Quantum dot/carbon nanotube/silicon double heterojunctions for multi-band room temperature infrared detection.

We report on the observation of room temperature multi-band photocurrent response from a novel structure formed by interior loading of PbS quantum dots into carbon nanotubes grown on silicon. In addition to a mid infrared photoresponse band at ∼ 0.22 eV due to the carbon nanotubes and one band at 1.1 eV corresponding to silicon, two bands in the mid/near infrared at 0.63 and 0.82 eV, corresponding to the first and second exciton bands of the PbS quantum dots, are observed in photocurrents measured at room temperature, in uncooled operation. We have also observed a red shift of the 0.63 and 0.82 eV bands with cooling that reflects a behavior typical for PbS and supports the hypothesis that these photoresponse bands are due to absorption in the PbS quantum dots.

Ultra-high redox enzyme signal transduction using highly ordered carbon nanotube array electrodes.

We report on a highly ordered array of carbon nanotubes (CNTs) that serves as a universally direct nanoelectrode interface for redox proteins and provides an efficient conduit for electron transfer. The site-selective, covalent docking of the enzyme glucose oxidase (GO(x)) on the CNT tips is found to have a marked effect on enhancing electron transfer properties, as measured by cyclic voltammetry. A unimolecular electron transfer rate of 1500 s(-1) has been measured for this system, a value exceeding the rate of oxygen reduction by glucose oxidase. Furthermore, the redox enzyme-CNT array conjugate can be utilized as a quantitative, substrate-specific biosensor.

Optical control over photoconductivity in polyferrocenylsilane films.

We report the study and elucidate the origin of the photoconductivity of polyferrocenylsilanes achieved through photooxidation performed by ultraviolet irradiation in the presence of chloroform. The persistence over months of the changes in the optoelectronic properties allowed more detailed studies of the charge photogeneration process. The photocurrent spectrum mimics that of the absorption indicating that the photooxidized material is not a mechanical mixture of oxidized and unoxidized polymer units. Photomodulation spectroscopy revealed the existence of long-lived photoexcited states with a lifetime in the millisecond range. They have been interpreted as trapped excitons at the oxidized sites where the polymer is deformed due to the presence of the chloroform derived counter ions. Because of the relatively long lifetime of the trapped excitons they can dissociate and the formed charge carriers can be separated in an externally applied electric field. The effect of the polymer chain deformation around the oxidized unit extends over the neighboring polymer units. In light of the potential applications of this class of polymers in various electronic and photonic devices, the clarification of such a basic process as the photocurrent generation will be a key factor for further technological development.

Electronic transport in a controllably grown carbon nanotube-silicon heterojunction array.

A uniform array of a new type of heterojunction formed between carbon nanotubes and silicon is studied. The heterojunction array was controllably grown with parallel and uniform nanotubes vertically aligned to the silicon substrate using a self-organized nanopore array template. The pronounced rectifying characteristics of the heterojunction were measured with an on/off ratio as high as 10(5) at 4 V. The analysis shows a large and type-I band offset at the heterojunction. The charge transport in the nanotubes is found to be strongly coupled to and limited by the dielectric charging and polarization in the hosting alumina matrix surrounding the nanotubes.