130 research outputs found
Effect of impurities on pentacene island nucleation
Pentacenequinone (PnQ) impurities have been introduced into a pentacene
source material in a controlled manner to quantify the relative effects of the
impurity content on grain boundary structure and thin film nucleation. Atomic
force microscopy (AFM) has been employed to directly characterize films grown
using 0.0-7.5% PnQ by weight in the source material. Analysis of the
distribution of capture zones areas of submonolayer islands as a function of
impurity content shows that for large PnQ content the critical nucleus size for
forming a Pn island is smaller than for low PnQ content. This result indicates
a favorable energy for formation of Pn-PnQ complexes, which in turn suggests
that the primary effect of PnQ on Pn mobility may arise from homogeneous
distribution of PnQ defects.Comment: 16 Pages, 5 figures, 1 Tabl
Pentacene islands grown on ultra-thin SiO2
Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at
room temperature and characterized by scanning tunneling microscopy. The
ultra-thin oxide films were then used as substrates for room temperature growth
of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm,
indicating standing up pentacene grains in the thin-film phase were formed.
Pentacene is molecularly resolved in the second and subsequent molecular
layers. The measured in-plane unit cell for the pentacene (001) plane (ab
plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The
films are unperturbed by the UTO's short-range spatial variation in tunneling
probability, and reduce its corresponding effective roughness and correlation
exponent with increasing thickness. The pentacene surface morphology follows
that of the UTO substrate, preserving step structure, the long range surface
rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.Comment: 15 pages, 4 figure
New chiral organosulfur donors related to bis(ethylenedithio)tetrathiafulvalene
Six new enantiopure chiral organosulfur donors, with structures related to BEDT-TTF, have been synthesised for use in the preparation of organic metals, starting either by double nucleophilic substitutions on the bis-mesylate of 2R,4Rpentane-2,4-diol or by a cycloaddition with subsequent elimination of acetic acid on the enol acetate of (+)-nopinone. Crystal structures of some of their radical cation triiodides salts and TCNQ complexes are reported
Tuning the thermoelectrical properties of anthracene-based self-assembled monolayers
It is known that the electrical conductance of single molecules can be controlled in a deterministic manner by chemically varying their anchor groups to external electrodes. Here, by employing synthetic methodologies to vary the terminal anchor groups around aromatic anthracene cores, and by forming self-assembled monolayers (SAMs) of the resulting molecules, we demonstrate that this method of control can be translated into cross-plane SAM-on-gold molecular films. The cross-plane conductance of SAMs formed from anthracene-based molecules with four different combinations of anchors are measured to differ by a factor of approximately 3 in agreement with theoretical predictions. We also demonstrate that the Seebeck coefficient of such films can be boosted by more than an order of magnitude by an appropriate choice of anchor groups and that both positive and negative Seebeck coefficients can be realised. This demonstration that the thermoelectric properties of SAMs are controlled by their anchor groups represents a critical step towards functional ultra-thin-film devices for future molecular-scale electronic
Effect of Impurities on Pentacene Thin Film Growth for Field-Effect Transistors
Pentacenequinone (PnQ) impurities have been introduced into a pentacene
source material at number densities from 0.001 to 0.474 to quantify the
relative effects of impurity content and grain boundary structure on transport
in pentacene thin-film transistors. Atomic force microscopy (AFM) and
electrical measurements of top-contact pentacene thin-film transistors have
been employed to directly correlate initial structure and final film
structures, with the device mobility as a function of added impurity content.
The results reveal a factor four decrease in mobility without significant
changes in film morphology for source PnQ number fractions below ~0.008. For
these low concentrations, the impurity thus directly influences transport,
either as homogeneously distributed defects or by concentration at the
otherwise-unchanged grain boundaries. For larger impurity concentrations, the
continuing strong decrease in mobility is correlated with decreasing grain
size, indicating an impurity-induced increase in the nucleation of grains
during early stages of film growth.Comment: 18 pages, 4 Figures, 1 Tabl
Organitzacions de tetratiafulvalens a escala nanomètrica
El projecte de tesis se centra en la síntesi, caracterització i estudi de les propietats estructurals, elèctriques, magnètiques i òptiques de noves organitzacions moleculars en dos i tres dimensions basades en compostos derivats del tetratiafulvalè (TTF). El treball es divideix en dues estratègies:- Per una part, en la sínetsi d'isocianurs quirals que incorporen unitats de tetratiafulvalè per la síntesis de poli(isocianur)s helicoïdals quirals conductors.- I per l'altra, en la preparació de nous TTFs que poden formar agregats supramoleculars per auto-ensamblatge sobre grafit i altres superficies, i el seu estudi estructural mitjançant les técniques de microscopia d'escombrat per efecte túnel (STM, scanning tunneling microscopy) i microscopia de força atómica (AFM, atomic force microscopy). Així com l'estudi de les propietats elèctriques d'aquets agregats mitjançant les tècniques d'espectroscopia d'efecte túnel (STS, scanning tunneling spectroscopy) i cs-AFM (current sensing atomic force microscopy).Design, chemical synthesis, structural and electronic characterization, materials preparation, study of new organic molecular and supramolecular materials based on tetrathiafulvalene derivatives showing novel electrical, magnetic and optical properties. Two strategies were followed:- Synthesis of chiral tetrathiafulvalens derivatives funcionalized with an isocyanide group to prepare conducting enanthiomeric helical poly(isocyanides).- Preparation and electrical-structural characterization of TTF self-assembled monolayers on surfaces - graphite and gold - using ellipsometry, single reflection ATR infrared spectrocopy, contact angle, scanning tunneling microscopy (STM) and atomic force microscopy (AFM)
Organitzacions de tetratiafulvalens a escala nanomètrica
Consultable des del TDXTítol obtingut de la portada digitalitzadaEl projecte de tesis se centra en la síntesi, caracterització i estudi de les propietats estructurals, elèctriques, magnètiques i òptiques de noves organitzacions moleculars en dos i tres dimensions basades en compostos derivats del tetratiafulvalè (TTF). El treball es divideix en dues estratègies: - Per una part, en la sínetsi d'isocianurs quirals que incorporen unitats de tetratiafulvalè per la síntesis de poli(isocianur)s helicoïdals quirals conductors. - I per l'altra, en la preparació de nous TTFs que poden formar agregats supramoleculars per auto-ensamblatge sobre grafit i altres superficies, i el seu estudi estructural mitjançant les técniques de microscopia d'escombrat per efecte túnel (STM, scanning tunneling microscopy) i microscopia de força atómica (AFM, atomic force microscopy). Així com l'estudi de les propietats elèctriques d'aquets agregats mitjançant les tècniques d'espectroscopia d'efecte túnel (STS, scanning tunneling spectroscopy) i cs-AFM (current sensing atomic force microscopy).Design, chemical synthesis, structural and electronic characterization, materials preparation, study of new organic molecular and supramolecular materials based on tetrathiafulvalene derivatives showing novel electrical, magnetic and optical properties. Two strategies were followed: - Synthesis of chiral tetrathiafulvalens derivatives funcionalized with an isocyanide group to prepare conducting enanthiomeric helical poly(isocyanides). - Preparation and electrical-structural characterization of TTF self-assembled monolayers on surfaces - graphite and gold - using ellipsometry, single reflection ATR infrared spectrocopy, contact angle, scanning tunneling microscopy (STM) and atomic force microscopy (AFM)
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