Simon Dorfman

Electron/ion emission from the plasma formed on the surface of ferroelectrics. I. Studies of plasma parameters without applying an extracting voltage

We present experimental results of plasma formation on the surface of ferroelectric samples. Different poled and unpoled ferroelectric samples having a disk or tube form and made of Pb(Zr, Ti)O3 or BaTiO3 were tested. Using fast framing photography and different electric probes it was found that the application of a high-voltage driving pulse to the ferroelectric sample causes a fast surface plasma formation. This plasma formation occurs within a few nanoseconds from the start of the driving pulse for all the tested ferroelectric samples and the methods of applying the driving pulse. It was found that reversing the polarization of a ferroelectric does not play a significant role in the process of the plasma formation. Parameters of the plasma and of the neutral flow formed during the plasma formation versus the polarity and the amplitude of the driving pulse are presented.

Atomistic study of interaction zone at copper-carbon interfaces

Abstract Formation of Cu–C composite is a difficult technological problem: carbon is practically insoluble in copper. We show that the heat treatment of the Cu–C composite leads to the formation of thin (approximately 50 nm) interface, which provides the bonding between fiber and matrix. The high-resolution scanning electron microscopy (HR SEM) study displays the formation of the interaction zone. Monte Carlo simulations with repulsive Cu–C interatomic potentials study this zone on the interface.

Theory of the growth mode for a thin metallic film on an insulating substrate

We have developed a novel theory predicting the growth mode of a thin metallic film on an insulating substrate. This combines ab initio electronic structure calculations for several ordered metal/insulator interfaces (varying both coverage and substrate lattice constant), with a thermodynamic approach based on microscopic calculations. We illustrate this approach for Ag film deposited on MgO(0 0 1) substrate. Ab initio calculations predict high mobility of adsorbed silver atoms on the perfect magnesia surface even at low temperatures. Our theoretical analysis clearly demonstrates that the growth of metallic islands is predominant at the initial stage of silver deposition, which agrees with the experimental data. 2001 Published by Elsevier Science B.V.

Electron/ion emission from the plasma formed on the surface of ferroelectrics. II. Studies of electron diode operation with a ferroelectric plasma cathode

We present experimental results of electron diode operation with an active plasma cathode. The plasma was formed by a noncomplete discharge on the surface of different unpoled ferroelectric samples having the form of disks or tubes made of BaTiO3 or Pb(Zr,Ti)O3. To produce the discharge, a positive or a negative driving pulse was applied to the front or to the rear electrode of the sample. We studied the operation of planar and coaxial electron diodes under the application of an accelerating high-voltage pulse ⩽45 kV with repetition rate ⩽5 Hz or ⩽250 kV in a single-mode operation. Electron beams with a current density of several hundreds of A/cm2 and a time duration of several hundreds of ns were generated. It was shown that the parameters of the electron beam as well as the operation of the electron diode depend strongly on the method of the plasma formation and the time delay between the beginning of the plasma formation and the application of the high-voltage pulse.

Lifetime of ferroelectric cathodes

We study the lifetime and emission properties of ferroelectric cathodes made of perovskites with the ABO3 composition. To excite electron emission, we applied negative driving pulses with different amplitudes and durations to the rear electrode of the ferroelectric cathodes. The composition of the samples before and after the experiments was checked by energy dispersive spectroscopy and by Auger electron spectroscopy. The image and the structure of the emitting surface of the samples were studied by scanning electron microscopy. It was found that the lifetime of the tested cathodes depends strongly on their composition as well as on the parameters of the driving pulse. Namely, the driving pulse causes a substantial damage in lead–zirconium–titanate-type samples and a structural change in the surface of barium–titanate-type samples. In addition, fast deterioration was found in the emission properties of the tested cathodes along with increasing number of driving pulses. We discuss our results within the fr...

Microstructure of Cu–C interface in Cu-based metal matrix composite

Abstract Existence of dilute copper–carbon solid solutions is one of the characteristic features of the interfaces of the metal matrix composites widely used in the electrical applications. Experimental high-resolution SEM study allows to visualize the formation of the interaction zone on carbon fibre. We model interstitial solid solutions formed in this interaction zone non-empirically within the embedded-cluster and supercell approaches. Atomistic approach allows selection of the geometry of the solid solution. Electronic structure studies show that the most favourable position of the carbon atom is shifted along the [110] direction from the centre of the octahedral position. Investigation of this physical phenomenon allows us to understand the nature of the chemical bonding in copper-based solid solutions with carbon.

Formation of nano-crystalline structure at the interface in Cu–C composite

Abstract Formation of Cu–C composite is a difficult technological problem: carbon is practically insoluble in copper. We show that the heat treatment of the Cu–C composite leads to the formation of a thin (approximately 50 nm) interface which provides the bonding between fiber and matrix. The HR SEM study displays the formation of small copper nano-crystals in the interaction zone. This structure of the interface is predicted by molecular dynamic and Monte Carlo simulations with semi-empirical repulsive Cu–C interatomic potentials. We show that inclusion of a small amount of carbon in fcc copper leads to strong deformation of the copper host matrix in the vicinity of carbon. Decrease of stresses in the lattice may be reached by the formation of the developed surface in nano-crystalline structure.

Diffusivity of carbon in the copper matrix. Influence of alloying

Abstract The heights of diffusion barriers for copper-based composite materials with carbon whiskers or fibers are calculated. It is shown that the alloying of the matrix by an additional element, substituting copper in an interstitial Cu C solid solution, changes the value of the barrier and the migration entropy. This substitutional impurity influences the diffusion of the carbon-copper matrix. Zirconium as the best alloying element for preventing the diffusion of carbon in Cu C alloy is predicted.

Interstitial carbon in copper: Electronic and mechanical properties

The effects of interstitial carbon on the electronic and mechanical properties of copper are studied theoretically. Semiempirical methodology, atomistic simulations and first-principles density-functional embedded-cluster schemes are combined to extract some understanding of the diffusion process and related degradation of Cu-C composite materials under extremes of temperature and stress. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu-C interface.

Carbon in copper and silver: Diffusion and mechanical properties

Abstract The effects of interstitial carbon on the diffusion and mechanical properties of copper and silver are studied theoretically. Semiempirical methodology, atomistic simulations, and first-principles density functional schemes are combined to extract some understanding of the diffusion process and lattice reconstruction in extremely dilute interstitial Cu–C and Ag–C alloys. It is demonstrated that carbon inclusion in the host matrix leads to sufficient non-uniform dilatation of the lattice. We also show that an account of static displacements is important in the calculations of the activation energy for the diffusion of the interstitial atoms. The “embedded” cluster scheme is suggested to simulate the relaxation in extremely dilute alloys. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu–C interface.