A qualitative comparison between the extended disorder model for charge transport and the measured charge density dependence of the field‐effect mobility is presented for field‐effect transistors (see Figure) using a poly(phenylenevinylene) layer. By varying the film morphology through the use of polymers of different molecular weights, further insight into the role of morphology is gained.
We report a systematic study of the optoelectronic processes occurring in composites made of near-infrared (IR) emitting nanocrystals and conjugated polymers. We focus on PbSe and InAs∕ZnSe blended with polyphenylenevinylene-type polymers. We find that the process responsible for quenching the visible luminescence of the polymer by the nanocrystal varies depending on the nanocrystal composite. Moreover, the high (66%) energy-transfer efficiency from the polymer to the PbSe nanocrystal does result in significant emission at the near IR. Our measurements suggest that the host may be doping the PbSe nanocrystal, thus making the nonradiative Auger process favorable. For InAs we find the energy levels well aligned inside the polymer band gap, making it an efficient charge trap which acts as a luminescence center. Through two-dimensional numerical modeling of the charge transport in such composite films we highlight the importance of morphology (nanocrystal distribution) control.
Carbon nanotube field-effect transistors (CNT FETs) have many possible applications in future nanoelectronics due to their excellent properties. However, one of the major challenges regarding their performance is the noticeable gate hysteresis which is often displayed in their transfer characteristics. The hysteresis phenomenon is often attributed to water-mediated charge transfer between the CNT and the dielectric layer or the CNT and the water layer itself. In this study, we implement the usage of current versus time measurements in addition to the traditional transfer characteristics to accurately extract the time constants of the hysteresis of suspended and on-surface CNT FETs. Following a thorough study, we provide experimental evidence that the hysteresis phenomenon of suspended CNT FETs, as well as of on-surface CNT FETs which operate at low gate voltage regimes (|V g | < 3 V), is based on gate-induced, water-assisted redistribution of mobile charge on the SiO 2 surface, and is not related to charge injection from the CNT itself. Our model is confirmed by an electronic-force-microscopy-based measurement technique which enables us to quantify the temporal surface charge distribution while measuring CNT currents.
In this paper, we present measurements of the chemical potential of single-layer graphene as a function of carrier density and temperature, including near the Dirac point. Far from the charge neutrality point, the graphene is homogenous with a single carrier type. However, as the Dirac point is approached, puddles form, and electrons and holes coexist. Hall effect analyses based on two charge carriers are not adequate in this regime. Hence, a new methodology is introduced, and by using the chemical potential and the transport data self-consistently, we were able to extract the density of each carrier. We obtained very good agreement with a recent theory that assumes a Gaussian distribution of the electrostatic disorder potential. Surprisingly, the temperature dependence of the minimum conductivity of graphene was primarily attributed to the temperature dependence of the disorder potential itself through the carrier charge densities, and not to the temperature dependence of the carrier's mobility. .
Since their discovery, carbon nanotubes have fascinated many researchers due to their unprecedented properties. However, a major drawback in utilizing carbon nanotubes for practical applications is the difficulty in positioning or growing them at specific locations. Here we present a simple, rapid, non-invasive and scalable technique that enables optical imaging of carbon nanotubes. The carbon nanotube scaffold serves as a seed for nucleation and growth of small size, optically visible nanocrystals. After imaging the molecules can be removed completely, leaving the surface intact, and thus the carbon nanotube electrical and mechanical properties are preserved. The successful and robust optical imaging allowed us to develop a dedicated image processing algorithm through which we are able to demonstrate a fully automated circuit design resulting in field effect transistors and inverters. Moreover, we demonstrate that this imaging method allows not only to locate carbon nanotubes but also, as in the case of suspended ones, to study their dynamic mechanical motion.
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