Fabrication and Characterization of n-ZnO Hexagonal Nanorods/p-Si Heterojunction Diodes: Temperature-Dependant Electrical Characteristics

This paper reports the temperature-dependant electrical characteristics of n-ZnO hexagonal nanorods/p-Si heterojunction diodes. The n-ZnO hexagonal nanorods were grown on p-Si substrate by a simple thermal evaporation process using metallic zinc powder in the presence of oxygen. The spectroscopic characterization revealed well-crystalline nanorods, quasi-aligned to the substrate and possessing hexagonal shape. The as-grown nanorods exhibited a strong near-band-edge emis- sion with very weak deep-level emission in the room-temperature photoluminescence spectrum, confirming good optical properties. Furthermore, the electrical properties of as-grown ZnO nanorods were examined by fabricating n-ZnO/p-Si heterojunction assembly and the I-V characteristics of the fabricated heterojunction assembly were investigated at different temperatures. The fabricated n-ZnO/p-Si heterojunction diodes exhibited a turn-on voltage of ~5 V at different temperatures with a mean built-in-potential barrier of 1.12 eV. Moreover, the high values of quality factor obtained from I-V analysis suggested a non-ideal behavior of Schottky junction.

Fabrication and Characterization of Field Effect Transistor Based on High-Aspect Ratio Sulfur-Doped ZnO Nanowires

Well-crystalline sulfur (S) doped ZnO nanowires have been grown via a simple thermal evaporation process on Si substrate using high purity zinc and sulfur powders in presence of oxygen. The as-grown S:ZnO nanowires were characterized in terms of their morphological structural, compositional and optical properties using several techniques such as FESEM, TEM, XRD, EDS and PL. The morphological characterizations revealed that the as-grown nanowires had diameters in the range of 60-100 nm with lengths 5-15 μm. The details structural properties confirmed the well-crystallinity and wurtzite hexagonal phase for the prepared nanowires. Room temperature photoluminescence (PL) spectrum showed a strong green band with a suppressed UV emission. The electrical properties of single S:ZnO nanowire was examined by fabricating single nanowire based field effect transistors (FETs). The detailed electrical transport results showed that S:ZnO nanowires possess n-type semiconducting behavior and exhibited an electron mobility of -67.7 cm2 V(-1) s(-1) and a carrier concentration of 2 x 10(17) cm(-3), respectively.

Possible use of BN-modified fullerene as a nano-biosensor to detect adenine–thymine Watson–Crick base pair in mutagenic tautomeric form: Theoretical approach

The present work deals with the theoretical investigation of electronic structure features and stability of adenine–thymine (AT) and rare tautomer of adenine–thymine (rAT) base pairs along with their complexes with Cu 2+ cation and their interactions with BN doped fullerene ( C 58 BN ). All the calculations have been performed with density functional theory using B3LYP functional. Electronic structures of the two base pairs are almost identical. Hence, it is rather difficult to distinguish between the two base pairs on the basis of their electronic properties. As per our theoretical calculations, we have observed that, BN modified fullerene could act as a nano-biosensor for detection of mispairing between these two complementary bases as well as their Cu 2+ complexes.

Quantum chemical investigations of AlN-doped C60 for use as a nano-biosensor in detection of mispairing between DNA bases

Quantum chemical calculations were carried out to study the electronic structure and stability of adenine-thymine and the rare tautomer of adenine-thymine base pairs along with their Cu 2+ complexes and their interactions with AlN-modified fullerene (C58AlN) using Density Functional Theory (B3LYP method). Since, these two forms of base pairs and their Cu 2+ complexes have almost similar electronic structures, their chemical differentiation is an extremely difficult task. In this investigation, we have observed that AlN-doped C 60 could be used as a potentially viable nanoscale sensor to detect these two base pairs as well as their Cu2+ complexes.

Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties

Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

Understanding the effect of flower extracts on the photoconducting properties of nanostructured TiO2

Here we report an easy method to improve the optoelectronic properties of commercially available TiO2 nanopowder using extracts of various flowers viz. Calendula Orange (CO), Calendula Yellow (CY), Dahlia Violet (DV), Dahlia Yellow (DY), Rabbit flower (RF), Sweet Poppy (SP), Sweet Williams (SW) and their Mixed Extracts (ME). Various analysis techniques such as UV-Vis, FTIR, FESEM, XRD, and Raman spectroscopy were used to characterize for elemental, structural and morphological properties of the unmixed/mixed TiO2 nanopowder. TiO2 nanopowder was also calcined at 550 degrees C. Thick films of the these unmixed/mixed powder were printed, using conventional screen printing method, on fluorine doped tin oxide (FTO) substrate with organic binders and dried at 45 degrees C. The photoconducting properties are investigated as a function of wavelength from ultra-violet (UV) to infra-red (IR) region at a constant illumination intensity. Photocurrent gradually decreases when irradiated from UV to IR region. In case of unmixed and uncalcined TiO2, conductance decreased continuously whereas when extracts are added, a flat region of conductance is observed. The overall effect of extracts (colour pigments) is seen as an increase in the photoconductance. Highest photoconductance is observed in case of DY flower extract. Anthocyanins, present in flowers are known to have antioxidative properties and hence can contribute in photoconduction by reducing the surface adsorbed oxygen. This investigation indicates the potential use of flower extracts for dye sensitized solar cell (DSSC).

Temperature dependant structural and electrical properties of ZnO nanowire networks

In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal evaporation process using metallic zinc powder in the presence of oxygen. The morphological investigations of the synthesized nanowire networks are conducted by using field emission scanning electron microscopy (FESEM) which reveals that the grown products are in high-density over the whole substrate surface and possessing nanowire networks like structures. The structural and compositional properties of the grown nanowire networks are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), respectively which confirm that the synthesized products are well-crystalline, with wurtzite hexagonal phase ZnO. The as-grown ZnO nanowire networks grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode and presented in this paper. The I-V characteristics of the fabricated heterojunction diode at different temperatures (77 K-477 K) are also investigated. High values of quality factor, which are obtained from this study, indicate a non-ideal behavior of the fabricated device. The mean barrier height of -0.84 eV is also estimated and presented in this paper.

Well-crystalline ZnO nanowire based field effect transistors (FETs)

Well-crystalline ZnO nanowires were grown on Si(100) via non-catalytic thermal evaporation process using metallic zinc powder in presence of oxygen. The detailed morphological characterizations by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed that the synthesized products are nanowires with the typical diameter and lengths of approximately 55 +/- 5 nm and several micrometers, respectively and are grown in high density over the silicon substrate. The detailed structural characterizations by high-resolution TEM and X-ray diffraction confirmed that the synthesized nanowires are well-crystalline and possessing wurtzite hexagonal phase. The presence of Raman-active optical-phonon E2(high) mode at 437 cm(-1) in the Raman-scattering spectrum confirms good crystal quality for the as-grown ZnO nanowires. The electrical transport properties of the as-grown nanowires were explored by fabricating single nanowire based field effect transistors (FETs). The fabricated single ZnO nanowire based FET exhibits carrier concentration and electron mobility of approximately 7.49 x 10(17) cm(-3) and approximately 8.42 cm2V(-1)s(-1), respectively.

Utilization of ZnO nanocones for the photocatalytic degradation of acridine orange

A facile aqueous solution process was used to synthesize well-crystalline ZnO nanocones at 60 degrees C by using zinc nitrate hexahydrate and sodium hydroxide. The morphological, structural and optical properties of the synthesized ZnO nanocones were investigated by using field emission scanning electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) equipped with high-resolution (HRTEM), X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) spectroscopy and UV-Vis. spectroscopy measurements. The structural and optical properties of the as-synthesized nanocones confirmed a pure and well crystalline product possessing wurtzite hexagonal phase. The as-synthesized ZnO nanocones were used as photocatalyst for the efficient photocatalytic degradation of acridine orange. The acridine orange was almost completely degraded within 105 minutes. This research demonstrates that the simply synthesized ZnO nanostructures could be efficient photocatalyst for the photocatalytic degradation of various organic dyes and chemicals.

A novel method for preparing stoichiometric SnO(2) thin films at low temperature

Tin oxide is a well known nonstoichiometric material with dual valency. The invariance of stoichiometry is very intriguing. As of today no report is available for preparing perfect stoichiometric tin oxide. Here we report a novel method to prepare stoichiometric tin oxide by modifying the known plasma enhanced chemical vapor deposition technique using SnCl(4)-xH(2)O as precursor and O(2) as reactant gas at various temperatures from 300 to 800 degrees C. Tetragonal rutile structure of SnO(2) was found, grown along the [110] direction. X-ray photoelectron spectroscopic measurement showed constant Sn/O ratio. Sn 3d and O 1s were found composed of only Sn(4+) (487.2 eV) and O-Sn(4+) (531.2 eV) with equal peak widths. Raman band intensity ( approximately 633 cm(-1)) was found increasing with temperature, indicating the morphological changes. Sheet resistance of approximately 0.5 kOmega/at 300 degrees C was measured that reduces to approximately 0.1 kOmega/at 600 degrees C. It is found that film stoichiometry remains unaltered, while the structural morphology changes significantly.