RESUMEN
We investigate the electronic and transport properties of HgTe 2D colloidal quantum wells. We demonstrate that the material can be made p- or n-type depending on the capping ligands. In addition to the control of majority carrier type, the surface chemistry also strongly affects the photoconductivity of the material. These transport measurements are correlated with the electronic structure determined by high resolution X-ray photoemission. We attribute the change of majority carriers to the strong hybridization of an n-doped HgS layer resulting from capping the HgTe nanoplatelets by S2- ions. We further investigate the gate and temperature dependence of the photoresponse and its dynamics. We show that the photocurrent rise and fall times can be tuned from 100 µs to 1 ms using the gate bias. Finally, we use time-resolved photoemission spectroscopy as a probe of the transport relaxation to determine if the observed dynamics are limited by a fundamental process such as trapping. These pump probe surface photovoltage measurements show an even faster relaxation in the 100-500 ns range, which suggests that the current performances are rather limited by geometrical factors.
RESUMEN
The absorptivities of polydiacetylenes (PDAs) used in Langmuir films or vesicles for the development of PDA sensor films or other applications such as nonlinear optics and field-effect transistors are not known, so the polymer contents cannot be deduced from experimental spectra. Here we introduce a novel method, using nuclear reaction analysis (NRA), that allows a quantitative determination of the polymer content X proportion of monomers that have been incorporated into PDA chains. We apply it to pentacosadiynoic acid (PCDA) evaporated microcrystalline films. A calibration curve giving X as a function of the area under an absorption spectrum normalized to the monomer areal density is obtained for blue and red PCDA. The method is applicable to all kinds of films and to other PDAs, provided films with known molecular areal density are available. An example of the application to a PCDA Langmuir film is given.
RESUMEN
We report here the synthesis and characterization of novel diethynylbenzene-based liquid crystalline semiconductor (P1) for organic thin-film transistors (OTFTs). Compound P1 was synthesized by the Sonogashira coupling reaction between 2-bromo-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene and 1,4-bis(dodecyloxy)-2,5-diethynylbenzene. Top contact OTFTs were fabricated by spin casting with 2 wt% solution of P1 in chloroform and their best performance, which exhibited a hole mobility of 4.5 x 10(-5) cm2/Vs, was showed after annealing of the films at liquid crystalline temperature. Time-of-flight (TOF) mobility measured at liquid crystalline phase was observed to be 1.5 x 10(-6) cm2/Vs for both positive and negative carriers. These results indicate that the liquid crystallinity helps to improve the molecular packing and enhance charge mobility for P1. These advantages can be applicable to design and construct solution-processable OTFT materials for electronic applications.
RESUMEN
A new reactive diacetylene molecule has been synthesized, incorporating a strongly luminescent chromophore, tetrazine (Tz). It readily polymerizes into the blue polydiacetylene (PDA) form, quenching the Tz luminescence already at concentrations ≤1 %. The blue to red PDA transition is thermally induced in the solid state and the original strong Tz emission is restored. This might lead to a new type of detection for sensors using the PDA color transition.
RESUMEN
We measured the charge carrier mobilities for two isomers of fluorenone-based liquid crystalline organic semiconductors from their isotropic down to crystalline states through one or two mesophases. Improved charge transport properties of melt-processed crystalline films were obtained for the isomer exhibiting a highly ordered mesophase below its disordered smectic phase.