A. W. Czanderna

Chromic Mechanism in Amorphous WO 3 Films

The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6{minus}} and W{sup 4{minus}} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polars transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.

Electrochromic coloration efficiency of a-WO3−y thin films as a function of oxygen deficiency

We report on how electrochromic coloration is affected by oxygen deficient stoichiometries in sputtered amorphous tungsten oxide (a-WO3−y) films. The electrochromic coloration efficiency increases with increasing oxygen deficiency in (a-WO3−y) films. No coloration is observed in nearly stoichiometric WO3 films. Raman spectroscopic studies reveal that the number of W5+ states generated with lithium insertion increases with the oxygen deficiency. Furthermore, there are no Raman peaks resulting from W5+ states in lithiated a-WO3−y films with near perfect stoichiometry, which is consistent with the absence of electrochromic coloration in those films. We conclude that the coloration efficiency of a-WO3−y films depends on the number of the W5+ states generated by lithium insertion and that the oxygen deficiency plays an important role in generating the W5+ states with lithium insertion.

Interactions and penetration at metal/self‐assembled organic monolayer interfaces

The purpose of research on metals (M) deposited onto self‐assembled monolayers (SAMs) is to understand the interactions between the metal and eventually metal oxide overlayers on well‐ordered organic surfaces. Applications of M/SAM and inorganic/SAM research results to the understanding of real inorganic/organic interfaces in vacuum and under environmental conditions can potentially play a key role in the development of advanced devices with stable interfacial properties. The results of M/SAM studies to date are reviewed, M/SAM combinations ranked according to reactivity and penetration, and specific examples of reactive interfaces (Cu/COOH, and Cr/COOH) and nonreactive interfaces with penetration (Ag/COOH) are used to illustrate the extremes.

Weak interactions between deposited metal overlayers and organic functional groups of self-assembled monolayers☆

The purpose of our research is to study the reactions, interactions or penetration between vacuum-deposited metals (M) and the organic functional end groups (OFGs) of self-assembled monolayers (SAMs) under controlled conditions. Metal/SAM systems are models for understanding bonding at M/organic interfaces and the concomitant adhesion between the different materials. In broad terms, the M/OFGs form interacting interfaces (e.g., Cr/COOH or Cu/COOH) in which the deposit resides on top of the OFGs or weakly interacting interfaces through which the overlayer penetrates and resides at the SAM/gold interface. We present a review of XPS results from weakly interacting systems (e.g., Cu/OH, Cu/CN, Ag/CH 3 , Ag/COOH) and discuss in more depth the time-temperature dependence of the disappearance of the metal from the M/SAM interface following deposition. In this work, XPS and ISS were used to characterize octadecanethiol (ODT, HS(CH 2 ) 17 CH 3 ), mercaptoundecanoic acid (MUA, HS(CH 2 ) 10 COOH), and mercaptohexadecanoic acid (MHA, HS(CH 2 ) 1S COOH) SAMs before and after depositing up to 1.0 nm Ag or Cu at ca. 10 -7 torr. The SAMs were prepared by self-assembly onto gold films on silicon substrates in an ethanolic thiol solution. XPS spectra indicate that no strong interaction occurs between the deposited Ag and the COOH organic functional group (OFG) of MUA or MHA, although a stronger interaction is evident for MHA, and a unidentate is formed for Cu on mercaptoundecanol (MUO). The Ag interaction with ODT is weak. ISS compositional depth profiles (CDPs) for Ag on MHA and MUA and ODT are compared over a temperature range of 113 to 293 K. The ISS results indicate that Ag remains on the surface of MUA for up to 1 h after deposition, whereas Ag penetrates ODT in less than 5 min at 295 K. The time for Ag to penetrate into MHA is several times longer than for MUA, depending on the SAM temperature. The time dependence of the slower Ag penetration through MUA and MHA is compared with that for ODT at temperatures below 295 K. Although Ag/OFGs are expected to have relatively weak interactions, the Ag/COOH system was anticipated to be more interactive than was found, so rapid penetration of Ag through the COOH SAM is an unexpected result.

Durability issues and service lifetime prediction of electrochromic windows for buildings applications

Abstract In general, the purposes of this paper are to elucidate the crucial importance of durability and service lifetime prediction (SLP) for electrochromic windows (ECWs) and to present an outline for developing a SLP methodology for ECWs. The specific objectives are (a) to illustrate the generic nature of SLP for several types of solar energy conversion or energy conservation devices, (b) to summarize the major durability issues associated with ECWs, (c) to justify using SLP in the triad of cost, performance, and durability rather than just durability, (d) to define and explain the seven major elements that constitute a generic SLP methodology, (e) to provide background for implementing the SLP methodology for ECWs, including the complexity of the potential degradation mechanisms, and (f) to provide an outline of studies using ECWs for improving the durability of ECW materials and predicting a service lifetime for ECWs using the SLP methodology outlined in objective (d). Our major conclusions are that substantial R&Dis necessary to understand the factors that limit ECW durability, and that it is possible to predict the service lifetime of ECWs.

Ion scattering and X-ray photoelectron spectroscopy of copper overlayers vacuum deposited onto mercaptohexadecanoic acid self-assembled monolayers

Abstract Metal overlayers deposited in vacuum onto self-assembled monolayer (SAM) systems serve as models for more complex metalized polymers. Metals (M) deposited onto SAMs with different organic functional end groups exhibit a wide range of behavior, ranging from strong chemical interactions with the end group to complete penetration of the metal through the SAM. In this work, we have characterized the interactions of Cu with the COOH of mercaptohexadecanoic acid (MHA, HOOC(CH 2 ) 15 SH) SAMs self assembled on gold films by using X-ray photoelectron spectroscopy (XPS) to examine the chemical interactions, and a combination of XPS and ion scattering spectroscopy (ISS) to deduce the growth mode and penetration rate of the deposited Cu. We found that submonolayer amounts of Cu react with HOOC, whereas the rest of the Cu remains metallic and penetrates beneath the SAM surface to the SAM ∣ Au interface. Considerable amounts of Cu (5 nm or more) will penetrate beneath the SAM layer, which is ca. 2.5 nm thick, despite the submonolayer presence of Cu at the SAM surface. The penetration rate depends strongly on the Cu deposition rate. Depositing copper onto MHA at 220 K or less, or using faster Cu deposition rates, results in slower or even completely suppressed penetration of the Cu through the SAM layer, whereas exposure to X-rays greatly enhances the penetration rate of large amounts of Cu through the SAM layer. The reacted copper is, based on the XPS 2p and LMM peaks, in the +2 oxidation state, but cannot be identified with a simple, stoichiometric oxide such as Cu 2 O, CuO, or Cu (OH) 2 .

Optimization Study of Solid‐State Electrochromic Devices Based on WO 3 / Lithium ‐ Polymer Electrolyte / V 2 O 5 Structures

Transmissive solid-state electrochromic devices based on the structure of WO[sub 3]/lithium-polymer electrolyte/V[sub 2]O[sub 5] were optimized for potential large-area window applications. The electrochromic layer thicknesses, polymer molecular weights, lithium-containing electrolytes, preassembly lithium-ion injection amounts, and transparent conductor substrates were systematically investigated for large optical modulation and fast response of the devices. The transmittance of the optimized device at 633 nm can be switched between 74 and 12% in 1 min. The coloring and bleaching voltages were [minus]1.8 and 1.2 V, respectively.

Metal overlayers on organic functional groups of self‐organized molecular assemblies. II. X‐ray photoelectron spectroscopy of interactions of Cu/CN on 12‐mercaptododecanenitrile

The interaction of evaporated copper overlayers, from 0.03 to 0.4 nm thick, with specific terminal functional groups of an organized molecular assembly (OMA) of HS(CH2)11CN formed on gold has been studied by x‐ray photoelectron spectroscopy. For average copper coverages above 0.1 nm, the peak intensities show fair agreement with a model that assumes an increasing fraction of each increment of the deposited copper penetrates the OMA and resides at the OMA/Au interface. For lower coverages, a weak Cu(CN) interaction is indicated by shifts of the N 1s level and the C 1s high binding energy (HBE) shoulder to lower binding of as well as by the presence of a Cu 2p HBE shoulder.

Accelerated durability testing of electrochromic windows

Abstract Prototype electrochromic windows made by several different US companies have been tested in our laboratory for their long-term durability. Samples were subjected to alternate coloring and bleaching voltage cycles while exposed to simulated 1-sun irradiance in a temperature-controlled environmental chamber with low relative humidity. The samples inside the chamber were tested under a matrix of different conditions. These conditions include: cycling at different temperatures (65, 85 and 107°C) under the irradiance, cycling versus no-cycling under the same irradiance and temperature, testing with different voltage waveforms and duty cycles with the same irradiance and temperature, cycling under various filtered irradiance intensities, and simple thermal exposure with no irradiance or cycling. The electro-optical characteristics of the samples were measured between 350 and 1,100 nm every 4,000 cycles for up to 20,000 cycles. Photographs of the samples were taken periodically with a digital camera to record cosmetic defects, the extent of residual coloration, and overall coloration and bleaching uniformity of the samples. Our results indicate that the most important cause of degradation is the combination of continuous cycling, elevated temperature and irradiance. The relative importance of these variables, when considered synergistically or separately, depends on the particular device materials and design.

Metal overlayers on organic functional groups of self-assembled monolayers: VIII. X-ray photoelectron spectroscopy of the Ni/COOH interface

The interaction of vacuum deposited Ni with the COOH organic functional groups of mercaptoundecanoic acid [HS(CH2)10COOH] self-assembled monolayers formed on an Au substrate has been characterized with in situ x-ray photoelectron spectroscopy. Steady loss and complete disappearance of the hydroxyl component of O 1s peak at 532.8 eV provides evidence for the formation of a Ni–O bond at the Ni/COOH interface. Further evidence for interfacial compound formation is provided by a binding energy shift in the high binding energy component of the Ni 2p3/2 peak from 854.8 to 854.4 eV for Ni coverages below ∼0.2 nm. These results are consistent with the donation of electrons from the deposited Ni to the COOH oxygens at low Ni coverages. The absence of the characteristic satellite feature in the Ni 2p peak excludes the possibility that a full electron charge is donated to each COOH organic functional group as a bidentate complex. However, the data are consistent with a two step reaction mechanism in which Ni initial...