Monica Veszelei

Electrochromic devices embodying W oxide/Ni oxide tandem films

Six-layer electrochromic devices of indium tin oxide (ITO)/NiOxHy/WO3/ZrP-electrolyte/WO3/ITO were made by reactive dc magnetron sputtering and lamination. The WO3 layer between the acidic ZrP-based electrolyte and the NiOxHy layer served as optically passive protective layer. The optical inactivity of the protective layer could be understood from arguments based on electron density of states.

Optical constants and Drude analysis of sputtered zirconium nitride films

Opaque and semitransparent dc magnetron-sputtered ZrN films on glass and silicon have been optically characterized with spectral reflectance measurements and ellipsometry. High rate sputtered ZrN has good optical selectivity, i.e., higher than 90% infrared reflectance and a pronounced reflectance step in the visible to a reflectance minimum of less than 10% at 350 nm. The results are comparable with those obtained for single crystalline samples and those prepared by chemical vapor deposition. The complex optical constant (N = n v ik) for opaque films has been determined in the 0.23-25-µm wavelength range with Kramers-Kronig integration of bulk reflectance combined with oblique incidence reflectance for p-polarized light. A variable angle of incidence spectroscopic ellipsometer has been used for determination of the optical constants in the 0.28-1.0-µm wavelength region. The results of the two methods show excellent agreement. The results indicate that ZrN is free electronlike and the Drude model can be applied. The best opaque films had Drude plasma energies (ħω(p) between 6.6 and 7.5 eV and relaxation energies (ħ/τ) between 0.29 and 0.36 eV. Ellipsometer data for the semitransparent films show that the refractive index (n) in the visible increases with decreasing film thickness whereas the extinction coefficient (k) is essentially unchanged. The optical properties are improved by deposition upon a heated substrate.

Transparent ion intercalation films of Zr–Ce oxide

Zr–Ce oxide films were made by reactive dc magnetron cosputtering. The elemental composition was determined by Rutherford backscattering spectrometery and the crystalline structure by x-ray diffraction. Li intercalation/deintercalation was accomplished potentiodynamically in a liquid electrolyte. The films remained fully transparent irrespective of their degree of lithiation, which may be reconciled with a population/depopulation of Ce 4f levels.

Zirconium nitride based transparent heat mirror coatings —preparation and characterisation

Transparent heat mirror coatings based on thin zirconium nitride films have been prepared using reactive magnetron sputtering. The zirconium nitride films have been sandwiched between layers of zirconium oxide. It is shown that the multilayer configuration ZrO2/ZrN/ZrO2 can be used as solar control coatings on window glazings. A visible transmittance of around 60% and a thermal emittance lower than 0.2 can be obtained, and the ratio between visible transmittance and total solar transmittance can be as high as 1.7. The influence of substrate temperature on the optical quality of the films is evaluated and it is shown that the crystal structure of the first oxide layer is of importance for the optical quality of the nitride. The influence of preparation conditions and accelerated ageing has been modelled using the optical constants of thin films prepared under identical conditions as the films in the multilayer coatings.

Optical and electrochemical properties of Li+ intercalated Zr–Ce oxide and Hf–Ce oxide films

Sputter deposited Zr–Ce oxide and Hf–Ce oxide films were investigated with regard to structure, optical absorption, and electrochemical properties. X-ray diffractometry and Rutherford backscattering spectrometry showed that polycrystalline Zr–Ce oxide and Hf–Ce oxide films had cubic crystal structures for 40–100 mol % CeO2 and 50–100 mol % CeO2, respectively. Cyclic voltammetry was performed in an electrolyte of propylene carbonate containing LiClO4. The charge capacity was ∼60 mC/cm2μm for a Zr–Ce oxide film with a Ce/Zr atom ratio of ∼13 as well as for a Hf–Ce oxide film with a Ce/Hf atom ratio of ∼2. A decrease of the charge capacity was noted after ∼1000 voltammetric cycles, with the mixed oxide films being far more stable than CeO2. In situ optical transmittance measurements showed that both Zr–Ce and Hf–Ce oxide films remained essentially transparent during Li+ intercalation. Chronopotentiometry measurements were used to elucidate effects of the electronic structure during Li+ intercalation.

Zr-Ce Oxides as Candidates for Optically Passive Counter Electrodes

Abstract Zr–Ce oxide films with compositions from pure Zr oxide to pure Ce oxide were made by reactive DC magnetron co-sputtering. The composition and structure were determined by Rutherford backscattering and X-ray diffraction. Pure Ce oxide films have high charge capacity and are optically passive under charge insertion; they are, however, chemically unstable in an electrolyte of LiClO 4 in propylene carbonate. Pure Zr oxide has practically zero charge capacity. Zr–Ce oxide films have high (above 80%) optical transmittance, high charge capacity, and good chemical stability. These films remain fully transparent irrespective of their degree of lithiation, which may be reconciled with electrons accommodating 4f states of Ce.

Cerium-containing counter electrodes for transparent electrochromic devices

Films of Me-Ce oxide (Me: Ti, Zr, Sn, W) and of Ni-Ce hydroxide were produced by reactive magnetron co-sputtering. Li intercalation in Me-Ce oxide, and H exchange in Ni-Ce hydroxide, were accomplished electrochemically. Electrochromism was quenched in proportion with the Ce content in Me-Ce oxide. Films of Zr-Ce (and to some extent Ti-Ce) oxide were able to serve as fully transparent counter electrodes, of much interest for transparent electrochromic devices. In Ni-Ce hydroxide, the Ce addition enhanced the capacity for charge exchange.

Optical properties and equilibrium temperatures of titanium-nitride- and graphite-coated Langmuir probes for space application

The equilibrium temperature of a coated Langmuir probe in space is determined by the optical properties of the coating and the geometry of the probe. In this investigation we report on the optical properties of graphite- and TiN-coated aluminium and titanium. Earlier results have shown that a TiN-coated sphere is preffered as a Langmuir probe for the Cassini satellite bound to Saturn owing to the hardness, chemical inertness and photoelectric stability of the TiN coating. The TiN coatings were prepared by high temperature nitriding of a titanium alloy in pure nitrogen gas. An epoxy-based graphite dispersion (DAG 213) was used to apply the graphite coating. The integrated total solar absorptance αs was calculated, for a spherical and a cylindrical probe, using measured total reflectance. Total hemispherical emittance ϵH(T) of spherical samples was measured using a calorimetric method and compared with infrared reflectance measurements from 2 to 30 μm. The ratio αsϵH for graphite was determined to be 0.95−1.11 for spherical and cylindrical probes in the temperature interval 90−380 K. For TiN the ratio αsϵH is 2.64−4.64 for temperatures between 130 and 490 K. Equilibrium temperatures for spherical and cylindrical probes were estimated for solar constants at Venus, Earth and Saturn.

Optical constants of sputtered ZrN films for heat mirror applications

Opaque and semi-transmitting film of ZrN have been reactively magnetron sputtered and their optical performance for solar control coating applications evaluated. The optical constants of the opaque films were determined from near normal reflectance measurements and Kramers- Kronig calculations over the interval 0.23 - 3.0 micrometers . The thin film optical constants were determined with combined R- and T-measurements. Systematic variations with growth conditions were observed. Thin films were observed to have higher n-values in the visible, a change that could be partly compensated by substrate heating. For the triple layers: glass / ZrO2 / ZrN / Zro2 it was noted that the crystallinity of the first oxide did not influence the refractive index of this oxide, but improved significantly the selectivity of the nitride growing upon it. Triple layers for solar control applications with 57% luminous transmittance and close to 1/3 each of solar transmittance, reflectance and absorption have been realized.

Drude analysis of transition metal nitride films for solar control and low-E multilayers

The Drude-like behavior of the group IVB metal nitrides: TiN, ZrN and HfN furnishes the physical basis for the use of these hard, inert materials as replacement for noble metals in optically selective multilayers. A low value of the refractive index, n, in the visible region and rapidly increasing extinction coefficient, k, when the wavelength increases into the infrared, is characteristic for these nitrides, although to a lesser extent than for the noble metals. A screened Drude model can be fitted to the experimental dielectric function over the near infrared and at least part of the visible spectrum to determine the parameters: plasma resonance energy hvp and relaxation time (tau) . Systematic studies of TiN and ZrN films show that n increases with decreasing film thickness below 60 nm when the film transmits. This increase can be modelled with a increasing Drude parameter (tau) and has previously been explained as an extrinsic effect from defects etc. It is argued that most of this change can be understood as an effect of diffuse scattering against the back surface of the film and is therefore not cured by improvements in deposition technology.