Effect of pyrolyzing time and temperature on the bandgap of camphor-pyrolyzed semiconducting carbon films (original) (raw)
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Semiconducting carbon films from a natural source: camphor
Diamond and Related Materials, 1999
Thin films of carbon have been grown on alumina substrates by the pyrolysis of camphor at 900°C for 2 h in an argon atmosphere, followed by sintering for various time periods. The effect of sintering time on the surface morphology, conductivity, carrier concentration, mobility and bandgap of camphor-pyrolyzed films is discussed. Structural characterizations are performed on the basis of XRD and SEM analyses. Electrical conductivity measurements of these films, as a function of temperature, suggest them to be semiconductors. Hall-effect study of the as-grown films shows their carrier concentrations to be of the order of 1017 cm−3. The Hall mobilities of these films are found to vary from 1702 to 10263 cm2 V−1 s−1. The thermal bandgaps of these films are found to decrease with increasing sintering time. Thus, by controlled sintering of camphor-pyrolyzed carbon films, it is possible to obtain a semiconductor with the desired bandgap. Therefore, camphor-pyrolyzed semiconducting carbon films seem to be a promising material to develop a photovoltaic solar cell.
Electrical and optical properties of semiconducting camphoric carbon films
Current Applied Physics, 2002
In situ variation in resistance of camphoric carbon versus time of pyrolysis, temperature of pyrolysis and effect of sintering are studied to perceive the time required for the completion of pyrolysis and the activation energy from the electrical conductance plot. Variation in the electrical conductance versus temperature and activation energies derived from these measurements, are reproducible when film is thermally treated below 750°C. Thermal treatment above 750°C changes the anatomy of the film causing a change in the conductance profile as well as decreases its band gap to 0.1 eV. Camphor pyrolyzed at 650°C gives semiconducting carbon with optical band gaps 1 eV (direct) and 0.8 eV (indirect). Increase in pyrolysis temperature also shifts G-band of Raman spectrum from 1605 to 1586 cm À1 i.e., towards value corresponding to graphitic carbon. SEM micrograph of camphoric film shows absence of any carbon nanobeads or fibers as normally observed with camphoric carbon pyrolysed in this temperature range.
Synthesis and analysis of thin conducting pyrolytic carbon films
Carbon, 2012
We report on an adjustable process for chemical vapour deposition of thin films of pyrolytic carbon on inert substrates using an acetylene feedstock. Through modification of the reaction parameters control over film thickness and roughness is attained. These conducting films can be deposited in a conformal fashion, with thicknesses as low as 5 nm and a surface roughness of less than 1 nm. The highly reliable, cost effective and scalable synthesis may have a range of applications in information and communications technology and other areas. Raman and X-ray photoelectron spectroscopies, as well as high resolution transmission electron microscopy are used to investigate the composition and crystallinity of these films. The suitability of these films as electrodes in transparent conductors is assessed through a combination of absorbance and sheet resistance measurements. The films have a resistivity of ~ 2 × 10 -5 m but absorb strongly in the visible range. The electrochemical properties of the films are investigated and are seen to undergo a marked improvement following exposure to O 2 or N 2 plasmas, making them of interest as electrochemical electrodes.
Characteristics of carbon films prepared by thermal chemical vapor deposition using camphor
Thin Solid Films, 2014
The properties of carbon films prepared by thermal chemical vapor deposition (thermal CVD) using camphor are investigated. As the deposition temperature increases from 1098 to 1198 K, the deposition rate follows the Arrhenius law with activation energy of 59.8 kJ/mol. The possible reaction paths and intermediate species of this thermal CVD process are also considered. The product gases CH 3 , CH 4 , and C 2 H 2 can be speculated as the main species for pyrolytic carbon deposition. The crystallinity and ordering degree of carbon films decrease with increasing the deposition temperature. Nevertheless, the sp 2 carbon sites increase with increasing the deposition temperature, and results in the decrease of electrical resistivity and the increase of water contact angle. When the camphor weight changes from 0.06 to 0.50 g, the CVD reaction is controlled by a process of half order. Moreover, as the camphor weight increases from 0.30 to 0.50 g, the surfaces of carbon films are partially covered with spherical particles, the water contact angle substantially increases. Finally, the results of this work are compared to those of using CH 4 and C 2 H 2 as the precursor gases.
Surface studies of carbon films from pyrolyzed photoresist
Thin Solid Films, 2001
Positive and negative photoresists, which are commonly used in the semiconductor industry, were deposited on silicon wafers by spin coating and then pyrolyzed at temperatures of 600-11008C in an inert environment to produce thin carbon films. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy involving current-sensing atomic force microscopy (CS-AFM) were utilized to characterize the properties of the carbon films. Raman spectroscopy showed two broad bands at approximately 1360 cm and 1600 cm , which deconvoluted to four Gaussian bands. The origin of these bands is y1 y1 discussed. CS-AFM showed that the surface conductance increased with increased pyrolysis temperature, and the results are consistent with measurements by a four-point probe method. The XPS spectra revealed the presence of oxygen functional groups (C_O and CO) on the carbon surface. The relative fraction of oxygen, OyC ratio, decreased as the pyrolysis temperature increased, in agreement with published results. The full-width at half-maximum of the C peak obtained by XPS also decreased 1s with increasing pyrolysis temperature.
Thermal conductivity of monolithic synthetic hard carbons as a function of pyrolysis temperature
Amorphous carbon samples with a total porosity of about 85% were synthesized via pyrolysis of sol-gel derived resin precursors. Since the pores in the samples investigated have dimensions of a few tens of nanometers only, the gaseous contribution to the thermal conductivity is largely suppressed at ambient pressure. Values for the total thermal conductivity as low as 0.054 W(mK) -1 at 300°C are detected. However, the pyrolysis temperature has a great impact on the contribution of the solid backbone to the total thermal conductivity. From the same precursor a series of samples was prepared via pyrolysis at temperatures ranging from 800 to 2500°C. The thermal conductivity of this series of carbons at 300°C under vacuum increases by a factor of about 8 if the pyrolysis temperature is shifted from 800 to 2500°C. To elucidate the reason for this strong increase the infrared radiative properties, the electrical conductivity, the macroscopic density, the microcristallite size, the sound ve...
Pyrolytic Carbon Electrodes and Their Potential Application in Electrochemical Sensors
Communications in Physics, 2022
In this work, pyrolytic carbon electrodes were prepared through pyrolysis of wellpatterned AZ 1505 positive photoresist films. The designed electrodes firstly were prepared via photolithography technique, then the polymer was thermally broken-down into carbon skeletons in an oxygen-free environment using pyrolysis technique. The effect of the highest temperature and ramping rate on the electrical properties of the carbon films were investigated. The results show that the pyrolysis process was optimal at the ramping rate of 3˚C/minute, annealing temperature of 900˚C, and annealing time of one hour. The lowest resistivity was obtained at 6.3 × 10 −5 Ωm for pyrolytic films prepared at the optimal pyrolysis conditions. Electrochemical measurements confirm the potential of this electrode for electrochemical sensing applications.
Carbon, 2010
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There is an increasing demand for semiconducting gas sensors for several monitoring applications that have sensitivity, selectivity and reliability on a long-term scale. In this paper, we have described the preparation of SnO ᎐Au thin film sensors by 2 the RGTO technique; these sensors have proved to be capable of sensitive and selective detection of CO. The TEM and AES analysis showed that 6 months of sensor aging at 400ЊC did not produce any valuable rearrangement of gold atoms onto a tin dioxide surface. Most of the sensor resistance variation was observed during the first 20 days, and a limited drift was observed in the remaining period. ᮊ