Andrzej Szczepkowicz

Observation of vertex-rounding transition for a crystal in equilibrium: Oxygen-covered tungsten

Equilibrium crystal shape of oxygen-covered tungsten is followed as a function of temperature using field ion microscopy. In the vicinity of the (111) region, at the temperature

Computer simulation of FIM images — the convex hull model

970\pm70

Image deformation in field ion microscopy of faceted crystals

K, the system undergoes a phase transition from a polyhedral form (sharp edges and sharp vertex) to a rounded form (sharp edges, rounded vertex).

Multi-scale simulations of field ion microscopy images--image compression with and without the tip shank.

Abstract A new simulation method of field emission ion images is proposed. The method can be applied to any crystal shape, size and atomic structure (possibly with point defects and dislocations), without any trial-and-error adjustment of parameters. The algorithm is illustrated by three simple examples: spherical crystals of perfect FCC, BCC and HCP structures.

Guided-mode resonance, resonant grating thickness, and finite-size effects in dielectric laser acceleration structures.

We perform detailed numerical simulations of field ion microscopy images of faceted crystals and compare them with experimental observations. In contrast to the case of crystals with a smooth surface, for a faceted topography we find extreme deformations of the ion image. Local magnification is highly inhomogeneous and may vary by an order of magnitude: from 0.64 to 6.7. Moreover, the anisotropy of the magnification at a point located on the facet edge may reach a factor of 10.

Optimal geometry for efficient loading of an optical dipole trap

Multi-scale simulations of field ion microscopy images of faceted and hemispherical samples are performed using a 3D model. It is shown that faceted crystals have compressed images even in cases with no shank. The presence of the shank increases the compression of images of faceted crystals quantitatively in the same way as for hemispherical samples. It is hereby proven that the shank does not influence significantly the local, relative variations of the magnification caused by the atomic-scale structure of the sample.

STM observation of steps and terraces on tungsten (2 1 1) surface

The possibility of exciting guided-mode resonances in dielectric grating laser accelerator structures is discussed. Finite-element method calculations of the accelerating electromagnetic field are presented both for periodic boundary conditions (infinite periodicity) and for finite gratings.

Application of transfer matrix and transfer function analysis to grating-type dielectric laser accelerators: Ponderomotive focusing of electrons

One important factor which determines efficiency of loading cold atoms into an optical dipole trap from a magneto-optical trap is the distance between the trap centers. By studying this efficiency for various optical trap depths (2--110 mK) we find that for optimum dipole trap loading, longitudinal displacements up to 15 mm are necessary. An explanation for this observation is presented and compared with other work and a simple analytical formula is derived for the optimum distance between the trap centers.

Electron dynamics in grating-type dielectric laser accelerators: Particle transfer function, generalized acceleration/deflection gradients and Panofsky–Wenzel theorem

Thermally cleaned W(211) surface with 0.7 degrees miscut consists of (211) terraces separated by monoatomic steps. When the surface is exposed to oxygen and subsequently annealed at 1100-1900 K, the width of (211) terraces increases and multilayer steps are formed. Similar step bunching is observed during routine cleaning of the sample by annealing in oxygen and thermal flashing in ultra high vacuum. During such cleaning procedure islands of c(6 x 4) reconstruction are observed.

Atomically Sharp Field Emitters and Oxygen Caused Thermal Faceting of W[111] Tip

The question of suitability of transfer matrix description of electrons traversing grating-type dielectric laser acceleration (DLA) structures is addressed. It is shown that although matrix considerations lead to interesting insights, the basic transfer properties of DLA cells cannot be described by a matrix. A more general notion of a transfer function is shown to be a simple and useful tool for formulating problems of particle dynamics in DLA. As an example, a focusing structure is proposed which works simultaneously for all electron phases.