No abstract

From comparative studies of dye sensitized solar cell (DSSCs) fabricated using nanotubes (NTs) filled with nanoparticles (NPs) and empty NTs it is shown that filling of TiO2 NTs with NPs significantly increase efficiency of DSSCs. This increase depended on NT diameter and was found to be 17.4%, 55.6%, and 131% for solar cells with 40 nm, 80 nm, and 160 nm diameter NTs. The highest efficiency was observed for samples with 80 nm diameter NTs, which was 5.94% for ∼5 μm NT thickness DSSCs.

A systematic study of titanium dioxide (TiO2) nanotubes (NTs) grown by electrochemical anodization in NH4F + glycerol electrolyte has been carried out in a broad range of anodization voltage of 5-350 V and acid concentration of 0.1-0.7 wt%. It is found that NTs can be grown in the voltage range from 10 to 240 V. The maximum NH4F acid concentration at which NTs can be formed decreases with the anodization voltage (V(a)). The maximum NH4F acid concentration is 0.7% for V(a)<60 V, and it decreases to 0.1% at V(a) = 240 V. Glancing angle x-ray diffractometer (GAXRD) measurements show that as-grown amorphous TiO2 transforms to the anatase phase when annealed at 400 degrees C, and further transforms to the rutile phase at annealing temperatures higher than 500 degrees C. The transition temperature from anatase to rutile phase depends on the anodization conditions. The electrical resistivity of the NT increases by eight orders of magnitude when V(a) increases from 10 to 240 V.

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO₂) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.

The purpose of this paper is to investigate the feasibility of a novel four-material decomposition technique for assessing the vulnerability of plaque with two contrast materials spectral computer tomography (CT) using two independent markers: plaque's inflammation and spotty calcification. A simulation study was conducted using an energy-sensitive photon-counting detector for k-edge imaging of the coronary arteries. In addition to detecting the inflammation status, which is known as a biological marker of a plaque's vulnerability, we use spotty calcium concentration as an independent marker to test a plaque's vulnerability. We have introduced a new method for detecting and quantifying calcium concentrations in the presence of two contrast materials (iodine and gold), calcium and soft tissue background. In this method, four-material decomposition was performed on a pixel-by-pixel basis, assuming there was an arbitrary mixture of materials in the voxel. The concentrations of iodine and gold were determined by the k-edge material decomposition based on the maximum likelihood method. The calibration curves of the attenuation coefficients, with respect to the concentrations of different materials, were used to separate the calcium signal from both contrast materials and different soft tissues in the mixtures. Three different materials (muscle, blood and lipid) were independently used as soft tissue. The simulations included both ideal and more realistic energy resolving detectors to measure the polychromatic photon spectrum in single slice parallel beam geometry. The ideal detector was used together with a 3 cm diameter digital phantom to demonstrate the decomposition method while a more realistic detector and a 33 × 24 cm(2) digital chest phantom were simulated to validate the vulnerability assessment technique. A 120 kVp spectrum was generated to produce photon flux sufficient for detecting contrast materials above the k-edges of iodine (33.2 keV) and gold (80.7 keV). By performing simulations on a 3 cm diameter digital phantom, we successfully identified four materials that were simultaneously present in the mixture at different proportions and in multiple locations on the phantom. Quantitative analysis with a chest digital phantom showed that the results for iodine, gold and calcium were highly correlated with the known concentrations. The analysis revealed a potentially powerful technique for assessing a plaque's vulnerability with two independent markers. High correlation and low relative errors between calculated and known materials' concentrations showed that the method is feasible. This technique can potentially have a high clinical impact.