Photothermal Laser Microsintering of Nanoporous Gold

Abstract

Photothermal processing of nanoporous gold using a microfocused continuous-wave laser at a wavelength of 532 nm and a 1/e(2) spot diameter of 2.9 μm has been studied. In addition, complementary experiments have been carried out via conventional annealing. Scanning electron microscopy has been used for characterization. Local laser irradiation at distinct laser powers and pulse lengths results in coarsening of the porous gold structures. During laser processing the pore size of the native nanoporous gold increases to maximum values in the range of 0.25-3 μm. The affected areas exhibit lateral dimensions in the range of 2-10 μm. Overall two regions are distinguished. An inner region, where large pores and ligaments are formed and an outer region, where the pore size and ligament size gradually change and approach the feature sizes of the native material. A qualitative thermokinetic model allows one to reproduce the experimentally observed dependence of the laser-induced morphologies on the laser parameters. On the basis of this model the underlying processes are attributed to sintering and melting of the gold structures. The presented results demonstrate the prospects of photothermal laser processing in engineering porous gold with spatially varying porosities on micrometer to nanometer length scales.

Electrically tunable pore morphology in nanoporous gold thin films

“…In this process, selective removal of silver atoms from a silver-rich gold alloy, accompanied by surface diffusion of gold atoms at the metal-electrolyte interface, results in an open-cell structure with interconnected ligaments of tens of nanometers [22,23]. Alloy composition [24] and preparation approach, dealloying method [25][26][27], and post-processing techniques [28,29] all influence pore morphology, resulting in a wide range of possible pore and ligament sizes ranging from tens of nanometers [25] up to several hundred of nanometers [23]. When np-Au films are subjected to homogenous thermal treatment (such as in annealing furnaces), pore and ligament sizes increase in a uniform fashion across the entire sample due to enhanced diffusion of surface atoms [23].…”

“…When np-Au films are subjected to homogenous thermal treatment (such as in annealing furnaces), pore and ligament sizes increase in a uniform fashion across the entire sample due to enhanced diffusion of surface atoms [23]. However, a controllable spatial gradient of pore morphology is highly desirable in order to rapidly identify optimal morphologies for desired application [29]. For example, it is often necessary to identify a specific range of nanostructures that increase surface-enhanced Raman signal from a metallic surface, improve biocompatibility, lower limit-of-detection of a sensor, or increase reactivity of a catalytic surface.…”

Nanostructure Introduces Artifacts in Quantitative Immunofluorescence by Influencing Fluorophore Intensity

“…Nanoporous gold is a versatile model nanostructured material as its feature size can be tuned by several techniques 12, 13 and gold is a common material system for biomaterial applications 14 . The thin film np-Au used in this study consists of a bi-continuous network of pores and gold ligaments with feature sizes in the range of 87 (average diameter) and 30 (average width) nanometers respectively (Fig.…”

Utilizing dynamic laser speckle to probe nanoscale morphology evolution in nanoporous gold thin films

“…The photothermal treatment and subsequent morphology changes of many porous metals have been demonstrated previously [19,22]. Nanoporous gold (np-Au) presents a good model material for the characterization of surface morphology changes due to an almost ten-fold increase in pore area over a wide range of laser powers [22].…”

“…Through the thermal treatment of np-Au it is possible to selectively evolve the Au network thereby altering the characteristic morphology [18], an attractive feature for many emerging np-Au applications. Specifically, photothermal treatment has received attention in order to selectively and precisely modify the np-Au nanostructure [19,20]. Here we couple dynamic laser speckle autocorrelation spectroscopy and the photothermal treatment of thin film np-Au to successfully probe both morphology evolution dynamics (length and time) of the films without the use of ex situ microscopy techniques.…”