Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M38: Invited Session: The Keithley Award Session: Submolecular Resolution and Exchange Force Measurements Using Atomic Force Microscopy with Quartz Cantilevers |
Hide Abstracts |
Sponsoring Units: GIMS Chair: Joseph Stroscio, National Institute of Standards and Technology Room: 709/711 |
Wednesday, March 5, 2014 11:15AM - 11:51AM |
M38.00001: Joseph F. Keithley Award: Force microscopy with subatomic spatial resolution Invited Speaker: Franz Giessibl For a long time, atomic force microscopy has been inferior to the scanning tunneling microscope (STM) in its spatial resolution, partially because measurements of small forces are more challenging than measurements of small currents. With the introduction of frequency modulation force microscopy, the static deflection measurement of a cantilever under a tip-sample force was replaced by a frequency measurement of an oscillating cantilever induced by an average force gradient. Atomic resolution of the challenging silicon reconstruction by frequency modulation atomic force microscopy has been demonstrated in 1995 using a silicon cantilever with a stiffness of $k=$17 N/m and an oscillation amplitude of $A=$34 nm. In 1996, a quartz cantilever (``qPlus sensor''), originally built from a quartz tuning fork from a wristwatch, has been proposed. At $k=$1800 N/m, this quartz sensor is 100 times stiffer than the original Si cantilever, allowing stable oscillation amplitudes down to fractions of an atomic diameter. It has a high Q factor, simple piezoelectric readout, little frequency variation with temperature and allows to simply mount metal tips as used in STM. The demonstration of high spatial resolution, the detection of very small forces, the capability to perform simultaneous STM and AFM as well as the ease of use of the qPlus sensor has led to its adaptation in leading scanning probe microscopy laboratories worldwide as well as in a growing number of commercial scanning probe instruments. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:27PM |
M38.00002: Mapping the force-field of a hydrogen bonded assembly Invited Speaker: Philip Moriarty Hydrogen-bonding underpins the structure, properties, and dynamics of a vast array of systems spanning a wide variety of scientific fields. From the striking complexity of the phase diagram of H$_{\mathrm{2}}$O and the elegance of base pair interactions in DNA, to the directionality inherent in supramolecular self-assembly at surfaces, hydrogen bonds play an essential role in directing intermolecular forces. Yet fundamental aspects of the H-bond, including the magnitude of the force and binding energy, force constant, and decay length associated with the interaction, have been vigorously debated for many decades. I will discuss how dynamic force microscopy (DFM) using a qPlus sensor can quantitatively map the tip-sample force-field for naphthalene tetracarboxylic diimide (NTCDI) molecules hydrogen-bonded in 2D assemblies. A comparison of experimental images and force spectra with their simulated counterparts from density functional theory calculations shows that image contrast due to intermolecular hydrogen bonds arises fundamentally from charge density depletion due to strong tip-sample interactions. Interpretation of DFM images of hydrogen bonds therefore necessitates detailed consideration of the coupled tip-molecule system: analyses based on intermolecular charge density in the absence of the tip fail to capture the essential physical chemistry underpinning the imaging mechanism. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 1:03PM |
M38.00003: Single Molecules Investigated using atomically functionalized qPlus Sensors Invited Speaker: Leo Gross Single organic molecules were investigated using scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM), and Kelvin probe force microscopy (KPFM) employing a qPlus sensor [F. J. Giessibl, \textit{Appl. Phys. Lett.} \textbf{73}, 3956 (1998)]. The resolution was increased due to tip functionalization by atomic manipulation. Using NC-AFM and CO functionalized tips, atomic resolution on molecules [L. Gross \textit{et al. Science} \textbf{325}, 1110 (2009)] and molecular structure identification was demonstrated [L. Gross \textit{et al. Nature Chem.} \textbf{2}, 821 (2010)]. Moreover, the bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes were distinguished [L. Gross \textit{et al.} \textit{Science} \textbf{337}, 1326 (2012)]. Using Xe terminated tips the adsorption height and tilt of individual molecules was determined [B. Schuler \textit{et al. PRL }\textbf{111}, 106103 (2013)]. With KPFM information about the intramolecular charge distribution was gained [F. Mohn \textit{et al.} \textit{Nature Nanotechnol.} \textbf{7}, 227 (2012)]. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:39PM |
M38.00004: Dynamic Force Imaging and Spectroscopy of Individual Molecules Invited Speaker: Jascha Repp In atomic force microscopy (AFM) the qPlus sensor [1] facilitates the use of metallic tips, which are typically used in scanning tunneling microscopy (STM), and thereby facilitates combined STM and AFM experiments at cryogenic temperatures. The use of CO-functionalized tips as has been introduced recently by Gross and co-workers [2] enabled unprecedented resolution and thereby fostered the rapid recent development of the field. We made use of the complementary information that STM and AFM can provide in different contexts. When applied to STM-based single-molecule synthesis, the combination of these techniques enables a direct quantification of the interplay of geometry and electronic coupling in metal-organic complexes in real space [3]. Further, we combined STM on semiconductors with Kelvin probe force spectroscopy (KPFS) performed simultaneously in the same setup with the very same tip. This combination of tools allows us to experimentally recover the zero point of the energy scale usually being obscured due to so-called tip-induced band bending when measuring on surfaces of semiconductors [4]. Finally, we used KPFS with sub-molecular resolution to image the polarity of individual bonds. \\[4pt] [1] F. J. Giessibl, Appl. Phys. Lett. 76, 1470 (2000);\\[0pt] [2] L. Gross et al., Science 325, 1110 (2009);\\[0pt] [3] F. Albrecht et al., JACS 135, 9200 (2013);\\[0pt] [4] G. M {\"u}nnich et al., Phys. Rev. Lett. 111, 216802 (2013). [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 2:15PM |
M38.00005: Real-space identification of intermolecular bonding with atomic force microscopy Invited Speaker: Xiaohui Qiu A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms, whose formation and breaking result in chemical reactions and the production of new substances. Distinct from the covalent bond, the intermolecular interactions are often a vague concept elusive in experimental observations. Nevertheless, intermolecular interactions virtually affect all physical and chemical properties of substances in the condensed phases. The interactions between molecules, particularly the hydrogen bond, are responsible for the structural transformations and functions of biological molecules. Because most of the molecular characterization techniques are more sensitive to the covalent structures of the molecules, it remains a challenge to quantitatively study the weak interactions between molecules despite the tremendous efforts toward this goal. Here we report a real-space identification of the formation of hydrogen bonding between molecules adsorbed on metal substrate using a non-contact atomic force microscope (nc-AFM). The atomically resolved molecular structures with unprecedented details enable a precise determination of the characteristics of the hydrogen bond network, including bonding sites, orientations and lengths. The observed bond contrast was interpreted by ab initio density functional calculations that indicate the electron density contribution from the hybridized electronic state of hydrogen bond. Given the extensively discussion on the nature of hydrogen bonding and the recent redefinition by IUPAC, the observation of hydrogen bonding in real-space may be a stimulating evidence for theoretical chemistry. Meanwhile, the direct identification of local bonding configurations by nc-AFM would advance the understanding of intermolecular interactions in complex molecules with multiple active sites, offering complementary structural information essential for various applications in materials and biological sciences. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700