S. S. Islam

Fine-tuning control on CNT diameter distribution, length and density using thermal CVD growth at atmospheric pressure: an in-depth analysis on the role of flow rate and flow duration of acetylene (C2H2) gas

An optimization control has been demonstrated to obtain carbon nanotubes having specific diameter distribution, length, homogeneity, and yield during its growth by thermal chemical vapor deposition technique under atmospheric pressure. Carbon nanotubes (CNTs) were grown on silicon wafer where a predeposition of iron catalyst of 2xa0nm thickness was made by sputtering. The growth was conducted under two variable parameters, i.e., flow rate and flow duration. Argon and hydrogen mixture was used for pretreatment of catalyst and as etching gas, and acetylene as a carbon precursor. In-depth analysis shows that increase in flow rate from 10 to 50xa0sccm resulted in increase in the concentration of amorphous carbon, CNTs diameter range and decrease in length, we found best result at 20xa0sccm flow rate of acetylene gas. On the other hand, as we varied flow duration from 6 to 14xa0min, with keeping flow rate of acetylene 20xa0sccm constant, dense homogeneous growth of horizontal CNTs network plus an increase in length and diameter range were observed. An optimization of flow rate and flow duration is presented here to obtain a selective diameter distribution and length as expected by this growth technique. Atomic force microscopy, field emission scanning electron microscopy and Raman spectroscopy were used to investigate the samples’ morphologies in support of the observations made.

Effect of Growth Temperature on the Diameter Distribution and Yield of Carbon Nanotubes

Growth of carbon nanotubes (CNTs) on iron sputtered Si substrate has been done by using self design Thermal Chemical Vapor Deposition (TCVD) at atmospheric pressure. Parameters of CNTs are highly dependent on the growth temperature. A strong relation between CNT’s diameter, yield and growth temperature was found. The experiments were done in the temperature range of 750–900 °C with an interval of 25 °C. It was found that at 750 °C there was no growth of CNT. However, at 775 °C, the horizontal network of CNTs having diameter range of 8–12 nm with sufficient yield was observed. As we increase the temperature, an increase in CNT’s diameter and decrease in yield was found. These results demonstrate that diameter and yields of CNTs can be controlled with the growth temperature.

Method for determination of nature of single-wall carbon nanotubes (SWCNTs) in a bundle prepared by chemical vapor deposition technique

We present a simple method to determine the nature of single wall nanotubes (SWNTs) in a bundle prepared by chemical vapor deposition technique by resonant Raman spectroscopy. The sample is irradiated with two wavelengths 633 nm from He-Ne laser and 514.5 nm from Ar+ laser. The spectra were taken in backscattering geometry and theoretical calculation has been carried out at one peak position 216 cm−1 in RBM spectra. The results reveal that one third of the carbon nanotubes are metallic in agreement with the previously proposed reports. The geometrical and electronic properties of nanotubes are also discussed.

Reduced graphene oxide (rGO) based wideband optical sensor and the role of Temperature, Defect States and Quantum Efficiency

We report a facile and cost-effective approach to develop self-standing reduced Graphene Oxide (rGO) film based optical sensor and its low-temperature performance analysis where midgap defect states play a key role in tuning the crucial sensor parameters. Graphite oxide (GO) is produced by modified Hummers’ method and reduced thermally at 250u2009°C for 1u2009h in Argon atmosphere to obtain rGO. Self-standing rGO film is prepared via vacuum filtration. The developed film is characterized by HRTEM, FESEM, Raman, and XRD techniques. The developed sensor exhibits highest sensitivity towards 635u2009nm illumination wavelength, irrespective of the operating temperature. For a given excitation wavelength, photoresponse study at low temperature (123K–303K) reveals inverse relationship between sensitivity and operating temperature. Highest sensitivity of 49.2% is obtained at 123u2009K for 635u2009nm laser at power density of 1.4u2009mW/mm2. Unlike sensitivity, response- and recovery-time demonstrate directly proportional dependence with operating temperature. Power dependent studies establish linear relation between power-density and sensitivity, and a safe limit beyond which sample heating prolongs the recovery time. Wavelength-dependent studies shows that proposed sensor can efficiently operate from visible to near NIR region. To the best of our knowledge such rGO based optical sensor performance at low temperature had not been reported earlier.

A new approach for orientation-controlled growth of CNTs: an in-depth analysis on the role of oxygen plasma treatment to catalyst

AbstractIn this paper,n a novel and easy technique is proposed for orientation controlled growth of MWNTs. The results indicate that when CNT growth was carried over the substrate, not treated with plasma, horizontal network of MWNTs was formed. Plasma treatment to the substrate prior to CNTs growth led to formation of vertically aligned MWNTs. An in situ growth as a function of plasma treatment time reveals the mechanism behind this flip process. All experiments were performed under atmospheric pressure. At every step during time-dependent growth process, CNTs were characterized using FESEM, HRTEM, andxa0Raman spectroscopy. Iron sputtered silicon substrate was also investigated to validate the excellent formation of as-grown vertical CNTs and also to analyze the role of oxygen plasma behind the orientation-controlled growth. The as-grown CNTs over the iron sputtered silicon substrate with or without plasma treatment were characterized by FESEM and AFM. The successful orientation-controlled growth of CNTs was achieved.

Growth of SWNTs using Cu(NO3)2 and CuO a systematic study on role of oxygen in growth of CNTs

We report an another unconventional growth of dense network Single Wall Carbon Nanotube (SCNTs) and Highly aligned Carbon Nanotubes using Cu(NO3)2 and CuO as catalyst. A systematic study for effects of oxygen on catalytic quality of Copper and on CNTs growth also studied. All reactions are performed in atmospheric pressure in thermal CVD chamber. The CNTs are characterized using HRSEM and micro-Raman. The ID/IG ratio and RBM peaks in raman spectra shows that grown CNTs are less defective SWNTs.

Investigation of effects produced by chemical functionalization in single-walled and multi-walled carbon nanotubes using Raman spectroscopy

Single-wall carbon nanotubes (SWNTs) as well as multi-wall carbon nanotubes (MWNTs) were characterized by Raman spectroscopy to observe the changes in their physical and structural properties on functionalization. When SWNTs or MWNTs are chemically treated, the defects are created. The analysis of radial breathing mode (RBM) showed that the diameter of the single wall carbon nanotubes changed after functionalization. In the carboxylated sample, the intensity of the disordered band (D-mode) increased more than in the pristine samples. The increase in the D-band intensity in SWNTs after functionalization can be attributed to carbon atoms excited from sp2 to sp3 hybridization. A higher intensity ratio in D-and G-mode (ID/IG) was observed after functionalization with carboxylic group (COOH). The intensity ratio ID/IG increased on acid treatment which was evident from the Raman spectra and their analysis. In case of MWNTs, the intensity of D band became equal to the intensity of G band, which was due to the huge number of defects that had been introduced in the sidewalls. Moreover, it was found in this study that the MWNTs can be much easier chemically functionalized than SWNTs under the same physical conditions.

Fabrication of SWCNTs Based Flexible, Trace Level NO2 Gas Sensor Using Spray Coating Technique

Flexible nitrogen dioxide (NO2) sensor using thin-film single-walled carbon nanotubes (SWCNTs) was fabricated by spray coating on Polyethylene terephthalate (PET) substrate. The SWCNTs dispersed in deionized water using sodium dodecyl sulphate (SDS) as the surfactant. The uniformly dispersed SWCNTs were deposited on the PET film by using spray gun, and then SDS surfactant was removed from the sample for its proper gas sensing. This was done by dipping the sample into the HNO3 and then washing with the deionized water followed by heat treatment at 110 °C for 1 h. The resultant devices were tested for sensing NO2 molecules and a trace level NO2 sensing was detected. The sensing mechanism was attributed by the electron transfer to the SWCNTs, as a result, the NO2 reduced on the nanotube surface.