Atomic-Layer-Deposition Assisted Formation of Wafer-Scale Double-Layer Metal Nanoparticles with Tunable Nanogap for Surface-Enhanced Raman Scattering

Abstract

A simple high-throughput approach is presented in this work to fabricate the Au nanoparticles (NPs)/nanogap/Au NPs structure for surface enhanced Raman scattering (SERS). This plasmonic nanostructure can be prepared feasibly by the combination of rapid thermal annealing (RTA), atomic layer deposition (ALD) and chemical etching process. The nanogap size between Au NPs can be easily and precisely tuned to nanometer scale by adjusting the thickness of sacrificial ALD Al2O3 layer. Finite-difference time-domain (FDTD) simulation data indicate that most of enhanced field locates at Au NPs nanogap area. Moreover, Au NPs/nanogap/Au NPs structure with smaller gap exhibits the larger electromagnetic field. Experimental results agree well with FDTD simulation data, the plasmonic structure with smaller nanogap size has a stronger Raman intensity. There is highly strong plasmonic coupling in the Au nanogap, so that a great SERS effect is obtained when detecting methylene blue (MB) molecules with an enhancement factor (EF) over 107. Furthermore, this plasmonic nanostructure can be designed on large area with high density and high intensity hot spots. This strategy of producing nanoscale metal gap on large area has significant implications for ultrasensitive Raman detection and practical SERS application.

Plasmonic Gold Trimers and Dimers with Air-Filled Nanogaps

“…Taken together, this work highlights the strengths of the ALD technique. Specifically, it demonstrates the effectiveness of ALD in forming conformal oxide layers on the subnanometer length scales that are inaccessible to the EBL technique, a capability that has been exploited to fabricate precisely defined dielectric-filled nanogaps for metamaterials, − nanoparticle on mirror (NPoM) configurations, and various nanostructure assemblies. − Other nanofabrication schemes have selectively removed the dielectric to form air-filled nanogaps ,, by capitalizing on the susceptibility of ALD-deposited amorphous Al 2 O 3 to relatively mild wet etchants. , …”

“…Specifically, it demonstrates the effectiveness of ALD in forming conformal oxide layers on the subnanometer length scales that are inaccessible to the EBL technique, a capability that has been exploited to fabricate precisely defined dielectric-filled nanogaps for metamaterials, 39−43 nanoparticle on mirror (NPoM) configurations, 45 and various nanostructure assemblies. 30−32 Other nanofabrication schemes have selectively removed the dielectric to form airfilled nanogaps 30,46,47 by capitalizing on the susceptibility of ALD-deposited amorphous Al 2 O 3 to relatively mild wet etchants. 33,47 With physical vapor deposition (PVD) techniques being integral to wafer-based processing, there has also been an impetus to incorporate innovative PVD-based schemes into nanofabrication.…”

TiOxNy Modified TiO2 Powders Prepared by Plasma Enhanced Atomic Layer Deposition for Highly Visible Light Photocatalysis

“…ALD is a novel and promising thin film deposition technique based on sequential self-limited and complementary surface chemisorption reactions, which is able to deposit ultrathin, uniform, and conformal layers, and it’s especially suitable for coating 3D complex structures. In recent years, ALD has attracted increasing attention in synthesis and surface engineering of complex nanostructures in recent years 23 – 26 . ALD has shown great prospects in various applications, such as lithium ion batteries 27 , 28 , supercapacitors 29 – 31 , catalysis 32 , 33 , and solar energy conversions 34 .…”

Active optical antennas driven by inelastic electron tunneling

“…Alternatively, dielectric spacer layers can be introduced between the antenna parts. Here atomic layer depositions offer excellent control over the thickness of conformally deposited oxide layers down to single atomic monolayers, which is particularly useful for vertical configurations [71], but have also been demonstrated to create lateral nanometer gaps [72,73]. The oxide can subsequently be etched away to create vertical air gaps [74].…”