R. Kassing

Recent results in cubic boron nitride deposition in light of the sputter model

Abstract In the field of c-BN deposition, ion-assisted processes are most common and best investigated. Understanding of the deposition mechanisms is the basic key to improve film quality and, therefore, to realize potential applications. Recently, Reinke et al. developed a sputter model for ion-assisted c-BN deposition in which material removal processes (sputtering and desorption) play major roles [1]. This model is used as a guideline in order to give an overview on c-BN deposition. The first part investigates the growth mechanisms of ion-assisted c-BN deposition. Therefore, a data collection which includes CVD and PVD deposition methods was performed. The resulting dependencies are discussed in light of the sputter model. By comparison with other models, it is found that most of the experimental facts can best be described in terms of the sputter model, whereas in the nucleation step compressive stress plays an additional role. In the second part, c-BN deposition is considered in a wider context. Current problems and some first approaches to overcome these problems are discussed. Furthermore boron nitride is compared with the sp 3 carbon modifications tetrahedral amorphous carbon (ta-C) and diamond. It is concluded that c-BN and ta-C rely on different growth mechanisms; the investigation of extended parameter ranges in the search for new ion-assisted carbon and BN modifications is proposed. Some approaches in c-BN deposition without ion assistance are discussed in accordance to diamond deposition. Nevertheless, the advances are small and no process yielding similar high-quality material as CVD diamond exists.

Determination of preferential binding sites for anti-dsRNA antibodies on double-stranded RNA by scanning force microscopy

The monoclonal anti-dsRNA antibody J2 binds double-stranded RNAs (dsRNA) in an apparently sequence-nonspecific way. The mAb only recognizes antigens with double-stranded regions of at least 40 bp and its affinity to poly(A) poly(U) and to dsRNAs with mixed base pair composition is about tenfold higher than to poly(I) poly(C). Because no specific binding site could be determined, the number, the exact dimensions, and other distinct features of the binding sites on a given antigen are difficult to evaluate by biochemical methods. We therefore employed scanning force microscopy (SFM) as a method to analyze antibody-dsRNA interaction and protein-RNA binding in general. Several in vitro-synthesized dsRNA substrates, generated from the Dictyostelium PSV-A gene, were used. In addition to the expected sequence-nonspecific binding, imaging of the complexes indicated preferential binding of antibodies to the ends of dsRNA molecules as well as to certain internal sites. Analysis of 2,000 bound antibodies suggested that the consensus sequence of a preferential internal binding site is A2N9A3N9A2, thus presenting A residues on one face of the helix. The site was verified by site-directed mutagenesis, which abolished preferential binding to this region. The data demonstrate that SFM can be efficiently used to identify and characterize binding sites for proteins with no or incomplete sequence specificity. This is especially the case for many proteins involved in RNA metabolism.

Deposition of TiO2 thin films by plasma-enhanced decomposition of tetraisopropyltitanate

Abstract We investigated the suitability of tetraisopropyltitanate as a source gas for plasma-enhanced deposition of titanium dioxide thin films. Whereas TiO2 deposition using a standard planar reactor as well as a remote plasma process with O2 as reactant were found difficult to control, stoichiometric, carbon-free TiO2 can be deposited if the remote process with inert reactants such as argon or xenon is used. Deposition rates of 15 nm min-1 can be achieved. The refractive index, being a most important property in view of possible applications of TiO2 films as optical coatings, can be varied from 1.8 to 2.5 by suitable choice of deposition parameters. Film stoichiometry was found to be almost parameter independent whereas film density ϱ and, strongly correlated with ϱ, properties such as the refractive index and the chemical resistance are mainly influenced by processing temperatures, in situ during deposition as well as ex situ by post-deposition annealing.

Functional properties of nanostructured materials

Preface.- 1. General Aspects.- Nanoscaled materials: A brief introduction R. Kassing, W. Kulisch.- 2. Basic Properties of Nanoscaled Materials.- 2.1. Electrical Properties.- Electronic Properties and characterization of disordered semiconductors J. Marshall.- A computer modeling study of hopping transport and variable range hopping in disordered soils J. Marshall.- Electrode-limited currents in thin ternary chalcogenide films P. Petkov.- 2.2. Optical Properties.- A short survey of optical properties of metal nanostructures U. Kreibig.- 2.3. Mechanical Properties.- Nanocomposite thin films with improved mechanical properties W. Kulisch.- 3. Techniques and Methods.- 3.1. Preparation of Nanoscaled Materials.- Fabrication of nanostructures R. Kassing.- 3.1.1. Bulk Materials.- Optical properties of metal nanoparticles formed by ion implantation and modified by laser annealing A.L. Stepanov.- Synthesis procedures of nanocomposites from gels J.-C. Pivin.- Phase separation and crystallization in high iron containing borosilicate glasses R. Harizanova et al.- Nanocomposites based on immiscible borate glasses V. Ivanova et al.- Investigation of the microstructure of polypropylene composites filled with wood flour modified with monochloracetic acid D. Dobreva et al.- 3.1.2. Thin Films.- Physics of deposition of hydroxyapatite layers by pulse laser deposition method W. Mroz.- Laser deposition of waveguiding films M. Jelinek.- Functionalized thin films and structures obtained by novel laser processing approaches R. Cristescu et al.- 3.2. Characterization of Nanoscaled Materials.- Nanostructured films on silicon surfaces P. Morgen et al.- On the origin of impurities in the window layers of CsTe/CdS solar cells M. Emziane et al.- 4. Nanoscaled Thin Films.- 4.1. Carbon and Related Materials.- Deposition, characterization and application of nanocrystalline diamond films W. Kulisch, C. Popov.- Nano-scale, multi-functional, cubic boron nitride coatings S. Ulrichet al.- Nanocrystalline cubic boron nitride films R. Freudenstein, W. Kulisch.- Boron nitride thin layers prepared using a krypton fluoride excimer laser R. Kosydar et al.- 4.2. Silicon-Based Films.- Metal induced crystallization - an advanced method for polycrystalline Si film preparation D. Dimova-Malinovska.- Modication of the optical and structural properties of a-Si1-xCx: H films by ion implantation D. Dimova-Malinovska.- Application of stain etched porous silicon in solar cells and light emitting diodes D. Dimova-Malinovska.- Structural properties of poly-Si thin films on ZnO:Al coated glass substrates obtained by aluminium induced crystallization in different atmospheres V. Grigorov et al.- 4.3. Oxide Films.- CVD-transition metal oxide films as functional layers in smart windows and X-ray mirrors K. Gesheva et al.- Plasma assisted deposition of tungsten oxide / silicon oxide multilayer films with sub-nanometer single layers F. Hamelmann et al.- Electrical and polarization properties of nanosized ZrO2 on polycrystalline silicon P.V. Aleksandrova et al.- Characterization of optical coatings for artwork protection by means of neutron reflectometry I. Di Sarcina et al.- Functional nanostructured metal oxide thin films for applications in optical gas detection G. Socol et al.- 4.4. Further Systems.- Structural characterization of Er: YAG thin films grown by pulsed laser deposition D. Stanoi et al.- Optical behavior of vacuum deposited amorphous and nano-crystalline As2S3 films before and after irradiation J. Dikova et al.- On the determination of the optical constants of very thin metallic films P. Gushterova et al.- 5. Special Nanostructures: Fullerenes, Nanotube, Nanowires.- Nanostructured carbon materials C. Popov.- Encapsulates: Nd-Fe-B@C and Fe@C for drug delivery systems and contrast elements, study of structure, chemical composition and magnetic properties M.J. Wozniak et al.-

Surface investigations by scanning thermal microscopy

A scanning thermal microscope has been developed which is capable of imaging thermal properties of materials with high spatial resolution. First results indicate a lateral resolution less than 200 nm. The microscope employs a miniaturized thermal probe whose tip is formed as a thermocouple. The probe is laser heated to generate a thermovoltage. A sample approaching the heated tip leads to a heat flow from the tip to the cooler sample surface and thus to a decrease of the measured voltage. In the initial experiments we scanned the tip above the sample surface with open feedback loop and mapped the thermovoltage at each location of the scan range. Furthermore, we closed the feedback loop keeping the thermovoltage constant and measured the z displacement of the piezoelectric tube carrying the probe. All these measurements yield topographical as well as thermal information of the sample surface.

Plasma-enhanced chemical vapour deposition of silicon dioxide using tetraethoxysilane as silicon source☆

The suitability of tetraethoxysilane (TEOS) as silicon source for the deposition of silicon dioxide films by low temperature plasma-enhanced chemical vapour deposition processes has been investigated. Experiments were carried out using a commercial standard planar deposition reactor. High quality stoichiometric SiO2 films with almost no contamination from the organic groups of the TEOS molecule can be deposited. In addition, the step coverage of surface structures (e.g. deep trenches) is excellent.

Influence of gas phase parameters on the deposition kinetics and morphology of thin diamond films deposited by HFCVD and MWCVD technique

Abstract This paper reports on the deposition of thin diamond films with rates of more than 15 μm/h with the Hot Filament CVD (HFCVD) technique. We compare in some detail deposition kinetics of films from different source gases. Using different oxygen-containing species like methanol, acetone, DMP and a CH4/H2/O2 gas mixture, we studied the influence of the carbon to oxygen ratio in the source material as well as the effect of free and bonded oxygen addition to the gas phase. On the other hand, deposition parameters, especially the filament to substrate distance, are found to strongly affect all the film parameters investigated. High deposition rates were obtained using low filament to substrate distances (dF ⩽1mm). The second part of this paper reports on the deposition of diamond using Micro Wave Chemical Vapour Deposition (MWCVD). Using oxygen-containing compounds at high carbon concentration in the gas phase (C/H⩾ 20%), we succeeded in depositing diamond at low substrate temperatures (⩽400 °C). We will report on the deposition of high quality diamond films without the addition of molecular hydrogen to the gas phase using only methanol.

Ion energy distributions in SF6 plasmas at a radio‐frequency powered electrode

An energy‐resolving quadrupole mass spectrometer (E‐QMS) was assembled underneath the powered electrode of a diode reactive ion etcher. The plasma ions reach the E‐QMS through an orifice in the powered electrode with a diameter of 100 μm. The ion energy distributions (IEDs) of ionic species from SF6 plasmas in the pressure range of 0.1–1.5 Pa for dc bias potentials between 50 and 300 V and a rf of 13.56 MHz were investigated. The IEDs always show a saddle shaped peak at an energy corresponding to a total potential drop across the sheath given by USh=Udc+UP, where Udc is the dc bias potential and UP is the time averaged plasma potential. In the energy range from 0 eV to eUdc there are multiple peaks in the IEDs of SF+x (x=1..5), whereas the F+, F+2, and S+ IEDs show only a single peak in this range. These peaks are the result of ion generating collisions in the sheath. On pressure variation the IEDs do not change significantly. We also measure IEDs of negative ions. The IEDs of these ions show a broad dist...

Low temperature remote plasma-enhanced deposition of thin metal oxide films by decomposition of metal alkoxides

Abstract The suitability of several metal alkoxides for deposition of thin films by low temperature remote plasma-enhanced chemical vapour deposition is investigated. In some cases other metal-organic compounds were also used. Among the systems studied are the deposition of SiO 2 from tetraethyl- ortho -silicate and hexamethyl-disiloxan as well as SiO x N y C z films from hexamethyldisilazan and TiO 2 from tetraisoprophyl titanate. Further investigations concerned ZrO 2 formation from bis-(cyclopentadienyl) diethoxyzircon and tetra( tert -butoxy)zircon. We will discuss the influence of gas phase composition on thin film growth and film properties. We will also present a short overview over general film properties obtained using the various starting materials. Our results show that TiO 2 SiO 2 and ZrO 2 can be deposited from their respective alkoxides. With respect to growth rate and impurity concentration these films are shown to be superior to films deposited from other organometallic sources. They also show good electrical and optical properties.

Investigation of gas phase mechanisms during deposition of diamond films

Abstract The deposition of diamond films is investigated by optical emission spectroscopy measurements. Using the microwave chemical vapour deposition technique, the system C:H:O is surveyed starting from hydrogen-rich oxygen-free mixtures by gradually adding oxygen and reducing the hydrogen content until finally reaching C:H:O = 1:4:1, i.e. CH4 + 1 2 O2. CH and C2 are shown to give good measures for different active carbon species, CH being correlated with the growth rate while C2 correlates inversely to the film quality. The main role of O2 is the transformation of active carbon into the more stable carbon monoxide.