Gold complexes for focused-electron-beam-induced deposition

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.

Focused electron beam induced processing and the effect of substrate thickness revisited

The current understanding in the study of focused electron beam induced processing (FEBIP) is that the growth of a deposit is mainly the result of secondary electrons (SEs). This suggests that the growth rate for FEBIP is affected by the SE emission from the support. Our experiments, with membranes thinner than the SE escape depth, confirm this hypothesis. We used membranes of 1.4 and 4.3 nm amorphous carbon as supports. At the very early stage, the growth is support-dominated and the growth rate on a 4.3 nm thick membrane is three times higher than on a 1.4 nm thick membrane. This is consistent with Monte Carlo simulations for SE emission. The results suggest that SEs are dominant in the dissociation of W(CO)6 on thin membranes. The best agreement between simulations and experiment is obtained for SEs with energies between 3 and 6 eV.With this work we revisit earlier experiments, working at a precursor pressure 20 times lower than previously. Then, despite using membranes thinner than the SE escape depth, we did not see an effect on the experimental growth rate. We explain our current results by the fact that very early in the process, the growth becomes dominated by the growing deposit itself.

Nanometer-scale lithography on microscopically clean graphene

Focused-electron-beam-induced deposition, or FEBID, enables the fabrication of patterns with sub-10 nm resolution. The initial stages of metal deposition by FEBID are still not fundamentally well understood. For these investigations, graphene, a one-atom-thick sheet of carbon atoms in a hexagonal lattice, is ideal as the substrate for FEBID writing. In this paper, we have used exfoliated few-layer graphene as a support to study the early growth phase of focused-electron-beam-induced deposition and to write patterns with dimensions between 0.6 and 5 nm. The results obtained here are compared to the deposition behavior on amorphous materials. Prior to the deposition experiment, the few-layer graphene was cleaned. Typically, it is observed in electron microscope images that areas of microscopically clean graphene are surrounded by areas with amorphous material. We present a method to remove the amorphous material in order to obtain large areas of microscopically clean graphene flakes. After cleaning, W(CO)(6) was used as the precursor to study the early growth phase of FEBID deposits. It was observed that preferential adsorption of the precursor molecules on step edges and adsorbates plays a key role in the deposition on cleaned few-layer graphene.

Ultrahigh resolution focused electron beam induced processing: the effect of substrate thickness

It is often suggested that the growth in focused electron beam induced processing (FEBIP) is caused not only by primary electrons, but also (and even predominantly) by secondary electrons (SEs). If that is true, the growth rate for FEBIP can be changed by modifying the SE yield. Results from our Monte Carlo simulations show that the SE yield changes strongly with substrate thickness for thicknesses below the SE escape depth. However, our experimental results show that the growth rate is independent of the substrate thickness. Deposits with an average size of about 3 nm were written on 1 and 9 nm thick carbon substrates. The apparent contradiction between simulation and experiment is explained by simulating the SE emission from a carbon substrate with platinum deposits on the surface. It appears that the SE emission is dominated by the deposits rather than the carbon substrate, even for deposits as small as 0.32 nm(3).

Growth behavior near the ultimate resolution of nanometer-scale focused electron beam-induced deposition

An attempt has been made to reach the ultimate spatial resolution for electron beam-induced deposition (EBID) using W(CO)(6) as a precursor. The smallest dots that have been written have an average diameter of 0.72 nm at full width at half maximum (FWHM). A study of the nucleation stage revealed that the growth is different for each dot, despite identical growth conditions. The center of mass of each dot is not exactly on the position irradiated by the e-beam but on a random spot close to the irradiated spot. Also, the growth rate is not constant during deposition and the final deposited volume varies from dot to dot. The annular dark field signal was recorded during growth in the hope to find discrete steps in the signal which would be evidence of the one-by-one deposition of single molecules. Discrete steps were not observed, but by combining atomic force microscope measurements and a statistical analysis of the deposited volumes, it was possible to estimate the average volume of the units of which the deposits consist. It is concluded that the volume per unit is as small as 0.4 nm(3), less than twice the volume of a single W(CO)(6) molecule in the solid phase.

Diffraction patterns of artificial two-dimensional crystals synthesized in situ in an environmental scanning transmission electron microscope

In this study, we demonstrated the use of electron-beam-induced deposition for synthesis of artificial two-dimensional crystals with an in situ scanning transmission electron microscope. The structures were deposited from W(CO)6 in an environmental scanning transmission electron microscope on a 30-nm-thick Si3N4 substrate. We present clear electron beam diffraction patterns taken from those structures. The distance between the diffraction peaks corresponded to the dot spacing in the self-made surface crystal. We propose using these arrays of dots as anchor points for making artificial crystals for diffraction analysis of weakly scattering or beam-sensitive molecules such as proteins.