Strain‐Driven Self‐Assembled Network of Antidots in Complex Oxide Thin Films

Structural strain due to lattice mismatch is used to promote the formation of a self‐assembled network of antidots in highly epitaxial La_2/3Sr_1/3MnO₃ thin films grown on (001) oriented SrTiO₃ substrates by radiofrequency magnetron sputtering. Size, depth, and separation between antidots can be controlled by changing deposition parameters and the miscut angle of the substrate. This morphology exhibits a remarkable magnetic anisotropy and offers unique opportunities for versatile nanostencils for the preparation of nano‐object networks that can be of major relevance for the fabrication of oxide‐based magnetic and magnetoelectronic devices.     

Self‐Assembled Ordered Three‐Phase Au–BaTiO3–ZnO Vertically Aligned Nanocomposites Achieved by a Templating Method

Complex multiphase nanocomposite designs present enormous opportunities for developing next‐generation integrated photonic and electronic devices. Here, a unique three‐phase nanostructure combining a ferroelectric BaTiO₃, a wide‐bandgap semiconductor of ZnO, and a plasmonic metal of Au toward multifunctionalities is demonstrated. By a novel two‐step templated growth, a highly ordered Au–BaTiO₃–ZnO nanocomposite in a unique “nanoman”‐like form, i.e., self‐assembled ZnO nanopillars and Au nanopillars in a BaTiO₃ matrix, is realized, and is very different from the random three‐phase ones with randomly arranged Au nanoparticles and ZnO nanopillars in the BaTiO₃ matrix. The ordered three‐phase “nanoman”‐like structure provides unique functionalities such as obvious hyperbolic dispersion in the visible and near‐infrared regime enabled by the highly anisotropic nanostructures compared to other random structures. Such a self‐assembled and ordered three‐phase nanocomposite is obtained through a combination of vapor–liquid–solid (VLS) and two‐phase epitaxy growth mechanisms. The study opens up new possibilities in the design, growth, and application of multiphase structures and provides a new approach to engineer the ordering of complex nanocomposite systems with unprecedented control over electron–light–matter interactions at the nanoscale.     

Pulse electric current sintering of alumina/nickel nanocomposites

Typical magnetically functionalized Al₂O₃/Ni nanocomposite materials were fabricated by pulse electric current sintering process. The rapid densification and various microstructures were accomplished with controlling PECS temperature. The PECSed Al₂O₃/Ni system exhibited peculiar mechanical and magnetic properties with microstructure developments. The mechanical properties of Al₂O₃/Ni nanocomposite were optimized as controlling microstructures, and fine metal dispersion into the Al₂O₃ matrix give to the various ferromagnetic properties. Electronic Publication     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

On‐Chip Chemical Self‐Assembly of Semiconducting Single‐Walled Carbon Nanotubes (SWNTs): Toward Robust and Scale Invariant SWNTs Transistors

In this paper, the fabrication of carbon nanotubes field effect transistors by chemical self‐assembly of semiconducting single walled carbon nanotubes (s‐SWNTs) on prepatterned substrates is demonstrated. Polyfluorenes derivatives have been demonstrated to be effective in selecting s‐SWNTs from raw mixtures. In this work the authors functionalized the polymer with side chains containing thiols, to obtain chemical self‐assembly of the selected s‐SWNTs on substrates with prepatterned gold electrodes. The authors show that the full side functionalization of the conjugated polymer with thiol groups partially disrupts the s‐SWNTs selection, with the presence of metallic tubes in the dispersion. However, the authors determine that the selectivity can be recovered either by tuning the number of thiol groups in the polymer, or by modulating the polymer/SWNTs proportions. As demonstrated by optical and electrical measurements, the polymer containing 2.5% of thiol groups gives the best s‐SWNT purity. Field‐effect transistors with various channel lengths, using networks of SWNTs and individual tubes, are fabricated by direct chemical self‐assembly of the SWNTs/thiolated‐polyfluorenes on substrates with lithographically defined electrodes. The network devices show superior performance (mobility up to 24 cm² V^?1 s^?1), while SWNTs devices based on individual tubes show an unprecedented (100%) yield for working devices. Importantly, the SWNTs assembled by mean of the thiol groups are stably anchored to the substrate and are resistant to external perturbation as sonication in organic solvents.     

Solution Combustion Synthesis: Low‐Temperature Processing for p‐Type Cu:NiO Thin Films for Transparent Electronics

Low‐temperature solution processing opens a new window for the fabrication of oxide semiconductors due to its simple, low cost, and large‐area uniformity. Herein, by using solution combustion synthesis (SCS), p‐type Cu‐doped NiO (Cu:NiO) thin films are fabricated at a temperature lower than 150 °C. The light doping of Cu substitutes the Ni site and disperses the valence band of the NiO matrix, leading to an enhanced p‐type conductivity. Their integration into thin‐film transistors (TFTs) demonstrates typical p‐type semiconducting behavior. The optimized Cu_5%NiO TFT exhibits outstanding electrical performance with a hole mobility of 1.5 cm² V^?1 s^?1, a large on/off current ratio of ≈10⁴, and clear switching characteristics under dynamic measurements. The employment of a high‐k ZrO₂ gate dielectric enables a low operating voltage (≤2 V) of the TFTs, which is critical for portable and battery‐driven devices. The construction of a light‐emitting‐diode driving circuit demonstrates the high current control capability of the resultant TFTs. The achievement of the low‐temperature‐processed Cu:NiO thin films via SCS not only provides a feasible approach for low‐cost flexible p‐type oxide electronics but also represents a significant step toward the development of complementary metal–oxide semiconductor circuits.     

Electrostatic Self‐Assembly of Au Nanoparticles onto Thermosensitive Magnetic Core‐Shell Microgels for Thermally Tunable and Magnetically Recyclable Catalysis

A facile route to fabricate a nanocomposite of Fe₃O₄@poly[N‐isopropylacrylamide (NIPAM)‐co‐2‐(dimethylamino)ethyl methacrylate (DMAEMA)]@Au (Fe₃O₄@PND@Au) is developed for magnetically recyclable and thermally tunable catalysis. The negatively charged Au nanoparticles with an average diameter of 10 nm are homogeneously loaded onto positively charged thermoresponsive magnetic core‐shell microgels of Fe₃O₄@poly(NIPAM‐co‐DMAEMA) (Fe₃O₄@PND) through electrostatic self‐assembly. This type of attachment offers perspectives for using charged polymeric shell on a broad variety of nanoparticles to immobilize the opposite‐charged nanoparticles. The thermosensitive PND shell with swollen or collapsed properties can be as a retractable Au carrier, thereby tuning the aggregation or dispersion of Au nanoparticles, which leads to an increase or decrease of catalytic activity. Therefore, the catalytic activity of Fe₃O₄@PND@Au can be modulated by the volume transition of thermosensitive microgel shells. Importantly, the mode of tuning the aggregation or dispersion of Au nanoparticles using a thermosensitive carrier offers a novel strategy to adjust and control the catalytic activity, which is completely different with the traditional regulation mode of controlling the diffusion of reactants toward the catalytic Au core using the thermosensitive poly(N‐isopropylacrylamide) network as a nanogate. Concurrent with the thermally tunable catalysis, the magnetic susceptibility of magnetic cores enables the Fe₃O₄@PND@Au nanocomposites to be capable of serving as smart nanoreactors for thermally tunable and magnetically recyclable catalysis.     

Nanocomposite Magnets and their Preparation under High Pressure

This article reports current studies on nanocomposite magnets and a newly developed route for their preparation, known as crystallization of amorphous alloy under high pressure (CAAHP). The microstructure and magnetic properties of nanocomposite magnets prepared by CAAHP are presented, and the influences of pressure on the microstructures of the magnets are discussed. α‐Fe/Sm₂(Fe,Si)₁₇C_x nanocomposite magnets with a grain size <10 nm have been successfully prepared by CAAHP, and a maximum energy product of about 25 MGOe is obtained.     

High‐Throughput Phase‐Field Design of High‐Energy‐Density Polymer Nanocomposites

Understanding the dielectric breakdown behavior of polymer nanocomposites is crucial to the design of high‐energy‐density dielectric materials with reliable performances. It is however challenging to predict the breakdown behavior due to the complicated factors involved in this highly nonequilibrium process. In this work, a comprehensive phase‐field model is developed to investigate the breakdown behavior of polymer nanocomposites under electrostatic stimuli. It is found that the breakdown strength and path significantly depend on the microstructure of the nanocomposite. The predicted breakdown strengths for polymer nanocomposites with specific microstructures agree with existing experimental measurements. Using this phase‐field model, a high throughput calculation is performed to seek the optimal microstructure. Based on the high‐throughput calculation, a sandwich microstructure for PVDF–BaTiO₃ nanocomposite is designed, where the upper and lower layers are filled with parallel nanosheets and the middle layer is filled with vertical nanofibers. It has an enhanced energy density of 2.44 times that of the pure PVDF polymer. The present work provides a computational approach for understanding the electrostatic breakdown, and it is expected to stimulate future experimental efforts on synthesizing polymer nanocomposites with novel microstructures to achieve high performances.     

Developing extreme hardness (>15 GPa) in iron based nanocomposites

Through a unique methodology, novel nanocomposite microstructures were created in a bulk iron based alloy by first processing into a glass condition followed by devitrifying the glass through heat treating above the crystallization temperature. The as-crystallized microstructure was made up of three nanoscale phases; α-Fe, Fe₂₃C₆, and Fe₃B phases. Vickers hardness testing revealed a maximum hardness of 16.2 GPa which is significantly harder than existing commercial steel alloys and hardmetals. Detailed structural studies uncovered two important factors which contribute to the development of this extreme hardness; reductions in microstructure scale to the nanometer regime and supersaturation of transition metal alloying elements significantly above their equilibrium solubility limits.     

Development of NiO-based thin film structures as efficient H2 gas sensors operating at room temperatures

P-type NiO thin films have been developed on high resistivity Si and SiO₂ substrates by a pulsed laser deposition technique using an ArF^? 193 nm excimer laser at deposition temperature of 300 °C and in 40 Pa partial oxygen pressure. Structures based on such NiO films as host material in the form of Au-NiO Schottky diodes have been subsequently developed under vacuum. In a different procedure, an n-SnO₂ layer has been deposited by a CVD technique on a NiO film to produce a p/n heterojunction. The sensing properties of all above structures have been tested upon exposure to a H₂ flow in air ambient gas at various operating temperature ranging from 30 to 180 °C. For the NiO films, the optimum temperature was about 150 °C exhibiting a sensitivity of 94%. After surface sensitization of NiO by Au the NiO films showed an H₂ response at operating temperature of 30 °C. The sensitivity of p-NiO/n-SnO₂ heterojunction devices was extracted from I-V measurements in air and under H₂ flow mixed in air. In this case a dramatic increase of the sensitivity was achieved at operating temperature of 30 °C for a forward bias of 0,2 V.     

Self‐Organized Epitaxial Vertically Aligned Nanocomposites with Long‐Range Ordering Enabled by Substrate Nanotemplating

Vertically aligned nanocomposites (VAN) thin films present as an intriguing material family for achieving novel functionalities. However, most of the VAN structures tend to grow in a random fashion, hindering the future integration in nanoscale devices. Previous efforts for achieving ordered nanopillar structures have been focused on specific systems, and rely on sophisticated lithography and seeding techniques, making large area ordering quite difficult. In this work, a new technique is presented to produce self‐assembled nanocomposites with long‐range ordering through selective nucleation of nanocomposites on termination patterned substrates. Specifically, SrTiO₃ (001) substrates have been annealed to achieve alternating chemical terminations and thus enable selective epitaxy during the VAN growth. La_0.7Sr_0.3MnO₃:CeO₂ (LSMO):CeO₂ nanocomposites, as a prototype, are demonstrated to form well‐ordered rows in matrix structure, with CeO₂ (011) domains selectively grown on SrO terminated area, showing enhanced functionality. This approach provides a large degree of long‐range ordering for nanocomposite growth that could lead to unique functionalities and takes the nanocomposites one step closer toward future nanoscale device integration.     

Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator

The Mott transistor is a paradigm for a new class of electronic devices—often referred to by the term Mottronics—which are based on charge correlations between the electrons. Since correlation‐induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal–insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO₃ grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band‐filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO_3+x thin films making it a promising channel material in future Mottronic devices.     

High‐Performance Piezoelectric Nanogenerators with Imprinted P(VDF‐TrFE)/BaTiO3 Nanocomposite Micropillars for Self‐Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high‐performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride‐trifluoroethylene (P(VDF‐TrFE))/barium titanate (BaTiO₃) for energy harvesting and highly sensitive self‐powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF‐TrFE)/BaTiO₃ nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm^?2, which an enhancement by a factor of 7.3 relatives to the pristine P(VDF‐TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF‐TrFE)/BaTiO₃ nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self‐powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.     

Exchange-biased NiFe2O4/NiO nanocomposites derived from NiFe-layered double hydroxides as a single precursor

NiFe₂O₄ nanoparticles (<10 nm) embedded in a NiO matrix have been fabricated by calcining the corresponding Ni^IIFe^III-layered double hydroxide (LDH) precursors at high temperature (500 °C). Compared with the NiFe₂O₄/NiO nanocomposite obtained by calcination of a precursor prepared by a traditional chemical coprecipitation method, those derived from NiFe-LDH precursors show much higher blocking temperatures (T _B) (?380 K). The enhanced magnetic stability can be ascribed to the much stronger interfacial interaction between NiFe₂O₄ and NiO phases due to the topotactic nature of the transformation of the LDH precursor to the NiFe₂O₄/NiO composite material. Through tuning the Ni^II/Fe^III molar ratio of the NiFe-LDH precursor, the NiFe₂O₄ concentration can be precisely controlled, and the T _B value as well as the magnetic properties of the final material can also be regulated. This work represents a successful example of the fabrication of ferro(ferri)magnetic (FM)/antiferrimagnetic (AFM) systems with high magnetic stability from LDH precursors. This method is general and may be readily extended to other FM/AFM systems due to the wide range of available LDH precursors.      

Neue Aspekte bei der physikalischen Abscheidung kompakter Dünnschichten aus der Gasphase am Beispiel einer praxisrelevanten Festschmierstoffschicht

New aspects regarding sputter‐depositing dense coatings, in particular a solid lubricant of practical interest Using MoS₂‐based solid lubricant films as an example, this paper focuses on approaches to preventing sputter‐deposited films from attaining columnar microstructures. This is how it becomes possible to deposit tribological coatings that are characterised by a high durability. As a result of scanning electron microscopy on microstructures, texture measurements by means of XRD, and surface analysis, focusing on sputter‐deposited MoS₂ films, a concept of how to develop thick and dense MoS₂‐based solid lubricant films was generated. At an early stage of film growth a dense and flawless microstructure forms. In order to make the favourable properties of these underlayers available for tribological applications, metallic intralayers were introduced, by means of which the MoS₂ film growth was to be repeatedly interrupted.     

Granular L10 FePt nanocomposite films fabricated by rapid thermal annealing

Granular (FePt)_100−x-(NiO)_x nanocomposite thin films with x = 0 − 42 vol% were fabricated on a natural-oxidized Si(100) substrate. It is found that both the coercivity and FePt domain size decrease with increasing NiO content for the (FePt)_100−x-(NiO)_x films. When the FePt-NiO composite film with NiO content of 10.4 vol% is post-annealed at 750 °C with a high heating ramp rate of 100 °C/s, the in-plane coercivity (H_c//) and perpendicular coercivity (H_c⊥) of the FePt films are 513 and 430 kA/m, respectively. On the other hand, we used conductive atomic force microscope (CAFM) to confirm that the NiO compound is distributed at boundary of FePt particles that will constrain the domain size of FePt and decrease the exchange coupling interactions between FePt magnetic particles.     

Magnetic‐Induced‐Piezopotential Gated MoS2 Field‐Effect Transistor at Room Temperature

Utilizing magnetic field directly modulating/turning the charge carrier transport behavior of field‐effect transistor (FET) at ambient conditions is an enormous challenge in the field of micro–nanoelectronics. Here, a new type of magnetic‐induced‐piezopotential gated field‐effect‐transistor (MIPG‐FET) base on laminate composites is proposed, which consists of Terfenol‐D, a ferroelectric single crystal (PMNPT), and MoS₂ flake. When applying an external magnetic field to the MIPG‐FET, the piezopotential of PMNPT triggered by magnetostriction of the Terfenol‐D can serve as the gate voltage to effectively modulate/control the carrier transport process and the corresponding drain current at room temperature. Considering the two polarization states of PMNPT, the drain current is diminished from 9.56 to 2.9 µA in the P_up state under a magnetic field of 33 mT, and increases from 1.41 to 4.93 µA in the P_down state under a magnetic field of 42 mT and at a drain voltage of 3 V. The current on/off ratios in these states are 330% and 432%, respectively. This work provides a novel noncontact coupling method among magnetism, piezoelectricity, and semiconductor properties, which may have extremely important applications in magnetic sensors, memory and logic devices, micro‐electromechanical systems, and human–machine interfacing.     

Superconducting properties of CVD tantalum films

Tantalum films on A1₂O₃ substrate are obtained by CVD of TaCl₅ at atmospheric pressure. The critical temperature of the transition to the superconducting state, the critical magnetic field and the volt-ampère characteristics of the films are investigated. Significant increase in the critical magnetic field and the typical behaviour of type II superconductors was established.     

Solar absorption and thermal emission properties of multiwall carbon nanotube/nickel oxide nanocomposite thin films synthesized by sol–gel process

Multiwall carbon nanotubes (MWCNTs)/nickel oxide (NiO) nanocomposites were successfully prepared by a sol–gel process and coated on an aluminium substrate. The MWCNTs were chemically functionalized and then added into NiO alcogels, and magnetic stirred for homogeneous dispersion into the NiO matrix solution. The morphology of the resulting nanocomposite thin films showed that the MWCNTs were embedded in the NiO nano-particle matrix, while HRTEM confirmed that the MWCNTs were surrounded by the NiO nano-particles. Raman spectra for functionalized MWCNTs displayed a red shift from the pristine MWCNTs suggesting successful purification/functionalization. The spectrum for the MWCNTs/NiO nanocomposite indicated the presence of both the TO and LO phonons of NiO, and the D and G bands of the MWCNTs. Red and blue shifts of the NiO phonons and the MWCNT phonons suggested that the vibrational properties of both materials were changed to form new nanocomposite vibrational properties. Despite unoptimized layer thickness and composition, the solar absorptance of the functionalized MWCNTs/NiO nanocomposite films was 0.84 (for a single layer). The thermal emittance at 100 °C was approximately 0.2. These results suggest that MWCNTs/NiO nanocomposite materials are suitable for solar thermal applications.