Papers by Keyword: Nanocolumn

Abstract: Indium tin oxide was prepared using RF magnetron sputtering at different substrate temperature. The morphological and electrical properties were investigated. Morphological properties were observed by atomic force microscopy. Electrical properties were measured using standard two-point probe measurements. The result shows that the average roughness and peak to valley value are highest at high substrate temperature. The watershed analysis shows that the total grain boundaries are highest at the substrate temperature of 200°C. The lowest resistivity value of 9.57×10^-5 Ωcm is obtained from ITO nanocolumn deposited at substrate temperature of 200°C. The improvement of morphological and electrical properties as transparent conducting oxide was observed from ITO nanocolumn deposited at substrate temperature of 200°C.

Abstract: In the present study, ITO nanocolumn was successfully deposited onto a glass substrate by RF magnetron sputtering. The effect of deposition pressure was investigated. X-ray diffraction analysis indicates that the intensity of the (400) peak orientation is highest at sputtering pressure of 5 mTorr. The results from UV-visible (UV-vis) spectroscopy revealed that the optical transmittance above 80 % was obtained from the all samples in the visible range of 400-800 nm. The larger grain size was observed from the top view of field emission scanning electron microscopy (FESEM) image as the sputtering pressure was increase. Dense nanocolumn arrays were obtained from the sample deposited at sputtering pressure of 5 mTorr. The surface roughness were decreased at high sputtering pressure of 10 mTorr was observed from atomic force microscopy (AFM) surface morphology. The electrical properties were obtained using standard two-point probe measurements. The lowest electrical resistivity was determined from the sample that prepared at sputtering pressure of 5 mTorr.

Abstract: Vertically aligned GaN nanocolumn arrays were grown by molecular beam epitaxy on Gallium coated silicon substrate. The dense packing of the NCs gives them the appearance of a continuous film in surface view, but cross-sectional analysis shows them to be isolated nanostructures. The GaN nanocolumns have uniform diameters of 85 nm, lengths up to 720 nm and possess a pyramid like tip. Photoluminescence measurements of NCs show excitonic emission with a dominant, narrow peak centered at 363 nm and FWHM of 68 meV. From the Raman spectrum, peaks at 566.9 and 730 cm-1 are assigned to the E2 and A1(LO) GaN phonons modes which clearly indicates that the grown nanocolumns are highly crystalline. The grown nanocolumns are highly oriented and perpendicular to the growth surface.

Abstract: Vertical GaN nano-columns arrays were grown on Au-coated silicon (111) substrate by Au+Ga alloy seeding method and pulsed flow of Gallium and ammonia using metalorganic chemical vapor deposition (MOCVD). A gold thin film was deposited on Si using an ion coating system. The Au coated Si substrate was annealed at 800 oC under hydrogen ambient for 5 min. The pre-deposition of gallium and nitrogen was performed for 60 sec to form Au+Ga and nitrogen solid solution, which acts as the initial nucleation islands. Then Gallium and ammonia were let in pulse method. Scanning electron microscopy (SEM) image reveals a vertical growth and cylindrical in shape GaN nano-column. From the sharp PL peak intensity it is clearly seen that the dislocation density is reduced considerably and the optical quality of the nano-column is improved.

Abstract: We have studied the Au+Ga alloy seeding method. Single-crystal GaN nano-column arrays were grown using metalorganic chemical vapor deposition (MOCVD) and their properties were investigated as a function of the growth parameters and Au thin film thickness. Au-coated Si(111) substrates were used for the growth of GaN nano-columns. The diameter and length of as-grown nano-column ranged from 100 to 500 nm and 1 to 5 μm, respectively. The morphology of the columns was investigated using scanning electron microscopy. Energy dispersive X-ray spectroscopy and photoluminescence were used for evaluating of its qualitative analysis and to evaluate the optical properties, respectively. Two important growth parameters were considered, the thickness of the Au thin film and the gallium flow rate. The density and tendency of the nano-columns depend on each of these growth parameters. It is believed that the catalytic activity of gold is determined by the size of the Au+Ga solid solution particles, and smaller Au+Ga clusters showed significant reactivity in the growth of one-dimensional GaN nano structures.

Abstract: ZnO nanowalls and nanocolumns were synthesized on Si3N4 (50 nm)/Si (001) substrates at low growth temperature (350 and 400 oC) by metalorganic chemical vapor deposition (MOCVD) with no metal catalysts. ZnO nanowalls with extremely small wall thicknesses below 10 nm and nanocolumns with diameters over 100 nm were formed on the Si3N4/Si substrates relying on MOCVD-growth temperature. It was found that ZnO nanowalls have a strong c-axis preferred orientation with a hexagonal structure, while ZnO nanocolumns have a weak c-axis preferred orientation with broken stacking orders in synchrotron x-ray scattering experiments. In addition, strong free-exciton emission from the ZnO nanowalls was clearly observed in photoluminescence measurements. On the other hand, we could not observe any emission bands from the ZnO nanocolumn samples.