Pseudoequilibrium between Etching and Selective Grain Growth: Chemical Conversion of a Randomly Oriented Au Film into a (111)-Oriented Ultrathin Au Film.

Metal thin films with a specific orientation play vital roles in electronics, catalysts, and epitaxial templates. Although oriented metal films have been produced in the recent years, ultrathin oriented metal films (<10 nm) have not been achieved owing to the interfacial instability of the ultrathin films during the thermal annealing process. This study investigates chemical conversion of randomly oriented multigrain Au ultrathin films into (111)-oriented Au ultrathin films. A novel chemical process, termed pseudoequilibrium of etching and selective grain growth, is presented for the chemical conversion by using a quaternary ammonium halide. The reaction variables (reaction time, reaction temperature, species of halide ions) for the chemical conversion process are systematically investigated. This study reveals the in-plane rotational degeneracy in the Au(111) thin film epitaxially grown on a Si(111) substrate. The chemical process can be applied to a broad range of thicknesses from 9 to 100 nm.

Ligand-induced evolution of intrinsic fluorescence and catalytic activity from cobalt ferrite nanoparticles.

To develop CoFe(2)O(4) as magneto-fluorescent nanoparticles (NPs) for biomedical applications, it would be advantageous to identify any intrinsic fluorescence of this important magnetic material by simply adjusting the surface chemistry of the NPs themselves. Herein, we demonstrate that intrinsic multicolor fluorescence, covering the whole visible region, can be induced by facile functionalization of CoFe(2)O(4) NPs with Na-tartrate. Moreover, the functionalized CoFe(2)O(4) NPs also show unprecedented catalytic efficiency in the degradation of both biologically and environmentally harmful dyes, pioneering the potential application of these NPs in therapeutics and wastewater treatment. Detailed investigation through various spectroscopic tools unveils the story behind the emergence of this unique optical property of CoFe(2)O(4) NPs upon functionalization with tartrate ligands. We believe our developed multifunctional CoFe(2)O(4) NPs hold great promise for advanced biomedical and technological applications.

Wafer-scale synthesis of two-dimensional ultrathin films.

Two-dimensional (2D) materials, consisting of atomically thin layered crystals, have attracted tremendous interest due to their outstanding intrinsic properties and diverse applications in electronics, optoelectronics, and catalysis. The large-scale growth of high-quality ultrathin 2D films and their utilization in the facile fabrication of devices, easily adoptable in industrial applications, have been extensively sought after during the last decade; however, it remains a challenge to achieve these goals. Herein, we introduce three key concepts: (i) the microwave assisted quick (∼1 min) synthesis of wafer-scale (6-inch) anisotropic conducting ultrathin (∼1 nm) amorphous carbon and 2D semiconducting metal chalcogenide atomically thin films, (ii) a polymer-assisted deposition process for the synthesis of wafer-scale (6-inch) 2D metal chalcogenide and pyrolyzed carbon thin films, and (iii) the surface diffusion and epitaxial self-planarization induced synthesis of wafer-scale (2-inch) single crystal 2D binary and large-grain 2D ferromagnetic ternary metal chalcogenide thin films. The proposed synthesis concepts can pave a new way for the manufacture of wafer-scale high quality 2D ultrathin films and their utilization in the facile fabrication of devices.

Wafer scale growth of single crystal two-dimensional van der Waals materials.

Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described.

Large-Area Epitaxial Film Growth of van der Waals Ferromagnetic Ternary Chalcogenides.

Following the first experimental realization of intrinsic ferromagnetism in 2D van der Waals (vdW) crystals, several ternary metal chalcogenides with unprecedented long-range ferromagnetic order have been explored. However, the synthesis of large-area 2D ternary metal chalcogenide thin films is a great challenge, and a generalized synthesis has not been demonstrated yet. Here, a quick and scalable synthesis of epitaxially aligned ferromagnetic ternary metal chalcogenide thin films (Cr2 Ge2 Te6 , Cr2 Si2 Te6 , Mn3 Si2 Te6 ) is reported. The synthesis is based on the flux-controlled surface diffusion of Te on metal (Cr, Mn)-deposited wafer (Ge, Si) substrates. Magnetic anisotropy study of the epitaxial ternary thin films reveals the intrinsic magnetic easy axis; out-of-plane direction for Cr2 Ge2 Te6 and Cr2 Si2 Te6 , and in-plane direction for Mn3 Si2 Te6 . In addition to the synthesis, this work creates an opportunity for transfer-free device fabrication for realizing magnetoelectronics based on the electrical control of both charge and spin degrees of freedom in 2D ferromagnetic semiconductors.

Electroactive 1T-MoS2 Fluoroelastomer Ink for Intrinsically Stretchable Solid-State In-Plane Supercapacitors.

Full advantage of stretchable electronic devices can be taken when utilizing an intrinsically stretchable power source. High-performance stretchable supercapacitors with a simple structure and solid-state operation are good power sources for stretchable electronics. This study suggests a new type of intrinsically stretchable, printable, electroactive ink consisting of 1T-MoS2 and a fluoroelastomer (FE). The active material (1T-MoS2/FE) is made by fluorinating the metallic-phase MoS2 (1T-MoS2) nanosheets with the FE under high-power ultrasonication. The MoS2 in the 1T-MoS2/FE has unconventional crystal structures in which the stable cubic (1T) and distorted 2H structures were mixed. The printed line of the 1T-MoS2/FE on the porous stretchable Au collector electrodes is intrinsically stretchable at more than ε = 50% and has good specific capacitance (28 mF cm-2 at 0.2 mA cm-2) and energy density (3.15 mWh cm-3). The in-plane all-solid-state stretchable supercapacitor is stretchable at ε = 40% and retains its relative capacity (C/Co) by 80%. This printable device platform potentially opens up the in-plane fabrication of stretchable micro-supercapacitor devices for wearable electronic applications.

Surface Diffusion and Epitaxial Self-Planarization for Wafer-Scale Single-Grain Metal Chalcogenide Thin Films.

Although wafer-scale single-grain thin films of 2D metal chalcogenides (MCs) have been extensively sought after during the last decade, the grain size of the MC thin films is still limited in the sub-millimeter scale. A general strategy of synthesizing wafer-scale single-grain MC thin films by using commercial wafers (Si, Ge, GaAs) both as metal source and epitaxial collimator is presented. A new mechanism of single-grain thin-film formation, surface diffusion, and epitaxial self-planarization is proposed, where chalcogen elements migrate preferentially along substrate surface and the epitaxial crystal domains flow to form an atomically smooth thin film. Through synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy, the formation of single-grain Si2 Te3 , GeTe, GeSe, and GaTe thin films on (111) Si, Ge, and (100) GaAs is verified. The Si2 Te3 thin film is used to achieve transfer-free fabrication of a high-performance bipolar memristive electrical-switching device.

Highly Deformable Transparent Au Film Electrodes and Their Uses in Deformable Displays.

With emerging interest in foldable and stretchable displays, the need to develop transparent deformable electrode and interconnection is increasing. Even though metal films have been standard electrodes in conventional electronic devices due to their high conductivity and well-established process, they have never been used for transparent deformable electrodes. We present highly conductive transparent deformable Au film electrodes and use them to fabricate a foldable perovskite light-emitting diode (PeLED) and a biaxially stretchable alternating current electroluminescence (ACEL) display. We exhibit the formation of an ultrathin (6 nm) continuous Au film on an anisotropic conductive ultrathin film (ACUF) of amorphous carbon. The ultrathin Au film was first formed on an ACUF-coated Si wafer (4 in. scale) through metal evaporation and transferred to the polymer substrates by a simple and effective water-assisted delamination process. Then, a hybrid electrode (ACUF/ACUF/Au) was produced as the transparent deformable electrode. Complicated interconnections could be created by metal deposition through a mask. The electrical conductance of the hybrid electrode was not affected by the crack formation in the Au film during electrode folding, crumpling, and stretching. We reveal the reason why the hybrid electrode can maintain such excellent electrical stability under deformation.

Fabrication of Foldable Metal Interconnections by Hybridizing with Amorphous Carbon Ultrathin Anisotropic Conductive Film.

With the advent of foldable electronics, it is necessary to develop a technology ensuring foldability when the circuit lines are placed on the topmost substrate rather than in the neutral plane used in the present industry. Considering the potential technological impacts, conversion of the conventional printed circuit boards to foldable ones is most desirable to achieve the topmost circuitry. This study realizes this unconventional conversion concept by coating an ultrathin anisotropic conductive film (UACF) on a printed metal circuit board. This study presents rapid large-area synthesis of hydrogenated amorphous carbon (a-C:H) thin films and their use as the UACF. Since the synthesized a-C:H thin film has electrical transparency, the metal/a-C:H hybrid board reflects the complexity of the underlying metal circuit board. The a-C:H thin film electrically connects the cracked area of the metal line; thus, the hybrid circuit board is foldable without resistance change during repeated folding cycles. The metal/UACF hybrid circuit board can be applied to the fabrication of various foldable electronic devices.

Synthesis of 2D Metal Chalcogenide Thin Films through the Process Involving Solution-Phase Deposition.

2D metal chalcogenide thin films have recently attracted considerable attention owing to their unique physicochemical properties and great potential in a variety of applications. Synthesis of large-area 2D metal chalcogenide thin films in controllable ways remains a key challenge in this research field. Recently, the solution-based synthesis of 2D metal chalcogenide thin films has emerged as an alternative approach to vacuum-based synthesis because it is relatively simple and easy to scale up for high-throughput production. In addition, solution-based thin films open new opportunities that cannot be achieved from vacuum-based thin films. Here, a comprehensive summary regarding the basic structures and properties of different types of 2D metal chalcogenides, the mechanistic details of the chemical reactions in the synthesis of the metal chalcogenide thin films, recent successes in the synthesis by different reaction approaches, and the applications and potential uses is provided. In the last perspective section, the technical challenges to be overcome and the future research directions in the solution-based synthesis of 2D metal chalcogenides are discussed.

Direct immobilization of antibodies on Zn-doped Fe3O4 nanoclusters for detection of pathogenic bacteria.

Zinc-doped magnetic nanoclusters (Zn-MNCs) were synthesized and used to detect pathogenic bacteria in milk. Hydrothermally synthesized Zn-MNCs exhibited stronger magnetic properties than pure MNCs, which facilitated the magnetic separation from the sample using a permanent magnet. The presence of accessible Zn sites allows the direct immobilization of half-fragmented antibodies over Zn-MNCs through strong ZnS bonds and prevents the tedious multiple steps of molecular functionalization or coating with costly noble metals prior to conjugation with an antibody. After the capture and magnetic separation of Salmonella in milk using the antibody-functionalized Zn-MNCs, the concentration of bacteria was determined with a portable ATP luminometer and the detection limit was found to be 10 CFU/mL.

Texture- and deformability-based surface recognition by tactile image analysis.

Deformability and texture are two unique object characteristics which are essential for appropriate surface recognition by tactile exploration. Tactile sensation is required to be incorporated in artificial arms for rehabilitative and other human-computer interface applications to achieve efficient and human-like manoeuvring. To accomplish the same, surface recognition by tactile data analysis is one of the prerequisites. The aim of this work is to develop effective technique for identification of various surfaces based on deformability and texture by analysing tactile images which are obtained during dynamic exploration of the item by artificial arms whose gripper is fitted with tactile sensors. Tactile data have been acquired, while human beings as well as a robot hand fitted with tactile sensors explored the objects. The tactile images are pre-processed, and relevant features are extracted from the tactile images. These features are provided as input to the variants of support vector machine (SVM), linear discriminant analysis and k-nearest neighbour (kNN) for classification. Based on deformability, six household surfaces are recognized from their corresponding tactile images. Moreover, based on texture five surfaces of daily use are classified. The method adopted in the former two cases has also been applied for deformability- and texture-based recognition of four biomembranes, i.e. membranes prepared from biomaterials which can be used for various applications such as drug delivery and implants. Linear SVM performed best for recognizing surface deformability with an accuracy of 83 % in 82.60 ms, whereas kNN classifier recognizes surfaces of daily use having different textures with an accuracy of 89 % in 54.25 ms and SVM with radial basis function kernel recognizes biomembranes with an accuracy of 78 % in 53.35 ms. The classifiers are observed to generalize well on the unseen test datasets with very high performance to achieve efficient material recognition based on its deformability and texture.

Vibrotactile feedback for conveying object shape information as perceived by artificial sensing of robotic arm.

This work is a preliminary study towards developing an alternative communication channel for conveying shape information to aid in recognition of items when tactile perception is hindered. Tactile data, acquired during object exploration by sensor fitted robot arm, are processed to recognize four basic geometric shapes. Patterns representing each shape, classified from tactile data, are generated using micro-controller-driven vibration motors which vibrotactually stimulate users to convey the particular shape information. These motors are attached on the subject's arm and their psychological (verbal) responses are recorded to assess the competence of the system to convey shape information to the user in form of vibrotactile stimulations. Object shapes are classified from tactile data with an average accuracy of 95.21 %. Three successive sessions of shape recognition from vibrotactile pattern depicted learning of the stimulus from subjects' psychological response which increased from 75 to 95 %. This observation substantiates the learning of vibrotactile stimulation in user over the sessions which in turn increase the system efficacy. The tactile sensing module and vibrotactile pattern generating module are integrated to complete the system whose operation is analysed in real-time. Thus, the work demonstrates a successful implementation of the complete schema of artificial tactile sensing system for object-shape recognition through vibrotactile stimulations.

Surface modification of MnFe2O4 nanoparticles to impart intrinsic multiple fluorescence and novel photocatalytic properties.

The MnFe2O4 nanoparticle has been among the most frequently chosen systems due to its diverse applications in the fields ranging from medical diagnostics to magnetic hyperthermia and site-specific drug delivery. Although numerous efforts have been directed in the synthesis of monodisperse MnFe2O4 nanocrystals, unfortunately, however, studies regarding the tuning of surface property of the synthesized nanocrystals through functionalization are sparse in the existing literature. Herein, we demonstrate the emergence of intrinsic multicolor fluorescence in MnFe2O4 nanoparticles from blue, cyan, and green to red, upon functionalization and further surface modification with a small organic ligand, Na-tartrate. Moreover, we have found an unprecedented photocatalytic property of the functionalized MnFe2O4 nanoparticles in the degradation of a model water contaminant. Detailed characterization through XRD, TEM, and FTIR confirms the very small size and functionalization of MnFe2O4 nanoparticles with a biocompatible ligand. Proper investigation through UV-visible absorption, steady-state and time-resolved photoluminescence study reveals that ligand-to-metal charge-transfer transition from the tartrate ligand to the lowest unoccupied energy level of Mn(2+/3+)or Fe(3+) of the NPs and Jahn-Teller distorted d-d transitions centered over Mn(3+) ions in the NPs play the key role behind the generation of multiple fluorescence from the ligand-functionalized MnFe2O4 nanoparticles. VSM measurements indicates that the superparamagnetic nature of MnFe2O4 nanoparticles remains unchanged even after surface modification. We believe that the developed superparamagnetic, multicolor fluorescent MnFe2O4 nanopaticles would open up new opportunities as well as enhance their beneficial activities toward diverse applications.