Herbert Wormeester

In situ spectroscopic ellipsometric investigation of vacuum annealed and oxidized porous silicon layers

Vacuum annealed and oxidized porous silicon layers (PSL) were investigated by in situ spectroscopic ellipsometry (SE). The nominal porosity of the layers was between 60 and 77% and the nominal thickness was 500 nm. The annealing was performed by direct ohmic heating (R.T.<450°C) in 5×10−10 Torr vacuum. The oxidation was performed in two steps, the first step at 5×10−5 Torr, the second at 10 Torr. Two optically different types of silicon compounds, a bulk-type silicon (c-Si) and a fine-grain polycrystalline silicon with enhanced absorption due to extensive grain-boundary regions (p-Si) were mixed with voids in the appropriate ratio to fit the spectra of as-prepared PSL. For the annealed PSL amorphous silicon (a-Si) was needed in conjunction with p-Si. The oxidized PSL could be fitted with a reduced a-Si content. We can interpret the annealing effect as a depassivation process of the inner surfaces of the PSL (a-Si fraction). At the same time, oxidation leads to a repassivation process.

Growth of hcp Cu on W(100)

Abstract Hcp Cu has been grown by epitaxy on the W(100) surface. The epitaxial relationship of the hcp films is determined by RHEED as (1120) ‖ (100) and [1100] ‖ [011]. The growth of Cu in the hcp structure is attributed to the small energy difference between the hcp and fcc structure and the much smaller misfit of this hcp orientation in the [1100] direction than of any fcc orientation. The RHEED oscillations at 150 K show a difference between the period of the even and odd oscillations, that coincides with changes in UPS intensity at selected energies. The electronic structure of the thin film grown at 150 and 300 K shows only small differences. At 500 K and above, the Cu grows in high and narrow islands.

Change of the surface induced optical anisotropy of the clean Si(110) surface by oxidation

Normal incidence ellipsometry has been used to measure the change in the complex anisotropic reflectance ratio ? upon oxidation of the clean Si(110)16 × 2 surface. The spectroscopic change in the amplitude of ? (tan(?)) shows a broad maximum of height 1.4 × 10?3 in the high energy region above 2.5 eV. No phase shift difference for the reflectance coefficients belonging to the surface principal optical axes has been measured. A Kramers-Kronig transformation of the amplitude ratio showed that a change in the phase is not expected. The change in tan(?) indicates that the change in reflection upon oxidation in the optical region ismainly in the (10) direction.

In-situ growth studies of sputtered ybco thin films by spectroscopic ellipsometry

Using spectroscopic ellipsometry we studied in-situ the growth of off-axis sputtered YBa2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Especially in the very first growth stage ( 106A cm?2 @ 77 K) is smooth and homogeneous, except for the first unit cell layer (initial stage regime). The smoothness of the response is indicative for a step-mode like growth mechanism. In contrast, the initial stage regime is governed by a 2D nucleation mechanism. This behaviour changes when the deposition temperature is lowered. Due to increased disorder, the initial stage regime is extended to larger thicknesses and a true 2D growth mode is no longer apparent. Similar behaviour is observed with increasing oxygen partial pressure, where the optical response is shifted from a step-flow mode like mechanism to an island-growth mode.

SURFACE DISORDER PRODUCTION DURING PLASMA IMMERSION IMPLANTATION AND HIGH ENERGY ION IMPLANTATION

High-depth-resolution Rutherford Backscattering Spectrometry (RBS) combined with channeling technique was used to analyze the surface layer formed during plasma immersion ion implantation (PIII) of single crystal silicon substrates. Single wavelength multiple angle of incidence ellipsometry (MAIE) was applied to estimate the thickness of the surface layer. The thickness of the disordered layer is much higher than the projected range of P ions and it is comparable with that of protons. n nAnother example of surface damage investigation is the analysis of anomalous surface disorder created by 900 keV and 1.4 MeV Xe implantation in 100 silicon. For the 900 keV implants the surface damage was also characterized with spectroellipsometry (SE). Evaluation of ellipsometric data yields thickness values for surface damage that are in reasonable agreement with those obtained by RBS.

Oxygen diffusion in laserablated YBa2Cu3Ox thin films studied by spectroscopic ellipsometry

In the photon energy range of 2.1 to 4.6 eV and in the temperature range of 20 to 700oC, the complex dielectric function of oxygen deficient YBa2Cu3O6 has been measured and compared to that of YBa2Cu3Ox in an ambient of 1 bar of oxygen, using spectroscopic ellipsometry. It has been observed that the optical 4 eV transition, which is associated with oxygen deficiency, vanishes before the YBCO thin film is fully oxygenated. Oxygen diffusion coefficients have been estimated by real-time monitoring of the dielectric function during isothermal in-diffusion. It has been found that for T?300oC oxygen can enter the YBCO thin film whereas for T=200oC, no oxygen in-diffusion has been observed.

Broad spectrum optical phase retarder using three metallic mirrors for normal and Brewster's angle of incidence ellipsometry

An optical phase retarder for the photon energy range of 1.5–5.5 eV (825–225 nm) is described. The use of metallic mirrors yields good transmission in the entire energy range and the smooth energy dependence of the phase shift is convenient for in situ spectroscopic ellipsometric applications. The optical properties of the retarder are in good agreement with its expected values. The retarder has proved to be a valuable improvement in ellipsometry measurements and enables the use of a conventional rotating polariser ellipsometer for normal incidence measurements.

Optical anisotropy of Ge(001)

The surface induced optical anisotropy in the electronic structure of clean Ge(001) 2×1 was studied with an ellipsometer at normal incidence. The change in the reflection difference between light polarized parallel and perpendicular to the dimer bond at this surface upon either absorption of molecular oxygen or Ar+ ion bombardment was recorded. Both procedures were found to give the same results. It was possible to obtain a qualitative agreement of the optical spectrum recorded and the position and parity of the occupied and unoccupied surface states known on the clean surface.

The use of splines to analyze scanning tunneling microscopy data

Scanning tunneling microscopy (STM) requires a two‐dimensional (2D) image displaying technique for its interpretation. The flexibility and global approximation properties of splines, characteristic of a solid data reduction method as known from cubic spline interpolation, is called for. Splines were used to implement 2D representation, deconvolution, and Fourier transform routines with still a good performance in case of noisy measured functions. The implementation was done on a small computer system (8086/8087 processor) with a reasonable execution time. The underlying mathematics of 2D spline‐based routines will be shown and tests on STM‐like images will be given to show the performance. A reduction of 25–100 in memory of stored data is achieved using splines if these routines are used while scanning a surface as in STM.