Papers by Keyword: Amorphous Carbon

Abstract: The a-C/a-C:B homojunction of palmyra sugar has been successfully fabricated using the nanospray method. Palmyra sugar was chosen as the main source of carbon because it is cheap, renewable, abundant and available around the clock. nanospray is used as a deposition method on glass ITO substrates because of several advantages, namely cheap, easy, portable, low power consumption, the deposited layer is more evenly distributed and thinner. Junction samples when in bright conditions [emitted light] showed an increase in current and voltage values ​​compared to dark conditions. Testing the current and voltage of the junction sample shows the characteristics of a rectifier diode. This confirms the results of the test using PES as a doping process with amorphous carbon with boron capable of changing the conduction type from a-C from an intrinsic semiconductor to a p-type semiconductor. Testing the junction sample when irradiated with visible light using a lamp shows symptoms of the photovoltaic effect. Tests directly on the sun when conditions AM 1.5 samples showed symptoms of the photovoltaic effect. This indicates that the a-C/a-C:B amorphous carbon homojunction junction sample functions as a solar cell.

Abstract: X-ray reflectivity technique is applied in evaluation of deposition of multilayer thin film fabrication process. Amorphous silicon carlbide (SiC) and carbon (rGO) was deposited alternatively on a glass substrate. Via X-ray reflectivity, every layer deposited can be analyzed, thus every flaws in defected layer can be figure out. This paper will explain further throughout the evaluation process. Deposition process carried out by radio frequency (RF) magnetron sputtering of 99% purity of silicon carbide (SiC) and carbon (C) as a target. Implementation of X-ray reflectivity technique had proven in fabricating better quality of thin film.

Abstract: Amorphous carbon (a-C) film is a unique material that attracts the attention of scientists to be investigated. Nitrogen- and boron- doped amorphous carbon (a-C:N and a-C:B) have been deposited on ITO glass substrates by using nanospray method. Palmyra sugar is heated at temperature 250^o C for 2.5 hours to obtain a-C. Boric acid (H₃BO₃) and amonium hidroxide (NH₄OH) are used as the sources of boron doping and nitrogen doping. a-C:N and a-C:B are made by the variations of mole ratio for doping and amorphous carbon, that are 1:15 and 1:20. Then, these samples are dissolved into mixed dymethyl sulfoxide (DMSO) and aquades. The exfoliation process of samples has been done by applying ultrasonic cleaner for 2 hours and also centrifugated at 4000 rpm for 45 minutes. Electrical conductivity and band gap are measured by using four point probe and UV Vis. The results show that electrical conductivity increases but band gap decreases than pure a-C. Furthermore, the larger mole ratio of a:C-N and a-C:B also increases conductivity and decreases band gap, resulting between 5.5×10^-1S/cm – 6.1×10^-1 S/cm and 1.43 eV – 1.71 eV.

Abstract: Amorphous carbon films have been explored and used in a wide variety of applications. With the n-type and p-type amorphous carbon film, it can be used to make p-n junctions for solar cells. This research aims to study the structure of boron- and nitrogen-doped amorphous carbon (a-C:B and a-C:N) films. This research uses the basic material of bio-product from palmyra sugar to form amorphous carbon. Amorphous carbon was synthesized by heating the palmyra sugar at 250°C. The results of XRD showed that the doped films produce an amorphous carbon phase. PES was used to analyze the bonding state of dopants in the sample. B₄C, BC₃, and BC₂O bonds formed in a-C:B, while pyridine and pyrrolic formed in a-C:N.

Abstract: Thin films of amorphous carbon have successfully been fabricated by radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD). Carbon film fabrication with a methane gas (CH₄) source has been fabricated with deposition parameters: 15 Watt of RF power, 13.5 MHz of frequency, 100 °C of substrate temperature, 450 m Torr of pressure and 120 minutes of deposition time. Methane gas flows were 40, 60, 80 sccm, respectively. Thin film can be in the form of DLC, Graphite or Amorphous Carbon depending on the ratio of hybridized orbitals of sp³, sp² and sp. The X-ray diffractrometry (XRD) show the amorphous phase of the thin film has been formed. Further analysis using Fourier transform infrared (FTIR) combined with synchrotron photoemission spectroscopy (PES) showed that the sp³ hybridization was more dominant than sp². This gives an indication that as fabricated thin films are tetrahedrally amorphous carbon (ta-C). Keywords: Amorphous carbon, methane gas, thin film.

Abstract: The amorphous carbon (a-C) thin films have been developed by many researchers due to many superior properties. The aim of this research to study the structure of amorphous carbon thin film. Amorphous carbon was successfully prepared by carbonization of up to 200°C. Organic compounds that used in this research were coconut sap and its derivatives. The variation used in this research was a calcinating temperature ranging from 250°C, 400°C, and 600°C. Amorphous carbon powder was then mixed with aquades. Exfoliation process has been applied using an ultrasonic cleaner for 2 hours and then centrifuged at 4000 rpm for 30 minutes. Deposition technique used in this research was spin - coating. The X-ray diffraction pattern shows that the carbonization process produces amorphous carbon phase at diffraction angle of 2θ =15-30°. The infrared absorbtion in the region 500 to 4000 cm^-1 was resolved into several peaks, which were assigned to C ̶ H, C ̶ O, C ̶ C, C=C and O ̶ H bonding. Photo Emission Spectroscopy (PES) was used to measure the percentage of sp² and sp³ configuration in the sample. From the PES data, the percentage of sp² configuration of coconut sap heated at 400°C is 55.32%. Four-point probe method was also used to measure the conductivity and band gap of each material, resulting in 2.67 – 8.33 S/m and 0.15 – 0.49 eV respectively.

Abstract: The effects of temperature and graphite-like structure additive on the graphitization process of amorphous carbon were investigated through molecular dynamics simulation. The molecular models of amorphous carbon and graphite-like structure-amorphous carbon were constructed with the initial density of 1.62 g/cm³ and carbon atoms number of 4096 by rapid quenching method. After annealing treatment at 3200 K, 3600 K and 4000 K respectively, the evolution rules of sp² C atoms and the instantaneous conformations of the graphite-like structure-amorphous carbon system were analyzed to investigate the effects of temperature and graphite-like structure on the graphitization process. It could be found that increasing graphitization temperature properly could improve graphitization degree of amorphous carbon. Addition of graphite-like structure could promote recrystallization of the irregular carbon atoms in amorphous carbon materials, thus accelerating graphitization process and promoting graphitization of the system.

Abstract: Hard multilayer coatings are technologically promising materials for reducing wear of tribological parts. Multilayer coatings with a systematic alternation of the pair [(TiC_x/Ti/C)÷(a-C)] were deposited on stainless and tool steel by the PVD technique. Hardness (H), elasticity modulus (E) and critical cracking load (P_cr) were determined by the nanoindentation method. Nanofrictional wear test was conducted under multipass sliding of a diamond indenter (Ø 50 nm) under constant load. The specific coefficient of nanofrictional wear of [(TiC_x/Ti/C)÷(a-C)]_n with different composition of titanium-containing layers was determined. The nanofrictional wear rate of [(TiC_x/Ti/C)÷a-C]_n depends on the elastic and plastic characteristics of multilayer coating as a whole. Coatings having H³/E² > 0.12 and P_cr > 58 mN demonstrate low wear rate.

Abstract: A focus point in this work was the research of the influence of deposition condition on properties of CrAlC films. CrAlC films were deposited by arc sputtering technique using arc sputtering of Cr-Al target and pulse arc sputtering of graphite target at different frequency. The multilayer [(CrAlC)+(a-C)]_n coatings were also obtained and investigated. Multilayer [(CrAlC)+(a-C)]_n were deposited with a systematic alternation of the pair [(CrAlC)+(a-C)], where a-C is the amorphous carbon layer. The structure, mechanical properties and fracture toughness of CrAlC films depend on pulse frequencies of the graphite sputtering. With increasing pulse frequency, the film structure changes from uniformly amorphous to amorphous with nanograins, the hardness of the films increases, the critical load of crack formation and film peeling tend to decrease. It is shown that a decrease in the thickness of the layers in [(CrAlC)+(a-C)]_n leads to an increase in the crack resistance.

Abstract: Organic/inorganic hybrids composites type have been reported as an alternative for the preparation of multifunctional materials with superior properties to those of individual constituents. In this work, hybrid composites of semiconductor oxides with amorphous carbon (C/ZnO and C/TiO₂) were synthesized by partial pyrolysis method and characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD patterns showed the presence of crystalline diffraction lines overlaid by diffraction halos. Infrared spectra showed bands associated to the stretching of Zn-O and Ti-O bonds, as well as bands assigned to the stretching vibrations of C-O, C=O and C-H. Micrographs showed the formation of organized structures in the shape of plates and agglomerates of particles. Structural characterizations showed that the composites present the characteristics of the pristine semiconductors as well of the amorphous carbon matrix, showing a great synergism between C/semiconductor.