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Article ; Online: Hydrogen-Induced Ultralow Optical Absorption and Mechanical Loss in Amorphous Silicon for Gravitational-Wave Detectors.

Molina-Ruiz, M / Markosyan, A / Bassiri, R / Fejer, M M / Abernathy, M / Metcalf, T H / Liu, X / Vajente, G / Ananyeva, A / Hellman, F

Physical review letters

2024 Volume 131, Issue 25, Page(s) 256902

Abstract: The sensitivity of gravitational-wave detectors is limited by the mechanical loss associated with the amorphous coatings of the detectors' mirrors. Amorphous silicon has higher refraction index and lower mechanical loss than current high-index coatings, ... ...

Abstract	The sensitivity of gravitational-wave detectors is limited by the mechanical loss associated with the amorphous coatings of the detectors' mirrors. Amorphous silicon has higher refraction index and lower mechanical loss than current high-index coatings, but its optical absorption at the wavelength used for the detectors is at present large. The addition of hydrogen to the amorphous silicon network reduces both optical absorption and mechanical loss for films prepared under a range of conditions at all measured wavelengths and temperatures, with a particularly large effect on films grown at room temperature. The uptake of hydrogen is greatest in the films grown at room temperature, but still below 1.5 at.% H, which show an ultralow optical absorption (below 10 ppm) measured at 2000 nm for 500-nm-thick films. These results show that hydrogenation is a promising strategy to reduce both optical absorption and mechanical loss in amorphous silicon, and may enable fabrication of mirror coatings for gravitational-wave detectors with improved sensitivity.
Language	English
Publishing date	2024-01-05
Publishing country	United States
Document type	Journal Article
ZDB-ID	208853-8
ISSN	1079-7114 ; 0031-9007
ISSN (online)	1079-7114
ISSN	0031-9007
DOI	10.1103/PhysRevLett.131.256902
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Book ; Online: Strategies to reduce the thermoelastic loss of multimaterial coated finite substrates

Zhou, Ruinan / Molina-Ruiz, Manel / Hellman, Frances

2022

Abstract: Thermoelastic loss is an important energy dissipation mechanisms in resonant systems. A careful analysis of the thermoelastic loss is critical to the design of low-noise devices for high-precision applications, such as the mirrors used for gravitational- ... ...

Abstract	Thermoelastic loss is an important energy dissipation mechanisms in resonant systems. A careful analysis of the thermoelastic loss is critical to the design of low-noise devices for high-precision applications, such as the mirrors used for gravitational-wave detectors. In this paper, we present analytical solutions to the thermoelastic loss due to thermoelasticity between different materials that are in contact. We find expressions for the thermoelastic loss of multimaterial coatings of finite substrates, and analyze its dependencies on material properties, mirror design and operating experimental conditions. Our results show that lower operating mirror temperature, thinner layers and higher number of interfaces in the coating, and the choice of the first layer of the coating that minimizes the thermal expansion mismatch with the substrate are strategies that reduce the thermoelastic loss and, therefore, diminish the thermal noise that limits the resolution in sensing applications. The results presented in this paper are relevant for the development of low-noise gravitational-wave detectors and for other experiments sensitive to energy dissipation mechanisms when different materials are in contact.
Keywords	Condensed Matter - Materials Science ; Astrophysics - Instrumentation and Methods for Astrophysics ; General Relativity and Quantum Cosmology
Subject code	620
Publishing date	2022-04-20
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Decoupling between propagating acoustic waves and two-level systems in hydrogenated amorphous silicon

Molina-Ruiz, M. / Jacks, H. C. / Queen, D. R. / Metcalf, T. H. / Liu, X. / Hellman, F.

2021

Abstract: Specific heat measurements of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large density of two-level systems at low temperature. Annealing at 200 {\deg}C, well below the growth temperature, does not significantly ... ...

Abstract	Specific heat measurements of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large density of two-level systems at low temperature. Annealing at 200 {\deg}C, well below the growth temperature, does not significantly affect the already-low internal friction or the sound velocity, but irreversibly reduces the non-Debye specific heat by an order of magnitude at 2 K, indicating a large reduction of the density of two-level systems. Comparison of the specific heat to the internal friction suggests that the two-level systems are uncharacteristically decoupled from acoustic waves, both before and after annealing. Analysis yields an anomalously low value of the coupling constant, which increases upon annealing but still remains anomalously low. The results suggest that the coupling constant value is lowered by the presence of hydrogen. Comment: 14 pages, 3 figures, 1 table
Keywords	Condensed Matter - Materials Science ; Physics - Applied Physics
Subject code	530
Publishing date	2021-05-06
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Structural tunability and origin of two-level systems in amorphous silicon

Jacks, H. C. / Molina-Ruiz, M. / Weber, M. H. / Maldonis, J. J. / Voyles, P. M. / Metcalf, T. H. / Liu, X. / Hellman, F.

2021

Abstract: Amorphous silicon films prepared by electron beam evaporation have systematically and substantially greater atomic density for higher thickness, higher growth temperature, and slower deposition rate, reaching the density of crystalline Si when films of ... ...

Abstract	Amorphous silicon films prepared by electron beam evaporation have systematically and substantially greater atomic density for higher thickness, higher growth temperature, and slower deposition rate, reaching the density of crystalline Si when films of thickness greater than ~300 nm are grown at 425 $^{\circ}$C and at <1 $\r{A}$/sec. A combination of spectroscopic techniques provide insight into atomic disorder, local strains, dangling bonds, and nanovoids. Electron diffraction shows that the short-range order of the amorphous silicon is similar at all growth temperatures, but fluctuation electron microscopy shows that films grown above room-temperature show a form of medium-range order not previously observed in amorphous silicon. Atomic disorder and local strain obtained from Raman spectroscopy reduce with increasing growth temperature and show a non-monotonic dependence on thickness. Dangling bond density decreases with increasing growth temperature and is only mildly dependent on thickness. Positron annihilation Doppler broadening spectroscopy and electron energy loss spectroscopy show that nanovoids, and not density variations within the network, are responsible for reduced atomic density. Specific heat and mechanical loss measurements, which quantify the density of tunneling two-level systems, in combination with the structural data, suggest that two-level systems in amorphous silicon films are associated with nanovoids and their surroundings; which are in essence loosely bonded regions where atoms are less constrained. Comment: 30 pages, 12 figures
Keywords	Condensed Matter - Materials Science
Subject code	530
Publishing date	2021-11-21
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Origin of Mechanical and Dielectric Losses from Two-Level Systems in Amorphous Silicon

Molina-Ruiz, M. / Rosen, Y. J. / Jacks, H. C. / Abernathy, M. R. / Metcalf, T. H. / Liu, X. / Dubois, J. L / Hellman, F.

2020

Abstract: Amorphous silicon contains tunneling two-level systems, which are the dominant energy loss mechanisms for amorphous solids at low temperatures. These two-level systems affect both mechanical and electromagnetic oscillators and are believed to produce ... ...

Abstract	Amorphous silicon contains tunneling two-level systems, which are the dominant energy loss mechanisms for amorphous solids at low temperatures. These two-level systems affect both mechanical and electromagnetic oscillators and are believed to produce thermal and electromagnetic noise and energy loss. However, it is unclear whether the two-level systems that dominate mechanical and dielectric losses are the same; the former relies on phonon-TLS coupling, with an elastic field coupling constant, $\gamma$, while the latter depends on a TLS dipole moment, $p_0$, which couples to the electromagnetic field. Mechanical and dielectric loss measurements as well as structural characterization were performed on amorphous silicon thin films grown by electron beam deposition with a range of growth parameters. Samples grown at 425 $^{\circ}$C show a large reduction of mechanical loss (34 times) and a far smaller reduction of dielectric loss (2.3 times) compared to those grown at room temperature. Additionally, mechanical loss shows lower loss per unit volume for thicker films, while dielectric loss shows lower loss per unit volume for thinner films. Analysis of these results indicate that mechanical loss correlates with atomic density, while dielectric loss correlates with dangling bond density, suggesting a different origin for these two energy dissipation processes in amorphous silicon. Comment: 17 pages, 4 figures, 1 table
Keywords	Condensed Matter - Materials Science
Subject code	535
Publishing date	2020-08-17
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Observation of spin-momentum locked surface states in amorphous Bi

Corbae, Paul / Ciocys, Samuel / Varjas, Dániel / Kennedy, Ellis / Zeltmann, Steven / Molina-Ruiz, Manel / Griffin, Sinéad M / Jozwiak, Chris / Chen, Zhanghui / Wang, Lin-Wang / Minor, Andrew M / Scott, Mary / Grushin, Adolfo G / Lanzara, Alessandra / Hellman, Frances

Nature materials

2023 Volume 22, Issue 2, Page(s) 200–206

Abstract: Crystalline symmetries have played a central role in the identification and understanding of quantum materials. Here we investigate whether an amorphous analogue of a well known three-dimensional strong topological insulator has topological properties in ...

Abstract	Crystalline symmetries have played a central role in the identification and understanding of quantum materials. Here we investigate whether an amorphous analogue of a well known three-dimensional strong topological insulator has topological properties in the solid state. We show that amorphous Bi
Language	English
Publishing date	2023-01-16
Publishing country	England
Document type	Journal Article
ZDB-ID	2088679-2
ISSN	1476-4660 ; 1476-1122
ISSN (online)	1476-4660
ISSN	1476-1122
DOI	10.1038/s41563-022-01458-0
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Article ; Online: Evaluation of a heart failure knowledge questionnaire and its use in guiding the educational intervention.

Sánchez-Ramos, J G / Lerma-Barba, M D / Segura-Rodríguez, D / Pardo-Cabello, A / Molina-Ruiz, M T / Burillo-Gómez, F / Martínez-Huertas, S / Nieto-García, E / Giner-Escobar, P / Moreno-Escobar, E

Revista clinica espanola

2022

Abstract: Introduction and objective: Patient education by nurses is a cornerstone of any heart failure (HF) program, but the models are widely heterogeneous and few specific instruments exist. Our objective is to evaluate our own questionnaire and its utility as ...

Abstract	Introduction and objective: Patient education by nurses is a cornerstone of any heart failure (HF) program, but the models are widely heterogeneous and few specific instruments exist. Our objective is to evaluate our own questionnaire and its utility as a guide for educational intervention. Methods: This work is a prospective cohort study of patients followed-up on in a specialized unit after diagnosis of HF. The intervention group received educational sessions guided according to their knowledge using the questionnaire and was compared to a group which received standard education. The validity and reliability of the questionnaire was evaluated. The utility of the educational model was determined by the primary composite endpoint of death and/or hospital admission or emergency care for HF. Results: A total of 152 patients were included, 88 which received guided education and 64 which received standard education, with a mean follow-up time of 16±4 months. In the guided education group, the evaluation questionnaire score (qs) rose from 59% to 78.5% (p=0.018), which was associated with greater self-care (28.5-0.6qs, p=0.04), a tendency toward better quality of life (51.1-1.1qs, p=0.09), and adherence (5.02+0.04qs, p=0.06), with acceptable reliability (Cronbach's alpha 0.75). The primary composite endpoint was met in 12 patients (13.6%) in the intervention group compared to 19 (29.7%) in the control group (hazard ratio: 0.46; 95% confidence interval: 0.24-0.88; p=0.019). Only educational level, age, NT-proBNP, and atrial fibrillation were predictors in the multivariate analysis. Conclusion:* The HF knowledge questionnaire proposed is a valid, reliable tool and allows for quantifying learning. Its utility in guiding education requires a certain degree of skill from the patient that determines a group with better prognosis.
Language	English
Publishing date	2022-08-08
Publishing country	Spain
Document type	Journal Article
ISSN	2254-8874
ISSN (online)	2254-8874
DOI	10.1016/j.rceng.2022.07.001
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Book ; Online: Compositional Trends in Surface Enhanced Diffusion in Lead Silicate Glasses

Annamareddy, Ajay / Molina-Ruiz, Manel / Horton-Bailey, Donez / Hellman, Frances / Li, Yuhui / Yu, Lian / Morgan, Dane

2022

Abstract: In this work, we use molecular dynamics simulations to study the enhancement of surface over bulk diffusion (surface enhanced diffusion) in (PbO)x(SiO2)1-x glasses. This work is motivated to better understand surface diffusion in glasses and its ... ...

Abstract	In this work, we use molecular dynamics simulations to study the enhancement of surface over bulk diffusion (surface enhanced diffusion) in (PbO)x(SiO2)1-x glasses. This work is motivated to better understand surface diffusion in glasses and its connection to fragility, and to enhance surface diffusion in silica and related glasses for greater thermodynamic stability during vapor-deposition. By adding PbO to silica, the fragility of glass increases continuously for 10% <= x <= 70% during experiments. The increase in fragility may correspond to an increase in surface enhanced diffusion, as fragility and surface diffusion are correlated. We observe that for the silicates investigated, while surface enhanced diffusion increases with fragility, the enhancement is quite small. The slower diffusing Si and O atoms have higher enhancements, which could allow for some surface stabilization effects. We demonstrate that there are only small changes in atomic arrangements, consistent with the similar diffusion rates, at the surface as compared to bulk. Finally, we examine the trend of bulk versus surface diffusion in view of previous observations in organic and metallic glasses and found that in oxides, fragility increase may not be strongly linked to enhanced surface diffusion.
Keywords	Condensed Matter - Materials Science
Subject code	541
Publishing date	2022-02-25
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Two-level systems and growth-induced metastability in hydrogenated amorphous silicon

Molina-Ruiz, M. / Jacks, H. C. / Queen, D. R. / Wang, Q. / Crandall, R. S. / Hellman, F.

2018

Abstract: Specific heat measurements from 2 to 300 K of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large excess specific heat at low temperature, significantly larger than the Debye specific heat calculated from the sound ... ...

Abstract	Specific heat measurements from 2 to 300 K of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large excess specific heat at low temperature, significantly larger than the Debye specific heat calculated from the sound velocity. The as-prepared films have a Schottky anomaly that is associated with metastable hydrogen in the amorphous network, as well as large linear and excess cubic term commonly associated with tunneling two-level systems in amorphous solids. Annealing at 200 {\deg}C, a temperature that enables hydrogen mobility but not evaporation, irreversibly reduces the heat capacity, eliminating the Schottky anomaly and leaving a reduced linear heat capacity. A non-monotonic dependence on growth temperature and H content is observed in all effects, except for sound velocity, which suggests that the tunneling two-level systems and the Schottky anomaly are associated with atomic hydrogen and require low density regions to form, while sound velocity is associated with the silicon network and improves with increasing growth temperature. Comment: 17 pages, 3 figures, 1 table
Keywords	Condensed Matter - Materials Science
Subject code	530
Publishing date	2018-09-20
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Temperature effects on the structure and mechanical properties of vapor deposited a-SiO2

Jambur, Vrishank / Molina-Ruiz, Manel / Dauer, Tom / Horton-Bailey, Donez / Vallery, Richard / Gidley, David / Metcalf, Thomas / Liu, Xiao / Hellman, Frances / Szlufarska, Izabela

2022

Abstract: Amorphous silica (a-SiO2) exhibits unique thermo-mechanical behaviors that set it apart from other glasses. However, there is still limited understanding of how this mechanical behavior is related to the atomic structure and to the preparation conditions ...

Abstract	Amorphous silica (a-SiO2) exhibits unique thermo-mechanical behaviors that set it apart from other glasses. However, there is still limited understanding of how this mechanical behavior is related to the atomic structure and to the preparation conditions of a-SiO2. Here, we used electron beam (e-beam) physical vapor deposition (PVD) to prepare a series of a-SiO2 films grown at different substrate temperatures and then combined molecular simulations with Positronium Annihilation Lifetime Spectroscopy and nanoindentation experiments to establish relations among processing, structure, and mechanical response of the films. Specifically, we found that increase in the growth temperature leads to increase in the elastic moduli and hardness of the films. The relative porosity in the films also increases while the a-SiO2 network itself becomes denser, resulting in an overall increase in density despite increased porosity. In addition, we found that the a-SiO2 films exhibit the same anomalous temperature dependence of elastic modulus as bulk a-SiO2. However, the rate of increase in the elastic modulus with the measurement temperature was found to depend on the density of the a-SiO2 network and therefore on the growth temperature. Our findings provide new insights into the influence of the atomic network structure on the anomalous thermomechanical behavior of a-SiO2 and in turn guidance to control the mechanical properties of a-SiO2 films.
Keywords	Condensed Matter - Materials Science
Subject code	620
Publishing date	2022-04-12
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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