M. Kwoka - Academia.edu (original) (raw)

Papers by M. Kwoka

ABSTRACT In this paper we present the results of comparative studies of the chemical stability of... more ABSTRACT In this paper we present the results of comparative studies of the chemical stability of L-CVD SnO2 ultra thin films (20nm) deposited on the atomically clean Si(100) substrate after their subsequent in situ hydrogenation and oxidation, and then after air exposure. For the control of surface chemistry of these films we used in a comparative way the X-ray Photoemission Spectroscopy (XPS) combined with ion depth profiling (DP XPS) and Thermal Desorption Spectroscopy (TDS). Our XPS experiments showed that the L-CVD SnO2 ultrathin films after subsequent in situ hydrogenation and oxidation consist of strongly nonstoichiometric layer at the top of Si dioxide substrate. After subsequent air exposure they were covered with undesired 3 monolayers of C contamination and various forms of oxygen. During the TDS procedure a two-step desorption of molecular hydrogen (H2), water vapor (H2O), carbon dioxide (CO2) and atomic oxygen (O) at the temperatures of ~530K and 600K was observed, respectively. The TDS results were in a good correlation with evident decreasing of the relative concentration of C contaminations, as well as variation of nonstoichiometry of the L-CVD SnO2 ultra thin films as determined by XPS combined with ion depth profiling.

In this paper we present the results of Atomic Force Microscopy (AFM) characterisation of the sur... more In this paper we present the results of Atomic Force Microscopy (AFM) characterisation of the surface morphology of the L-CVD SnO 2 thin films prepared by L-CVD technology and studied after exposure to air, dry air oxidation, and ion beam profiling. The L-CVD SnO 2 thin films after air exposure have a very smooth surface morphology with an average surface roughness (RMS) smaller than 0.5 nm, and average and maximal grain heights of about 1 and 2 nm, respectively. After dry air oxidation the L-CVD SnO 2 thin films exhibit an average surface roughness (RMS), as well as the average and maximal grain height, increased by one order of magnitude. Finally, after the ion beam profiling the L-CVD SnO 2 thin films exhibit an evidently disordered structure with a lot of craters. These experiments showed that the L-CVD SnO 2 thin films exhibit a very high quality surface morphology, what can be useful for solar cells and gas sensors application.

Thin Solid Films, 2009

In this paper experimental results of a comparative X-ray Diffraction (XRD), Scanning Electron Mi... more In this paper experimental results of a comparative X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) study of the crystalline structure, the local morphology, and the surface and in-depth chemistry of SnO 2 thin films obtained by Rheotaxial Growth and Thermal Oxidation (RGTO) method are presented. XRD rules out even a minor presence of a coexisting SnO phase. AFM and SEM show a fractal like morphology of nanograins (20 nm typical size) agglomerated in clusters of crystallites with a bimodal size distribution. XPS shows that the surface of the SnO 2 crystallites is slightly under-stoichiometric as expected from the oxygen deficient termination of their facets. Noteworthy, as evidenced by XPS depth profiles, there are no significant changes of the surface chemistry of the RGTO film with argon ion sputtering.

Thin Solid Films, 2011

ABSTRACT In this paper, the results of XPS and AFM studies of the surface chemistry and morpholog... more ABSTRACT In this paper, the results of XPS and AFM studies of the surface chemistry and morphology of In2O3 nanolayers obtained by rheotaxial growth and vacuum oxidation (RGVO) technology are presented. The ultrathin In films were deposited under UHV by thermal evaporation of indium pellets on the well defined Si substrate maintained at different temperatures. Optimal conditions to obtain the smallest grains and highest surface coverage have been determined, which was controlled by AFM, whereas the cleanness of deposited In nanolayers was controlled by XPS method. The ultrathin films of In2O3 (nm scale) were obtained in two ways, i.e. by oxidation of ultrathin films of In after their deposition, as well as by oxidation of In ultrathin films already during the deposition process. The XPS experiments showed that in both cases the obtained ultrathin films of In2O3 were almost stoichiometric. In turn, the AFM studies confirmed that only ultrathin films obtained during the simultaneous In deposition and oxidation exhibit almost flat surface morphology with average roughness at the level of about 0.85nm.

Nanoscale Research Letters, 2014

In this paper we investigate the surface chemistry, including surface contaminations, of SnO 2 na... more In this paper we investigate the surface chemistry, including surface contaminations, of SnO 2 nanowires deposited on Ag-covered Si substrate by vapor phase deposition (VPD), thanks to x-ray photoelectron spectroscopy (XPS) in combination with thermal desorption spectroscopy (TDS). Air-exposed SnO 2 nanowires are slightly non-stoichiometric, and a huge amount of C contaminations is observed at their surface. After the thermal physical desorption (TPD) process, SnO 2 nanowires become almost stoichiometric without any surface C contaminations. This is probably related to the fact that C contaminations, as well as residual gases from air, are weakly bounded to the crystalline SnO 2 nanowires and can be easily removed from their surface. The obtained results gave us insight on the interpretation of the aging effect of SnO 2 nanowires that is of great importance for their potential application in the development of novel chemical nanosensor devices.

Applied Surface Science, 2006

In this paper we present the results of the XPS atomic depth profile analysis, using ion beam spu... more In this paper we present the results of the XPS atomic depth profile analysis, using ion beam sputtering, of L-CVD SnO 2 thin films grown on an atomically clean SiO 2 substrate after annealing at 400 8C in dry atmospheric air. From the evolution of the Sn 3d 5/2 , O 1s, Si 2p and C 1s core level peaks our experiments allowed the determination of the in depth atomic concentration of the main components of the SnO 2 /SiO 2 interface. Thin (few nm) nearly stoichiometric SnO 2 films are present at the topmost layer of the thin films, and progressive intermixing with SnO and silicon oxide is observed at deeper layer. The interface between the Sn and the Si oxide layers (i.e. the effective Sn oxide thickness) is measured at 13 nm. #

Applied Surface Science, 2012