Charging Process and Coulomb-Force-Directed Printing of Nanoparticles with Sub-100-nm Lateral Resolution

Abstract

This article reports on a new charging process and Coulomb-force-directed assembly of nanoparticles onto charged surface areas with sub-100-nm resolution. The charging is accomplished using a flexible nanostructured thin silicon electrode. Electrical nanocontacts have been created as small as 50 nm by placing the nanostructured electrode onto an electret surface. The nanocontacts have been used to inject charge into 50 nm sized areas. Nanoparticles were assembled onto the charge patterns, and a lateral resolution of 60 nm has been observed for the first time. A comparison of the nanoparticle patterns with the surface potential distribution recorded by Kelvin probe force microscopy (KFM) revealed a mismatch in the lateral resolution. One possible explanation is that nanoparticles may visualize charge patterns at a sub-60-nm length scale that is not well resolved using KFM.Inorganic, metallic, and semiconducting nanomaterials in the form of nanoparticles, nanowires, nanobelts, or nanodisks are considered key building blocks in the design of novel high-performance nanotechnological devices. The process to fabricate such devices, however, will require new additive concepts to integrate, orient, and assemble such building blocks at desired locations on a substrate. Current approaches that address the integration of nanomaterials at desired locations on a substrate include serial scanning probe based concepts to print 1,2 or manipulate 3 nanomaterials at the sub-100-nm length scale, semiparallel inkjet-based concepts 4,5 to print materials from suspensions with 10 µm scale resolution, parallel nanotransfer methods 6,7 to transfer nanomaterials from one substrate to another retaining a copy of the order, and a vast variety of programmable or "receptor based" assembly concepts 8-18 that use unordered nanomaterials as an input. Scanning probe and inkjet-based methods enable rapid reconfiguration of the patterns and the formation of heterogeneous assemblies at an early stage but remain too slow to print materials over large areas at the sub-10-µm length scale. Nanotransfer concepts are most suitable to transfer nanomaterials from one substrate to another over large areas. Nanotransfer maintains the arrangement of the nanomaterials on a donor substrate; i.e., it does not order or rearrange the materials as part of the process."Receptor"-based concepts focus on the directed assembly of randomly oriented nanomaterials. The materials are suspended in solution or gas phase and are assembled at desired locations (receptors) on a substrate using specific interactions. Most actively investigated areas, currently, use protein recognition, 19,20 DNA hybridization,9,21,22 hydrophobicity/hydrophilicity, surface tension and self-assembled monolayers, 10 topography-directed concepts, 23-25 magnetic 11 and dielectrophoretic assembly and transport, 22,[26][27][28] and electrostatic forces. [12][13][14][15][16][17][18]25,27 In recent years there has been an increased focus on the use of long range electrostatic forces to direct th...

Gas Phase Nanoparticle Integration

“…We refer to this process as electric nanocontact printing of charge. The electrode structures used in electric nanocontact printing are made from lithographically patterned thin silicon (10 µm thick) wafers [14] and metal coated poly(dimethylsiloxane) (PDMS) stamps [1,9]. For the dielectric substrate, we used a 60 nm thick film of PMMA spin coated onto a silicon wafer.…”

“…The primary aim of this approach is to direct single nanoparticles into addressable regions on a surface. It combines Coulomb force directed assembly [10,13,14] with topographically patterned materials that can be formed by conventional lithography. Figure 1 helps illustrate the fringing field directed assembly concept.…”

“…[15] We and others have already demonstrated three fundamentally different assembly strategies using powders of nanoparticles [9]; nanoparticles from the liquid phase [1,11,16]; and most recently nanoparticles from the gas phase [10,13,14,17]. A system that forms nanoparticles by evaporation of metals (Au, Ag, Ga, In, Zn, Cu) and semiconductor (Ge) precursors [10,14] as well as a system that forms organic protein nanoparticle aerosols from solution [17] were employed to aid in the directed assembly process. Using these systems, we were able to show 30-100 nm resolution site specific assembly of nanoparticles from the gas phase.…”

“…Using these systems, we were able to show 30-100 nm resolution site specific assembly of nanoparticles from the gas phase. [14,15,17] An example of one of these systems, shown in figure 2, involves the use of a tube furnace that generates nanoparticles in the gas phase by evaporation, nucleation, and condensation. An argon carrier gas transports the particles out of the furnace and into the particle assembly module.…”

Sub-50 nm positioning of organic compounds onto silicon oxide patterns fabricated by local oxidation nanolithography

“…[1][2][3][4] Taking advantage of several nanolithographies [5][6][7] as well as the self-organisation of functional molecules, it has been possible to fabricate surface patterns of these functional units with the proper position and shape and establish connections with other components of the device [8][9][10][11][12] . These approaches make use of specific interactions, such as hydrophobicity/hydrophilicity, electrostatic or protein recognition, between the components and the substrate.…”