Description of particle induced damage on protected silver coatings

Schwinde, Stefan; Schürmann, M.; Jobst, Paul Johannes; Kaiser, Norbert; Tünnermann, Andreas

doi:10.1364/ao.54.004966

Cited by 25 publications

(6 citation statements)

References 25 publications

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“…In this work, we introduce the fabrication of a very simple and lowcost SERS substrate in which the metallic thin film surface is cracked uniformly by a sodium chloride (NaCl) sacrificial layer even at room temperature without any other process. Thin metal film (especially Ag) coated above the NaCl sacrificial film tends to form nano-size cracks with time due to the water molecule intercalated interfacial reaction by forming AgCl [30]. It is well known that the silver is unstable when exposed to ambient air, resulting in a sulfide and oxide compounds on the surface while the silver belongs to the noble metal [31].…”

Section: Introductionmentioning

confidence: 99%

Spontaneous nano-gap formation in Ag film using NaCl sacrificial layer for Raman enhancement

et al. 2018

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We report the method of fabrication of nano-gaps (known as hot spots) in Ag thin film using a sodium chloride (NaCl) sacrificial layer for Raman enhancement. The Ag thin film (20-50 nm) on the NaCl sacrificial layer undergoes an interfacial reaction due to the AgCl formed at the interface during water molecule intercalation. The intercalated water molecules can dissolve the NaCl molecules at interfaces and form the ionic state of Na and Cl, promoting the AgCl formation. The Ag atoms can migrate by the driving force of this interfacial reaction, resulting in the formation of nano-size gaps in the film. The surface-enhanced Raman scattering activity of Ag films with nano-size gaps has been investigated using Raman reporter molecules, Rhodamine 6G (R6G).

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Section: Introductionmentioning

confidence: 99%

Spontaneous nano-gap formation in Ag film using NaCl sacrificial layer for Raman enhancement

et al. 2018

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“…The existence of high humidity can lead to condensation on the reflectors surface. Due to hygroscopic airborne particles condensation on the coated reflector is also possible at a relative humidity of < 80 % [13]. Beside the unintended condensation, a cleaning process of the coated mirror can require a sufficient resistance to liquid solutions.…”

Section: Introductionmentioning

confidence: 99%

“…If SiO2 is exposed to a basic solution, a higher concentration of OH-ions goes along with a stronger reaction of SiO2 [16,17]. The material Al2O3 also reacts with basic solutions [13]. Therefore, when these materials are used to protect an Ag-layer, the durability to basic solution is of special interest.…”

Section: Introductionmentioning

confidence: 99%

Protected silver coatings for reflectors

Schwinde

Schürmann

Schlegel

et al. 2019

International Conference on Space Optics — ICSO 2018

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For ground-and spaced based applications, Ag coated reflectors are indispensable because of their high reflectivity. The transport, assembling and storage of these reflectors takes a long time, before they are finally commissioned for the actual applications. To endure this period without a decrease of reflectivity, protective coatings with a final layer, which offers a high resistance to aqueous solutions and a low mechanical stress should be used. These criteria were taken into account for the selection of a final layer for a protected Ag-coating, which was applied for reflectors utilized in the CRIRES +instrument (an IR spectrograph used at the VLT). Reactively sputtered Al2O3, SiO2 and Si3N4 layers were investigated with regard to these criteria. In aqueous (basic) solutions, the investigated Si3N4 layers are more stable than the SiO2 layers, and the SiO2 layers are more stable than the Al2O3 layers. This shows the influence of the intrinsic material properties. The mechanical stress of the sputtered layers depends on the deposition conditions and thus on the selected parameters. A Si3N4 layer with a high resistance to aqueous solutions also offers a low and stable mechanical stress. Therefore, the depositionparameters which have been used for this layer were applied for sputtering the final layer of the protected Ag-coating for the reflectors.

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“…Atomic layer deposition (ALD) offers an ideal solution of pinhole-free barrier overlayers because of its excellent conformality over complex threedimensional structures. 27−31 Although it has been shown that Ag mirrors protected by both PVD-and ALD-based barrier films are prone to hygroscopic air borne particles inducing corrosion, 32 the low-stress, amorphous nature of ALD films is expected to improve overall mechanical integrity by reducing or eliminating crystalline grain boundaries and defects in barrier overlayers, which serve as diffusion pathways for corrosion of the underlying Ag. 32−35 In addition, ALD produces smooth films with precise thickness and excellent uniformity, which is critical to achieve uniform spectral response across large-area optical substrates.…”

Section: Introductionmentioning

confidence: 99%

“…Robust uniform films of precise thickness can be applied using PVD for many optical applications including reflective, − anti-reflective (AR), − and transparent barrier coatings. − However, because of extrinsic factors such as the necessary large deposition area, non-cleanroom environment during substrate cleaning, and subsequent film deposition, pinholes are unavoidable and can be a significant problem as they provide moisture and other chemicals a means to permeate into the metal thin film, leading to corrosion. − Because PVD conditions require line-of-sight deposition, high aspect ratio substrate defects, including pinholes, may not be completely encapsulated. Atomic layer deposition (ALD) offers an ideal solution of pinhole-free barrier overlayers because of its excellent conformality over complex three-dimensional structures. − Although it has been shown that Ag mirrors protected by both PVD-and ALD-based barrier films are prone to hygroscopic air borne particles inducing corrosion, the low-stress, amorphous nature of ALD films is expected to improve overall mechanical integrity by reducing or eliminating crystalline grain boundaries and defects in barrier overlayers, which serve as diffusion pathways for corrosion of the underlying Ag. − In addition, ALD produces smooth films with precise thickness and excellent uniformity, which is critical to achieve uniform spectral response across large-area optical substrates. High-quality dielectric films are realized by ALD, with processing temperatures lower than conventional chemical vapor deposition (CVD) and vacuum requirements less stringent than high-vacuum conditions necessary for PVD.…”

Section: Introductionmentioning

confidence: 99%

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Fryauf¹,

Phillips²,

Bolte³

et al. 2018

ACS Appl. Mater. Interfaces

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Atomic Layer Deposition (ALD) is very attractive for producing optical quality thin films, including transparent barrier films on metal-coated astronomical mirrors. To date, ALD of mirror coatings has been limited to relatively small-sized substrates. A new ALD tool has been designed, constructed, and tested to apply uniform protective coatings over a 0.9 m diameter substrate in a 1 m diameter scale deposition plane. The new tool, which we have named the meter scale ALD system (MSAS), employs a unique chamber design that isolates a large substrate surface to be coated by utilizing the substrate as a wall of the reaction chamber. The MSAS is mechanically designed to be rapidly reconfigurable for selective area coating of custom substrates with arbitrary shape, size, and permanent backside hardware attachments. The design, implementation, results, and future applications of this new tool are discussed for coating large-area optical substrates, specifically protective coatings for silver mirrors, and other future large astronomical optics. To demonstrate the potential of this new design, aluminum oxide was deposited by thermal ALD using trimethylaluminum and water at a low reaction temperature of 60 °C. Growth rate and uniformity, which are dependent on precursor pulse times and chamber purge times, show that the two half-reactions occur in a saturated regime, matching typical characteristics of ideal ALD behavior. Aluminum oxide deposition process parameters of the MSAS are compared with those of a conventional 100 mm wafer-scale ALD tool, and saturated ALD growth over the 0.9 m substrate is realized with a simple scaling factor applied to precursor pulse and purge times. This initial test shows that lateral thickness uniformity across a 0.9 m substrate is within 2.5% of the average film thickness, and simple steps to realize 1% uniformity have been identified for next growths. Results show promising application of transparent robust dielectric films as uniform coatings across large optical components scaled to meter-sized substrates.

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Description of particle induced damage on protected silver coatings

Cited by 25 publications

References 25 publications

Spontaneous nano-gap formation in Ag film using NaCl sacrificial layer for Raman enhancement

Spontaneous nano-gap formation in Ag film using NaCl sacrificial layer for Raman enhancement

Protected silver coatings for reflectors

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

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