Yoyok Cahyono

Preparing Fe3O4 Nanoparticles from Fe2+ Ions Source by Co‐precipitation Process in Various pH

Magnetite ( Fe 3 O 4 ) nanoparticles were synthesized from the Fe 2+ ions in the form of ferrous chloride tetrahydrate ( FeCl 2 .4 H 2 O ) by coprecipitation method at low temperature (⩽70 ° C ). During the precipitation process pH was kept constant at 7.37, 8.07, 9.12, 10.37 and 10.55 respectively. It was found that the magnetite nanoparticles was formed as a result of the dehydration reaction of ferrous hydroxide and ferric oxyhydroxide, in which the latter compound was produced by the partial oxidation of ferrous hydroxide by O 2 in dissolved air during the synthesis. The X‐ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to characterize these resulted particles. The average crystalline size of Fe 3 O 4 was obtained in the range between 18–55 nm for the corresponding range of pH used in the process. These results show that the pH of precipitation and the valence of the metal salt used in the synthesis have played an important role in influencing the particle size.

Synthesis of amorphous carbon from bio-products by drying method

Amorphous carbon (a-C) has extensively been studied in the last two decades due to many superior properties. Amorphous carbon was successfully prepared by carbonization of organic compounds exposed up to 200°C. Organic compounds that used in this research were coconut sap, lontar palm sap and their derivatives. The X-ray diffraction pattern shows that carbonization of organic compounds produce amorphous carbon phase at 2θ =20°. The infrared absorption in the region from 500 to 4000 cm-1 were resolved into several peaks, which were assigned to C-H, C=C, C-O, C=O and O-H. Four point probe method was also used to measure the conductivity and band gap of each material, resulting in 1.73 – 29.6 S/m and 0.08 – 0.49 eV respectively.Amorphous carbon (a-C) has extensively been studied in the last two decades due to many superior properties. Amorphous carbon was successfully prepared by carbonization of organic compounds exposed up to 200°C. Organic compounds that used in this research were coconut sap, lontar palm sap and their derivatives. The X-ray diffraction pattern shows that carbonization of organic compounds produce amorphous carbon phase at 2θ =20°. The infrared absorption in the region from 500 to 4000 cm-1 were resolved into several peaks, which were assigned to C-H, C=C, C-O, C=O and O-H. Four point probe method was also used to measure the conductivity and band gap of each material, resulting in 1.73 – 29.6 S/m and 0.08 – 0.49 eV respectively.

Reduced energy bandgap of a-Si:H films deposited by PECVD at elevating temperatures

The hydrogenated amorphous silicon (a-Si:H) films with the thickness of several hundreds nanometer have successfully been grown on the glass substrates by plasma enhanced (PE) chemical vapor deposition (CVD), employing SiH4 gas with H2 dilution. The deposition temperatures being set from 150°C up to 250°C was intended to induce nanocrystalline clusters in the amorphous structure, to reduce dangling bond and to recover defect states in the gap, in order to obtain films with reduced energy band gap. The X-ray diffractometry, UV-Vis spectrometric and atomic force microscopic examinations were conducted to structurally study the samples. The reduction of energy bandgap from 1.89 eV down to 1.03 eV was obtained from the deposited films.

Annealing treatment of a-Si:H films deposited by PECVD and their properties

The hydrogenated amorphour silicon (a-Si:H) films have been grown on the glass substrates by plasma enhanced chemical vapor deposition (PE-CVD) employing silane (SiH4) with hydrogen (H2) dilution. The as – deposited films were then annealed at various temperatures of 200, 300 and 400°C for 30 minutes. Annealing process at 300°C was also performed for 60 and 90 minutes. Examinations using X-ray diffractometry, infrared and UV-Vis spectroscopy demonstrated that the annealed films show an increasing crystalinity of 3.26 – 6.80% and reduced dangling bond content down to more than one order of magnitude (from 2.3 × 1019 to 1.2 × 1018 cm−3). Meanwhile, the energy bandgap and Urbach energy of the films are around 1.71 – 1.75 eV and 0.21 – 0.27 eV respectively.

Synthesis and Photoluminesence Study of Reduced Graphene Oxide (rGO)/ZnO for Solar Energy Absorbing Materials

Materials combining reduced graphene oxide (rGO) from coconut shells and commercial ZnO have been synthesized by dry-mixing in weight ratio of 1:2, 2:2, and 3:2. For photoluminesence (PL) characterization, the solutions with concentration of rGO/ZnO in aquadest up to 0.003 mg/mL were prepared. The absorbing photon energy by the samples at wavelength 280-426 nm (ultraviolet-purple) has induced electron transition to conduction band. Further, the returning electron to valence band was followed by photon emission at wavelength of 530-880 nm (green-infrared). The PL intensity was observed to drastically enhance with increasing content of rGO in the solution by 252.5%, 285.0% and 291.3% for the corresponding samples compared to the solution containing pure ZnO. The rGO/ZnO materials exhibit higher absorbance with wider wavelength range, and therefore can potentially be used as solar energy absorbing materials to enhance the efficiency of solar cell.

Preparing Fe3O4Nanoparticles from Fe2+Ions Source by Co‐precipitation Process in Various pH

Magnetite ( Fe 3 O 4 ) nanoparticles were synthesized from the Fe 2+ ions in the form of ferrous chloride tetrahydrate ( FeCl 2 .4 H 2 O ) by coprecipitation method at low temperature (⩽70 ° C ). During the precipitation process pH was kept constant at 7.37, 8.07, 9.12, 10.37 and 10.55 respectively. It was found that the magnetite nanoparticles was formed as a result of the dehydration reaction of ferrous hydroxide and ferric oxyhydroxide, in which the latter compound was produced by the partial oxidation of ferrous hydroxide by O 2 in dissolved air during the synthesis. The X‐ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to characterize these resulted particles. The average crystalline size of Fe 3 O 4 was obtained in the range between 18–55 nm for the corresponding range of pH used in the process. These results show that the pH of precipitation and the valence of the metal salt used in the synthesis have played an important role in influencing the particle size.

Preparing Fe[sub 3]O[sub 4] Nanoparticles from Fe[sup 2+] Ions Source by Co-precipitation Process in Various pH

Magnetite ( Fe 3 O 4 ) nanoparticles were synthesized from the Fe 2+ ions in the form of ferrous chloride tetrahydrate ( FeCl 2 .4 H 2 O ) by coprecipitation method at low temperature (⩽70 ° C ). During the precipitation process pH was kept constant at 7.37, 8.07, 9.12, 10.37 and 10.55 respectively. It was found that the magnetite nanoparticles was formed as a result of the dehydration reaction of ferrous hydroxide and ferric oxyhydroxide, in which the latter compound was produced by the partial oxidation of ferrous hydroxide by O 2 in dissolved air during the synthesis. The X‐ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to characterize these resulted particles. The average crystalline size of Fe 3 O 4 was obtained in the range between 18–55 nm for the corresponding range of pH used in the process. These results show that the pH of precipitation and the valence of the metal salt used in the synthesis have played an important role in influencing the particle size.