Simple physical mixing of zeolite prevents sulfur deactivation of vanadia catalysts for NOx removal.

NOx abatement has been an indispensable part of environmental catalysis for decades. Selective catalytic reduction with ammonia using V2O5/TiO2 is an important technology for removing NOx emitted from industrial facilities. However, it has been a huge challenge for the catalyst to operate at low temperatures, because ammonium bisulfate (ABS) forms and causes deactivation by blocking the pores of the catalyst. Here, we report that physically mixed H-Y zeolite effectively protects vanadium active sites by trapping ABS in micropores. The mixed catalysts operate stably at a low temperature of 220 °C, which is below the dew point of ABS. The sulfur resistance of this system is fully maintained during repeated aging/regeneration cycles because the trapped ABS easily decomposes at 350 °C. Further investigations reveal that the pore structure and the amount of framework Al determined the trapping ability of various zeolites.

Top-down fabrication of high-uniformity nanodiamonds by self-assembled block copolymer masks.

Nanodiamonds hosting colour centres are a promising material platform for various quantum technologies. The fabrication of non-aggregated and uniformly-sized nanodiamonds with systematic integration of single quantum emitters has so far been lacking. Here, we present a top-down fabrication method to produce 30.0 ± 5.4 nm uniformly-sized single-crystal nanodiamonds by block copolymer self-assembled nanomask patterning together with directional and isotropic reactive ion etching. We show detected emission from bright single nitrogen vacancy centres hosted in the fabricated nanodiamonds. The lithographically precise patterning of large areas of diamond by self-assembled masks and their release into uniformly sized nanodiamonds open up new possibilities for quantum information processing and sensing.

Quick vaporization of sprayed sodium hypochlorite (NaClO(aq)) for simultaneous removal of nitrogen oxides (NOx), sulfur dioxide (SO2), and mercury (Hg0).

Sodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NOx; NO + NO2), sulfur dioxide (SO2), and mercury (Hg0) removals in a wet scrubber. However, they are each uniquely dependent on NaClO(aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1 L/Nm3) of NaClO(aq) to vaporize quickly at 165 °C. Results have shown that the maximized NOx, SO2, and Hg0 removals can be achieved at the pH range between 4.0 and 6.0. When NOx and Hg0 coexist with SO2, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO(s), NaClO2(s), OClO, ClO, and Cl species, originated from the reaction between SO2 and NaClO(aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NOx, SO2, and Hg0 removals, respectively. These findings led us to conclude that the spray of NaClO(aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NOx, SO2, and Hg0 possible. Implications: The simple spray of NaClO(aq) at temperatures above 165 °C can cause the simultaneous removal of gaseous NOx, SO2, and Hg0 by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NOx and Hg0 removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO2 with NaClO(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant.

Investigation of the Physical Properties of Plasma Enhanced Atomic Layer Deposited Silicon Nitride as Etch Stopper.

Correlations between physical properties linking film quality with wet etch rate (WER), one of the leading figures of merit, in plasma-enhanced atomic layer deposition (PEALD) grown silicon nitride (SiN x) films remain largely unresearched. Achieving a low WER of a SiN x film is especially significant in its use as an etch stopper for technology beyond 7 nm node semiconductor processing. Herein, we explore the correlation between the hydrogen concentration, hydrogen bonding states, bulk film density, residual impurity concentration, and the WERs of PEALD SiN x using Fourier transform infrared spectrometry, X-ray reflectivity, and spectroscopic ellipsometry, etc. PEALD SiN x films for this study were deposited using hexachlorodisilane and hollow cathode plasma source under a range of process temperatures (270-360 °C) and plasma gas compositions (N2/NH3 or Ar/NH3) to understand the influence of hydrogen concentration, hydrogen bonding states, bulk film density, and residual impurity concentration on the WER. Varying hydrogen concentration and differences in the hydrogen bonding states resulted in different bulk film densities and, accordingly, a variation in WER. We observe a linear relationship between hydrogen bonding concentration and WER as well as a reciprocal relationship between bulk film density and WER. Analogous to the PECVD SiN x processes, a reduction in hydrogen bonding concentration arises from either (1) thermal activation or (2) plasma excited species. However, unlike the case with silane (SiH4)-based PECVD SiN x, PEALD SiN x WERs are affected by residual impurities of Si precursors (i.e., chlorine impurity). Thus, possible wet etching mechanisms in HF in which the WER is affected by hydrogen bonding states or residual impurities are proposed. The shifts of amine basicity in SiN x due to different hydrogen bonding states and the changes in Si electrophilicity due to Cl impurity content are suggested as the main mechanisms that influence WER in the PEALD processes.

Stepped Propane Adsorption in Pure-Silica ITW Zeolite.

Gas adsorption over zeolites is at the basis of important applications of this class of microporous crystalline solids, notably as separation media and catalysts, but it may also be complex and not straightforward to understand. Here we report that for temperature below 323 K propane adsorption on the small-pore pure-silica zeolite ITW exhibits a clear step (pseudosaturation). This is absent in the case of propene and the other small linear alkanes. An intermediate plateau, clearly observed in the 293 K isotherm, always occurs when one molecule of propane is loaded in every other cage, i.e., at half-saturation. The simulation results show a swelling of the ITW structure upon propane adsorption. The strong dependence of available pore volume on the adsorbate loading level implies that adsorption cannot occur on the void structure while saturation can only be reached on highly loaded structures. To account for this unprecedented adsorption phenomenon, we propose the term "guest-modulated effect".

Hollow Cathode Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride Using Pentachlorodisilane.

In this work, a novel chlorodisilane precursor, pentachlorodisilane (PCDS, HSi2Cl5), was investigated for the growth of silicon nitride (SiN x) via hollow cathode plasma-enhanced atomic layer deposition (PEALD). A well-defined self-limiting growth behavior was successfully demonstrated over the growth temperature range of 270-360 °C. At identical process conditions, PCDS not only demonstrated approximately >20% higher growth per cycle than that of a commercially available chlorodisilane precursor, hexachlorodisilane (Si2Cl6), but also delivered a better or at least comparable film quality determined by characterizing the refractive index, wet etch rate, and density of the films. The composition of the SiN x films grown at 360 °C using PCDS, as determined by X-ray photoelectron spectroscopy, showed low O content (∼2 at. %) and Cl content (<1 at. %; below the detection limit). Fourier transform infrared spectroscopy spectra suggested that N-H bonds were the dominant hydrogen-containing bonds in the SiN x films without a significant amount of Si-H bonds originating from the precursor molecules. The possible surface reaction pathways of the PEALD SiN x using PCDS on the surface terminated with amine groups (-NH2 and -NH-) are proposed. The PEALD SiN x films grown using PCDS also exhibited a leakage current density as low as 1-2 nA/cm2 at 2 MV/cm and a breakdown electric field as high as ∼12 MV/cm.

Effects of H2 High-pressure Annealing on HfO2/Al2O3/In0.53Ga0.47As Capacitors: Chemical Composition and Electrical Characteristics.

We studied the impact of H2 pressure during post-metallization annealing on the chemical composition of a HfO2/Al2O3 gate stack on a HCl wet-cleaned In0.53Ga0.47As substrate by comparing the forming gas annealing (at atmospheric pressure with a H2 partial pressure of 0.04 bar) and H2 high-pressure annealing (H2-HPA at 30 bar) methods. In addition, the effectiveness of H2-HPA on the passivation of the interface states was compared for both p- and n-type In0.53Ga0.47As substrates. The decomposition of the interface oxide and the subsequent out-diffusion of In and Ga atoms toward the high-k film became more significant with increasing H2 pressure. Moreover, the increase in the H2 pressure significantly improved the capacitance‒voltage characteristics, and its effect was more pronounced on the p-type In0.53Ga0.47As substrate. However, the H2-HPA induced an increase in the leakage current, probably because of the out-diffusion and incorporation of In/Ga atoms within the high-k stack.

Impurity and silicate formation dependence on O3 pulse time and the growth temperature in atomic-layer-deposited La2O3 thin films.

Atomic-layer-deposited La2O3 films were grown on Si with different O3 pulse times and growth temperatures. The interfacial reactions and impurity behaviors were observed using in situ X-ray photoelectron spectroscopy. Longer pulse time of O3 formed the solid SiO2 interfacial barrier layer, which suppressed La-silicate formation. Meanwhile, the carboxyl compound acting as an impurity phase was replaced with LaCO3 on increasing the O3 pulse time due to further oxidation and reaction of La. Higher growth temperatures enhanced La-silicate formation by mixed diffusion of Si and La2O3, during which most of the La2O3 phase was consumed at 400 °C. C and N impurities decreased with increasing growth temperature and completely disappear at 400 °C.

Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks.

With the continued miniaturization of devices in the semiconductor industry, atomic layer deposition (ALD) of silicon nitride thin films (SiNx) has attracted great interest due to the inherent benefits of this process compared to other silicon nitride thin film deposition techniques. These benefits include not only high conformality and atomic-scale thickness control, but also low deposition temperatures. Over the past 20 years, recognition of the remarkable features of SiNx ALD, reinforced by experimental and theoretical investigations of the underlying surface reaction mechanism, has contributed to the development and widespread use of ALD SiNx thin films in both laboratory studies and industrial applications. Such recognition has spurred ever-increasing opportunities for the applications of the SiNx ALD technique in various arenas. Nevertheless, this technique still faces a number of challenges, which should be addressed through a collaborative effort between academia and industry. It is expected that the SiNx ALD will be further perceived as an indispensable technique for scaling next-generation ultra-large-scale integration (ULSI) technology. In this review, the authors examine the current research progress, challenges and future prospects of the SiNx ALD technique.

A family of molecular sieves containing framework-bound organic structure-directing agents.

Organic structure-directing agents (OSDAs), such as quaternary ammonium cations and amines, used in the synthesis of zeolites and related crystalline microporous oxides usually end up entrapped inside the void spaces of the crystallized inorganic host lattice. But none of them is known to form direct chemical bonds to the framework of these industrially important catalysts and adsorbents. We demonstrate that ECR-40, currently regarded as a typical silicoaluminophosphate molecular sieve, constitutes instead a new family of inorganic-organic hybrid networks in which the OSDAs are covalently bonded to the inorganic framework. ECR-40 crystallization begins with the formation of an Al-OSDA complex in the liquid phase in which the Al is octahedrally coordinated. This unit is incorporated in the crystallizing ECR-40. Subsequent removal of framework-bound OSDAs generates Al-O-Al linkages in a fully tetrahedrally coordinated framework.

Tailoring the interface quality between HfO2 and GaAs via in situ ZnO passivation using atomic layer deposition.

We investigated ZnO surface passivation of a GaAs (100) substrate using an atomic layer deposition (ALD) process to prepare an ultrathin ZnO layer prior to ALD-HfO2 gate dielectric deposition. Significant suppression of both Ga-O bond formation near the interface and As segregation at the interface was achieved. In addition, this method effectively suppressed the trapping of carriers in oxide defects with energies near the valence band edge of GaAs. According to electrical analyses of the interface state response on p- and n-type GaAs substrates, the interface states in the bottom half of the GaAs band gap were largely removed. However, the interface trap response in the top half of the band gap increased somewhat for the ZnO-passivated surface.

Formation of chlorinated species through reaction of SO2 with NaClO2 powder and their role in the oxidation of NO and Hg°.

This study examines gaseous chlorinated species generated from the reaction of sulfur dioxide (SO2) with sodium chlorite powder (NaClO2(s)) to obtain insight into the propensity of this process to enhance NO and Hg° oxidation. A packed bed reactor containing NaClO2(s) was used and the reaction temperature was set to 130 °C. Initially, we determined that the presence of SO2 enhances the oxidation of NO and Hg° by reaction with NaClO2(s). We then introduced NO2 into the gas mixture as a radical scavenger and determined that the chlorinated species generated by the reaction of SO2 with NaClO2(s) are OClO, Cl, ClO, and Cl2. Based on these results, we suggest that such gaseous chlorinated ones are responsible for the enhancement of NO and Hg° oxidation.

Comparative study of atomic-layer-deposited stacked (HfO2/Al2O3) and nanolaminated (HfAlOx) dielectrics on In0.53Ga0.47As.

The high-k gate dielectric structures in stacked (HfO2/Al2O3) and nanolaminated (HfAlOx) forms with a similar apparent accumulation capacitance were atomic-layer-deposited on n-type In0.53Ga0.47As substrates, and their electrical properties were investigated in comparison with a single-layered HfO2 film. Al-oxide interface passivation in both forms proved to be effective in preventing a significant In incorporation in the high-k film and reducing the interface state density. The measured valence band spectra in combination with the reflection electron energy loss spectra were used to extract the energy band parameters of various dielectric structures on In0.53Ga0.47As. A further decrease in the interface state density was achieved in the stacked structure than in the nanolaminated structure. However, in terms of the other electrical properties, the nanolaminated sample exhibited better characteristics than the stacked sample, with a smaller border trap density and lower leakage current under substrate injection conditions with and without voltage stressing.

Surface modification of carbon post arrays by atomic layer deposition of ZnO film.

The applicability of atomic layer deposition (ALD) process to the carbon microelectromechanical system technology was studied for a surface modification method of the carbon post electrodes. A conformal coating of the ALD-ZnO film was successfully demonstrated on the carbon post arrays which were fabricated by the traditional photolithography and subsequent two-step pyrolysis. A significant Zn diffusion into the underlying carbon posts was observed during the ALD process. The addition of a sputter-deposited ZnO interfacial layer efficiently blocked the Zn diffusion without altering the microstructure and surface morphology of the ALD-ZnO film.

Polarity effect of pulsed corona discharge for the oxidation of gaseous elemental mercury.

The effect of polarity on the oxidation of Hg(0) was examined in the presence of O(2) via a pulsed corona discharge (PCD). The experimental result showed no difference in the energy yield of Hg(0) oxidation at both positive and negative PCDs (∼8 µg Hg Wh(-1) at following conditions: total flow rate=2 L min(-1) (Hg(0)=50 µg Nm(-3), O(2)=10%, and N(2) balance), temperature=150°C, and specific energy density=5-15 Wh Nm(-3)). This suggests that the positive PCD process used to control gaseous air pollutants may play an essential key role in Hg(0) oxidation because it consumes enough energy (∼15 Wh Nm(-3)) but an electrical precipitator could not because it consumes less energy (∼0.3 Wh Nm(-3)) to oxidize Hg(0).

Hydrogen recovery from the thermal plasma gasification of solid waste.

Thermal plasma gasification has been demonstrated as one of the most effective and environmentally friendly methods for solid waste treatment and energy utilization in many of studies. Therefore, the thermal plasma process of solid waste gasification (paper mill waste, 1.2 ton/day) was applied for the recovery of high purity H(2) (>99.99%). Gases emitted from a gasification furnace equipped with a nontransferred thermal plasma torch were purified using a bag-filter and wet scrubber. Thereafter, the gases, which contained syngas (CO+H(2)), were introduced into a H(2) recovery system, consisting largely of a water gas shift (WGS) unit for the conversion of CO to H(2) and a pressure swing adsorption (PSA) unit for the separation and purification of H(2). It was successfully demonstrated that the thermal plasma process of solid waste gasification, combined with the WGS and PSA, produced high purity H(2) (20 N m(3)/h (400 H(2)-Nm(3)/PMW-ton), up to 99.99%) using a plasma torch with 1.6 MWh/PMW-ton of electricity. The results presented here suggest that the thermal plasma process of solid waste gasification for the production of high purity H(2) may provide a new approach as a future energy infrastructure based on H(2).

Removal mechanism of elemental mercury by using non-thermal plasma.

The removal mechanism of elementary mercury (Hg(0)) by non-thermal plasma (NTP) has been investigated, where dielectric barrier discharge and O(3) injection methods as oxidation techniques are employed, together with the analysis of mercury species deposited on the reactor surface using temperature-programmed desorption and dissociation (TPDD) and scanning electron microscopy-energy dispersive spectroscopy. The removal of Hg(0) by NTP is found to be time-dependent and proceed through three domains; the Hg(0) concentration just slightly decreases as soon as NTP is initiated and then becomes constant for several minutes (Region 1), thereafter starts to decrease rapidly for 1h (Region 2) and, after passing fall-off region, very slowly decreases for about 4h (Region 3). The deposited mercury species on the reactor surface were conglomerated like islands, rather than dispersed uniformly, and their ratio of Hg(0) to O composition is observed to be 1:2. Additionally, the new peak in TPDD spectra observed in the region of 260-380°C is proposed as HgO(3). These results lead us to conclude that the deposited mercury species by NTP have extra O atoms to oxidize the adsorbed Hg(0), resulting in the acceleration of removal rate as the oxidation of Hg(0) proceeds.

Demonstration of thermal plasma gasification/vitrification for municipal solid waste treatment.

Thermal plasma treatment has been regarded as a viable alternative for the treatment of highly toxic wastes, such as incinerator residues, radioactive wastes, and medical wastes. Therefore, a gasification/vitrification unit for the direct treatment of municipal solid waste (MSW), with a capacity of 10 tons/day, was developed using an integrated furnace equipped with two nontransferred thermal plasma torches. The overall process, as well as the analysis of byproducts and energy balance, has been presented in this paper to assess the performance of this technology. It was successfully demonstrated that the thermal plasma process converted MSW into innocuous slag, with much lower levels of environmental air pollutant emissions and the syngas having a utility value as energy sources (287 Nm3/MSW-ton for H2 and 395 Nm3/MSW-ton for CO), using 1.14 MWh/MSW-ton of electricity (thermal plasma torch (0.817 MWh/MSW-ton)+utilities (0.322 MWh/MSW-ton)) and 7.37 Nm3/MSW-ton of liquefied petroleum gas.

Insight into the unique oxidation chemistry of elemental mercury by chlorine-containing species: experiment and simulation.

This work investigated the oxidation chemistry of elemental mercury (Hg(0)) by chlorine-containing species produced indirectly through the gas-to-solid phase reaction between NO(x) gases and NaClO(2) powder (NaClO(2)(s)), where both experiment and simulation results were compared to clarify which species are responsible for the oxidation of Hg(0). At first, we introduced 30 ppm of NO(2) into the pack-bed reactor containing NaClO(2)(s) to produce OClO species and then injected NO and Hg(0) (260 microg/Nm(3)) to Mixer, where the concentration of NO was varied up to 180 ppm and the reaction temperature was set to 130 degrees C. We observed for the first time that the degree of Hg(0) oxidation is completely controlled by the introduced concentration of NO: for example, the oxidation efficiency of Hg(0) is drastically increased to become 100% at near 7 ppm NO, but further increasing NO concentration results in the oxidation efficiency of Hg(0) being gradually decreased. The simulation results indicated that such a propensity of Hg(0) oxidation efficiency to NO concentration can be attributed to the NO concentration-dependent Cl, ClO, and Cl(2) formation which plays a critical role in the oxidation of Hg(0).