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Dispersion stability of tin(IV) oxide nanoparticles dispersed in N-Methy-2-Pyrrolidone (NMP), dimethylformamide (DMF) and distilled water assisted by ultrasonication was investigated, aiming to identify a suitable liquid medium to effectively disperse tin(IV) oxide for many useful applications. The dispersions’ stability was characterized using field emission scanning electron microscopy, ultraviolet–visible spectroscopy and Zeta potential. The results show that distilled water has the highest stability with optimum sonication of 1 h. NMP shows better stability and consistency than DMF at different sonication timings. Good agreement between ultraviolet–visible absorbance and Zeta potentials shows that both distilled water and NMP are good mediums to produce highly stable tin(V) oxide dispersion.

Carbon nanotubes (CNTs) exhibit extremely high nanoscopic thermal/electrical transport and mechanical properties. However, the macroscopic properties of assembled CNTs are significantly lower than those of CNTs because of the boundary structure between the CNTs. Therefore, it is crucial to understand the relationship between the nanoscopic boundary structure in CNTs and the macroscopic properties of the assembled CNTs. Previous studies have shown that the nanoscopic phonon transport and macroscopic thermal transport in CNTs are improved by Joule annealing because of the improved boundary Van-der-Waals interactions between CNTs via the graphitization of amorphous carbon. In this study, we investigate the mechanical strength and thermal/electrical transport properties of CNT yarns with and without Joule annealing at various temperatures, analyzing the phenomena occurring at the boundaries of CNTs. The obtained experimental and theoretical results connect the nanoscopic boundary interaction of CNTs in CNT yarns and the macroscopic mechanical and transport properties of CNT yarns.

Carbon nanohorns (CNHs) are mixed with cellulose to make freestanding thin-film conductive sheets. CNHs, at different ratios (5, 10, 25, 50 wt%), form composites with cellulose (hydroxyethylcellulose). Freestanding cellulose–carbon nanohorn (CCN) sheets were fabricated using a 100 μm-thick metal bar coater. Surfactants or any other chemical treatments to tailor the surface properties of CNHs were avoided to obtain composite sheets from pristine CNHs and cellulose. Utilizing the hygroscopic property of hydroxyethylcellulose and the electrical conductivity of CNHs paved a path to perform this experiment. The synthesis technique is simple, and the fabrication and drying of the sheets were effortless. As the loading concentration of CNH increased, the resistance, flexibility, and strength of the CCN composite sheets decreased. The maximum loading concentration possible to obtain a freestanding CCN sheet is 50 wt%. The resistance of the maximum loading concentration of CNH was 53 kΩ. The response of the CCN sheets to water vapor was 4 s and recover time was 13 s, and it is feasible to obtain a response for different concentrations of water vapor. High-resolution transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, resistance measurement, tensile strength measurement, and thermogravimetric analysis were used to investigate the mechanical, morphological, electrical, and chemical properties of the CCN sheets.

We have developed a vacuum-compatible chamber for in-situ X-ray diffraction (XRD) studies and have used it to characterize the changing crystal structure of an inorganic–organic hybrid perovskite material, CH3NH3PbI3 (MAPbI3), during interactions with water vapor at room temperature. In the XRD spectra, we have observed the degradation of MAPbI3 and the creation of MAPbI3 hydrates, which follow simple rate equations. The time constant for the degradation of MAPbI3 during accelerated aging suggests that multiple collisions of water molecules with the MAPbI3 crystal trigger the degradation of the crystal.

Demixing in a solid-soluted Co–40 at. % Pd alloy has been induced by microwave plasma hydrogen irradiation on mixture of Pd–Co island grains on Si substrate. The microstructure observation and X-ray microanalysis by a transmission electron microscope before and after the microwave plasma hydrogen irradiation provide a clear evidence of demixing in metallic Co–Pd alloys, that may indicate a possibility of the decomposition into Pd hydride and Co under a hydrogen irradiation at high temperatures.

In this paper, we describe the effects of helium plasma and ozone treatments on the dispersibility of carbon nanohorns (CNHs) in water. The experimental setups have been designed to efficiently generate helium plasma and ozone by dielectric barrier discharge at atmospheric pressure. After being treated with ozone, the oxygen-containing functional groups were introduced to the surface of CNHs, and are responsible for better dispersion. Helium plasma treatment was performed separately and it resulted in hydroxyl functional groups on the surface of CNHs. It was also found that the sizes of CNHs in water were smaller after ozone treatment. However, plasma-treated CNHs were bigger than ozone treated CNHs. The dispersed CNHs modified by ozone treatment were stable for more than three months without precipitation. In contrast, though helium plasma treatment introduced hydroxyl groups to the surface of CNHs, the dispersibility decreased and the flocculation of CNHs was observed in a few minutes.

The properties of soluble zinc phthalocyanines with trifluoroethoxy substituents (TFEO–ZnPcs) were studied to evaluate their possible use in organic thin-film solar cells. We prepared five TFEO–ZnPcs with different numbers and positions of the TFEO substituents. The solubilities, UV–visible absorption spectra, and cyclic voltammograms of these ZnPcs varied with their substituents. TFEO–ZnPc thin-films fabricated by spin-casting exhibited photocurrent generation at wavelengths between 600 and 850 nm. Flat heterojunction solar cells consisting of a poly(3-hexylthiophene) (P3HT) layer as a donor and a TFEO–ZnPc layer as an acceptor exhibited photocurrent generation over a wide range of wavelengths corresponding to both the P3HT and TFEO–ZnPc absorption spectra. The best solar cell performance was obtained with (β-TFEO)4ZnPc film.

We investigated the potential of trifluoroethoxy-coated phthalocyanine [(4TFEO)4-ZnPc] as an organic thin-film solar cell material. (4TFEO)4-ZnPc dissolves well in several organic solvents, thus a fluorinated phthalocyanine (Pc) thin film can be fabricated by a wet process. Additionally, (4TFEO)4-ZnPc has lowest unoccupied molecular orbital (LUMO) energy level close to that of a fullerene derivative owing to the electron-withdrawing effect of fluorine substituents. We fabricated two types of fluorinated Pc solar cells by spin casting “(4TFEO)4-ZnPc single-layer solar cells” and “two-layer heterojunction solar cells” consisting of a (4TFEO)4-ZnPc layer and a poly(3-hexylthiophene) (P3HT) layer. P3HT is a common donor solar cell material. On the other hand, we used (4TFEO)4-ZnPc as an acceptor material. For the single-layer solar cells, the (4TFEO)4-ZnPc film acts as the photoactive layer of the solar cells, and P3HT/(4TFEO)4-ZnPc solar cell properties were improved as compared with that of P3HT or (4TFEO)4-ZnPc single-layer solar cells. Additionally, the photovoltaic properties of these solar cells were significantly improved by annealing treatment.

Germanium (Ge) surfaces were irradiated by argon (Ar+) ions at 600 eV with a simultaneous Ge, Al, or Au supply at room temperature. The surfaces thus ion-irradiated were characterized by densely distributed nanowalls, nanobelts (narrower than the nanowalls in width), and cones tipped with nanoribbons (narrower than the nanobelts in width), depending on the supplied particle species and the supply rate. The higher the melting points of the supplied materials, the narrower the width of the top of the nanostructures. Thus the melting point and the supply rate of the supplied material are the key parameters for controlling the shape and size in the fabrication of ion-induced Ge nanostructures. It was also demonstrated that for nanowalls and nanobelts, a higher particle supply rate yielded wider nanostructures. For many nanoribbon-tipped cones, the width of the nanoribbon increased with distance from the cone top, and hence resulted in a bottleneck structure.

Poly [2-methoxy-5(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) was used as a sensitizer in a photovoltaic cell. The cell was fabricated by depositing MEH-PPV in between wide band gap n-TiO2 and p-CuI films. A maximum open circuit voltage of 390 mV and short circuit current of 0.29 mA·cm-2 were observed for the TiO2|MEH-PPV|CuI cell, under AM 1.5 conditions (100 mW·cm-2 of white light illumination).

To understand the motion of DNA and DNA complexes, the real-time visualization of living DNA in liquids is quite important. Here, we report the high-resolution imaging of plasmid DNA in water using a rapid-scan atomic force microscopy (AFM) system equipped with a carbon nanofiber (CNF) probe. To achieve a rapid high-resolution scan, small SiN cantilevers with dimensions of 2 (width) × 0.1 (thickness) × 9 µm (length) and a bent end (tip view structure) were employed as base cantilevers onto which single CNFs were grown. The resonant frequencies of the cantilever were 1.5 MHz in air and 500 kHz in water, and the spring constant was calculated to be 0.1 N/m. Single CNFs, typically 88 nm in length, were formed on an array of the cantilevers in a batch process by the ion-irradiation method. An AFM image of a plasmid DNA taken in water at 0.2 fps (5 s/image) using a batch-fabricated CNF-tipped cantilever clearly showed the helix turns of the double strand DNA. The average helical pitch measured 3.4 nm (σ: 0.5 nm), which was in good agreement with that determined by the X-ray diffraction method, 3.4 nm. Thus, it is presumed that the combined use of the rapid-scan AFM system with the ion-induced CNF probe is promising for the dynamic analysis of biomolecules.

The effect of ion species and fabrication temperature on the size of ion-induced carbon nanofibers (CNFs) grown on tips of scanning probe microscope cantilevers was investigated in detail. Similarly to that using Ar+ ions, the fabrication of CNF probes using Ne+ and Xe+ ions was possible. Xe+ sputtering yielded the shortest CNF probes owing to its large sputtering effect; however, a significant difference in the size of the CNF probes between Ne+ and Ar+ ion irradiation was not observed. The CNFs increased in length with fabrication temperature owing to the enhanced diffusion of C atoms at elevated temperatures; however, the CNF diameter remained almost constant independent of fabrication temperature. Therefore, the fabrication at elevated temperatures was effective for the rapid fabrication of practical CNF probes. Thus, the CNF probe size was controllable by adjusting the fabrication temperature and ion species.

We demonstrate the improvement in the surface properties of an indium tin oxide (ITO) anode contact to an organic bulk-heterojunction device via cooling down the ITO glass substrate by liquid nitrogen treatment. This treatment effectively improves the smoothness of ITO glass, the transmittance and the contact angle measurement, which thereby results in fairly good contact with organic material. The enhancement of short circuit current, efficiency and fill factor of the photovoltaic devices was also achieved. The surface properties of both the untreated and the treated ITO substrates were studied by atomic force microscopy and the electrical properties of the substrates were studied by the Hall effect measurement.

Graphite surfaces were bombarded by Ar+ ions with and without a simultaneous Ni supply at room temperature. The sputtered surfaces without Ni supply were characterized by densely distributed conical protrusions with aligned single carbon nanofibers (CNFs) on the tops. By contrast, an excess Ni supply during Ar+ bombardment suppressed the CNF formation, while under the proper Ni supply conditions, single Ni-doped CNFs grew on slender needle-like structures or conical protrusions depending on the supply rate of Ni atoms. Non-doped CNFs were characterized by the amorphous-like or very fine-crystallites nature, whereas the Ni-doped CNFs were featured by polycrystalline structure. Thus, the crystalline structure was controllable by Ni doping. Because any kinds of materials can be doped into ion-induced CNFs, it is believed that the ion-irradiation method will open up a new approach to fabricate 1-dimensional composite nanomaterials at room temperature.

We have fabricated both blended and bilayered organic photovoltaic cells (OPVCs) using C60 and poly[2-methoxy-5-(2'-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV). Improvements in photovoltaic performance are seen in blended OPVCs when the C60 concentration is increased. It is believed that the optimized surface morphology of MEH-PPV/C60 composite and improved donor-acceptor proximity, leading to electron conductivity, contribute to the increase in power conversion efficiency E ff. Two broad peaks were observed in the spectral response of the blended OPVCs, with maximum peaks at ∼490 nm (=I BL1) and ∼350 nm (=I BL2). The intensity ratio of I BL1 to I BL2 (I BL1/I BL2) decreases with an increase in the C60 concentration. Also, I BL1 is blue-shifted by 25–30 nm with an increase in the C60 concentration. The significant improvement in the performance was observed in the bilayered OPVCs on the thermally induced interdiffusion of C60 into the MEH-PPV network, leading to the existence of C60 molecules within the exciton diffusion radius of the MEH-PPV network. The spectral response of bilayered OPVCs reveals two peaks at 535 nm and 345 nm. The former peak is red-shifted by 45 nm compared to that in blended OPVCs. We also investigate the effect of top electrode materials on the photovoltaic performances. To the best of our knowledge, we have obtained the best performances of blended and bilayered OPVCs fabricated with the Al and Mg electrodes, respectively. In both OPVC structures, the nanoscale composition control of the two materials, the choice of metal electrode, and the device processing techniques all play an important role in determining or enhancing the solar cell performance.

We have studied the influence of radio frequency (RF) power on material properties of hydrogenated amorphous carbon (a-C:H) films prepared by RF plasma-enhanced chemical vapor deposition (CVD). The RF power has a significant impact on film properties such as electron spin resonance (ESR) spin density, the optical band gap, chemical bonding and photoluminescence (PL). Raman spectroscopy, infrared (IR) absorption and ESR measurements reveal that the residual defect density (ESR spin density) increases with increasing RF power due to the increase of sp 2 C–Hx components. We obtained an ESR spin density as small as 8 ×1016 spins/cm3 at a low RF power, which is comparable to that of high-quality amorphous silicon films. Plasma optical emission spectroscopy indicates that the intensity ratio (I C–H/I H) between hydrogen peaks (I H) and hydrocarbon peaks (I C–H) significantly decreases with increasing RF power. The optical band gap, obtained from UV-visible spectroscopy, varies from 3.0 to 1.9 eV with increasing RF power. The broad emission band centered around 2.4 eV was observed in the PL spectra of the samples deposited at lower RF powers. We found a 0.5–0.3 eV Stokes shift by comparing the PL emission and the absorption coefficient spectrum from the films deposited at ≤100 W RF powers, whereas, we failed to observe a clear Stokes shift from the films deposited at >100 W RF powers. A weak correlation between the PL peak and the optical band gap is demonstrated.

The theoretical hole transport characteristics (Hall and drift mobilities, and effective Hall factor) are reported for the cubic phase of p-type GaN. These characteristics are calculated using the “relaxation time approximation” as a function of temperature. The calculations show that the dominant lattice scattering mechanism for holes is the acoustic deformation potential. In the calculation of the scattering rate for ionized impurity mechanism, the activation energy of 120 or 250 meV is used at different compensation ratios of given acceptor concentrations. Comparing the scattering time in these activation energies, it is found that the activation energy difference is negligible at high compensation ratios. We determined the anisotropy factors separately, due to the anisotropy of the energy surface for heavy- and light-hole bands, and these parameters are taken into account in the Hall factor calculations. The Hall factors are very important when we attempt to compare the calculated drift mobility with measured Hall ones. The theoretical Hall mobilities at total hole concentrations of 3.5 ×1015 and 3.5 ×1016 cm-3 are about 312 and 225 cm2V-1s-1, respectively, with the activation energy of 120 meV and the compensation ratio of 0.5 at 300 K. It is found that Hall mobilities are strongly affected by the compensation ratios. The obtained effective Hall factor in the cubic phase of GaN is in the range of 1.4 (T=120 K) to 1.8 (T=400 K).