We use scanning tunneling microscope (STM) manipulation and density functional theory calculation... more We use scanning tunneling microscope (STM) manipulation and density functional theory calculation to investigate the structural properties of individual sexiphenyl molecules physisorbed on a Ag(111) surface at 6 K. The molecule−surface atomic registry is precisely determined by using atomic markers and a sexiphenyl functionalized tip. The calculations confirm the alternating twist of the sexiphenyl π-rings on Ag(111). The π-ring torsional angle, 11.4°, is directly determined from the geometry of STM manipulation. This innovative experiment opens up a novel application of STM manipulation to probe the properties of "physisorbed" species on surfaces at the atomic level.
Complexes containing rare-earth ions attract great attention for their technological applications... more Complexes containing rare-earth ions attract great attention for their technological applications ranging from spintronic devices to quantum information science. While charged rare-earth coordination complexes are ubiquitous in solution, they are challenging to form on materials surfaces that would allow investigations for potential solid-state applications. Here we report formation and atomically precise manipulation of rareearth complexes on a gold surface. Although they are composed of multiple units held together by electrostatic interactions, the entire complex rotates as a single unit when electrical energy is supplied from a scanning tunneling microscope tip. Despite the hexagonal symmetry of the gold surface, a counterion at the side of the complex guides precise threefold rotations and 100% control of their rotational directions is achieved using a negative electric field from the scanning probe tip. This work demonstrates that counterions can be used to control dynamics of rare-earth complexes on materials surfaces for quantum and nanomechanical applications. Rare-earth (RE) elements are tantalizing to explore for advanced technological applications 1-8 because of their distinct magnetic, optical and catalytic properties 9-16. One of the best options for an efficient usage of RE elements is to place them inside coordination complexes; such systems are uniquely advantageous due to their well-defined and reproducible shapes and sizes. The ligands not only protect the RE ion, but also play vital roles in determining its electronic, magnetic, and optical properties 1,11,17. Thus, single molecule studies of charged RE complexes are of great interest to explore the environment of the RE ion that would allow the design of appropriate ligands to tailor their properties. How a charged complex behaves under an external electric field is yet another unexplored question. Here we form rare-earth complexes by coordinating a positively charged Europium base molecule with negatively charged counterions on a Au(111) surface. Electronic and structural properties of these complexes are then investigated on a one complex at-a-time basis using scanning tunneling microscopy (STM) and tunneling spectroscopy methods. We show that an entire RE complex can be rotated like a single molecule 18-27 with precise control of their rotational dynamics at the atomic scale.
The conductivity of a single graphene nanoribbon can be measured by lifting the nanoribbon off a ... more The conductivity of a single graphene nanoribbon can be measured by lifting the nanoribbon off a surface with the tip of a scanning tunnelling microscope.
A range of artificial molecular systems has been created that can exhibit controlled linear and r... more A range of artificial molecular systems has been created that can exhibit controlled linear and rotational motion. In the further development of such systems, a key step is the addition of communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching when applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated when in a hexagonal rotor network on a Cu(111) surface by applying biases above 1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degeneracy of the ground-state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors can occur, resulting in the rotator arms pointing in different directions. Analysis reveals that the rotator arm directions are not random, but are coordinated to minimize energy via crosstalk among the rotors through dipolar interactions.
Scanning tunneling microscopy study of O 2 dissociation on Rh͑110͒ at 170 K shows a low-energy di... more Scanning tunneling microscopy study of O 2 dissociation on Rh͑110͒ at 170 K shows a low-energy dissociation coordinate for a precursor with the O-O axis aligned in the ͓001͔ azimuth, indicating a strong influence of the surface anisotropy on the potential-energy surface. This results in pairs of oxygen atoms oriented along ͓001͔, which aggregate in chains along ͓11 0͔. The atomic distance in the pairs, 3.3 Å, is shorter than the ͓001͔ lattice constant, which led to the conclusion that the oxygen sits in adjacent asymmetric short bridge sites and that the creation of ''hot'' oxygen atoms is not favored. ͓S0163-1829͑99͒15335-9͔
45701-One of the goals of nanotechnology is to have billions of nano-molecular machines packed in... more 45701-One of the goals of nanotechnology is to have billions of nano-molecular machines packed in a tiny area that can operate under control. Simultaneous operation of such nano-machines requires developing a system in which the nanomachines can communicate each other. Here we investigate a doubledecker class molecular motor adsorbed on Au(111) and Cu(111) surfaces using low temperature scanning tunneling microscopy in an ultrahigh vacuum environment. Our molecular motor is formed by a porphyrin based stator, and a dipole active rotor. An Eu atom is used to link the rotation and stationary parts of the motor, and therefore it acts as a single atom ball bearing. On Cu(111) surface, however, the molecules form selfassembled structures with a hexagonal pattern. The stable positions are maintained by balancing two interactions; the internal interactions between the upper and lower decks, and the dipolar interactions with the neighboring rotors. On Au(111) surface, however, we observe thermal induced rotations of the individual molecular motors at 80K. This work is a step forward in the development of molecular machines for nanoscale information transport.
We describe a complete picture of how single Ag atoms move on the various potential energy landsc... more We describe a complete picture of how single Ag atoms move on the various potential energy landscapes of a Ag(111) surface during a quantum corral construction by using a scanning tunneling microscope (STM) tip at 6 K. The threshold tunneling resistance and tip-height to move the Ag atom across the surface are experimentally measured as 210 ± 19 kΩ and 1.3 ± 0.2 Å. The experimental atom manipulation signals reveal remarkably detailed atom movement behaviors dependent on the surface crystallographic orientation and offer atomic-level tribology information.
... Violeta Ianrcu, Apama Deslpande, and Saw-Wai Hla Department of Physics anid Astronomy and Nan... more ... Violeta Ianrcu, Apama Deslpande, and Saw-Wai Hla Department of Physics anid Astronomy and Nanoscale Quantum Phenomema Institute Athens, Ohio 45701, USA Magphy.ohiou. edu, http://ww.phy.ohiou.edu/hla ... than subsequent imaging. ...
We use scanning tunneling microscope (STM) manipulation and density functional theory calculation... more We use scanning tunneling microscope (STM) manipulation and density functional theory calculation to investigate the structural properties of individual sexiphenyl molecules physisorbed on a Ag(111) surface at 6 K. The molecule−surface atomic registry is precisely determined by using atomic markers and a sexiphenyl functionalized tip. The calculations confirm the alternating twist of the sexiphenyl π-rings on Ag(111). The π-ring torsional angle, 11.4°, is directly determined from the geometry of STM manipulation. This innovative experiment opens up a novel application of STM manipulation to probe the properties of "physisorbed" species on surfaces at the atomic level.
Complexes containing rare-earth ions attract great attention for their technological applications... more Complexes containing rare-earth ions attract great attention for their technological applications ranging from spintronic devices to quantum information science. While charged rare-earth coordination complexes are ubiquitous in solution, they are challenging to form on materials surfaces that would allow investigations for potential solid-state applications. Here we report formation and atomically precise manipulation of rareearth complexes on a gold surface. Although they are composed of multiple units held together by electrostatic interactions, the entire complex rotates as a single unit when electrical energy is supplied from a scanning tunneling microscope tip. Despite the hexagonal symmetry of the gold surface, a counterion at the side of the complex guides precise threefold rotations and 100% control of their rotational directions is achieved using a negative electric field from the scanning probe tip. This work demonstrates that counterions can be used to control dynamics of rare-earth complexes on materials surfaces for quantum and nanomechanical applications. Rare-earth (RE) elements are tantalizing to explore for advanced technological applications 1-8 because of their distinct magnetic, optical and catalytic properties 9-16. One of the best options for an efficient usage of RE elements is to place them inside coordination complexes; such systems are uniquely advantageous due to their well-defined and reproducible shapes and sizes. The ligands not only protect the RE ion, but also play vital roles in determining its electronic, magnetic, and optical properties 1,11,17. Thus, single molecule studies of charged RE complexes are of great interest to explore the environment of the RE ion that would allow the design of appropriate ligands to tailor their properties. How a charged complex behaves under an external electric field is yet another unexplored question. Here we form rare-earth complexes by coordinating a positively charged Europium base molecule with negatively charged counterions on a Au(111) surface. Electronic and structural properties of these complexes are then investigated on a one complex at-a-time basis using scanning tunneling microscopy (STM) and tunneling spectroscopy methods. We show that an entire RE complex can be rotated like a single molecule 18-27 with precise control of their rotational dynamics at the atomic scale.
The conductivity of a single graphene nanoribbon can be measured by lifting the nanoribbon off a ... more The conductivity of a single graphene nanoribbon can be measured by lifting the nanoribbon off a surface with the tip of a scanning tunnelling microscope.
A range of artificial molecular systems has been created that can exhibit controlled linear and r... more A range of artificial molecular systems has been created that can exhibit controlled linear and rotational motion. In the further development of such systems, a key step is the addition of communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching when applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated when in a hexagonal rotor network on a Cu(111) surface by applying biases above 1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degeneracy of the ground-state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors can occur, resulting in the rotator arms pointing in different directions. Analysis reveals that the rotator arm directions are not random, but are coordinated to minimize energy via crosstalk among the rotors through dipolar interactions.
Scanning tunneling microscopy study of O 2 dissociation on Rh͑110͒ at 170 K shows a low-energy di... more Scanning tunneling microscopy study of O 2 dissociation on Rh͑110͒ at 170 K shows a low-energy dissociation coordinate for a precursor with the O-O axis aligned in the ͓001͔ azimuth, indicating a strong influence of the surface anisotropy on the potential-energy surface. This results in pairs of oxygen atoms oriented along ͓001͔, which aggregate in chains along ͓11 0͔. The atomic distance in the pairs, 3.3 Å, is shorter than the ͓001͔ lattice constant, which led to the conclusion that the oxygen sits in adjacent asymmetric short bridge sites and that the creation of ''hot'' oxygen atoms is not favored. ͓S0163-1829͑99͒15335-9͔
45701-One of the goals of nanotechnology is to have billions of nano-molecular machines packed in... more 45701-One of the goals of nanotechnology is to have billions of nano-molecular machines packed in a tiny area that can operate under control. Simultaneous operation of such nano-machines requires developing a system in which the nanomachines can communicate each other. Here we investigate a doubledecker class molecular motor adsorbed on Au(111) and Cu(111) surfaces using low temperature scanning tunneling microscopy in an ultrahigh vacuum environment. Our molecular motor is formed by a porphyrin based stator, and a dipole active rotor. An Eu atom is used to link the rotation and stationary parts of the motor, and therefore it acts as a single atom ball bearing. On Cu(111) surface, however, the molecules form selfassembled structures with a hexagonal pattern. The stable positions are maintained by balancing two interactions; the internal interactions between the upper and lower decks, and the dipolar interactions with the neighboring rotors. On Au(111) surface, however, we observe thermal induced rotations of the individual molecular motors at 80K. This work is a step forward in the development of molecular machines for nanoscale information transport.
We describe a complete picture of how single Ag atoms move on the various potential energy landsc... more We describe a complete picture of how single Ag atoms move on the various potential energy landscapes of a Ag(111) surface during a quantum corral construction by using a scanning tunneling microscope (STM) tip at 6 K. The threshold tunneling resistance and tip-height to move the Ag atom across the surface are experimentally measured as 210 ± 19 kΩ and 1.3 ± 0.2 Å. The experimental atom manipulation signals reveal remarkably detailed atom movement behaviors dependent on the surface crystallographic orientation and offer atomic-level tribology information.
... Violeta Ianrcu, Apama Deslpande, and Saw-Wai Hla Department of Physics anid Astronomy and Nan... more ... Violeta Ianrcu, Apama Deslpande, and Saw-Wai Hla Department of Physics anid Astronomy and Nanoscale Quantum Phenomema Institute Athens, Ohio 45701, USA Magphy.ohiou. edu, http://ww.phy.ohiou.edu/hla ... than subsequent imaging. ...
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