Browsing by Author "Lee, SJ"

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A refined model for ozone mass transfer in a bubble column
(1998-01-01)
Huang, WH
;
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
A refined model for ozone mass transfer in a bubble column
(1998-01-01)
Huang, WH
;
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Marinas et ai. (1993) for a bubble column gas-liquid contactor is refined to described the mass transfer of ozone absorption and decomposition in the aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGb), and the superficial gas rise velocity (u(G)), respectively. The variation of u(G) and the effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of chemical to pure physical mass fluxes according to the film model of gas liquid absorption, are considered in the refined model. This analysis thus extends the applicability of the model of Marinas et al. (1993) and is of special importance for the ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant. An example of such case is the cyanide wastewater treatment in the strong basic condition.
A refined model for ozone mass transfer in a semibatch stirred vessel
(1997-11-01)
Chiu, CY
;
Chang, CY
;
Huang, WH
;
Lee, SJ
;
Yu, YH
The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas-liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C-ALb), the hold-up gas (C-AGi), and the outlet gas in the free volume above the liquid surface (C-AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E-r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E-r with C-ALb, which changes with time during the course of gas-liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.
Combined absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance
(1996-05-01)
Chang, CY
;
Chiu, CY
;
Lee, SJ
;
Huang, WH
;
Yu, YH
A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient k(g). A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/k(g)),the acidic and basic self-decomposition reaction rate parameters (M(m)(0.5), M(n)(0.5); M(m) = [2D(A)k(m)C(Ai)(m-1)/((m+1)]/k(L)(0))(2), M(n) = (2D(A)k(n)C(Ai)(n-1)/(n+1))/k(L)(0))(2), the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (k(L)(0)). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of M(m) and M(n) as well as with higher pH values. Also, for any particular finite value of k(L)(0)/k(g), the reduction effect encountered is greater for a gas liquid contactor with a lower k(L)(0). The reduction effect should be avoided in order to maintain a higher mass transfer rate of ozone in aqueous solution. This analysis is of importance for the efficient use of ozone in water/wastewater treatment processes in the presence of interfacial resistance substances such as surface active agents. For some known special cases (for example, cases with no interfacial resistance), the present solution reduces to the previous works of other investigators.
Germanium pMOSFETs with Schottky-barrier germanide S/D, high-kappa gate dielectric and metal gate
(2005-02-01)
Zhu, SY
;
Li, R
;
Lee, SJ
;
Li, MF
;
Du, AY
Schottky-barrier source/drain (S/D) germanium p-channel MOSFETs are demonstrated for the first time with HfAlO gate dielectric, HfN-TaN metal gate and self-aligned NiGe S/D. The drain drivability is improved over the silicon counterpart with PtSi S/D by as much as similar to5 times due to the lower hole Schottky barrier of the NiGe-Ge contact than that of PtSi-Si contact as well as the higher mobility of Ge channel than that of Si.
Low temperature MOSFET technology with Schottky barrier source/drain, high-K gate dielectric and metal gate electrode
(2004-10-01)
Zhu, SY
;
Yu, HY
;
Chen, JD
;
Whang, SJ
;
Chen, JH
Both P- and N-channel MOSFET's with Schottky barrier silicide source/drain (S/D), high-K gate dielectric and metal gate were successfully fabricated using a simplified low temperature process. The highest temperature after the high-K dielectric formation is 420degreesC. PMOSFETs with PtSi S/D show excellent electrical performance of an I-on/I-off similar to 10(7)-10(8) and a subthreshold slope of 66 mV/dec, similar to those formed by a normal process with an optimized sidewall spacer. NMOSFETs with DySi2-x S/D have similar to3 orders of magnitude larger I-off than that of PMOSFETs and show two slopes in the subthreshold region, resulting in the I-on/I-off similar to 10(5) at low drain voltage. It can be attributed to the relatively higher barrier height (Phi(n)) of DySi2-x/n-Si than that of PtSi/p-Si (Phi(p)) and the rougher DySi2-x film. Adding a thin intermediate Ge layer (similar to1nm) between Dy and Si can improve the film morphology significantly. As a result, the improved performance of N-MOSFET is observed. (C) 2004 Published by Elsevier Ltd.
N-type Schottky barrier source/drain MOSFET using ytterbium silicide
(2004-08-01)
Zhu, SY
;
Chen, JD
;
Li, MF
;
Lee, SJ
;
Singh, J
Ytterbium silicide, for the first time, was used to form the Schottky barrier source/drain (S/D) of N-channel MOSFETs. The device fabrication was performed at low temperature, wich is highly preferred in the establishment of Schottky barrier S/D transistor (SSDT) technology, including the HfO2 gate dielectric, and HaN/TaN metal gate. The YbSi2-x, silicided N-SSDT has demonstrated a very promising characteristic with a recorded high I-on/I-off ratio of similar to10(7) and a steep subthreshold slope of 75 mV/dec, which is attributed to the lower electron barrier height and better film morphology of the YbSi2-x/Si contact compared with other self-aligned rare earth metal-(Erbium, Terbium, Dysprosium) silicided Schottky junctions.
Photochemistry and photodissociation of benzosultine and naphthosultine: electronic relaxation of sultines and kinetics and theoretical studies of fragment o-quinodimethanes
(2005-02-28)
Tang, KC
;
Lee, SJ
;
Chi, SH
;
Lu, KL
;
Chen, WC
Fluorescence decays of benzosultine and naphthosultine excited at 263 nm are detected with time-correlated single-photon counting (TCSPC). Both molecules display biexponential decay with a rapid component (time constants 90 and 350 ps for benzosultine and naphthosultine, respectively) assigned to an electronically excited state S-n at high energy and the slow one (constants 7.5 and 9.0 ns for benzosultine and naphthosultine, respectively) to the S-1 state. Dissociation of both molecules was investigated with nanosecond laser flash photolysis combined with transient absorption to detect the intermediates and products. With excitation at 266 nm, benzosultine yields a transient with absorption maximum at lambda(max) = 370 nm; this transient has a short-lived component with lifetime around 1 mus and a long-lived component. Both components are insensitive to molecular oxygen. The short-lived component is tentatively assigned to the dissociation intermediate and the long-lived to be singlet o-benzoquinodimethane (o-BQDM). Photolysis of naphthosultine yields two transient species with absorption at; lambda(max) = 420 and 520 nm; we assign the former band to triplet-triplet absorption of naphthosultine and the latter to absorption by the product singlet o-naphthoquinodimethane. Optimal geometries, energetics, and vertical transitions of benzosultine, naphthosultine, o-benzoquinodimethane, and o-naphthoquinodimethane are calculated using methods based on density-functional theory (B3LYP/6-311++G**) and time-dependent density-functional theory (TD-DFT). The results of these calculations imply that the ground electronic state of these two o-quinodimethanes (o-QDM) is singlet with a structure of diene form. Their triplet states display a biradical structure. The energy separation between singlet and triplet states of o-benzoquinodimethane is calculated to be ca. 93.6 kJ/mol, but for o-naphthoquinodimethane, it is only ca. 27.8 kJ/mol. (C) 2004 Elsevier B.V. All rights reserved.
Schottky-barrier S/D MOSFETs with high-K gate dielectrics and metal-gate electrode
(2004-05-01)
Zhu, SY
;
Yu, HY
;
Whang, SJ
;
Chen, JH
;
Shen, C
This letter presents a low-temperature process to fabricate Schottky-barrier silicide source/drain transistors (SSDTs) with high-kappa gate dielectric and metal gate. For p-channel SSDTs (P-SSDT) using PtSi source/drain (S/D), excellent electrical performance of I-on/I-off similar to 10(7) - 10(8) and subthreshold slope of 66 mV/dec have been achieved. For n-channel SSDTs (N-SSDTs) using DySi2-x S/D, I-on/I-off can reach similar to 10(5) at V-ds of 0.2 V with two subthreshold slopes of 80 and 340 mV/dec. The low-temperature process relaxes the thermal budget of high-kappa dielectric and metal-gate materials to be used in the future generation CMOS technology.