Bo Bai

Dr Bo Bai, Executive Chairman of MetaVerse Green Exchange, says regulation should reflect the duality of carbon credits to drive green finance growth.

Singapore, already a trading hub bridging East and West, now needs to become the carbon trading hub the future needs

Blockchain can help bring transparency, accuracy and integrity to managing carbon assets and liabilities

In this article the major kinetics models for plasma-surface interactions were reviewed highlighting their strengths and limitations. As a subset of reactive-site modeling, mixing-layer kinetics model was developed based upon the assumption of random atomic mixing in the top surface layer. The translation of the layer enabled the modeling of both etching and deposition. A statistical concept, nearest-neighbor bonding probability, was defined to express the concentration of any surface moieties… Show more

In this article the major kinetics models for plasma-surface interactions were reviewed highlighting their strengths and limitations. As a subset of reactive-site modeling, mixing-layer kinetics model was developed based upon the assumption of random atomic mixing in the top surface layer. The translation of the layer enabled the modeling of both etching and deposition. A statistical concept, nearest-neighbor bonding probability, was defined to express the concentration of any surface moieties with the surface elemental composition. A lumped set of reactions was adopted to carry on the overall physichemical processes including ion incorporation, neutral adsorption, physical sputtering, ion-enhanced etching, dangling bond generation and annihilation, and spontaneous etching. The rate coefficients were fitted to the experimental etching yields at various beam etching conditions. The good match between the kinetics modeling and the experimental results verified the capability of the mixing-layer model of predicting the poly-Si etching in chlorine plasma at various operating conditions. Then the kinetics model was incorporated into the three-dimensional Monte Carlo profile simulator. The concept of the mixing layer was simulated by a cellular-based model through composition averaging among neighboring cells. The reactions were sorted out in terms of ion initiated and neutral initiated, respectively, as discrete events. The reaction rates were calculated based upon the cellular composition and used as probabilities to remove particles from the cell. Results showed that the profile simulation combined with the kinetics, the numeric kinetics model, and the experimental etching yields are in quantitative agreement, which demonstrated the accuracy of kinetics after incorporation into the profile simulation. The simulation was compared to the published research work comprehensively including the etching yields, surface compositions, and dominant product distributions. Show less

In this article the major kinetics models for plasma-surface interactions were reviewed highlighting their strengths and limitations. As a subset of reactive-site modeling, mixing-layer kinetics model was developed based upon the assumption of random atomic mixing in the top surface layer. The translation of the layer enabled the modeling of both etching and deposition. A statistical concept, nearest-neighbor bonding probability, was defined to express the concentration of any surface moieties… Show more

In this article the major kinetics models for plasma-surface interactions were reviewed highlighting their strengths and limitations. As a subset of reactive-site modeling, mixing-layer kinetics model was developed based upon the assumption of random atomic mixing in the top surface layer. The translation of the layer enabled the modeling of both etching and deposition. A statistical concept, nearest-neighbor bonding probability, was defined to express the concentration of any surface moieties with the surface elemental composition. A lumped set of reactions was adopted to carry on the overall physichemical processes including ion incorporation, neutral adsorption, physical sputtering, ion-enhanced etching, dangling bond generation and annihilation, and spontaneous etching. The rate coefficients were fitted to the experimental etching yields at various beam etching conditions. The good match between the kinetics modeling and the experimental results verified the capability of the mixing-layer model of predicting the poly-Si etching in chlorine plasma at various operating conditions. Then the kinetics model was incorporated into the three-dimensional Monte Carlo profile simulator. The concept of the mixing layer was simulated by a cellular-based model through composition averaging among neighboring cells. The reactions were sorted out in terms of ion initiated and neutral initiated, respectively, as discrete events. The reaction rates were calculated based upon the cellular composition and used as probabilities to remove particles from the cell. Results showed that the profile simulation combined with the kinetics, the numeric kinetics model, and the experimental etching yields are in quantitative agreement, which demonstrated the accuracy of kinetics after incorporation into the profile simulation. The simulation was compared to the published research work comprehensively including the etching yields, surface compositions, and dominant product distributions. Show less

A novel surface kinetic model using translating mixed-layer representation was proposed and demonstrated. In this model, a translating mixed layer was constructed where the total number of atoms is conserved as the etching or deposition proceeds, to have a convection or movement flux from or to the substrate volume (the volume under the translating mixed layer) that corresponds to the difference between the adsorption flux and removal flux. The model is demonstrated for silicon etching with… Show more

A novel surface kinetic model using translating mixed-layer representation was proposed and demonstrated. In this model, a translating mixed layer was constructed where the total number of atoms is conserved as the etching or deposition proceeds, to have a convection or movement flux from or to the substrate volume (the volume under the translating mixed layer) that corresponds to the difference between the adsorption flux and removal flux. The model is demonstrated for silicon etching with chlorine chemistry and silicon oxide etching with fluorine chemistry, with results agreeing well with measured data, as well as with previously developed Monte Carlo simulation results. The computation speed of the translating mixed-layer model was 100–10 000 times faster than that of Monte Carlo simulation. Show less

The addition of 3% nitrogen to a mixture of perfluorocarbon/oxygen/argon in a remote toroidal plasma source was shown to double the etching rate of both silicon dioxide and silicon in a downstream process. It is believed that the nitrogen blocks the surface recombination sites for COF2 formation on the wall of the transfer tube, thereby transporting more fluorine atoms to the downstream process chamber and increasing the etching rate.

The authors would like to thank DuPont Electronic Gas… Show more

The addition of 3% nitrogen to a mixture of perfluorocarbon/oxygen/argon in a remote toroidal plasma source was shown to double the etching rate of both silicon dioxide and silicon in a downstream process. It is believed that the nitrogen blocks the surface recombination sites for COF2 formation on the wall of the transfer tube, thereby transporting more fluorine atoms to the downstream process chamber and increasing the etching rate.

The authors would like to thank DuPont Electronic Gas group for funding support. Show less

The neutral gas temperature of fluorocarbon plasmas in a remote toroidal transformer-coupled source was measured to be greater than 5000K, under the conditions of a power density greater than 15W/cm3 and pressures above 2torr. The rovibrational bands of C2 molecules (swan bands, 𝑑𝛱𝑔3→𝑎𝛱𝑢3) were fitted to obtain the rotational temperature that was assumed to equal the translational temperature. This rotational-translational temperature equilibrium assumption was supported by the comparison… Show more

The neutral gas temperature of fluorocarbon plasmas in a remote toroidal transformer-coupled source was measured to be greater than 5000K, under the conditions of a power density greater than 15W/cm3 and pressures above 2torr. The rovibrational bands of C2 molecules (swan bands, 𝑑𝛱𝑔3→𝑎𝛱𝑢3) were fitted to obtain the rotational temperature that was assumed to equal the translational temperature. This rotational-translational temperature equilibrium assumption was supported by the comparison with the rotational temperature of second positive system of added N2. For the same gas mixture, the neutral gas temperature is nearly a linear function of plasma power, since the conduction to chamber wall and convection are the major energy-loss processes, and they are both proportional to neutral gas temperature. The dependence of the neutral gas temperature on O2 flow rate and pressure can be well represented through the power dependence, under the condition of constant current operation. An Arrhenius type of dependence between the etching rate of oxide film and the neutral gas temperature is observed, maybe indicating the importance of the pyrolytic dissociation in the plasma formation process when the temperature is above 5000K. Show less

Spatially resolved neutral gas temperature of Ar plasmas within a new type of transformer-coupled toroidal plasma source was measured by fitting unresolved rovibrational bands of trace gas N2 (𝐶𝛱𝑢3→𝐵𝛱𝑔3). With power density as high as 4.8W/cm3, the maximum neutral gas temperature inside Ar plasmas was found to be 2000K. The position with maximum neutral gas temperature was off the center of the cross section and close to the ferrite core, where higher electric field contributes to higher… Show more

Spatially resolved neutral gas temperature of Ar plasmas within a new type of transformer-coupled toroidal plasma source was measured by fitting unresolved rovibrational bands of trace gas N2 (𝐶𝛱𝑢3→𝐵𝛱𝑔3). With power density as high as 4.8W/cm3, the maximum neutral gas temperature inside Ar plasmas was found to be 2000K. The position with maximum neutral gas temperature was off the center of the cross section and close to the ferrite core, where higher electric field contributes to higher heating power. The dependence of neutral gas temperature on pressure was measured and can be empirically fitted by proportionality between gas temperature and logarithm of the pressure, as found by other researchers. A simple physical model gives the dependence of pressure as the sixth order of neutral gas temperature, which fits the experimental data as well. It was also found that added N2 gas perturbed Ar plasmas obviously, and therefore we recommend adding less than 1% N2 as trace gas. There is no dependence of fitted neutral gas temperature on the optical resolution of monochromator, as would be expected. Show less

Research on the Alcator C-Mod tokamak [1] is focused on high particle- and power-density plasma regimes to understand particle and energy transport in the core, the dynamics of the H-mode pedestal, and scrape-off layer and divertor physics. The auxiliary heating is provided exclusively by RF waves, and both the physics and technology of RF heating and current drive are studied. The momentum which is manifested in strong toroidal rotation, in the absence of direct momentum input, has been shown… Show more

Research on the Alcator C-Mod tokamak [1] is focused on high particle- and power-density plasma regimes to understand particle and energy transport in the core, the dynamics of the H-mode pedestal, and scrape-off layer and divertor physics. The auxiliary heating is provided exclusively by RF waves, and both the physics and technology of RF heating and current drive are studied. The momentum which is manifested in strong toroidal rotation, in the absence of direct momentum input, has been shown to be transported in from the edge of the plasma following the L–H transition, with timescale comparable to that for energy transport. In discharges which develop internal transport barriers, the rotation slows first inside the barrier region, and then subsequently outside of the barrier foot. Heat pulse propagation studies using sawteeth indicate a very narrow region of strongly reduced energy transport, located near r/a = 0.5. Addition of on-axis ICRF heating arrests the buildup of density and impurities, leading to quasi-steady conditions. The quasi-coherent mode associated with enhanced D-Alpha (EDA) H-mode appears to be due to a resistive ballooning instability. As the pedestal pressure gradient and temperature are increased in EDA H-mode, small ELMs appear; detailed modelling indicates that these are due to intermediate n peeling–ballooning modes. Phase contrast imaging has been used to directly detect density fluctuations driven by ICRF waves in the core of the plasma, and mode conversion to an intermediate wavelength ion cyclotron wave has been observed for the first time. The bursty turbulent density fluctuations, observed to drive rapid cross-field particle transport in the edge plasma, appear to play a key role in the dynamics of the density limit. Preparations for quasi-steady-state advanced tokamak studies with lower hybrid current drive are well underway, and time dependent modelling indicates that regimes with high bootstrap fraction can be produced. Show less

The intermittent turbulent transport in the scrape-off-layer (SOL) of Alcator C-Mod [I.H. Hutchinson, R. Boivin, P.T. Bonoli et al., Nucl. Fusion 41, 1391 (2001)] is studied experimentally by imaging with a very high density of spatial measurements. The two-dimensional structure and dynamics of emission from a localized gas puff are observed, and intermittent features (also sometimes called “filaments” or “blobs”) are typically seen. The characteristics of the spatial structure of the… Show more

The intermittent turbulent transport in the scrape-off-layer (SOL) of Alcator C-Mod [I.H. Hutchinson, R. Boivin, P.T. Bonoli et al., Nucl. Fusion 41, 1391 (2001)] is studied experimentally by imaging with a very high density of spatial measurements. The two-dimensional structure and dynamics of emission from a localized gas puff are observed, and intermittent features (also sometimes called “filaments” or “blobs”) are typically seen. The characteristics of the spatial structure of the turbulence and their relationship to the time-averaged SOL profiles are discussed and compared with those measured on the National Spherical Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Pong et al., Nucl. Fusion 40, 557 (2000)]. The experimental observations are compared also with three-dimensional nonlinear numerical simulations of edge turbulence. Radial profiles of the poloidal wave number spectra and the poloidal scale length from the simulations are in reasonable agreement with those obtained from the experimental images, once the response of the optical system is accounted for. The resistive ballooning mode is the dominant linear instability in the simulations. The ballooning character of the turbulence is also consistent with fluctuation measurements made at the inboard and outboard midplane, where normalized fluctuation levels are found to be about 10 times smaller on the inboard side. For discharges near the density limit, turbulent structures are seen on closed flux surfaces. Show less

A new feature in the Thomson scattering spectrum is observed from a laser-produced aluminium plasma, which may be the Thomson scattering off entropy waves in the plasma. Such a feature is only observable when the energy of the heater beam is low enough.

Detailed measurements of gold plasmas produced with 0.351 μm laser light are reported. The temporal and spatial variations of Z̄Te are obtained in the case that pump intensities are 6.5×1013 and 1.4×1014 W/cm2. The experimental results are qualitatively consistent with two nonlocalized absorption models.

Time-resolved Thomson scattering was successfully performed to diagnose the parameters (ZTe, Ue and Ui) of laser-produced gold plasma. The results show that the collisionless dynamic form factor is accurate enough to be used for reducing the plasma parameters from the experimental data.