Supercritical CO2 Fluid Treatment Research Articles

Diffusion behaviors of Sn dopant in ITO films upon supercritical CO2 treatment and annealing

Indium Tin Oxide (ITO) thin films have been extensively studied for their excellent photoelectric performance. Nevertheless, the diffusion mechanism of doped-tin in ITO thin film is not sufficiently illuminated to date. Herein, the diffusion behaviors of Sn dopant in ITO films fabricated by RF-sputtering were investigated. As-deposited ITO thin films were treated by supercritical CO2 (SCCO2) fluid with aqua ammonia, then they were annealed at different temperatures. X-ray diffraction patterns (XRD) showed that the crystallization of ITO films occurred upon annealing above 300 °C, which resulted in the higher mobility of electron carriers. Relatively lower electron carrier concentrations were found for the ITO films after SCCO2 treatment and successive annealing at temperatures of 500 and 600 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed that the content of tin element near the surface of ITO thin films can be reduced by SCCO2 fluid treatment. Subsequently, the annealing process results in the diffusion of the tin element to the sub-surface region of the films at different levels depending on the annealing temperature. The present work provides direct evidence for bleaching of tin dopant in the sub-surface region of ITO films by SCCO2 treatments and diffusion of tin from deeper regions to the sub-surface region of the ITO films upon annealing.

Application of nanoindentation technology for characterizing the mechanical properties of shale before and after supercritical CO2 fluid treatment

To better implement super critical carbon dioxide (SC-CO2) fracturing on shale, it is important to investigate effects of SC-CO2 on rock mechanical properties. Because micro-scale mechanical properties determine the overall mechanical response, the determination of micro-scale mechanical properties is necessary. In this paper, continuous stiffness measurement (CSM) and constant loading rate (CLR) mode nanoindentation was performed on shale samples before and after SC-CO2 treatment. With the aid of scanning electron microscope and energy dispersive spectra mapping technique, mechanical strength difference on clay-rich and quartz –rich areas in shale sample can be identified. The results demonstrated that samples treated by SC-CO2 present lower Hardness, Young’s modulus and fracture toughness. The average decrease rates of hardness and Young’s modulus under CSM mode for three sample are 32.01 % and 11.75 %. The hardness, Young’s modulus and fracture toughness under CLR mode for the three samples have decreased at average rates of 29.5 %, 11.0 %, and 11.3 %, respectively. Moreover, the mechanical strength substantially decreases in the clay-rich area because CO2 adsorption and mineral dissolution happen after the SC-CO2 treatment. The change in mechanical properties in quartz-rich area is much smaller because there is little effect on quartz. The close examination of indentation fracture geometry indicate more micro fractures have been generated in the post SC-CO2 treated shale, thus we can expect the capability of SC-CO2 for rock weaken. This study can provide more insights for fracture mechanism in target areas with different mineral distribution, which is beneficial for SC-CO2 engineering applications.

Physical and chemical mechanisms in oxide-based resistance random access memory.

In this review, we provide an overview of our work in resistive switching mechanisms on oxide-based resistance random access memory (RRAM) devices. Based on the investigation of physical and chemical mechanisms, we focus on its materials, device structures, and treatment methods so as to provide an in-depth perspective of state-of-the-art oxide-based RRAM. The critical voltage and constant reaction energy properties were found, which can be used to prospectively modulate voltage and operation time to control RRAM device working performance and forecast material composition. The quantized switching phenomena in RRAM devices were demonstrated at ultra-cryogenic temperature (4K), which is attributed to the atomic-level reaction in metallic filament. In the aspect of chemical mechanisms, we use the Coulomb Faraday theorem to investigate the chemical reaction equations of RRAM for the first time. We can clearly observe that the first-order reaction series is the basis for chemical reaction during reset process in the study. Furthermore, the activation energy of chemical reactions can be extracted by changing temperature during the reset process, from which the oxygen ion reaction process can be found in the RRAM device. As for its materials, silicon oxide is compatible to semiconductor fabrication lines. It is especially promising for the silicon oxide-doped metal technology to be introduced into the industry. Based on that, double-ended graphene oxide-doped silicon oxide based via-structure RRAM with filament self-aligning formation, and self-current limiting operation ability is demonstrated. The outstanding device characteristics are attributed to the oxidation and reduction of graphene oxide flakes formed during the sputter process. Besides, we have also adopted a new concept of supercritical CO2 fluid treatment to efficiently reduce the operation current of RRAM devices for portable electronic applications.

RETRACTED: Improvement mechanism of resistance random access memory with supercritical CO2 fluid treatment

We demonstrated that the supercritical CO2 fluid treatment was a new concept to efficiently reduce the operation current of resistance random access memory. The dangling bonds of tin-doped silicon oxide (Sn:SiOx) thin film were passivated by the hydration–dehydration reaction through supercritical CO2 fluid treatment, which was verified by the XPS and FTIR analyses. The current conduction mechanism of low resistance state in post-treated Sn:SiOx thin film was transferred to hopping conduction from Ohmic conduction. Furthermore, the current conduction mechanism of high resistance state in the memory device was transferred to Schottky emission from Frenkel–Poole conduction. The phenomena were attributed to the discontinuous metal filament formed by hydration–dehydration reaction in Sn:SiOx thin film through supercritical fluid treatment. Finally, a reaction model was proposed to explain the mechanism of current reduction in Sn:SiOx thin film with supercritical CO2 fluid treatment.

Dehydroxyl effect of Sn-doped silicon oxide resistance random access memory with supercritical CO2 fluid treatment

The tin-doped can supply conduction path to induce resistance switching behavior. However, the defect of tin-doped silicon oxide (Sn:SiOx) increased the extra leakage path lead to power consumption and joule heating degradation. In the study, supercritical CO2 fluids treatment was used to improve resistive switching property. The current conduction of high resistant state in post-treated Sn:SiOx film was transferred to Schottky emission from Frenkel-Poole due to the passivation effect. The molecular reaction model is proposed that the defect was passivated through dehydroxyl effect of supercritical fluid technology, verified by material analyses of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Reducing operation current of Ni-doped silicon oxide resistance random access memory by supercritical CO2 fluid treatment

In the study, we reduced the operation current of resistance random access memory (RRAM) by supercritical CO2 (SCCO2) fluids treatment. The power consumption and joule heating degradation of RRAM device can be improved greatly by SCCO2 treatment. The defect of nickel-doped silicon oxide (Ni:SiOx) was passivated effectively by the supercritical fluid technology. The current conduction of high resistant state in post-treated Ni:SiOx film was transferred to Schottky emission from Frenkel-Pool due to the passivation effect. Additionally, we can demonstrate the passivation mechanism of SCCO2 for Ni:SiOx by material analyses of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Low-Temperature Synthesis of ZnO Nanotubes by Supercritical CO2 Fluid Treatment

Low-Temperature Synthesis of ZnO Nanotubes by Supercritical CO2 Fluid Treatment

A low temperature fabrication of HfO2 films with supercritical CO2 fluid treatment

To improve the dielectric properties of sputter-deposited hafnium oxide (HfO2) films, the supercritical CO2 (SCCO2) fluid technology is introduced as a low temperature treatment. The ultrathin HfO2 films were deposited on p-type (100) silicon wafer by dc sputtering at room temperature and subsequently treated with SCCO2 fluids at 150°C to diminish the traps in the HfO2 films. After SCCO2 treatment, the interfacial parasitic oxide between the Si substrate and HfO2 layer is only about 5Å, and the oxygen content of the HfO2 films apparently increased. From current-voltage (I-V) and capacitance-voltage (C-V) measurements, the leakage current density of the SCCO2-treated HfO2 films is repressed from 10−2to10−7A∕cm2 at electric field=3MV∕cm due to the reduction of traps in the HfO2 films. The equivalent oxide thickness also obviously decreased. Besides, the efficiency of terminating traps is relative to the pressure of the SCCO2 fluids.

Structural Modification of Polyester Fibers in Supercritical Carbon Dioxide Fluid

Several types of polyester fibers, i.e. high speed spun (HSS) fibers, partially oriented yarns (POY), and fully oriented yarns (FOY), were subjected to the supercritical CO2 fluid treatment (SFT) at 120deg, 20MPa for 1 h and structural modifications were investigated. Large shrinkage and not a small amount of oligomer deposition on the fiber surface were observed for POY and FOY. On the contrary, as for HSS fibers produced at a spinning speed of 6 km/min the shrinkage was suppressed within 2 % as compared with an initial fiber length and the oligomer deposition could hardly be observed. The shrinkproof property for HSS fibers seems to be closely related to the well developed fibrous structure. Such structure can be easily confirmed via the alkaline etching. The oligomer migration can be lowered by accelerating the orientation-induced crystallization rate on the high speed spinning line and disordering the molecular orientation in amorphous regions. In addition ultra-crystallites formed in amorphous regions during SFT will also be effective for the suppression to the oligomer migration. The disordered macromolecules and the ultra-crystallites formed in amorphous regions will develop a network-like structure that suppresses the oligomer migration. Therefore, a novel polyester fiber suitable for the supercritical CO2 fluid dyeing is producible by controlling the fibrous structure and designing the amorphous regions using the high speed spinning process.

Structural Modification of Polyester Shin-Gosen by the Treatment in Supercritical Carbon Dioxide Fluids

Polyester Shin-gosen fibers were heat-set and subjected to supercritical CO2 fluid treatment (SFT, 125 °C, 25 MPa, 60 min) or pressurized water treatment (PWT, 130 °C, 60 min), where the shrink behavior and the mechanism were compared. As for PWT, heat-set temperature over than 160 °C was enough for the suppression of shrinkage lower than 2%. On the contrary, as for SFT, the shrinkage could not be suppressed at the same level even in the case for the fibers heat-set at 200 °C. The large shrinkage seems to be brought about by the migration of oligomer through SFT. The oligomer migration lowered the tensile modulus, and gained the elongation of the treated fibers. However, the tensile strength of the fiber was hardly affected by SFT.

Structure of Poly(ethylene terephthalate) Fibers Treated in Supercritical Carbon Dioxide Fluid.

The dyeing behaviors and changes in fiber structure in supercritical CO2 fluid for several types of high-speed spun and regular fully oriented poly (ethylene terephthalate) (PET) fibers were compared. At lower temperature and pressure, the high-speed spun fibers, which had inherently larger crystallite sizes and lower birefringence, showed a larger dye uptake than the other fibers. However, when the supercritical conditions were elevated to 125°C and 23 MPa, the dye uptake of both types increased markedly and the difference in dye uptake between the fibers became small. This suggests that the swelling of fibers in supercritical CO2 fluid exceeded a certain degree and then the diffusion of dye molecules was promoted. The swelling also promoted the rearrangement of molecular chains. The combination of the high speed spinning technique and the supercritical CO2 fluid treatment can provide a new PET fiber with both larger crystallite sizes and higher molecular orientation in the amorphous regions.