- Award ID(s):
- 0802907
- NSF-PAR ID:
- 10041138
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry C
- Volume:
- 116
- Issue:
- 30
- ISSN:
- 1932-7447
- Page Range / eLocation ID:
- 15918 to 15924
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings of
(silica) and (titania-doped tantala) and post-deposition annealing to 500°C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the sensitivity of the detectors. This paper describes optical scattering measurements for single-layer, ion-beam-sputtered thin films on fused silica substrates: two samples of and two of . Using an imaging scatterometer at a fixed scattering angle of 12.8°, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500°C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25–30% for tantala and up to 74% for titania-doped tantala, while the scatter from the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggest some improvement in three of the four samples. These results demonstrate that post-deposition, high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter. -
The use of thin Ta3N5films in tandem Si‐Ta3N5photoelectrochemical (PEC) devices motivates understanding of the surface Ta3N5properties, as they may have a strong effect on the device performance. The bulk and surface properties can change as a function of nitridation temperature; thus its effect is studied, ranging from 700 to 1000 °C, on the PEC performance, morphology, and composition of thin (10 nm) Ta3N5films deposited on planar and nanostructured Si substrates. Scanning electron microscopy (SEM), scanning Auger electron spectroscopy (AES), X‐ray photoelectron spectroscopy (XPS), and X‐ray diffraction (XRD) are employed to gain fundamental understanding in the differences of the Ta3N5films. By controlling Ta3N5morphology and composition with nitridation temperature, it is determined that Ta3N5with high crystallinity and surface N/Ta ratio, synthesized at 800 °C, yields the highest PEC performance with the earliest photocurrent onset and highest photocurrent. Samples nitrided at 700 °C have lower crystallinity and that likely leads to lower performance. For samples nitrided at temperatures above 800 °C, the N/Ta ratio decreases forming chemically reduced tantalum nitride phases, as well as N‐deficient and correspondingly O‐rich morphological domains that can adversely affect the PEC performance as hole‐blocking layers or O trap‐mediated recombination centers at the surface of Ta3N5.
-
Abstract With the aid of neutron diffraction and electrochemical impedance spectroscopy, we have demonstrated the effect of the increase in lithium concentration and distribution on Li‐ion conductivity. This has been done through the synthesis of a layered oxide Li2(La0.75Li0.25)(Ta1.5Ti0.5)O7, with the so‐called Ruddlesden‐Popper type structure, where bilayer stacks of (Ta/Ti)O6octahedra are separated by lithium ions, located in inter‐stack spaces. There are also intra‐stack spaces that are occupied by a mixture of La and Li, as confirmed by neutron diffraction. The distribution of lithium over both inter‐ and intra‐stack positions leads to the enhancement of Li‐ion conductivity in Li2(La0.75Li0.25)(Ta1.5Ti0.5)O7compared to Li2La(TaTi)O7, which has a lower concentration of lithium ions, located only in inter‐stack spaces. The analyses of real and imaginary components of electrochemical impedance data confirm the enhanced mobility of ions in Li2(La0.75Li0.25)(Ta1.5Ti0.5)O7. While the Li‐ion conductivity needs further improvement for practical applications, the success of the strategy implemented in this work offers a useful methodology for the design of layered ionic conductors.