The creation of functional nanostructures by electron-beam-induced deposition (EBID) is becoming more widespread. The benefits of the technology include fast 'point-and-shoot' creation of three-dimensional nanostructures at predefined locations directly within a scanning electron microscope. One significant drawback to date has been the low purity level of the deposition. This has two independent causes: (1) partial or incomplete decomposition of the precursor molecule and (2) contamination from the residual chamber gas. This frequently limits the functionality of the structure, hence it is desirable to improve the decomposition and prevent the inclusion of contaminants. In this contribution we review and compare for the first time all the techniques specifically aimed at purifying the as-deposited impure EBID structures. Despite incomplete and scattered data, we observe some general trends: application of heat (during or after deposition) is usually beneficial to some extent; working in a favorable residual gas (ultra-high vacuum set-ups or plasma cleaning the chamber) is highly recommended; gas mixing approaches are extremely variable and not always reproducible between research groups; and carbon-free precursors are promising but tend to result in oxygen being the contaminant species rather than carbon. Finally we highlight a few novel approaches.

The technique of electron-beam-induced deposition (EBID), when performed with organic precursors, typically results in relatively low metal content due to the partial decomposition of the organic precursor, leaving carbon-rich remnants in the deposition. Here we describe a method applied to noble-metal structures deposited using EBID, consisting of a post-treatment step of heating in a reactive atmosphere of oxygen, whereby the amount of carbon in the structure is strongly reduced. As a result, we have been able to increase the purity of platinum deposits from 15 at.% to nearly 70 at.%, and gold similarly from 8 at.% to nearly 60 at.%. The resistivity of these structures has also been improved by up to four orders of magnitude, to achieve (1.4 ± 0.2) × 104 µΩ cm in the case of platinum.

Thermally assisted electron beam induced deposition can result in an improvement of the purity of nano-scale depositions. Six commonly used organic precursors were examined: W(CO)(6), TEOS (tetraethylorthosilicate), MeCpPtMe(3), Co(CO)(3)NO, Co(2)(CO)(8), and Me(2)Auacac. The last two precursors were also tested on two different instruments to confirm reproducibility of the results. The influence of the substrate temperature on the composition of the deposition has been quantified systematically in the temperature range 25-360 °C. It has been shown that most purities improve when applying an elevated temperature, while the shape of the deposition remains intact. The purity improvement is achieved at the cost of a lower deposition yield. The amount of improvement is different for each precursor. Within the maximum temperature range of 360 °C, the best improvement was found for W(CO)(6): from 36.7 at.% at 25 °C to 59.2 at.% at 280 °C. For both cobalt precursors an additional transition region between patterned electron beam induced deposition (EBID) and thermal thin film growth has been identified. In this region seeded growth occurs with strongly increased growth rates.

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Electron beam induced deposition (EBID) is a process used for the fabrication of three-dimensional nanostructures of a variety of materials, but direct deposition of pure metallic structures has rarely been achieved. Typically, MeCpPtMe3 as a precursor for Pt leads to a carbon rich deposit with ~15 at.% Pt, which negatively affects its application as an electrical contact. We report a new process for Pt purification: in situ annealing with electron beam post-irradiation under oxygen flux, which can completely purify a thin (<100 nm) Pt EBID structure at substrate temperatures as low as 120 °C. We have developed a sequential method in which a thin Pt EBID structure is deposited on a previously purified structure and subsequently purified. The resistivity of the contact grown by this sequential procedure is observed to be ~70 ± 8 μΩ cm-only six times higher than that of pure bulk Pt. Thus, sequential deposition and purification proves to be an effective method for fabricating pure Pt structures of desired dimensions.

Fabrication of pure gold nanostructures by electron beam induced deposition with Au(C0)CI precusor: deposition characteristics and primary beam scattering effects.

Four gold complexes were tested as a precursor for focused-electron-beam-induced deposition: [ClAu(III)Me2]2, ClAu(I)(SMe2), ClAu(I)(PMe3), and MeAu(I)(PMe3). Complexes [ClAu(III)Me2]2 and MeAu(I)(PMe3) are volatile, have sufficient vapor pressure at room temperature for deposition experiments, and were found to yield deposits that contain gold (29-41 and 19-25 atom %, respectively). Electrons easily remove the Cl ligand from [ClAu(III)Me2]2, and predominantly both methyl ligands are incorporated into the deposit. Electrons remove at least one methyl group from MeAu(I)(PMe3). Complexes ClAu(I)(SMe2) and ClAu(I)(PMe3) are not suitable as a precursor. They dissociate in vacuum, and the only volatile components are Cl, SMe2, and PMe3, respectively.