Continuing liveblogging of Foresight 2010.
Oscar Custance winner of the 2009 experimental Feynmann prize presents his work on the experimental demonstration of mechanosynthesis
Oscar Custance is a scientist specialized in atomic resolution dynamic force microscopy (DFM) operated using the frequency modulation detection method –a technique also known as non-contact atomic force microscopy (NC-AFM). He also has a strong background on atomic resolution scanning tunneling microscopy (STM) and spectroscopy (STS) in ultra high vacuum environment.
Motivated by the potential of atomic resolution DFM, as well as by a marked interest in the Japanese culture, he joined Prof. Seizo Morita’s Laboratory (Osaka University, Japan) as a postdoctoral fellow in February of 2002. Due to his remarkable research results, published in high visibility journals, and the impact of his skills for the direction and coordination of both research lines and researchers in the work of the group, he was promoted to Visiting Associate Professor in 2005.
Since February 2008, he is a permanent researcher at the National Institute for Materials Sciences (NIMS), and leader of the Nanomechanics Group of the Advanced Nano Characterization Center. His current research activities focus on applying dynamic force microscopy and the atomic manipulation, force spectroscopy and chemical identification tools he has contributed to develop to clarify problem in material science at atomic and molecular scale. He also has a strong commitment to further develop the DFM detection technique towards the achievement of highest sensitivity, and explore other instruments and techniques with relevance in nanomechanics studies and nanoscience in general.
Brief intro to experimental technique FM-AFM
Nano structuring atom by atom using AFM
Atomic Resolution Dynamic Force microscopy
Frequency modulation AFM
non-contact AFM (length 225 microns, width 38 microns, thickness 7 microns, height 12 microns)
Ch. Loppacher et al , Phys Rev B, 62, 16944 (2000)
UFV-AFM & Interferometric Detection.
Oscar reviews the history of moving atoms from Eigler forward and a lot of scientific and technical detail.
Controlling the natural diffusion energy barriers.
Use the AFM tip to lower the energy barrier between two atoms in a controlled way.
Manipulation procedure –
* Appropriate selection of the tip scan direction
* Tuning the tip-surface interaction force
the scan driection is working over a 1.9 nanometer square
Atomic force microscopy as a tool for atom manipulation
Nature Nanotechnology 4, 803 2009.
During the past 20 years, the manipulation of atoms and molecules at surfaces has allowed the construction and characterization of model systems that could, potentially, act as building blocks for future nanoscale devices. The majority of these experiments were performed with scanning tunnelling microscopy at cryogenic temperatures. Recently, it has been shown that another scanning probe technique, the atomic force microscope, is capable of positioning single atoms even at room temperature. Here, we review progress in the manipulation of atoms and molecules with the atomic force microscope, and discuss the new opportunities presented by this technique.
Reproducibilty on other surfaces at room temperature
Tin, silicon, germanium, indium
An instrument that combines the strengths of AFM and STM allows determination of the forces required to move a single atom on a surface.
Verical interchange manipulations in Tin and silicon.
Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy
Science 322, 413 (2008
Nature nanotechnology 4, 803 2009
Manipulation mechanism: DFT (density function theory) simulations
Doing atom manipulations in 1.5 hours instead of 9+ hours.
Chemical identification with STM:IETS
Bonding forces should bear chemical information
Look at the force pattern on the tip as distance closes over the distance of fractions of angstroms. Match the pattern to see what atom is being addressed.
Chemical identification of individual surface atoms by atomic force microscopy
Nature 446 , 64 (2007)
Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with atomic resolution. At cryogenic temperatures, scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed molecules and of the electronic properties of magnetic impurity atoms, thereby allowing chemical identification. But in many instances, and particularly for insulating systems, determining the exact chemical composition of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true atomic resolution by detecting and precisely measuring the short-range forces that arise with the onset of chemical bonding between the tip and surface atoms and that depend sensitively on the chemical identity of the atoms involved. Here we report precise measurements of such short-range chemical forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows us to use the chemical force measurements as the basis for atomic recognition, even at room temperature. We illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the three constituent atomic species silicon, tin and lead, even though these exhibit very similar chemical properties and identical surface position preferences that render any discrimination attempt based on topographic measurements impossible
First principle calculations for tin and silicon
Using the same composition of tips but different structure
Using the same structure but different composition
the relative interation ratio for two atomic species probed with the same tip is quantification of the relative strength these surface atoms.
– atomic resolution AFM a fundamental tool of science and tech
– AFM provides access to the atomic structure of insulating surfaces
– similar atomic scale results are now starting to be reproduced in liquid environment