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Alloying in monolayers enables bandgap tuning in twodimensions. On page 2648, L. Xie, J. Zhang, and co-workers demonstrate that by direct evaporation of two end materials (MoS₂ and MoSe₂) and deposition at low temperatures, large-area 2D MoS_2(1−x)Se_2x monolayers are obtained. By changing the S/Se composition, the bandgap of MoS_2(1−x)Se_2x monolayers can be continuously tuned.

Soft X-ray spectroscopy (SXS) techniques such as photoelectron spectroscopy, soft X-ray absorption spectroscopy and X-ray emission spectroscopy are efficient and direct tools to probe electronic structures of materials. Traditionally, these surface sensitive soft X-ray techniques that detect electrons or photons require high vacuum to operate. Many recent in situ instrument developments of these techniques have overcome this vacuum barrier. One can now study many materials and model devices under near ambient, semi-realistic, and operando conditions. Further developments of integrating the realistic sample environments with efficient and high resolution detection methods, particularly at the high brightness synchrotron light sources, are making SXS an important tool for the energy research community. In this progress report, we briefly describe the basic concept of several SXS techniques and discuss recent development of SXS instruments. We then present several recent studies, mostly in situ SXS experiments, on energy materials and devices. Using these studies, we would like to highlight that the integration of SXS and in situ environments can provide in-depth insight of material's functionality and help researchers in new energy material developments. The remaining challenges and critical research directions are discussed at the end.

Recent instrumentation developments have advanced soft X-ray spectroscopic tools for studying real-world samples. Both photon-in-electron-out and photon-in-photon-out spectroscopy can be perfor­med under semi-realistic, and operando conditions through high-efficiency and high-resolution detection systems at high-brightness synchrotron light sources. This Progress Report focuses on many recent advancements on in situ soft X-ray spectroscopic tools and their applications in developing energy materials.

Wetting-transparent graphene films grown in situ by chemical vapor deposition on hydrophobic (roughened) copper surfaces offer excellent resistance to copper corrosion while maintaining the intrinsic hydrophobicity of the surface, enabling superior performance for water-harvesting applications.

A composite transparent composite electrode using silver nanowire (AgNW) with sol–gel derived ZnO and AZO is proposed by J. Moon and co-workers with careful analysis of the electrical conduction behavior using conductive-atomic force microscopy. On page 2462, low temperature (≈200 °C) processes are achieved by a combustion reaction based sol-gel method, demonstrating a comparable performance to the sputtered ITO based device.

Ab initio calculations show that a cleanly cleaved nonpolar surface of considered nonmagnetic insulating metal oxides always has a band gap. If the bulk valence band edge has mainly oxygen 2p character while the bulk conduction band edge has mainly metal d character, then there is no in-the-band-gap surface state. A simple procedure to identify the polarity of a given arbitrary surface is presented.

Si-Fe hollow nanoparticles are synthesized facilely using an ambient hetero­geneous plasma for the first time for both biomedical and energy storage applications. This provides new perspectives and useful information for the design of efficient, low-cost, environmentally-friendly nanomaterials for biomedical (drug/gene carriers) and energy storage (anode materials in lithium ion batteries) applications.

This work demonstrates the growth of crystalline SrTiO₃ (STO) directly on germanium via a chemical method. After thermal deoxidation, the Ge substrate is transferred in vacuo to the deposition chamber where a thin film of STO (2 nm) is deposited by atomic layer deposition (ALD) at 225 °C. Following post-deposition annealing at 650 °C for 5 min, the STO film becomes crystalline with epitaxial registry to the underlying Ge (001) substrate. Thicker STO films (up to 15 nm) are then grown on the crystalline STO seed layer. The crystalline structure and orientation are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and transmission electron microscopy. Electrical measurements of a 15-nm thick epitaxial STO film on Ge show a large dielectric constant (k ≈ 90), but relatively high leakage current of ≈10 A/cm² for an applied field of 0.7 MV/cm. To suppress the leakage current, an aluminum precursor is cycled during ALD growth to grow crystalline Al-doped STO (SrTi_1-x­Al_xO_3-δ) films. With sufficient Al doping (≈13%), the leakage current decreases by two orders of magnitude for an 8-nm thick film. The current work demonstrates the potential of ALD-grown crystalline oxides to be explored for advanced electronic applications, including high-mobility Ge-based transistors.

Crystalline SrTiO₃ is grown directly on Ge (001) via a chemical deposition method. This growth technique has wide reaching potential for the monolithic integration of many functional perovskite oxides with semiconductors. The current work exhibits the promise for ALD-grown crystalline oxides for advanced electronic applications, especially high-mobility Ge-based transistors.

The microstructure of Bi₂Se₃ topological-insulator thin films grown by molecular beam epitaxy on InP(111)A and InP(111)B substrates that have different surface roughnesses has been studied in detail using X-ray diffraction, X-ray reflectivity, atomic force microscopy and probe-corrected scanning transmission electron microscopy. The use of a rough Fe-doped InP(111)B substrate results in complete suppression of twin formation in the Bi₂Se₃ thin films and a perfect interface between the films and their substrates. The only type of structural defect that persists in the twin-free films is an antiphase domain boundary, which is associated with variations in substrate height. We also show that the substrate surface termination influences which family of twin domains dominates.

Twin formation is a common defect in Bi₂Se₃ topological-insulator thin films and can influence their transport properties. In this work the growth of Bi₂Se₃ layers without twin domains on a rough Fe-doped InP(111)B substrate is reported and a detailed description of the mechanism of twin suppression on the nanoscale is provided.

The white stripes of the pyjama squid (Sepioloidea lineolata) contain multilayer reflectors with an unordered plate arrangement, enabling reflectance of diffuse white light over a range of viewing angles. Ultrastructural analysis and mathematical modeling are employed to elucidate functional mechanisms of diffuse reflectance. This optical system may provide a bio-inspired template for low-energy, reflectance-based synthetic displays.

Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time.

A facile one-step printing process by 3D micro-extrusion affording binder-free thermally reduced graphene oxide (TRGO) based electrochemical capacitors (ECs) that display high-rate performance is presented. Key intermediates are binder-free TRGO dispersion printing inks with concentrations up to 15 g L⁻¹. This versatile printing technique enables easy fabrication of EC electrodes, useful in both aqueous and non-aqueous electrolyte systems. The as-prepared TRGO material with high specific surface area (SSA) of 593 m² g⁻¹ and good electrical conductivity of ≈16 S cm⁻¹ exhibits impressive charge storage performances. At 100 and 120 Hz, ECs fabricated with TRGO show time constants of 2.5 ms and 2.3 ms respectively. Very high capacitance values are derived at both frequencies ranging from 3.55 mF cm⁻² to 1.76 mF cm⁻². Additionally, these TRGO electrodes can be charged and discharged at very high voltage scan rates up to 15 V s⁻¹ yielding 4 F cm⁻³ with 50% capacitance retention. Electrochemical performance of TRGO electrodes in electrolyte containing tetraethyl ammonium tetrafluoroborate and acetonitrile (TEABF4-ACN) yields high energy density of 4.43 mWh cm⁻³ and power density up to 42.74 kW cm⁻³, which is very promising for AC line filtering application and could potentially substitute state of the art electrolytic capacitor technology.

3D micro extrusion of binder-free graphene ink enables the printing of high rate performance electrochemical capacitor electrodes. These printed electrodes can be charged and discharged at very high voltage scan rates up to 15 V s⁻¹ yielding 4 F cm⁻³, which is very promising for AC line filtering application and could potentially replace the state of the art electrolytic capacitor technology.

Novel light emitting electrochemical cells (LECs) are fabricated using CdSe-CdS (core-shell) quantum dots (QDs) of tuned size and emission blended with polyvinylcarbazole (PVK) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆). The performances of cells constructed using sequential device layers of indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), the QD/PVK/IL active layer, and Al are evaluated. Only color saturated electroluminescence from the QDs is observed, without any other emissions from the polymer host or the electrolyte. Blue, green, and red QD-LECs are prepared. The maximum brightness (≈1000 cd m^-2) and current efficiency (1.9 cd A^-1) are comparable to polymer LECs and multilayer QD-LEDs. White-light QD-LECs with Commission Internationale d'Eclairage (CIE) coordinates (0.33, 0.33) are prepared by tuning the mass ratio of R:G:B QDs in the active layer and voltage applied. Transparent QD-LECs fabricated using transparent silver nanowire (AgNW) composites as the cathode yield an average transmittance greater than 88% over the visible range. Flexible devices are demonstrated by replacing the glass substrates with polyethylene terephthalate (PET).

Quantum dot based light emitting electrochemical cells are prepared by blending of quantum dots, polyvinylcarbazole and an ionic liquid. Saturated red, orange, green, blue, and white electroluminescences are demonstrated and the performance of these simple, single-layered devices is comparable to that of multilayer LED devices. Transparent and flexible devices are also demonstrated and enable a broad range of application.

A copper(II)-oxide-based exhaust catalyst exhibits better activity than Pt- and Rh-nanoparticle catalysts in NO remediation at 175 °C. Following theoretical design, the CuO catalyst is rationally prepared; CuO nanoplates bearing a maximized amount of the active {001} facet are arranged in interleaved layers. A field test using a commercial gasoline engine demonstrates the ability of the catalyst to remove NO from the exhaust of small vehicles.

M13 bacteriophages act as versatile scaffolds capable of organizing single-walled carbon nanotubes and fabricating three-dimensional conducting nanocomposites. The morphological, electrical, and electrochemical properties of the nanocomposites are presented, as well as its ability to disperse and utilize single-walled carbon nanotubes effectively.

Nanoporous microparticles are produced in a single step based on hydrogen bonding between a neutral polymer and tannic acid. These particles are stable in physiological medium, are non-toxic to in vitro cultured cells, and can efficiently encapsulate proteins. In vitro and in vivo experiments show that these porous hydrogen bonded microparticles are able to induce antigen-specific cellular and humoral immune responses against encapsulated vaccine antigens. Considering the easy and low cost manufacturing of this dry powder formulation from approved readily available components, it is anticipated that this technology holds great promise for the formulation of vaccines for developing countries or for pandemic vaccines where long term storage under refrigerated conditions is a major issue. Additionally, due to the versatility of the approach facilitates straightforward co-encapsulation of a wide variety of additional components to further modulate the immune response.

Tannic acid and poly(vinylpyrrolidone) form nanoporous microparticles in a single economically attractive assembly step involving atomization and hydrogen bonding. Vaccine antigen can be entrapped within the network of these particles and can still be internalized and presented by dendritic cells to T cells, inducing antigen-specific immune responses in vitro and in vivo.

Graphene papers have a potential to overcome the gap from nanoscale graphene to real macroscale applications of graphene. A unique process for preparation of highly conductive graphene thin paper by means of Ar⁺ ion irradiation of graphene oxide (GO) papers, with carbon/oxygen ratio reduced to 100:1, is presented. The composition of graphene paper in terms of carbon/oxygen ratio and in terms of types of individual oxygen-containing groups is monitored throughout the process. Angle-resolved high resolution X-ray photoelectron spectroscopy helps to investigate the depth profile of carbon and oxygen within reduced GO paper. C/O ratios over 100 on the surface and 40 in bulk material are observed. In order to bring insight to the processes of oxygen removal from GO paper by low energy Ar⁺ ion bombardment, the gases released during the irradiation are analyzed by mass spectroscopy. It is proven that Ar⁺ ion beam can be applied as a technique for fabrication of highly reduced graphene papers with high conductivities. Such highly conductive graphene papers have great potential to be used in application for construction of microelectronic and sensor devices.

Graphene papers are prepared by irradiation of graphene oxide papers with Ar⁺ ion beam. Surface of the paper is chemically reduced and C/O ratios over 100 are achieved. The resulting surface is highly conductive and electrical Ohmic behavior is observed. Gases evolved during irradiation process are also analyzed.

Organic nanomaterials have drawn great interest for their potential applications in high-speed miniaturized photonic integration due to their high photoluminescence quantum efficiency, structural processability, ultrafast photoresponse, and excellent property engineering. Based on the rational design on morphological and componential levels, a series of organic nanomaterials have been controllably synthesized in recent years, and their excitonic/photonic behaviors has been fine-tuned to steer the light flow for specific optical applications. This review presents a comprehensive summary of recent breakthroughs in the controlled synthesis of organic nanomaterials with specific structures and compositions, whose tunable photonic properties would provide a novel platform for multifunctional applications. First, we give a general overview of the tailored construction of novel nanostructures with various photonic properties. Then, we summarize the design and controllable synthesis of composite materials for the modulation of their functionalities. Subsequently, special emphasis is put on the fabrication of complex nanostructures towards wide applications in isolated photonic devices. We conclude with our personal viewpoints on the development directions in the novel design and controllable construction of organic nanomaterials for future applications in highly integrated photonic devices and chips.

Recent advances in the controlled synthesis of organic nanomaterials with desired structure and composition, for application in integrated photonic circuits, are discussed.

Superlattice@GO heterostructures: a simple method for the preparation of monolayer superlattices containing a Wells–Dawson-type polyoxometalate (POM) is developed. POM-based building blocks are assembled on the surface of graphene oxide (GO) to form a superlattice@GO structure that shows excellent performance in hydrogen peroxide sensing and catalysis of water photo-oxidation.

Gravure printing of graphene is demonstrated for the rapid production of conductive patterns on flexible substrates. Development of suitable inks and printing parameters enables the fabrication of patterns with a resolution down to 30 μm. A mild annealing step yields conductive lines with high reliability and uniformity, providing an efficient method for the integration of graphene into large-area printed and flexible electronics.

Highly uniform, ultrathin, layer-by-layer heteroatom (N, B) co-doped graphene films are fabricated for high-performance on-chip planar micro-supercapacitors with an ultrahigh volumetric capacitance of ∼488 F cm⁻³ and excellent rate capability due to the synergistic effect of nitrogen and boron co-doping.

Structural distortions in the oxygen octahedral network in transition-metal oxides play crucial roles in yielding a broad spectrum of functional properties, and precise control of such distortions is a key for developing future oxide-based electronics. Here, it is shown that the displacement of apical oxygen atom shared between the octahedra at the heterointerface is a determining parameter for these distortions and consequently for control of structural and electronic phases of a strained oxide film. The present analysis by complementary annular dark- and bright-field imaging in aberration-corrected scanning transmission electron microscopy reveals that structural phase differences in strained monoclinic and tetragonal SrRuO₃ films grown on GdScO₃ substrates result from relaxation of the octahedral tilt, associated with changes in the in-plane displacement of the apical oxygen atom at the heterointerface. It is further demonstrated that octahedral distortions and magnetrotransport properties of the SrRuO₃ films can be controlled by interface engineering of the oxygen displacement. This provides a further degree of freedom for manipulating structural and electronic properties in strained films, allowing the design of novel oxide-based heterostructures.

The manipulation of the displacement of the apical oxygen atom at the hetero­interface is demonstrated as a tool to control the structural distortions that determine functional properties of transition-metal oxide thin films. High-resolution ABF-STEM imaging reveals that the interfacial octahedral connection angle is characterized by the picometer-order displacement of apical the oxygen atom. The findings provide a further degree of freedom for designing novel oxide-based heterostructures.

Stable graphene oxide monoliths (GOMs) have been fabricated by exploiting epoxy groups on the surface of graphene oxide (GO) in a ring opening reaction with amine groups of poly(oxypropylene) diamines (D₄₀₀). This method can rapidly form covalently bonded GOM with D₄₀₀ within 60 s. FTIR and XPS analyses confirm the formation of covalent C-N bonds. Investigation of the GOM formation mechanism reveals that the interaction of GO with a diamine cross-linker can result in 3 different GO assemblies depending on the ratio of D₄₀₀ to GO, which have been proven both by experiment and molecular dynamics calculations. Moreover, XRD results indicate that the interspacial distance between GO sheets can be tuned by varying the diamine chain length and concentration. We demonstrate that the resulting GOM can be moulded into various shapes and behaves like an elastic hydrogel. The fabricated GOM is non-cyctotoxic to L929 cell lines indicating a potential for biomedical applications. It could also be readily converted to graphene monolith upon thermal treatment. This new rapid and facile method to prepare covalently cross-linked GOM may open the door to the synthesis and application of next generation multifunctional 3D graphene structures.

An ultrafast cross-linking method for the fabrication of graphene oxide monoliths (GOM) with poly(oxypropylene) diamines as a cross-linker is reported. This method can form self-assembled 3D GO structures with controllable interlayer spacing. The covalently bonded GOM structure demonstrates high cell viability, could be molded into various shapes, and when hydrated behaves like an elastic hydrogel.