Papers by Keyword: Thermal Annealing

Abstract: Graphene, as a typical zero band gap material, possesses excellent electrical conductivity and mechanical property, but is hardly applied in functional field directly. Hence, how to effectively modify the energy structure of graphene and apply it as functional material in physical signal sensing, information processing and energy management has become a widely attentional research field in recent decades. In this work, a two-dimensional (2D) organic molecular named 5, 10, 15, 20-tetra (4-aminopyenyl) porphyrin is selected to in-situ crosslink with graphene oxide (GO), and the nitrogen-doped graphene (NG) film is prepared through further graphitization. In this paper, the influence of the content of porphyrin molecular on the microstructure and nitrogen content of the NG film is mainly discussed. With the increasing of porphyrin content, the layer space of GO film rises gradually and the GO nanosheets are laid out more smoothly. After graphitization, nitrogen element is well preserved inside the NG film, and the electrical conductivity and Seebeck coefficient is greatly improved. Taking advantage of these properties, a NG film-based temperature sensor is prepared.

Abstract: We present an epitaxy-based approach for designing a 3C-SiC Capacitive Micromachined Ultrasonic Transducer (CMUT). The design requires to consider a 3C-SiC/Si/3C-SiC heterostructure on a Si substrate. This implies to address different growth steps of SiC on Si and Si on SiC. We present some specific growth related issued, namely the control of selectively grown Si on a masked SiC(100) and the further regrowth of 3C-SiC on a Si (110) layer. The final release of the SiC membrane, to define a CMUT, is also addressed using a simple thermal treatment allowing to suppress several technological steps.

Abstract: Metalloporphyrin-based nanostructures were fabricated on 3-aminopropylmethoxysilane-modified indium tin oxide (ITO) surface. UV-visible spectroscopy and cyclic voltammetry are used for investigating electronic absorption spectra and catalytic activity in oxygen reduction reactions as alternative cathode electrochemical catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Using of 5,10,15,20-tetrakis-(4-amiophenyl)-porphyrin-Co (II) as a building block and 1,4-phenylene diisocyanate as a linker, the mixed toluene/chloroform solution-based layer-by-layer process can produce linear growth of 5,10,15,20-tetrakis-(4-amiophenyl)-porphyrin-Co (II) up to 30 layers through urea bonds. The vacuum thermal annealing process demonstrated the improvement of catalytic activity in oxygen reduction reaction.

Abstract: This work describes the development of a new post-implant crystal recovery technique in 4H-SiC using XeCl (l=308 nm) multiple laser pulses in the ns regime. Characterization was carried out through micro-Raman spectroscopy, Photoluminescence (PL), Transmission Electron Microscopy (TEM) and outcomes were than compared with 1h thermally annealed at 1650-1770-1750 °C P implanted samples (source implant) and P and Al implanted samples for 30 minutes at 1650 °C (source and body implants). Experimental results demonstrate that laser annealing enables crystal recovery in the energy density range between 0.50 and 0.60 J/cm². Unlike the results obtained with thermal annealing where stress up to 172 Mpa and high carbon vacancies (V_c) concentration is recorded, laser annealing provides almost stress free samples and much less defective crystal avoiding intra-bandgap carrier recombination. Implant was almost preserved except for step-bouncing and surface oxidation phenomena leading to surface roughening. However, the results of this work gives way to laser annealing process practicability for lattice damage recovery and dopant activation.

Abstract: The scratch damage that caused the generation of double Shockley stacking faults (DSFs) in heavily nitrogen doped 4H-SiC crystal was investigated quantitatively. Scratch tests were carried out on 4H-SiC substrates with a nitrogen concentration of 2.6 × 10¹⁹ cm^-3. A residual tensile stress of 40 MPa was detected around the scratch loaded at 30 mN with a diamond tip. DSFs were generated from this scratch by annealing at 1100°C for 2 h in Ar atmosphere. After annealing, the residual stress around the scratch was reduced to a tensile stress of 10 MPa. This result suggests that the reduction of residual stress around the scratch coincided with the formation of DSFs.

Abstract: In this work, we have studied the crystal defectiveness and doping activation subsequent to ion implantation and post-annealing by using various techniques including photoluminescence (PL), Raman spectroscopy and transmission electron microscopy (TEM). The aim of this work was to test the effectiveness of double step annealing to reduce the density of point defects generated during the annealing of a P implanted 4H-SiC epitaxial layer. The outcome of this work evidences that neither the first 1 hour isochronal annealing at 1650 - 1700 - 1750 °C, nor the second one at 1500 °C for times between 4 hour and 14 hour were able to recover a satisfactory crystallinity of the sample and achieve dopant activations exceeding 1%.

Abstract: Vertically aligned anatase TiO2 nanotubes (NTs) were fabricated by anodization of a pureTi foil in ethylene glycol solutions containing different concentrations of deionized (DI) water. Themorphology, elemental composition, and crystallization of TiO2 nanostructures were analyzed byfield emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Ramanspectroscopy, and X-ray spectroscopy (XPS), respectively. The diameter and length of TiO2 NTswere controlled by varying concentrations of DI water. Furthermore, we found that TiO2 NTs in DIwater 12 wt. % was suitable for further applications in UV photodetector due to it has a high volumeto surface area ratio and long tube. TiO2 NTs have a high potential in various applications such as UVphotodetectors, gas sensor, dye sensitized solar cells, and photocatalysts.

Abstract: The aim of this study is to show the possibility to control structural and optical properties of Au nanoparticles (AuNPs) by changing their size and concentration and make comparison between methods of their formation. 1.4 nm thick Au films were formed on borosilicate glass substrates by the vacuum evaporation method. AuNPs were formed on the surface of the substrate by two methods. First is the irradiation by the Nd:YAG laser pulses with intensities from 75 to 180 MW/cm². Second is thermal annealing, at temperature T=400 °C and the time of curing was varied from 24 to 72 hours. The irradiation of Au film by laser leads to formation of AuNPs. The increase of intensity of laser radiation causes the disappearing of small Au nanoparticles and growing of big nanoparticles from 113-180 nm due to the agglomeration of small particles into big ones and, correspondingly, concentration of particles decreases. In contrast, thermal annealing at T=400 °C from 48 to 72 hours leads to the island formation with the non-spherical shape and their dividing into several islands according to the spinodal dewetting model. As a result, the mean diameter of AuNPs is decreased from 161 to 85 nm but concentration increases.

Abstract: The expansion behavior of double Shockley stacking faults (DSFs) was investigated in heavily nitrogen doped 4H-SiC crystals at high temperatures up to 1350°C. An immobilization phenomenon of partials surrounding DSFs was discovered by a thermal annealing at temperatures over 1275°C. The electric properties of SiC crystal were maintained after the partial dislocations were immobilized with a high temperature annealing. The mobile partial dislocations extended straight, but the immobile ones bent toward the glide direction. This immobilization phenomenon is significant and useful for achieving low-resistance SiC substrates without DSFs.

Abstract: We synthesized a reduced graphene oxide (r-GO) multi-walled carbon nanotube (MWCNTs) nanocomposite film via layer by layer (LBL) assembly. This structure was prepared by vacuum filtration and heat-treated at a low temperature of 500°C. The morphology of the sample was determined by field emission electron spectroscopy (FE-SEM). The structural detail and the chemical analysis were characterized by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The cyclic voltammetry (CV) curve of r-GO/MWCNTs nanocomposite appeared nearly rectangular in shape. The current density (A/g) was gradually increased by increasing the scan rate of the voltage, as high as a scan rate of 500 mVs^-1. At a current density of 10 mAg^-1, the specific capacitance of the nanocomposite, estimated by galvanostatic (GA) charge/discharge measurement, is 150 Fg^-1. These nanocomposites can be developed for supercapacitor electrodes.