Low-resistivity Pd nanopatterns created by a direct electron beam irradiation process free of post-treatment steps

Abstract

The ability to create metallic patterned nanostructures with excellent control of size, shape and spatial orientation is of utmost importance in the construction of next-generation electronic and optical devices as well as in other applications such as (bio)sensors, reactive surfaces for catalysis, etc. Moreover, development of simple, rapid and low-cost fabrication processes of metallic patterned nanostructures is a challenging issue for the incorporation of such devices in real market applications. In this contribution, a direct-write method that results in highly conducting palladium-based nanopatterned structures without the need of applying subsequent curing processes is presented. Spin-coated films of palladium acetate were irradiated with an electron beam to produce palladium nanodeposits (PdNDs) with controlled size, shape and height. The use of different electron doses was investigated and its influence on the PdNDs features determined, namely: (1) thickness of the deposits, (2) atomic percentage of palladium content, (3) oxidation state of palladium in the deposit, (4) morphology of the sample and grain size of the Pd nanocrystals and (5) resistivity. It has been probed that the use of high electron doses, 30000 μC·cm-2 results in the lowest resistivity reported to date for PdNDs, namely 145.1 μΩ·cm, which is only one order of magnitude higher than metallic palladium. This result paves the way for development of simplified lithography processes of nanostructured deposits avoiding subsequent post-treatment steps.

High-Throughput Direct Writing of Metallic Micro- and Nano-Structures by Focused Ga+ Beam Irradiation of Palladium Acetate Films

“…As recently reported, the irradiation of Pd 3 (OAc) 6 thin films with an electron beam produces the decomposition of the organometallic precursor, varying the Pd-oxidation state and therefore the electrical resistivity associated with the resulting nanostructures by up to 2 orders of magnitude. In particular, the reduction of Pd 2+ into metallic palladium, Pd 0 , occurs when applying a dose of 30,000 μC/cm 2 . In order to quantify this conversion for Ga + irradiated films, the Pd 2+ conversion into Pd 0 in ion-irradiated films, an XPS study was performed.…”

“…First, they pave the way for their straightforward use in various applications where metallic micro- and nano-patterns are needed, such as interconnects, conductive micro- and nano-meshes, metallic micro- and nano-templates, nanogaps, electrical contacts to nano-objects, and so forth. Second, these Pd 3 (OAc) 6 films can also be decomposed by electron irradiation , or light irradiation, offering the capability of applying on the same film several micro- and nano-lithography techniques that span a wide range of lateral sizes. Third, there exist other acetates and organometallic films that contain elements such as Au, Co, Fe, and so forth, and their patterning by focused ion beam irradiation could lead to structures exhibiting additional functional properties beyond electrical conductivity, such as plasmonic or magnetic behavior.…”

“…Recently, our group has shown that by irradiating a Pd 3 (OAc) 6 thin film with a high electron dose, it is possible to produce metallic nanostructures without the need of post-processing annealing steps . Unfortunately, the high dose required (30,000 μC/cm 2 ) limits the applications of this approach to small-area patterning or low-throughput device fabrication.…”

“…31−35 Recently, our group has shown that by irradiating a Pd 3 (OAc) 6 thin film with a high electron dose, it is possible to produce metallic nanostructures without the need of postprocessing annealing steps. 36 Unfortunately, the high dose required (30,000 μC/cm 2 ) limits the applications of this approach to small-area patterning or low-throughput device fabrication. Motivated by the search for a high-throughput and annealing-free patterning process of Pd 3 (OAc) 6 thin films, we have investigated whether Ga + FIB irradiation could be effective toward a decrease in the required charge dose without putting in jeopardy the low electrical resistivity of the nanostructure.…”

“…Experimental Details. Ga + FIB irradiations were carried out in a Helios NanoLab 650 (FEI company) on palladium acetate films with thicknesses in the 100−350 nm range; the palladium acetate films were previously deposited by spin coating onto Si/SiO 2 substrates 36 (see the sketch in Figure 1). Spin-coated films with thicknesses in the range of 100 to 200 nm were prepared by spreading 10 μL of a 0.09 M Pd 3 (OAc) 6 filtered solution in chloroform.…”