Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum

Abstract

We propose a new approach to nanoscience and technology for ionic liquids (ILs): molecular beam deposition of IL in ultrahigh vacuum by using a continuous wave infrared (CW-IR) laser deposition technique. This approach has made it possible to prepare a variety of "nano-IL" with the given composition on the substrate: a nanodroplet, on one hand, the volume of which goes down to 1 aL and, on the other hand, an ultrathin film with a thickness to several 100 nm or less. The result of fractional distillation of a binary mixture of ILs, investigated by nuclear magnetic resonance as well as electrospray ionization time-of-flight mass spectrometry, indicates that this deposition process is based on the thermal evaporation of ILs, and thus this process also can be used as a new purification method of ILs in vacuum. Furthermore, the fabrication of binary mixture droplets of two ILs on the substrate by alternating deposition of two ILs was demonstrated; the homogeneity of the composition was confirmed even for one single droplet by high-spatial-resolution Raman spectroscopy.

Potential applications of deep eutectic solvents in nanotechnology

“…As common with most studies, the basic concern on nanomaterial properties is placed [37] or by molecular beam deposition route [88], (3) and as confinement by confining the IL in nano-sized spaces of nanomaterials such as the tubular space in CNT [89] or the narrow pores in nanoporous silica [90]. Confinement is the most reported case to study the physicochemical behavior of IL in nano-volumes.…”

High-throughput CW-IR laser deposition and laser microscope imaging of binary ionic liquids in vacuum

“…For the ILs, we used 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([bmim][NTf2]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF6]), which were purchased from Kanto Chemical (Japan). These ILs can be deposited without significant decomposition, which was estimated to be less than 1% by nuclear magnetic resonance and electrospray ionization time-of-flight mass spectrometry in our previous study [6]. Binary mixtures of these ILs with different mixing ratios were prepared on a single sapphire (0001) room temperature.…”

“…For this sample, about 0.24 µg cm −2 (∼ 0.17 pl cm −2 ) of each IL was deposited per cycle at a rate of 3 ng cm −2 s −1 (∼ 2 nl cm −2 s −1 ) for each IL so that 5.6 µg cm −2 (3.9 pl cm −2 ) of each IL accumulated after 23 repetitions. A schematic illustration of the Raman measurement of an isolated IL droplet is shown in figure 2(a), and details of this measurement system are described elsewhere [6]. Another sample was prepared for UHV-LM observation, where 0.67 µg cm −2 (∼ 0.47 pl cm −2 ) of each IL was deposited per cycle at a rate of 7 ng cm −2 s −1 (∼ 5 nl cm −2 s −1 ) to yield ∼ 35 µg cm −2 (25 pl cm −2 ) after 53 repetitions.…”

“…The low vapor pressure of ILs allows their characterization [3] and processing [4,5] using high-vacuum techniques. In our previous works, we developed a new deposition technique of ILs in vacuum using a continuous-wave infrared (CW-IR) laser to prepare nanoscale IL droplets and thin films on a substrate without any decomposition [6], and also demonstrated that IL nanodroplets can be used as microreactors for crystal growth in vacuum [7]. Considering the use of ILs as a solvent or electrolyte in vacuum, the mixing of different ILs is one means of improving their functions.…”

Development of compact CW-IR laser deposition system for high-throughput growth of organic single crystals

“…CW-IR laser deposition can be applied to various organic materials. Even if they do not absorb IR light, as is the case of ionic liquids (ILs), the heat can be provided through the addition of an IR absorbent such as Si powder [6].…”