Self-assembled monolayers of 4-thiobiphenyl and 2-thiophenanthrene molecules on Au{111} were probed using scanning tunneling microscopy (STM) to investigate their assembled order, to measure the ...conductance through them, and to determine what molecular features are necessary for molecules to exhibit conductance switching. The 4-thiobiphenyl molecules assemble into two distinct packing structures, whereas no order is observed for 2-thiophenanthrene. Both molecules show rectifying behavior, but although 4-thiobiphenyl is more conductive at positive sample biases, 2-thiophenanthrene is more conductive at negative sample bias. Individual molecules of each type were also inserted into alkanethiol SAMs and tracked over several hours to investigate the conductance states of each molecule. Both molecules exhibit two conductance states, indicating that internal ring rotation is not required for conductance switching.
We characterized the prominent electron transport layer 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) via single-crystal X-ray diffraction, grazing incidence X-ray diffraction ...(GIXRD), infrared reflection absorption spectroscopy (IRRAS), and quantum mechanical calculations. The crystals generated via vapor diffusion are of the orthorhombic space group Pbca , with a unit cell a = 19.3935(2) b = 12.81750(10) c = 28.5610(3) Å containing eight TPBi molecules, and screw axes and glide planes along all three crystallographic axes. Thin-film analysis becomes viable with unit cell and symmetry data, and GIXRD measurements, which demonstrate that when the amorphous TPBi thin films are annealed, the molecules preferentially orient with the a–b crystallographic face exposed at the surface and with the central benzene rings oriented 29° from the surface normal. Changes in vibrational modes at the surface, studied via infrared reflection absorption spectroscopy (IRRAS), concur with the X-ray based assignments. A minor conformer of TPBi with C 3 symmetry was also identified via computational methods, appearing 0.95 kcal/mol higher in energy at the MP2/6-31G*//B3LYP/6-31G* level of theory. The combined structural insight allows fine-tuning of a device structure for organic light-emitting diodes (OLEDs) and organic photovoltaic applications.
Electronic conduction through single molecules is affected by the molecular electronic structure as well as by other information that is extremely difficult to assess, such as bonding geometry and ...chemical environment. The lack of an independent diagnostic technique has long hampered single-molecule conductance studies. We report simultaneous measurement of the conductance and the Raman spectra of nanoscale junctions used for single-molecule electronic experiments. Blinking and spectral diffusion in the Raman response of both p-mercaptoaniline and a fluorinated oligophenylyne ethynylene correlate in time with changes in the electronic conductance. Finite difference time domain calculations confirm that these correlations do not result from the conductance modifying the Raman enhancement. Therefore, these observations strongly imply that multimodal sensing of individual molecules is possible in these mass-producible nanostructures.
Ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), two-photon photoemission spectroscopy (2PPES), and electronic structure calculations of ...4,4′-bis(phenylethynyl)benzenethiol are compared. The result is a better understanding of the valence electronic structure for this system, of the spectroscopic methods involved, and of previous measurements.
Ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and two-photon photoemission spectroscopy are techniques commonly used to examine the electronic structure of surfaces and interfaces. We have used all three to study self-assembled monolayers of 4,4′-bis(phenylethynyl)benzenethiol on gold, a system often studied for potential application in molecular electronic junctions. We compare the results of these measurements and discuss them in relation to electronic structure calculations. The result is a better understanding of the valence electronic structure for this system, of the spectroscopic methods involved, and of previous measurements.
Molecular orientation within organic solids limits the range of applicable surface reactions, with reactive functionalities often recessed and inaccessible to adsorbates. To induce reactivity in ...heretofore inert orientations of acenes, a defect-mediated mechanism is utilized to functionalize thin-film phase pentacene. This mechanism was demonstrated via correlation of reaction data to defect density, determined via polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and atomic force microscopy (AFM). By controllably varying the amount of grain boundaries in the acene films, the reaction can be varied from near zero to coverage exceeding a monolayer. The extensive coverage suggests that the reaction propagates from the defects throughout the grains, a prediction borne out via direct observation of reaction progression along the surface from a single dislocation (via scanning electron microscopy). The results support a mechanism whereby the reaction is initialized at the defect sites, especially boundaries of crystal domains, which opens the unfavorable molecular orientation of the (001) pentacene to incoming adsorbates. This exact film configuration and its successful reaction is especially relevant to organic thin-film transistor (OTFT) devices.
A high quality solar cell with a bandgap in the range of 2.0-2.1 eV may enable the development of four- and five-junction solar cells for terrestrial and space applications. In this paper we describe ...a set of 2.0-2.1 eV nVp solar cells fabricated from Ga x ln 1-x P and grown on compositional step-grades of GaAs 1-y P y , on GaAs substrates. Cells were grown by atmospheric pressure organometallic vapor phase epitaxy. The tensile grades were designed to achieve nearly complete relaxation of the active layers, and the in-situ stress as monitored during growth showed a residual tensile stress of <;10 MPa in the best samples. We have fabricated 1.98 eV cells with 1-sun and 70-sun efficiencies of 14.4% and 15.9%, respectively, under the direct spectrum, and 2.07 eV cells with 1-sun efficiencies of 10.7%. Improvements in the grade design that reduce the threading dislocation density below 106 cm -2 are expected to lead to efficiency increases. Matching the lattice constants of the confinement and contact layers to the junction layers is critical to achieving low interface recombination velocities, and can be a challenge in lattice-mismatched structures if the graded layers are not sufficiently relaxed.
A Single-Molecule Switch and Memory Element Lörtscher, E; Tour, J M; Ciszek, J W ...
Journal of physics. Conference series,
04/2007, Letnik:
61, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The mechanically controllable break-junction technique enables us to investigate charge-carrier transport through an individually contacted and addressed molecule. Using a statistical measurement and ...analysis approach, we acquire simultaneously current-voltage curves during the repeated formation and breaking of a molecular junction. Thereby, a reversible and controllable switching between two distinct conductive states of a single-molecule system was investigated. Voltage pulses are used to switch from a low to a high conductive on state, and, furthermore, to reset the switch again to the off state. On this single-molecule level, collective phenomena can be excluded and therefore the observed switching mechanism has a truly molecular origin. Both conductive states are stable and accessible via non-destructive reading. Combined with the ability to reset the switch, this opens the way to employ this single-molecule as a memory element which is demonstrated by repeated write-read-erase-read cycles with non-destructive read-outs.
Aims
Many heart transplant recipients will develop end‐stage renal disease in the post‐operative course. The aim of this study was to identify the long‐term incidence of end‐stage renal disease, ...determine its risk factors, and investigate what subsequent therapy was associated with the best survival.
Methods and results
A retrospective, single‐centre study was performed in all adult heart transplant patients from 1984 to 2016. Risk factors for end‐stage renal disease were analysed by means of multivariable regression analysis and survival by means of Kaplan–Meier. Of 685 heart transplant recipients, 71 were excluded: 64 were under 18 years of age and seven were re‐transplantations. During a median follow‐up of 8.6 years, 121 (19.7%) patients developed end‐stage renal disease: 22 received conservative therapy, 80 were treated with dialysis (46 haemodialysis and 34 peritoneal dialysis), and 19 received a kidney transplant. Development of end‐stage renal disease (examined as a time‐dependent variable) inferred a hazard ratio of 6.45 (95% confidence interval 4.87–8.54, P < 0.001) for mortality. Tacrolimus‐based therapy decreased, and acute kidney injury requiring renal replacement therapy increased the risk for end‐stage renal disease development (hazard ratio 0.40, 95% confidence interval 0.26–0.62, P < 0.001, and hazard ratio 4.18, 95% confidence interval 2.30–7.59, P < 0.001, respectively). Kidney transplantation was associated with the best median survival compared with dialysis or conservative therapy: 6.4 vs. 2.2 vs. 0.3 years (P < 0.0001), respectively, after end‐stage renal disease development.
Conclusions
End‐stage renal disease is a frequent complication after heart transplant and is associated with poor survival. Kidney transplantation resulted in the longest survival of patients with end‐stage renal disease.
PDF
