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Showing papers on "Amorphous solid published in 2015"


Journal ArticleDOI
TL;DR: The structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques is reported, which combines the stability advantages of a controlled, stable crystalline material with high catalytic activity thanks to the structural flexibility of its active amorphous oxides.
Abstract: Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co(3+/4+) ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.

623 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied how changes in the structural features of poly(3-hexylthiophene (P3HT) polymers affect exciton dissociation processes and concluded that excitons in disordered regions between crystalline and amorphous phases dissociate extrinsically with yield and spatial distribution.
Abstract: The optoelectronic properties of macromolecular semiconductors depend fundamentally on their solid-state microstructure and phase morphology. Hence, it is of central importance to manipulate—from the outset—the molecular arrangement and packing of this special class of polymers from the nano- to the micrometer scale when they are integrated in thin film devices such as photovoltaic cells, transistors or light-emitting diodes, for example. One effective strategy for this purpose is to vary their molecular weight. The reason for this is that materials of different weight-average molecular weight (Mw) lead to different microstructures. Polymers of low Mw form unconnected, extended-chain crystals because of their non-entangled nature. As a result, a polycrystalline, one-phase morphology is obtained. In contrast, high-Mw materials, in which average chain lengths are longer than the length between entanglements, form two-phase morphologies comprised of crystalline moieties embedded in largely un-ordered (amorphous) regions. Here, we discuss how changes in these structural features affect exciton dissociation processes. We utilise neat regioregular poly(3-hexylthiophene) (P3HT) of varying Mw as a model system and apply time-resolved photoluminescence (PL) spectroscopy to probe the electronic landscape in a range of P3HT thin-film architectures. We find that at 10 K, PL originating from recombination of long-lived charge pairs decays over microsecond timescales. Tellingly, both the amplitude and decay-rate distribution depend strongly on Mw. In films with dominant one-phase, chain-extended microstructures, the delayed PL is suppressed as a result of a diminished yield of photoinduced charges. Its decay is significantly slower than in two-phase microstructures. We therefore conclude that excitons in disordered regions between crystalline and amorphous phases dissociate extrinsically with yield and spatial distribution that depend intimately upon microstructure, in agreement with previous work [Paquin et al., Phys. Rev. Lett., 2011, 106, 197401]. We note, however, that independent of Mw, the delayed-PL lineshape due to charge recombination is representative of that in low-Mw microstructures. We thus hypothesize that charge recombination at these low temperatures—and likely also charge generation—occur in torsionally disordered chains forming more strongly coupled photophysical aggregates than those in the steady-state ensemble, producing a delayed PL lineshape reminiscent of that in paraffinic morphologies at steady state.

580 citations


Journal ArticleDOI
TL;DR: In this article, a cubic framework of amorphous carbon and uniformly dispersed core-shell Fe@graphitic carbon nanoparticles is used to construct a high-performance microwave absorber.
Abstract: Composites of magnetic metal nanoparticles and carbon materials are highly desirable for high-performance microwave absorbers due to their compatible dielectric loss and magnetic loss abilities. In this article, novel nanocomposites, Fe/C nanocubes, have been successfully prepared through an in situ route from a metal–organic framework, Prussian blue, by controlled high-temperature pyrolysis. The resultant nanocubes are actually composed of a cubic framework of amorphous carbon and uniformly dispersed core–shell Fe@graphitic carbon nanoparticles. Within the studied pyrolysis temperature range (600–700 °C), the porous structure, iron content, magnetic properties, and graphitization degree of the Fe/C nanocubes can be well modulated. Particularly, the improved carbon graphitization degree, both in amorphous frameworks and graphitic shells, results in enhanced complex permittivity and dielectric loss properties. The homogeneous chemical composition and microstructure stimulate the formation of multiple dielectric resonances by regularizing various polarizations. The synergistic effect of dielectric loss, magnetic loss, matched impedance, and dielectric resonances accounts for the improved microwave absorption properties of the Fe/C nanocubes. The absorption bands of the optimum one obtained at 650 °C are superior to most composites ever reported. By considering the good chemical homogeneity and microwave absorption, we believe that the as-fabricated Fe/C nanocubes will be promising candidates as highly effective microwave absorbers.

545 citations


Journal ArticleDOI
TL;DR: An integrated preparation of safety-reinforced poly(propylene carbonate)-based all-solid polymer electrolyte is shown to be applicable to ambient-temperature solid polymer lithium batteries as discussed by the authors.
Abstract: An integrated preparation of safety-reinforced poly(propylene carbonate)-based all-solid polymer electrolyte is shown to be applicable to ambient-temperature solid polymer lithium batteries. In contrast to pristine poly(ethylene oxide) solid polymer electrolyte, this solid polymer electrolyte exhibits higher ionic conductivity, wider electrochemical window, better mechanical strength, and superior rate performance at 20 degrees C. Moreover, lithium iron phosphate/lithium cell using such solid polymer electrolyte can charge and discharge even at 120 degrees C. It is also noted that the solid-state soft-package lithium cells assembled with this solid polymer electrolyte can still power a red light-emitting diode lamp without suffering from internal short-circuit failures even after cutting off one part of the battery. Considering the aspects mentioned above, the solid polymer electrolyte is eligible for practical lithium battery applications with improved reliability and safety. Just as important, a new perspective that the degree of amorphous state of polymer is also as critical as its low glass transition temperature for the exploration of room temperature solid polymer electrolyte is illustrated. In all, this study opens up a kind of new avenue that could be a milestone to the development of high-voltage and ambient-temperature all-solid-state polymer electrolytes.

497 citations


Journal ArticleDOI
TL;DR: It is shown that a blend of two polymers with high miscibility and appropriately chosen linker structure can yield a dense and homogeneously distributed thermal network.
Abstract: A high density of strong hydrogen bonds connecting two polymers that are homogeneously mixed in a thin film is shown to enhance the intrachain thermal conductance, boosting thermal transport in fully organic layers. Thermal conductivity is an important property for polymers, as it often affects product reliability (for example, electronics packaging), functionality (for example, thermal interface materials) and/or manufacturing cost1. However, polymer thermal conductivities primarily fall within a relatively narrow range (0.1–0.5 W m−1 K−1) and are largely unexplored. Here, we show that a blend of two polymers with high miscibility and appropriately chosen linker structure can yield a dense and homogeneously distributed thermal network. A sharp increase in cross-plane thermal conductivity is observed under these conditions, reaching over 1.5 W m−1 K−1 in typical spin-cast polymer blend films of nanoscale thickness, which is approximately an order of magnitude larger than that of other amorphous polymers.

424 citations


Journal ArticleDOI
TL;DR: It is demonstrated that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-Trapping, i.e., WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance.
Abstract: There is keen interest in the use of amorphous WO3 thin films as cathodic electrodes in transmittance-modulating electrochromic devices1–4. However, these films suer from ion-trapping-induced degra ...

415 citations


Journal ArticleDOI
TL;DR: In this article, a non-crystalline thin films of chalcogenide Cd 50 S 50−x Se x system were obtained by thermal evaporation technique onto a pre-cleaned glass substrate at a vacuum of 8.2 × 10 −4 ǫ.

412 citations


Journal ArticleDOI
TL;DR: This tutorial review focuses on introducing the more recent advances in the CVD growth of MX2 monolayers via the sulphurisation/decomposition of pre-deposited metal-based precursors, or the one-step reaction and deposition of gaseous metal and chalcogen feedstocks.
Abstract: As structural analogues of graphene but with a sizeable band gap, monolayers of group-VIB transition metal dichalcogenides (MX2, M = Mo, W; X = S, Se, Te, etc.) have emerged as the ideal two dimensional prototype for exploring fundamental issues in physics such as valley polarization, and for engineering a wide range of nanoelectronic, optoelectronic and photocatalytic applications. Recently, chemical vapour deposition (CVD) was introduced as a more efficient preparation method than traditional chemical or physical exfoliation options, and has allowed for the successful synthesis of large-area MX2 monolayers possessing a large domain size, high thickness uniformity and continuity, and satisfactory crystal quality. This tutorial review therefore focuses on introducing the more recent advances in the CVD growth of MX2 (MoS2, WS2, MoS2(1−x)Se2xetc.) monolayers via the sulphurisation/decomposition of pre-deposited metal-based precursors, or the one-step reaction and deposition of gaseous metal and chalcogen feedstocks. Differences in growth behaviour caused by commonly used amorphous SiO2/Si, and newly adopted insulating single crystal substrates such as sapphire, mica and SrTiO3, are also comparatively presented. Also discussed are the essential parameters that influence the growth of MX2, such as the temperature, the source–substrate distance and the composition of the carrier gas (Ar/H2). Finally, an assessment is provided for viable future pathways for fine-tuning of the domain size and orientation, thickness uniformity, and the bandgap of MX2 and its alloys.

322 citations


Journal ArticleDOI
TL;DR: Solid state NMR data provide clear evidence for the existence of precursor complexes in the gelatine phase, which were not involved in the formation of apatite crystals, proving hence theoretical predictions on the structural pre-treatment ofgelatine by ion impregnation.
Abstract: The mesocrystal system fluoroapatite-gelatine grown by double-diffusion is characterized by hierarchical composite structure on a mesoscale. In the present work we apply solid state NMR to characterize its structure on the molecular level and provide a link between the structural organisation on the mesoscale and atomistic computer simulations. Thus, we find that the individual nanocrystals are composed of crystalline fluorapatite domains covered by a thin boundary apatite-like layer. The latter is in contact with an amorphous layer, which fills the interparticle space. The amorphous layer is comprised of the organic matrix impregnated by isolated phosphate groups, Ca3F motifs and water molecules. Our NMR data provide clear evidence for the existence of precursor complexes in the gelatine phase, which were not involved in the formation of apatite crystals, proving hence theoretical predictions on the structural pre-treatment of gelatine by ion impregnation. The interfacial interactions, which may be described as the glue holding the composite materials together, comprise hydrogen bond interactions with the apatite PO4(3-) groups. The reported results are in a good agreement with molecular dynamics simulations, which address the mechanisms of a growth control by collagen fibers, and with experimental observations of an amorphous cover layer in biominerals.

317 citations


Journal ArticleDOI
TL;DR: This work utilizes Raman spectroscopy and X-ray absorptionSpectroscopy as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst and surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.
Abstract: The generation of chemical fuel in the form of molecular H2 via the electrolysis of water is regarded to be a promising approach to convert incident solar power into an energy storage medium. Highly efficient and cost-effective catalysts are required to make such an approach practical on a large scale. Recently, a number of amorphous hydrogen evolution reaction (HER) catalysts have emerged that show promise in terms of scalability and reactivity, yet remain poorly understood. In this work, we utilize Raman spectroscopy and X-ray absorption spectroscopy (XAS) as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst. Ex situ measurements reveal that the as-deposited CoSx catalyst is composed of small clusters in which the cobalt is surrounded by both sulfur and oxygen. Operando experiments, performed while the CoSx is catalyzing the HER, yield a molecular model in which cobalt is in an octahedral CoS2-like state where the cobalt center is predominantly surrounded by a first shell of sulfur atoms, which, in turn, are preferentially exposed to electrolyte relative to bulk CoS2. We surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.

302 citations


Journal ArticleDOI
TL;DR: In this paper, NiCo2.7(OH)x amorphous double hydroxides nanomaterials with a hollow structure and tunable Ni/Co molar ratio were synthesized using a template method.
Abstract: Ni–Co amorphous double hydroxides nanomaterials with a hollow structure and tunable Ni/Co molar ratio are synthesized using a template method. The amorphous NiCo2.7(OH)x nanocages demonstrate high surface reactivity, comparable catalytic activity, and excellent stability for efficient water oxidation. Density functional theory simulations suggest that the component-dependent electrocatalytic activities are connected to the binding energies of oxygen radical on diverse hydroxides.

Journal ArticleDOI
TL;DR: In this paper, a coaxial ternary hybrid material comprising of amorphous Ni(OH)2 deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) is demonstrated.
Abstract: The utilization of Ni(OH)2 as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)2 deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)2 is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g−1 at 5 mV s−1 and excellent rate capability (71.9% capacitance retention at 100 mV s−1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)2 nanomaterials. Using the ternary Ni(OH)2 hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg−1 at the power density of 780 W kg−1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)2 can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.

Journal ArticleDOI
TL;DR: Amorphous TiO2@C nanospheres were synthesized via a template approach in this article, and two types of polyphase TiO 2 hollow nanosphere were obtained.
Abstract: Amorphous TiO2@C nanospheres were synthesized via a template approach. After being sintered under different conditions, two types of polyphase TiO2 hollow nanospheres were obtained. The electrochemical properties of the amorphous TiO2 nanospheres and the TiO2 hollow nanospheres with different phases were characterized as anodes for the Na-ion batteries. It was found that all the samples demonstrated excellent cyclability, which was sustainable for hundreds of cycles with little capacity fading, although the anatase TiO2 presented a capability that was better than that of the mixed anatase/rutile TiO2 or the amorphous TiO2@C. Through crystallographic analysis, it was revealed that the anatase TiO2 crystal structure supplies two-dimensional diffusion paths for Na-ion intercalation and more accommodation sites. Density functional theory calculations indicated lower energy barriers for the insertion of Na+ into anatase TiO2. Therefore, anatase TiO2 hollow nanospheres show excellent high-rate performance. Thro...

Journal ArticleDOI
TL;DR: In this article, a new framework model of catalysis in an amorphous, hydrated and volume-active oxide is proposed: within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo CoII↔ CoIII ↔ CoIV oxidation-state changes coupled to structural modification and deprotonation of Cooxo bridges, and an active site is formed at which the O-O bond-formation step can take place.
Abstract: Water oxidation by amorphous oxides is of high interest in artificial photosynthesis and other routes towards non-fossil fuels, but the mode of catalysis in these materials is insufficiently understood. We tracked mechanistically relevant oxidation-state and structural changes of an amorphous Co-based catalyst film by in situ experiments combining directly synchrotron-based X-ray absorption spectroscopy (XAS) with electrocatalysis. Unlike a classical solid-state material, the bulk material is found to undergo chemical changes. Two redox transitions at midpoint potentials of about 1.0 V (CoII0.4CoIII0.6 ↔ all-CoIII) and 1.2 V (all-CoIII ↔ CoIII0.8CoIV0.2) vs. NHE at pH 7 are coupled to structural changes. These redox transitions can be induced by variation of either electric potential or pH; they are broader than predicted by a simple Nernstian model, suggesting interacting bridged cobalt ions. Tracking reaction kinetics by UV-Vis-absorption and time-resolved mass spectroscopy reveals that accumulated oxidizing equivalents facilitate dioxygen formation. On these grounds, a new framework model of catalysis in an amorphous, hydrated and volume-active oxide is proposed: Within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo CoII ↔ CoIII ↔ CoIV oxidation-state changes coupled to structural modification and deprotonation of Co-oxo bridges. By the encounter of two (or more) CoIV ions, an active site is formed at which the O–O bond-formation step can take place. The Tafel slope is determined by both the interaction between cobalt ions (width of the redox transition) and their encounter probability. Our results represent a first step toward the development of new concepts that address the solid-molecular Janus nature of the amorphous oxide. Insights and concepts described herein for the Co-based catalyst film may be of general relevance also for other amorphous oxides with water-oxidation activity.

Journal ArticleDOI
TL;DR: In this article, the history, featured properties and modern state of inorganic, physical and materials chemistry of transparent oxyfluoride glass ceramics are discussed. And the authors discuss the preparation methods for these materials (e.g., synthesis from starting glass and/or amorphous matrices, devitrification, etc.), comparative description of their spectral and luminescent properties, formation of rare earth-containing nanofluoride phases in oxide glass matrices by oriented attachment mechanism, distribution of dopants in oxyfluoric glass ceramic, as well as the

Journal ArticleDOI
TL;DR: The strong green emission quenching observed from photoluminescence of TiO2-ZnO hybrid nanostructures implied an enhanced charge transfer/separation process resulting from the novel type II heterostructure with fine interfaces.
Abstract: We studied the photocatalytic properties of rational designed TiO2-ZnO hybrid nanostructures, which were fabricated by the site-specific deposition of amorphous TiO2 on the tips of ZnO nanorods. Compared with the pure components of ZnO nanorods and amorphous TiO2 nanoparticles, these TiO2-ZnO hybrid nanostructures demonstrated a higher catalytic activity. The strong green emission quenching observed from photoluminescence of TiO2-ZnO hybrid nanostructures implied an enhanced charge transfer/separation process resulting from the novel type II heterostructures with fine interfaces. The catalytic performance of annealing products with different TiO2 phase varied with the annealing temperatures. This is attributed to the combinational changes in Eg of the TiO2 phase, the specific surface area and the quantity of surface hydroxyl groups.

Journal ArticleDOI
TL;DR: Amorphous black phosphorus ultrathin films deposited by pulsed laser deposition offer not only a new nanoscale member in the BP family, but also a new opportunity to develop nano-electronic devices.
Abstract: Amorphous black phosphorus (a-BP) ultrathin films are deposited by pulsed laser deposition. a-BP field-effect trans-istors, exhibiting high carrier mobility and moderate on/off current ratio, are demonstrated. Thickness dependence of the bandgap, mobility, and on/off ratio are observed. These results offer not only a new nanoscale member in the BP family, but also a new opportunity to develop nano-electronic devices.

Journal ArticleDOI
TL;DR: In this article, the effect of scan speed v and laser power P on the microstructure, thermal stability and soft magnetic properties has been investigated, and the results indicate that low v and high P lead to the formation of SLM samples with high relative densities, which can reach values of about 99.7%.

Journal ArticleDOI
TL;DR: This Account focuses on the recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations.
Abstract: ConspectusThe ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called “nanochemistry” for short, primarily studies the microstructures and macroscopic properties of a nanomaterial’s aggregation states. Due to abundant microstruct...

Journal ArticleDOI
01 Aug 2015-Small
TL;DR: The design of crystalline core@amorphous shell architecture may open up new strategies for synthesizing promising electrode materials for supercapacitor electrodes, which exhibit high specific capacitance and high capacitance retention.
Abstract: Transition metal sulfides gain much attention as electrode materials for supercapacitors due to their rich redox chemistry and high electrical conductivity. Designing hierarchical nanostructures is an efficient approach to fully utilize merits of each component. In this work, amorphous MoS2 is firstly demonstrated to show specific capacitance 1.6 times as that of the crystalline counterpart. Then, crystalline core@amorphous shell (Ni3S4@MoS2) is prepared by a facile one-pot process. The diameter of the core and the thickness of the shell can be independently tuned. Taking advantages of flexible protection of amorphous shell and high capacitance of the conductive core, Ni3S4@amorphous MoS2 nanospheres are tested as supercapacitor electrodes, which exhibit high specific capacitance of 1440.9 F g−1 at 2 A g−1 and a good capacitance retention of 90.7% after 3000 cycles at 10 A g−1. This design of crystalline core@amorphous shell architecture may open up new strategies for synthesizing promising electrode materials for supercapacitors.

Journal ArticleDOI
TL;DR: In this article, the authors proposed that the synergistic effect between the Ni core and the amorphous NiO shell can accelerate both Volmer and Heyrovsky processes to drive HER at low overpotentials.

Journal ArticleDOI
Xin Mu1, Xufei Wu1, Teng Zhang1, David B. Go1, Tengfei Luo1 
TL;DR: This work uses large-scale molecular dynamics simulations with reactive potentials to systematically study the role of oxygen adatoms on the thermal transport in graphene oxide, andalyses show that the large reduction in thermal conductivity is due to significantly enhanced phonon scattering induced by the oxygen defects which introduce dramatic structural deformations.
Abstract: Graphene oxide is being used in energy, optical, electronic and sensor devices due to its unique properties. However, unlike its counterpart – graphene – the thermal transport properties of graphene oxide remain unknown. In this work, we use large-scale molecular dynamics simulations with reactive potentials to systematically study the role of oxygen adatoms on the thermal transport in graphene oxide. For pristine graphene, highly ballistic thermal transport is observed. As the oxygen coverage increases, the thermal conductivity is significantly reduced. An oxygen coverage of 5% can reduce the graphene thermal conductivity by ~90% and a coverage of 20% lower it to ~8.8 W/mK. This value is even lower than the calculated amorphous limit (~11.6 W/mK for graphene), which is usually regarded as the minimal possible thermal conductivity of a solid. Analyses show that the large reduction in thermal conductivity is due to the significantly enhanced phonon scattering induced by the oxygen defects which introduce dramatic structural deformations. These results provide important insight to the thermal transport physics in graphene oxide and offer valuable information for the design of graphene oxide-based materials and devices.

Journal ArticleDOI
TL;DR: Electrochemical characterization indicated that the unsatisfied open-circuit voltage and fill factor were caused by the inherent charge recombination, and solution-processed amorphous WO(x) thin film was prepared facilely at low temperature and used as ESL in PSCs.
Abstract: The electron-selective layer (ESL) is an indispensable component of perovskite solar cells (PSCs) and is responsible for the collection of photogenerated electrons. Preparing ESL at a low temperature is significant for future fabrication of flexible PSCs. In this work, solution-processed amorphous WOx thin film was prepared facilely at low temperature and used as ESL in PSCs. Results indicated that a large quantity of nanocaves were observed in the WOx thin film. In comparison with the conventional TiO2 ESL, the WOx ESL exhibited comparable light transmittance but higher electrical conductivity. Compared with the TiO2-based PSCs, PSCs that use WOx ESL exhibited comparable photoelectric conversion efficiency, larger short-circuit current density, but lower open-circuit voltage. Electrochemical characterization indicated that the unsatisfied open-circuit voltage and fill factor were caused by the inherent charge recombination. This study demonstrated that this material is an excellent candidate for ESL.

Journal ArticleDOI
TL;DR: In this paper, an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiOtBu), H2O, trimethylphosphate (TMP), and plasma N2 (PN2) as precursors is presented.
Abstract: We demonstrate an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiOtBu), H2O, trimethylphosphate (TMP), and plasma N2 (PN2) as precursors. We use in-situ spectroscopic ellipsometry to determine growth rates for process optimization to design a rational, quaternary precursor ALD process where only certain substrate–precursor chemical reactions are favorable. We demonstrate via in-situ XPS tunable nitrogen incorporation into the films by variation of the PN2 dose and find that ALD films over approximately 4.5% nitrogen are amorphous, whereas LiPON ALD films with less than 4.5% nitrogen are polycrystalline. Finally, we characterize the ionic conductivity of the ALD films as a function of nitrogen content and demonstrate their functionality on a model battery electrode—a Si anode on a Cu current collector.

Journal ArticleDOI
TL;DR: An atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP, finding that decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorus like skeleton remains.
Abstract: With a semiconducting band gap and high charge carrier mobility, two-dimensional (2D) black phosphorus (BP)—often referred to as phosphorene—holds significant promise for next generation electronics and optoelectronics. However, as a 2D material, it possesses a higher surface area to volume ratio than bulk BP, suggesting that its chemical and thermal stability will be modified. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP. From in situ scanning/transmission electron microscopy, decomposition of 2D BP is observed to occur at ∼400 °C in vacuum, in contrast to the 550 °C bulk BP sublimation temperature. This decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorus like skeleton remains. In situ electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss near-edge structure changes provide quantitative insight into this chemical transformation process.

Journal ArticleDOI
TL;DR: It is shown that aging is accompanied by a progressive change of the local chemical order towards the crystalline one, which sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.
Abstract: Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

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TL;DR: In this paper, the interface layer formation between LiPON and metallic lithium using an in-situ X-ray photoemission spectroscopy (XPS) surface science approach was studied.

Journal ArticleDOI
TL;DR: In this article, the amorphous ternary mixed-metal hydroxide pseudocapacitor was used as a supercapacitor with a long-term cycling stability.
Abstract: Supercapacitors or electrochemical capacitors, as energy storage devices, require very stable positive electrode materials for useful applications. Although most positive electrodes are based on crystalline mixed-metal hydroxides, their pseudocapacitors usually perform poorly or have a short cycle life. High activities can be achieved with amorphous phases. Methods to produce amorphous materials are also not typically amenable towards mixed-metal compositions. It is demonstrated that electrochemistry in an ambient environment can be used to produce a series of amorphous mixed-metal hydroxides with a homogeneous distribution of metals for use as positive electrode materials in a supercapacitor. The integrated performance of the amorphous ternary mixed-metal hydroxide pseudocapacitor is superior to that of crystalline materials. The amorphous Ni-Co-Fe hydroxide supercapacitor is characterized by a long-term cycling stability that retained 94% of its capacity after 20 000 cycles. This is much higher than the cycle life of crystalline devices. These results show the broad applicability of this methodology towards new electrode materials for high-performance supercapacitors, especially amorphous mixed-metal hydroxides, as advanced electrode materials.

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TL;DR: In this article, the authors investigated diamond scratching at a high speed comparable to that in a grinding process on an ultraprecision grinder and found that an amorphous layer is formed on top of the pristine Si-I phase before the onset of chip formation.

Journal ArticleDOI
TL;DR: It is demonstrated that the loading of amorphous Co3O4 is a facile strategy to enhance the photocatalytic activity of CdS nanorods, which may provide some potential opportunities for designing other composite photoc atalysts for water splitting.
Abstract: In this work, amorphous Co3O4 modified CdS nanorods were synthesized by a two-step solvothermal/hydrothermal method, and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy, UV-visible spectroscopy, nitrogen absorption and X-ray photoelectron spectroscopy. The photocatalytic performance of the as-synthesized Co3O4–CdS nanorods was evaluated through H2 generation from an aqueous solution containing sulfide and sulfite under visible light (λ ≥ 420 nm). The results showed that the photocatalytic activity of CdS nanorods for H2 evolution could be significantly enhanced by loading the amorphous Co3O4. The optimal Co3O4 loading was found to be approximately 3.0 mol%. The as-prepared CdS nanorods with 3 mol% Co3O4 exhibited the highest photocatalytic activity for H2 evolution under visible light irradiation, 236 μmol g−1 h−1, which is 33-fold higher than that of the pristine CdS nanorods. Furthermore, the co-loading of 1 wt% Pt can lead to another three times enhancement in the photocatalytic H2-production activity. The mechanism for the enhanced H2-production performance of Co3O4–CdS nanorods was discussed. The excellent performance of Co3O4–CdS nanorods is mainly ascribed to the loading of amorphous Co3O4 onto the surface of CdS nanorods, which could promote the separation of electron–hole pairs and enhance the stability of CdS nanorods due to the formation of p–n heterojunctions between the Co3O4 and CdS nanorods, thus leading to an enhanced activity for H2 generation. This work demonstrated that the loading of amorphous Co3O4 is a facile strategy to enhance the photocatalytic activity of CdS nanorods, which may provide some potential opportunities for designing other composite photocatalysts for water splitting.