Roland Resch

Nanoparticle manipulation by mechanical pushing: underlying phenomena and real-time monitoring

Experimental results that provide new insights into nanomanipulation phenomena are presented. Reliable and accurate positioning of colloidal nanoparticles on a surface is achieved by pushing them with the tip of an atomic force microscope under control of software that compensates for instrument errors. Mechanical pushing operations can be monitored in real time by acquiring simultaneously the cantilever deflection and the feedback signal (cantilever non-contact vibration amplitude). Understanding of the underlying phenomena and real-time monitoring of the operations are important for the design of strategies and control software to manipulate nanoparticles automatically. Manipulation by pushing can be accomplished in a variety of environments and materials. The resulting patterns of nanoparticles have many potential applications, from high-density data storage to single-electron electronics, and prototyping and fabrication of nanoelectromechanical systems.

Nanorobotic assembly of two-dimensional structures

Precise control of the structure of matter at the nanometer scale will have revolutionary implications for science and technology. Nanoelectromechanical systems (NEMS) will be extremely small and fast, and have applications that range from cell repair to ultrastrong materials. This paper describes the first steps towards the construction of NEMS by assembling nanometer-scale objects using a scanning probe microscope as a robot. Our research takes an interdisciplinary approach that combines knowledge of macrorobotics and computer science with the chemistry and physics of phenomena at the nanoscale. We present experimental results that show how to construct arbitrary patterns of gold nanoparticles on a mica or silicon substrate, and describe the underlying technology. We also discuss the next steps in our research, which are aimed at producing connected structures in the plane, and eventually three-dimensional nanostructures.

Manipulation of gold nanoparticles in liquid environments using scanning force microscopy

Precise and controlled manipulation of individual gold nanoparticles (deposited on a Si/SiO2 surface) in liquid environments using the tip of a scanning force microscope is reported for the first time. Experiments were performed in deionized water and in ethanol as a prototype for an organic solvent. Analysis of the amplitude signal of the cantilever before and during manipulation reveals that the particles are pushed across the surface, similar to the manipulation of nanoparticles in air.

Growth of zinc sulfide thin films on (100)Si with the successive ionic layer adsorption and reaction method studied by atomic force microscopy

Zinc sulfide (ZnS) thin films were grown on (100)Si substrates from solution with the successive ionic layer adsorption and reaction (SILAR) method. Aqueous solutions of ZnCl2 and Na2S were used as precursors. The morphological development of the films with increasing number of SILAR cycles was monitored ex situ by atomic force microscopy (AFM) operated in tapping mode. Their roughness increased vs. the growth cycles. AFM studies on (100)Si substrates treated with Na2S solution revealed that the dissolution of the silicon substrates is a process competing with the thin film growth and has to be considered when interpreting the AFM images.

Dissolution of the barite (001) surface by the chelating agent DTPA as studied with non-contact atomic force microscopy

Abstract DTPA (diethylenetriaminepentaacetic acid) is a chelating agent widely used for removal of barium sulfate (barite) scale in the petroleum industry. In this paper we report ex-situ investigations of barite dissolution in deionized water and in 0.18 M DTPA aqueous solutions. Non-contact atomic force microscopy (NC-AFM) was used to observe dissolution on the BaSO 4 (001) cleavage surface. Dissolution was carried out at room temperature in a 10 ml reactor. Each sample was first etched in solution and dried before examination by NC-AFM. Dissolution on the BaSO 4 (001) surface took place via development of etch pits. In deionized water, triangular etch pits were observed on the (001) terraces at room temperature. And, zigzag shaped etch pits were found at the edges of steps. In DTPA solutions, etch pits on the (001) terraces were observed and these became deeper and longer with increasing time. The geometry of these etch pits was trapezoidal, and/or trapezohedral. To explain this characteristic morphology caused by dissolution we suggest that the active sites of one DTPA molecule bind to two or three Ba 2+ cations exposed on the (001) surface.

Layered nanoassembly of three-dimensional structures

NEMS (nanoelectromechanical systems) loom beyond the MEMS horizon as the new frontier in miniaturization. Nanorobots and other NEMS are expected to find revolutionary applications in science, engineering and everyday life. Until now, nanostructures have been built primarily in 2D, because of the difficulties of 3D fabrication. This paper describes a promising approach to the construction of 3D nanostructures by working in successive layers, much like the rapid prototyping techniques used in the macroscopic world. Each object nanolayer is built by nanomanipulation, or possibly by programmed self-assembly, and then surrounded by a sacrificial layer that planarizes the sample and serves as a substrate for the deposition of the next object nanolayer. Initial experimental results which show that the approach is feasible are presented.

Towards hierarchical nanoassembly

Assembly of nanometer-scale objects by scanning probe microscope (SPM) as a promising approach for the fabrication of nanoelectromechanical systems (NEMS). This paper describes several techniques for positioning nanoparticles, linking them to form subassemblies, and moving entire subassemblies. These are first steps towards the hierarchical construction of complex nanoassemblies. Results of experiments conducted in ambient air and in liquid environments are presented. Nanomanipulation in liquids opens new research directions involving interactions with single biomolecules, and fine control of forces between tips, particles and surface substrates.