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Flexible pressure sensors present enormous potential for applications in health monitoring, human-machine interfacing, and electronic skins (e-skin). However, at the cost of flexibility, the design of flexible pressure sensors has been facing the trade off between high sensitivity and wide sensing range. Herein, we propose a sandwiched structure composed of monolayer films of calcium niobate nanosheets to endow the device with both ultrahigh sensitivity and a wide sensing range. Tunable contact between the two electrodes of the pressure sensor through the gaps in the insulative monolayer film and precise thickness modulation of the monolayer films at the nanoscale result in an ultrahigh sensitivity and wide sensing range of the sensors. By virtue of these two traits, the pressure sensor distinguishes itself with unprecedented performances of ultrahigh sensitivity (6.43 × 10 4 kPa -1 ), a wide sensing range (1.94-60.00 kPa), a fast response time (<165 ms), and reliable repeatability. In addition, the sensor has a sensing mechanism transition from capacitive mode to piezoresistive mode from low pressure to high pressure. The sensors demonstrates the ability for motion detection of the human body. This work sheds light on the development of highly sensitive flexible pressure sensors.

Quasi-2D perovskites have attracted attention as potential solar energy absorber materials due to their balanced efficiency and stability and their unique quantum-well structures. In order to facilitate directional excitons and charge carrier transport and preferential energy transfer landscape in photovoltaic thin films, the phase distribution formed by different types of microstructural domains should be regulated. In this work, the Dion-Jacobson-type spacer 1,4-phenylenedimethanammonium (PDMA) was used, and different strategies were pursued to control the phase distribution in formamidinium-based (FA) quasi-2D perovskites based on the composition of (PDMA)FA 4 Pb 5 I 16 . In general, doping with FACl modulated the crystallization kinetics, forming 2D low- n crystals on the top surface or a reversed-gradient phase distribution, depending on whether excess or substitutional doping was employed. Alternatively, mixing with a Ruddlesden-Popper spacer helped bridging to adjacent octahedra in pure PDMA-based perovskites and improved crystallization, while regulating the quantum-well structures to give a normal-gradient phase distribution, where 2D domains resided on the bottom side. By combining FACl doping and spacer mixing, the film showed both a reversed-gradient phase distribution and larger vertically aligned grains. This work contributes to the knowledge of how to manipulate and regulate the phase distribution in FA-based quasi-2D perovskites and further paves the way for fabricating corresponding devices with high efficiency and stability., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

The diammonium precursor 1,4-phenylenedimethanammonium (PDMA) was used as a large organic spacer for the preparation of Dion-Jacobson-type quasi-2D perovskites (PDMA)(MA) n -1 Pb n I 3 n +1 (MA = methylammonium). Films with composition ⟨ n ⟩ = 5 comprised randomly orientated grains and multiple microstructural domains with locally differing n values. However, by mixing the Dion-Jacobson-type spacer PDMA and the Ruddlesden-Popper-type spacer propylammonium (PA), the crystal orientation in both the vertical and the horizonal directions became regulated. High crystallinity owing to well-matched interlayer distances was observed. Combining this spacer-engineering approach with the addition of methylammonium chloride (MACl) led to full vertical alignment of the crystal orientation. Moreover, the microstructural domains at the substrate interface changed from low- n ( n = 1, 2, 3) to high- n ( n = 4, 5), which may be beneficial for hole extraction at the interface between perovskite and hole transport layer due to a more finely tuned band alignment. Our work sheds light on manipulating the crystallization behavior of quasi-2D perovskite and further paves the way for highly stable and efficient perovskite devices.

Dual-phase TiO 2 consisting of bronze and anatase phases is an attractive electrode material for fast-charging lithium-ion batteries due to the unique phase boundaries present. However, further enhancement of its lithium storage performance has been hindered by limited knowledge on the impact of cation doping as an efficient modification strategy. Here, the effects of Ru 4+ doping on the dual-phase structure and the related lithium storage performance are demonstrated for the first time. Structural analysis reveals that an optimized doping ratio of Ru:Ti = 0.01:0.99 (1-RTO) is vital to maintain the dual-phase configuration because the further increment of Ru 4+ fraction would compromise the crystallinity of the bronze phase. Various electrochemical tests and density functional theory calculations indicate that Ru 4+ doping in 1-RTO enables more favorable lithium diffusion in the bulk for the bronze phase as compared to the undoped TiO 2 (TO) counterpart, while lithium kinetics in the anatase phase are found to remain similar. Furthermore, Ru 4+ doping leads to a better cycling stability for 1-RTO-based electrodes with a capacity retention of 82.1% after 1200 cycles at 8 C as compared to only 56.1% for TO-based electrodes. In situ X-ray diffraction reveals a reduced phase separation in the lithiated anatase phase, which is thought to stabilize the dual-phase architecture during extended cycling. The simultaneous enhancement of rate ability and cycling stability of dual-phase TiO 2 enabled by Ru 4+ doping provides a new strategy toward fast-charging lithium-ion batteries.

To meet the increasing demands of high-energy and high-power-density lithium-ion microbatteries, overlithiated Li 1+ x Mn 2 O 4 (0 ≤ x ≤ 1) is an attractive cathode candidate due to the high theoretical capacity of 296 mAh g -1 and the interconnected lithium-ion diffusion pathways. However, overlithiation triggers the irreversible cubic-tetragonal phase transition due to Jahn-Teller distortion, causing rapid capacity degradation. In contrast to conventional lithium-ion batteries, microbatteries offer the opportunity to develop specific thin-film-based modification strategies. Here, heterointerfacial lattice strain is proposed to stabilize the spinel crystal framework of an overlithiated Li 1+ x Mn 2 O 4 (LMO) cathode by epitaxial thin film growth on an underlying SrRuO 3 (SRO) electronic conductor layer. It is demonstrated that the lattice misfit at the LMO/SRO heterointerface results in an in-plane epitaxial constraint in the full LMO film. This suppresses the lattice expansion during overlithiation that typically occurs in the in-plane direction. It is proposed by density functional theory modeling that the epitaxial constraint can accommodate the internal lattice stress originating from the cubic-tetragonal transition during overlithiation. As a result, a doubling of the capacity is achieved by reversibly intercalating a second lithium ion in a LiMn 2 O 4 epitaxial cathode with a complete reversible phase transition. An impressive cycling stability can be obtained with reversible capacity retentions of above 90.3 and 77.4% for the 4 and 3 V range, respectively. This provides an effective strategy toward a stable overlithiated Li 1+ x Mn 2 O 4 epitaxial cathode for high-performance microbatteries.

Quasi-two-dimensional (2D) metal halide perovskites (MHPs) are promising photovoltaic (PV) materials because of their impressive optical and optoelectronic properties and improved stability compared to their 3D counterparts. The presence of domains with varying numbers of inorganic layers between the organic spacers ( n -phases), each with different bandgaps, makes the photoinduced carrier dynamics in films of these materials complex and intriguing. Existing interpretations of the ultrafast femto- or picosecond spectroscopy data have been inconsistent, most of them focusing either on exciton/charge transfer from low- n to high- n phases or on hot carrier cooling, but not combined. Here, we present a comprehensive study of the carrier dynamics in the Dion-Jacobson type (PDMA)(MA) ( n -1) Pb n I (3 n +1) (PDMA = 1,4-phenylenedimethylammonium, MA = methylammonium) perovskite, stoichiometrically prepared as ⟨ n ⟩ = 5. Within the film, a coexistence of various n -phases is observed instead of solely the n = 5 phase, resulting in an interesting energy landscape for the motion of excitons and charge carriers. We disentangle hot carrier cooling from exciton transfer between low- n and high- n phases using ultrafast time-resolved photoluminescence and transient absorption spectroscopy. Photophysical modeling by target analysis shows that carrier cooling occurring on a subpicosecond time scale is followed by exciton transfer from low- n into high- n phases in ca. 35 ps when the film is excited by 532 or 490 nm light. Carriers in the high- n phase are much longer lived and decay in a ns time window. Overall, our results provide a comprehensive understanding of the photophysics of this material, which helps to optimize quasi-2D MHP materials for a new generation of PV devices., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Here, we describe how to synthesise proton-conductive transition metal phosphates (TMPs) by direct thermal processing of precursor M-struvites, NH 4 MPO 4 ·6H 2 O, with M = Ni 2+ , Co 2+ . In the as-derived TMP phases their thermal history and bulk proton conductivity were linked with the structural information about the metal coordination, phosphate groups, and volatile compounds. These aspects were investigated with vibrational and synchrotron-based spectroscopic methods (FT-IR, FT-RS, XAS). We elucidated the structures of amorphous and crystalline Ni- and Co phosphate phases in association with different coordination changes and distortion degrees of the metal polyhedra as they developed upon heating. Ni-struvite transformed to a stable amorphous phase over a broad range of temperatures (90 °C < T < 600 °C), in which it remained in an octahedral coordination environment, but the degree of distortion changed with T . In contrast, heating of Co-struvite led to several successive crystalline phases with only unstable transitional and short-lived amorphous components. Among the as-occurring phases, a highly functional layered M-dittmarite NH 4 MPO 4 ·H 2 O obtained at low temperatures ( T < 200 °C) demonstrated high proton conductivity values of 4.2 × 10 -5 S cm -1 for Ni-dittmarite and Co-dittmarite > 10 -4 S cm -1 at room temperature. Even at low humidity, these values are comparable with those found for Nafion, MOFs, some perovskites or composite materials. Coprecipitation of phosphates and transition metal cations in the form of struvite is potentially a viable method to extract these elements from wastewater. Thus, we propose that recycled M-struvites could be potentially further directly upcycled into crystalline and amorphous TMPs useful for electrochemical applications.

We present how mesoporosity can be engineered in transition metal phosphate (TMPs) materials in a template-free manner. The method involves the transformation of a precursor metal phosphate phase, called M-struvite (NH 4 MPO 4 ·6H 2 O, M = Mg 2+ , Ni 2+ , Co 2+ , Ni x Co 1- x 2+ ). It relies on the thermal decomposition of crystalline M-struvite precursors to an amorphous and simultaneously mesoporous phase, which forms during degassing of NH 3 and H 2 O. The temporal evolution of mesoporous frameworks and the response of the metal coordination environment were followed by in situ and ex situ scattering and diffraction, as well as X-ray spectroscopy. Despite sharing the same precursor struvite structure, different amorphous and mesoporous structures were obtained depending on the involved transition metal. We highlight the systematic differences in absolute surface area, pore shape, pore size, and phase transitions depending on the metal cation present in the analogous M-struvites. The amorphous structures of thermally decomposed Mg-, Ni- and Ni x Co 1- x -struvites exhibit high surface areas and pore volumes (240 m 2 g -1 and 0.32 cm -3 g -1 for Mg and 90 m 2 g -1 and 0.13 cm -3 g -1 for Ni). We propose that the low-cost, environmentally friendly M-struvites could be obtained as recycling products from industrial and agricultural wastewaters. These waste products could be then upcycled into mesoporous TMPs through a simple thermal treatment for further application, for instance in (electro)catalysis.

The relatively large ionic radius of the Na ion is one of the primary reasons for the slow diffusion of Na ions compared to that of Li ions in de/intercalation processes in sodium-ion batteries (SIBs). Interlayer expansion of intercalation hosts is one of the effective techniques for facilitating Na-ion diffusion. For most ionic layered compounds, interlayer expansion relies on intercalation of guest ions. It is important to investigate the role of these ions for material development of SIBs. In this study, alkali-metal ions (Li + , Na + , K + , and Cs + ) with different sizes were intercalated into lepidocrocite-type layered titanate by a simple ion-exchange technique to achieve interlayer modulation and those were then evaluated as anode materials for SIBs. By controlling the intercalated alkaline ion species, basal spacings of layered titanates (LTs) in the range of 0.68 to 0.85 nm were obtained. Interestingly, the largest interlayer spacing induced by the large size of Cs did not yield the best performance, while the Na intercalated layered titanate (Na-ILT) demonstrated a superior performance with a specific capacity of 153 mAh g -1 at a current density of 0.1 A g -1 . We found that the phenomena can be explained by the high alkaline metal ion concentration and the efficient utilization of the active sites in Na-ILT. The detailed analysis indicates that large intercalating ions like Cs can hamper sodium-ion diffusion although the interlayer spacing is large. Our work suggests that adopting an appropriate interlayer ion species is key to developing highly efficient layered electrode materials for SIBs.

The microstructure of the PbZr 0.52 Ti 0.48 O 3 (PZT) films is known to influence the ferroelectric properties, but so far mainly the effect of the deposition conditions of the PZT has been investigated. To our knowledge, the influence of the underlying electrode layer and the mechanisms leading to changes in the PZT microstructure have not been explored. Using LaNiO 3 (LNO) as the bottom electrode material, we investigated the evolution of the PZT microstructure and ferroelectric properties for changing LNO pulsed-laser deposition conditions. The explored deposition conditions were the O 2 pressure, total pressure, and thickness of the electrode layer. Increasing both the O 2 pressure and the thickness of the electrode layer changes the growth of PZT from a smooth, dense film to a rough, columnar film. We explain the origin of the change in PZT microstructure as the increased roughness of the electrode layer in relaxing the misfit strain. The strain relaxation mechanism is evidenced by the increase in the crystal phase with bulk LNO unit cell dimensions in comparison to the crystal phase with substrate-clamped unit cell dimensions. We explain the change from a dense to a columnar microstructure as a result of the change in the growth mode from Frank-van der Merwe to Stranski-Krastanov. The ferroelectric properties of the columnar films are improved compared to those of the smooth, dense films. The ability to tune the ferroelectric properties with the microstructure is primarily relevant for ferroelectric applications such as actuators and systems for energy harvesting and storage., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The potential of the electrospray deposition technique as new method to make nanosheet-based multilayer films is evaluated. Densely packed nanosheet-based films with thicknesses of 1-20 nm with rms roughnesses of 2.1-2.4 nm were fabricated on samples of 1 cm 2 size with a growth rate of 0.5 nm/min. Electrosprayed Ti 0.87 O 2 nanosheet films were successfully used as oriented growth templates for 40 nm perovskite SrRuO 3 thin films grown by pulsed laser deposition. The electrospray method provides a fast and easy alternative to the more commonly used Langmuir-Blodgett (LB) deposition method for nanosheet films., (© 2022. The Author(s).)

Two-dimensional freestanding thin films of single crystalline oxide perovskites are expected to have great potential in integration of new features to the current Si-based technology. Here, we showed the ability to create freestanding single crystalline (011)- and (111)-oriented SrRuO 3 thin films using Sr 3 Al 2 O 6 water-sacrificial layer. The epitaxial Sr 3 Al 2 O 6 (011) and Sr 3 Al 2 O 6 (111) layers were realized on SrTiO 3 (011) and SrTiO 3 (111), respectively. Subsequently, SrRuO 3 films were epitaxially grown on these sacrificial layers. The freestanding single crystalline SrRuO 3 (011) pc and SrRuO 3 (111) pc films were successfully transferred on Si substrates, demonstrating possibilities to transfer desirable oriented oxide perovskite films on Si and arbitrary substrates.

Two-dimensional oxide materials are a well-studied, interesting class of materials, enabled by the fact that their bulk layered metal oxides, such as titanates and niobates, can be easily exfoliated within minutes into 2D nanosheets. However, some promising oxide materials, such tantalum oxide, are much more difficult to delaminate, taking several weeks, due to the higher charge density resulting in stronger Coulombic interactions between the layers. This intrinsic constraint has limited detailed studies for exploiting the promising properties of tantalum oxide 2D nanosheets towards enhanced catalysis and energy storage. Here, we have studied in detail the exfoliation mechanism of high charge density 2D materials, specifically tantalum oxide (TaO 3 ) nanosheets. Optimization of tetrabutylphosphonium hydroxide (TBPOH) as the exfoliation agent in a 2 : 1 ratio to HTaO 3 has resulted in a dramatic reduction of the exfoliation time down to only 36 hours at 80 °C. Furthermore, single monolayers of TaO 3 nanosheets with >95% coverage have been achieved by Langmuir-Blodgett deposition, while thicker layers (ranging from several tens of nanometers up to microns) exhibiting long-range ordering of the present nanosheets have been realized through inkjet printing. Interestingly, scanning tunneling microscopy analysis indicated a wide bandgap of ∼5 eV for the single TaO 3 nanosheets. This value is significantly higher than the reported values between 3.5 and 4.3 eV for the layered RbTaO 3 parent compound, and opens up new opportunities for 2D oxide materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Research into 2-dimensional materials has soared during the last couple of years. Next to van der Waals type 2D materials such as graphene and h-BN, less well-known oxidic 2D equivalents also exist. Most 2D oxide nanosheets are derived from layered metal oxide phases, although few 2D oxide phases can be also made by bottom-up solution syntheses. Owing to the strong electrostatic interactions within layered metal oxide crystals, a chemical process is usually needed to delaminate them into their 2D constituents. This Review article provides an overview of the synthesis of oxide nanosheets, and methods to assemble them into nanocomposites, mono- or multilayer films. In particular, the use of Langmuir-Blodgett methods to form monolayer films over large surface areas, and the emerging use of ink jet printing to form patterned functional films is emphasized. The utilization of nanosheets in various areas of technology, for example, electronics, energy storage and tribology, is illustrated, with special focus on their use as seed layers for epitaxial growth of thin films, and as electrochemically active electrodes for supercapacitors and Li ion batteries., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

In complex chemical syntheses (e.g., coprecipitation reactions), nucleation, growth, and coarsening often occur concurrently, obscuring the individual processes. Improved knowledge of these processes will help to better understand and optimize the reaction protocol. Here, a form-free and model independent approach, based on a combination of time-resolved small/wide-angle X-ray scattering, is employed to elucidate the effect of reaction parameters (such as precursor concentration, reactant stoichiometry, and temperature) on the nucleation, crystallization, and growth phenomena during the formation of nanocrystalline barium titanate. The strength of this approach is that it relies solely on the total scattered intensity (i.e., scattering invariant) of the investigated system, and no prior knowledge is required. As such, it can be widely applied to other synthesis protocols and material's systems. Through the scattering invariant, it is found that the amorphous-to-crystalline transformation of barium titanate is predominantly determined by the total amount of water released from the gel-like barium hydroxide octahydrate precursor, and three rate-limiting regimes are established. As a result of this improved understanding of the effect of varying reaction conditions, elementary boundary conditions can be set up for a better control of the barium titanate nanocrystal synthesis., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The application of luminescent materials in display screens and devices requires micropatterned structures. In this work, we have successfully printed microstructures of a two-dimensional (2D), orange-colored organic/inorganic hybrid perovskite ((C 6 H 5 CH 2 NH 3 ) 2 PbI 4 ) using two different soft lithography techniques. Notably, both techniques yield microstructures with very high aspect ratios in the range of 1.5-1.8. X-ray diffraction reveals a strong preferential orientation of the crystallites along the c-axis in both patterned structures, when compared to nonpatterned, drop-casted thin films. Furthermore, (time-resolved) photoluminescence (PL) measurements reveal that the optical properties of (C 6 H 5 CH 2 NH 3 ) 2 PbI 4 are conserved upon patterning. We find that the larger grain sizes of the patterned films with respect to the nonpatterned film give rise to an enhanced PL lifetime. Thus, our results demonstrate easy and cost-effective ways to manufacture patterns of 2D organic/inorganic hybrid perovskites, while even improving their optical properties. This demonstrates the potential use of color-tunable 2D hybrids in optoelectronic devices.

In view of their possible application as high temperature solid lubricants, the tribological and thermochemical properties of several organosilica networks were investigated over a range of temperatures between 25 and 580 °C. Organosilica networks, obtained from monomers with terminal and bridging organic groups, were synthesized by a sol-gel process. The influence of carbon content, crosslink density, rotational freedom of incorporated hydrocarbon groups, and network connectivity on the high temperature friction properties of the polymer was studied for condensed materials from silicon alkoxide precursors with terminating organic groups, i.e., methyltrimethoxysilane, propyltrimethoxysilane, diisopropyldimethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane and 4-biphenylyltriethoxysilane networks, as well as precursors with organic bridging groups between Si centers, i.e., 1,4-bis(triethoxysilyl)benzene and 4,4'-bis(triethoxysilyl)-1,1'-biphenyl. Pin-on-disc measurements were performed using all selected solid lubricants. It was found that materials obtained from phenyltrimethoxysilane and cyclohexyltrimethoxysilane precursors showed softening above 120 °C and performed best in terms of friction reduction, reaching friction coefficients as low as 0.01. This value is lower than that of graphite films (0.050 ± 0.005), a common bench mark for solid lubricants., Competing Interests: The authors declare no conflict of interest.

The effect of water addition during preparation of a CH 3 NH 3 PbI 3 layer on the photodynamics is studied by femtosecond transient absorption. Both the regular perovskite and the aqueous analogue show charge thermalisation on a timescale of about 500 fs. This process is, however, less pronounced in the latter layer. The spectral feature associated with hot charges does not fully decay on this timescale, but also shows a long-lived (sub-ns) component. As water molecules may interfere with the hydrogen bonding between the CH 3 NH 3 + cations and the inorganic cage, this effect is possibly caused by immobilisation of cation motion, suggesting a key role of CH 3 NH 3 + dipole reorientation in charge thermalisation. This effect shows the possibility of controlling hot charge carrier cooling to overcome the Shockley-Queisser limit., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nanosheet Ca 2 Nb 3 O 10 (CNOns) layers were deposited on ultralow expansion glass substrates by the Langmuir-Blodgett method to obtain preferential (001)-oriented growth of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) thin films using pulsed laser deposition (PLD) to enhance the ferroelectric and piezoelectric properties of the films. The PLD deposition temperature and repetition frequency used for the deposition of the PZT films were found to play a key role in the precise control of the microstructure and therefore of the ferroelectric and piezoelectric properties. A film deposited at a high repetition frequency has a columnar grain structure, which helps to increase the longitudinal piezoelectric coefficient (d 33f ). An enhanced d 33f value of 356 pm V -1 was obtained for 2-μm-thick PZT films on CNOns/glass substrates. This high value is ascribed to the preferential alignment of the crystalline [001] axis normal to the substrate surface and the open columnar structure. Large displacement actuators based on such PZT films grown on CNOns/glass substrates should be useful in smart X-ray optics applications.

The nature of the external crystal facets is critical to control the (photo)catalytic properties. Two-dimensional materials can expose only one type of crystal facet among zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) materials. Controllable tuning of the nature of the external crystal facets of 2D materials is highly desirable but very challenging. Here, we show that 2D particles with the desirable crystal facet for high-performance photocatalytic H 2 generation can be obtained by using 2D metal oxide materials (i.e., nanosheets of Ca 2 Nb 3 O 10 and Ti 0.87 O 2 ) as templates taking consideration of the crystal configuration of 2D oxide and target compounds. We demonstrate that anatase TiO 2 crystals grown on different nanosheet templates exhibit variations in photocatalytic hydrogen production rates from aqueous phase methanol solutions (6.7%), which can be attributed to the nature of the main crystal facet exposed. In view of the large number of 2D materials that have already been synthesized, this work offers a key to design and synthesize nanoparticles with the desirable specific external crystal facet for (photo)catalysis application.

It is generally assumed that the hydrothermal stability of organically modified silica networks is promoted by high monomer connectivity, network flexibility, and the presence of hydrophobic groups in the network. In this study a range of organosilica compositions is synthesized to explore the extent to which these factors play a role in the hydrothermal dissolution of these materials. Compositions were synthesized from hexafunctional organically bridged silsesquioxanes (OR 1 ) 3 Si-R-Si(OR 1 ) 3 (R = -CH 2 -, -C 2 H 4 -, -C 6 H 12 -, -C 8 H 16 -, -p-C 6 H 4 -; R 1 = -CH 3 , -C 2 H 5 ), tetrafunctional (OEt) 2 Si(CH 3 )-C 2 H 4 -Si(CH 3 )(OEt) 2 and Si(OEt) 4 , trifunctional silsesquioxanes R'-Si(OMe) 3 (R'=CH 3 , n-C 3 H 7 , cyclo-C 6 H 11 , phenyl), and bifunctional Si(i-C 3 H 7 ) 2 (OMe) 2 . The bond strain, connectivity and hydroxyl concentration of all networks were estimated using 29 Si cross-polarized magic angle spinning nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The hydrophilicity was characterized by monitoring the water uptake of the materials in moisture treatments with thermogravimetric analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The resistance of each network against hydrothermal dissolution in a water/1,5-pentanediol mixture at 80 °C and pH 1, 7, and 13 was analyzed with inductively coupled plasma optical emission spectroscopy and X-ray fluorescence. Bond strain appears to significantly increase the tendency to dissolve under hydrothermal conditions. The stabilizing influences of increased connectivity and hydrophobicity were found to be weak.

Porous magnesium-aluminium layered double hydroxides (LDH) were prepared through intercalation and decomposition of hydrogen peroxide (H 2 O 2 ). This process generates oxygen gas nano-bubbles that pierce holes in the layered structure of the material by local pressure build-up. The decomposition of the peroxide can be triggered by microwave radiation or chemically by reaction with iodide (I - ) ions. The carbonate LDH version [Mg 0.80 Al 0.20 (OH) 2 ](CO 3 ) 0.1 ∙mH 2 O was synthesized by microwave-assisted urea coprecipitation and further modified by iodide or H 2 O 2 intercalation. High resolution Scanning Electron Microscopy (HR-SEM) and Brunauer-Emmet-Teller (BET) analysis were used to assess the morphology and surface area of the new porous materials. The presence of H 2 O 2 in the interlayer region and later decomposition triggered by microwave radiation generated more pores on the surface of the LDH platelets, increasing their specific surface area from initially 9 m 2 /g to a maximum of 67 m 2 /g. X-Ray Diffraction showed that the formation of the pores did not affect the remaining crystal structure, allowing possible further functionalization of the material.

Renewed interest has been witnessed in utilizing the piezoelectric response of PbZr 0.52 Ti 0.48 O 3 (PZT) films on glass substrates for applications such as adaptive optics. Accordingly, new methodologies are being explored to grow well-oriented PZT thin films to harvest a large piezoelectric response. However, thin film piezoelectric response is significantly reduced compared to intrinsic response due to substrate induced clamping, even when films are well-oriented. Here, a novel method is presented to grow preferentially (100)-oriented PZT films on glass substrates by utilizing crystalline nanosheets as seed layers. Furthermore, increasing the repetition frequency up to 20 Hz during pulsed laser deposition helps to tune the film microstructure to hierarchically ordered columns that leads to reduced clamping and enhanced piezoelectric response evidenced by transmission electron microscopy and analytical calculations. A large piezoelectric coefficient of 250 pm/V is observed in optimally tuned structure which is more than two times the highest reported piezoelectric response on glass. To confirm that the clamping compromises the piezoelectric response, denser films are deposited using a lower repetition frequency and a BiFeO 3 buffer layer resulting in significantly reduced piezoelectric responses. This paper demonstrates a novel method for PZT integration on glass substrates without compromising the large piezoelectric response.

The fabrication process of ceramic yttria-stabilized zirconia (YSZ) and nickel oxide nanofibers by electrospinning is reported. The preparation of hollow YSZ nanofibers and aligned nanofiber arrays is also demonstrated. The influence of the process parameters of the electrospinning process, the physicochemical properties of the spinning solutions, and the thermal treatment procedure on spinnability and final microstructure of the ceramic fibers was determined. The fiber diameter can be varied from hundreds of nanometers to more than a micrometer by controlling the solution properties of the electrospinning process, while the grain size and surface roughness of the resulting fibers are mainly controlled via the final thermal annealing process. Although most observed phenomena are in qualitative agreement with previous studies on the electrospinning of polymeric nanofibers, one of the main differences is the high ionic strength of ceramic precursor solutions, which may hamper the spinnability. A strategy to control the effective ionic strength of precursor solutions is also presented.

Ca 2 Nb 3 O 10 (CNOns) and Ti 0.87 O 2 (TiOns) metal oxide nanosheets (ns) are used as a buffer layer for epitaxial growth of piezoelectric capacitor stacks on Si and Pt/Ti/SiO 2 /Si (Pt/Si) substrates. Highly (001)- and (110)-oriented Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) films are achieved by utilizing CNOns and TiOns, respectively. The piezoelectric capacitors are characterized by polarization and piezoelectric hysteresis loops and by fatigue measurements. The devices fabricated with SrRuO 3 top and bottom electrodes directly on nanosheets/Si have ferroelectric and piezoelectric properties well comparable with devices that use more conventional oxide buffer layers (stacks) such as YSZ, CeO 2 /YSZ, or SrTiO 3 on Si. The devices grown on nanosheets/Pt/Si with Pt top electrodes show significantly improved polarization fatigue properties over those of similar devices grown directly on Pt/Si. The differences in properties are ascribed to differences in the crystalline structures and the density of the films. These results show a route toward the fabrication of single crystal piezoelectric thin films and devices with high quality, long-lifetime piezoelectric capacitor structures on nonperovskite and even noncrystalline substrates such as glass or polished metal surfaces.

The intercalation of different primary n-alkylamines in the structure of a layered titanate of the lepidocrocite type (H 1.07 Ti 1.73 O 4 ) for application in high-temperature solid lubrication is reported. The intercalation process of the amines was explored by means of in situ small-angle X-ray scattering (SAXS), with variations in alkyl chain length (3-12 carbon atoms) and the amine/titanate ratio. The intercalation process was found to be completed within 5 min after mixing of the precursors in water at 80 °C. The topotactic transformation of the layered titanate is driven by an acid-base reaction. The thermal degradation of the modified titanates was investigated by thermogravimetric analysis (TGA), and the chemical changes were investigated by temperature-dependent infrared spectroscopy (DRIFTS). The coefficient of friction of the lubricants was assessed by means of high-temperature pin-on-disc experiments up to 580 °C. The intercalation of amine rendered a deformable layered ceramic upon heating. It was found that the hydrocarbon chain length exerts an influence on the mechanical properties of the titanates, resulting in lower friction forces for lubricants with longer intercalated amine molecules. Films of solid lubricants with longer amine chain lengths showed coefficients of friction as low as 0.01, lower than that of the state-of-the-art material graphite.

Currently, the main drawback of ceramic scaffolds used in hard tissue regeneration is their low mechanical strength. Stabilized zirconia, especially the tetragonal 3% yttrium-stabilized zirconia (YSZ) phase, has been considered as a bioinert ceramic material with high mechanical strength. In the present work, flexible nanofibrous YSZ scaffolds were prepared by electrospinning. The obtained scaffolds showed remarkable flexibility at the macroscopic scale, while retaining their stiffness at the microscopic scale. The surface nanoroughness of the scaffolds could be tailored by varying the heat treatment method. Our results demonstrate that the osteogenic differentiation and mineralization of seeded human mesenchymal stromal cells were supported by the nanofibrous YSZ scaffolds, in contrast to the well-known bioinert behavior of bulk YSZ. These findings highlight that flexible ceramic scaffolds are an appealing alternative to the current brittle ceramics for bone tissue regeneration applications.

Well aligned nanowires of ZnO have been made with an electrospinning technique using zinc acetate precursor solutions. Employment of two connected parallel collector plates with a separating gap of 4 cm resulted in a very high degree of nanowire alignment. By adjusting the process parameters, the deposition density of the wires could be controlled. Field effect transistors were prepared by depositing wires between two gold electrodes on top of a heavily doped Si substrate covered with a 300 nm oxide layer. These devices showed good FET characteristics and photosensitivity under UV-illumination. The method provides a fast and scalable fabrication route for functional nanowire arrays with a high degree of alignment and control over nanowire spacing.

One of the main trends in the past decades is the reduction of wastage and the replacement of toxic compounds in industrial processes. Some soft metallic particles can be used as nontoxic solid lubricants in high-temperature processes. The behavior of bismuth metal particles, bismuth sulfide (Bi2S3), bismuth sulfate (Bi2(SO4)3), and bismuth oxide (Bi2O3) as powder lubricants was studied in a range of temperatures up to 580 °C. The mechanical behavior was examined using a high-temperature pin-on-disc setup, with which the friction force between two flat-contact surfaces was recorded. The bismuth-lubricated surfaces showed low coefficients of friction (μ ≈ 0.08) below 200 °C. Above the melting temperature of the metal powder at 271 °C, a layer of bismuth oxide developed and the friction coefficient increased. Bismuth oxide showed higher friction coefficients at all temperatures. Bismuth sulfide exhibited partial oxidation upon heating but the friction coefficient decreased to μ ≈ 0.15 above 500 °C, with the formation of bismuth oxide-sulfate, while some bismuth sulfate remained. All surfaces were studied by X-ray diffraction (XRD), confocal microscopy, high-resolution scanning electron microscopy (HR-SEM), and energy-dispersive X-ray spectroscopy (EDS). This study reveals how the partial oxidation of bismuth compounds at high temperatures affects their lubrication properties, depending on the nature of the bismuth compound.

An increasing demand exists for biomaterials that are able to actively participate in the process of repair and regeneration of damaged or diseased organs and tissues. Patterning of surfaces of biomaterials with distinct chemical or physical cues is an attractive way to obtain spatial control over their interactions with the biological system. In the current study, micromoulding in capillaries method was used to pattern silicon substrates with bioinert yttria-stabilised zirconia or with bioactive calcium phosphate ceramics, both widely used biomaterials in orthopaedics and dentistry. Micrometer-scale patterns consisted of parallel lines with varying width and spacing. Both ceramics were successfully deposited on the substrate in a pattern defined by the mould. While the yttria-stabilised zirconia pattern was highly homogenous and smooth (R q = 5.5 nm), the calcium phosphate pattern, consisting of dicalcium phosphate anhydrous before, and of β-tricalcium phosphate after annealing, exhibited a less homogenous morphology and higher roughness (R q = 893 nm). Both materials allowed attachment and proliferation of the MG-63 osteosarcoma cell line, independent of the pattern used. While a preferential orientation of cells in the direction of the pattern lines was observed for all patterns, this effect was more pronounced on the lines with a width of up to 20 μm on both yttria-stabilised zirconia and calcium phosphate ceramics, as compared to wider patterns. Furthermore, the cells retained an elongated morphology for a longer period of time on narrow patterns. Micromoulding in capillaries appeared to be a suitable method to pattern both types of ceramics, however further optimisation is needed to improve homogeneity and obtain better control over the chemical phase and crystalline structure of calcium phosphate patterns.

The layered perovskite-type niobate KCa2Nb3O10 and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 μm. We report a flux synthesis method to obtain KCa2Nb3O10 crystals with significantly larger sizes. By using different flux materials (K2SO4 and K2MoO4), crystals with average sizes of 8 and 20 μm, respectively, were obtained. The KCa2Nb3O10 crystals from K2SO4 and K2MoO4 assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO3/PbZr0.52Ti0.48O3/SrRuO3, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca2Nb3O10(-) (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d33 of 100 pm/V, while the larger sized sheets had a d33 of 72 pm/V. An enhanced transverse piezoelectric coefficient d31 of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V.

Two-dimensional (2D) (hydro)oxide materials, that is, nanosheets, enable the preparation of advanced 2D materials and devices. The general synthesis route of nanosheets involves exfoliating layered metal (hydro)oxide crystals. This exfoliation process is considered to be time-consuming, hindering their industrial-scale production. Based on in situ exfoliation studies on the protonated layered titanate H(1.07)Ti(1.73)O4⋅H2O (HTO), it is now shown that ion intercalation-assisted exfoliation driven by chemical reaction provides a viable and fast route to isolated nanosheets. Contrary to the general expectation, data indicate that direct exfoliation of HTO occurs within seconds after mixing of the reactants, instead of proceeding via a swollen state as previously thought. These findings reveal that ion intercalation-assisted exfoliation driven by chemical reaction is a promising exfoliation route for large-scale synthesis., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Research on human skin interactions with healthcare and lifestyle products is a topic continuously attracting scientific studies over the past years. It is possible to evaluate skin mechanical properties based on human or animal experimentation, yet in addition to possible ethical issues, these samples are hard to obtain, expensive and give rise to highly variable results. Therefore, the design of a skin equivalent is essential. This paper describes the design and characterization of a new Epidermal Skin Equivalent (ESE). The material resembles the properties of epidermis and is a first approach to mimic the mechanical properties of the human skin structure, variable with the length scale. The ESE is based on a mixture of Polydimethyl Siloxane (PDMS) and Polyvinyl Alcohol (PVA) hydrogel cross-linked with Glutaraldehyde (GA). It was chemically characterized by XPS and FTIR measurements and its cross section was observed by macroscopy and cryoSEM. Confocal Microscope analysis on the surface of the ESE showed an arithmetic roughness (Ra) between 14-16 μm and contact angle (CA) values between 50-60°, both of which are close to the values of in vivo human skins reported in the literature. The Equilibrium Water Content (ECW) was around 33.8% and Thermo Gravimetric Analysis (TGA) confirmed the composition of the ESE samples. Moreover, the mechanical performance was determined by indentation tests and Dynamo Thermo Mechanical Analysis (DTMA) shear measurements. The indentation results were in good agreement with that of the target epidermis reported in the literature with an elastic modulus between 0.1-1.5 MPa and it showed dependency on the water content. According to the DTMA measurements, the ESE exhibits a viscoelastic behavior, with a shear modulus between 1-2.5MPa variable with temperature, frequency and the hydration of the samples., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Crystals of K2[SiF6] were grown in agar gel, silica gel and jelly. Crystals grown in agar gel or jelly exhibit birefringence and consist of six double refracting growth sectors, each having the shape of a tetragonal pyramid. Nevertheless, the structure of the crystals from agar gel could be refined as cubic (space group Fm3m) with a weighted R factor of 0.043. The amount of birefringence was estimated by the Senarmont compensation method and the rotating polarizer method.

Nanocrystalline barium titanate (8-10 nm crystallite size) was prepared at temperatures of 23-78 °C through reaction of a modified titanium alkoxide precursor in benzyl alcohol with barium hydroxide octahydrate. The room temperature formation of a perovskite phase from solution is associated with the use of benzyl alcohol as solvent medium. The formation mechanism was elucidated by studying the stability and interaction of each precursor with the solvent and with each other using various experimental characterization techniques. Density functional theory (DFT) computational models which agreed well with our experimental data could explain the formation of the solid phase. The stability of the Ti precursor was enhanced by steric hindrance exerted by phenylmethoxy ligands that originated from the benzyl alcohol solvent. Electron microscopy and X-ray diffraction indicated that the crystallite sizes were independent of the reaction temperature. Crystal growth was inhibited by the stabilizing phenylmethoxy groups present on the surface of the crystallites.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10(-) nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

The nucleation and growth of niobium pentaethoxide (NPE)-derived clusters in ethanol, through acid-catalyzed hydrolysis/condensation in the presence and absence of the silsesquioxane 1,2-bis(triethoxysilyl)ethane (BTESE), was monitored at 298-333 K by small-angle X-ray scattering. The data were analyzed with a newly derived model for polydisperse mass-fractal-like structures. At 298-313 K in the absence of BTESE the data indicated the development of relatively monodisperse NPE-derived structures with self-preserving polydispersity during growth. The growth exponent was consistent with irreversible diffusion-limited cluster agglomeration. At 333 K the growth exponent was characteristic for fast-gelling reaction-limited cluster agglomeration. The reaction yielded substantially higher degrees of polydispersity. In the presence of BTESE the growth exponents were substantially smaller. The smaller growth exponent in this case is not consistent with irreversible Smoluchowski-type agglomeration. Instead, reversible Lifshitz-Slyozov-type agglomeration seems to be more consistent with the experimental data.

The exfoliation and deposition of large (10-100 μm) Ti0.87O2 and small (0.1-1 μm) Ti0.91O2 nanosheets from lepidocrocite-type protonated titanates was investigated for getting high quality films. Exfoliation was carried out with different tetra-alkyl ammonium ions (TAA(+)) and varying TAA(+)/H(+) ratios, and the colloidal solutions were characterized by small-angle X-ray scattering (SAXS) and ultraviolet-visible (UV-vis) spectroscopy. Using Langmuir-Blodgett deposition the titanate nanosheets were directly transferred onto a Si substrate. The resulting films were characterized by atomic force microscopy (AFM).The results indicate that the H1.07Ti1.73O4 titanate exfoliated at very low ratios of TAA(+)/H(+); no lower threshold for exfoliation was observed for the TAA(+) concentration. Nanosheets exfoliated at very low ratios of TAA(+)/H(+) typically showed a small size and porous surface. Subsequent exfoliation of the remaining layered titanate particles yielded much higher quality nanosheets. The optimized deposition parameters for Langmuir-Blodgett films suggest that the surface pressure is a key parameter to control the coverage of the film. The bulk concentration of nanosheets was found to be a less important deposition parameter in the LB deposition process. It only influenced whether the desired surface pressure could be reached at a given maximum degree of compression.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 µm were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

The common facets of anatase crystals are the (001) and (101) planes. However, the phase transformation from lepidocrocite-type titanate into anatase by hydrothermal processing yields an anatase microstructure with high concentration of exposed (010) planes. The phase transformation of a lepidocrocite-type protonated layered titanate (HTO) into anatase was studied using XRD, TEM, FTIR, and measurement of pH and zeta potential. It was found that HTO is proton-deficient. The phase transformation process begins after uptake of a sufficient number of protons into the lepidocrocite-type structure. With the uptake of protons new hydroxyl groups form on the internal surfaces of the layered titanate and result in a bilayer state of HTO. The phase transformation reaction is a topotactic dehydration reaction in which anatase forms and water is expelled by syneresis.

Nanosheets of Ti0.87O2 and Ca2Nb3O10 were synthesized and transferred onto Si substrates by Langmuir-Blodgett deposition. Using pulsed laser deposition, SrRuO3 films were formed on top of these samples. The underlying nanosheets determined both the morphology and crystallographic orientation of the films. SrRuO3 grew preferentially in the [110]pc direction on Ti0.87O2 nanosheets, while growth proceeded in the [001]pc direction on Ca2Nb3O10 nanosheets (pc refers to the pseudocubic unit cell of SrRuO3). Besides macroscopic control over the out-of-plane crystal direction, single crystal orientations were measured by electron backscatter diffraction on the level of individual nanosheets, indicating that epitaxial growth was achieved on the nanosheets as imposed by their well-defined crystal lattices. The nanosheets also had a clear effect on the magnetic properties of the films, which showed anisotropic behavior only when a seed layer was used. A monolayer consisting of a mixture of both types of nanosheets was made to locally control the nucleation of SrRuO3. In this context, SrRuO3 was used as model material, as it was used to illustrate that nanosheets can be a unique tool to control the orientation of films on a (sub-)micrometer length scale. This concept may pave the way to the deposition of various other functional materials and the fabrication of devices where the properties are controlled locally by the different crystallographic orientations.

Core-shell PMMA-Au nanocube structures made by a combination of nanoimprint lithography and sidewall deposition were used as template for electrodeposition of MoS2, Ni, and Pt. Linear sweep voltammetry experiments obtained in an aqueous solution containing 0.29 M H2SO4 (pH 0.24) showed that the onset potential of the core-shell-shell PMMA-Au-MoS2 nanocube electrode for the hydrogen evolution reaction (HER) was shifted to the positive direction (i.e., requiring a lower overpotential) by 20-40 mV compared to planar MoS2 films. This indicates that the nanocube electrodes have a significantly increased HER activity, which is probably because of a higher density of catalytically active edge sites available at the nanocube surface. It was also found that the HER activity initially increased with increasing MoS2 deposition time, but decreased after deposition for 60 min because the edges of the nanocubes became rounded, thereby decreasing the number of active edge sites. By depositing Ni and Pt on top of PMMA-Au nanocubes, it was shown that this method can also be used for the synthesis of nanocube structures with varying compositions.

Due to their shape anisotropy, high aspect ratio magnetic nanoparticles offer many advantages in biomedical applications. For biocompatibility, it is essential to have full control over the dimensions and surface chemistry of the particles. The aim of this study was to synthesize biocompatible nanowires with tuneable dimensions. This was achieved by electrodeposition of Ni in polycarbonate membranes. To ensure biocompatibility, a continuous gold coating was deposited onto the Ni wires by a newly developed electroless deposition method. The coating was analysed using electron microscopy and X-ray diffraction. Magnetic properties, anisotropy and Au film thickness were studied using vibrating sample magnetometry. After biofunctionalization, no significant cytotoxic effects were found in studies involving a diverse range of primary and tumour cells exposed to increasing concentrations of nanowires for up to 7 days. These nanowires may thus be used for in vivo applications such as magnetic drug delivery.

A method for the reproducible formation of Ni and Cu2O nanocubes with dimensions of 200-500 nm and a small size distribution is introduced. For this, the well-known templated electrodeposition technique was extended to cubic PMMA templates made by nanoimprint lithography. When making cubic templates in larger quantities, this method has the potential to become simple and cost-effective. This method was successfully used for the formation of Ni and p-Cu2O nanocubes as well as for the formation of segmented nanobars containing both phases. The lateral dimensions of the nanocubes exactly resembled the dimensions of the template, and the height could be varied by adjusting the deposition time. Nanocubes formed via this method can remain attached to the substrate or can be dispersed in solution. p-Cu2O is considered to be one of the most promising photocathode materials for solar water splitting. It is demonstrated that the activity of the p-Cu2O nanocubes for photocatalytic water splitting can be measured, and it was found that the nanocube morphology enhances the photocatalytic activity compared to thin films.

The evolution of structure in sol-gel derived mixed bridged silsesquioxane-niobium alkoxide sols and drying thin films was monitored in situ by small-angle X-ray scattering. Since sol-gel condensation of metal alkoxides proceeds much faster than that of silicon alkoxides, the incorporation of d-block metal dopants into silica typically leads to formation of densely packed nano-sized metal oxide clusters that we refer as metal oxide building blocks in a silica-based matrix. SAXS was used to study the process of niobia building block formation while drying the sol as a thin film at 40-80°C. The SAXS curves of mixed niobia-hybrid silica sols were dominated by the electron density contrast between sol particles and surrounding solvent. As the solvent evaporated and the sol particles approached each other, a correlation peak emerged. Since TEM microscopy revealed the absence of mesopores, the correlation peak was caused by a heterogeneous system of electron-rich regions and electron poor regions. The regions were assigned to small clusters that are rich in niobium and which are dispersed in a matrix that mainly consisted of hybrid silica. The correlation peak was associated with the typical distances between the electron dense clusters and corresponded with distances in real space of 1-3 nm. A relationship between the prehydrolysis time of the silica precursor and the size of the niobia building blocks was observed. When 1,2-bis(triethoxysilyl)ethane was first hydrolyzed for 30 min before adding niobium penta-ethoxide, the niobia building blocks reached a radius of 0.4 nm. Simultaneous hydrolysis of the two precursors resulted in somewhat larger average building block radii of 0.5-0.6 nm. This study shows that acid-catalyzed sol-gel polymerization of mixed hybrid silica niobium alkoxides can be rationalized and optimized by monitoring the structural evolution using time-resolved SAXS., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Large area low-cost patterning is a challenging problem in graphene research. A resist-free, single-step, large area and cost effective soft lithographic patterning strategy is presented for graphene. The technique is applicable on any arbitrary substrate that needs to be covered with a graphene film and provides a viable route to large-area patterning of graphene for device applications.

Typical surface areas of 5 × 5 mm(2) were patterned with high-aspect-ratio micrometer- and submicrometer-sized structures of yttria-stabilized zirconia using a combination of micromolding in capillaries and sol-gel chemistry. The influence of precursor solution concentration and mold geometry on the final shape and dimensions of the patterned structures was investigated. At a precursor concentration of [Zr] = 0.724 mol/dm(3), isolated objects-due to the controlled cracking of patterned films-such as crosses (height 1.4 μm, width 6.0 μm) and "dog bones" (height 800-900 nm, width 900 nm) or patterned films (height 450 nm) were obtained, depending on the mold geometry. Lower precursor concentrations led to differently sized and shaped structures, with changes in dimensions of more than an order of magnitude. Employing a precursor concentration of [Zr] = 0.036 mol/dm(3) yielded isolated rings (height 100-150 nm, line width 20 nm) and squares (height 40 nm, line width 40 nm). A better understanding of the relationship between the precursor concentration, mold geometry, and observed coherent crack patterns in as-dried sol-gel structures may lead to new techniques in patterning isolated features.

The evolution of nanostructure in sol-gel derived lead zirconate titanate (PZT) and zirconia precursor sols at different hydrolysis ratios was investigated by small angle X-ray scattering (SAXS). The shape of the clusters in the zirconia sol could be described by the length-polydisperse cylindrical form factor. The zirconia-based clusters were characterized by a cross-sectional radius, r(0), of 0.28 nm and a practically monodisperse length of ca. 1.85 nm. These clusters were probably constructed of zirconia-related tetrameric building blocks. Similar cylindrical structural motifs were observed in PZT precursor sols with [H(2)O]/[Zr+Ti]=9.26 and 27.6, but the polydispersity in length was much higher. Clear scattering contributions from Ti and Pb centers were not detected, which was interpreted in terms of a homogeneous distribution of unbound lead ions in solution and the relatively low scattering intensity from any Ti-based clusters or oligomers that may have been present in the sols., (Copyright © 2011 Elsevier Inc. All rights reserved.)

A simple methodology to fabricate micrometer- and nanometer-scale patterned surfaces with multiple chemical functionalities is presented. Patterns with lateral dimensions down to 110 nm were made. The fabrication process involves multistep gas-phase patterning of amine, thiol, alkyl, and fluorinated alkyl-functional organosilane molecules using PDMS molds as shadow masks. Also, a combination process of channel diffused plasma etching of organosilane molecular thin films in combination with masked gas-phase deposition to fabricate multilength scale, multifunctional surfaces is demonstrated.

Thin films of two laterally patterned functional oxides of uniform thickness were obtained in a two-step soft-lithographic micromolding process. CoFe(2)O(4)/ZnO and CoFe(2)O(4)/BaTiO(3) dual-phase patterns were fabricated. The films showed good replication of the pattern that was defined in the first patterning step. X-ray diffraction showed that the films consisted of two distinct phases, and magnetic force microscopy showed that the compounds were laterally separated, the separation pattern being the same as that of the initial soft-lithographic process. The films exhibited slight height variations near the edges of the phases, which were introduced in the first deposition step and were not fully compensated in the second deposition step. The films are sufficiently smooth to allow fabrication of multilayer structures., (© 2011 American Chemical Society)