Search

Protein-based bottom-up synthesis of functional nanomaterials and devices is one of the most promising areas in bio-nanotechnology. Here, we demonstrate that organic assemblies can serve as biologically controllable scaffolds for the deposition of inorganic nanoparticles. In this work, wild-type M13 phages were employed for controlled mineralization of zinc oxide particles. Our aim was to construct layered structures of organic and inorganic materials which contain alternating layers on a smooth substrate. The structure, elemental composition, and also the integrity of the organic and the biologically-templated inorganic layers were studied. A uniform nano-hybrid structure without significant thickness fluctuations was fabricated by using a high concentration of M13 phages and a carbon-coated substrate. The current study gives insight into the combination of organic–inorganic materials to form a multilayered structure, which in turn sets the stage for the fabrication of electronic devices, e. g. actuators or capacitors.

Silicon Carbide (SiC) samples with controlled carbon contents are manufactured from polymeric precursors. Based on X-ray diffraction (XRD) data, a correlation of the excess carbon content and the crystallization kinetics of silicon carbide are determined for the obtained pyrolysates. The crystallization mechanisms as well as the corresponding activation energies EA are also determined. Furthermore, the influence of the carbon content on the oxidation behavior of these pyrolysates is studied. A model for the oxidation of the prepared silicon carbide-based materials is proposed.

Aluminum-doped ZnO (AZO) thin films were produced via template-directed deposition at 60 °C. By adding organic molecules to the deposition solution, it is possible to control the crystallite growth, and nanocrystallinity is achieved. An organic template, 3-aminopropyltriethoxysilane (APTES), is used to direct the attachment of the crystallites on the substrate. The optical properties and the incorporation of the aluminum from solution into the ZnO films were measured using photoluminescence (PL) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The morphology of the film was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The latter revealed a preferred orientation of the crystallites in the samples where more than 15 mol% Al was added to the stock solution. For values higher than 30 mol% Al in solution, no ZnO was found at all.

International audience; The structure and properties of polymer-derived Si-(B-)O-C glasses have been shown to be significantly influenced by the boron content and pyrolysis temperature. This work determined the impact of these two parameters on the thermodynamic stability of these glasses. High-temperature oxide melt solution calorimetry was performed on a series of amorphous samples, with varying boron contents (0-7.7 at.%), obtained by pyrolysis of precursors made by a sol-gel technique. Thermodynamic analysis of the calorimetric results demonstrated that at a constant pyrolysis temperature, adding boron makes the materials energetically less stable. While the B-containing glasses pyrolyzed at 1000 degrees C were energetically less stable than the competitive crystalline components, increasing the pyrolysis temperature to 1200 degrees C led to their enthalpic stability. Si-29 and B-11 MAS nuclear magnetic resonance (NMR) spectroscopy measurements on selected samples confirmed a decrease in the concentrations of mixed Si-centered SOiC4-i and B-centered BOjC3-j bonds at the expense of formation of SiO4 and B (OSi)(3) species (indicating a tendency toward phase separation) when the boron content and pyrolysis temperature increased. In light of the findings from calorimetry and NMR spectroscopy, we propose a structure-energetic relationship in Si-(B-) O-C glasses.

The reason for the higher thermal persistence of amorphous polymer-derived Si B C N ceramics (T ∼ 1700–2000 °C) compared to Si C N ones (T ∼ 1500 °C) has been a matter of debate for more than a decade. Despite recent experimental results which indicate a major kinetic effect of boron on the thermal persistence of the ceramics, no experimental investigation of the thermodynamic stability of the materials has been reported. In this work, we present measured energetics of a series of the amorphous ceramics with various boron contents (0–8.3 at.%) using high-temperature oxidative drop-solution calorimetry. Through measurement of the drop-solution enthalpies in molten sodium molybdate at 811 °C, the formation enthalpies of the amorphous ceramics from crystalline components (SiC, BN, Si3N4, C) at 25 °C were obtained and found to be between −1.4 and −26.6 kJ g-atom−1. The determined enthalpy data plus the estimated positive entropy of formation values point to the thermodynamic stability of the amorphous ceramics relative to the crystalline phases, but such stabilization diminishes with increasing boron content. In contrast, the higher boron content increases the temperature of Si3N4 crystallization despite less favorable energetics for the amorphous phase, implying more favorable energetics for crystallization. Thus the so-called “stability” of Si B C N ceramics in terms of persistence against Si3N4 crystallization appears to be controlled by kinetics rather than by thermodynamic stability.

Calcium carbonate (CaCO3) occurs in the three polymorphs calcite, aragonite and vaterite. The formation of these crystals in inorganic solutions is influenced by parameters like pH, temperature or impurities. Living freshwater microalgae can also induce the formation of CaCO3 when they live in a suitable environment containing saturated amounts of Ca2+. Through this biologically induced biomineralization only the formation of the polymorph calcite has been reported yet. We investigated the precipitates which have been formed in solutions containing the freshwater microalgae Scenedesmus obliquus and different zinc amounts (0, 3.27 and 6.53 mg Zn2+/l) by XRD and SEM. As references precipitates from the same solutions but without algae were investigated. We could show that the presence of living microalgae has a great influence on the precipitation of calcium carbonate crystals. In algae-containing media without or with a low zinc amount always calcite and aragonite are formed. In the corresponding medium with 6.53 mg Zn2+/l pure aragonite crystals were built. In contrast, in the inorganic, algae-free solutions without zinc, pure calcite is precipitated. Both inorganic solutions with zinc show major calcite precipitation and weak aragonite precipitation. Thus the algae cells advance significantly the formation of aragonite, which is enhanced by the presence of zinc cations in the media. Possible mechanisms are discussed.

Up to now, chemical synthesis routes only provide restricted opportunities for the formation of structured nano particles. In contrast, living microorganisms generate nano materials of well defined shapes by the precise control of biomineralization. Here we reveal new principles for the generation of functional nano materials through the process of biomineralization. We used the detoxification mechanism of the unicellular alga Scenedesmus obliquus to generate a techno logically interesting zinc-phosphate-based nano material. The algae were incubated in media with a sublethal zinc concentration (6.53 mg Zn dm-3) for 4 weeks. Using BF-and ADF-STEM imaging combined with analytical XEDS we could show that nano needles containing phosphorus and zinc were formed inside the living cells. Further more, the cells incubated with zinc show a strong fluorescence. Our findings indicate that the algae used polyphosphate bodies for detoxification of the zinc ions, leading to the generation of intracellular zinc-phosphate-based nano needles. Beside the technological application of this material, the fluorescent cells can be used for labeling of e.g. biological probes. This new experimental protocol for the production of an inorganic functional material can be applied also for other substances.

The amorphous Si–B–C–N ceramics with a similar Si/C/N atomic ratio and various boron contents of 3.7 and 6.0 at.% B were synthesized and then isothermally annealed at temperatures ranging from 1550 to 1775 °C. The course of crystallization for the modifications of Si3N4 was examined by quantitative analysis of the corresponding x-ray diffraction patterns. Additionally, recent results of similar investigations on the ceramic with 8.3 at.% B were also considered. The kinetic analysis demonstrates that the controlling mechanisms of the Si3N4 crystallization, continuous nucleation and diffusion-controlled growth, are independent of the boron content. Nevertheless, the estimated activation energy of the crystallization significantly increases from 7.8 to 11.5 eV with the amount of boron ranging from 3.7 to 8.3 at.%. It is concluded that the role of boron in the crystallization kinetics is mainly due to the effect of boron on the nucleation process. Beside the kinetic analysis, the correlation between the boron content and the Si3N4 crystallite size has been discussed.

The isothermal mass loss of two polymer-derived ceramics with compositions SiC 1.4 N 0.9 and SiC 1.5 N 1.0 B 0.05 were measured as a function of time using thermal gravimetric analysis at various temperatures ranging between 1580 and 1720 °C. The process of mass loss, attributed to the reaction Si 3 N 4 + 3C → 3SiC + 2N 2 ↑ , takes substantially more time for the boron-containing ceramic compared with the boron-free one. The continuous formation of SiC crystallites as the product of the reaction between Si 3 N 4 and C was revealed through X-ray diffraction (XRD) measurements during the course of the reaction. The kinetics of this reaction was studied using a generalized model for the analysis of chemical reaction kinetics. Consequently, the effective activation energies for the Si 3 N 4 degradation were estimated to be 11.6 ± 0.5 eV and 17.1 ± 0.7 eV for the Si–C–N and Si–B–C–N ceramics, respectively. Moreover, the results obtained indicate that the dominant mechanisms of the Si 3 N 4 degradation are strongly influenced by the presence of boron. For the Si–C–N ceramic, the chemical reaction at interfaces of the reactants and the crystallization of SiC as the reaction product are proposed to be the main probable stages controlling the progress of the investigated reaction. However, the local diffusion of C out of BNC x turbostratic layers surrounding the Si 3 N 4 nanocrystals and the gas (N 2 ) release from the reaction zone are suggested to be the most plausible processes limiting the progress of Si 3 N 4 degradation for the Si–B–C–N ceramic.

Uniform and well ordered zirconium oxide–organic nacre-like nanocomposites were synthesized by sequential solution deposition of zirconium oxide and organic LbL layers. The width of zirconia in threefold nanostructures was 75 nm, 95 nm and 170 nm, while the thickness of organic layer was 14 nm. A solution-deposited bulk zirconia layer with a thickness of 1 μm served as a reference material. Mechanical properties measured using a depth-sensing nanoindentation technique exhibited systematic increase in hardness and reduced modulus of nanocomposites compared to the bulk sample. The measured hardness was 1.1 GPa, 0.77 GPa, 0.56 GPa, respectively and 0.55 GPa for the bulk sample. Reduced modulus of the same samples was 23 GPa, 17 GPa, 13 GPa, respectively and 12 GPa for the bulk sample.

The formation of nanoscale zinc oxide particles with an almost-monomodal size distribution synthesized by microwave heating of solutions of mononuclear zinc oximato or zinc acetylacetonato complexes in various alkoxyethanols is investigated. Transparent stable suspensions that contain these particles can be obtained from the zinc oximato precursor. Based on electron paramagnetic resonance (EPR) studies, a core/shell model with a finite surface shell thickness of 1.000 ± 0.025 nm is proposed for the ZnO nanoparticles. Field-effect transistor (FET) devices with these ZnO particles as the active semiconducting layer exhibited a charge carrier mobility of 0.045 cm2/(V s) and Ion/off current ratios of ∼460.000, with a threshold voltage of 8.78 V.

Indium tin oxide (ITO) has attracted intense interest as the most important transparent conducting oxide (TCO) that sees wide use in many opto-electronic and photo-chemical devices. The goal of this study is to explore the possibility of depositing ITO thin films using a bioinspired aqueous deposition route as an alternative. On the surface of sulfonated-self assembled monolayers, Sn-doped indium hydroxide films are obtained via a hydrogen peroxide-assisted method. As a result, the as-deposited indium tin hydroxide films possess a single hexagonal phase of In(OH) 3 ·xH 2 O (0 ≤ x < 1) with Sn doping percentage of (1.7 ± 0.2) at % and a column-like hierachical microstructure. Structural, compositional and property studies, including electron microscopy, X-ray diffraction, photoelectron spectroscopy, optical transmittance, photoluminescence and four-probe conductivity measurements, are conducted. The possible mechanism based on oriented attachment is discussed for the film growth. Strong room temperature photoluminescence within the near UV range is observed in the case of Sn-doped, but not in the one of the pure In(OH) 3 ·xH 2 O films. Annealing of the indium tin hydroxide films above 200 °C gives nanocrystalline Sn:In 2 O 3 films with higher UV and visible transparency and electrical conductivity compared with those of pure In 2 O 3 films. The influence of annealing atmosphere is investigated.

Titania thin films were prepared on bare Si and Pt/Ti/SiO 2 /Si substrates by chemical bath deposition (CBD) from solutions of a titanium peroxo complex and subsequent calcinations at 350 and 700 °C, respectively. The CBD process allowed deposition on both uncoated and metal-coated Si substrates with the same deposition rate. Optimization of the annealing process yielded uniform and crack-free nanocrystalline anatase films. The influence of the film thickness, irradiation of visible light, measuring frequency, temperature and substrate on the dielectric properties will be discussed in the paper. Films with a final thickness of about 600 nm showed comparably high relative permittivity of 31.8 on silicon and of 52.7 on Pt/Ti/SiO 2 /Si substrates, respectively. The present route provides anatase thin films with higher dielectric constants than classical sol–gel routes and is therefore a promising candidate for potential applications in large scale integration.

When soluble zinc salts are hydrolyzed in water, usually elongated micrometer-sized zincite crystals are formed. In this study, polyvinylpyrrolidone (PVP) in a methanolic solution is used as an agent to control the morphology of the deposition product. It prevents crystal growth and yields zinc oxide nanocrystals. Thin films consisting of zinc oxide nanocrystals are formed on self-assembled monolayers (SAMs) of sulfonate-terminated alkylsiloxanes. Patterned films are deposited after local decomposition of the SAM by UV irradiation. The films fabricated from methanolic solutions containing PVP are particularly smooth, uniform and stable. Their thickness is determined by the deposition time and the molar ratio [PVP]:[Zn 2+ ], so that films of arbitrary thickness and nearly constant roughness can be obtained. The crystal grains are oriented preferentially with (001) direction perpendicular to the substrate surface. The films show ultraviolet, orange-red and green-yellow photoluminescence; the latter is quenched by heat treatment. Based on the obtained experimental results, a deposition mechanism is suggested.

Sea urchin embryos produce an endoskeleton composed of two symmetric spicules that consist of calcite, containing approximately 5% magnesium. The function of magnesium ions in mineral formation in vivo and the consequence of their incorporation into the mineral on mechanical properties are largely unknown. The authors investigated the in vivo effects of excess magnesium ion concentrations in the medium on skeletal development of Arbacia lixula. Morphological deformations of pluteus larval spicules were observed after cultivation in Mg2+-enriched sea water. Energy dispersive X-ray spectroscopy showed that magnesium ions were homogeneously distributed for complete larvae and spicule cross-sections. Magnesium ion content was quantified by inductively coupled plasma optical emission spectrometry, which revealed a considerable increased incorporation of magnesium ions into spicules of larvae from Mg2+-enriched sea water. However, no change in crystal polymorph formation was observed by X-ray diffraction. Mechanical properties of spicule cross-sections were analysed by nanoindentation and revealed significantly higher stiffness values for spicules from Mg2+-enriched sea water compared to the control, whereas no significant change in hardness values was obtained. This in vivo study shows that increased magnesium ion incorporation into sea urchin larval spicules modifies the mineral properties and supports this model to investigate the effect of minor ions on biomineralisation.

The coccolithophore Emiliania huxleyi is covered with elaborated calcite plates, the so-called coccoliths, which are produced inside the cells. We investigated the incorporation of zinc into the coccoliths of E. huxleyi by applying different zinc and calcium amounts via the culture media and subsequently analyzing the zinc content in the cells and the Zn/Ca ratio of the coccoliths. To investigate the Zn/Ca ratio of coccoliths built in the manipulated media, the algae have first to be decalcified, i.e. coccolith free. We used a newly developed decalcification method to obtain 'naked' cells for cultivation. E. huxleyi proliferated and produced new coccoliths in all media with manipulated Zn/Ca ratios. The cells and the newly built coccoliths were investigated regarding their zinc content and their Zn/Ca ratio, respectively. High zinc amounts were taken up by the algae. The Zn/Ca ratio of the coccoliths was positively correlated to the Zn/Ca ratio of the applied media. The unique feature of the coccoliths was maintained also at high Zn/Ca ratios. We suggest the following pathway of the zinc ions into the coccoliths: first, the zinc ions are bound to the cell surface, followed by their transportation into the cytoplasm. Obviously, the zinc ions are removed afterwards into the coccolith vesicle, where the zinc is incorporated into the calcite coccoliths which are then extruded. The incorporation of toxic zinc ions into the coccoliths possibly due to a new function of the coccoliths as detoxification sites is discussed.

Composite titania/vanadium oxide thin films were prepared by chemical bath deposition. The reaction solution consisted of aqueous solutions of ammonium vanadate and a titanium peroxo complex. Deposition could be achieved on surface-oxidized silicon substrates at reaction temperatures of 333 K. The films consisted of titania as well as vanadium(IV) and (V) oxide nanoparticles. For the elucidation of the deposition mechanism the reaction solutions were investigated by dynamic light scattering to monitor the particle agglomeration in the reaction solution and UV/Vis spectroscopy to gain information about the change in chemical composition. The deposition mechanism was discussed in terms of attachment of colloidal particles. Thereby an optimum size exists for the colloids in which deposition can take place, whereas below no deposition occurs and above only the sedimentation of larger agglomerates on the surface is possible. This kinetic control leads to rather uniform films with compositions in a narrow range.

Crystalline In(OH)3 and UV-emitting In2O3 thin films with a unique columnar morphology have been successfully prepared for the first time via a simple aqueous solution deposition method. In the present study, sulfonate-terminated self-assembled monolayers on single-crystal Si wafers were used as substrates for the film deposition. Uniform In(OH)3 thin films formed on self-assembled monolayers in aqueous solutions of InCl3.4H2O at 60°C. These films, containing columnar In(OH)3 crystals, showed preferential growth orientation along the [100] direction. The current understanding of the film formation mechanism was discussed. After annealing in air at 400°C, these films were converted to nanocrystalline In2O3 films without modification of the morphology. Photoluminescence emission from In2O3 films was reported at approximately 3.4eV, which was ascribed to the near-band-edge emission.

Chemical bath deposition has been introduced as a means to produce films of inorganic substances with low engineering expenditure and close to ambient temperature. Organic additives have been used to control the growth of zinc oxide particles in solution and prevent the formation of the typical rod-like morphology. In the present work an attempt is made to combine these two approaches in order to produce thin films of zinc oxide. In the presence of β-cyclodextrin, spherical nano-crystalline deposits were obtained from solution; polyethylene glycol induced the formation of nano-structured thin films. With polyvinylpyrrolidone as an additive, uniform films were deposited. The structure of these films was analyzed by X-ray diffraction and transmission electron microscopy, which revealed the presence of domains of locally oriented nanocrystals. A mechanism of oriented attachment is proposed to explain the formation of domained ZnO films.

Thin films consisting of ZnO nanoparticles were prepared by solvolysis from solutions of zinc acetate, polyvinyl pyrrolidone (PVP) and sodium hydroxide in 2-propanol at temperatures of 328 K. Uniform, photoluminescent films with homogeneous surface coverage were obtained on silicon wafers modified with SO 3 –H terminated self-assembled monolayers (SAMs). High resolution transmission electron micrographs and the corresponding electron diffraction patterns in combination with X-ray Photoelectron Spectroscopy revealed that nanocrystalline wurtzite-type ZnO is present in the films.

Deposition experiments from aqueous solutions of zinc nitrate were performed in a bio-inspired way using biomolecules as directing agents. A global overview of the effect of various amino acids (8) and dipeptides (21) was done in term of structure and morphology of the obtained coating. The selection of certain biomolecules leads to the formation of smooth ZnO thin films. Variations of the amino acid chemical function and the sequence used within the peptides combination give rise to a wide variety of morphologies ranging from films to three dimensional nets. The data obtained from scanning electron microscopy and X-ray diffraction are discussed and correlated to the chemical properties of the biomolecules.

The suitability of amino acids and dipeptides as structure-directing agents for the deposition of coatings from aqueous solutions of zinc salts is discussed. According to a bio-inspired approach, the influence of these biomolecules was investigated with respect to the evolution of architectures based on zinc oxide and basic zinc salts. The small molecules were able to trigger the morphology of these materials ranging from grainlike to two-dimensional up to three-dimensional features. Besides morphological aspects, the structural characterization of these solids by means of electron and atomic force microscopies, photoelectron and infrared spectroscopies, and X-ray diffraction are discussed in order to extract the function of the biomolecules with regard to the formation of the inorganic phases.

A “green” route to ultrahigh-temperature Si–B–C–N ceramic from vacuum-degassing waste gas of polyborosilazane {B[C2H4Si(CH3)NH]3}n (T2-1) has been developed. After gas-to-gel transformation, an amorphous ceramic Si5.3B1.0C19N3.7 was derived from the gel by dehydrocoupling and polymer-to-ceramic transformation. The ceramic started to form a nanostructure at 1700°C and resisted thermal degradation up to 2200°C in argon. This suggests that vacuum-degassing waste gases of polymer precursors may be perfect raw materials for various advanced ceramics.

Titania thin films were prepared on polyethylene terephthalate (PET) substrates by hydrolysis of a peroxo complex in aqueous solutions at 333 K. Dynamic light scattering was used to monitor the particle growth in the reaction solution at various pH values. These findings were used to optimize the microstructure of the titania films by avoiding sedimentation of agglomerates and rapid depletion of the reaction solution. Films deposited on pristine PET, surface hydrolyzed PET and surface oxidized silicon were investigated by atomic force microscopy and show no significant difference in morphology.

Amorphous Si-B-C-N ceramic powder samples obtained by thermolysis of boron-modified polysilazane, {B[C2H4Si(H)NH]3}n, were isothermally annealed at different temperatures (1400–1800°C) and hold times (3, 10, 30, and 100 h). A qualitative and semiquantitative analysis of the crystallization behavior of the materials was performed using X-ray diffraction (XRD). The phase evolution was additionally followed by 11B and 29Si MAS NMR as well as by FT-IR spectroscopy in transmission and diffuse reflection (DRIFTS) modes. Bulk chemical analyses of selected samples were performed to determine changes in the chemistry/phase composition of the materials. It was observed that silicon carbide is the first phase to nucleate around 1400–1500°C, whereas silicon nitride nucleates at and above 1700°C. Crystallization accelerates with increasing annealing temperature and proceeds with increasing annealing time. Furthermore, the surface area of the powders strongly influences the thermal stability of silicon nitride and thus controls overall chemical and phase composition of the materials on thermal treatment.

Ceramic materials derived from a boron modified polysilazane were investigated by means of energy-filtering transmission electron microscopy (EFTEM). After cross-linking of the polymer and subsequent thermolysis, a coarse powder with average composition Si24.0B8.0C44.0N24.0 is obtained. For further investigation, monolithic particles with sizes of several millimeters were heat treated in crucibles under a flowing nitrogen atmosphere at 1800 °C for 10 h. During thermolysis, the particles developed internal cracks on the macroscopic scale. At the crack surfaces, a layer of pure carbon was found. In the crack-free region, the material is composed of Si3N4 and SiC nano crystallites which are embedded in a turbostratic BNC-matrix. Quantitative electron spectroscopic imaging (ESI) shows an atomic ratio of the elements B:C:N of 1.0:4.0:1.1 in this matrix. In the vicinity of the cracks, silicon nitride locally decomposes with formation of silicon carbide because of its reaction with excess carbon. A detailed EFTEM study of the phase distribution near the crack surfaces showed that the first Si3N4 crystallites occur at a distance of approx. 5 μm from the carbon covered crack surface. In additional experiments the composition of the BNC-layers as a function of the distance from the crack surface was investigated.

Boron-modified poly(propenylsilazanes) [B{C 3 H 6 Si(CH 3 )NH} 3 ] n are synthesized via both ammonolysis of B(C 3 H 6 Si(CH 3 )Cl 2 ) 3 (monomer route) and hydroboration of [(H 2 CCHCH 2 )Si(CH 3 )NH] n ( n =3, 4) (polymer route) and subsequently transformed into ceramic materials by pyrolysis up to 1400 °C. Thermogravimetric analysis of the as-obtained materials as well as X-ray diffraction of annealed samples were performed to investigate high temperature properties, revealing the stability of the materials toward thermal degradation up to 1800 °C and the presence of silicon nitride at 1800/2000 °C. The crystallization is additionally investigated by transmission electron microscopy. SiC crystallization is observed first, followed by the evolution of a composite material which is composed of a turbostratic BNC matrix embedding SiC and Si 3 N 4 nanocrystals.

Starting from five different Si−B−C−N polymeric precursors with B/N atomic ratios ranging from 1:3 to 1:0.5, ceramic materials were synthesized by thermolysis at 1400 °C in about 70−75% yield. During this transformation, the Si/B/N ratio remained roughly constant, whereas H and C contents were reduced. The crystallization behavior of as-obtained ceramics was studied by X-ray diffraction. SiC was detected as the first crystalline phase forming during thermolysis or subsequent annealing. Further phase evolution can be predicted following thermodynamic calculations depending on the composition which is, for the different as-obtained materials, located in or close to the phase fields BN + Si3N4 + C, BN + Si3N4 + SiC + C, BN + SiC + C, or BN + B4+δC + SiC + C. The SiC-poor (Si3N4-rich) material was not high-temperature stable and decomposed releasing nitrogen, whereas SiC-rich (Si3N4-poor) materials were mass stable up to 2000 °C.

We carried out silicon self-diffusion studies in amorphous precursor-derived ceramics of composition Si3BC4.3N2 and Si2.6C4.1N2.3 to compare the atomic transport properties of a boron containing and of a boron free material in the system Si–(B)–C–N. Ion implanted stable 30 Si isotopes were used as tracers and secondary ion mass spectrometry (SIMS) was used for depth profiling. The experimentally determined diffusivities are lower by a factor of 10 for Si3BC4.3N2 than for Si2.6C4.1N3.3 in the whole temperature range investigated. This might be a hint that the mobility of the constituent elements plays an important role in the stabilization of the amorphous state of Si3BC4.3N2 at high temperatures. Both ceramics obey an Arrhenius behaviour with activation enthalpies and pre-exponential factors of ΔH=5.7 eV and D 0 =0.001 m 2 / s for Si3BC4.3N2, and ΔH=5.55 eV and D 0 =0.003 m 2 / s for Si2.6C4.1N3.3, respectively. These results are consistent with a diffusion mechanism mediated by vacancy like defects operating in these amorphous ceramics, which is analogous to the related crystalline silicon based non-oxide ceramics Si3N4 and SiC.

Chemical liquid deposition was used to form Ga- and N-containing thin films on single-crystal silicon and sapphire substrates. Films were grown from a gallium carbodiimide-based polymeric precursor solution at room temperature on the substrates which were previously functionalized by amine-terminated self-assembled monolayers followed by pyrolysis in NH3 at 900 °C. On sapphire, epitaxial growth of hexagonal gallium nitride islands was found after pyrolysis. The composition, morphology and microstructure of the films were characterized by Auger electron spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy.

Multinuclear (29Si,13C,11B,15N,1H) solid-state NMR and FT IR spectroscopy is employed to investigate the thermolysis of boron-modified polyhydridovinylsilazane, [B(C2H4SiHNH)3]n, from which a high-temperature stable Si–B–C–N ceramic can be formed. The study is focused primarily on the characterization of the amorphous intermediates on the atomic scale, where such spectroscopic techniques have demonstrated their particular suitability. In addition, data are provided for the transformation from the amorphous to the crystalline ceramic. It is shown that the transformation of the polymeric precursor to the (amorphous) pre-ceramic network is completed at around 500 °C. At this temperature the BN domains and Si–C–N units of mixed composition are formed. Above this temperature a continuous transformation to the ceramic takes place. At 1050 °C the amorphous ceramic consists of three main components: (i) amorphous (graphite-like) carbon; (ii) planar BN domains; and (iii) an Si–C–N matrix (SiCxN4−x units with x = 0, 1, 2). In addition, a considerable amount of hydrogen is present even at this temperature. The NMR studies have further shown that above 1700 °C the amorphous ceramic demixes, along with the formation of crystalline silicon nitride and silicon carbide. Likewise, structural changes for BN domains have been registered that are attributed to the formation of turbostratic BN(C) interface layers. In summary, the present study has demonstrated that the combination of multinuclear solid-state NMR and FT IR spectroscopy is a powerful method to probe the thermolytic preparation of ternary and quaternary ceramic materials. Copyright © 2001 John Wiley & Sons, Ltd.

The preparation of silicon nitride- and carbide-based ceramics by solid-state thermolysis of polysilazanes and polysilylcarbodiimides is described. Results on the ceramization of the preceramic compounds and the architecture of the corresponding amorphous states obtained by spectroscopic means and by X-ray and neutron scattering are reviewed. Fundamental correlations between the composition and structure of the preceramic compounds and the architecture of the amorphous state are revealed. Furthermore, the crystallization behavior of the amorphous precursor-derived Si–C–N ceramics is treated. Moreover, the influence of boron on the thermal stability of the amorphous state is described. The high-temperature behavior of these Si–B–C–N solids can be correlated with their phase composition. Ceramic materials with compositions located close to the three-phase equilibrium SiC + BN + C exhibit a high temperature stability up to 2000 °C. This effect is accompanied by the formation of a metastable solid consisting of Si3N4 and SiC nanocrystals that are embedded in a turbostratic B–C–N matrix phase. Based on thermodynamic considerations, a model for the high-temperature stability effect is proposed. Copyright © 2001 John Wiley & Sons, Ltd.

Self-assembled monolayers (SAMs) on single-crystal Si wafers have been used as substrates for the deposition of oxide thin films. The organic surface has been shown to be effective for promoting the growth of films from aqueous solutions at temperatures below 100 °C. In the present study, the formation of a titanium complex in the presence of H2O2 is used to stabilize an otherwise spontaneously precipitating aqueous titanium solution. Uniform titania films have been formed at 80 °C on sulfonated SAMs, whereas hydroxyl and amine functionalities led to inhomogeneous coatings. The films were characterized by a variety of techniques, including ellipsometry, RBS, AFM, SEM, and TEM, to determine the thickness, topography, microstructure, and chemical composition of the films. An electronegativity−pH diagram is used to explain how the composition of the deposition solution is reflected in the final thin film, both for the present films and for titania films reported earlier in the literature. Finally, the curren...

This study treats the preparation of polyborosilazanes which are obtained by hydroboration of oligovinylsilazane [–(H 2 CCH)SiHNH–] n with different amounts of H 3 B . SMe 2 . Pyrolysis of these precursors yields amorphous ceramic materials, which only differ in their relative boron content whereas their Si/C/N ratio is very similar. High temperature thermogravimetric analysis reveals that with increasing boron content the material's thermal degradation is shifted toward higher temperatures. Furthermore, the observed mass loss due to nitrogen evaporation during the material's decomposition is noticeably smaller in boron-rich materials than thermodynamically calculated. X-ray diffraction (XRD) experiments support the presence of crystalline silicon nitride in heat treated samples with a minimum boron content of 5 at.%. The decomposition temperature of this phase strongly depends on the amount of boron and can exceed 2000°C. However, high temperature stable materials are not only characterized by a definite B/N ratio, but also by the ability to develop appropriate microstructures.

A chemical solution deposition method was used to grow thin epitaxial GaN films on C - and R -plane sapphire substrates. The films were grown by spin-coating a gallium carbodiimide based polymeric precursor onto sapphire and pyrolyzing in NH 3 at 900°C. During heat treatment α-GaN formed on the R -plane of the sapphire with the following epitaxial orientation relationship: α-Al 2 O 3 (0 1 1 2)‖α-GaN(1 1 2 0); α-Al 2 O 3 [2 1 1 0]‖α-GaN[1 1 0 0]. A multiple coating process resulted in films fully covering the R -plane substrates. Films deposited on C -plane sapphire were not continuous and single islands were present on the substrate surface. The morphology and microstructure of the films were characterised by SEM, XRD, and conventional and analytical electron microscopy.

The surface of sp2-hybridized boron nitride, namely well-crystallized hexagonal and poorly-crystallized turbostatic boron nitride, after its treatment in a hydrogen plasma was studied with the aid of high-resolution Auger spectroscopy. The surface state of both modifications of boron nitride is found to change due to interaction with excited hydrogen species. This interaction is thought to lead to termination of π (dangling) bonds of sp2-hybridized boron nitride by hydrogen atoms, which results in transformation of the sp2-hybridized state into the sp3-hybridized state on the surface of boron nitride.

Boron carbide nitride can be considered to be a graphite-like ceramic material with a partial substitution of carbon atoms by boron and nitrogen atoms in the hexagonal layers or as a two-dimensional solid solution of hexagonal boron nitride and graphite. These materials exhibit remarkable properties such as high temperature stability, chemical resistivity and semiconducting behavior.

Single-phase cubic boron nitride films of high quality might be of great importance as superhard wear-resistant coatings and semiconductive materials. This paper reviews deposition techniques, precursors, deposition parameters and substrates employed in plasma-assisted CHEMICAL VAPOR DEPOSITION (PACVD) of cubic boron nitride (c-BN) as well as procedures applied for the characterization of c-BN-containing films. Mechanisms of the formation of sp3-hybridized boron nitride during PACVD by use of either high-energy nitrogen and argon ions or hydrogen plasmas are discussed. All experimental results on PACVD of c-BN are thought to fit either “physical” or “chemical” routes for c-BN low-pressure synthesis, which are based on principles of c-BN physical vapor deposition or diamond CVD.

Thin B-C-N and B-N films containing various proportions of cubic boron nitride (c-BN) have been obtained in the present study by plasma assisted chemical vapour deposition (PACVD) as a result of the in-situ decomposition of either dimethylamine borane (CH3)2NHBH3 or borane-ammonia BH3-NH3 in the hydrogen plasma. The structure and composition of the films are strongly affected by the precursor to hydrogen ratio in the gas phase. The films deposited at high values of the hydrogen excess contain c-BN and are free of sp 2 -hybridized boron nitride. The mechanism of depositing sp 3 -hybridized boron nitride is proposed, which includes the selective etching of sp 2 -hybridized BN and the formation of metastable BNHx species in the hydrogen plasma. © 1997 Elsevier Science S.A.

Thin films of the BCN system deposited by use of gas mixtures composed of a boron- and nitrogen-containing organic precursor, argon and hydrogen are investigated with the aid of a radiofrequency PACVD procedure. The structure and composition of these films are found to be strongly affected by the mole ratio between the organoboron precursor and hydrogen. The films obtained at high values of this ratio are amorphous: they become partially crystalline on decreasing this ratio. The deposit obtained at a relatively low value of this ratio is composed of a mixture of cubic boron nitride and boron carbide. Use of a considerable excess of hydrogen in the gas mixture is found to allow poorly crystalline and amorphous phases in the BCN system to be completely removed from the deposit.

The synthesis of BCN nanotubes and boron doped (1 to 5 at.% B) carbon nanotubes is achieved by an electric arc-discharge between an anode made of homogeneous BC 4 N and a cathode made of graphite. The BC 4 N anode is prepared by pyrolysis of polymer precursors. The effect of boron doping is seen to increase the tube lenghts up to 100 μm and to improve graphitization. Boron and nitrogen are enriched at the surfaces of tubes with overall BCN composition. The observed structure of BCN tubes consists of concentric cylinders of BC 2 N and pure carbon.

The thermal properties of polycarbosilanes from the gas phase pyrolysis of SiMe 4 , Me 3 SiCl, Me 2 SiCl 2 and the polymeric (Me 2 SiCH 2 ) n has been investigated. They decompose above 400 °C to form volatile methylsilanes, H 2 , CH 4 , viscous carbosilanes and insoluble glassy products via condensation reactions. The ceramic yield is between 10 and 20 wt.% at about 900 °C and falls to only a few weight per cent when heating is continued to 1000 °C. The gas phase pyrolysis of Me 2 SiH 2 at 650 °C produces plastic, meltable polycarbosilanes (PCS). Tempering the compounds to 900 °C gives a ceramic residue in 85% yield with Si:C:H 1:1.2:0.4. Heating this residue under thermal gravimetry (TG) conditions to 1500 °C (argon atmosphere) results in a further weight loss of 0.7% and formation of β-SiC. Silicon carbide is also formed when the PCS from Me 2 SiH 2 (Si:C:H 1:1.5:2.5) are heated to 1400 °C, with a weight loss of 16.3% under nitrogen and one of 42% in vacuum.

Recent results on the crystallization behaviour of nanosized boron-doped silicon carbonitride ceramics as revealed by structural characterization with various transmission electron microscopy methods are described. Ceramic composites in the quaternary system Si C N B were produced by polymer pyrolysis of doped polysilazanes without the presence of oxide sintering additives. Annealing at elevated temperatures induces the crystallization of the initially amorphous materials, resulting in a microstructure consisting of nanocrystalline Si3N4, SiC and turbostratic BN(C). Attention is focused on the BN(C) interface layers and the lattice structure of the small-scaled crystallites in these nanocrystalline ceramics.

Composite titania/vanadia thin films were prepared on sulfonate-terminated self-assembled monolayers and surface-oxidized silicon substrates by chemical bath deposition. Films consist of homogeneously distributed titania and vanadia nanoparticles. No concentration gradient of these components was observed.

The influence of dopants on the microstructure of quaternary Si-C-N-M-ceramics (M=B, P) is investigated. Monolithic amorphous ceramics are obtained by the polycocondensation of polysilazanes ((RR`SiNH)y) with the appropriate alkyl amide (M(NRR`)x) of boron or phosphorus and subsequent pyrolysis in argon atmosphere at 1000°C. The electron spectroscopic imaging method (ESI) in TEM reveals a homogeneous distribution of the elements Si, C, N and M. Upon annealing in nitrogen atmosphere at temperatures around 1400°C, crystallisation of the appropriate thermodynamically stable phases occurs. Heat treatment at temperatures up to 1800°C results in micro/nano-, nano/nano- or micro/microcrystalline microstructures with design-tailored properties which depend on the element M. Boron as dopant forms turbostratic boron nitride which coats the crystalline phases, inhibits the further crystal growth and thus leads to nanosize composite structure of the ceramics.

An amorphous covalent silicon-, carbon- and nitrogen-containing solid is prepared by the thermolysis of a polyvinylsilazane. Crystallization of the metastable material is induced by subsequent heat treatment at 1600°C. For that purpose, microwave and conventional heating are applied and compared. The resulting materials are investigated by conventional and analytical transmission electron microscopy and X-ray diffraction. In the case of the conventionally heated material, thermal degradation occurs accompanied by a strong reduction of the nitrogen content. In contrast, kinetic stabilization of the Si–C–N solid by microwave heating is observed. Based on thermodynamic considerations, a model for the high-temperature behavior of the material is presented.