Low‐Ion‐Dose FIB Modification of Monomicellar Layers for the Creation of Highly Ordered Metal Nanodot Arrays

Abstract

There is considerable interest in the fabrication of metal and metal oxide nanostructures for applications in fields of technology such as molecular electronics, biosensors, and materials science. [1][2][3][4][5] Specifically, gold nanodots are of interest for their optical, conductive, and catalytic properties. [6][7][8][9] Different approaches have been followed for the creation of controlled patterns of gold nanoparticles and nanowires on surfaces, either by preparing the particles in solution and then depositing them on a surface, or by generating the structure directly on the surface. In the first case, fabrication of defined aperiodic patterns requires local control of the deposition of the particles, [10,11] typically achieved by photoresist technology. [12] In the second case, particle formation must be effected with local control. Here, particle size, size uniformity, and interparticle distances are critical issues.There are examples of both approaches where an electron beam (e-beam) has been used to define chemical patterns either for the guided adsorption of solution-synthesized particles, [13] or for the direct modification of films of pre-made nanoparticles or of gold solutions. [14,15] We have previously shown that rather regular patterns of metal and metal oxide nanodots on surfaces can be obtained by selfassembly of monofilms from block-copolymer micelles with metal precursor salts sequestered in their cores. [16] Under the right conditions, the micelles spontaneously form a closed monofilm with hexagonal order. Subsequent plasma treatment has been employed to reduce the metal salt and remove the organic polymer completely, to yield a single metal nanoparticle per micelle at the sites of the micelle cores, that is, in the regular pattern of the micelles. To create aperiodic patterns of gold nanodots, we took advantage of the fact that the micellar layer can serve as an ebeam negative resist. [17] As the resist contains nanoscopic deposits of a metal salt, it is possible to create patches of nanodots by plasma treatment of the developed films, that is, the functional identities are generated from the resist with a minimum of process steps.Although the e-beam proved to be a successful choice for direct lithography of the micellar layer, there are limitations because of the very high doses that were needed to pin the irradiated micelles effectively to the substrate. In detail, these are electrostatic charging and the concurrent beam deflection, slow writing rates, and a limitation in the choice of the substrate. Here, a focused ion beam (FIB) system is an interesting and in some cases superior alternative that has proven to be a versatile tool for micro-and nanodevice prototyping. FIB systems can be used for imaging, high-resolution milling, and direct modification of a resist layer and self-assembled monolayers. [18,19] Furthermore, commercially available FIB systems have reached a similar resolution as e-beam systems. As a result of the higher mass of ions with respect to electrons, in FIB lithogra...

Cell adhesion and response to synthetic nanopatterned environments by steering receptor clustering and spatial location

“…Here, cells on surfaces with an interparticle spacing of 73 nm could not adhere and no FAs were formed, but FAs were perfectly established on surfaces with 58 nm spaced nanoparticles in micropatches even though the average (global) concentration of particles on the surface was lower than in the latter case. The fabrication process involves the selective irradiation of a micellar monolayer with ultraviolet light (Gorzolnik et al, 2006), focused ions (Mela et al, 2007) or electrons and removal of nonirradiated parts. The different methods exhibit advantages and limitations with regard to structured surface area, feature size, and necessary equipment.…”

Micro‐Nanostructured Protein Arrays: A Tool for Geometrically Controlled Ligand Presentation

“…Both effects limit the practical usability of these approaches. Only electron or focused ion beam (FIB) lithography using micellar monolayer as negative resist were capable of producing sharp borders 11, 16. Nevertheless, both processes have disadvantages compared to the present approach.…”

Control of the average spacing between aligned gold nanoparticles by varying the FIB dose

“…15 Particularly in comparison with electron-beam lithography, FIB has proven to be more versatile in nano-structuring resists because the energy transfer is better and the milling time is shorter, due to higher mass of the ion. 16 In addition, FIB has minimized the typical problems of e-beam lithography, such as backscattering, low resist sensitivity, and proximity effect. 17,18 The diameters of focused ion beams can systematically be controlled by varying the beam current.…”

“…15 Mela et al listed the advantages of the FIB over the e-beam systems in the field of interest. 16 In the present work, a fine beam of Ga + ions was used to remove the OTS SAM in sub-100 nm lateral lines (Scheme 1b). Then, the OTS SAM removed regions were re-filled with MPTS (Scheme 1c) to allow nucleation and growth of OMCVD Au NPs (Scheme 1d).…”