Characterization of thin film lithium electrode materials

Thin rf-sputtered films of Li₄Fe_0.5±xTi_4.5±yO_11.75±z, Li₄Co_0.5±xTi_4.5±yO_11.5±z, Li₄Ti_5±xO_12±y, LiCo_1±xO_2±y and C were investigated by X-ray diffraction, thickness and weight determination, ICP/AAS, EDX and coulometric titration experiments employing the following liquid electrolytes (PC:EC:DMC=1:1:3, 1 M LiPF₆), (PC:DEC=1:4, 1 M LiPF₆), (EC:DMC=1:1, 1 M LiPF₆), (PC:DME=1:1, 1 M LiClO₄) and (γ-buthyrolactone, 1M LiClO₄). For comparison, cold isostatically pressed monolithic pellets of Li₄Fe_0.5Ti_4.5O_11.75, Li₄Co_0.5Ti_4.5O_11.5 and Li₄Ti₅O₁₂ were examined. The slope of the coulometric titration curves depends strongly on the employed liquid electrolyte. In the case of thin films, the stoichiometric width of the liquid electrolyte salt may have an additional impact on the results.     

Change of the oxidation state of phosphorus in sputtered Li3±xPO4±y and Li3±xPO4±yNz films

Thin Li_3±xPO_4±yN_zLi⁺- electrolyte films prepared by reactive rf-magnetron sputtering of Li₃PO₄ incorporate a certain amount of nitrogen which is made responsible for increased Li⁺-conductivity as well as at least kinetic stability with lithium metal. A possible change of the oxidation state +5 of phosphorus as a result of the sputter process has not yet been considered for explanation. We have found out that it cannot be generally assumed that reactive low power rf-magnetron sputtering of Li₃PO₄ results in fully oxidized films, even when pure O₂ is employed as sputtering gas. Our films immediately react with H₂O releasing a garlic smelling gas. The reaction area is surrounded by a white crust afterwards. CuSO₄ and AgNO₃ aqueous solutions become reduced. Impedance measurements yield an ionic conductivity of 2·10⁻⁶ S/cm at 25 °C and an activation energy of 0.62 eV.     

FTIR and spectroscopic ellipsometry investigations of the electron beam evaporated silicon oxynitride thin films

FTIR and variable angle spectroscopic ellipsometer in conjunction with computer simulation were employed to investigate the electron beam evaporated SiO_xN_y thin films. FTIR showed a large absorption band located between 600 and 1250 cm⁻¹, which indicates that Si-O and Si-N bands are overlap in SiO_xN_y films. A three layers model was used to fit the calculated data to the experimental ellipsometric spectra. The main layer was described by Cauchy model while the interface layer and the surface layer were described using Tauc-Lorenz oscillator and Bruggeman effective medium approximation, respectively. The thickness, the refractive index and the extinction coefficient were accurately determined. The refractive index at 630 nm was found to increase from 1.74 to 1.85 with increasing the film thickness from 191.6 to 502.2 nm. The absorption coefficient was calculated from the obtained extinction coefficient values and it has been used to calculate the Tauc and Urbach energies.     

Improving the gas barrier properties of a-SiOxCyNz film at low temperature using high energy and suitable nitrogen flow rate

Amorphous silicon oxycarbonitride thin films were synthesized on polyethylene terephthalate (PET) substrates at low temperatures (～80 °C) by plasma-enhanced chemical vapor deposition (PECVD). A high ion flux and suitable nitrogen flow rate improved the gas barrier properties and deposition rate of the resulting a-SiO_xC_yN_z film. The a-SiO_xC_yN_z films were deposited at a high deposition rate and low water WVTR properties as a result of the high ion flux and nitrogen chemistry. The high ion flux modified the chemical structure and nitrogen atomic composition of the resulting a-SiO_xC_yN_z film coatings. The substrate temperature was characterized using a thermometer. In addition, the coating properties were characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and the water vapor transmission rate (WVTR).     

Lithium electrochromic properties of atmospheric pressure plasma jet-synthesized tungsten/molybdenum-mixed oxide films for flexible electrochromic device

An investigation is conducted into the enhanced lithium electrochromic performance of flexible tungsten/molybdenum-mixed oxide (WMo _x O _y C _z ) films deposited onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates, using a low temperature (~23 °C) atmospheric pressure plasma-enhanced chemical vapor deposition with an atmospheric pressure plasma jet at various substrate distances. The rapid synthesis of flexible WMo _x O _y C _z films is performed by injecting the mixed hexacarbonyl and precursors W(CO)₆ and Mo(CO)₆ into an air plasma jet and exposing the substrate in the plasmas for short exposure durations (19–34 s) at various substrate distances. The flexible WMo _x O _y C _z films possess the remarkable Li⁺ ion electrochromic performance, even though after being bent 360° around a 2.5-cm diameter rod for 1,000 cycles and tested for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1-M LiClO₄-propylene carbonate electrolyte, respectively, by a potential sweep switching at the scan rates of ±50 mV/s from the potential of ?1 to 1 V and a potential step switching at the potentials of ?1 and 1 V. Significant optical modulation and optical density change of up to 71.2 % and 0.73 at a wavelength of 622 nm are respectively achieved.     

Effect of N2 ambient annealing on the field emission properties of HfNxOy thin films

HfN_xO_y thin films were deposited on Si substrates by direct-current sputtering. The influence of N₂ ambient annealing on the morphology, structure and field emission properties of the HfN_xO_y thin films was studied systematically. Scanning electron microscopy indicates that both the as-deposited and the annealed films are composed of nanoparticles, and the particle sizes of these films do not change much before and after annealing. Atomic force microscopy shows that the surface of the as-deposited films is smooth while that of the annealed films becomes rough, with many protrusions. X-ray diffraction patterns demonstrate that the as-deposited films are amorphous while the samples annealed at over 500 °C are polycrystalline. It is found that the field electron emission properties of the annealed films are better than those of the as-deposited films. The film annealed at 800 °C shows the best field emission properties. The mechanism for the improvement of the field electron emission property of the annealed thin films is also discussed. PACS 73.61.-r; 79.70.+q; 81.05.-t     

X-ray spectra and specific features of the structure of lithium-sodium cobaltite Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Na<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>CoO<Subscript>2</Subscript>

The electronic structure and specific features of the structure of nonstoichiometric cobaltite Li _x Na _y CoO₂ (x = 0.42, y = 0.36) have been studied comprehensively. The calculated multiplet for the lowspin state of the Co³⁺ ion agrees with the experimental spectra. It has been established using X-ray absorption spectra measured in the total photoelectric effect yield and total fluorescence yield modes that the Li _x Na _y CoO₂ cobaltite is stoichiometric with respect to the alkali metal near its surface and is defective inside. It has been demonstrated that the charge compensation in the case of an alkali metal deficit in LixNayCoO₂ is due to holes in O 2p states.     

Thermally activated ionic conduction and local structure in solid LiPON thin films

Compact lithium phosphorous oxynitride (LiPON) thin films, as a solid-state electrolyte for all solid-state Li batteries and electrochromic (EC) devices, with the high ratio of the triply coordinated –N< (N_t) over the doubly coordinated –N= (N_d) structural units was deposited by a conventional reactive RF magnetron sputtering of a Li₃PO₄ target at a low pure N₂ pressure. The effect of heat treatment from 200 to 500 °C on the ionic conductivity and local structure of LiPON thin films were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) core level analysis. A dramatical improvement of ionic conductivity from 1.1 to 3.28 μS/cm and microstructure changes were happened on the LiPON thin films while annealed for 1 h at 300 °C, which was linked to structural differences with a highest ratio of –N< over –N= structural units. The work proves that a proper heat treatment on LiPON thin film can effectively improve its ionic conductivity and change its microstructure.     

LixNayCoO2的制备和热电性质

用固相反应方法，成功地合成了具有交互生长结构的Li_xNa_yCoO₂单相多晶系列样品. 热电势测量表明，该系统的室温热电势比Na_xCoO₂体系约高出60μV/K. 基于空穴载流子具有O2p特征，提出Li_xNa_yCoO₂中额外的热电势来源于氧空穴的占位熵. 关键词： xNa_yCoO₂')" href="#">Li_xNa_yCoO₂ 热电势 热电材料     

ESR identification of a new N2− defect in X-ray irradiated NaN3

A relatively weak ESR spectrum is observed in single crystals of NaN₃ after X-ray irradiation at 77 K. This spectrum, which has an anisotropic g value and exhibits a resolved 5-line hyperfine structure with components in the ratio 1:2:3:2:1, corresponds to a single unpaired electron interacting symmetrically with two spin-one nuclei, in three inequivalent sites. The spin-Hamiltonian parameters are: g_x = 2.0054 ± 0.0005, g_y = 2.0045 ± 0.0005, g_z = 1.9688 ± 0.0005, |A_x| = 4.0 ± 0.2 G, |A_y| = 20.0 ± 0.2 G, and |A_z| = 4.9 ± 0.2 G, c-axis, and y is perpendicular to the c-axis. This spectrum, which is clearly different from that of substitutional N₂^?reported by Gelerinter and Silsbee, is attributed to interstitial N₂^?.     

Structural, optical properties and band gap alignments of ZrOxNy thin films on Si (1 0 0) by radio frequency sputtering at different deposition temperatures

ZrO_xN_y thin films have been prepared by radio frequency magnetron sputtering at various substrate temperatures. The effect of substrate temperature on structural, optical properties and energy-band alignments of as-deposited ZrO_xN_y thin films are investigated. Atomic force microscopy results indicate the decreased root-mean-square (rms) values with substrate temperature. Fourier transform infrared spectroscopy spectra indicate that an interfacial layer has been formed between Si substrate and ZrO_xN_y thin films during deposition. X-ray photoelectron spectroscopy and spectroscopy ellipsometry (SE) results indicate the increased nitrogen incorporation in ZrO_xN_y thin films and therefore, the decreased optical band gap (E_g) values as a result of the increased valence-band maximum and lowered conduction-band minimum.     

Influence of the substrate material on the properties of pulsed laser deposited thin Li1+xMn2O4−δ films

Thin Li_1+xMn₂O_4−δ films were deposited on several substrate materials (stainless steel, p-doped silicon and glassy carbon) by pulsed laser deposition. To obtain the correct thin film stoichiometries, targets with a different amount of excess lithium were required (Li_1.03Mn₂O₄ + xLi₂O; x = 2.5 and 7.5 mol%). The resulting polycrystalline thin films were characterized with respect to their morphology and electrochemical activity. It was found that only thin Li_1+xMn₂O_4−δ films deposited on stainless steel and glassy carbon showed the typical insertion and deinsertion peaks of Li⁺ during cycling.     

X-ray reflectivity and photoelectron spectroscopy of superlattices with silicon nanocrystals

The structural properties and features of the chemical composition of SiO _x N _y /SiO₂, SiO _x N _y /Si₃N₄, and SiN _x /Si₃N₄ multilayer thin films with ultrathin (1–1.5 nm) barrier SiO₂ or Si₃N₄ layers are studied. The films have been prepared by plasma chemical vapor deposition and have been annealed at a temperature of 1150°С for the formation of silicon nanocrystals in the SiO _x N _y or SiN _x silicon-rich layers with a nominal thickness of 5 nm. The period of superlattices in the studied samples has been estimated by X-ray reflectivity. The phase composition of superlattices has been studied by X-ray electron spectroscopy using the decomposition of photoelectron spectra of the Si 2p, N 1s, and O 1s levels into components corresponding to different charge states of atoms.     

Li3V2(PO4)3 modified LiFePO4/C cathode materials with improved high-rate and low-temperature properties

LiFePO₄/C surface modified with Li₃V₂(PO₄)₃ is prepared with a sol–gel combustion method. The structure and electrochemical behavior of the material are studied using a wide range of techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. It is found that LiFePO₄/C surface modified with Li₃V₂(PO₄)₃ has the better electrochemical performance. The discharge capacity of the as-prepared material can reach up to 153.1, 137.7, 113.6, and 93.3 mAh g^?1 at 1, 2, 5, and 10 C, respectively. The capacitance of the LiFePO₄/C modified by Li₃V₂(PO₄)₃ is higher under lower discharging rate at ?20 °C, and the initial discharge capacity of 0.2 C is 131.4 mAh g^?1. It is also demonstrated that the presence of Li₃V₂(PO₄)₃ in the sample can reduce the charge transfer resistance in the range of ?20 to 25 °C, resulting in the enhanced electrochemical catalytic activity.     

The influence of lithium excess in the target on the properties and compositions of Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2</Subscript>O<Subscript>4−<Emphasis Type="Italic">δ</Emphasis></Subscript> thin films prepared by PLD

Li–Mn–O thin films were deposited by pulsed laser deposition (PLD) onto stainless steel substrates using targets containing different concentrations of added Li₂O. The influence of the target composition on the stoichiometry of the resulting thin films, the surface morphology and the electrochemical properties was studied. The application of the target with added 7.5 mol% Li₂O results in an almost ideal lithium content, while all films were still oxygen deficient. The thin films were applied as electrodes in Li//Li_1+x Mn₂O_4−δ cells (i.e. model cells for a rechargeable Li-ion battery) and characterized by cyclic voltammetry and galvanostatic charge/discharge experiments. The electrochemical measurements of the thin films confirmed that the thin films can serve as good model systems and that they show a sufficient cyclability.     

XPS and SIMS characterisation of TiOxNy solar absorber films

Solar thermal collectors have been prepared with thin TiO_xN_y films deposited using ion beam assisted deposition, on Si and Cu substrates. The films are amorphous and x and y were controlled by altering the O₂/N₂ ratio in the gas source. After annealing at temperatures of 200 – 400 °C, films have been depth profiled using Secondary Ion Mass Spectrometry. Profiles reveal the degradation of the film, particularly for films on Cu substrates, by migration of the substrate atoms through the films, to the sample surface. In general, films with x<1 and y>1 show improved temperature stability, ultimately at the expense of a reduced transmission window. Contrary to previous suggestions in the literature, the degradation mechanism initially involves the formation of a nitrogen rich phase, rather than an oxide at the film surface. On copper substrates, the nature of the films and of this phase, formed by diffusion of the substrate atoms, have been investigated by X-ray photoelectron spectroscopy (XPS). These investigations reveal complex behaviour in the early stages of film failure, with the suggestion that the initial films, at least near the surface, are two phase, and the reaction layer mixes the TiO_xN_y with some Ti replacement by ions from the Cu substrate.     

Lithium ion conductive glass and its application to solid state batteries

Three kinds of coin-type battery, In-Li_x / Li_1−xCoO₂, Li_4/3+xTi_5/3O₄ / Li_1−xCoO₂, and Li_2+xFeS₂ / Li_1−xCoO₂, were fabricated with a Li⁺ ion conductive glass as an electrolyte, and their properties were investigated. They show excellent performance thanks to the solid electrolyte. Iron sulfide is found to be an excellent electrode material in solid state rechargeable batteries. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

High thermoelectric power in a NaxCoO2 thin film prepared by sputtering with rapid thermal annealing

Na_xCoO₂ thin films were fabricated by means of RF-magnetron sputtering. We measured and analyzed the thermal properties and changes of the Na_xCoO₂ crystal structure by XRD, SEM, Raman spectra, and XPS analyses. Sodium ions diffused from the bulk of the thin film to the surface as the temperature increased. The diffused Na ions reacted with oxygen ions and Na₂O was formed on the surface of the thin film, resulting in a decrease of the carrier concentration and a change of the crystal structure from a layer to a spinel structure. The Seebeck coefficient of the Na_xCoO₂ thin film annealed at 550 °C is larger than the value (100 μV/K) for single crystal NaCo₂O_4.     

ZrN, ZrxAlyN and ZrxGayN thin films – novel materials for hard coatings grown using pulsed laser deposition

High-quality thin films of ZrN, Zr_xAl_yN and Zr_xGa_yN have been grown by pulsed reactive crossed-beam laser ablation using Zr, Zr-Al and Zr-Ga ablation targets, respectively, and a N₂ gas pulse. The films were characterized for their chemical, crystallographic and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between room temperature and 600 °C. High-quality epitaxial films could be grown on Si (001) at 400 °C, though the crystallinity was disrupted at 525 °C by Si diffusion into the film bulk and the formation of ZrSi₂ crystallites. Films grown on stainless steel were polycrystalline. The ratios of the metals in the alloy targets were in general not equal to those in the films: the Al content in the Zr_xAl_yN films was lower than the target value, which we attribute to differential scattering in the ablation plume. The Ga content in the Zr_xGa_yN films fell with increasing substrate temperature, indicative of re-evaporation of Ga from the substrate surface. Those Zr_xGa_yN films with the highest Ga content, grown at the lowest temperatures, were particularly nitrogen-deficient, which we attribute to the low reactivity of Ga with N₂. The Zr_xAl_yN films had an exceptionally low coefficient of friction (0.20) versus steel and the greatest nanohardness of 28 GPa. Received: 9 November 2000 / Accepted: 14 November 2000 / Published online: 28 February 2001     

Optimization of plasma-deposited silicon oxinitride films for optical channel waveguides

In view of applications of SiO_xN_y thin films in MOEMS technology, a study of the optomechanical characteristics of the PECVD deposited material are investigated. To optimize the quality of SiO_xN_y layers we establish the relationship between the chemical properties, optical performances, micromechanical stress, and growth parameters of deposited films. To use the SiO_xN_y thin film for the core layer of a strip-loaded waveguide, we propose preparation conditions of SiO_xN_y that offer a low-loss optical waveguide with well-controlled refractive index, based on a low-internal stress multilayer structure.