Coatings and surface treatments for enhanced performance suspensions for future gravitational wave detectors

Further improvements in the low frequency sensitivity of gravitational wave detectors are important for increasing the observable population of astrophysical sources, such as intermediate mass compact black hole binary systems. Improvements in the lower stage mirror and suspension systems will set challenging targets for the required thermal noise performance of the cantilever blade springs, which provide vertical softness and, thus, isolation to the mirror suspension stack. This is required due to the coupling between the vertical and horizontal axes due to the curvature of the Earth. This can be achieved through use of high mechanical Q materials, which are compatible with cryogenic cooling, such as crystalline silicon. However, such materials are brittle, posing further challenges for assembly/jointing and, more generally, for long-term robustness. Here, we report on experimental studies of the breaking strength of silicon at room temperature, via both tensile and 4-point flexural testing; and on the effects of various surface treatments and coatings on durability and strength. Single- and multi-layer DLC (diamond-like carbon) coatings, together with magnetron-sputtered silica and thermally-grown silica, are investigated, as are the effects of substrate preparation and argon plasma pre-treatment. Application of single- or multi-layer DLC coatings can significantly improve the failure stress of silicon flexures, in addition to improved robustness for handling (assessed through abrasion tests). Improvements of up to 80% in tensile strength, a twofold increase in flexural strength, in addition to a 6.4 times reduction in the vertical thermal noise contribution of the suspension stack at 10 Hz are reported (compared to current Advanced LIGO design). The use of silicon blade springs would also significantly reduce potential 'crackling noise' associated with the underlying discrete events associated with plastic deformation in loaded flexures

Erratum to: Beyond (Nature Geoscience, (2018), 11, 7, (474-485), 10.1038/s41561-018-0146-0)

In the version of this Review Article originally published, ref. 10 was mistakenly cited instead of ref. 107 at the end of the sentence: “This complexity of residual ice cover makes it likely that HTM warming was regional, rather than global, and its peak warmth thus had different timing in different locations.” In addition, for ref. 108, Scientific Reports was incorrectly given as the publication name; it should have been Scientific Data. These errors have now been corrected in the online versions

Erratum to: Beyond (Nature Geoscience, (2018), 11, 7, (474-485), 10.1038/s41561-018-0146-0)

In the version of this Review Article originally published, ref. 10 was mistakenly cited instead of ref. 107 at the end of the sentence: “This complexity of residual ice cover makes it likely that HTM warming was regional, rather than global, and its peak warmth thus had different timing in different locations.” In addition, for ref. 108, Scientific Reports was incorrectly given as the publication name; it should have been Scientific Data. These errors have now been corrected in the online versions

Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise