Single Stage Photoelectronic Image Intensifiers

The limit of image detectobility determined by the shot noise of the incident photons is discussed and the sensitivity of the ideal detector is evaluated. The advantages of a phatoelectric. as compared with a photographic, primary detector are enumerated and some of the practical methods ond problems involved in taking advantage of the greater quontum efficiency of the photoelectric effect ore then described. The methods described are limited to single-stage image intensifiers. The first of these is Lallemand’s electronic camera in which the electrons from a photocathode are focused at high energy on a photographic plate in the same vacuum chamber. The second is the modified type of the some device in which the vacuum chamber is divided into two compartments by a thin membrane; the photoelectrons being projected through this membrane from the photocathode on the high vacuum side onto the photographic plate in the relatively low vacuum side. Thirdly the method is described in which the electron image is formed on a phosphor screen and the light from this image is recorded on a photographic emulsion. The development of a ~hin window to enable contact records to be made and the reduction of spurious background are the main points of this development. Lastly. as a result of this work. it has become possible to project the electron image through a very thin mica window and record it directly on a photographic plate in contact with the window.     

Calculation of integral characteristics of electron radiation in substance

A method is proposed for calculating energy release and other characteristics of a fast electron beam in a substance, based on a numerical solution to the conjunctive equation. This method allows one to take into account both the fluctuations of energy losses and the formation of secondary electrons. The proposed method was compared to calculations using the Monte Carlo method and, in the case of propagation of a sheet beam in a uniform absorber, to the experimental data.     

Characteristic X-ray excitation in thin films by 4–50 keV electron bombardment

X-ray excitation by electron bombardment has been used to analyse thin films, the main objective being non-destructive thickness determination. In a specially designed, but otherwise conventional, electron probe the thin film targets were irradiated with 4–50 keV electrons. Al, Mg, Cu and Zn films evaporated and/or sputtered onto aluminium and copper substrates were measured and the influence of the excitation energy on the sensitivity was studied in the thickness range from 20 to 5000 Å. Typical sigmoid-shaped calibration curves are found, provided X-ray excitation by the primary electrons is the dominating process. Good agreement can then be expected with calculations based on the depth distribution of characteristic X-ray generation. This is not true, however, of film-substrate systems in which X-ray excitation by electrons backscattered from the substrate becomes comparable with direct excitation (e.g. Al on Cu). Artificial enhancement of the ionization density by thin surface layers is demonstrated and applications of this effect are discussed with particular reference to energy-dispersive measurements.     

Sound modes of a two-dimensional electron gas bound to a helium film

The dispersion relation for a two-dimensional gas of electrons bound to a helium film on a metal substrate is derived and shown to be linear ink for smallk. Both the bulk compressibility of the dipole gas and the response of the electrons in the substrate contribute to the sound velocity. The collision time for electron scattering from third-sound excitations is calculated in the limit of low temperatures, low electron densities, and thin films and the effective mass of self-trapped electrons is estimated.This work is supported in part by the National Science Foundation.Fulbright-Hays Fellow.     

Position-sensitive focal plane detectors for electron (ESCA) spectrometers

Different techniques for multidetectors in electron spectrometers are presented. The techniques are the parallel plate channel multipliers, micro channel plates followed by a phosphor plate viewed by a video camera, micro channel plates followed by a resistive strip detector, electron accelerating grid followed by a diode array detector, micro channel plates followed by a multiple anode detector and a new concept with a position sensitive electron detector with integrated electronic circuitry on a chip.     

Monte Carlo simulation of X-ray photoemission electron microscopic image for Ag/Si nano-structure

With the development of the third generation synchrotron radiation sources the X-ray photoemission electron microscopy (XPEEM) is playing as a powerful tool for analyzing specimens with spatial resolution about tens of nanometer. It has been used to observe the chemical reaction process, and to investigate the surfaces, interfaces, thin films, buried layers and nano-structures. XPEEM image signals are contributed from photoelectrons, Auger electrons, backscattering electrons and secondary electrons excited by X-rays of certain energy. In this work, a Monte Carlo model for XPEEM image simulation is built. XPEEM images in total electron yield (TEY) mode are simulated with this model for several nanostructures (spheres and cylinders) of silver deposited on/in a silicon substrate (Ag/Si). The simulated XPEEM image in TEY mode for Ag dot array on a Si substrate is quite close to an experimental image. Furthermore, the XPEEM image simulation has been performed for different incident X-rays and for different geometric structures.     

Properties of a fast timing detector using an electron multiplier

A new timing detector for the time-of-flight method has been invented and successfully tested with heavy-ion beams. The detector consists of a thin foil and an electron multiplier. The best time resolution of 260 ps is obtained for ⁸¹Br. The time resolution is also studied in relation to the number of secondary electrons emitted from the foil.     

Ice-assisted electron beam lithography of graphene

We demonstrate that a low energy focused electron beam can locally pattern graphene coated with a thin ice layer. The irradiated ice plays a crucial role in the process by providing activated species that locally remove graphene from a silicon dioxide substrate. After patterning the graphene, the ice resist is easily removed by sublimation to leave behind a clean surface with no further processing. More generally, our findings demonstrate that ice-assisted e-beam lithography can be used to pattern very thin materials deposited on substrate surfaces. The procedure is performed in situ in a modified scanning electron microscope. Desirable structures such as nanoribbons are created using the method. Defects in graphene from electrons backscattered from the bulk substrate are identified. They extend several microns from the e-beam writing location. We demonstrate that these defects can be greatly reduced and localized by using thinner substrates and/or gentle thermal annealing.     

Theoretical and experimental study of nanopore drilling by a focused electron beam in transmission electron microscopy

Sub-10 nm nanopores drilled by a focused electron beam in a transmission electron microscope are widely used in solid-state nanopore devices for DNA translocation. However, there still remains much controversy surrounding the drilling mechanism. In order to explain the drilling of nanopores by electrons, we undertook a theoretical consideration of the energy transfer from the fast electrons to the solid through such mechanisms as elastic and inelastic scattering. According to the calculations based on the scattering cross-section, the direct atomic displacement cross-section induced by elastic scattering increases with increasing incident electron energy, while the ionization cross-section and temperature increment decrease. We performed nanopore drilling in a Si3N4 membrane using two different electron energies, 200 and 300 kV, to identify the drilling mechanism. The dependence of the nanopore drilling on the incident electron energy was well matched with the direct atomic displacement.     

Hadron and electron response in a uranium liquid argon calorimeter from 10 to 150 GeV

A uranium liquid argon calorimeter, with a total depth of nine absorption lengths, has been exposed to electrons and hadrons in the energy range of 10–150 GeV. Two configurations with different uranium plate thicknesses were successfully operated. In both cases the response was found to be linear over the entire energy regime. We present measurements of various contributions to energy resolution, differences in electron/hadronm/muon response, longitudinal and transverse shower profiles and electron position resolution.     

A new method for studying surface scattering of electrons in thin metallic plates

A determination of the surface scattering, mean free path, and bulk resistivity of electrons in a specimen requires three independent experiments. A new method is proposed making use of the measurement of the first and second terms in the expansion of a decaying eddy current in a thin plate. The decay rates have been calculated and tabulated using the free electron model and assuming an isotropic electron mean free path.     

Behaviour of spiral vortices on a rotating cone in axial flow

Summary The purpose of the present paper is to investigate experimentally in detail the boundary layer transition process and the behaviour of spiral vortices appearing in the transition range of the boundary layer on a 30°-cone, rotating in axial flow. Counterrotating spiral vortices in the transition range are visualized with a white smoke method, and observed the time dependent behaviour of them using a drum camera and a light sheet illumination method with a stroboscope flash light. The light passes a slit in order to illuminate only a thin sheet in the flow. With this method, the time dependent growing up and breaking down process of these spiral vortices is greatly clarified. A hot wire anemometer is also used for measuring in the flow field quantitatively. The results show that the spiral vortices are generated in the thin region of the steep shear velocity gradients near the wall. As the vortices grow up in z-direction, they are strongly distorted by the mean velocity field there, and finally they are teared off.With 7 Figures     

A transition radiation detector for electron identification in a high energy experiment

We have built a transition radiation detector consisting of four sets of multilayered polyethylene radiators each followed by a xenon-filled proportional chamber. This detector has been used in a hadron-proton scattering experiment at CERN SPS to discriminate electrons from hadrons in the final state. Using the technique of recording chamber signals of amplitude exceeding a fixed threshold we normally achieved 0.5% pion contamination at 80% electron efficiency.     

Magnetic domains in thin-film recording heads as observed in the SEM by a lock-in technique

In a thin-film magnetic recording head, a magnetic circuit made from two Permalloy thin films, one above the other, is magnetized by a spixally plated thin-film copper coil which is located (together with insulating layers) between those two films. The magnetic domains in a thin Permalloy film can be studied by type-2 magnetic constrast using backscattered electrons (BSE) in the scanning electron microscope (SEM) provided that the film has a smooth surface and is deposited on a flat substrate. In practice, the upper Permalloy film follows the contours of the underlying layers. This gives a topographic signal which is large enough to mask the type-2 magnetic contrast signal in its simple form. The domain walls can, however, be seen if the magnetic recording head is excited with a sinusoidal current and if the video waveform is processed with a lock-in amplifier referenced either to the fundamental or to the second harmonic of the excitation frequency. This lock-in image processing technique has now been applied to obtain images of the magnetic domains both from the upper Permalloy film of an incompletely fabricated head and also from the exposed cross sections of the Permalloy films in an operational thin-film head.     

Mécanisme d'émission électronique dans les structures mim et propagation des électrons dans les métaux

The distribution of electrons emitted by MIM structures has been measured by recording an electron image on a photographic plate. Electrons are emitted into vacuum by “formed” structures when a negative voltage is applied to the outer metal films.The escape depth of the electrons emitted by “unformed” structures does not depend on the applied voltage. We conclude that the energy distribution of the electrons injected into the outer electrode does not depend on the applied voltage.     

Design of a 10 nm electron collector for a track-nanodosimetric counter

Recently we have developed a track-nanodosimetric counter, which is a gas detector that measures the distributions of electrons induced by a charged particle in nanometric volumes of tissue equivalent matter, positioned at different distances from the track. Sites equivalent to 20 and 24 nm were defined by means of an electron collector, which is a system of electrodes enclosing an almost wall-less cylindrical volume. In this paper, we present the design of a new electron collector that is able to simulate a volume as small as 10 nm in diameter.     

Three-dimensional waves beneath an ice sheet due to a steadily moving pressure

Solutions of the nonlinear water wave equations under an ice sheet are computed using a boundary integral equation method. The ice sheet is modelled as a thin elastic plate and the fluid equations are nonlinear. Depending on the velocity of the moving disturbance generating the flow, different types of responses of the floating ice sheet are discussed.     

Particle image velocimetry: image labeling by use of adaptive optics to modify the point-spread function

A simple method of labeling the first- and second-exposure images of a particle-image-velocimetry recording is discussed. One achieves this method by changing the transfer characteristics of the recording optics between exposures by inserting a rotating optic into the iris plane of the camera objective. Spatial filtering can then be used to address the images recorded by each exposure independently, permitting cross-correlation analysis to be implemented. Two practical systems using either an aperture plate or a phase plate are demonstrated, and we show that the phase plate is significantly more light efficient. Finally, the feasibility of image labeling high-speed flows using electro-optic devices is discussed.     

The measurement of magnetic microfields

A new transmission electron microscope method of measuring fine scale magnetic flux distributions, and in particular the fields associated with magnetic recording heads, is described. An island structured metallic foil or an amorphous film acts as a diffuse scatterer of transmitted electrons. A magnetic field in the region below the scatterer deflects the electron trajectories and as a result distorts the image of the scatterer. The local shearing of the image is compared to a reference zero field image by a double exposure of a photographic plate. Optical Fraunhofer diffraction by transmission through the developed plate shows Young's fringes which reveal the direction and magnitude of the local image shift which is related to the magnetic field component perpendicular to the electron trajectories. In some applications the method is potentially several orders of magnitude more sensitive than other electron beam methods.     

A novel type of parallel plate chamber with resistive germanium anode and a two-dimensional readout

A parallel plate counter with a resistive anode and a two-dimensional readout is presented. The anode is made of a thin germanium layer with a sheet resistivity ⩾ 1 Mω/square and the cathode is made of aluminized mylar 5 μm thick. The anode is transparent to the fast impulse due to the collection of the multiplication electrons. A chessboard of “pads” placed behind the anode plane is used to obtain the positional information. The detector and the readout system are physically and logically separated. An overall spatial resolution of 70 μm (rms) for both coordinates has been measured.