@article {11792, title = {Electrochromic lithium nickel oxide by pulsed laser deposition and sputtering}, journal = {Solar Energy Materials and Solar Cells}, volume = {54}, number = {4-Jan}, year = {1998}, month = {07/1998}, pages = {59-66}, chapter = {59}, abstract = {

Thin films of lithium nickel oxide were deposited by sputtering and pulsed laser deposition (PLD) from targets of pressed LiNiO2 powder. The composition and structure of these films were analyzed using a variety of techniques, such as nuclear-reaction analysis, Rutherford backscattering spectrometry (RBS), X-ray diffraction, infrared spectroscopy, and atomic-force microscopy. Crystalline structure, surface morphology and chemical composition of LixNi1-xO thin films depend strongly on deposition oxygen pressure, temperature as well as substrate{\textendash}target distance. The films produced at temperatures lower than 600{\textdegree}C spontaneously absorb CO2 and H2O at their surface once they are exposed to the air. The films deposited at 600{\textdegree}C proved to be stable in air over a long period. Even at room temperature the PLD films are denser and more stable than sputtered films. RBS determined the composition of the best films to be Li0.5Ni0.5O deposited by PLD at 60\ mTorr O2 pressure. Electrochemical tests show that the films exhibit excellent reversibility in the range 1.0{\textendash}3.4\ V versus lithium. Electrochemical formatting which is used to develop electrochromism in other films is not needed for the stoichiometric films. The optical transmission range is almost 70\% at 550\ nm for 150\ nm-thick films. Devices made from these films were analyzed using novel reference electrodes and by disassembling after cycling.

}, keywords = {Lithium nickel oxide, pulsed laser deposition, sputtering}, doi = {10.1016/S0927-0248(97)00223-7}, author = {Michael D. Rubin and Shi-Jie Wen and Thomas J. Richardson and John B. Kerr and Klaus von Rottkay and Jonathan L. Slack} } @conference {11545, title = {Analysis of Durability in Lithium Nickel Oxide Electrochromic Materials and Devices}, booktitle = {2nd International Meeting on Electrochromism}, year = {1996}, month = {10/1996}, address = {San Diego, CA}, abstract = {

Thin films of lithium nickel oxide were deposited by sputtering and laser ablation from targets of pressed nickel oxide and lithium oxide powders. These films were assembled into electrochromic test devices with tungsten oxide as the opposite electrode and a polymer electrolyte. Analysis of the failure modes was carried out at several levels: The composition and structure of the films were examined before and after cycling using a variety of techniques, such as infrared spectroscopy, nuclear-reaction analysis, Rutherford backscattering spectrometry, x-ray diffraction and atomic force microscopy. Absorption of water vapor was found to be a major factor determining the cyclic stability of the films. A new technique is described for incorporating reference electrodes made from an electronically isolated corner into devices. This structure enabled identification of potential problems associated with a particular interface. Finally, some of the devices were disassembled and the components examined. For example, a small quantity of the polymer was extracted and studied by gas chromatography and mass spectroscopy. Small organic fragments were discovered which correspond to expected weak points in the polymer structures.

}, author = {Shi-Jie Wen and John B. Kerr and Michael D. Rubin and Jonathan L. Slack and Klaus von Rottkay} } @conference {11793, title = {Electrochromic Lithium Nickel Oxide Thin Film by Pulsed Laser Deposition}, booktitle = {Electrochemical Society Meeting}, volume = {96-24}, year = {1996}, month = {10/1996}, pages = {54-63}, address = {San Antonio, TX}, abstract = {

Thin films of lithium nickel oxide were deposited by pulsed laser deposition (PLD) from targets of pressed LiNiO2 powder with layered structure. The composition, structure and surface air sensitivity of these films were analyzed using a variety of techniques, such as nuclear reaction analysis, Rutherford backscattering spectrometry (RBS), x-ray diffraction, infrared spectroscopy, and atomic force microscopy. Optical properties were measured using a combination of variable angle spectroscopic ellipsometry and spectroradiometry. Crystalline structure, surface morphology and chemical composition of LixNi1-xO thin films depend strongly on deposition oxygen pressure, temperature as well as substrate target distance. The films produced at temperatures lower than 600 {\textdegree}C spontaneously absorb CO2 and H2O at their surface once they are exposed to the air. The films deposited at 600 {\textdegree}C proved to be stable in air over a long period. Even when deposited at room temperature the PLD films are denser and more stable than sputtered films. RBS determined that the best electrochromic films had the stoichiometric composition Li0.5Ni0.5O when deposited at 60 mTorr O2 pressure. Electrochemical tests show that the films exhibit excellent reversibility in the range 1.0 V to 3.4 V versus lithium and long cyclic life stability in a liquid electrolyte half cell. Electrochemical formatting which is used to develop electrochromism in other films and nickel oxide films is not needed for these stoichiometric films. The optical transmission range is almost 70\% at 550 nm for 120 nm thick films.

}, author = {Shi-Jie Wen and Klaus von Rottkay and Michael D. Rubin} } @article {12146, title = {Optical Indices of Electrochromic Tungsten Oxide}, journal = {Thin Solid Films}, volume = {306}, number = {1}, year = {1996}, month = {08/1997}, pages = {10-16}, chapter = {10}, abstract = {

Tungsten trioxide (WO3) is the most widely used material for the active layer of electrochromic devices. Knowledge of the complex refractive index over the range of coloration states is required for device design. Optical constants of WO3 over the whole solar spectrum were determined as a function of injected charge. Films of WO3 were prepared by electron-beam evaporation, then colored in several steps by reduction with lithium (Li) up to 68 mC cm-2 {\textmu}m-1 injected charge. Measurements included variable-angle spectroscopic ellipsometry and spectroscopic transmittance and reflectance at normal incidence. Analysis was complicated by the fact that a transparent-conducting layer of indium tin oxide (ITO) was required to perform lithiation. Optical indices of the glass substrate and ITO transparent conductor were determined separately and then fixed in the model. The indices of WO3 could then be extracted from measurements on the complete structure. A parametric dispersion model corresponding to Gaussian broadening of the oscillators was used to represent the dielectric response of WO3.

}, keywords = {Colored state, Complex refractive index, electrochromic, tungsten oxide}, doi = {10.1016/S0040-6090(97)00254-X}, author = {Klaus von Rottkay and Michael D. Rubin and Shi-Jie Wen} } @article {12147, title = {Optical Indices of Lithiated Electrochromic Oxides}, journal = {Solar Energy Materials and Solar Cells}, volume = {54}, number = {4-Jan}, year = {1996}, month = {07/1998}, pages = {49-57}, chapter = {49}, abstract = {

Optical indices have been determined for thin films of several electrochromic oxide materials. One of the most important materials in electrochromic devices, WO3, was thoroughly characterized for a range of electrochromic states by sequential injection of Li ions. Another promising material, Li0.5Ni0.5O, was also studied in detail. Less detailed results are presented for three other common lithium-intercalating electrochromic electrode materials: V2O5, LiCoO2, and CeO2-TiO2. The films were grown by sputtering, pulsed laser deposition (PLD) and sol-gel techniques. Measurements were made using a combination of variable-angle spectroscopic ellipsometry and spectroradiometry. The optical constants were then extracted using physical and spectral models appropriate to each material. Optical indices of the underlying transparent conductors, determined in separate studies, were fixed in the models of this work. The optical models frequently agree well with independent physical measurements of film structure, particularly surface roughness by atomic force microscopy. Inhomogeneity due to surface roughness, gradient composition, and phase separation are common in both the transparent conductors and electrochromics, resulting sometimes in particularly complex models for these materials. Complete sets of data are presented over the entire solar spectrum for a range of colored states. This data is suitable for prediction of additional optical properties such as oblique transmittance and design of complete electrochromic devices.

}, doi = {10.1016/S0927-0248(97)00222-5}, author = {Michael D. Rubin and Klaus von Rottkay and Shi-Jie Wen and Nilg{\"u}n {\"O}zer and Jonathan L. Slack} }