Benjamin M. Siegel

H2 and rare gas field ion source with high angular current

We have built and carried out initial tests on a field ion source that has been designed to operate at very low temperatures with a physisorbed surface supply to the ionization region. This mode has been found to give beams of high angular current density and is expected to have low energy spread in the beam. Presently we have measured dI/dΩ?10 to 60/sr with a probable energy spread of ?l eV. The UHV system allows processing of the field emitter under clean, high vacuum conditions. A liquid He cooled finger maintains the tip at controlled temperatures from that of liquid He to room temperature. The tip is mounted on a sapphire block to provide both excellent thermal conduction and electrical insulation to ?30 kV. Differential pumping allows a high supply pressure of H2, He, Ar, etc. in the region of the tip (≳ 10−2 Torr) and a low pressure in the rest of the system. Observation on the characteristics of the field ionization pattern are made under varying conditions of pressure, temperature, field and tip ...

Imaging of Single Atoms with the Electron Microscope by Phase Contrast

Calculations have been made on image contrast by computing the Kirchhoff diffraction integral assuming the amplitudes of elastic scattering from single atoms and linear chains of atoms given by the first Born approximation using either the Hartree‐Fock or Thomas‐Fermi atomic models. Phase shifts occur due to diffraction, spherical aberration, and defocusing which can be optimized by suitable choices of defocus and aperture size. Balancing of phase shifts due to defocus and spherical aberration produces a relatively uniform phase shift over a considerable part of the objective aperture and allows maximum contrast in the image which does not depend critically on atomic spacing. For atoms with Z>10 image contrasts of at least 5%−10% are indicated with presently available objective lenses. Resolutions down to ∼2.5 A may be achieved at 100 kV and as low as ∼1.5 A at 750 kV if spherical aberration sets the ultimate limit.

Observations on the Morphological Changes in Thin Copper Deposits during Annealing and Oxidation

Thin copper films were deposited in an ultrahigh vacuum on carbon and silicon monoxide substrates at room temperature. Their morphological changes after annealing and oxidation were investigated by electron microscopy and electron diffraction. The changes during annealing of very thin deposits (<50 A mean thickness) are strongly influenced by the substrate. The copper on carbon substrates grows into large crystallites during heat treatment at 500°C whereas on silicon monoxide substrates very little recrystallization occurs. During the annealing of thicker deposits of copper, self‐diffusion of the metal can take place and the change in structure of the heat‐treated film is independent of the substrate. The structures of the cuprous oxide particles formed during exposure to different pressures of oxygen at 150° to 200°C indicate that different transport mechanisms are involved in the oxidation process at very low oxygen pressures from those at pressures above 10−2 Torr.

Quantitative reflection electron diffraction in an ultra high vacuum camera

Abstract An ultra high vacuum electron diffraction camera for intermediate energies (10–50 kV) is described. A Faraday cup scans the diffraction pattern while another monitors the incident beam, reading out the intensities with high accuracy. The performance of the instrument is illustrated with typical diffraction patterns and scans. Reasons are discussed for expecting that the intensity data from high-energy electron diffraction is more satisfactory than from low-energy electron diffraction for the determination of surface structure, since dynamical theory must be used.

Comparison of local-lesion and electron-microscope particle-count methods for assay of potato virus X from plants doubly infected by potato viruses X and Y

Abstract Evidence of large increases of potato virus X in plants also infected by potato virus Y was obtained by different methods of assay. Parallel assays by means of local lesions on plants of Gomphrena globosa and by electron-microscope particle counts were in agreement. Results of both methods showed that in tobacco plants simultaneously inoculated with both viruses the virus X concentration in extracted juice of the first noninoculated leaves to develop symptoms is up to ten times as great as in juice of comparable leaves infected with virus X alone. Smaller relative increases were recorded with juice from inoculated leaves and with juice from leaves in the chronic stage of the disease. A difference in virus content of doubly and singly infected plants was apparent early in the infection process. Parallel assays by the local-lesion method and by a serological method also were in agreement.

High resolution structuring of emitter tips for the gaseous field ionization source

Extraction of a stable, high brightness ion beam from an apertured field ion emitter surface requires microfabrication procedures to sculpture the surface topography on both microscopic (100 –1000 nm) and near atomic (10 –100 nm) length scales. Structuring on a near atomic scale is required to confine and stabilize the ion beam by local enhancement of the surface electrostatic field and to orient that emission on the optical axis. Control of the emitter contour on a microscopic scale is required for manipulating the supply of neutral molecules to the ionization site and also affects beam stability. We have developed a method using ion milling for configuring surface contour on microscopic and near atomic length scales which utilizes the morphological changes occurring at ion bombarded surfaces as a result of erosion by sputtering. A SEM study of the microscopic emitter topographical development is compared to computer simulations of the kinematical wave equation which depicts the erosion process. In this way, prediction of configuration on a length scale large compared to the ion penetration depth has been established. TEM observations show the surface development on the length scale of ion penetration depth. Preliminary results using this microfabricated emitter in a gaseous field ion source to produce a hydrogen ion beam with high angular beam confinement are given. Requirements for surface topography that are essential to obtain stable high brightness ion beams are discussed.Extraction of a stable, high brightness ion beam from an apertured field ion emitter surface requires microfabrication procedures to sculpture the surface topography on both microscopic (100 –1000 nm) and near atomic (10 –100 nm) length scales. Structuring on a near atomic scale is required to confine and stabilize the ion beam by local enhancement of the surface electrostatic field and to orient that emission on the optical axis. Control of the emitter contour on a microscopic scale is required for manipulating the supply of neutral molecules to the ionization site and also affects beam stability. We have developed a method using ion milling for configuring surface contour on microscopic and near atomic length scales which utilizes the morphological changes occurring at ion bombarded surfaces as a result of erosion by sputtering. A SEM study of the microscopic emitter topographical development is compared to computer simulations of the kinematical wave equation which depicts the erosion process. In this ...

Systematic design of an electrostatic optical system for ion beam lithography

An electrostatic optical system has been designed to produce a high resolution (10–100 nm) ion beam probe based on a very high brightness H+2 field ionization source developed in our laboratory.1 The system described here includes two electrostatic lenses, postlens octupole and quadrupole deflectors, beam blanker, stigmation and alignment deflectors. Since the resolution of this system is limited by the aberrations of the optics, a systematic approach is employed to minimize these aberrations. First, individual lenses were designed by many trial evaluations using appropriately constructed figures of merit. The scales and magnifications of both lenses then were determined simultaneously to minimize the axial aberrations of the combined lens. The deflectors were also optimized using analytical expressions of deflection aberration coefficients to achieve small deflection aberrations. The beam blanker at the beam crossover point can also give reasonably high blanking rates (10–300 MHz) for H+2 ions with small...

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.

Electron Microscopy of Golden Nematode Cyst Wall

An exocuticle and an endocuticle are visible in electron micrographs of ultrathin sections of golden nematode cyst wall. More detail can be seen in the endocuticle than has been reported from light microscope studies. Details of the exocuticle described from light microscope observations, are not imaged in the electron microscope.

SEM and TEM observations of first and second order sputter-induced topography☆

Abstract Morphological changes of a solid that occur under ion and atom bombardment due to erosion by sputtering have been used to produce a conical end-cap, of prescribed cone half angle, to an emitter wire. First order erosion theory, that predicts the development of this conical shape, associates morphological changes with the variation in sputter efficiency due to variation in the angle of incidence between the ion flux and target surface. Transmission Electron Microscopy (TEM) of the cone apex region reveals details associated with the spatial distribution of the sputter process on a length scale on the order of the ion penetration depth. This second order effect links the events taking place on an atomic scale within the atomic collision cascade with those features that can be predicted from the macroscopic first order theory. A competing process, such as surface smoothing due to atomic surface and volume migration, that can be radiation enhanced, limits the scale of surface roughness which develops due to the second order mechanism at an equilibrium temperature for the sputtering process.