اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEffect of heat treatment on mechanical dissipation in Ta$_2$O$_5$ coatings
572
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Thermal noise arising from mechanical dissipation in dielectric reflective coatings is expected to critically limit the sensitivity of precision measurement systems such as high-resolution optical spectroscopy, optical frequency standards and future generations of interferometric gravitational wave detectors. We present measurements of the effect of post-deposition heat treatment on the temperature dependence of the mechanical dissipation in ion-beam sputtered tantalum pentoxide between 11,K and 300,K. We find the temperature dependence of the dissipation is strongly dependent on the temperature at which the heat treatment was carried out, and we have identified three dissipation peaks occurring at different heat treatment temperatures. At temperatures below 200,K, the magnitude of the loss was found to increase with higher heat treatment temperatures, indicating that heat treatment is a significant factor in determining the level of coating thermal noise.
قيم البحث
اقرأ أيضاً
Amorphous oxide thin films play a fundamental role in state-of-the art interferometry experiments, such as gravitational wave detectors where these films compose the high reflectance mirrors of end and input masses. The sensitivity of these detectors
is affected by thermal noise in the mirrors with its main source being the mechanical loss of the high index layers. These thermally driven fluctuations are a fundamental limit to optical interferometry experiments and there is a pressing need to understand the underlying processes that lead to mechanical dissipation in materials at room temperature. Two strategies are known to lower the mechanical loss: employing a mixture of Ta$_2$O$_5$ with $approx$ 20% of TiO$_2$ and post-deposition annealing, but the reasons behind this are not completely understood. In this work, we present a systematic study of the structural and optical properties of ion beam sputtered TiO$_2$-doped Ta$_2$O$_5$ films as a function of the annealing temperature. We show for the first time that low mechanical loss is associated with a material morphology that consists of nanometer sized Ar-rich bubbles embedded into an atomically homogeneous mixed titanium-tantalum oxide. When the Ti cation ratio is high, however, phase separation occurs in the film which leads to increased mechanical loss. These results indicate that for designing low mechanical loss mixed oxide coatings for interferometry applications it would be beneficial to identify materials with the ability to form ternary compounds while the dopant ratio needs to be kept low to avoid phase separation.
High finesse optical cavities of current interferometric gravitational-wave detectors are significantly limited in sensitivity by laser quantum noise and coating thermal noise. The thermal noise is associated with internal energy dissipation in the m
aterials that compose the test masses of the interferometer. Our understanding of how the internal friction is linked to the amorphous material structure is limited due to the complexity of the problem and the lack of studies that span over a large range of materials. We present a systematic investigation of amorphous metal oxide and Ta$_2$O$_5$-based mixed oxide coatings to evaluate their suitability for low Brownian noise experiments. It is shown that the mechanical loss of metal oxides is correlated to their amorphous morphology, with continuous random network materials such as SiO$_2$ and GeO$_2$ featuring the lowest loss angles. We evaluated different Ta$_2$O$_5$-based mixed oxide thin films and studied the influence of the dopant in the optical and elastic properties of the coating. We estimated the thermal noise associated with high-reflectance multilayer stacks that employ each of the mixed oxides as the high index material. We concluded that the current high index material of TiO$_2$-doped Ta$_2$O$_5$ is the optimal choice for reduced thermal noise among Ta$_2$O$_5$-based mixed oxide coatings with low dopant concentrations.
We report on the development and extensive characterization of co-sputtered tantala-zirconia thin films, with the goal to decrease coating Brownian noise in present and future gravitational-wave detectors. We tested a variety of sputtering processes
of different energies and deposition rates, and we considered the effect of different values of cation ratio $eta =$ Zr/(Zr+Ta) and of post-deposition heat treatment temperature $T_a$ on the optical and mechanical properties of the films. Co-sputtered zirconia proved to be an efficient way to frustrate crystallization in tantala thin films, allowing for a substantial increase of the maximum annealing temperature and hence for a decrease of coating mechanical loss. The lowest average coating loss was observed for an ion-beam sputtered sample with $eta = 0.485 pm 0.004$ annealed at 800 $^{circ}$C, yielding $overline{varphi} = 1.8 times 10^{-4}$. All coating samples showed cracks after annealing. Although in principle our measurements are sensitive to such defects, we found no evidence that our results were affected. The issue could be solved, at least for ion-beam sputtered coatings, by decreasing heating and cooling rates down to 7 $^{circ}$C/h. While we observed as little optical absorption as in the coatings of current gravitational-wave interferometers (0.5 parts per million), further development will be needed to decrease light scattering and avoid the formation of defects upon annealing.
The envisioned existence of an excitonic-insulator phase in Ta$_2$NiSe$_5$ has attracted a remarkable interest in this material. The origin of the phase transition in Ta$_2$NiSe$_5$ has been rationalized in terms of crystal symmetries breaking driven
by both electronic correlation and lattice distortion. However, the role of structural and electronic effects has yet to be disentangled. Meanwhile its complementary material Ta$_2$NiS$_5$, which has the chalcogen species exchanged with Sulfur, does not show any experimental evidence of an excitonic insulating phase. Here we present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta$_2$NiSe$_5$ and Ta$_2$NiS$_5$ by means of extensive first-principles calculations for both the high temperature orthorhombic and low-temperature monoclinic crystal phases. We show that, despite the difference in electronic behaviour, the structural origin of the phase transition is the same in the two crystals. In particular our first-principles results suggest, that the high temperature phase of Ta$_2$NiSe$_5$ is metallic and the structural transition to the low-temperature phase leads to the opening of an electronic gap. By analysing the phononic modes of the two phases we single out the mode responsible for the structural transition and demonstrate how this phonon mode strongly couples to the electronic structure. We demonstrate that, despite the very similar phononic behaviour, in Ta$_2$NiS$_5$ the electronic transition from metal to semiconductor is lacking and the crystal remains a semiconductor in both phases. To disentangle the effect of electronic correlation, we calculate electronic bandstructures with increasing accuracy in the electron-electron interaction and find that the structural transition alone allows for the metal to semiconductor phase transition, ...
Brownian thermal noise associated with highly-reflective mirror coatings is a fundamental limit for several precision experiments, including gravitational-wave detectors. Recently, there has been a worldwide effort to find mirror coatings with improv
ed thermal noise properties that also fulfill strict optical requirements such as low absorption and scatter. We report on the optical and mechanical properties of ion-beam-sputtered niobia and titania-niobia thin films, and we discuss application of such coatings in current and future gravitational-wave detectors. We also report an updated direct coating thermal noise measurement of the HR coatings used in Advanced LIGO and Advanced Virgo.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
