Petr Dub

Control and near-field detection of surface plasmon interference patterns.

The tailoring of electromagnetic near-field properties is the central task in the field of nanophotonics. In addition to 2D optics for optical nanocircuits, confined and enhanced electric fields are utilized in detection and sensing, photovoltaics, spatially localized spectroscopy (nanoimaging), as well as in nanolithography and nanomanipulation. For practical purposes, it is necessary to develop easy-to-use methods for controlling the electromagnetic near-field distribution. By imaging optical near-fields using a scanning near-field optical microscope, we demonstrate that surface plasmon polaritons propagating from slits along the metal-dielectric interface form tunable interference patterns. We present a simple way how to control the resulting interference patterns both by variation of the angle between two slits and, for a fixed slit geometry, by a proper combination of laser beam polarization and inhomogeneous far-field illumination of the structure. Thus the modulation period of interference patterns has become adjustable and new variable patterns consisting of stripelike and dotlike motifs have been achieved, respectively.

Dual ion-beam deposition of metallic thin films

Abstract The influence of argon ion-beam bombardment of growing Al, Mo and Ti thin films deposited by ion-beam sputtering on their composition and optical properties was studied. The Ar ion energy and ion-to-atom arrival ratio were 100–600 eV and 0.15–1.75 respectively. The concentration of Mo (A1) in the thin films decreased (increased) with ion energy as the Ar content increased (decreased). The Ti content was below 35% for all ion energies. The ratio O/Ti was close to the stoichiometric value of two for all ion energies up to 400 eV. Higher ion-beam energies and doses led to higher values of the index of refraction for Al and Ti thin films. Furthermore, an increase in the energy of the ions caused a decrease in the deposition rates of all films due to resputtering of the thin film atoms and, in the case of Al thin films, intensified the amorphization process in the Al/Si structure.

Response of plasmonic resonant nanorods: an analytical approach to optical antennas.

An analytical model of the response of a free-electron gas within the nanorod to the incident electromagnetic wave is developed to investigate the optical antenna problem. Examining longitudinal oscillations of the free-electron gas along the antenna nanorod a simple formula for antenna resonance wavelengths proving a linear scaling is derived. Then the nanorod polarizability and scattered fields are evaluated. Particularly, the near-field amplitudes are expressed in a closed analytical form and the shift between near-field and far-field intensity peaks is deduced.

The Ewald dynamical diffraction theory--ninety years later.

Diffraction on a crystalline slab formed by point-like scattering centres is treated as a multiple scattering problem based on the Ewald equations. Using general results expressed in a lucid matrix form, the two-beam solution for both coplanar and non-coplanar cases valid near and far from Bragg peaks is found and a detailed comparison of the final formulae obtained with those following from Laues theory is performed.

A note on the problem of scattering from a single atomic plane and a stack of planes. Differences between the Ewald and other diffraction theories

The scattering of a scalar plane wave (neutrons) from a single atomic plane consisting of any two-dimensional lattice with a basis is studied using the Ewald dynamical theory of diffraction. Formulae for the reflection and transmission coefficients obtained by evaluating the optical plane lattice sums are valid for general geometries, including nonsymmetrical and noncoplanar diffractions. The approach adopted is different from and more general than that by Yashiro & Takahashi [Acta Cryst. (2000), A56, 1663–167]. The structure factor yielded by this procedure differs from that used in the kinematical or Laue dynamical diffraction theories.

Is the border surface of a crystal indeed the weakest point of the dynamical theory of diffraction

In Laues dynamical theory of diffraction, the boundary conditions claim to introduce a mathematical plane instead of the discrete atomic surface of the crystal. This assumption is analysed from the point of view of Ewalds theory based on the microscopic discrete model of a crystal, where no boundary conditions are needed.

Imaging of near-field interference patterns by aperture-type SNOM – influence of illumination wavelength and polarization state

Scanning near-field optical microscopy (SNOM) in combination with interference structures is a powerful tool for imaging and analysis of surface plasmon polaritons (SPPs). However, the correct interpretation of SNOM images requires profound understanding of principles behind their formation. To study fundamental principles of SNOM imaging in detail, we performed spectroscopic measurements by an aperture-type SNOM setup equipped with a supercontinuum laser and a polarizer, which gave us all the degrees of freedom necessary for our investigation. The series of wavelength- and polarization-resolved measurements, together with results of numerical simulations, then allowed us to identify the role of individual near-field components in formation of SNOM images, and to show that the out-of-plane component generally dominates within a broad range of parameters explored in our study. Our results challenge the widespread notion that this component does not couple to the aperture-type SNOM probe and indicate that the issue of SNOM probe sensitivity towards the in-plane and out-of-plane near-field components - one of the most challenging tasks of near field interference SNOM measurements - is not yet fully resolved.

Multiple wave scattering on a bordered crystal. Translation symmetry breaking and forbidden reflections

The interaction of a scalar wave (thermal neutrons) with a single Si crystal is treated using Ewalds self-consistent field method. Considering from the very beginning the two-dimensional translation symmetry of the problem, the reflectivities of allowed and forbidden reflections in the Bragg geometry valid for both coplanar and non-coplanar cases are derived. It is shown that there exists a very narrow reflectivity peak of the forbidden reflection as a result of the symmetry breaking due to a crystal surface.

Vibrational analysis of the cantilever in non‐contact scanning force microscopy

In this paper the basic principles of non-contact scanning force microscopy (SFM) are explained. The major long-range forces acting between a tip and a sample, and consequently the changes of vibration characteristics with the tip-sample distance, are discussed. To estimate the resolution limits of the non-contact method, the motion of a vibrating silicon cantilever above testing silicon nanostructure models was simulated numerically. This was done both in the mode of constant height and of constant force. To simulate the real behaviour of the tip in the mode of constant force, we included into our calculations the feedback loop. It was shown that by using long-range van der Waals forces an atomic lattice periodicity and individual adatoms can be recognized by non-contact SFM only when the equilibrium tip-surface distance is ∼1.0 nm.