Jakub Zlámal

Guided Assembly of Gold Colloidal Nanoparticles on Silicon Substrates Prepatterned by Charged Particle Beams

Colloidal gold nanoparticles represent technological building blocks which are easy to fabricate while keeping full control of their shape and dimensions. Here, we report on a simple two-step maskless process to assemble gold nanoparticles from a water colloidal solution at specific sites of a silicon surface. First, the silicon substrate covered by native oxide is exposed to a charged particle beam (ions or electrons) and then immersed in a HF-modified solution of colloidal nanoparticles. The irradiation of the native oxide layer by a low-fluence charged particle beam causes changes in the type of surface-terminating groups, while the large fluences induce even more profound modification of surface composition. Hence, by a proper selection of the initial substrate termination, solution pH, and beam fluence, either positive or negative deposition of the colloidal nanoparticles can be achieved.

The influence of humidity on the kinetics of local anodic oxidation

In this paper the influence of relative humidity on fabrication of nanostructures at GaAs (100) surfaces by local anodic oxidation (LAO) is reported. The attention was paid both to the dimensions of oxide nanolines prepared at different relative humidities for tip-surface voltages of 6 - 9 V and tip speeds of 10 - 200 nm/s, and to the profiles corresponding to line trenches (etched in HCl after the nanoxidation). Contrary to the expectations the height and the half-width of oxide nanolines did not increase with relative humidity in the whole interval from 35% to 90%, but for lower relative humidities (< 50%) the lines were comparable in size to those prepared at 90%. However, this was accompanied with instabilities in the oxidation process resulting most probably from enhanced size variations of the water meniscus between the tip and the surface at these low humidities.

Deposition of metal nitrides by IBAD

Abstract Nitrides of metallic elements like Ti, Mo and Al were synthesized by ion beam-assisted deposition (IBAD). This technique was provided via dual ion beam deposition method in an apparatus based on two Kaufman ion beam sources. In our study an influence of the energy of assisting nitrogen ions (50–400 eV) and of the substrate temperature (up to 400°C) on the characteristics and properties of deposited thin films (roughness, thickness, chemical composition, structure, electrical and optical properties, etc.) was investigated. Different ex situ analytical techniques and measurements such as XPS, RBA, XRD, STM, profilometry, ellipsometry and other methods were applied. The composition of thin films prepared by the sputtering of Ti, Mo and Al targets was close to oxinitrides for all ion energies (fluxes). The nitrogen content in all films was increased by assisting ion bombardment; however, it sustained under their stoichiometric values. Structure of all thin films was generally dependent on ion beam energy and substrate temperature. The roughness and thickness (50–400 nm) of the films increased, respectively, decreased with ion energy (flux). Higher substrate temperature (400°C) substantially improved the adhesion of MoN films to silicon substrates. A significant influence of the assisting ion beam on electrical resistivity and index of refraction of Ti–N and Al–N films was observed.

Calculation of the performance of magnetic lenses with limited machining precision.

To meet a required STEM resolution, the mechanical precision of the pole pieces of a magnetic lens needs to be determined. A tolerancing plugin in the EOD software is used to determine a configuration which both meets the optical specifications and is cost effective under the constraints of current manufacturing technologies together with a suitable combination of correction elements.

Deposition of magnetic thin films by IBAD

Abstract Cobalt and nickel magnetic films were prepared by ion-beam assisted deposition method (IBAD). The main goal of the work was to study the influence of the assisting low-energy-argon-ion beam and substrate temperature on the characteristics and properties of the films, in particular on thickness, roughness, chemical composition, structure and magnetic properties of thin films. The experiments revealed that the assisting argon ions influence most remarkably an in-plane magnetic anisotropy of the films. On the other hand, enhanced substrate temperatures suppress the anisotropy of the films. Influence of these two deposition parameters on roughness, composition and structure of thin films was not dramatic.

An ultra-low energy (30-200 eV) ion-atomic beam source for ion-beam-assisted deposition in ultrahigh vacuum.

The paper describes the design and construction of an ion-atomic beam source with an optimized generation of ions for ion-beam-assisted deposition under ultrahigh vacuum (UHV) conditions. The source combines an effusion cell and an electron impact ion source and produces ion beams with ultra-low energies in the range from 30 eV to 200 eV. Decreasing ion beam energy to hyperthermal values (≈10(1) eV) without loosing optimum ionization conditions has been mainly achieved by the incorporation of an ionization chamber with a grid transparent enough for electron and ion beams. In this way the energy and current density of nitrogen ion beams in the order of 10(1) eV and 10(1) nA/cm(2), respectively, have been achieved. The source is capable of growing ultrathin layers or nanostructures at ultra-low energies with a growth rate of several MLs/h. The ion-atomic beam source will be preferentially applied for the synthesis of GaN under UHV conditions.

Mid-IR plasmonic antennas on silicon-rich oxinitride absorbing substrates: Nonlinear scaling of resonance wavelengths with antenna length

We report on the resonant properties of platinum dipole antennas fabricated on a silicon-rich-oxinitride thin film that exhibits significant absorption in the mid-infrared of the electromagnetic spectrum (λ−1≈1100 cm−1). A nonlinear scaling between the resonant wavelength and the antenna length has been found and quantitatively confirmed by full-field electromagnetic simulations. The resonant wavelength increases linearly with antenna length for small lengths and tends to saturate for large ones (length >4 μm). This saturation effect is attributed to the coupling of a geometrical antenna resonance and an absorption resonance of the substrate material.

Optimization of ion-atomic beam source for deposition of GaN ultrathin films

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Experimental and simulated signal amplification in variable pressure SEM

The presence of gases (mostly water vapour with pressure range from 1 Pa to over 2000 Pa) in the specimen chamber of a variable pressure scanning electron microscope (VP-SEM) makes completely different conditions for the detection of signal electrons than for the conventional SEM, and specially designed detectors must be used. In the high pressure conditions, gas ionisation cascade amplifies the signal of secondary electrons (SE), accelerated by the applied field of detection electrode of the ionisation detector [1].

DESIGN OF THE ENTRANCE ION OPTICS FOR SIMS AND LEIS IN SITU MONITORING OF DEPOSITION PROCESSES

Abstract A six-lens-entrance ion optics and its retractable vacuum housing for ion beam analytical instrument was designed. Based on an electrostatic energy analyser and mass spectrometer the instrument will allow us to carry out in situ monitoring of ion beam deposition (IBD) processes and relevant technologies via SIMS, low energy ion scattering (LEIS) and energy analysis of charge-exchange ions. To optimize the entrance optics, the computer code SIMION 4.0 was used.