R. D. Heidenreich

Electron Microscope and Diffraction Study of Metal Crystal Textures by Means of Thin Sections

Bethes dynamical theory of electron diffraction in crystals is developed using the approximation of nearly free electrons and Brillouin zones.The use of Brillouin zones in describing electron diffraction phenomena proves to be illuminating since the energy discontinuity at a zone boundary is a fundamental quantity determining the existence of a Bragg reflection. The perturbation of the energy levels at a corner of a Brillouin zone is briefly discussed and the manner in which forbidden reflections may arise at a corner pointed out. It is concluded that the kinematic theory is inadequate for interpreting electron images of crystalline films.An electrolytic method for preparing thin metal sections for electron microscopy and diffraction is introduced and its application to the structure of cold‐worked aluminum and an aluminum‐copper alloy demonstrated. It is concluded that cold‐worked aluminum initially consists of small, inhomogeneously strained and disoriented blocks about 200A in size. These blocks are n...

Physical Structure and Magnetic Anisotropy of Alnico 5. Part II

As a result of measurements of magnetic anisotropy and coercive force on single crystals of Alnico 5 and the electron metallography of Part I, the following conclusions were obtained. When the crystals are heat treated in a field in the principal crystallographic directions, the easy direction of magnetization is the field direction, and magnetically the crystals have twofold symmetry. However, there is a strong tendency because of crystal forces for the precipitate to grow in 〈100〉 directions; and, therefore, the crystal has the highest anisotropy when the heat‐treating field and a 〈100〉 direction are parallel. The large increase in residual induction of Alnico 5 which results from the magnetic field heat treatment is caused by the easy directions of the crystal changing from the 〈111〉 directions to a single easy direction approximately parallel to the field. Domain rotations rather than boundary movements account for the coercive force of the alloy, since the dimensions of the individual particles are a...

Fundamental aspects of electron beam lithography. I. Depth‐dose response of polymeric electron beam resists

The application of a phenomenological depth‐dose theory to the exposure of negative electron resists is described in detail. The model predicts a cross‐linking rate dnc/dt=(Gc/100) × (J0/e)(Va/RG)Λ(f) cm−3 sec−1, where Gc is the number of crosslinks produced per 100 eV lost in the polymer. Jo is the incident current density, Va the initial kinetic energy, RG the electron Grun range, and Λ(f) the depth‐dose function in terms of the normalized penetration f=z/RG. Since the G value of a negative resist decreases with exposure, it is suggested that a more meaningful parameter characterizing a negative resist is the absorbed energy required to gel the polymer at the resist‐substrate interface. This interface or threshold gel energy density, Eg(i), is independent of the beam parameters and varies from about 1022 eV cm−3 for polyvinyl ferrocene to 3.8×1018 eV cm−3 for epoxidized polybutadienes. The model predicts that the threshold sensitivity should vary as Va0.75 which agrees reasonably well with published exp...

Attenuation of Fast Electrons in Crystals and Anomalous Transmission

The two‐beam dynamical theory of electron diffraction (Laue case) with attenuation is treated using imaginary potentials and a damping vector α in the Schrodinger equation. Explicit formulas are obtained for centrosymmetric crystals when the Bragg condition is realized relating the damping vectors for the two wave fields with the mean imaginary inner potential P0 and the imaginary Fourier coefficient Pg.Using a simplified model, the imaginary Fourier coefficients are expressed in terms of the imaginary potential Pf for nearly free electrons (plasma) and Pc for bound atom cores. It is shown that the imaginary potentials can be directly related to the total inelastic collision cross sections and absolute numerical values so calculated. The values computed in this way are sufficiently near experimental results reported in the literature to warrant confidence in the approach. For 105‐V electrons, the damping vectors α are around 10−3 A−1, and the imaginary potential Pf≅0.6 V.The question of anomalous transmis...

A Necessary Factor for Heat Treatment of the Permalloys in a Magnetic Field

Recently, we have been able to show that Perminvar (Ni-Fe-Co alloy) has an inhomogeneous structure and that this inhomogeneity is due to an impurity fault. Evidence was obtained that small amounts of oxygen as an impurity in Perminvar caused both the faulting and the heat treatment in a magnetic field. It was exceedingly difficult, however, to remove sufficient oxygen from this material to prevent heat treatment in a magnetic field. More conclusive experiments have now been done to demonstrate the effect of oxygen on the response to magnetic annealing in the nickel-iron alloys without cobalt (Permalloys). Magnetic torque curves on a single crystal of 63% Ni-35% Fe-2% Mo for two different heat treatments illustrate this point. When the crystal was purified in hydrogen and then was heat treated in a magnetic field, it did not respond. However, after a slightly oxidizing heat treatment (pot annealing at 1000°C for 16 hrs), it did respond to the field heat treatment by developing a uniaxial anisotropy of appr...

Magnetic Annealing in Perminvar. II. Magnetic Properties

Previous work on Alnico single crystals (permanent magnet alloy) showed that magnetic torque reversals are associated with an inhomogeneous structure. More recently, it has been found that alloys of iron, nickel, and cobalt in the Perminvar region also exhibit these torque reversals although the alloys are considered to be solid solutions. An inhomogeneous structure occurs simultaneously with the torque reversals in some of these alloys. The inhomogeneous structure has been observed by means of electron diffraction, and the observations have been interpreted to mean that there are faults in the lattice normal to [111] directions. The faults form in the temperature region where the magnetic field heat treatment is effective and their density is roughly proportional to the response of the magnetic field treatment. When the crystals are not heat treated in a field, the faults are arranged to have cubic symmetry and their magnetic anisotropy has cubic symmetry. When the crystals are heat treated in a magnetic...

Mechanism by Which Cobalt Ferrite Heat Treats in a Magnetic Field

Magnetic torque measurements and electron diffraction patterns on several cobalt ferrite and cobalt‐zinc ferrite crystals show that those compositions which respond to heat treatment in a magnetic field contain precipitated particles of a second phase. Response of these crystals to heat treatment in a magnetic field is apparently due to the tendency of the precipitated particles to grow preferentially along the field direction in a manner similar to that previously reported by Heidenreich and Nesbitt [J. Appl. Phys. 23, 352 (1952)] for Alnico 5. When the crystals are heat treated without a magnetic field the precipitated particles are oriented along the crystal axes, and the shape anisotropy of the particles arrayed in this manner causes a reversal in sign of the torque as the measuring field is increased from zero. This anomalous variation of the torque with field was previously observed with Fe2NiAl and explained on the same basis. Thus a single mechanism explains the aforementioned magnetic phenomena o...

Thermionic Emission Microscopy of Metals. Part I. General

An electrostatic emission microscope operating with an accelerating voltage of 10–25 kv is briefly described. Factors determining image quality, particularly contrast and resolution, are discussed and the interpretation of images on the basis of the Schottky emission equation is considered. The instrument can be operated at magnifications of 250, 1000, 2500, and 4000× with a resolution consistently better than 1000 A.It has been found that the iron group metals can be activated easily using barium formate rather than evaporated Ba or Sr. The level of thermionic emission from such surfaces is determined primarily by the partial pressure of chemical reducing agent at the surface (such as carbon) to reduce BaO to free barium. The effect of various impurities and alloying metals is discussed from the standpoint of interpretation of emission images. The most important single agent for promoting emission from Ni, Cu, and Fe, etc., is carbon.Examples of emission images include nickel, stainless steel, and plain ...

Empirical electron backscatter model for thin resist films on a substrate

An electron backscatter model applicable to the exposure of resists in electron lithography is developed. The model is empirical, being based on the direct observation of chemical change produced by backscatter electrons at different accelerating voltages on several substrates. The model is independent of scattering, trajectory, and energy dissipation calculations and is essentially a radial exponential decay of backscatter current density out to the backscatter radius determined by electron range. Predictions of the simple model are compared directly with published results of several authors. The model indicates, in agreement with Nosker, that substrate backscatter is not as deleterious to transverse resolution as predicted by other calculations. The actual numerical agreement among the scattering‐model calculations themselves and this chemical‐effect empirical model is not altogether satisfactory. The empirical model is in better agreement with Nosker at the higher backscatter angles and with Hawryluk e...

Fundamental aspects of electron beam lithography. II. Low‐voltage exposure of negative resists

A study has been made of the use of low‐voltage exposure of negative resists for electron lithography. Three resists have been investigatd; an esterified terpolymer, epoxidized polybutadiene, and polyglycidyl methacrylate. The optimum exposure conditions have been determined for each material, and the use of a low accelerating voltage (5 kV) found to be advantageous. The application of this technique for the pattern delineation of silicon dioxide and tungsten is described.