Addition Of HF Research Articles

Selective one-step Chemical Etching of the Silicon Nitride/Silicon PBL stack for 0.5μm device Fabrication

ABSTRACTAbstract Wet chemical removal of a silicon nitride/silicon Poly Buffer LOCUS (PBL) film stack with a phosphoric/nitric acid solution was characterized. Though silicon nitride etch rates remain constant, silicon etch rates decrease as a function of loading which severely limits the usable lifetime of the bath. This is caused by buildup of etching products which limits the amount of silicon that can be dissolved in the solution. Addition of HF to the phosphoric/nitric acid solution enhances the dissolution chemistry presumably by decomposing the silica reaction products and shifting the equilibrium. Characterization of this process was done to determine whether it could be applied towards PBL removal. Depending on the relative amounts of HF and HNO3 added, silicon etch rates could be enhanced by two orders of magnitude (200–400A/min) and silicon nitride etch rates by a factor of two. Selectivities for etching silicon to oxide and silicon nitride to oxide were typically between 8–12:1 and 8–20:1 respectively.

XPS Analysis of Lithium Surface and Modification of Surface State for Uniform Deposition of Lithium

ABSTRACTThe surface modification of lithium deposited at various current densities in propylene carbonate containing 1.0 ml dm−3 LiCIO4 was performed by addition of various amount of HF into the electrolyte, in order to investigate the effect of the HF addition on the surface reaction of lithium. XPS and SEM analyses showed that the surface state of lithium was influenced by the concentration of HF and the electrodeposition current. These two parameters are related to the chemical reaction rate of the lithium surface with HF and the electrodeposition rate of lithium, respectively. The surface modification was highly effective in suppressing lithium dendrite formation when the chemical reaction rate with HF was greater than the electrochemical deposition rate of lithium.

Effect of Hf addition (0.24 w/o) on the oxidation behavior of TiAl at high temperatures

The isothermal oxidation behavior of TiAl coupons containing 0.24 wt.% Hf has been studied in the temperature range 1100 to 1400 K in a flow of purified oxygen at atmospheric pressure. The addition of Hf is very effective in decreasing the overall oxidation rate at temperatures up to 1300 K, although the oxidation rate was slightly increased during the initial period of about 10 ks, after which a very low oxidation rate was maintained. However, at 1350 K the effect becomes small, and at 1400 K it is inverted. The excellent oxidation resistance obtained is attributable to the formation of two alumina-rich layers in the scale; one is beneath the outer rutile layer and the other at the scale/substrate interface. In addition, no internal oxides were formed in the substrate up to 1300 K.

Gradient line reaction path of HF addition to ethylene

The gradient line reaction path of the HF addition to ethylene is shown to consist of two distinct gradient lines. The first connects the reactant minimum via one transition state to another transition state. The second is associated with the internal rotation about the carbon-carbon bond in ethyl fluoride and this gradient line also passes through the second transition state. The main feature of this reaction path is that the first gradient line is not connected to the product minima directly.

The influence of HF on the incorporation of silicon into the erionite‐like AlPO4‐17 molecular sieve

AbstractThe synthesis of SAPO‐17 with high silicon content (up to 18 weight‐%) succeeded with the addition of HF to the reaction mixtures. The characterization of the samples with chemical analysis, XRD, and adsorption measurements show the incorporation of silicon into tetrahedrally coordinated framework positions. Spectroscopic methods (IR, 19F MAS NMR) demonstrate the presence of fluorine in the as‐synthesized samples. The effect of the fluorine consists in (i) the improvement of the silicon incorporation into framwork positions, (ii) the stabilization of the as‐synthesized samples and (iii) the charge compensation of the template ion by F−.

Effect of Ternary Additions on the Intrinsic Ductility of Ni3Al Alloys

AbstractDuctility of binary and ternary Ni3Al alloys with conventional purity, fabricated by isothermal hot-forging, was examined by tensile tests in dry oxygen to eliminate environmental embrittlement. Re crystallized Ni-23A1 doped with approximately 0.4 mol% X(X=Hf, Nb, and Zr) alloys exhibits pronounced ductility, whereas recrystallized Ni-23A1–2X alloys exhibits elongation of less than 3%. Ductility of a highly purified binary Ni-23A1 alloy was also examined and showed remarkable ductility, resulting in trans granular fracture. This indicates that a Ni-rich Ni3Al alloy inherently exhibits marked ductility without intergranular fracture if impurity atoms and other extrinsic factors(e.g., environmental effect and internal microcracks) are eliminated in the alloy. Thus it is found that Hf, Nb and Zr in the significant ductilization of Ni-23A1 can act as a scavenger of harmful impurities when added in a small amount. With further increasing amount of additions of Hf, Nb and Zr, elongation decreases rapidly and reaches almost no ductility at 2 mol% additions, indicating that Hf, Nb and Zr lower the intrinsic ductility of Ni3Al alloy.

Prediction of whole reaction paths for large molecular systems

Reaction pathways for large systems such as proteins or other macromolecules are difficult to model using standard methods owing to the many degrees of freedom in such systems. Standard Euler-type methods which require knowledge of a transition structure, from which the path to two energy minima may be obtained are very inefficient when a whole reaction path is required since only small steps may be used with such methods. Furthermore, the location of a transition may itself be very difficult for large systems. Given these problems, an alternative approach (as suggested by Elber and Karplus, Chem. Phys. Lett., 1987, 139, 375), based on minimizing a functional of the entire path appears very attractive. This approach has not, previously, been evaluated for quantum-mechanical reaction surfaces, only for molecular mechanical surfaces. The assessment of a scheme, based on the Elber–Karplus approach, within both an ab initio and semi-empirical molecular orbital framework is presented. The method is evaluated by comparing the predicted paths with those obtained by the much used Gonzalez–Schlegel method for three model systems (isomerization of HCN, SN2 reaction of F– and CH3F and the addition of HF to ethene). The method is also tested on reactions without a transition state (hydride attack on an ester and a thioester). In the latter case, the conventional methods are more difficult to apply. The extension of the method to describe reactions in solution is discussed.

ChemInform Abstract: Advanced Ultrapure Water by HF Addition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Advanced Ultrapure Water by HF Addition

To improve ultrapure water, the additional effect of in pure water was investigated. Both formation of native oxide on the Si wafer surface and generation of viable cells in pure water can be prevented by using pure water containing on the order of parts per million instead of conventional pure water. Moreover, by using PFA or PTFE as a pipe material, pure water containing which was not contaminated by metal ions and viable cells can be fed to point of use without a circular line such as a conventional pure water feeding line.

The reactions of xenon difluoride with ‘inert’ solvents

The reactions of XeF 2 with a variety of organic solvents are described. XeF 2 is foundto undergo both hydrogen- and chlorine-fluorine exchange over a relatively short timescalewith chloroform, dichloromethane and dibromomethane. XeF 2 reacts very slowly withtetrachloromethane and fluorotrichloromethane, although the addition of a catalytic amountof HF increases the rate of reaction considerably. XeF 2 dissolves in acetonitrile withnegligible reaction to the extent of 2.25 mol kg −1.

Correcting for basis set superposition error in aggregates containing more than two molecules: ambiguities in the calculation of the counterpoise correction

The counterpoise correction (CP) for the basis set superposition error (BSSE) for multimolecular aggregates can (in principle) be calculated by several different procedures, which give significantly different results. Three of these procedures are discussed and illustrated with the HF---(HF) n ---HF H-bonding aggregate. The three methods are (a) proceeding as if a dimer were formed between a unit of HF added to the H end of the growing aggregate, (b) as above, but with the HF being added to the F end, and (c) using the difference between the calculated CPs for the two aggregates before and after addition of the last HF, where the CPs for each aggregate are calculated using each monomeric unit in each aggregate with the ghost orbitals of all the other monomers

Fluoride Interference in the Determination of Boron by Inductively Coupled Plasma Emission Spectroscopy

Boron determination in borophosphosilicate glass films by the ICP-AES or ICP-MS technique can be performed after dissolution of the sample in HF solution. However, addition of HF to boric acid standard solution can cause a drift in the slope of the calibration curve. The signal change was correlated with the kinetics of the borontetrafluoride complex formation reaction. The mechanism was explained by the selectively increased boron transport into the plasma, which was caused by the more efficient diffusion of borontrifluoride gas through the aerosol particles into the nebulizer gas. With the kinetics of borontetrafluoride complex formation taken into consideration, an accurate and precise method was developed for the determination of boron in BPSG films.

Effect of Ti/Al ratio and Cr, Nb, and Hf additions on material factors and mechanical properties in TiAl

The effect of the Ti/Al ratio and Cr, Nb, and Hf additions on material factors, such as the grain size, second phase, la tice parameters and the axial ratio, and on mechanical properties in TiAl-base alloys has been studied. The grain size was decreased by the deviation from the stoichiometric composition o the Ti-rich side and the addition of the third elements. The Cr element was contained a little more in Ti3Al phase than in TiAl phase in two-phase Ti-rich alloys. The lattice parameters,a andc, and the axial ratio,c/a, of the binary alloys varied linearly with decreasing Al content even in the dual-phase region. The Cr addition decreased thea and c and alsoc/a. The Nb addition increased weakly thea andc andc/a. On the contrary, the Hf addition increased thea andc but decreased thec/a ratio. In the Cr added alloys, the decrease of volume of a unit cell, due to the substitution of Cr atoms for Ti and Al atoms, was larger than that expected from the difference of atom sizes. The Nb addition should decrease the volume of a unit cell, but it increased the volume. The Hf addition caused a larger increase of volume of a unit cell than that expected from the difference of atom sizes. We suggested that the Cr addition increases and the Nb and Hf additions decrease the bond strength in TiAl. The deviation from stoichiometry and the addition of third elements caused an increase of work-hardening rate. The alloys with Ti-rich composition have superior mechanical properties compared to those of alloys vith Al-rich composition. The Cr addition resulted in high solution hardening, and the Ti-47A1 3Cr (in atomic percent) alloys had the highest fracture strain of 2.7 pct in all alloys tested. The Nb addition resulted in poor ductility in both Ti- and Al-rich alloys. The Hf additions to the Ti-rich composition caused better mechanical properties than those of Al-rich alloys. Thi; trend was also similar to the Nb-added alloys. In the Hf-added alloys, the Ti-49Al-2Hf alloy has rather high ductility of about 2.15 pct. The effect of structural parameters on mechanical properties was discussed. The smaller grain size and the smaller axial ratio tended to result in larger ductility. The increase of the bond strength might improve ductility.

Bronze-processed Nb 3Sn with addition of germanium to matrix

The effects of addition of Ge to the matrix of bronze-processed Nb 3Sn on the structure and superconducting properties have been studied. The simultaneous addition of Ta, Hf and Ti to the Nb core has also been carried out. The critical current density, J c, of Nb 3Sn was appreciably increased by the addition of Ge. The simultaneous addition of 0.5 at% Ge to the matrix and 1 at% Ta to the core enhances the J c of Nb 3Sn at 12 T by one order of magnitude. This increase in the J c of Nb 3Sn seems to be attributed to the grain refinement of Nb 3Sn by the addition of Ge. The formation of a thin layer richer in Ge is observed in the matrix adjacent to the Nb 3Sn layer, which may be effective in reducing the proximity effect between Nb 3Sn filaments in cases of a.c. use.

High temperature thermal expansion characteristics of Ni 3Al alloys

The thermal expansion of Ni 3Al alloys with and without ternary additions have been investigated with the aid of a dilatometer. The Ni 3Al alloys were studied over the temperature range 25–1000 °C. The coefficient of thermal expansion α of all the aluminides studied in this investigation varies linearly with the temperature. The coefficient of thermal expansion of Ni 3Al is found to show an increase with the decrease in Al content from stoichiometric composition. B and Zr additions decrease the value α of Ni 3Al alloys at room temperature while Hf and Ti additions do not alter it significantly.

Ｂｉ系酸化物超伝導体のＨｆ添加によるＴｃへの影響

Ｂｉ系酸化物超伝導体のＨｆ添加によるＴｃへの影響

Effect of third elements on the microhardness of Ni 3Al

The room-temperature microhardness of Ni 3Al with and without third elements has been studied using the Vicker's indentation technique. In pure Ni 3Al phase alloys, the hardness value increased with decreasing Al concentration from stoichiometric composition. This increase is attributed to the defects present at off-stoichiometric compositions. The addition of third elements Hf, Zr, Ti and Si increased the hardness value of Ni 3Al suggesting the solid-solution strengthening effect. The presence of 0.20 at% boron in Hf- and Zr-containing alloys shows a softening effect at small concentrations of Hf and Zr.

Catalytic liquid phase fluorination of C 2 chloroalkanes and C 2 chloro alkenes with SbCl 5-HF

The catalytic liquid phase fluorination of C 2 chloroalkanes and C 2 chloroalkenes to produce hydrogenochlorofluorocarbons is carried out with SbCl 5 and HF at 60–70 °C and 1 MPa. The catalytic species is prepared by reacting SbCl 5 and HF (xs) at 60 °C, for 3 hr. The excess of HF is vented; the chlorocompound is added to the reactor, followed by addition of HF. The following results are obtained: CH 3CCl 2F (73%) and CH 3CClF 2 (27%) are obtained from CH 3CCl 3 with a reaction rate equal to 1.45×10 −2 mole h −1 g −1 (SbCl 5). CCl 2HCCl 2F (82%) and CHCl 2CF 2Cl (18%) are obtained from CCl 2CCl2 with a reaction rate of 4.52×10 −3 mole h −1 g −1 (SbCl 5). The fluorination of CH 3CCl 3 is accompanied by a dehydrochlorination which gives CHCCl 2. This chloroolefin oligomerizes to give partially dehydrochlorinated by-products with general formula CH 3−(CClCH) x−CCl 3 (linear or branched). The compounds x=2 and x=4 could be isolated and hydrolysed with 6N H 2SO 4 to give 6-methyl-4-chloropyrone, 3,5-dichlorophenol and 2-methyl-5,7-dichlorochromone. Minor amounts of partially fluorinated oligomers are also formed. We thank the Atochem Company for financial support.

Fluorocarbon synthesis: halogen exchange fluorination with alkali metal polyhydrogen fluorides

A variety of fluorocarbons of current interest can be efficiently prepared via halogen exchange fluorination with alkali metal polyhydrogen fluorides, MF·nHF, where M = K, Rb, Cs or mixtures thereof and n = 0.5 to 3. [R.E. Fernandez, et al., US Pats. 4 990 701, 4 990 702 and 5 045 634 (1991)]. The alkali metal polyhydrogen fluorides can be thought of as ‘participatory solvents’ for traditional alkali metal fluoride halogen exchange reactions, since the amount of free fluoride can be readily controlled by the addition/ removal of HF as well as by varying the temperature. Thus, by controlling “n”, this methodology can be used not only for substitution reactions, but HF addition and HF elimination reactions as well. Once the desired halogen exchange/addition/elimination has taken place, the fluoride source can be easily regenerated via the addition of HF and removal of HCl. The chemical and physical properties of these systems as well as their applicability towards fluorocarbon synthesis will be presented.

Reliability of sublattice occupancies determined by ALCHEMI

The atom location by channeling enhanced microanalysis (ALCHEMI) technique is an attractive method for sublattice (site) occupancy determination, especially in multiphase materials. It has been applied to a wide range of ceramics, minerals, semiconductors and metallic alloys with varying degrees of success. The simplicity of the method originally proposed has not always been borne out in practice; applications of the technique have revealed limitations due to crystallography, microstructure, specimen preparation, ionization delocalization, and weak channeling discrimination. Some of these limitations have been encountered in work at ORNL on ALCHEMI of intermetallic alloys such as Ll2-ordered Ni3Al-based alloys (with additions of Hf, Co, and Fe) and Ll0-ordered Cu50Au50-y(X)y alloys with X = Pd or Ni. These applications have been motivated by the technological importance of ordered intermetallic alloys. Commercial materials often have complex compositions with ternary (or higher) additions present at substantial levels. The distribution of the various components on the different sublattices is an important facet of characterization for structure property correlations to help guide alloy development.