An official website of the United States government
Post deposition annealing of molecular layer- deposited (MLD) hafnicone films was examined and compared to that of hafnium oxide atomic layer-deposited (ALD) films. Hafnicone films were deposited using tetrakis(dimethylamido)- hafnium (TDMAH), and ethylene glycol and hafnia films were deposited using TDMAH and water at 120 °C. The changes in the properties of the as-deposited hafnicone films with annealing were probed by various techniques and then compared to the as-deposited and annealed ALD hafnia films. In situ X-ray reflectivity indicated a 70% decrease in thickness and ∼100% increase in density upon heating to 400 °C yet the density remained lower than that of hafnia control samples. The largest decreases in thickness of the hafnicone films were observed from 150 to 350 °C. In situ X-ray diffraction indicated an increase in the temperature required for crystallization in the hafnicone films (600 °C) relative to the hafnia films (350 °C). The changes in chemistry of the hafnicone films annealed with and without UV exposure were probed using Fourier transformed infrared spectroscopy and X-ray photoelectron spectroscopy with no significant differences attributed to the UV exposure. The hafnicone films exhibited lower dielectric constants than hafnia control samples over the entire temperature range examined. The CF4/O2 etch rate of the hafnicone films was comparable to the etch rate of hafnia films after annealing at 350 °C. The thermal conductivity of the hafnicone films initially decreased with thermal processing (up to 250 °C) and then increased (350 °C), likely due to porosity generation and subsequent densification, respectively. This work demonstrates that annealing MLD films is a promising strategy for generating thin films with a low density and relative permittivity.
more »
« less
High-temperature electrical and optical properties of sputtered iridium at wavelengths of 300 nm to 15 µm
Due to its refractory properties and higher oxidation resistance, iridium (Ir) exhibits great potential for applications such as thermophotovoltaic emitters or contamination sensing. However, the lack of its temperature-dependent optical data prevents accurate modeling of Ir-based optical devices operating at higher temperatures. In this work, refractive indices of as-deposited and annealed Ir films, sputter-deposited, are characterized at between room temperature and 550°C over 300 nm to 15 µm of wavelength. The extinction coefficients of both as-deposited and annealed Ir films tend to decrease as temperature increases, with the exception of as-deposited Ir at 550°C due to significant grain growth. Under 530°C, optical constants of as-deposited Ir are less sensitive to temperature than those of annealed Ir. These characteristics of Ir films are correlated with their microstructural changes.
more »
« less
- Award ID(s):
- 2120581
- PAR ID:
- 10434571
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 13
- Issue:
- 8
- ISSN:
- 2159-3930
- Page Range / eLocation ID:
- 2227
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Haasch, Richard; Graham, Dan; Podraza, Nikolas; Shard, Alexander (Ed.)Spectroscopic ellipsometry and ultraviolet-visible (UV-VIS) spectrometry were utilized to study the optical properties of ferroelectric lead lanthanum zirconate titanate (PLZT) films. These films were deposited on platinized silicon [Si(100)/ SiO2/TiO2/Pt(111)] substrates using the chemical solution deposition method. Films were annealed at two different temperatures (650 and 750 °C) using rapid thermal annealing. Shimadzu UV-1800 UV-VIS spectrophotometer with a resolution of 1 nm was used to measure the reflectance data in the spectral range of 300–1000 nm with a step size of 1 nm. The bandgap values were determined from the reflectance spectra using appropriate equations. A J.A. Woollam RC2 small spot spectroscopic ellipsometer was used to obtain the change in amplitude (Ψ) and phase (Δ) of polarized light upon reflection from the film surface. The spectra were recorded in the wavelength range of 210–1500 nm at an incident angle of 65°. Refractive index (n) and extinction coefficient (k) were obtained by fitting the spectra (Ψ, Δ) with the appropriate models. No significant changes were observed in the optical constants of PLZT films annealed at 650 and 750 °C. The optical transparency and the strong absorption in the ultraviolet (UV) region of PLZT films make them an attractive material for optoelectronic and UV sensing applications.more » « less
-
Brownian thermal noise as a result of mechanical loss in optical coatings will become the dominant source of noise at the most sensitive frequencies of ground-based gravitational-wave detectors. Experiments found, however, that a candidate material, amorphous Ta2O5, is unable to form an ultrastable glass and, consequently, to yield a film with significantly reduced mechanical loss through elevated-temperature deposition alone. X-ray scattering PDF measurements are carried out on films deposited and subsequently annealed at various temperatures. Inverse atomic modeling is used to analyze the short and medium range features in the atomic structure of these films. Furthermore, in silico deposition simulations of Ta2O5 are carried out at various substrate temperatures and an atomic level analysis of the growth at high temperatures is presented. It is observed that upon elevated-temperature deposition, short range features remain identical, whereas medium range order increases. After annealing, however, both the short and medium range orders of films deposited at different substrate temperatures are nearly identical. A discussion on the surface diffusion and glass transition temperatures indicates that future pursuits of ultrastable low-mechanical-loss films through elevated temperature deposition should focus on materials with a high surface mobility, and/or lower glass transition temperatures in the range of achievable deposition temperatueres.more » « less
-
The ability to observe astronomical events through the detection of gravitational waves relies on the quality of multilayer coatings used on the optical mirrors of interferometers. Amorphous Ta2O5 (including TiO2:Ta2O5) currently limits detector sensitivity due to high mechanical loss. In this paper, mechanical loss measured at both cryogenic and room temperatures of amorphous Ta2O5 films grown by magnetron sputtering and annealed in air at 500 ◦C is shown to decrease for elevated growth temperature. Films grown at 310 ◦C and annealed yield a mechanical loss of 3.1×10−4 at room temperature, the lowest value reported for pure amorphous Ta2O5 grown by magnetron sputtering to date, and comparable to the lowest values obtained for films grown by ion beam sputtering. Additionally, the refractive index n increases 6% for elevated growth temperature, which could lead to improved sensitivity of gravitational-wave detectors by allowing a thickness reduction in the mirrors’ coatings. Structural characterization suggests that the observed mechanical loss reduction in amorphous Ta2O5 films with increasing growth temperature correlates with a reduction in the coordination number between oxygen and tantalum atoms, consistent with TaOx polyhedra with increased corner-sharing and reduced edge- and facesharing structures.more » « less
-
Strong metal–support interaction catalysts have been shown to improve desired product selectivity at the cost of fractional rates due to active site coverage. The goal of this study was to determine if the active site coverage of metallic nanoparticles could be controlled to lower levels than have been previously reported in SMSI catalysts with the aim of improving the rate while maintaining high selectivity. 2Pd– X Ti/SiO 2 (2 wt% Pd, X wt% Ti) strong metal–support interaction (SMSI) catalysts with Ti loadings between 0–1.0 wt% were synthesized to control Pd nanoparticle coverage. Calcination at 450 °C and reduction at 550 °C were sufficient for forming ∼2 nm sized Pd particles in all catalysts. Increasing the Ti loading from 0.1 to 1.0 wt% increased the surface coverage from 40 to 85% at a fixed reduction temperature of 550 °C. The IR spectra of the SMSI catalysts were similar with a high fraction of linear bonded CO which was much higher than that of Pd nanoparticles of similar size. The SMSI overlayer could be removed by oxidation at 350 °C and re-reduction at 200 °C. EXAFS of the oxidized catalysts indicates that nearly full oxidation of the metallic nanoparticle was required to remove the SMSI overlayer. Oxidation temperatures from 30 to 300 °C partially oxidized the Pd nanoparticles and subsequent re-reduction at 200 °C partially decreases the SMSI coverage. The fractional surface coverage was determined by measuring the rate of propylene hydrogenation with and without the SMSI overlayer. Increasing the reduction temperature from 200 to 550 °C increased the SMSI coverage from 0 to 85% depending on the Ti loading and temperature. After reduction at 550 °C and oxidation at 350 °C, the range of coverages varied between ∼10% with 0.1 wt% Ti after re-reduction at 300 °C and ∼85% with 1 wt% Ti after reduction at 550 °C.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/OME.495250
