Localized Physical Vapor Deposition via Focused Laser Spike Dewetting of Gold Thin Films for Nanoscale Patterning

Abstract

Focused laser spike (FLaSk) excitation has been demonstrated as a reliable technique for the patterning of micro-to-nanoscale features locally by thermocapillary shear of thin films. Recent work on polymer thin films has revealed that overlapping laser scans can leverage coupled thermal and fluid effects to create subwavelength patterns. Compared to polymeric films, metallic thin films possess both a lower melt viscosity and higher surface tension. Here, we investigate overlapping effects in the dewetting of ∼15 nm gold thin films on borosilicate and quartz glass substrates with a 532 nm continuous wave laser. During this process, FLaSk initiates capillary and thermocapillary dewetting simultaneously. Further, the low oxidation potential and high vapor pressure of gold lead to nonequilibrium vaporization during heating. Since the parameters of overlapping scans control the amount of material that is heated and to what temperature it is heated, selection of laser power, scanning distance, writing speed, and numerical aperture results in particles with different sizes and spacing deposited on the writing substrates or a positioned superstrate through a laser-induced localized physical vapor deposition (LILPVD) process. If the laser parameters are selected within a specific working range, uniform or periodic particle distributions can be repeatably deposited in this fashion, which can then be used as seeds for nanomaterial growth. In addition, if the substrate melts during FLaSk, the viscous force of the liquid-on-liquid dewetting broadens the range of patterning conditions by resisting the motion of the gold leading to more uniform particles over a large range of parameters.

Direct Laser Writing from Aqueous Precursors for Nano to Microscale Topographical Control, Integration, and Synthesis of Nanocrystalline Mixed Metal Oxides

“…The DLW of inorganic materials is of particular interest for integration into devices and applications including flexible electronics, photonic devices, sensors, and catalysts. 2 Often, approaches to DLW of metals and oxides involve laser-assisted photothermal sintering using precursors such as nanoparticle dispersions 3 or the laser-induced thermal pattern-transfer of solid thin films (e.g., via laser-induced forward transfer 4 or focused laser spike excitation 5 ). For these techniques, the laser is used for patterning rather than material synthesis, and films or nanoparticles must be produced in an additional processing step.…”

Thin film rheology via focused laser spike thermocapillary dewetting

“…The sample was placed on a three-axis 532 nm continuous wave (CW) Nd:YAG laser direct write system used in previous work [9]. The beam profile was manually adjusted to be in the TEM 00 mode.…”

“…As demonstrated in our previous work [9], by combinations of different power and NA of the objective lens, the applied stress and temperature can be tuned, though a systematic study of the individual influence of stress and temperature will be left for future work.…”

“…Here, we propose the measurement of thermocapillary (TC) shear as a materials-agnostic mechanical activation method to probe thin film materials. Previous research introduced focused laser spike (FLaSk) heating to generate thermal gradients up to ∼1000 K/µm, corresponding to 10 MPa of surface shear, for studying the dewetting of polymeric [3][4][5][6][7], metallic [8,9] and semiconductor thin films [10,11], and the arrangement of block copolymers [12,13]. In the FLaSk heating process, continuous wave laser excitation produces TC gradients with * jonathan.singer@rutgers.edu a high degree of spatial and temporal control.…”

Focused Laser Spike Dewetting as a Rheology Method for Soft Matter Thin Films

“…Here, we propose the measurement of thermocapillary (TC) shear as a materials-agnostic mechanical activation method to probe thin film materials. Previous research introduced focused laser spike (FLaSk) heating to generate thermal gradients up to ∼1000 K/µm, corresponding to 10 MPa of surface shear, for studying the dewetting of polymeric [3][4][5][6][7], metallic [8,9] and semiconductor thin films [10,11], and the arrangement of block copolymers [12,13]. In the FLaSk heating process, continuous wave laser excitation produces TC gradients with * jonathan.singer@rutgers.edu a high degree of spatial and temporal control.…”