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Papers by Francisco Javier Mendez Penin

Research paper thumbnail of Adsorption and electronic properties of PTCDA molecules onSi(111)−(7×7): Scanning tunneling microscopy and first-principles calculations

Physical Review B, 2010

Scanning tunneling microscopy ͑STM͒ experiments and density-functional theory ͑DFT͒ calculations ... more Scanning tunneling microscopy ͑STM͒ experiments and density-functional theory ͑DFT͒ calculations are combined to unravel the complex shifts and splittings of molecular orbitals ͑MOs͒ for the prototype system of a single-conjugated molecule bonded to a semiconductor surface. Intramolecular resolution in STM images of 3,4,9,10-perylene tetracarboxylic dianhydride ͑PTCDA͒ on Si͑111͒-͑7 ϫ 7͒ cannot be understood as resulting from a simple rigid shift of the MOs of the free molecule. DFT calculations and simulations of STM images with realistic tips show large splittings of the original MOs that contribute in a complex way to the tunnel current and are understood under symmetry and charge-transfer arguments. The system is characterized by a strong, partially ionic covalent bonding involving the carboxyl groups of the PTCDA and the Si dangling bonds.

Research paper thumbnail of Properties of Metallic Nanowires: From Conductance Quantization to Localization

Science, 1995

order-disorder elongation process. The N. Garcia, uzi andm man,* W. D. Luedtke, E. N. ~o~a c h e ... more order-disorder elongation process. The N. Garcia, uzi andm man,* W. D. Luedtke, E. N. ~o~a c h e k , dominance of disorder and the onset of H.-P. Cheng localization in long wires (longer than the localization length) are shown by a nonlinear dependen& of the resistance R on the Material structures of reduced dimensions exhibit electrical and mechanical properties length of the wire t as it is pulled contindifferent from those in the bulk. Measurements of room-temperature electronic transport uously [that is, In R (t)-t2]. Moreover,

Research paper thumbnail of Nanostructured Organic Material: From Molecular Chains to Organic Nanodots

Advanced Materials, 2006

We present a new strategy for nanostructuring organic molecules in order to create either molecul... more We present a new strategy for nanostructuring organic molecules in order to create either molecular chains or organic nanodots. The method is based on the use of patterned surfaces as templates for nucleation of the organic molecules. As the patterned substrate we use iron-island arrays grown on Au(111). These metallic arrays are formed spontaneously on the gold reconstructed surface via strain-relief nucleation. We show that deposited 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules anchor at the iron islands forming new structures that are not observed for PTCDA adsorption on clean gold. Namely, PTCDA forms either chains of molecules connecting contiguous iron clusters, or aggregates surrounding the metallic core. The resulting arrangement of organic dots exhibits a different density of states than the twodimensional self-assembled molecular monolayer. Scanning tunneling spectroscopy (STS) studies indicate that the main modifications are the absence of the gold surface state and the appearance of an iron state induced in the PTCDA highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Organic molecules are one of the most promising candidates to substitute inorganic materials in nanoscale devices. Up to now, these organic materials have found several optoelectronic applications such as organic light-emitting devices, [1,2] organic transistors, [3,4] organic lasers, [5,6] organic rectifiers, [7] and organic memories. [8] Most of these devices take advantage of the confinement properties due to the nanostructuring of the organic molecules in 2D thin films or 1D nanowires. Naturally, organic 0D nanostructures are envisioned as systems with potential applications. Among the strategies for nanostructuring organic materials, landing of molecules or tip-induced manipulation have been successfully used for single-molecule setups. [9-12] More extended assemblies can be achieved by self-organization of molecules, by choosing the appropriate chemistry of the molecules, [13,14] or COMMUNICATIONS

Research paper thumbnail of Nanostructured Organic Material: From Molecular Chains to Organic Nanodots

Advanced Materials, 2006

We present a new strategy for nanostructuring organic molecules in order to create either molecul... more We present a new strategy for nanostructuring organic molecules in order to create either molecular chains or organic nanodots. The method is based on the use of patterned surfaces as templates for nucleation of the organic molecules. As the patterned substrate we use iron-island arrays grown on Au(111). These metallic arrays are formed spontaneously on the gold reconstructed surface via strain-relief nucleation. We show that deposited 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules anchor at the iron islands forming new structures that are not observed for PTCDA adsorption on clean gold. Namely, PTCDA forms either chains of molecules connecting contiguous iron clusters, or aggregates surrounding the metallic core. The resulting arrangement of organic dots exhibits a different density of states than the twodimensional self-assembled molecular monolayer. Scanning tunneling spectroscopy (STS) studies indicate that the main modifications are the absence of the gold surface state and the appearance of an iron state induced in the PTCDA highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Organic molecules are one of the most promising candidates to substitute inorganic materials in nanoscale devices. Up to now, these organic materials have found several optoelectronic applications such as organic light-emitting devices, [1,2] organic transistors, [3,4] organic lasers, [5,6] organic rectifiers, [7] and organic memories. [8] Most of these devices take advantage of the confinement properties due to the nanostructuring of the organic molecules in 2D thin films or 1D nanowires. Naturally, organic 0D nanostructures are envisioned as systems with potential applications. Among the strategies for nanostructuring organic materials, landing of molecules or tip-induced manipulation have been successfully used for single-molecule setups. [9-12] More extended assemblies can be achieved by self-organization of molecules, by choosing the appropriate chemistry of the molecules, [13,14] or COMMUNICATIONS

Research paper thumbnail of Adsorption and electronic properties of PTCDA molecules onSi(111)−(7×7): Scanning tunneling microscopy and first-principles calculations

Physical Review B, 2010

Scanning tunneling microscopy ͑STM͒ experiments and density-functional theory ͑DFT͒ calculations ... more Scanning tunneling microscopy ͑STM͒ experiments and density-functional theory ͑DFT͒ calculations are combined to unravel the complex shifts and splittings of molecular orbitals ͑MOs͒ for the prototype system of a single-conjugated molecule bonded to a semiconductor surface. Intramolecular resolution in STM images of 3,4,9,10-perylene tetracarboxylic dianhydride ͑PTCDA͒ on Si͑111͒-͑7 ϫ 7͒ cannot be understood as resulting from a simple rigid shift of the MOs of the free molecule. DFT calculations and simulations of STM images with realistic tips show large splittings of the original MOs that contribute in a complex way to the tunnel current and are understood under symmetry and charge-transfer arguments. The system is characterized by a strong, partially ionic covalent bonding involving the carboxyl groups of the PTCDA and the Si dangling bonds.

Research paper thumbnail of Properties of Metallic Nanowires: From Conductance Quantization to Localization

Science, 1995

order-disorder elongation process. The N. Garcia, uzi andm man,* W. D. Luedtke, E. N. ~o~a c h e ... more order-disorder elongation process. The N. Garcia, uzi andm man,* W. D. Luedtke, E. N. ~o~a c h e k , dominance of disorder and the onset of H.-P. Cheng localization in long wires (longer than the localization length) are shown by a nonlinear dependen& of the resistance R on the Material structures of reduced dimensions exhibit electrical and mechanical properties length of the wire t as it is pulled contindifferent from those in the bulk. Measurements of room-temperature electronic transport uously [that is, In R (t)-t2]. Moreover,

Research paper thumbnail of Nanostructured Organic Material: From Molecular Chains to Organic Nanodots

Advanced Materials, 2006

We present a new strategy for nanostructuring organic molecules in order to create either molecul... more We present a new strategy for nanostructuring organic molecules in order to create either molecular chains or organic nanodots. The method is based on the use of patterned surfaces as templates for nucleation of the organic molecules. As the patterned substrate we use iron-island arrays grown on Au(111). These metallic arrays are formed spontaneously on the gold reconstructed surface via strain-relief nucleation. We show that deposited 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules anchor at the iron islands forming new structures that are not observed for PTCDA adsorption on clean gold. Namely, PTCDA forms either chains of molecules connecting contiguous iron clusters, or aggregates surrounding the metallic core. The resulting arrangement of organic dots exhibits a different density of states than the twodimensional self-assembled molecular monolayer. Scanning tunneling spectroscopy (STS) studies indicate that the main modifications are the absence of the gold surface state and the appearance of an iron state induced in the PTCDA highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Organic molecules are one of the most promising candidates to substitute inorganic materials in nanoscale devices. Up to now, these organic materials have found several optoelectronic applications such as organic light-emitting devices, [1,2] organic transistors, [3,4] organic lasers, [5,6] organic rectifiers, [7] and organic memories. [8] Most of these devices take advantage of the confinement properties due to the nanostructuring of the organic molecules in 2D thin films or 1D nanowires. Naturally, organic 0D nanostructures are envisioned as systems with potential applications. Among the strategies for nanostructuring organic materials, landing of molecules or tip-induced manipulation have been successfully used for single-molecule setups. [9-12] More extended assemblies can be achieved by self-organization of molecules, by choosing the appropriate chemistry of the molecules, [13,14] or COMMUNICATIONS

Research paper thumbnail of Nanostructured Organic Material: From Molecular Chains to Organic Nanodots

Advanced Materials, 2006

We present a new strategy for nanostructuring organic molecules in order to create either molecul... more We present a new strategy for nanostructuring organic molecules in order to create either molecular chains or organic nanodots. The method is based on the use of patterned surfaces as templates for nucleation of the organic molecules. As the patterned substrate we use iron-island arrays grown on Au(111). These metallic arrays are formed spontaneously on the gold reconstructed surface via strain-relief nucleation. We show that deposited 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules anchor at the iron islands forming new structures that are not observed for PTCDA adsorption on clean gold. Namely, PTCDA forms either chains of molecules connecting contiguous iron clusters, or aggregates surrounding the metallic core. The resulting arrangement of organic dots exhibits a different density of states than the twodimensional self-assembled molecular monolayer. Scanning tunneling spectroscopy (STS) studies indicate that the main modifications are the absence of the gold surface state and the appearance of an iron state induced in the PTCDA highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Organic molecules are one of the most promising candidates to substitute inorganic materials in nanoscale devices. Up to now, these organic materials have found several optoelectronic applications such as organic light-emitting devices, [1,2] organic transistors, [3,4] organic lasers, [5,6] organic rectifiers, [7] and organic memories. [8] Most of these devices take advantage of the confinement properties due to the nanostructuring of the organic molecules in 2D thin films or 1D nanowires. Naturally, organic 0D nanostructures are envisioned as systems with potential applications. Among the strategies for nanostructuring organic materials, landing of molecules or tip-induced manipulation have been successfully used for single-molecule setups. [9-12] More extended assemblies can be achieved by self-organization of molecules, by choosing the appropriate chemistry of the molecules, [13,14] or COMMUNICATIONS