Direct-Write Fabrication of Cellulose Nano-Structures via Focused Electron Beam Induced Nanosynthesis

In many areas of science and technology, patterned films and surfaces play a key role in engineering anddevelopment of advanced materials. Here, we introduce a new generic technique for the fabricationof polysaccharide nano-structures via focused electron beam induced conversion (FEBIC). For theproof of principle, organosoluble trimethylsilyl-cellulose (TMSC) thin films have been deposited byspin coating on SiO2 / Si and exposed to a nano-sized electron beam. It turns out that in the exposedareas an electron induced desilylation reaction takes place converting soluble TMSC to rather insolublecellulose. After removal of the unexposed TMSC areas, structured cellulose patterns remain on thesurface with FWHM line widths down to 70 nm. Systematic FEBIC parameter sweeps reveal a generallyelectron dose dependent behavior with three working regimes: incomplete conversion, ideal doses andover exposure. Direct (FT-IR) and indirect chemical analyses (enzymatic degradation) confirmed thecellulosic character of ideally converted areas. These investigations are complemented by a theoreticalmodel which suggests a two-step reaction process by means of TMSC → cellulose and cellulose → noncellulosematerial conversion in excellent agreement with experimental data. The extracted, individualreaction rates allowed the derivation of design rules for FEBIC parameters towards highest conversionefficiencies and highest lateral resolution.