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High-energy-density systems with fast charging rates and suppressed dendrite growth are critical for the implementation of efficient and safe next-generation advanced battery technologies such as those based on Li metal. However, there are few studies that investigate reliable cycling of Li metal electrodes under high-rate conditions. Here, by employing a superconcentrated ionic liquid (IL) electrolyte, we highlight the effect of Li salt concentration and applied current density on the resulting Li deposit morphology and solid electrolyte interphase (SEI) characteristics, demonstrating exceptional deposition/dissolution rates and efficiency in these systems. Operation at higher current densities enhanced the cycling efficiency, e.g., from 64 ± 3% at 1 mA cm-2 up to 96 ± 1% at 20 mA cm-2 (overpotential

Silicon is a promising alloying anode for lithium-ion batteries because of its high capacity and low cost. However, its use has been hampered by mechanical failure arising from the large volume cha...

Silicon is a promising anode material for lithium-ion batteries because of its high capacity, but its widespread adoption has been hampered by a low cycle life arising from mechanical failure and t...

Although high energy density and fast charging rates are vital for future advanced battery applications such as electric vehicles (EVs), the impact of fast charge rates is not widely investigated for key technologies such as those based on lithium metal. Here, for the first time, Li metal deposition/dissolution in a superconcentrated ionic liquid (IL) is demonstrated at the high current densities necessary for fast charge technologies. Operation at high current is shown to enhance the cycling efficiency from 64 ± 3% at 1 mA cm−2 up to 96 ± 1% at 20 mA cm−2 on a bare Ni substrate, providing a new path to enable these technologies. XPS, ToF-SIMS and SEM measurements revealed that a stable and LiF-dominated SEI, favourable nucleation and compact dendrite-free Li morphology enabled enhanced cycling efficiency at higher currents.

Lepidocrocite-type titanates that reversibly intercalate sodium ions at low potentials (∼0.6 V vs Na/Na+) are promising anode candidates for sodium-ion batteries. However, large amounts of carbon additives are often used to improve their electrical conductivity and overcome poor cycling performance in the electrode composites. To ameliorate electronic transport issues of lepidocrocite titanate (K0.8Ti1.73Li0.27O4, KTL) in sodium-ion batteries, we have designed and synthesized heterostructures of exfoliated lepidocrocite-type titanium oxide (LTO) nanosheets with alternating carbon layers via a solution-based self-assembly approach. Positively charged dopamine (Dopa) was used as the carbon precursor and intercalated between negatively charged exfoliated titania nanosheets through electrostatic interaction. Dopa-intercalated LTO was then annealed under argon to form conductive carbon layers between titania sheets. The carbon content in the heterostructures was controlled by modifying the self-assembly conditions (i.e., pH, stirring duration, and Dopa-to-LTO ratio). Electrodes were prepared using carbonized heterostructures (LTO-C) without adding more carbon to the composites and tested in sodium half-cell configurations. Higher capacities and improved capacity retention over 250 cycles and lower impedance were observed, as the carbon content of LTO-C heterostructures was increased from 0% (LTO nanosheets) to 30%. These results indicate that the self-assembly approach for 2D heterostructured electrode materials is a promising strategy to overcome electronic transport limitations of layered transition-metal oxides and improve their electrochemical performance for next-generation energy storage applications.

Alloying anodes such as silicon are of great interest for lithium-ion batteries due to their high lithium-ion storage capacities, but have only seen minimal commercial deployment due to their limited calendar life. This has been attributed to an intrinsically unstable solid electrolyte interphase (SEI) that is aggravated by mechanical failure. An amorphous structure can mitigate lithiation strains, and amorphous alloys, or metallic glasses, often exhibit exceptional fracture toughness. Additional elements can be added to metallic glasses to improve passivation. Splat quenching was utilized to prepare an amorphous Al64Si25Mn11 Li-ion anode with a specific capacity >900 mAh g-1 that remains amorphous upon cycling. On this metallic glass electrode, parasitic electrolyte reduction is found to be much reduced in comparison to pure Si or Al, and comparable to that on Cu. The SEI is much thinner, more stable, and richer in fluorinated inorganic phases than the SEI formed on Si, while organic carbonate compounds such as lithium ethylene decarbonate (LiEDC) are notably absent. This study indicates that metallic glasses can become a viable new class of Li-ion anode materials with improved surface passivity.

Ternary nitride semiconductors with wurtzite-derived crystal structures are an emerging class of materials for optoelectronic applications compatible with GaN and related III–V compounds. In particular, II–IV–V2 materials such as ZnSnN2 and ZnGeN2 have been very actively studied for applications in photovoltaics and light emitting devices. However, many other possible wurtzite-derived ternary nitrides have not been reported, and hence their optical and electrical properties remain unknown. Here, we report on Zn2SbN3 – the first Sb-based nitride and a photoactive semiconductor. Surprisingly, Zn2SbN3 contains Sb in the highest (5+) oxidation state, and in the unusual tetrahedral coordination. This new Zn2SbN3 material has a solar-matched 1.6–1.7 eV band gap and shows near-band-edge room-temperature photoluminescence, demonstrating its promise as an optoelectronic semiconductor. Finally, Zn2SbN3 can be synthesized at low temperature under a wide range of processing conditions, despite being metastable according to theoretical calculations. All these results, as well as the band position measurements, indicate that Zn2SbN3 is a promising emerging semiconductor for applications as an absorber in photovoltaic- and photoelectrochemical solar cells.

A stable solid electrolyte interphase (SEI) has been proven to be a key enabler to most advanced battery chemistries, where the reactivity between the electrolyte and the anode operating beyond the electrolyte stability limits must be kinetically suppressed by such SEIs. The graphite anode used in state-of-the-art Li-ion batteries presents the most representative SEI example. Because of similar operation potentials between graphite and silicon (Si), a similar passivation mechanism has been thought to apply on the Si anode when using the same carbonate-based electrolytes. In this work, we found that the chemical formation process of a proto-SEI on Si is closely entangled with incessant SEI decomposition, detachment, and reparation, which lead to continuous lithium consumption. Using a special galvanostatic protocol designed to observe the SEI formation prior to Si lithiation, we were able to deconvolute the electrochemical formation of such dynamic SEI from the morphology and mechanical complexities of Si and showed that a pristine Si anode could not be fully passivated in carbonate-based electrolytes.

Silicon is a promising anode material for lithium-ion batteries because of its high capacity, but its widespread adoption has been hampered by a low cycle life arising from mechanical failure and the absence of a stable solid-electrolyte interphase (SEI). Understanding SEI formation and its impact on cycle life is made more complex by the oxidation of silicon materials in air or during synthesis, which leads to SiO

ZnSnN2 (ZTN) has been proposed as a new earth abundant absorber material for photovoltaic (PV) applications. While carrier concentration has been reduced to values suitable for device implementation, other properties such as ionization potential, electron affinity, and work function are not known. Here, we experimentally determine the value of ionization potential (5.6 eV), electron affinity (4.1 eV), and work function (4.4 eV) for ZTN thin film samples with Zn cation composition Zn/(Zn+Sn) = 0.56 and carrier concentration $n$ = 2 × 1019 cm−3 . Using both experimental and theoretical results, we build a model to simulate the device performance of a ZTN/Mg:CuCrO2 solar cell, showing a potential efficiency of 23% in the limit of no defects present. We also investigate the role of band tails and recombination centers on the cell performance. In particular, device simulations show that band tails are highly detrimental to the cell efficiency, and recombination centers are a major limitation if present in concentration comparable to the net carrier density. The effect of the position of the band edges of the p- type junction partner was assessed too. Through this study, we determine the major bottlenecks for the development of ZTN-based solar cell and identify avenues to mitigate them.

Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically for nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigati...

The expectation to progress towards Terawatts production by solar technologies requires continuous development of new materials to improve efficiency and lower the cost of devices beyond what is currently available at industrial level. At the same time, the turnaround time to make the investment worthwhile is progressively shrinking. Whereas traditional absorbers have developed in a timeframe spanning decades, there is an expectation that emerging materials will be converted into industrially relevant reality in a much shorter timeframe. Thus, it becomes necessary to develop new approaches and techniques that could accelerate decision-making steps on whether further research on a material is worth pursuing or not. In this review, we will provide an overview of the photoemission characterization methods and theoretical approaches that have been developed in the past decades to accelerate the transfer of emerging solar absorbers into efficient devices.

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

We report on the theoretical prediction and experimental realization of new ternary zinc molybdenum nitride compounds. We used theory to identify previously unknown ternary compounds in the Zn-Mo-N systems, Zn3MoN4 and ZnMoN2, and to analyze their bonding environment. Experiments show that Zn-Mo-N alloys can form in broad composition range from Zn3MoN4 to ZnMoN2 in the wurtzite-derived structure, accommodating very large off-stoichiometry. Interestingly, the measured wurtzite-derived structure of the alloys is metastable for the ZnMoN2 stoichiometry, in contrast to the Zn3MoN4 stoichiometry, where ordered wurtzite is predicted to be the ground state. The formation of Zn3MoN4-ZnMoN2 alloy with wurtzite-derived crystal structure is enabled by the concomitant ability of Mo to change oxidation state from +VI in Zn3MoN4 to +IV in ZnMoN2, and the capability of Zn to contribute to the bonding states of both compounds, an effect that we define as "redox-mediated stabilization". The stabilization of Mo in both the +VI and +IV oxidation states is due to the intermediate electronegativity of Zn, which enables significant polar covalent bonding in both Zn3MoN4 and ZnMoN2 compounds. The smooth change in the Mo oxidation state between Zn3MoN4 and ZnMoN2 stoichiometries leads to a continuous change in optoelectronic properties-from resistive and semitransparent Zn3MoN4 to conductive and absorptive ZnMoN2. The reported redox-mediated stabilization in zinc molybdenum nitrides suggests there might be many undiscovered ternary compounds with one metal having an intermediate electronegativity, enabling significant covalent bonding, and another metal capable of accommodating multiple oxidation states, enabling stoichiometric flexibility.

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr2O3. Conductivities as high as 28 S cm−1 were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr2O3 contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr2O3. Furthermore, it is experimentally proven that Ni has a higher solubility in Cr2O3 than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr2O3 than Mg and explains the improved conductivity observed for the former.

We present an analysis of the Raman spectra of p -type transparent conducting Cr 2 O 3 :Mg grown by various techniques including spray pyrolysis, pulsed laser deposition, molecular beam epitaxy and reactive magnetron sputtering. The best performing films show a distinct broad range Raman signature related to defect-induced vibrational modes not seen in stoichiometric, undoped material. Our comparative study demonstrates that Raman spectroscopy can quantify unwanted dopant clustering in the material at high Mg concentrations, while also being sensitive to the Mg incorporation site. By correlating the Raman signature to the electrical properties of the films, growth processes can be optimised to give the best conducting films and the local defect structure for effective p -type doping can be studied.

Highly regular step and terrace structures have been produced on surfaces of single crystalline MgO, miscut from the low-index (001) plane, upon annealing in air. Here, the evolution of the surface morphology of such surfaces is investigated. We demonstrate that the periodicity of these structures can be widely tuned in the submicron range by controlling the annealing conditions. Surface faceting resulted from annealing in the temperature range 1100-1580 °C. The surfaces were characterized by atomic force microscope, X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy to assess the role of contamination, temperature, and miscut angle in the final morphology. The presence of Al contamination in the post-annealed samples was found to be essential for the formation of the step and terrace structure. The stability of the resultant structures when exposed to ambient conditions is discussed. The cause of the apparent destruction of the surface morphology upon long-term atmospheric exposure has been identified, and a method to recover the faceted morphology is proposed. Overall, the study further facilitates the growth of nanostructures on such faceted surfaces.

In this contribution the effect of different deposition conditions on the physical properties of ZnO:Al grown by spray pyrolysis is outlined. In particular, it will be shown that the solvent composition affects the crystallographic orientation of the deposited films, as well as their roughness and electrical properties. Using water leads to higher resistive films than methanol. The choice of precursor salts also has an effect on the electrical properties, as using organic precursors leads to lower resistivity films. In both cases post-annealing helps to reduce the overall resistivity of the films. The reduction in resistivity will change depending on the initial deposition condition of the films, with lower values observed for films deposited at lower temperature. In optimum conditions a resistivity of 7 × 10 − 3 Ω cm can be reproducibly achieved with inexpensive air blast nozzles at atmospheric pressure.

Lithium-ion batteries (LiBs) have been successfully utilized as power sources in various applications ubiquitous in our daily lives, ranging from portable electronic devices to electric vehicles. To meet the increasing energy demand, however, development of LiBs with a higher energy density is inevitable. Using silicon (Si) as an anode is promising due to its high theoretical capacity (approximately 4200 mAhg-1), appropriate operating voltage (~0.4 V vs. Li/Li+), abundance, and environmentally benign nature.1 Despite the aforementioned advantages, several challenges remain before the commercial utilization of Si anodes, namely the low conductivity of its readily-formed surface oxide (SiO2), a large volume change (up to 400 %) during lithiation/delithiation, and the instability of Si/electrolyte interface (SiEI).2-3 As the large volume change leads to fracture and continuous evolution of SiEI, achieving a stable SiEI is a key to developing successful LiBs with Si anodes. Water, which is known to react with LiPF6 salt in carbonate-based electrolytes to generate corrosive hydrofluoric acid (HF),4 is a source for the electrode/electrolyte interface destabilization. Thus, it is essential to understand how the presence of even trace amounts of water in the system affects the interfacial chemistry of the LiB electrodes. While the performance of LiBs with graphite or lithium titanate negative electrodes have been previously studied with excess water in the electrolyte,5-6 information on the effect of water concentration in the electrolyte on Si anodes, and the SiEI in particular, is limited. In this work, we evaluated the electrochemical performance of Si anodes in a standard electrolyte (1.2 M LiPF6 in EC:EMC (3:7 wt%)) with varying concentration of water (10 - 1,000 ppm). Subsequent analyses on the cycled Si anodes were performed utilizing a variety of surface and bulk characterization techniques. The surface chemistry (e.g., composition and evolution) of SiEI was analyzed using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). Surface morphologies of cycled Si anodes were measured with tapping-mode atomic force microscopy (AFM), and the surface resistivities were mapped in contact-mode with scanning spreading resistance microscopy (SSRM). The information obtained is utilized to understand water concentration effects on the properties, reactivity, and evolution of the SiEI and the electrochemical cell performance. References Feng, K.; Li, M.; Liu, W.; Kashkooli, A. G.; Xiao, X.; Cai, M.; Chen, Z., Silicon-Based Anodes for Lithium-Ion Batteries: From Fundamentals to Practical Applications. Small 2018, 14 (8), 1702737. Chae, S.; Ko, M.; Kim, K.; Ahn, K.; Cho, J., Confronting Issues of the Practical Implementation of Si Anode in High-Energy Lithium-Ion Batteries. Joule 2017, 1 (1), 47-60. Philippe, B.; Dedryvere, R.; Allouche, J.; Lindgren, F.; Gorgoi, M.; Rensmo, H.; Gonbeau, D.; Edstrom, K., Nanosilicon Electrodes for Lithium-Ion Batteries: Interfacial Mechanisms Studied by Hard and Soft X-ray Photoelectron Spectroscopy. Chem. Mater. 2012, 24 (6), 1107-1115. Xu, K., Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries. Chem. Rev. 2004, 104 (10), 4303-4417. Burns, J. C.; Sinha, N. N.; Jain, G.; Ye, H.; VanElzen, C. M.; Scott, E.; Xiao, A.; Lamanna, W. M.; Dahn, J. R., The impact of intentionally added water to the electrolyte of Li-ion cells. I. Cells with graphite negative electrodes. J. Electrochem. Soc. 2013, 160 (11), A2281-A2287. Burns, J. C.; Sinha, N. N.; Jain, G.; Ye, H.; Van Elzen, C. M.; Scott, E.; Xiao, A.; Lamanna, W. M.; Dahn, J. R., The impact of intentionally added water to the electrolyte of Li-ion cells: II. Cells with lithium titanate negative electrodes. J. Electrochem. Soc. 2014, 161 (3), A247-A255.

Zinc tin nitride ( ZnSnN2) is an emerging ternary nitride semiconductor studied for applications in solar cells, light-emitting diodes, and other optoelectronic devices. For all of these applications, the charge carrier mobility is an important property. However, the dominant electron scattering mechanisms in ZnSnN2 are unclear, especially in the presence of oxygen that is often incorporated during thin film sputter deposition of this material. In addition, there are no experimental reports on the concentration of defects in such polycrystalline sputtered zinc tin oxynitride Zn1+xSn1−xN2−2xO2x (ZTNO) thin films. Here, we address both of these questions using temperature-dependent Hall effect measurements of sputtered ZTNO thin films as a function of Zn composition and O content. The measured temperature dependence of the mobility is fitted to scattering on ionized and neutral defects and to grain boundary scattering. The results indicate that ZTNO is a heavily compensated semiconductor, with a high density of neutral defects dominating the electron scattering processes. First principles theoretical calculations indicate that these neutral defects are likely to originate from the abundant ZnSn−2ON complexes in the ZTNO material. Overall, these results establish the dominant electron scattering mechanisms in polycrystalline sputtered ZTNO and help position this material for future use in optoelectronic devices.Zinc tin nitride ( ZnSnN2) is an emerging ternary nitride semiconductor studied for applications in solar cells, light-emitting diodes, and other optoelectronic devices. For all of these applications, the charge carrier mobility is an important property. However, the dominant electron scattering mechanisms in ZnSnN2 are unclear, especially in the presence of oxygen that is often incorporated during thin film sputter deposition of this material. In addition, there are no experimental reports on the concentration of defects in such polycrystalline sputtered zinc tin oxynitride Zn1+xSn1−xN2−2xO2x (ZTNO) thin films. Here, we address both of these questions using temperature-dependent Hall effect measurements of sputtered ZTNO thin films as a function of Zn composition and O content. The measured temperature dependence of the mobility is fitted to scattering on ionized and neutral defects and to grain boundary scattering. The results indicate that ZTNO is a heavily compensated semiconductor, with a high dens...

The reduction of electrolyte is well known to result in the formation of the solid electrolyte interphase (SEI) at the interface of electrolyte and silicon electrodes which determines the reversibility of lithium ion battery chemistry. The SEI formation is usually coupled with the mechanical deformation of silicon electrode because of its large volume changing of about 300% during the cycling lithiation and delithiation. We may know more about the chemistry of SEI by decoupling it from the silicon mechanical deformation. In this talking, we will present a novel electrochemical methodology having achieved this decoupling which results in a special surface species - “early-stage SEI”. The chemistry of the early-stage SEI was well studied to distinguish the following challenging questions: Can the early-stage SEI passivate the silicon surface? How is the stability of the early-stage SEI during the long rest in the electrolyte? In comparison with the regular SEI coupled by the mechanical deformation of silicon, the early-stage SEI was found with a lot of new chemistry by using the characterization of X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopes-Scanning Spreading Resistance Microscopy (AFM-SSRM). The composition of early-stage SEI was verified by XPS to include lithium ethylene dicarbonate (LiEDC) and lithium carbonate (Li2CO3). Meanwhile, the silicon was verified without lithiation behavior. The evolution of surface roughness and electrical conductivity of early-stage SEI was addressed by AFM-SSRM. This study may gain much attention due of the fundamental understanding of the silicon electrode surface chemistry with potential application in lithium ion battery of high energy density.

The electrochemical energy storage market is growing rapidly, and is currently dominated by lithium ion batteries. Replacing the standard graphite anode with silicon, whose theoretical gravimetric capacity is roughly ten times higher, promises a step-change improvement in capacity. Unfortunately, the use of silicon in lithium ion battery anodes frequently leads to poor cycle life, related at least in part to the challenges in creating a stable solid-electrolyte interphase (SEI). This issue is made more complex by the fact that the silicon used in composite anodes is typically nanostructured, with a poorly defined and often oxidized surface, especially when the silicon was prepared at elevated temperature. SiOx has been proposed as an alternative anode material to Si, whereas SiO2 is an electronic insulator. It is therefore valuable to understand the effect of surface oxides in more detail. In this work, we take a fundamental approach to understanding how an oxide on a silicon surface affects SEI formation and lithiation. Silicon wafers with precisely controlled thermal SiO2 thicknesses were prepared by thinning thicker oxides down to 1-30nm SiO2 using buffered hydrofluoric acid solution. These wafers were then cycled against a Li counter and reference electrode in Gen2 electrolyte (1.2M LiPF6 in EC:EMC (3:7 by wt.)) using custom three-electrode cells, which use an O-ring seal on the silicon to prevent contact between the electrolyte and the edges or rear of the wafers. Galvanostatic cycling at 20µAcm-2 indicates that while Si with 1nm SiO2 will lithiate above 0V vs Li, Si with 3nm SiO2 will only lithiate after a potential spike to -0.4V vs Li. Thereafter, it actually cycles with higher Coulombic efficiency (CE) than Si with 1nm SiO2. However, Si with 5-30nm SiO2 initially requires voltages below -1.0V vs Li to sustain 20µAcm-2, resulting in localized Li plating at pinholes in the SiO2 rather than lithiation. The voltages required to induce this pinhole plating will be compared to the dielectric breakdown strength of the SiO2 layers. To understand these phenomena in more detail, cyclic voltammetry (CV) was performed on Si with 1-5nm SiO2 (1mV/s, see abstract figure). Lithiation only occurred in the 1.0nm sample in the first cycle, but by the fourth cycle, lithiation occurred in samples with up to 2.9nm SiO2. Samples with 3.9nm and 4.8nm SiO2 on the other hand exhibit no lithiation or reversible electrochemistry during ten CV cycles. Two distinct delithiation peaks are observed for 1.0 and 1.4nm SiO2, but only the higher-voltage peak is observed for the 2.9nm SiO2, suggesting a unique delithiation chemistry that may be correlated to the high CE during galvanostatic cycling, and which will be studied by XPS. The peak currents (0.05V for lithiation, 0.5V for delithiation) decrease exponentially with SiO2 thickness, indicating that tunneling electron transfer across the SiO2 may play a key role in the reaction kinetics. Overall, we find that dense thermal oxides of 5nm or more severely impede lithiation, whereas 1nm SiO2 allows lithiation to proceed unimpeded. Intermediate thicknesses of ~3nm alter the delithiation chemistry while yielding improved CE during galvanostatic cycling. These effects will be discussed in relation to the bonding of the SiO2 network in thermal oxides, as compared to native or sputtered oxides. Figure 1

Cr2O3:(Mg,N) has been reported as a p-type transparent conducting oxide. In this contribution the effect of each precursor used for deposition by spray-pyrolysis will be explored and their role in determining the optical and electrical properties of Cr2O3 will be outlined. A correlation between the structural, electrical, and optical properties upon introducing nitrogen precursors has been established. In particular it has been shown that the presence of ammonium salts in the deposition environment results in less absorbing films. By combining optical measurements and NEXAFS studies, a mechanism is proposed to explain the change in the optical properties. Moreover, it is shown that the presence of the nitrate moiety in the reaction environment is necessary to improve the electrical conductivity of the deposited films. The reaction of the nitrate moiety with the ammonium moiety has been proposed as the mechanism to explain the boost in conductivity.

One of the current challenges faced by material scientists is the development of a p-type transparent conducting oxide with levels of optical transparency and electronic conductivity to equal those of the universally n-type industry leaders such as Sn-doped In2O3. The discovery of a p-type analogue would allow for the combination of both polarities into a heterojunction, accessing the potential for transparent electronics. In this study, an insulating material, Cr2O3, is investigated both experimentally and computationally to determine if it is a viable p-type host matrix as has been recently proposed in the literature. The geometric and electronic structure are examined by high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and periodic density functional theory (specifically, PBE + U). By incorporating Mg and performing a comprehensive defect analysis, the dominant intrinsic and extrinsic carriers in the material are determined, and it is shown that Cr2O3 has the potential to display p-type conductivity when appropriately doped.

An alternative, non-toxic precursor was employed for the synthesis of SnO2:F transparent conducting oxide. The performance of benzenesulfonyl fluoride (BSF) as F source for spray pyrolysis was investigated. Its decomposition and the actual incorporation of fluorine in the tin oxide matrix were confirmed by X-ray photoelectron spectroscopy while its effect on the electrical properties was investigated by resistance and Hall measurements. Results were compared with respect to samples grown using a common fluorine source (NH4F), a commercial available sample and a sample grown by spray pyrolysis at an independent laboratory. We show that BSF leads to actively doped conductive SnO2 with good carrier mobility, though the fluorine incorporation rate and hence overall conductivity of the films is lower than for fluorine precursors commonly used in spray pyrolysis.

The present chapter deals with the difficult task of giving a brief survey of the synthetic routes employed to prepare materials with characteristic features on the nanometer scale. Definitions and general concepts regarding nanostructured and nanometer-sized materials are shortly tackled in the introductory part, which is followed by an overview of the most important approaches developed to synthesize such materials. No attempt is made to create a comprehensive and detailed synopsis of the experimental methods currently available. Rather, attention is focused on a selected number of general methodologies, the choice of which can be usually motivated by a mix of historical perspective, scientific significance and technological potential. So-called “top-down” approaches are discussed first, whereas the second part of the chapter is devoted to “bottom-up” ones. The former group includes mechanical processing, melt quenching, and de-vitrification methods. Sonochemistry, pulsed laser ablation, wet chemical synthesis, sol-gel processing, microwave processing, spray pyrolysis, flame synthesis, inert gas condensation, vapor deposition, and vapor-liquid-solid growth form instead the latter group.

The effect of the solution composition on the properties of ZnO thin films grown by spray pyrolysis has been investigated. The ZnO films, both undoped and doped with either magnesium or aluminum, have been grown employing different solvents and different precursor salts. Afterward the effects of these have been correlated to the morphology and optical and electrical properties of the films. In general it was found that organic salts are preferable over inorganic ones such as chlorides and nitrates. In the case of inorganic salts, unwanted etching processes, caused by acids formed as a result of the precursor decomposition, lead to degradation of the films performance. Similarly, organic solvents are preferable over water due to a better droplet size distribution and, also, due to additional heat transfer toward the sample surface by their burning.

Anatase TiO 2 powders have been subjected to mechanical treatment for selected time intervals. The mechanical processing induced a gradual microstructural refinement, accompanied by a two-stage phase transformation into TiO 2 II phase and then rutile. Thin film electrodes were then prepared by depositing the processed powders on Ti supports from an organic suspension. The electrodes were successively exposed to irradiation with Hg lamps and the photoelectrochemical response of the powders evaluated in terms of efficiency of photocurrent generation. The experimental findings clearly show that the efficiency of the photoelectrochemical response drops as the duration of mechanical treatment increases. A suitably developed model indicates that the observed efficiency decrease is mostly due to the formation of nanostructured phases consequent to the mechanical deformation at impacts.

Three Pt-Co mixtures of composition Pt 25 Co 75 , Pt 50 Co 50 and Pt 75 Co 25 respectively, were synthesized using the high-energy ball milling technique of the elemental powders with a view to prepare catalysts for fuel cells. The kinetics of phase evolution, their structure and average microstructure properties were quantitatively investigated by X-ray powder diffraction with the Rietveld method. The results show that the ball milling technique is able to produce Pt-Co solid solutions soon after few minutes of mechanical treatment. Of the two polymorphs of cobalt the fcc allotrope appears to be involved preferentially in the early stage of alloying reaction with fcc platinum. For the three compositions, a sigmoidal equation based on an interdiffusion-controlled mechanism satisfactorily accounts for the evolution of the solid solution as a function of mechanical treatment time. A characteristic reaction time of 3–6 h is observed for the solid state transformation reaction with the milling conditions adopted in our reactor. In the case of the Pt 25 Co 75 composition, a competitive-consecutive reaction is observed. Lattice parameters of the solid solutions after extended times of milling and related atomic volumes turn out to be slightly above the values ideally predicted on the basis of the Vegard’s law. For the Pt 75 Co 25 composition the average crystallite size is reduced down to ca. 150 A after 12 h when the lattice microstrain is also at a maximum, but further mechanical treatment increases the average crystal size value and to decrease the strain. Similar results are found for equiatomic and Co-rich compositions. Annealing of the alloyed equiatomic powders promotes a cubic-to-tetragonal transformation which is already operative at 600 °C. In fact, after this treatment two tetragonal phases are observed. Further thermal treatment and annealing at 700 °C induces peak sharpening of the diffraction patterns, due to ordering phenomena still in progress.

The realization of transparent electronic and optoelectronic devices requires the use of transparent p-n junctions. In this context, understanding the band alignment at the interface between the p- and n-components represents a fundamental step towards the realization of high performance devices. In this work, the band alignment at the interface between Al-doped ZnO (AZO) and Ni-doped Cr2O3 has been analysed. The formation and evolution of the core levels as the interface progressively forms have been followed by means of x-ray Photoelectron Spectroscopy, x-ray diffraction and x-ray reflectivity. A type two (staggered) band alignment was identified, with the valence band offset and conduction band offset found to be 2.6 eV and 2.5 eV, respectively. The electrical behaviour will be discussed in terms of the position of the bands, the presence of band bending and the expected built-in potential and how these can be engineered in order to achieve the maximum performance for this hetero-structure.

One of the current challenges faced by material scientists is the development of a p-type transparent conducting oxide with levels of optical transparency and electronic conductivity to equal those of the universally n-type industry leaders such as Sn-doped In2O3. The discovery of a p-type analogue would allow for the combination of both polarities into a heterojunction, accessing the potential for transparent electronics. In this study, an insulating material, Cr2O3, is investigated both experimentally and computationally to determine if it is a viable p-type host matrix as has been recently proposed in the literature. The geometric and electronic structure are examined by high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and periodic density functional theory (specifically, PBE + U). By incorporating Mg and performing a comprehensive defect analysis, the dominant intrinsic and extrinsic carriers in the material are determined, and it is shown that Cr2O3 has the potential to display p-type conductivity when appropriately doped.

Pt–Co alloys prepared by high energy ball milling synthesis were tested as electrocatalysts for hydrogen fueled Polymer Electrolyte Membrane Fuel Cells (PEMFC). In the present contribution we report on the first results regarding the electrochemical behaviour of two samples of Pt–Co alloys. One sample contains 20 wt.% alloy Pt:Co in the molar ratio 0.25:0.75 and C 80 wt.% and the second one Pt:Co in the molar ratio 0.75:0.25 and C 80 wt.%. The electrochemically active surface (EAS) was determined by cyclic voltammetry data while the electrocatalyst performance in a real cell was obtained by assembling Membrane Electrode Assemblies (MEAs) with the considered sample at the cathode. The results obtained, though indicating a lower performance than all-Pt catalysts, are quite interesting as they point out the importance of the C/Pt, Nafion/Pt and Pt/Co ratios that exert a deep influence onto the cell performance.

We focus on the synthesis by ball milling and on the electrochemical characterization of nanocrystalline bimetallic and composite materials to be employed as anodes in Li ion batteries. Ni3Sn4 and Ni3Sn2 based compounds were obtained by ball milling of three different Ni–Sn mixtures. The properties of the resulting anodes for Li ion batteries were evaluated as a function of composition. Moreover, a biphasic system is presented, with CoSn2 and CoSn type structures, arising from the synthesis of the Sn31Co28C41 composition. When cycled in a Li cell, this material showed a high reversible specific capacity, about 450 mA h g−1, and a very good electrochemical and structural stability, making it of interest for application purposes.

Molecular dynamics simulations have been employed to investigate thermally-induced phase separation processes in nanometer-sized ${\text{Ag}}_{50}{\text{Cu}}_{50}$ rods and wires. In the absence of concentration gradients, the mechanism underlying the system decomposition consists of two stages. Roughly below 260 K, the thermal response is governed by the displacement of individual surface atoms. Above such temperature, phase separation proceeds via cooperative rearrangements involving also bulklike atomic species. The result is the formation of systems with an Ag-rich phase segregated at the surface. Significantly different thermal responses are obtained in the presence of concentration gradients perpendicular or parallel to the wire axis. First, the phase separation process is favored and takes place at lower temperatures. Second, an almost complete decomposition of the system in Ag- and Cu-rich domains is obtained and not the surface segregation of the Ag-rich phase. The decomposition is also accompanied by a considerable distortion of the originally regular nanowire shape.

A ternary mixed oxide Zn1−xMgxO has been doped with aluminium to create a range of transparent conducting oxides with tunable refractive index as well as work function. Conductive material was synthesised up to a magnesium concentration of x = 0.45, although the conductivity is reduced compared to standard ZnO:Al. The changes in band gap, work function, and conductivity have been attributed to a modified band structure and energetic position of the aluminium induced donor state.

A p-type transparent conductive oxide (TCO) was synthesised by codoping of poorly conducting chromium oxide (Cr2O3) with magnesium and nitrogen. We demonstrated that the codoping produced a TCO with good figure of merit despite using spray pyrolysis for deposition. The nitrogen enhances the specular transparency of the films in the visible range (400-700 nm), and Mg improves the conductivity while retaining the p-type character of the material. Co-doping with both elements produces a p-type oxide with a low resistivity of 3 Ω cm and transmission up to 65% for a 150 nm thick film. A comparison with other known p-type materials is given.

This work focuses on the growth of nanometre-sized Ag clusters in solution. Molecular dynamics simulations have been employed to gain the necessary detail on the dynamics of solute species and to study the mechanistic features of the processes governing the association of solute atoms in aggregates. Supersaturated liquid solutions of Ag in tetrachloromethane have been considered. A systematic variation of the concentration of Ag atoms in solution permitted us to show the different mechanistic scenarios responsible for the growth processes of solid Ag clusters. It is shown that such processes are limited by the thermal diffusion of solute in the solution bulk at relatively low supersaturation degrees, whereas the growth is limited by interfacial effects at relatively high supersaturation degrees.