Low-temperature Aqueous Chemical Method Research Articles

Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si

The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW0) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.

An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods

We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 °C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g ∼ 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zni+) as CDs and oxygen vacancy (VO) or oxygen interstitial (Oi) as surface defects. As a result, Co was found to likely occupy the Zni+, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method.

Piezoelectric and opto-electrical properties of silver-doped ZnO nanorods synthesized by low temperature aqueous chemical method

In this paper, we have synthesized Zn1−xAgxO (x = 0, 0.03, 0.06, and 0.09) nanorods (NRs) via the hydrothermal method at low temperature on silicon substrate. The characterization and comparison between the different Zn1−xAgxO samples, indicated that an increasing Ag concentration from x = 0 to a maximum of x = 0.09; All samples show a preferred orientation of (002) direction with no observable change of morphology. As the quantity of the Ag dopant was changed, the transmittances, as well as the optical band gap were decreased. X-ray photoelectron spectroscopy data clearly indicate the presence of Ag in ZnO crystal lattice. A nanoindentation-based technique was used to measure the effective piezo-response of different concentrations of Ag for both direct and converse effects. The value of the piezoelectric coefficient (d33) as well as the piezo potential generated from the ZnO NRs and Zn1−xAgxO NRs was found to decrease with the increase of Ag fraction. The finding in this investigation reveals that Ag doped ZnO is not suitable for piezoelectric energy harvesting devices.

Effect of PbTe on Thermoelectric Properties of Co0.88Ni0.12Sb2.91Sn0.09

The Co0.88Ni0.12Sb2.91Sn0.09 compound was synthesized by a metallurgical route, and PbTe powder was prepared by the low-temperature aqueous chemical method. Composite materials (xPbTe/Co0.88Ni0.12Sb2.91Sn0.09) were prepared by the ball-milling and the hot-pressed process. Electrical conductivities of xPbTe/Co0.88Ni0.12Sb2.91Sn0.09 hot-pressed samples decrease with increase of PbTe content, but their thermal conductivities were effectively improved due to induction of disperse phase. Due to agglomeration of the disperse phase, little thermal conductivity improvement occurs for composite material with low PbTe content. The ZT values of xPbTe/Co0.88Ni0.12Sb2.91Sn0.09 samples were hardly enhanced due to the negative contribution of electrical conductivity.

Surfactant assisted low temperature synthesis of nanocrystalline ZnO and its gas sensing properties

Vertically aligned ZnO nanorods, faceted microrods, nanoneedles and nanotowers were grown on glass substrates by a cost effective and low temperature aqueous chemical method. Various polymers viz. polyethylenimine (PEI), polyacrylic acid (PAA) and diaminopropane (DAP) were used as structure directing agents. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) pattern. The aligned ZnO nanorod formation takes place with the predominant orientation along (0 0 2) plane. These nanocrystalline ZnO samples were used to explore gas response properties for acetone, ammonia, LPG and ethanol. It is observed that the sensors based on DAP-directed nanoneedles showed higher response (90%) for acetone gas at 275 °C. The high acetone gas sensitivity and low operating temperature of ZnO nanoneedles can be attributed to the surface morphology.

ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method

We demonstrate white light luminescence from ZnO-organic hybrid light emitting diodes grown at 90 °C on flexible plastic substrate by aqueous chemical growth. The configuration used for the ZnO-organic hybrid white light emitting diodes (WLEDs) consists of a layer of poly (9, 9-dioctylfluorene) (PFO) on poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) coated plastic with top ZnO nanorods. Structural, electrical, and optical properties of these WLEDs were measured and analyzed. Room temperature electroluminescence spectrum reveals a broad emission band covering the range from 420 to 750 nm. In order to distinguish the white light components and contribution of the PFO layer we used a Gaussian function to simulate the experimental data. Color coordinates measurement of the WLED reveals that the emitted light has a white impression. The color rendering index and correlated color temperature of the WLED were calculated to be 68 and 5800 K, respectively.

Study of Au/ZnO nanorods Schottky light-emitting diodes grown by low-temperature aqueous chemical method

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission.

Influence of NaOH on the synthesis of Bi2Te3 via a low-temperature aqueous chemical method

NaOH was used to adjust the pH of the solution in the synthesis of nanostructured Bi2Te3 alloys via hydrothermal and solvothermal process. However, it is still elusive whether NaOH is necessary and how it affects on the size and morphology of Bi2Te3 which contributes a lot to the thermoelectric figure of merit ZT. The present work suggested that bulk quantity of nanostructured Bi2Te3 with considerable uniform morphology of nanoflake could be yielded without NaOH when the reaction time ranged from 6 h to 48 h. These nanoflakes have about 10–30 nm thickness and 50–300 nm width. When adding NaOH, the morphology of Bi2Te3 becomes various.

Thermoelectric Bi 2Te 3 nanotubes synthesized by low-temperature aqueous chemical method

Bismuth telluride (Bi 2Te 3) nanotubes have been synthesized by a low-temperature aqueous chemical method, using Te powders and BiCl 3 as the reactants, NaBH 4 as the reductant and NaOH as the pH-controller. Microstructure investigations of powders show that the Bi 2Te 3 nanotubes have an average diameter of about 100 nm, with the length varying from about 500 nm to 1 μm. The tube walls have a thickness of about 30–40 nm. The growth mechanism of Bi 2Te 3 nanotubes is discussed in this paper. It is suggested that Bi 2Te 3 crystals initially grow as flat sheets, and then form a three-dimensional closed shell with the lowest surface energy. The shell must be curved, which could outcome to a Bi 2Te 3 nanotube at last.