Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT-a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics, such as Bi(2)Te(3)/Sb(2)Te(3) thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm x 20 nm and 20 nm x 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT approximately 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.

A bottom-up approach was the key to the successful fabrication of this memory. This approach both minimized the number of processing steps following deposition of the molecular monolayer, as well as protected the molecules from remaining processing steps. In the following paragraphs, we briefly describe the nanofabrication procedures utilized to construct the memory circuit. A full paper describing these procedures in more detail will be submitted for publication in the near future. form an array of top Ti NW electrodes, and the crossbar structure is complete.

We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.

There are currently great needs to develop low-cost inorganic materials that can efficiently perform solar water splitting as photoelectrolysis of water into hydrogen and oxygen has significant potential to provide clean energy. We investigate the Si/TiO2 nanowire heterostructures to determine their potential for the photooxidation of water. We observed that highly dense Si/TiO2 core/shell nanowire arrays enhanced the photocurrent by 2.5 times compared to planar Si/TiO2 structure due to their low reflectance and high surface area. We also showed that n-Si/n-TiO2 nanowire arrays exhibited a larger photocurrent and open circuit voltage than p-Si/n-TiO2 nanowires due to a barrier at the heterojunction.

Intimate electrical contact occurs between a substituted poly(metaphenylenevinylene) (PmPV) and bundles of single‐walled nanotubes (SWNT) as evidenced by atomic force microscopy, optical, and electronic measurements carried out on single, isolated SWNT/PmPV structures (see picture). PmPV may provide a useful route toward “functionalizing” the SWNT without destroying their electrical character.

We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell. End-functionalized oligo-and poly-thiophenes were grafted onto ZnO nanowires to produce p-n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and electron microscopy to determine the optoelectronic properties and to probe the morphology at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, Jsc= 0.32 mA/cm 2 , Voc= 0.4 V, and a FF= 0.28 under AM 1.5 illumination with 100 mW/cm 2 light intensity. These individual test structures will enable detailed analysis to be carried out in areas that have been difficult to study in bulk heterojunction devices. are an area of immense study as they are alternatives to organic bilayer 3 and bulk heterojunction device structures. 4,5 The organic/inorganic hybrid system [6][7][8][9] has opened new opportunities for the development of future generation solar cells, new device technologies, and a platform to study three-dimensional morphology. 10A multitude of concepts have been demonstrated by combining p-type donor polymers with n-type acceptor inorganic nanostructures such as CdSe, 6,7,11 TiO 2 , [8][9][10][12][13][14][15] and ZnO. [8][9][10]14 One-dimensional (1-D) inorganic semiconductor nanostructures are among some of the most attractive nanomaterials for solar cell devices because they provide a direct path for charge transport. 2Other advantages include high carrier mobilities, solution processability, thermal and ambient stability, and a high electron affinity necessary for charge injection from the complementary organic donor material. ZnO nanowires are an example of this class of materials that have been used for hybrid solar cells. [8][9][10]14,16 Poly(3-hexylthiophene) (P3HT)/ZnO nanowire composite solar cells are benchmark systems that have attained power conversion efficiencies ranging from 0.02 to 2%. 9,16,17 In spite of the vast efforts in this area of research, solar cells based on hybrid composites have yielded efficiencies only close to those of organic bilayer devices and significantly less than organic bulk heterojunction solar cells. Knowledge regarding interfacial charge separation and/or transport in hybrid nanowire devices is only partly understood. 10,17 If this class of materials is to play a part in the future of next generation solar cells, then there must be an improved fundamental understanding of the organic/inorganic interface in order to improve power conversion efficiencies. While nanowire array and bulk inorganic/organic blend devices are technologically relevant, their electrical properties 2 depend on nanostructure size, uniformity, crystallinity, phase segregation, interfacial interactions, mobility, trap density and many other factors. For macroscopic devices, these parameters can vary significantly over the active area, making it difficult to attribute any change in performance to a particular phenomenon. Si...

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Nanofabrication methods and a device architecture are combined to allow for four‐point electric, thermoelectric, and electric field‐effect measurements on individual Bi nanowires. The figure shows a false‐color SEM image of a typical device used in this study, with the 11 Bi nanowires shown as a red → white gradient. The temperature dependence of the various transport properties as a function of nanowire width is investigated and discussed.