@article{13399, abstract = {Nature has long inspired scientists with its seemingly unlimited ability to harness solar energy and to utilize it to drive various physiological processes. With the help of man-made molecular photoswitches, we now have the potential to outperform natural systems in many ways, with the ultimate goal of fabricating multifunctional materials that operate at different light wavelengths. An important challenge in developing light-controlled artificial molecular machines lies in attaining a detailed understanding of the photoisomerization-coupled conformational changes that occur in macromolecules and molecular assemblies. In this issue of ACS Nano, Bléger, Rabe, and co-workers use force microscopy to provide interesting insights into the behavior of individual photoresponsive molecules and to identify contraction, extension, and crawling events accompanying light-induced isomerization.}, author = {Kundu, Pintu K. and Klajn, Rafal}, issn = {1936-086X}, journal = {ACS Nano}, keywords = {General Physics and Astronomy, General Engineering, General Materials Science}, number = {12}, pages = {11913--11916}, publisher = {American Chemical Society}, title = {{Watching single molecules move in response to light}}, doi = {10.1021/nn506656r}, volume = {8}, year = {2014}, } @article{17984, abstract = {A direct measurement of the potential energy surface that characterizes individual chemical bonds in complex materials has fundamental significance for many disciplines. Here, we demonstrate that the energy profile for metallic single-atom contacts and single-molecule junctions can be mapped by fitting ambient atomic force microscope measurements carried out in the near-equilibrium regime to a physical, but simple, functional form. We extract bond energies for junctions formed through metallic bonds as well as metal–molecule link bonds from atomic force microscope data and find that our results are in excellent quantitative agreement with density functional theory based calculations for exemplary junction structures. Furthermore, measurements from a large number of junctions can be collapsed to a single, universal force–extension curve, thus revealing a surprising degree of similarity in the overall shape of the potential surface that governs these chemical bonds. Compared to previous studies under ambient conditions where analysis was confined to trends in rupture force, our approach significantly expands the quantitative information extracted from these measurements, particularly allowing analysis of the trends in bond energy directly.}, author = {Aradhya, Sriharsha V. and Nielsen, Aileen and Hybertsen, Mark S. and Venkataraman, Latha}, issn = {1936-086X}, journal = {ACS Nano}, number = {7}, pages = {7522--7530}, publisher = {American Chemical Society}, title = {{Quantitative bond energetics in atomic-scale junctions}}, doi = {10.1021/nn502836e}, volume = {8}, year = {2014}, } @article{17998, abstract = {We measure simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature. We observe the formation of contacts with a conductance close to 1 G0, the quantum of conductance, which can be attributed to a single-atom contact, similar to those formed by Au. We also find two additional conductance features at ∼0.4 G0 and ∼1.3 G0, which have been previously ascribed to contacts with oxygen contaminations. Here, using a conductance cross-correlation technique, we distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness. Our results allow us to assign the ∼0.4 G0 conductance feature to an Ag–O–Ag contact and the ∼1.3 G0 feature to an Ag–Ag single-atom contact with an oxygen atom in parallel. Utilizing complementary information from force and conductance, we thus demonstrate the correlation of conductance with the structural evolution at the atomic scale.}, author = {Aradhya, Sriharsha V. and Frei, Michael and Halbritter, András and Venkataraman, Latha}, issn = {1936-086X}, journal = {ACS Nano}, number = {4}, pages = {3706--3712}, publisher = {American Chemical Society}, title = {{Correlating structure, conductance, and mechanics of silver atomic-scale contacts}}, doi = {10.1021/nn4007187}, volume = {7}, year = {2013}, } @article{18008, abstract = {The break-junction technique is widely used to measure electronic properties of nanoscale junctions including metal point-contacts and single-molecule junctions. In these measurements, conductance is measured as a function of electrode displacement yielding data that is analyzed by constructing conductance histograms to determine the most frequently observed conductance values in the nanoscale junctions. However much of the rich physics in these measurements is lost in this simple analysis technique. Conductance histograms cannot be used to study the statistical relation of distinct junction configurations, to distinguish structurally different configurations that have similar conductance values, or to obtain information on the relation between conductance and junction elongation. Here, we give a detailed introduction to a novel statistical analysis method based on the two-dimensional cross-correlation histogram (2DCH) analysis of conductance traces and show that this method provides new information about the relation of different junction configurations that occur during the formation and evolution of metal and single-molecule junctions. We first illustrate the different types of correlation effects by using simulated conductance traces. We then apply this analysis method to several different experimental examples. We show from break-junction measurements of different metal point-contacts that in aluminum, the first conductance histogram peak corresponds to two different junction structures. In tantalum, we identify the frequent absence of adhesive instability. We show that conductance plateaus shift in a correlated manner in iron and vanadium junctions. Finally, we highlight the applicability of the correlation analysis to single-molecule platinum–CO–platinum and gold–4,4′-bipyridine–gold junctions.}, author = {Makk, Péter and Tomaszewski, Damian and Martinek, Jan and Balogh, Zoltán and Csonka, Szabolcs and Wawrzyniak, Maciej and Frei, Michael and Venkataraman, Latha and Halbritter, András}, issn = {1936-086X}, journal = {ACS Nano}, number = {4}, pages = {3411--3423}, publisher = {American Chemical Society}, title = {{Correlation analysis of atomic and single-molecule junction conductance}}, doi = {10.1021/nn300440f}, volume = {6}, year = {2012}, }