Piotr Mazur

Nanotexturing of GaN light-emitting diode material through mask-less dry etching

We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

Structural and surface properties of TiO2 thin films doped with neodymium deposited by reactive magnetron sputtering

Thin films were deposited using modified, high energy magnetron sputtering method from Ti-Nd mosaic targets. The amount of neodymium dopant incorporated into two sets of thin films was estimated to be 0.8 and 8.5 at.%, by means of energy dispersive spectroscopy. On the basis of x-ray diffraction method, the type of crystalline structure and crystallites size were evaluated directly after the deposition process and after additional post-process annealing at 800 °C temperature. The influence of annealing on the surface properties was evaluated with the aid of atomic force microscopy. Uniformity of the dopant distribution in titanium dioxide matrix was examined with the aid of secondary ion mass spectroscopy. Additionally, using atomic force microscope, diversification and roughness of the surface was determined. Chemical bonds energy at the surface of TiO2:Nd thin films was investigated by x-ray photoelectron spectroscopy method. Wettability measurements were performed to determine contact angles, critical surface tensions and surface free energy of prepared coatings. On the basis of performed investigations it was found, that both factors, the amount of neodymium dopant and the post-process annealing, fundamentally influenced the physicochemical properties of prepared thin films.

Measurement of the effect of Coriolis and centrifugal forces on the trajectory of a body in a rotating frame

A method is described for recording and analysing the trajectory of a ball that moves horizontally as a result of the Coriolis and centrifugal forces. This topic is very important for a better understanding of problems accompanying many atmospheric phenomena and the launching of space rockets. Our experiment shows how the value of the Coriolis force changes during the motion of the ball.

Evaluation of hybrid anion exchanger containing cupric oxide for As(III) removal from water

The aim of this study was investigate of arsenite adsorption on a hybrid polymer based on a polystyrene/divinylbenzene macroporous anion exchanger containing cupric oxide deposited within its porous structure. The study included batch kinetic and equilibrium experiments, and investigation of influence of the pH, regeneration of spent adsorbent and the column process on arsenic(III) adsorption. The experimental data were evaluated using kinetic, isotherm and fixed-bed column models. The adsorption capacity calculated from the Langmuir model was 6.61 mg As(III) g-1. The adsorption rate was controlled by both chemisorption of arsenic on the adsorbent surface and external diffusion, and at a higher initial As(III) concentration also by intraparticle diffusion. The spent adsorbent was easily regenerated with 1.0 M NaOH solution. Based on batch adsorption studies and X-ray photoelectron spectroscopic analyses a mechanism of As(III) adsorption was proposed. Arsenite removal proceeded in two stages: oxidation to arsenate on the CuO surface, followed by an ion exchange reaction. The studied hybrid polymer also showed very good adsorption characteristics under the dynamic regime. The S-shape of breakthrough curves and insignificant influence of bed height, initial concentration and flow rate on the adsorption capacity confirmed its applicability in water treatment.

Phthalocyanine arrangements on Ag(100): From pure overlayers of CoPc and F16CuPc to bimolecular heterostructure

We have utilized scanning tunneling microscopy (STM) and low energy electron diffraction to determine the structural properties of two types of metal-phthalocyanines (MPcs), i.e., cobalt-phthalocyanine (CoPc) and hexadecafluorinated copper-phthalocyanine (F16CuPc) on the Ag(100) surface. For coverage close to one monolayer, both systems form long-range ordered structures with square unit cells. The size and rotation of the unit cell with respect to the silver lattice depend on the chemical composition of MPc. Both types of molecules prefer adsorption with around a 30° angle between the molecular axis and the [011] silver direction. The CoPcs mainly arrange in a (5 × 5)R0 phase; however, two additional local arrangements, a 26 × 26 R 1 1 ○ and a (7 × 7)R0, were detected by STM. The F16CuPcs form a 29 × 29 R 2 2 ○ structure. The co-adsorption of CoPc and F16CuPc on the Ag(100) surface in a 1:1 ratio leads to the formation of a compositionally ordered chessboard-like 5 2 × 5 2 R 4 5 ○ structure. During filled states imaging, the different appearance of the central part of each MPc allows us to distinguish CoPcs from F16CuPcs. Regardless of the applied voltage polarity, the ligands of F16CuPcs appear brighter than the ligands of CoPcs.

Preparation technique of 6H-SiC(0001) wafers

We investigated 6H-SiC(0001) crystal Si face-oriented, prepared by ex situ hydrogen etching in a home made cold-wall tubular reactor. The atomic structure and topography were characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Surface reconstructions were monitored by low energy electron diffraction (LEED). Chemical composition was determined using X-ray photoelectron spectroscopy under ultrahigh vacuum. Specific preparation conditions have been found for removing all scratches arising from the polishing process. We report the procedure how to achieve an atomically smooth, oxygen-free surface of SiC(0001).

Preparation of TiO 2 thin films by reactive evaporation method

Thin films of TiO2 were prepared on glass substrates by reactive evaporation of TiO. Properties of the thin films were investigated under ultrahigh vacuum conditions by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM topography exhibits a uniformity structure of the thin films and shows a high quality nanocrystalline structure of TiO2 with grain size ranging from 28 nm to 35nm. The XPS Ti-2p spectra confirmed the occurrence of the 4+oxidation state of Ti and the O-1s spectra revealed the presence of an O−2 photoelectron peak. The calculated O/Ti ratio in TiO2 thin films was in the range 1.85–2.15 depending on the samples. Additional analysis of the thin films was carried out by X-ray powder diffraction (XRD).