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A superior field electron emission (FEE) source made from a hierarchical heterostructure, where two-dimensional hexagonal boron nitride (hBN) nanowalls were coated on one-dimensional diamond nanorods (DNRs), is fabricated using a simple and scalable method. FEE characteristics of hBN-DNR display a low turn-on field of 6.0 V mu m(-1), a high field enhancement factor of 5870 and a high life-time stability of 435 min. Such an enhancement in the FEE properties of hBN-DNR derives from the distinctive material combination, i.e., high aspect ratio of the heterostructure, good electron transport from the DNR to the hBN nanowalls and efficient field emission of electrons from the hBN nanowalls. The prospective application of these heterostructures is further evidenced by enhanced microplasma devices using hBN-DNR as a cathode, in which the threshold voltage was lowered to 350 V, affirming the role of hBN-DNR in the improvement of electron emission. The authors like to thank the financial support of the Research Foundation Flanders (FWO) via Research Projects G.0456.12 and G.0044.13N, the Methusalem "NANO" network. KJ Sankaran, and P Pobedinskas are Postdoctoral Fellows of the Research Foundation-Flanders (FWO).

The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole (TzTz) acceptor units, were selected toward effective device scalability by roll-coating. The influence of the partial exchange (5% or 10%) of the solubilizing 2-hexyldecyloxy by alternative 2-phenylethoxy groups on efficiency and stability was investigated. With an increasing 2-phenylethoxy ratio, a decrease in solar cell efficiency was observed for the BT-based series, whereas the efficiencies for the devices based on the TzTz polymers remained approximately the same. The photochemical degradation rate for PSCs based on the TzTz polymers decreased with an increasing 2-phenylethoxy ratio. Lifetime studies under constant sun irradiance showed a diminishing initial degradation rate for the BT-based devices upon including the alternative side chains, whereas the (more stable) TzTz-based devices degraded at a faster rate from the start of the experiment upon partly exchanging the side chains. No clear trends in the degradation behavior, linked to the copolymer structural changes, could be established at this point, evidencing the complex interplay of events determining PSCs' lifetime. This work has been supported by the Villum Foundation's Young Investigator Program (second round; project: Materials for Energy Production). The work was partly done during an external research stay of Ilona Heckler at Hasselt University in the group of Wouter Maes. The Hasselt University co-authors acknowledge the support by the IAP (Interuniversity Attraction Poles) 7/05 project FS2 (Functional Supramolecular Systems), granted by the Science Policy Office of the Belgian Federal Government (BELSPO), and the Research Foundation-Flanders (Fonds voor Wetenschappelijk Onderzoek-Vlaanderen) (Projects G.0415.14N, G.0B67.15N and M.ERA-NET Project RADESOL).

In this study we demonstrate and explain the direct relationship between precursor chemistry and phase formation of LiMn2O4 powders and thin films from aqueous chemical solution deposition (CSD). The processing conditions applied to transform the precursor into the LiMn2O4 phase are investigated with a focus on the heating atmosphere and temperature. We found that the Mn2+ ions, used as a starting product, already partially oxidize into Mn3+/Mn4+ in the precursor solution. The Mn3+ ions present in the gel or the dried film are extremely sensitive to O-2, leading to fast oxidation towards Mn4+. Here, we suggest that the oxygen, introduced in the precursor solution by the citrate complexing agent, suffices to oxidize the Mn2+ into Mn3+/Mn4+ which is crucial in the formation of phase pure spinet and stoichiometric LiMn2O4. Any additional oxygen, available as O-2 during the final processing, should be avoided as it leads to further oxidation of the remaining Mn3+ into Mn4+ and to the formation of the gamma-Mn2O3 and lambda-MnO2 secondary phases. Based on these insights, the preparation of phase pure, spinet and stoichiometric LiMn2O4 in a N-2 ambient was achieved both in powders and films. Moreover, the study of the precursor chemistry and final annealing leads to the possibility of reducing the final temperature to 450 degrees C, enabling the use of temperature and oxidation sensitive current collectors such as TiN. This inert ambient and low temperature processing of LiMn2O4 provides the opportunity to have large flexibility and compatibility with process conditions for other materials in the thin film battery stack, without undesired oxidations. The authors acknowledge financial support by the IWT Flanders (SBO project SOSLion). Special thanks to K. Elen and B. Ruttens for XRD analysis, Thomas Vranken for TEM, Wouter Marchal for thermal analysis, Christopher De Dobbelaere and Dries De Sloovere for FT-IR and GATR and Elsy Thijssen for ICP-AES.

Ultrathin lanthanide (Nd, Pr, Eu, Sm) oxide films with functional dielectric properties down to 3.3 nm thickness were deposited by aqueous chemical solution deposition (CSD) onto hydrophilic SiO2/Si substrates. Precursor solutions were prepared from the oxides via an intermediate, solid Ln(III)citrate. A film heat treatment scheme was derived from thermogravimetric analysis of the precursor gels, showing complete decomposition by 600 °C. Crystalline phase formation in the films depended on the lanthanide, annealing temperature, and citric acid content in the precursor. Through variation of the precursor concentration and number of deposited layers, thickness series of uniform films were obtained down to ∼3 nm. The film uniformity was demonstrated both by atomic force microscopy and cross-section transmission electron microscopy. The lanthanide oxide films possessed good dielectric properties. It was concluded that aqueous CSD allows deposition of uniform ultrathin films and may be useful for the evaluation of new high-k candidate materials.

The fabrication of narrow Cu trenches using a conformal TEOS backfill approach is shown. Cu trenches with widths down to 30-40nm were achieved. With an adequate Ta-based PVD barrier and Cu seed layer scheme, narrow Cu lines with high yield were obtained. An increase of the electrical resistivity in the narrowest dimensions was observed as a result of the size effect. Electromigration assessment demonstrated that a bilayer TaN/Ta barrier outperforms the monolayer Ta barrier. Electron backscattering diffraction (EBSD) analysis was carried out to determine grain orientation and texture in narrow copper trenches. For the first time, EBSD data reveal that Cu trenches down to 30-40nm wide have mostly a random texture. The narrower the Cu lines get, the weaker the (111) texture with both monolayer and bilayer Ta-based barriers.

The pH-sensitive properties of hydrogen- and oxygen-terminated nanocrystalline diamond (NCD) films have been investigated using a field-effect-based capacitive electrolyte-diamond-insulator-semiconductor (EDIS) structure as transducer. The NCD thin films (100-500 nm) were grown on p-Si-SiO 2 substrates by microwave plasma-enhanced chemical vapour deposition. The electrochemical characterisation of EDIS sensors with NCD films of different thicknesses has been performed in buffer solutions of pH 3 to pH 11 by means of capacitance-voltage and constant-capacitance methods. The developed EDIS sensors with 0-terminated NCD surfaces show an average pH-sensitivity of 38 mV/pH. A slightly smaller pH-sensitivity of 29-36 mV/pH was observed for the EDIS structure with H-terminated NCD surfaces.

This study describes the synthesis of nanocrystalline titania layers on silicon and glass substrates by chemical solution deposition, using a water-based citratoperoxo-Ti(IV) precursor solution. The same aqueous solution–gel precursor is used for deposition of, both, thin dense layers by spin-coating and thicker porous layers by tape-casting. In the latter, the precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore-forming agent. Phase composition, film morphology, and the hydrophilic character of the films are studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS transmission measurements, variable angle spectroscopic ellipsometry (VASE), and by contact angle measurements. The thin 180 nm titania film, deposited from the unmodified precursor solution, shows a density of about 96%. Upon ultraviolet illumination, it acquires a highly hydrophilic surface. One hour of illumination is sufficient to obtain a water contact angle of almost 0°. Furthermore, the hydrophilisation process shows to be reversible. Tape-casting and thermal treatment of the modified precursor solution gives rise to the formation of a 500 nm thick, porous, pure anatase film. The nanocrystalline thick film is composed of 20–40 nm particles, and contains clearly defined pores of 20 nm, homogeneously distributed along the surface.

A new, entirely aqueous method for the deposition of ferroelectric lanthanum substituted bismuth titanate including cosubstitution of Ti4+ with higher valent metal ions (W6+, Mo6+, Nb5+, and V5+) is presented. The strong tendency toward hydrolysis and condensation of highly valent metal ions, causing precipitation of (oxy)hydroxides, was adequately prevented by new synthesis routes for stable, aqueous (mono)metal ion precursor solutions based on citratoperoxo or nitrilotriacetatoperoxo complexes. The (mono)metal ion precursors are optimized for convenient mixing into multimetal ion precursors with the desired composition, which are deposited using spin-coating. The effect of the La3+ content as well as the different cosubstitutions on the films' ferroelectric remanent polarization, crystalline, and microstructural properties was studied. A maximal 2Pr value of 17.2 μC/cm2 was obtained for the Bi3.5La0.5Ti2.97V0.03O12+δ thin film after annealing at a temperature as low as 650 °C. The cosubstituting metal i...

In the present work, crystalline one-dimensional ZnO nanorods were synthesized by a PVP (polyvinylpyrrolidone)-assisted hydrothermal process with zinc acetate as the precursor. The major advantage of this technique is the use of water as the solvent: cheaper and more environmentally friendly than alcohol. The as-synthesized ZnO nanorods have diameters of 50–200 nm and lengths up to 5 μm. X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), Fourier transmission infrared spectroscopy (FTIR) were used to characterize the structural and the chemical features of the ZnO nanorods.

Due to its exceptional properties, semiconducting diamond is expected to be used for electrically active devices which can be operated in harsh environments. Such devices need reliable ohmic contacts that can also stand hostile environments. Titanium nitride (TiN) is a chemically stable material with good electrical conductivity. In this work, TiN contacts on boron-doped diamond have been made and characterised. TiN films were deposited by reactive magnetron sputtering. Boron-doped diamond layers were deposited by plasma enhanced chemical vapour deposition. Optimal deposition conditions have been determined to obtain TiN films with low resistivity (∼100 µΩ · cm), high reflectance in the IR region and low stress. TiN contacts show ohmic behaviour after annealing at 750 °C.

Lanthanum substituted bismuth titanate thin films were deposited using an aqueous chemical solution deposition method. Varying the composition of Bi4−x La x Ti3O12, with x = 0.5, 0.65, 0.75 and 0.85, is shown to have a large influence on the microstructure and properties of the films. Increasing the amount of La3+, x, from 0.5 to 0.85 led to a decrease of the remanent polarization (P r) from 6.2 to eventually 0 μC/cm2. This decrease of P r is explained by means of X-ray diffraction (XRD) study, which shows that there is an increased preference for c-axis orientation upon increasing the La3+ concentration. Furthermore, a strong decrease of the grain size upon increasing x is observed in a scanning electron microscopic (SEM) study. The concurrent increase of domain pinning on the grain boundaries is a second effect which may be responsible for the deterioration of the ferroelectric property at larger x.

State-of-the-art organic bulk heterojunction (BH) solar cells, also called excitonic solar cells, are based on intimate mixtures of donor and acceptor organic materials of which the nanoscale morphology strongly influences both the photovoltaic performances and the stability of the device. In particular, the form and the size of the three-dimensional (3D) interpenetrating network of donor/acceptor material is shown to be crucial for the electrical transport properties and the resulting photovoltaic properties. Powerful high-resolution characterisation tools to locally map the morphology of these material systems are Scanning and Transmission Electron Microscopy (SEM/TEM), Atomic Force Microscopy (AFM) and Nuclear Magnetic Resonance (NMR). Yet, to correlate morphology with local electrical properties, significant progress has been made by the recent introduction of advanced Scanning Probe Microscopy (SPM) methods based on electrostatic force microscopy (EFM) and conductive atomic force microscopy (C-AFM). EFM related methods measure the electrostatic interaction between the probe and the surface of the organic thin films, hence to derive the variations in the sample surface potential. C-AFM based methods perform two-dimensional (2D) current mapping of sample conductivity and local spectroscopy to analyse transversal charge transport mechanisms in the blends. In case the space charge limiting current (SCLC) regime is dominating the charge transport mechanisms, carrier mobility can also be determined. Finally, the sensitivity of C-AFM to photovoltaic properties is reported. In this paper a review dealing with the different SPM methods currently used and the respective achievements performed on organic blends for BH solar cells is proposed. Copyright © 2007 John Wiley & Sons, Ltd.

In this work, thick nanocrystalline mesoporous titania layers are synthesized via chemical solution deposition using a water based citratoperoxo-Ti(IV)-precursor solution. The aqueous citratoperoxo-Ti(IV)-precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore forming agent. Layers are tape casted onto ITO-coated glass substrates and are thermally processed. The influence of process parameters like Ti(IV)-concentration, blade thickness, crystallization temperature and time on the film's phase composition, morphology and thickness are investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), variable angle spectroscopic ellipsometry (VASE), atomic force microscopy (AFM) and profilometry. It is shown that the Ti(IV)-concentration and heat treatment influence the size and shape of the grains of which the films are composed, the film morphology (porosity, surface roughness) and the layer thickness, but no influence on the phase formation is observed. In all cases phase pure anatase layers are obtained.

In this work, a porous nanocrystalline anatase TiO 2 layer is prepared by tape casting a viscous dispersion of nanoparticles. Phase pure anatase titanium dioxide nanoparticles with a particle size of 10–20 nm are prepared by a very simple low temperature (100 °C) hydrothermal synthesis route in a pressure vessel, using only water as the medium and Ti(IV)-isopropoxide as starting material without additives. The size, shape and phase composition of the particles are studied by means of X-ray diffraction and transmission electron microscopy. A dispersion of the as-prepared nanoparticles with a narrow particle size distribution, confirmed by photon correlation spectroscopy, is prepared. After increasing the viscosity of this dispersion by addition of hydroxypropyl cellulose, anatase titanium dioxide layers are tape cast on a transparent conducting metal oxide substrate. Pores are induced by burning out the organic additive at 450 °C. The morphology and the final phase composition of the deposited TiO 2 layers are examined by X-ray diffraction and scanning electron microscopy.

Amylase and lysozyme are components of the salivary pellicle, exposing considerable enzymatic activity in the immobilized state. The purpose of the present study was to elucidate the influence of different solid substrata on the amount and distribution of amylase and lysozyme exposed on the surface of the salivary pellicle formed in situ. Slabs of titanium, feldspar ceramic, and bovine enamel were fixed on the buccal sites of individual splints worn by three subjects for 3 or 30 min, respectively, to allow pellicle formation. Subsequently, slabs were removed from the splints and rinsed with running water. Detection of amylase and lysozyme was performed by FEI-SEM after gold-immunolabeling of the enzymes. Both enzymes were found to be distributed randomly at the pellicle surface. Irrespective of formation time and substratum, significantly more labeled lysozyme molecules (5.23 ± 4.5 μm−2) were detected compared with amylase (3.4 ± 2.9 μm−2). Neither the substratum nor the pellicle formation time had significant impact on the amount of the respective enzyme that could be detected. This study for the first time provides evidence, that amylase and lysozyme are exposed at the surface of the salivary pellicle formed in situ on titanium and ceramics. Both enzymes are distributed randomly on the surface of the pellicle, irrespective of the underlying substratum. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2007

Functional nanocarriers were synthesized using an in situ inverse miniemulsion polymerization employing thiol–isocyanate reactions at the droplet interface to encapsulate hydrophilic payloads. The morphology of the nanocarriers is conveniently tunable by varying the reaction conditions and the dispersions are easily transferable to the aqueous phase.

© 2015, Springer Science+Business Media New York. This paper reports a thorough microstructural investigation of bismuth ferrite (BFO) thin films subjected to various processing conditions and discusses their influence on the stability of the BiFeO3 perovskite phase. The formation of secondary phases in BFO thin films is studied as a function of annealing temperature and time, film thickness, Bi excess, and Ti substitution. While films annealed at 600 °C consist of the desired BiFeO3 phase, higher temperatures induce the decomposition leading to a significant amount of secondary phases, particularly the iron-rich Bi2Fe4O9 phase. A longer annealing time at 700 °C further enhances the decomposition of BiFeO3. Qualitative microstructural analysis of the films is performed by electron backscattered diffraction which provides phase analysis of individual grains. The morphology of the single-crystalline Bi2Fe4O9 grains that are embedded in the BiFeO3 matrix drastically changes as a function of the film thickness. Nucleation of these Bi2Fe4O9 grains probably occurs at the film/substrate interface, after which grain growth continues toward the surface of the film through the depletion of the BFO phase. Addition of Bi excess or the substitution of Fe with Ti in the precursor solutions significantly reduces the formation of an iron-rich secondary phase. Influence of the secondary phases as well as Ti substitution on magnetic properties of BFO films was investigated. ispartof: Journal of Materials Science vol:50 issue:13 pages:4463-4476 status: published

The nanoscale morphology of the active layer in bulk-heterojunction solar cells consisting of regioregular poly(3-hexylthiophene-2, 5-diyl) (P3HT) and methanofullerene([6-6]-phenyl C 61 butyric acid methyl ester) (PCBM) was extensively studied using Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and optical microscopy. Different weight ratios of P3HT:PCBM were investigated as a function of annealing temperature and time revealing the occurrence of crystallization of both components. Firstly, the as-prepared films can be described as a semi-crystalline blend. Secondly, it has been demonstrated that for a short annealing time (5 min) at lower annealing temperatures (75–115 °C) an increased crystallization of P3HT occurs. Thirdly, it has been observed that a prolonged annealing at the given temperature range or a short annealing at higher temperatures ( ≥ 120 °C) leads to the formation of a new ordered crystalline structure of PCBM. These new ordered structures, a few μ m up to 100 μ m in length, form a network of needle-like and even fan-shaped crystals. Key-parameters to “tune” this new ordered structure of PCBM are blend ratio and annealing conditions. The growth mechanism of these new PCBM-structures is described by means of diffusion.

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti4+ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15–20 nm grains. At higher crystallization temperatures (600, 650°C) also larger particles (40–70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450°C. Crystallization temperatures equal to or higher than 600 °C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness (≤1.1 nm) measured by AFM.

The performance of organic solar cells based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) is strongly influenced by blend composition and thermal annealing conditions. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) diffraction measurements show that in the considered blends, ordering of P3HT plays a key role in understanding the PV-performance. It is demonstrated that the natural tendency of regioregular P3HT to crystallize is disturbed by the addition of PCBM. Annealing however improves the crystallinity, explaining the observed spectral broadening and is also resulting in a higher mobility of the holes in P3HT.

The performance of poly(1-trimethylsilyl-1-propyne) (PTMSP)/silica nanocomposites was studied for membranes with a filler content between 0 and 50 wt%. An increase in permeability and a decrease in vapor selectivity was measured with increasing filler content. The free volume sizes and interstitial mesopore sizes of the composites were determined by use of positron annihilation lifetime spectroscopy (PALS). In addition to an increase in large free volume size with increasing filler content, interstitial mesopores were observed in all PTMSP/silica nanocomposites. The size of these interstitial cavities, located between the particles of a silica agglomerate, was increasing with increasing filler concentration. The presence of these agglomerates was visualized by TEM. The existence of the cavities was confirmed by nitrogen adsorption measurements. The hydrogen, nitrogen and propane permeability was clearly correlated with the size of the interstitial mesopores. (c) 2005 Elsevier B.V. All rights reserved. (Less)

We have synthesized a poly( p -phenylene vinylene) (PPV) derivative bearing nonyloxy side groups via two different precursor routes: “the sulphinyl precursor route” and “the dithiocarbamate route”, both developed within our research group. The conversion process, in which the soluble precursor is transformed into the insoluble conjugated polymer, is examined by means of several spectroscopic techniques like in situ UV–VIS, in situ FTIR, TGA and DIP-MS. By post-heat treatment, the conjugated polymer shows additional structural ordering. This specificity was studied by X-ray Diffraction Spectroscopy (XRD).

Thin-film silicon solar cells on low-cost foreign substrates could lead to a large cost reduction of photovoltaic electricity if sufficiently high efficiencies could be obtained. A possible approach is to make polycrystalline-silicon solar cells by epitaxial thickening of large-grained thin seed layers made by aluminium-induced crystallization (AIC) of silicon. Until now however, obtained efficiencies are too low to lead to the desired cost reduction. We report on the influence of the AIC seed layer morphology (grain size and presence/absence of secondary crystallites on top of the surface) on the epitaxial growth of absorber layers and on the resulting cell parameters. To increase the grain size of the seed layers, we investigated the use of a nitric acid treatment to oxidize the Al layers prior to the amorphous silicon deposition. We compared seed layers oxidized by nitric acid treatment to seed layers oxidized by a short exposure to the ambient air. The nitric acid treatment led to a larger grain size and strongly affected the structure of the secondary crystallites on most investigated samples. Removing these crystallites before epitaxial growth clearly led to larger grains and increased the open-circuit voltages (Voc) of our solar cells. Using the nitric acid treatment, absorber layers with grain diameters up to 50 μm were made, that reached efficiencies of 4.9%, with Voc values around 500 mV. However, seed layers that were made through oxidation by air exposure and had grain diameters below 12 μm led to similar Voc values and even higher efficiencies (5.3%). We believe that regions with very small grain size on the large-grained samples are responsible for the relative poor behaviour of the large-grained solar cells. Our results show that increasing the average grain size of AIC seed layers does not automatically lead to better solar cells.

A new ordered structure of the C 60 derivative PCBM ([6-6]-phenyl C 61 -butyric acid methyl ester) is obtained in thin films based on the blend PCRM:regioregular P3HT (poly(3-hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans, Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as-obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and conlbcal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in tennis of diffusion of PCBM towards the PCBM crystals. leaving highly crystalline P3HT behind in the surrounding matrix.

The interest in freestanding, low defect density, single crystalline CVD diamond films for electronic applications led to several studies of homoepitaxial CVD diamond growth. The aim of our work is to obtain nearly atomically flat surfaces even for several hundred microns thick CDV diamond films by controlling the growth mechanism on (100) surfaces. The effect of pre-growth etching of the substrate with a O2/H2 plasma and the influence of a high methane concentration on the growth on type Ib (100) HPHT synthetic diamonds were investigated. Using a MW PE CVD ASTeX PDS17-5 kW reactor at a pressure of about 180 Torr and temperatures typically around 700 °C, CVD diamond films were grown. A precise control of the growth mechanism led to the preparation of optical quality freestanding monocrystalline CVD diamond films of 600 μm thickness, practically free of hillocks and unepitaxial crystallites, with a relatively high growth rate of 4 to 5 μm/h. These films were characterized by optical microscopy, AFM, SEM and Raman spectroscopy. It is shown that even the thickest films have a mean roughness (Rms) remaining as low as 1 nm for a scanning area of 5 × 5 μm2.

In this paper we compare and contrast the growth and properties of ultrananocrystalline (UNCD) and nanocrystalline (NCD) diamond. These two structures, grown from hydrogen poor and hydrogen rich plasmas, respectively, have markedly different structural properties. We characterise the plasmas used for growth with in situ optical emission spectroscopy and dual wavelength pyrometry. The films are characterised with scanning electron microscopy in both plan view and cross section. Raman spectroscopy was used to investigate bonding. Finally we make a clear definition of these two different microstructures.

This study describes the synthesis of core–shell particles, consisting of a ZrO 2 or Al 2 O 3 submicron nucleus coated by a nanolayer of Al 2 O 3 or ZrO 2 , respectively. The oxide layers around the cores are deposited via a heterocoagulation route, based on the attraction of oppositely charged core and shell particles. TEM micrographs clearly show a homogeneous Al 2 O 3 shell (originating from boehmite or γ-Al 2 O 3 particles) around the ZrO 2 cores and in the other case, a ZrO 2 layer (originating from hydrothermally prepared ZrO 2 ) around the submicron Al 2 O 3 cores. From PCS measurements, it can also be deduced that the cores are enwrapped by a shell and it is calculated that the thickness of the Al 2 O 3 shell is about 30–35 nm and the ZrO 2 layer is approximately 80 nm. The coated powders are additionally characterized by XRD.

Several crystallization parameters were studied during the fabrication of Bi3.5La0.5Ti3O12 thin films by means of a new aqueous chemical solution deposition method. Their effect on the microstructure, orientation, crystal structure and ferroelectric properties of the thin films was examined using scanning electron microscopy, X-ray and electron back-scattering diffraction and ferroelectric hysteresis loop measurements. The thermal treatment was optimized by applying an intermediate crystallization step for each layer, which led to the formation of dense films with ferroelectric properties. Without this intermediate crystallization, the films were shortcircuited due to the high porosity. Subsequently, the effect of the crystallization temperature on Bi3.5La0.5Ti3O12 thin films prepared from precursors containing 10 mol% Bi3+ excess, was looked into. The Pr increased linearly with the crystallization temperature between 600 and 700 °C. Finally, the concentration of O2 in the ambient during the crystallization was varied. Hillocking occurred below 10% O2 due to a reaction of the substrate. The ferroelectric properties also deteriorated when crystallization was carried out below a critical O2 partial pressure.

Nickel monosilicide (NiSi) is a key material in microelectronics and its thermomechanical properties play an important role in determining the stress/strain field generated in a transistor structure. The Coefficient of Thermal Expansion (CTE) is of particular importance in the determination of such a field. As NiSi is used in microelectronics in its polycrystalline form, it becomes of particular interest to study the thermomechanical behaviour of the NiSi aggregate, considered as a unique macroscopic body. The grain orientation of a 120 nm polycrystalline NiSi film grown on single crystal silicon has been studied by means of electron diffraction, and the evaluation of the CTE tensor of the film in the wafer reference frame has been performed by weighted averaging the single grain contributions. The results clearly show the importance of orientation distribution in determining the value of the equivalent coefficient of thermal expansion of the aggregate.

Diamond films were grown in an ASTeX MW PE CVD reactor. The effect of pre-growth etching with a O2/H2 plasma and the influence of the methane concentration on growth on type Ib (100) HPHT synthetic diamonds were investigated. By controlling step flow growth we were able to prepare optical quality thick diamond films, free of hillocks and unepitaxial crystallites, with a relatively high growth rate of 4 to 5 µm/h using higher pressures and methane concentrations than standard growth conditions in combination with a modified substrate holder. All diamond films were characterized by optical microscopy, SEM, AFM and Raman spectroscopy. The mean roughness (Rms) of the films grown with a thickness of 120 µm was approximately 0.5 to 0.8 nm for scanning regions of 5 × 5 µm2. For the first time nearatomically flat films thicker than 200 µm could be prepared. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A homogeneous distribution of luminescent lanthanide(III) 2-thenoyltrifluoroacetonate complexes (Ln = Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) in an organic−inorganic hybrid material was obtained by grafting the complexes to the solid matrix via 2-substituted imidazo[4,5-f]-1,10-phenanthroline moieties. Thin films of the silica hybrid material were prepared by the sol−gel method and by spin-coating of the gelating solution on glass slides or on oxidized silicon wafers. The thickness of the thin films was determined by scanning electron microscopy (SEM). High-resolution luminescence spectra of the lanthanide complexes were recorded, and the luminescence decay times were measured. The luminescence quantum yields of europium(III)-doped thin films exposed to different drying conditions were determined by using an integrating sphere.

Bi 3.5 La 0.5 Ti 3 O 12 thin films for ferroelectric random access memory application were fabricated by the aqueous chemical solution deposition method. The precursor films were deposited by spin coating and subsequently transformed into the oxide by thermal treatment on three hot plates and crystallizing in a rapid thermal processing furnace at a temperature as low as 650 °C. The temperature of the third hot plate step was varied, which affected the ferroelectric properties of the prepared films. The ferroelectric properties of the crystallized films as well as their crystallographic structure, texture and microstructure were characterized using various experimental techniques. The evolution of the precursor chemical structure of the thin films, containing organic compounds, was studied at different temperatures during the thermal treatment. In order to maximize the remanent polarization of the crystalline Bi 3.5 La 0.5 Ti 3 O 12 thin films to approximately 6 μC cm −2 it is preferable to remove all the organic components of the thin-film precursor prior to the intermediate crystallization step in the rapid thermal processing furnace. A temperature of 370 °C has been shown to be the minimal temperature for achieving the complete decomposition of the organic constituents of the precursor thin film.

This paper reports on the spin deposition of LSCO thin films on a SiO 2 /Si substrate by a new aqueous solution–gel route. Stable and monometallic precursor solutions are prepared from common and inexpensive oxides or hydroxides. The aqueous La 3+ precursor is synthesized by reaction of La 2 O 3 with citric acid. In order to prepare an aqueous Sr 2+ precursor Sr(OH) 2 is complexed by EDTA. The new peroxo citrato Co 2+ precursor is synthesized by reaction of Co(OH) 2 with hydrogen peroxide in an aqueous solution of citric acid. Mixing the individual precursors in stoichiometric quantities results in a clear and stable aqueous LSCO precursor solution. Evaporation of water transforms this solution in an amorphous gel that is homogeneous down to nanometer scale. In situ high temperature X-ray diffraction analysis of the gel reveals that phase pure LSCO powder is formed at 550 °C without detection of any intermediate crystalline phase. Spin deposition and crystallization at 625 °C in pure O 2 of this aqueous precursor solution resulted in a phase pure conductive LSCO thin film. The sheet resistance of this thin film amounted to 235 Ω/sq. Since the thickness of the film is 120 nm, the specific resistivity was calculated to be 2.8 mΩ cm at room temperature.

Tissue and cellular compartmentation of Cd in roots and leaves of the hyperaccumulator Thlaspi caerulescens was investigated, using energy-dispersive X-ray microanalysis. In roots, Cd was determined in cortex parenchyma cells, endodermis, parenchyma cells of the central cylinder and xylem vessels. In leaves, it was found in cells lying on the way of water migration from the vascular cylinder to epidermal cells, which is in line with passive Cd transport by the transpiration stream. The mechanisms of Cd-detoxification in roots seem to be localized both in apoplast (e.g. binding to cell wall compounds) and inside cells since Cd was accumulated in these two compartments. On the other hand, in leaves Cd was found only in electron-dense deposits inside vacuoles, which suggests that vacuoles are the main compartment of its storage and detoxification in these organs.

We have grown a variety of thin nanocrystalline diamond thin layers on silicon substrates with thicknesses ranging from 100 to 2000 nm. Using a bias enhanced nucleation for nucleation density over 10 10 cm −2 and changing the deposition conditions and/or using argon dilution we have obtained nanodiamond layers of different structural properties. The nucleation process and growth was monitored with Scanning Electron Microscopy (SEM); cross-section SEM and micro-Raman measurements were used to access the nanodiamond microstructure. Surface topography was followed by SEM and Atomic Force Microscopy. Windows were opened in the silicon substrate to get self-supporting diamond membrane. Diamond membranes are very smooth, homogeneous and transparent from UV to IR. Fourier Transform Photocurrent Spectroscopy has been used to access main electronic defects in the gap of this material. New defects were observed with a peak photoionization energy of 0.37 and 0.40 eV.

Phase pure lanthanum substituted bismuth titanate was prepared by an aqueous solution-gel route. In this route aqueous precursors are synthesized by stabilization of the metal ion in the aqueous medium through complexation with strong electron donor ligands. The chemical structure of metal-less, monometal ion as well as multimetal ion precursorgels was studied by means of FTIR and FT-Raman spectrometry. The precursors were transformed to phase pure oxides by heat treatment in an appropriate dynamic atmosphere. The decomposition reactions of the gels were studied by means of several hyphenated thermal analysis techniques (thermogravimetry coupled on-line to FTIR or MS (TGA-MS, TGA-FTIR) and high temperature—diffuse reflectance infrared spectrometry by fourier transform (HT-DRIFT)) and reactions are proposed. The phase formation was studied by means of X-ray diffraction. Phase segregation during gel calcination was correlated to the oxygen partial pressure. An explanation for this phenomenon was suggested based on thermal analysis and on SEM and TEM studies.

A high sensitive approach is presented to detect in particular the low level absorption features in pure and blended organic semiconductor films, revealing a.o. defect induced sub gap absorption and new interactions between the materials. Because sub bandgap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements. Therefore the very sensitive and ground state spectroscopic technique of Photothermal Deflection Spectroscopy (PDS) has been developed, and introduced to characterize thin films of MDMO-PPV and PCBM, as well as films of MDMO-PPV containing an increasing amount of PCBM ranging from 5 to 90% weight fraction. The measured spectra of MDMO-PPV are interpreted in terms of defect induced absorption phenomena. The spectral position of the observed transitions in PCBM have been determined and verified. The PDS-study on MDMO-PPV/PCBM blended films revealed for the first time interaction between the two materials in the ground state. To get more insight in the interaction mechanism between the constituting materials a systematic Transmission Electron Microscopy (TEM) study has been carried out to reveal the morphology of the films. The obtained TEM-results on nanomorphology of the blended films show clear correlations with the PDS-results.

[La(C6H5O7)(H2O)2]·H2O was synthesized as precursor material for an aqueous solution–gel route to La-containing multimetal oxides. The compound was characterized by means of FTIR, TGA and pycnometry. The crystallographic structure was solved from powder diffraction data. The symmetry is monoclinic [a=17.097(3) A, b=9.765(2) A, c=6.3166(8) A and β=90.42(1)°, Zexp=3.96] with space group P 2 1 / n (14). Direct methods were applied and the model was subsequently least-squares refined (RB=5.1% and RwP=12.0%). La3+ is nine-fold coordinated, the LaO9 forming a mono-capped square antiprism. The basic unit is a binuclear entity of two LaO9 polyhedra having one edge in common. These units are connected along the c-axis through citrate molecules. The carboxylate groups of the citrate are coordinated to La3+ in monodentate, bidentate and bridging way. Also the alkoxide group, which carries the proton, is coordinated to La3+. Two water molecules complete the coordination sphere, while the third one can be found inbetween the La3+-citrate network.

We report on the microstructural analyses, by means of X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive X-ray analysis (SEM-EDX) and cross-section transmission electron microscopy (X-TEM), of chemically prepared Pb(Zr 0.3 Ti 0.7 )O 3 thin films deposited on IrO 2 substrates. The purpose of this study is to detail temperature and time dependence of the lead zirconate titanate (PZT) film microstructure on this type of conductive oxide substrate, partly through a comparison with identically processed PZT films deposited on Pt substrates. It was observed that PZT 30/70 films on IrO 2 bottom electrodes, fired at temperatures up to 620 °C, are not single phase, due to extensive lead losses during the processing. The IrO 2 substrate was found to be indirectly responsible for these losses. Nevertheless, good ferroelectric properties were measured ( P r was 50 μC/cm 2 for the 620 °C film). Based on the observed morphology and texture with increasing annealing time, a mechanism for phase evolution in sol–gel-derived PZT 30/70 films on IrO 2 substrates is proposed.

Limburgs Univ Ctr, IMO, Lab Inorgan & Phys Chem, B-3590 Diepenbeek, Belgium. IMOMEC, B-3590 Diepenbeek, Belgium.Geuzens, E, Limburgs Univ Ctr, IMO, Lab Inorgan & Phys Chem, Univ Campus, B-3590 Diepenbeek, Belgium.

Phase pure RUO 2 and SrRuO 3 powders were obtained by a water-based solution-gel route. By reacting ruthenium(III)acetylacetonate with H 2 O 2 in a citric acid solution, a stable aqueous Ru-precursor solution could be prepared. An aqueous Sr-precursor is synthesized by dissolving Sr acetate in a citric acid solution. After mixing the Ru-precursor with the Sr-precursor solution in stoichiometric quantities, a clear aqueous solution for the preparation of SrRuO 3 could be obtained. Gelation resulted in amorphous precursors that were homogeneous down to nanoscale as was confirmed by means of transmission electron microscopy. With the appropriate thermal treatment phase pure RUO 2 and SrRuO 3 powders were synthesised as verified by X-ray diffraction.

A new aqueous solution-gel route for the synthesis of ferroelectric lanthanum substituted bismuth titanate was developed, based on aqueous Bi 3+ - and La 3+ -citrate solutions and an aqueous peroxocitrato-Ti(IV) solution. A homogeneous, amorphous precursor gel was prepared by evaporation of the BLT precursor solution. The homogeneity was maintained throughout the entire thermo-oxidative decomposition of the gel, as shown by TEM measurements on freestanding thin films. This molecular scale mixing and high degree of homogeneity led to the direct crystallization of the Aurivillius phase from the amorphous phase. As a consequence the crystallization temperature was as low as 525 °C, which was shown by a high temperature X-ray diffraction study of the stoichiometric precursor. The addition of an excess of Bi 3+ decreased the crystallization temperature, but also introduced a Bi 2 O 3 secondary phase.

A new, environmentally friendly, aqueous chemical solution deposition (CSD) route for the fabrication of BLT thin films is presented. Well crystallized, preferentially c-axis oriented films were obtained at 650°C. The grain size and remanent polarization were increased by the addition of an excess of Bi3 + to the precursor solution. At 10% Bi excess a Pr of 6.2 μ C/cm2 and Ec of 105 kV/cm were obtained.

Sr0.9Bi2.2Ta2O9 thin films were prepared on a Pt-substrate by aqueous chemical solution deposition. The applied heat treatment seems to have a significant influence on the ferroelectric response, crystallinity and surface morphology. For two-layer thin films annealed at 700°C in oxygen, the Pr-value increased from 3.6 until 5.5 μ C/cm2, c-axis preferred orientation was considerably lowered and rod-like instead of spherical grains were grown when the second pyrolysis step at 520°C was omitted.

Here we present first data on P-doped polycrystalline diamond prepared by in-situ doping with phosphine. By optimisation of the growth conditions and use of polished polycrystalline CVD diamond plates we were able to incorporate P actively in the grains of polycrystalline films and to prepare n-type diamond, as confirmed by Hall measurements. We studied the P-incorporation in variously oriented grains by cathodoluminescence.

IMOMEC, IMEC Div, B-3590 Diepenbeek, Belgium. IMEC, B-3001 Heverlee, Belgium. Limburgs Univ Ctr, Inst Mat Res, B-3590 Diepenbeek, Belgium.Aresu, S, IMOMEC, IMEC Div, Wetenschapspk 1, B-3590 Diepenbeek, Belgium.

Diamond based surface acoustic wave (SAW) devices are extremely versatile devices that are just beginning to realize their commercial potential for use from sensors till high frequency (HF) filters for wireless telecommunications. One of the most promising piezoelectric materials for diamond based HF-SAW devices is aluminium nitride (AlN) thin film. The ability of AlN and diamond to be used for SAW applications depends both on the piezoelectric AlN layer properties and the diamond substrate properties. In this work, optimised piezoelectric (002) oriented AlN layers have been deposited on polycrystalline diamond substrates aiming at HF-SAW filter applications. Polycrystalline diamond layers were deposited on silicon substrates by microwave plasma enhanced chemical vapour deposition (MW-PECVD). SAW filters with unique characteristics have been obtained due to exceptional diamond's mechanical properties [1,2]. One of the important characteristics of CVD diamond substrate concerns its surface roughness. Smooth diamond surfaces were obtained without polishing by a wet chemical etching of the silicon substrate at the diamond layer nucleation side. Very low surface roughness (R MS ≤1 nm) can be achieved by this technique for bias enhanced nucleated (BEN) samples. In this paper, we report the structural characterization of the AlN films and diamond substrates by X-ray diffraction, atomic force microscopy, and transmission electron microscopy methods.

IMEC, B-3001 Heverlee, Belgium. IMOMEC, B-3590 Diepenbeek, Belgium. Katholieke Univ Leuven, EE Dept, Louvain, Belgium.Brongersma, SH, IMEC, Kapeldreef 75, B-3001 Heverlee, Belgium.

The microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells is studied by atomic force microscopy (AFM) to image the surface morphology and by means of transmission electron microscopy (TEM) to disclose the bulk nanostructure of the film. Typical thin films, as used for state-of-the-art organic bulk hetero-junction solar cells consist of a 1:4 ratio by weight of MDMO-PPV as electron donating polymer and PCBM, a soluble electron accepting C 60 derivative. For these films it is found, using both TEM an AFM, that phase separation occurs. A two-phase system is observed that consists of PCBM-rich domains that are embedded in a matrix consisting of a mixture of MDMO-PPV and PCBM. By combining planar and cross-sectional views, three-dimensional information is obtained on the phase separated PCBM-rich regions, formed during spincoating. Changing the solvent is found to influence the size of the phase separated PCBM-rich domains. But not only the dimensions of the phase separated regions are affected by changing the solvent. Also the composition of the matrix is found to be determined by the choice of solvent. This was studied by changing the ratio of PCBM compared to MDMO-PPV. Since it is commonly believed that the morphology of the active layer influences electrical properties and photovoltaic performance, the nanostructural information obtained with the presented analytical techniques will attribute to a better understanding and improvement of present organic photovoltaic devices.

Highly oriented aluminium nitride (AlN) has been successfully deposited on silicon substrates and on the back side of unpolished, thick, freestanding, polycrystalline diamond films. Structural and electrical properties of the (0 0 2) oriented AlN films have been investigated. Using optimised AlN and chemical vapour deposited diamond films, high quality surface acoustic wave (SAW) filters were constructed by deposition of aluminium inter-digital transducers. The effects of the AlN thickness on the diamond-based SAW filter properties and the SAW propagation were investigated. A phase velocity of 17.1 km/s was observed, which is, to the best of our knowledge, the highest reported value for diamond. The dependence of the phase velocity (v) on the AlN thickness was compared to theoretical predictions. SAW filters with rather low insertion loss, high suppression and high electromechanical coefficient could be obtained. We also report on piezoelectric d33 measurements of AlN films by atomic force microscopy.