Tetramethylammonium Hydroxide Aqueous Solution Research Articles

Quartz crystal microbalance analysis of effects of surfactants on dissolution kinetics of poly(4-hydroxystyrene) partially protected with t-butoxycarbonyl group

Abstract Surfactants comprise water-repellent and water-attracting moieties and have been used to improve the lithographic performance of resist materials. However, the effects of surfactants on the dissolution kinetics of these materials are still unclear. In this study, the effects of surfactants on the dissolution kinetics of partially-protected poly(4-hydroxystyrene) (PHS) in 0.26 N tetramethylammonium hydroxide aqueous solution was investigated using a quartz crystal microbalance method. Anionic (sodium n-octanonate, sodium 1-hexanesulfonate, n-dodecylbenzenesulfonic acid, and sodium n-dodecyl sulfate), cationic (methylamine hydrochloride, dodecyltrimethylammonium chloride, and 30% ammonium lauryl sulfate solution), nonionic (sorbitan monooleate, polyoxyethylene(23)lauryl ether, and polyoxyethylene(10)hydrogenated castor oil), and amphoteric (35% lauryl dimethylaminoacetic acid solution) surfactants were examined. The surfactant significantly affected the dissolution kinetics of the PHS films. The surfactant effects were significantly reduced by protecting the hydroxyl groups of PHS. The effect of the surfactant on the dissolution kinetics depended on the surfactant rather than on the surfactant type.

Relationship between the surface free energy of underlayers and the dissolution kinetics of poly(4-hydroxystyrene) partially protected by t-butoxycarbonyl groups in tetramethylammonium hydroxide aqueous developer

In the lithography used for the high-volume production of semiconductor devices, the photoresist film becomes thin with the reduction in pattern size to prevent the pattern collapse due to the surface tension of rinsing liquids. The interfacial effect becomes strong with the reduction in photoresist film thickness. In the development process, it is of importance to clarify the relationship between the photoresist and the underlayer for fine patterning. In this study, the dissolution kinetics of poly(4-hydroxystyrene) (PHS) partially protected by t-butoxycarbonyl (t-Boc) groups in tetramethylammonium hydroxide (TMAH) aqueous solution was found to be related to the surface free energy of the underlayer. The attenuation rate of developer viscosity first decreased and then increased with the polar-to-dispersion component ratio. An inflection point with the lowest rate existed. The TMAH concentration affected not only the attenuation rate but also the ratio of polar to dispersion components at the minimum attenuation rate.

Dissolution dynamics of partially protected poly(4-hydroxystyrene) in tetraalkylammonium hydroxide aqueous solution

A 0.26 M tetramethylammonium hydroxide (TMAH) aqueous solution has been used as a standard developer for manufacturing semiconductor devices. Alternative developers have recently attracted much attention because the 0.26 M TMAH developer may be approaching its performance limit. In this study, we measured the dissolution and swelling behavior of resist polymers in tetraalkylammonium hydroxide (TAAH) aqueous solutions using a quartz crystal microbalance method to clarify the effects of the alkyl chain length of TAAH. The resist polymer was poly(4-hydroxystyrene), whose hydroxyl groups were partially protected with t-butoxycarbonyl groups. When the alkyl chain length of TAAH was increased from two (ethyl) to three (propyl), the dissolution mode markedly changed. The dissolution mode did not depend on the polymer polarity. The change in the dissolution mode is probably caused by the size effect of TAAH, considering the independence of polymer polarity and the discrete change in the dissolution mode.

Effects of film thickness and alkaline concentration on dissolution kinetics of poly(4-hydroxystyrene) in alkaline aqueous solution

The dissolution behavior of a simple combination of poly(4-hydroxystyrene) films and tetramethylammonium hydroxide aqueous solution was analyzed to gain a fundamental understanding of the effects of film thickness and alkaline concentration on the dissolution kinetics of chemically amplified resists. Films of four different thicknesses, from thick (approximately 900 nm) to thin (approximately 50 nm), were developed in 22 different developers of different concentrations. The dissolution behavior of each combination was observed using a quartz crystal microbalance. Differences in dissolution kinetics due to film thickness were observed even between relatively thick films such as 900 and 500 nm thick films in dilute developers. These differences were considered to be caused by the diffusion of the solution into the films. Thin films also showed characteristic behavior with dilution. This behavior was due to the interaction between the substrate and the films, unlike in the case of thick films.

Purification of Diatomaceous Earth using Acid Leaching Process to Produce High Purity Silica for Solar-Grade Silicon

ABSTRACT The core focus of this research study was preparation of high-purity silica by the wet-chemical process for solar grade silicon (SOG-Si) using diatomaceous earth expecting a huge amount of resources in the earth crust. Our purification method involved dissolution and precipitation of silica in sodium hydroxide (NaOH) and tetramethylammonium hydroxide (TMAH) aqueous solution followed by acid leaching with HCl solution. By decreasing the pH, more than 90% of the impurities like Al and Fe were precipitated. A large amount of Na impurities were noticed in the final silica product as NaOH was used for the preparation of aqueous alkaline solution. To overcome this serious issue deteriorating the semiconductor characteristics, the mixture of NaOH and TMAH was introduced in order to lower the Na levels during the preparation of alkaline solution. Experimental results suggested that the Na+ ions were needed to have a better dissolution rate of silica in aqueous alkaline solution. This also resulted in the optimum concentration of 0.05 M NaOH and 1.40 M TMAH for the dissolution and precipitation process in order to help the purification of silica. The 3 stages of leaching process with the above mentioned concentration helped us in achieving the 5 N (99.999 wt%) level of silica purity.

Relationship between surface free energy and development process (swelling and dissolution kinetics) of poly(4-hydroxystyrene) film in water and 2.38 wt% tetramethylammonium hydroxide aqueous solution

With the sharpening of optical images, the capability of resist materials has become a serious concern in lithography. The dissolution of a resist polymer is key to the realization of ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the relationships of surface free energy with swelling and dissolution kinetics were investigated using poly(4-hydroxystyrene) (PHS) film with triphenylsulfonium-nonaflate (TPS-nf). Developers were water and 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution. PHS and TPS-nf are a typical backbone polymer (a dissolution agent) and a typical acid generator of chemically amplified resists, respectively. The water intake and dissolution of PHS film with TPS-nf became fast with increasing UV exposure dose. It was found that the increase in the polar components (particularly, the hydrogen bonding component) and the decrease in the dispersion component of surface free energy underlie the fast water intake and dissolution.

Electrochemical exfoliation of porous antimonene as anode materials for sodium-ion batteries

Porous antimony has attracted wide attention in the area of energy storage as it can accommodate large volume change and facilitate Na+ ions diffusion. Herein, stable porous antimonene sheets with mesopores ranging from 2 to 50 nm have successfully fabricated through electrochemical exfoliation of layered bulk antimony rod in tetramethylammonium hydroxide aqueous solution with the aid of large TMA+ cations insertion and strong alkaline electrolyte environment. When utilized as anode materials for sodium-ion batteries, the as-exfoliated porous antimonene can deliver a high specific capacity of 569.1 mAh g−1 upon 200 cycles at 100 mA g−1, and it can still keep a high capacity of 277.8 mAh g−1 even at fast charge/discharge rate of 5000 mA g−1.

Enhancement of Enzymatic Hydrolysis of Lignocellulose by Tetrabutylammonium Hydroxide (TBAOH) and Tetramethylammonium Hydroxide (TMAOH) Aqueous Solution Pretreatment

AbstractBACKGROUNDLignocellulose is usually pretreated as a raw material, and then it undergoes hydrolysis, fermentation, and other processes to produce biofuels, which is conducive to improving the utilization of agricultural and forestry wastes. However, most pretreatments, such as acid–base, CO2 explosion, and microbial degradation, could enhance the yield of enzymatically hydrolyzed (EH) sugars, but the conditions are relatively harsh, environmentally unfriendly, and economically unfeasible. Ionic liquids, in view of their excellent physical and chemical properties and strong solubility, have been proven to be an effective green solvent for pretreating lignocellulose. The aim of this study was to exploit tetrabutylammonium hydroxide (TBAOH) and tetramethylammonium hydroxide (TMAOH) aqueous solutions to pretreat corn cob under relatively mild conditions.RESULTSThe optimal pretreatment conditions for the two solutions were 30 °C, TBAOH concentration of 20 wt%, 60 min, 5 wt/wt, and 20 °C, TMAOH concentration of 10 wt%, 60 min, 5 wt/wt, and the corresponding sugar yields were 88.9% and 92.2%, respectively. Compared with the unpretreated corn cob, the yield of EH sugar increased by about 2.7–2.8 times. Characterization results confirmed that hemicelluloses and lignin were removed from the raw material during the pretreatment process, and that the cellulose was purified. Furthermore, after 5 cycles of reuse of the TBAOH and TMAOH aqueous solutions, the pretreated corn cob could still achieve a sugar yield higher than 70%.CONCLUSIONThe pretreatment with TBAOH and TMAOH aqueous solutions significantly enhanced the enzymatic hydrolysis, which provided a green, simple, and economical new approach for the pretreatment of agricultural waste biomass. © 2021 Society of Chemical Industry

Controllable arrangement of integrated obstacles in silicon microchannels etched in 25 wt.% TMAX

In this paper, fabrication of silicon microchannels with integrated obstacles by using 25 wt.% tetramethylammonium hydroxide (TMAH) aqueous solution at the temperature of 80?C is presented and analysed. We studied basic island patterns, which present union of two symmetrical parallelograms with the sides along predetermined crystallographic directions <n10> (2<n<8) and <100>. Acute angles of the parallelograms were smaller than 45?. We have derived analytical relations for determining dimensions of the integrated obstacles. The developed etching technique provides reduction of the distance between the obstacles. Before the experiments, we performed simulations of pattern etching based on the level set method and presented evolution of the etched basic patterns for the predetermined crystallographic directions <n10>. Combination of basic patterns with sides along the <610> and <100> crystallographic directions is used to fabricate a matrix of two row of silicon obstacles in a microchannel. We obtained a good agreement between the experimental results and simulations. Our results enable simple and cost-effective fabrication of various complex microfluidic silicon platforms with integrated obstacles.

Low‐temperature curable, alkaline‐developable, and negative‐type photosensitive polyimide with high resolution and mechanical properties based on chain extendable poly(amic acid) and photo‐base generator

A negative‐type photosensitive polyimide (PSPI) based on a chain extendable poly(amic acid) (PAA) and a photo‐base generator (PBG) (E)‐1‐piperidino‐3‐(2‐hydroxyphenyl)‐2‐propen‐1‐one (PHPP) have been developed. The chain extendable PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) and end‐capped with di‐tert‐butyl dicarbonate (DIBOC) in N‐methyl‐2‐pyrrolidone (NMP), which has a controlled molecular weight for developing in a 2.38 wt% tetramethyl ammonium hydroxide aqueous solution (TMAHaq) and underwent a chain‐extending reaction during a curing stage. The PSPI was formulated with the polymerization solution (20 wt% in NMP) and PHPP (15 wt% for the polymer). The PSPI showed a sensitivity of 152 mJ cm−2 and a contrast of 5.9 when exposed to the i‐line, followed by post exposure baking at 160°C for 2 minutes and development with the 2.38 wt% TMAHaq containing 10 wt% iPrOH at room temperature. A fine negative image with 2‐μm pattern was obtained on a 3‐μm thick film in the contact‐printed mode. After thermal curing at 200°C for 1 hour, the resulting PSPI features low curable temperature, high resolution and excellent mechanical properties.

Alkaline‐developable positive‐type photosensitive polyimide with high mechanical strength and high resolution based on chain extendable poly(amic acid), thermally degradable cross‐linker and photoacid generator

AbstractA positive‐type photosensitive polyimide (PSPI) based on a chain extendable poly(amic acid) (PAA), a thermally degradable cross‐linker 1,3,5‐tris[(2‐vinyloxy)ethoxy]benzene (TVEB), and a photoacid generator (PAG) (5‐propylsulfonyloxyimino‐5H‐thiophene‐2‐ylidene)‐(2‐methylphenyl)acetonitrile (PTMA) has been developed. The chain extendable PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) and end‐capped with di‐tert‐butyl dicarbonate (DIBOC) in N‐methyl‐2‐pyrrolidone (NMP), which has a controlled molecular weight for developing in a 2.38 wt% tetramethyl ammonium hydroxide aqueous solution (TMAH aq) and undergoes a chain extending reaction during curing stage. The photosensitive resist solution was formulated with the polymerization solution (30 wt% in NMP), TVEB (15 wt% for the polymer), and PAG (4.5 wt% for the polymer). The PSPI showed a sensitivity of 47 mJ cm−2 and a contrast of 5.8 when exposed to 365‐nm light, followed by postexposure baking at 90 °C for 10 min and development with the 2.38 wt% TMAH aq at room temperature. A fine‐positive image with 3‐μm line‐and‐space patterns was obtained on a 3‐μm thick film exposed to UV light at 365 nm in the contact‐printed mode. After thermal curing at 350 °C for 1 hr, the resulting PSPI features excellent mechanical strength and elongation.

Oxygen Reduction Activity of Nb-Doped Titanate Nanosheets in an Acidic Electrolyte

Introduction Polymer electrolyte fuel cells (PEFCs) are of great importance as consumer use energy devices, such as fuel cell vehicles and residential micro-cogeneration systems. To reduce usage of platinum in PEFCs, non-noble metal oxide catalysts for oxygen reduction reaction (ORR) have extensively been investigated to date. From the viewpoint of stability, titanium oxides are promising candidates, though conductive path between support and active site should properly be designed because of their low conductivity. In this study, we focus on the use of titanate nanosheets as a cathode catalyst. Because titanate nanosheets are very thin, they can reduce conductive length between support and active sites. In addition, they are advantageous to form uniform composite with support materials because titanate nanosheets can be handled as a colloidal solution. From our previous study on titanium oxide nanoparticles,1) hetero-atom doping is expected to enhance the ORR activity. Here, we report the ORR activity of TNS and Nb-doped TNS (Nb-TNS) supported on carbon nanotube in an acidic electrolyte. Experimental TNS was synthesized according to the literature.2) Titanium isopropoxide (TIP) was refluxed in an aqueous solution of tetramethylammonium hydroxide for 30 min to provide titanate nanosheets with small lateral size. To synthesize Nb-TNS, niobium ethoxide was used instead of 10 mol% of TIP. Electrode materials were prepared as follows. A carbon nanotube (Flotube® 9110, denoted as CNT) was dispersed in the nanosheet dispersion, followed by stirring, sonication, and filtration with a membrane (pore size: 0.20 μm). The obtained composite was again dispersed in 1-hexanol containing Nafion® to prepare a catalyst ink. The catalyst ink was dropped onto a glassy carbon (GC) rod and dried at 60 °C for 1 h. The GC rod was used as a working electrode without rotation. The samples without titanate nanosheets, with TNS, and with Nb-TNS were named as CNT, TNS/CNT, and Nb-TNS/CNT, respectively. Electrochemical measurement was performed in a 3-electrode cell at 30 °C. 0.1 mol L–1 H2SO4 was used as an electrolyte. A reversible hydrogen electrode (RHE) and a GC plate were used as reference and counter electrodes, respectively. As a pre-treatment, 300 cyclic voltammetry (CV) cycles (0.05–1.2 V vs. RHE, 200 mV s–1) were performed under N2 atmosphere. CV (0.2–1.2 V vs. RHE, 50 mV s–1) was performed under N2 atmosphere to evaluate electric double layer capacitance (C dl) from the charges in 0.8–1.0 V vs. RHE. CV (0.2–1.2 V, 5 mV s–1) under N2 and O2 atmospheres were performed to evaluate ORR current (i ORR) which is calculated by subtracting the currents under N2 atmosphere from those under O2 atmosphere. Results and discussion The XRD pattern of the powdery samples showed diffraction peaks assignable to layered titanate (ICSD79800) without any peaks related to impurity. The d 020 value of Nb-TNS was larger than that of TNS by 0.5%. Because the d 020 reflects only in-plane crystal structure of a titanate sheet, these results imply the lattice expansion due to substitution of Ti atom with Nb. The Nb/Ti ratio of Nb-TNS was 13 mol% by XRF, which is consistent with the incorporation of Nb in Nb-TNS. Consequently, Nb-doped TNS was successfully synthesized. Fig. 1 shows the polarization curves of CNT, TNS/CNT, and Nb-TNS/CNT, normalized by the weight of CNT. The onset potential of TNS/CNT and Nb-TNS/CNT were 0.45 and 0.51 V, respectively. These were higher than that of CNT, suggesting the ORR activity due to titanate nanosheets. To compare ORR activities of TNS and Nb-TNS, the polarization curves normalized by the weight of titanate nanosheets are also shown in Fig. 2. Nb-TNS showed higher onset potential than that of TNS by 0.09 V. The Tafel plots whose current density is normalized by C dl is shown in Fig. 3. The activity of TNS/CNT was similar to that of CNT only; thus, the increased ORR activity of TNS/CNT was possibly due to increased C dl. On the other hand, the ORR activity of Nb-TNS was obviously higher than the others. Therefore, the hetero-atom doping is shown to be a useful way to improve the activity of titanate nanosheets as cathode catalyst for PEFCs. Conclusion In conclusion, TNS are advantageous to form powdery electrode composites because they are obtained as dispersions. TNS was shown to have ORR activity and the activity is enhanced by the hetero-atom doping. References 1) A. Ishihara et al, Electrochim. Acta, 283, 1779–1788 (2018). 2) E. L. Tae et al, J. Am. Chem. Soc., 130, 6534–6543 (2008). Figure 1

The dependence of AlN molar fraction of AlGaN in wet etching by using tetramethylammonium hydroxide aqueous solution

We investigated the etching rate of the m-plane of AlGaN by wet etching with tetramethylammonium hydroxide aqueous solutions (25 wt%, 85 °C). After dry etching was performed along the m-plane of AlGaN, wet etching was performed to stably form the m-plane facet of AlGaN. Also, the etching rate increases as the increased AlN molar fraction. In the case of forming a heterojunction such as a UV light-emitting diode, by performing wet etching for 5 min, the flat m-plane facets were formed even though there was a large dependence in AlN molar fraction. These facets were almost vertical and flat with respect to the c-plane, so it has the potential for the use as laser mirror. Also, no change in current density–voltage characteristics was confirmed after the wet etching. Therefore, this method is effective for deep UV laser diode fabrication technology on sapphire substrate.

Effective improvement in the etching characteristics of Si{110} in low concentration TMAH solution

An aqueous tetramethylammonium hydroxide (TMAH) solution is widely used for silicon wet anisotropic etching to perform bulk micromachining for the fabrication of microstructures on a silicon wafer. To reduce the etching time to increase the productivity, etchant must provide high etch rate. In the present work, the etching characteristics of Si{110} in low concentration TMAH (5 wt%) with the addition of various concentrations (5–20%) of reducing agent hydroxylamine (NH2OH) have been studied to increase the etch rate of Si{110} to reduce the etch time for the fabrication of microstructures. Moreover, it is aimed to enhance the undercutting at convex corner for the fast release of the structure. The etch rate of Si{110} and the undercutting at convex corners with the addition of NH2OH increases by more than three times that in pure TMAH. In addition to the etch rate and undercutting, the effect of NH2OH on etched surface morphology is investigated systematically. The present study is focused to enhance the application of wet etching in silicon micromachining for the fabrication of various kinds of microstructures for applications in microelectromechanical systems.

Accurate determination of non-metallic impurities in high purity tetramethylammonium hydroxide using inductively coupled plasma tandem mass spectrometry

The content of non-metallic impurities in high-purity tetramethylammonium hydroxide (HPTMAH) aqueous solution has an important influence on the yield, electrical properties and reliability of the integrated circuit during the process of chip etching and cleaning. Therefore, an efficient analytical method to directly quantify the content of non-metallic impurities in HPTMAH aqueous solutions is necessary. The present study was aimed to develop a novel method that can accurately determine seven non-metallic impurities (B, Si, P, S, Cl, As, and Se) in an aqueous solution of HPTMAH by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). The samples were measured using a direct injection method. In the MS/MS mode, oxygen and hydrogen were used as reaction gases in the octopole reaction system (ORS) to eliminate mass spectral interferences during the analytical process. The detection limits of B, Si, P, S, Cl, As, and Se were 0.31, 0.48, 0.051, 0.27, 3.10, 0.008, and 0.005μgL−1, respectively. The samples were analyzed by the developed method and the sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) was used for contrastive analysis. The values of these seven elements measured using ICP-MS/MS were consistent with those measured by SF-ICP-MS. The proposed method can be utilized to analyze non-metallic impurities in HPTMAH aqueous solution.

Measurement and correlation of the physical properties of aqueous solutions of ammonium based ionic liquids

In this study, thermo physical properties such as density, viscosity, refractive index and surface tension of aqueous solutions of tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH) was investigated as a function of temperature. These properties were measured in temperatures ranging from 298.15 to 333.15 K and the temperature was increased by an interval of 5 K from 298.15 K and after 303.15 K, it was increased by an interval of 10 K, while the concentrations of all the aqueous solutions were changed from 2.5 to 30 mass percent. The results revealed that the measured properties of all aqueous ILs are inversely related to temperature, while the increase in concentration had different effects on these properties. In the case of density, an increase in the concentration of ILs TMAOH and TEAOH increased their density, while the increase in the concentration of TPAOH and TBAOH decreased their density. On the other hand, the viscosities and refractive indices of all aqueous ILs increased with an increase in concentration, but the surface tensions decreased with the increase in concentration. The derived properties including thermal expansion and excess molar volume of all the aqueous ILs were determined using density data. The thermal expansion data showed an increasing trend with an increase in the temperatures and concentrations of ILs whereas the negative values of excess molar volumes decreased with an increase in temperatures. The correlation of thermo physical properties with temperatures exhibits a good agreement between experimental and predicted values.

Formation of Positive- and Negative-tone Patterns of Poly(lactic acid) by Reaction Development Patterning

Reaction development patterning (RDP) was applied to poly(lactic acid) (PLA) to realize formation of a fine pattern by a photolithography process. The RDP of PLA using an aqueous solution of tetramethylammonium hydroxide (TMAH) as a developer gave a positive-tone fine pattern. It was also revealed that addition of polyfunctional aromatic acids such as 3,5-dihydroxybenzoic acid to the film of PLA largely shortened the development time. When an alcoholic solution of TMAH was used as a developer, a negative-tone fine pattern was obtained, and pattern formation was achieved by a very short-time development without adding an acidic compound to the film.

Development of an analytical method for the determination of polybrominated diphenyl ethers in mussels and fish by gas chromatography—Inductively coupled plasma mass spectrometry

Six congeners of polybrominated diphenyl ethers (PBDEs): BDE 28, BDE 47, BDE 99, BDE 100, BDE 153 and BDE 154, were determined by a reliable and sensitive analytical method based on gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) in mussel and fish tissue samples. For their extraction, 30min of ultrasound-assisted extraction with a 25% aqueous solution of tetramethylammonium hydroxide (TMAH) and an additional 2h of mechanical shaking with tris(hydroxymethyl)aminomethane (Tris)-citrate buffer and iso-octane were applied. An effective cleaning, with minor solvent consumption, was achieved by passing the extract through a column filled with Florisil. PBDEs in the organic phase were quantified by GC-ICP-MS. Accuracy checks were performed by analyzing reference materials NIST SRM 2974a (freeze-dried mussel tissue) and SRM 1946 (fresh fish tissue homogenate) samples with a standard addition calibration method and by comparative analysis with species-specific isotope-dilution GC-ICP-MS. Good agreement of results between the determined and certified values were obtained (recoveries lied between 94 and 105%). Limits of detection (LODs) expressed on wet weight (ww) basis were 0.003ngg−1 for BDE 28, 0.006ngg−1 for BDE 47, 0.008ngg−1 for BDE 99, 0.004ngg−1 for BDE100, 0.005ngg−1 for BDE 153 and 0.009ngg−1 for BDE 154. The analytical method was applied for the determination of PBDEs in marine mussels and fish samples from the northern Adriatic Sea and fish samples from the Sava River. Among the six PBDEs congeners determined, BDE 47, BDE 100 and BDE 99 were commonly detected in the samples analysed.

A Cation Study on Rice Husk Biomass Pretreatment with Aqueous Hydroxides: Cellulose Solubility Does Not Correlate with Improved Enzymatic Hydrolysis

Biomass pretreatment is a key first step in converting recalcitrant lignocellulosic biomass into value-added products. Aqueous hydroxide solutions can be effective biomass pretreatment media, and the cation of the hydroxide salt can have an extremely significant effect upon the physicochemical behavior of the hydroxide solution. However, the cation effect has not been comprehensively investigated with respect to biomass pretreatment. Here, we investigated pretreatment of rice husks (from Oryza sativa) and show that the cation indeed has a significant effect upon downstream enzymatic hydrolysis of the cellulose (with cellulase). In particular, the ability of the solution to dissolve cellulose was negatively correlated with pretreatment effectiveness, as judged by the downstream glucose yield. This was observed by investigating aqueous solutions of lithium, potassium, cesium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, and tetrahexylammonium hydroxide. Silica solubility...

3D silicon shapes through bulk nano structuration by focused ion beam implantation and wet etching

The work presented in this paper concerns the synthesis of silicon (Si) 2D and 3D nanostructures using the delayed effect, caused by implanted Ga ions, on the dissolution of Si in aqueous solutions of tetramethylammonium hydroxide (TMAH). The crystalline silicon substrates (100) are first cleaned and then hydrogenated by immersion in an aqueous solution of hydrofluoric acid. The ion implantation is then carried out by a focused ion beam by varying the dose and the exposure time. Chemical etching in aqueous solutions of TMAH at 80 °C leads to the selective dissolution of the Si planes not exposed to the ions. The preliminary results obtained in the laboratory made it possible to optimize the experimental conditions for the synthesis of 2D and 3D nanoobjects of controlled shape and size. Analysis by transmission electron microscopy and energy dispersive x-ray showed the amorphous nature of the nanostructures obtained and the presence of 5%–20% Ga in these nanoobjects. The first experiments of recrystallization by rapid thermal annealing allowed to reconstitute the crystal structure of these nanoobjects.