Papers by Keyword: Raman Spectroscopy

Abstract: Large area epitaxial graphene (EG) layers are synthesized on 6H-SiC (0001) by annealing at 1500 °C for 5 min in a closed graphite chamber at low vacuum of 10-3 mbar and its 2D band in Raman spectra can be satisfactorily fitted by a single Lorentzian. From Raman spectroscopy, measurements indicate that too high growth temperature is to the disadvantage of the formation of graphene. The results of atomic force microscope (AFM) and field-emission scanning electronic microscope (FE-SEM) reveal the surface morphology of graphene is related with its growth temperature.

Abstract: Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO₃/H₂O₂. This strong oxidizing agent HNO₃/H₂O₂ removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm^-1 corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm^-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm^-1) has been minimized after purifying CNTs with HNO₃/H₂O₂ for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

Abstract: Comparative studies of two multi-walled carbon nanotubes (MWCNT) from different manufacturers were reported. The purification and functionalization of commercial multiwall carbon nanotubes were investigated. MWCNTs were treated with boiling concentrated HNO3 under a reflux condenser for 2 hours at 100 °C in order to purify and oxidize the raw material. The oxidized MWCNTs were rinsed with deionized water until stabilization of the filtrate pH. The measurement technique was by thermogravimetric analysis (TGA) for thermal analysis decomposition products. Meanwhile, the chemical shifted in MWCNTs can be determined by using Raman Spectroscopy.

Abstract: Nanostructured Porous Silicon templates (NPSiT) were prepared by photo-electrochemical anodization of p-type crystalline silicon in HF electrolyte at different etching time. Five samples were prepared with etching time varied from 10 to 50 minutes at 20 mA/cm2 of current density. The effects of etching time on NPSiT were observed based on nanocrystallite size, photon energy and surface distribution. These studied was demonstrated by Raman spectroscopy, photoluminescence (PL) and Fourier transforms infrared spectroscopy (FTIR). It was found that NPSiT sample with large pore diameter, which is smaller nanocrystallites size of Si between pore. The optical properties of NPSiT were investigated by photoluminescence (PL) and PL peak broadening and shifting towards higher energy can be observed with increasing etching time. The optimum etching time with respect to PL intensity was obtained at 30 minutes, for which uniform pores and a shift of the PL maximum to a higher energy of 1.9 eV is observed.

Abstract: The correlation of Diamond-Like Carbon (DLC) bonding structure versus film corrosion protective capability against Hydrofluoric (HF) acid exposure was made. Raman analysis of DLC films that were subjected to repeated thermal cycle heating showed that were more clustering in sp² sites upon exposure to high temperature and increasing time. When these films were subsequently exposed to HF acid, there was also corresponding increase in the amount of pitting corrosion features. The increase in sp² clustering size is seen as a weak point in the overall DLC structure which subsequently allowed the acid to penetrate the film structure.

Abstract: Diamond-like carbon (DLC) films were deposited on magnetic recording head by Filtered Cathodic Arc (FCA) technique and a-Si base material was ion beam deposited as seed layer. To investigate the thermal stability of stack film, repeated cycle thermal heating at 200 °C was employed. Raman spectroscopy and nanoindenter (Hysitron) were performed to understand film structure and mechanical property as a function of thermal heating conditions. The roles of heating in material composition and wear behavior of DLC films are discussed. The Raman spectra revealed that G position, FWHM of G peak and Id/Ig change as with increasing heating cycle which agreed well with wear depth measured. With these results suggesting DLC film degraded with repeated heating at 200 °C.

Abstract: In this paper, carbon nanotubes on porous silicon substrate were developed in order to get high quality nanotubes for various kind of application. CNTs were deposited on porous silicon nanostructures (PSiN) at 750 0C on porous silicon by using double-furnace thermal chemical vapor deposition technique. Align carbon nanotubes with diameters of 15 to 30 nm were successfully synthesized on a porous silicon substrate. In this system, carbon nanotubes were grown directly on the p-type porous silicon surface at 750 0C for a total time of 30 minutes. The samples were characterized using field emission scanning electron microscopy and micro-Raman spectroscopy. Align carbon nanotubes (ACNTs) bundle with uniform diameter (~20 nm) were found grown on porous silicon at certain area. Based on micro-Raman spectroscopy result, the peak of silicon at ~520 nm and peak of carbon nanotube (around 1 300 to 1 600 nm) was detected.

Abstract: In this paper, carbon nanotubes were characterized by several characterization methods such as FESEM (field emission scanning electron microscopy), Raman spectroscopy and fourier transform infrared (FTIR) spectroscopy. FESEM is used to characterize the morphology of carbon nanotubes, the structural is characterize by raman spectroscopy and bonding characteristic is determine by FTIR. The morphology of CNTs is found to be multiwall carbon nanotubes with diameter around 30-50 nm. D-peak was observed at 1341 Cm-1 and G-peak at 1575 Cm-1 based on raman spectroscopy result. The chemical bonding observed at range 2400 - 400 from FTIR spectra. These CNTs will be used for in vitro study in future.

Abstract: Nanostructured porous silicon templates (NPSiT) were prepared by photo-electrochemical anodization of p-type crystalline silicon in HF electrolyte at different etching time. Two set anodisation parameter were observed, anodisation time nd current density applied. For set one, five samples were prepared with etching time varied from 10 to 50 minutes at 20 mA/cm2 of current density. For set two, five samples were prepared with current density varied from 5 to 40 mA/cm2 for 30 minutes. The effects of these anodisation parameter on NPSiT were observed based on nanocrystallite size. These studied was demonstrated by Raman spectroscopy. It was found that NPSiT sample with large pore diameter, which is smaller nanocrystallites size of Si between pore.

Abstract: Iodine doped amorphous carbon (a-C: I) thin films were prepared by using Thermal Chemical Vapor Deposition (CVD) with deposition temperature ranging from 5000C to 7000C. The physical and electrical properties of deposited a-C:I thin films were characterized by Raman spectroscope and Solar Simulator system. The presence of 2 peaks known as Raman D peaks and Raman G peaks ensure the amorphous structure of carbon (C). As deposition temperature increase, the ID/IG ratio shows difference value, which indicates the effects of the temperature towards the a-C: I structures. An ohmic graph was obtained for the IV measurement, and the conductivity varies from 10-4 to 101 Scm-1. The photoresponse was also determined for all samples. As a reference, an undoped a-C thin film was prepared to differentiate the characteristic between a-C and a-C: I.