Toward Efficient Electrochromic NiO x Films: A Study of Microstructure, Morphology, and Stoichiometry of Radio Frequency Sputtered Films

Abstract

In this work, NiO films were deposited by reactive radio frequency sputtering, varying either the oxygen flow or the power during deposition. The morphology was studied by atomic force microscopy. The Ni/O and Ni/H ratios were determined by Rutherford backscattering spectroscopy and forward recoil spectroscopy. The microstructure of pristine and colored or bleached films were investigated by means of X-ray diffraction. The electrochromic and mechanical behavior in aqueous alkaline electrolyte were investigated in situ. Samples deposited at low oxygen flow (or high power) are transparent, and have the highest Ni/O ratio and the lowest Ni/H ratio. The effective area is also greater for these samples. Samples deposited at high oxygen flow (or low power) are dark brown and present the lowest Ni/O ratio and the highest Ni/H ratio. For all samples, the Ni/O ratio is lower than 1. All films were cubic NiO, with preferred orientation in the (111) direction. Lattice parameters and crystalline grain size increase with the increase of oxygen flow (or decrease of power) during deposition. The highest optical contrast and lowest stress changes upon intercalation were obtained for samples deposited at low oxygen flow. Nonintentional, low-size dopants, like H, favor the mechanical stability of the films.

Electrochemical characterization of NiO electrodes deposited via a scalable powder microblasting technique

“…(1)] is not controlled by the surface area or by the mesoporosity of the electrodes. 59 It is more likely that current density is controlled by bulk characteristics such as the more ordered structure of NiO x of the microblast deposited coatings (Figure 6), 60 and, consequently, higher electron mobility and higher diffusion lengths within the larger grains of the microblast sample with respect to the sintered nanoparticles of the same material or nanoporous solgel deposits. 6b,14b In addition to that, intraparticle charge transfer properties of semiconductor nanoparticles (sample B) may be affected by quantum confinement effects, 61 which are not relevant in microblast sample A.…”

Evidence of local and global scaling regimes in thin films deposited by sputtering: An atomic force microscopy and electrochemical study

“…Changes in transmittance as high as 70% can be attained, depending on the films' physical properties. 2 Interaction with the electrolyte is through the surface, whose characteristics can influence performance of the materials. Roughness is the parameter commonly used to perform quantitative analysis of the surface.…”

Structural, electrochemical and optical properties of NiOxHy thin films prepared by electrochemical deposition

“…Among various EC oxides of transition metals, nickel oxide/hydroxide is an anodic coloring material which is able to change color from transparent to a deep brown at positive potentials and is reversibly bleached when a negative potential is applied [7]. Nickel oxide/hydroxide films are also known as counter electrochromic films in electrochromic devices which are optically and electrochemically compatible with the well-known tungsten trioxide films [8].…”