10 A set by mechanical instabilities.

Electron phase microscope

Since the beginning of the electron microscopy, it has been well known that the phase contrast due to interference of the coherent wave plays a very important role in image formation. Distinctive examples are: Fresnel diffraction fringes as demonstrated by Boersch(1), Hibi (2) and others; interference fringes in crystals by Heidenreich (3) and Menter (4); biprism-interference fringes obtained by Mollenstedt (5) and Fert (6); a possibility of interferometer introduced by Marton (7), and so on.

Quantitative analysis of electron microscope images recorded on thin polymer films

A quantitative procedure for the evaluation of object mass-thickness in electron microscopy by the use of a new recording method is described on the basis of single and plural scattering theories. With this method, recorded images can be observed as colour images, and the difference in mass-thickness of a specimen is estimated directly from the observed colours as well as from the photographic density. Because of the high contrast, the detectable limit of difference in thickness is found to be about ten times smaller than that with usual emulsions.