Ultralow reflectance metal surfaces by ultrafast laser texturing

Iyengar, Vikram V.; Nayak, Barada K.; Gupta, Mool C.

doi:10.1364/ao.49.005983

Cited by 65 publications

(27 citation statements)

References 21 publications

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“…The balance of the dominant formation mechanisms is shown to depend critically on the laser fluence, which strongly determines the overall formation processes. Most of the work on the formation of self-organized micro/nanostructures on metals using femtosecond laser pulses has focused on the formation of recessed structures similar to the BSG-mounds discussed here [14,15,34,39,40,45,48]. Some published work may contain images of structures similar to the ASG-mounds in this work, but there is no specific discussion on the difference in the structures and there is never a mention of the upward growth of the structures [13,32,[37][38][39].…”

Section: Summary Of Growth Mechanisms For Bsg-mounds and Asg-moundsmentioning

confidence: 99%

“…BSG-mounds always have peaks below the original surface and are representative of the most frequently published self-organized microstructures that form on metals via focused femtosecond laser illumination [14,23,32,34,[38][39][40]48]. In contrast, ASG-mounds exhibit upward growth and result in structures with peaks above the original surface.…”

Section: Introductionmentioning

confidence: 99%

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Formation of multiscale surface structures on nickel via above surface growth and below surface growth mechanisms using femtosecond laser pulses

2013

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"Formation of multiscale surface structures on nickel via above surface growth and below surface growth mechanisms using femtosecond laser pulses" (2013 Abstract:The formation of self-organized micro-and nano-structured surfaces on nickel via both above surface growth (ASG) and below surface growth (BSG) mechanisms using femtosecond laser pulse illumination is reported. Detailed stepped growth experiments demonstrate that conical mound-shaped surface structure development is characterized by a balance of growth mechanisms including scattering from surface structures and geometric effects causing preferential ablation of the valleys, flow of the surface melt, and redeposition of ablated material; all of which are influenced by the laser fluence and the number of laser shots on the sample. BSG-mound formation is dominated by scattering, while ASG-mound formation is dominated by material flow and redeposition. This is the first demonstration to our knowledge of the use of femtosecond laser pulses to fabricate metallic surface structures that rise above the original surface. These results are useful in understanding the details of multi-pulse femtosecond laser interaction with metals.

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Section: Summary Of Growth Mechanisms For Bsg-mounds and Asg-moundsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Formation of multiscale surface structures on nickel via above surface growth and below surface growth mechanisms using femtosecond laser pulses

2013

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“…Patterning is an effective route to change the surface properties such as adhesion [1][2][3][4], cell-response [5,6], friction [7,8], reflectance [9,10], and wetting [3,11,12]. Numerous techniques such as lithography [13][14][15], embossing [16][17][18], self-assembly [19,20], electrochemical etching [21], and laser processing [22] have been developed for patterning of semiconductors and polymers.…”

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confidence: 99%

High strain rate thermoplastic demolding of metallic glasses

Hasan

Kumar

2016

Scripta Materialia

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Silicon templates are ideal for thermoplastic patterning of metallic glasses but their thermal expansion mismatch prevents demolding without chemical etching. Besides limiting the template life, chemical exposure alters the surface chemistry and properties of metallic glasses. To overcome these issues, we develop thermoplastic demolding which enables template reusability and fabrication of pristine metallic glass structures. Chemicalfree demolding allows decoupling of topographic and compositional effects on properties of metallic glasses. We show that mechanically and chemically demolded samples exhibit distinct wetting behavior despite similar topography. The versatility of demolding technique is demonstrated for structures of different shapes and metallic glass formers.Patterning is an effective route to change the surface properties such as adhesion [1][2][3][4], cell-response [5,6], friction [7,8], reflectance [9,10], and wetting [3,11,12]. Numerous techniques such as lithography [13][14][15], embossing [16][17][18], self-assembly [19,20], electrochemical etching [21], and laser processing [22] have been developed for patterning of semiconductors and polymers. These methods are either not readily applicable to metals or require complex hardware. Metallic glasses (MGs) are unique alloys of metals which can be patterned by simple thermoplastic methods due to the existence of their supercooled liquid state [23][24][25][26][27]. This is achieved by molding of MGs against templates heated above the glass transition temperature (T g ) followed by cooling below T g and demolding [27]. MG surfaces textured with micro [28-30], nano [31][32][33], and hierarchical [34] structures have been synthesized by using suitable templates. Structures harvested from the patterned surfaces have also been used for characterization of size-effects in MGs [35]. However, in all these cases the templates are chemically etched away to release the MGs. Use of chemicals not only limits the template reusability but can also affect the properties of molded MGs. It has been reported that KOH typically used for wet etching of silicon and alumina templates can de-alloy some Zr-based MGs [36]. KOH is known to decrease the hydrophobicity of materials by altering the surface chemistry and topography [37]. Size-effects are also very sensitive to the processing conditions in MGs due to their metastable structure [38]. Therefore, chemical-free demolding of templates is essential to use thermoplastic fabrication for surface engineering and characterization of small structures in MGs.Mechanical separation of templates and MGs after thermoplastic molding is prevented by their thermal expansion mismatch (Fig. 1). The coefficient of thermal expansion (α) for MG formers is often higher than templates (Table 1). But any combination of mismatch in α (α MG N α template or α MG b α template ) results in thermal stress build up on the multiple MG-template interfaces during cooling below T g (Fig. 1a). To estimate the extent of residual thermal stress, a 2D th...

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“…This surface oxide acts as a protection layer that prevents major oxidation of sintered coatings when being heated in air at 650 1C. Authors in [19] present a similar observation where the optical properties of laser textured titanium surface remains unchanged before and after heat treatment in air at 500 1C. Tungsten combines with oxygen to form tungsten oxide of various compositions.…”

Section: Solar Absorptance Measurementsmentioning

confidence: 69%