Fine Patterning of Silver Metal by Electron Beam Irradiation onto Room-temperature Ionic Liquid

Abstract

A new silver micropatterning method has been developed by electron beam irradiation to room-temperature ionic liquid containing silver salts. This is the first achievement that uses liquid media to obtain metal deposits by electron beam lithography. Silver deposits were obtained as designed with high resolution and purity compared to the existing direct writing method.Fabrication of micro/nano metal structures on semiconductor substrates is an essential technique for the development of the micro-electromechanical system (MEMS).1,2 To date, there have been many achievements for the patterning of metals such as gold, silver, and copper.36 Among them, the direct writing techniques are considered to be the most efficient method because of the simplicity of their process. They include direct drawing by inkjet printing, 7 or reactive deposition from precursors contained in liquids 8 and those existing in the gas phase 9 by using lasers and a quantum beam, respectively. The last case, using the quantum beam, achieved a resolution as small as 100 nm. However, liquids are considered to be advantageous because they can provide larger amounts of metals in a short time compared with vapor phase deposition.It is well-known that the interaction of ionizing radiation, such as γ-rays, electron beams (EB), and ion beams, with target materials yields radical ions and solvated electrons of 1020 eV energy in spurs.10 These species are easy to trigger in chemical reactions. Room-temperature ionic liquids (RTILs) are one of the good media for radiation chemistry. They generate radicals and solvated electrons as many conventional solvents do, and their reactivity is tunable, depending on the type of anions and cations.11 Besides, the slow solvation of electrons provides higher reactivity against subsequent reactions, and the property of ionic liquids being in the glass state over the wide temperature region facilitates the time-dependent spectroscopic analyses of these processes at low temperatures. In addition, there are many reports about the high radiation stability of RTILs, and they reveal that RTILs have potential as solvents for radiation chemical reactions. 1215 Recently, we have reported the preparation of various kinds of colloidal metal nanoparticles dispersed in RTILs by γ-ray radiation irradiation.16,17 Similar reduction reactions were observed during electron microscopic observations (20300 kV), where the metal nanoparticles were formed on the surface of or inside the ionic liquids around the observation area. 1820 We have recently succeeded in the fabrication of various three-dimensional micro/nano polymer structures by introducing a thin layer of polymerizable RTIL into a quantum beam writing system to trigger the polymerization reaction of RTIL monomers at the nanoscale.21,22 Herein, we demonstrate a new direct writing technique that deposits metals at will on a substrate by introducing RTILs containing silver salts instead of polymerizable ones. The largest difference is the role of RTIL, which was a reactant pre...

Radiation-Assisted Formation of Metal Nanoparticles in Molten Salts

“…Exposure of a molten salt to an electromagnetic, , energetic electrons, , or ion irradiation source produce solvated electrons. Solvated electrons are highly reactive transient species that reduce metal ions and ultimately may cause the formation of agglomerated structures, such as metal nanoparticles, that are not spontaneously formed in unirradiated molten salts except by powerful reducing agents , or reduction methods such as electrochemical deposition or plasma electrochemistry .…”

In Situ Time-of-Flight Mass Spectrometry of Ionic Fragments Induced by Focused Electron Beam Irradiation: Investigation of Electron Driven Surface Chemistry inside an SEM under High Vacuum

“…Metalorganic precursors, such as MeCpPtMe 3 [ 55 , 56 ] and W(CO) 6 [ 57 , 58 ], as a condensed resist, were used in cryogenic conditions due to their high volatility. Non-volatile room-temperature metalorganic resist lithography so far comprises compounds of Pd [ 27 , 59 , 60 ], Ir [ 61 ], Au [ 26 , 62 ], Ag [ 63 ], and Cu [ 64 ]. Gas-assisted FEBID employs volatile precursors continuously supplied to the substrate via a gas injection system.…”

Optical Binding‐Driven Micropatterning and Photosculpting with Silver Nanorods

“…In fact, photosculpting with AgNRs yields similar structures to those achieved by plasma‐induced oxidation of silver to silver oxide and subsequent removal of the oxide, [ 33 ] micropatterns by reducing electron beam lithography, [ 34 ] nanoimprint and electrodeposition techniques, [ 35 ] or laser‐induced ablation, transfer, and deposition, [ 36 ] but, in our case, with a much simpler and straightforward approach.…”