Low Bond Energy Research Articles

Investigation of Nitrogen Induced closely coupled Sb based Quantum Dots for Infrared Sensors Application

ABSTRACTWe report the growth and structural properties of InSb and InSb:N quantum dots on InAs and GaAs substrates. Strain induced, self-assembled quantum dots are grown using solid-source molecular beam epitaxy. For improved growth control, we developed a growth technique similar to atomic layer epitaxial methods. InSb and InSb:N multiple quantum dots formed on both InAs and GaAs. We explain the formation of multiple quantum dots by the anisotropic distribution of strain energy within the quantum dot, the long adatom lifetime during atomic layer epitaxy, and the low bond energy of InSb. Nitrogen incorporation during formation of quantum dots changes surface energy barrier and causes anisotropic distribution of strain energy, results in formation of closely coupled multiple quantum dots in <110> orientation. We obtained mid infrared luminescence around 3.6 μm from InNSb QDs grown on InAs substrate, where it exhibits relatively low efficiencies of nitrogen incorporation compared to the quantum well structure.

Enhanced TiO 2 photocatalytic degradation of bisphenol A by β-cyclodextrin in suspended solutions

Enhancement of β-cyclodextrin (β-CD) on TiO 2 photocatalytic degradation of bisphenol A (BPA) was investigated under a 250 W metal halide lamp ( λ ≥ 365 nm) in this work. In the system of photocatalytic degradation of BPA, the photodegradation rate of BPA in aqueous solutions containing β-CD and TiO 2 was obviously faster than that in aqueous solutions containing only TiO 2. After 60 min of irradiation, β-CD could increase the photodegradation efficiency by about 23% for 10 mg l −1 BPA in the UV–vis/TiO 2 system, the photodegradation of 2.5–20.0 mg l −1 BPA in aqueous solutions was found to follow pseudo-first-order law, and the adsorption constant and the reaction rate constant of BPA in the system containing β-CD and TiO 2 are obviously higher than those in the system containing only TiO 2, the influence factors on photodegradation of BPA were studied and described in details, such as β-CD concentration, pH, BPA initial concentration and gas medium. The formation of CO 2 as a result of mineralization of BPA was observed during the photodegradation process. After 120 min of irradiation, the mineralization efficiency of BPA reached 100% in the presence of β-CD, whereas mineralization efficiency was only 36.7% in the absence of β-CD. The enhancement of photodegradation of BPA mainly results from the enhancement of adsorption of BPA on TiO 2 surface and the lower bond energy between some atoms in BPA molecule after inclusion interactions with β-CD.

Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide.

The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

Self‐assembly of compounds based on a glycerin skeleton as a C‐3 building block. Part I

AbstractBiological structures from proteins through viruses to cellular organelles with dimensions of 1 to 100 nm require molecular self‐assembly and self‐organization to form nanostructures. In contrast to covalent bonding, noncovalent interactions such as hydrogen bonding and hydrophobic association involve lower bond energies (2–20 kcal/mol) to attain the mobility and fluidity properties of biological structures. Noncovalent interactions are also well‐known with amphiphilic molecules bearing both hydrophilic head groups and hydrophobic groups and are responsible for the formation of several types of self‐assemblies such as micelles, liquid crystals, and lipid bilayers. As typical amphiphiles with a glycerin skeleton as a C‐3 building block, alkyl glyceryl ethers and their derivatives have been of interest since they show unique self‐assembly structures such as liquid crystals with hitherto unknown character.

Density Functional Study of Metal−Arene Compounds: Mono(benzene)chromium, Bis(benzene)chromium and Their Cations

To investigate the elementary events of the decomposition of transition metal complexes, a density functional study of the systems Cr(C6H6)2 and Cr(C6H6) as well as their corresponding cations, has been carried out. The results give a low bond energy (0.36 eV) for the neutral Cr(C6H6) compound while the binding energy of the cation Cr(C6H6)+ is much higher (1.84 eV), in good agreement with previous theoretical and experimental studies. Concerning the dissociation of Cr(C6H6)2, the first process (dissociation of the first ligand) needs much higher energy than the second one, and depends on the intersystem crossing relaxation (ISC) of the intermediate Cr(C6H6) compound. Taking into account the ISC process, the three-body decomposition occurs at 3.40 eV, in good agreement with recent experimental results. In the case of the Cr(C6H6)2+ dissociation, both processes (with and without ISC) may be available from recent experimental works. Our theoretical results reproduce very well the values corresponding to bot...

Gas-Phase Structures of Acetyl Peroxynitrate and Trifluoroacetyl Peroxynitrate

The molecular structures and conformational properties of acetyl peroxynitrate (PAN, CH3C(O)OONO2) and trifluoroacetyl peroxynitrate (FPAN, CF3C(O)OONO2) were investigated in the gas phase by electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical methods (HF/3-21G, HF/6-31G*, MP2/6-31G*, B3PW91/6-31G*, and B3PW91/6-311+G*). All experimental and theoretical methods show the syn conformer (C=O bond of acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-NO2 bonds are extremely long, 1.492(7) A in PAN and 1.526(10) A in FPAN, which correlates with their low bond energy and the easy formation of CX3C(O)OO* and *NO2 radicals in the atmosphere. The O-O bonds (1.418(12) A in PAN and 1.408(8) A in FPAN) are shorter than that in hydrogen peroxide (1.464 A). In both compounds the C-O-O-N dihedral angle is close to 85 degrees.

Structure and bonding of transition metal-boryl compounds. Theoretical study of [(PH3)2(CO)ClOs-BR2] and [(PH3)2(CO)2ClOs-BR2] (BR2 = BH2, BF2, B(OH)2, B(OCH=CHO), Bcat).

Quantum chemical DFT calculations using the B3LYP functionals have been carried out for the electronically unsaturated 16 VE five-coordinate osmium boryl-complexes [(PH3)2(CO)ClOs-BR2] and the 18 VE six-coordinate complexes [(PH3)2(CO)2ClOs-BR2] with BR2 = BH2, BF2, B(OH)2, B(OHC=CHO), and Bcat (cat = catecholate O2C6H4). The bonding situation of the Os-BR2 bond was analyzed with the help of the NBO partitioning scheme. The Os-B bond dissociation energies of the 16 VE complexes are very high, and they do not change very much for the different boryl ligands. The 18 VE complexes have only slightly lower bond energies than the 16 VE species. The Os-B bond in both classes of compounds is provided by a covalent sigma-bond which is polarized toward osmium and by strong charge attraction. Os-->B pi-donation is not important for the Os-B binding interactions, except for the Os-BH2 complexes. The stability of the boryl complexes [Os]-BR2 comes mainly from B<--R pi-donation, which is clearly higher than the Os-->B pi-donation. The intraligand charge distribution of the BR2 group changes little when the Os-B bond is formed, except for BH2. The CO ligand in [(PH3)2(CO)2ClOs-BR2] which is trans to BR2 has a relatively weak bond to the osmium atom.

Formation of tantalum hydrides in high electric field

During the low-temperature field evaporation of the emitter of tantalum, carried out in the presence of a small amount of hydrogen in the system, tantalum mono-, di- and trihydride ions are detected. The formation process of hydrides is explained based on the electric field-induced, localized energy states of tantalum, which combines with the field adsorbed hydrogen to produce a transition complex on the emitter surface. The complex with its low surface bond energy undergoes desorption in the high electric field applied.

Ab initio study of the potential energy well of dithiomalondialdehyde on varying the S⋯S distance

The potential energy well evolution on varying the S⋯S distance of the intramolecular S–H⋯S hydrogen bridge of dithiomalondialdehyde and the related frequencies of the S–H stretching vibration mode were calculated at different levels of ab initio calculations. The trend of the curves, as well as that of the proton transfer barrier, are similar to those of malondialdehyde, which was previously studied. The limit distance for passing from double to single minima is 3.15–3.2Å. The very low hydrogen bond energy (EHB) undergoes remarkable changes on changing the approach adopted for the correlation energy calculation (MP2 or B3LYP) and on the zero point energy correction. To test its dependence on the conjugation and steric effects, calculations were extended also to 3-formyl-dithiomalondialdehyde, 3-t-butyl-dithiomalondialdehyde, dithioacetylacetone and 3-t-butyl-dithioacetylacetone. Unlike in malondialdehyde and acetylacetone, cumbersome groups in the 3 position cause weakening or complete breaking of the hydrogen bridge.

Theoretical studies of H 2 desorption processes in chemical vapor deposition of boron-doped silicon surfaces

The desorption of hydrogen in the chemical vapor deposition (CVD) of boron-doped silicon (100) surfaces is investigated using density functional theory and cluster models. The cluster models examine reactions of hydrogen atoms bound to adjacent BSi surface sites that would arise during the decomposition of B 2H 6 and SiH 4 on a B-doped polysilicon film that is being formed by CVD. Comparisons are made with the analogous processes involving desorption of H 2 from Si dimers, as well as with previous studies in the literature. Calculations show a barrier of approximately 25 kcal/mol for desorption of H 2 from Si 8BH 14 (‘HBSiH’) and Si 8BH 15 (‘HBSiH 2’) clusters. These calculated barriers may be compared to values of (a) 75–85 kcal/mol typically obtained from other cluster calculations for ‘prepairing’ and ‘isomerization pathways’ from Si dimers on the surface; (b) 53–58 kcal/mol for desorption from SiH 2 ‘defects’; and (c) 55–60 kcal/mol from two-dimensional periodic slab calculations of hydrogen desorption from Si surfaces. These results indicate that barriers for desorption of H 2 from BSi-containing surface dimers are lower than desorption of H 2 from Si surface dimers. These lower barriers arise in part because the hydrogen bound to the B surface atom involves four-coordinate B species which have lower bond energies than classical BH or SiH bonds. These lower barriers could play a role in explaining the increased growth rate of Si observed when chemical vapor deposition is carried out using both SiH 4 (or SiCl 2H 2) and B 2H 6 precursors. Finally we examined briefly the role of subsurface B atoms in the desorption of hydrogen from Si surfaces, as occurs in desorption studies on annealed B-doped Si films. Small lowerings in the hydrogen desorption energy (from 54 to 52 kcal/mol) and activation barrier (from 76 to ∼70 kcal/mol) were found due to the effect of subsurface B atoms in Si clusters.

Stability of hollow spheroidal silicon clusters Sin and SinHn

The structures of Sin and SinHn fullerenes with 20 ≶n ≶60 are calculated in the MINDO/3 approximation using the Monte Carlo technique for geometry optimization. The calculations show that spheroidal silicon clusters consisting of more than 36 atoms are stable and the bond energy increases with their size. This increase is not noticed for compact clusters calculated as an alternative. For n ≥40-50, the latter have lower bond energies compared to fullerenes. The geometry optimization of the tetrahedral cluster Si45 results in a structure close to spheroidal, which gains in bond energy. The addition of hydrogen atoms to small deformed fullerenes and their geometry optimization make it possible to obtain stable spheroidal structures SinHn whose bond energy is greater than that of alternative compact silicon hydride clusters. When the size of spheroidal clusters SinHn increases, i. e., when n > 36, the hydrogen elimination barriers decrease abruptly; the SinHn diamond structure of the cluster is more advantageous when n ≥50.

Ultraviolet Photodissociation of Gas-Phase Alcohols, Amines, and Nitroalkanes

The 193-nm photochemistry of alcohols, amines, and nitroalkanes in the C3-C6 size range is presented. The photolysis products are photoionized with coherent vacuum ultraviolet radiation and analyzed by time-of-flight mass spectrometry. For alcohols and amines, C-C bond dissociation competes with dissociations involving the heteroatom (C-O, O-H, C-N, N-H). Dissociation of the α(C-C) bond is preferred over other locations. Dissociation of a C-C bond is suppressed when a methyl radical would be produced. This behavior is similar to that observed for other substituted alkanes. Nitroalkanes exhibit both C-N and N-O bond dissociation pathways. Their low bond energies cause a substantial amount of internal energy to be partitioned among the primary photodissociation products. Under collision-free conditions, the alkyl radicals produced from these molecules undergo extensive secondary fragmentation. If the photodissociation step is performed in a free jet expansion, collisional cooling stabilizes the primary products and allows large species, such as intact pentyl and hexyl radicals, to be detected.

On some fundamental factors in the effect of alloying elements on passivation of alloys

Passsivity promoters and dissolution moderators are identified among metallic elements and classified by considering two fundamental properties, which are the metal-oxygen bond strength and the metal-metal bond strength. Passivity promoters are elements which combine a high metal-oxygen bond strength (high heat of adsorption of oxygen or OH ( ΔH ads(ox)) with a low metal-metal bond energy ( ε M-M), because the transition from adsorbed O or OH overlayer to 3D oxide requires the breaking of metal-metal bonds. In contrast, dissolution moderators are expected to be elements with a high metal-metal bond energy. Groups of metals appear clearly in a diagram of ΔH ads (oxygen) and ε M-M.

In Situ Chamber Cleaning Using Halogenated–Gas Plasmas Evaluated by Plasma-Parameter Extraction

We have demonstrated that high-efficiency in situ chamber cleaning with high gas flow rate is possible for SiO2 reactive-ion-etching chambers by use of NF3 plasma. The plasma of NF3 gas, which has a low bond energy, can generate a high density of ions and radicals with low kinetic energy. The cleaning efficiency of several halogenated-gas plasmas has been evaluated based on extracted-plasma-parameter analysis. In this analysis important plasma parameters, such as ion energy and ion flux density, could be extracted from a simple rf waveform analysis at the excitation electrode. The accuracy of this technique has been confirmed with a newly developed rf-plasma direct probing method. Furthermore, the waveform of the rf-excited plasma potential has been directly measured by the rf-plasma probing method, which has clarified the relationship between the plasma potential and the rf electrode voltage.

Radiation induced degradation of Si/SiO2 structures and the nature of defects

Differently prepared specimen show after different irradiation treatments (VUV or X-ray) the same character of interface state distribution and hole trap related oxide charge. The dominating interface state generation process is considered to be a breaking-up of Si-H bonds. Centres of both hack bond configurations (Si3)≡Si-H and (Si2O)≡Si-H are involved, where the latter has stronger irradiation effects due to the lower bond energy. The radiation induced oxide charge consists of positively charged hole traps with a trap energy of Et = 6.3 eV. They are dischargeable by electron tunneling from the adjacent Si. This leads to a dynamical trapping behaviour dependent only on the hole current density. Our results confirm that the paramagnetic E'-centre constitutes the positively charged hole trap.

Die Wechselwirkung von N3F mit Lewis-Säuren und HF. N3F als möglicher Vorläufer für die Synthese von N3 +-Salzen / The Interaction of N3F with Lewis-Acids and HF. N3F as Possible Precursor for the Synthesis of N3 + Salts

Triazadienyl fluoride, N3F, forms stable adducts with BF3 and AsF5 at low temperatures, as demonstrated by infrared measurements. The Lewis acids are bonded to the Nα-atom of N3F, as deduced from the data for 15N-isotopically enriched N3F. The basicity of N3F is comparable to that of ethine and ethene, according to the HF stretching frequency of the N3F/HF complex isolated in an argon matrix. Despite the low NF bond energy (&amp;lt; 150 kJ/mol), abstraction of the fluoride ion and formation of an N3 + salt was not possible. The different behavior of N3F and ClN3 towards Lewis acids is discussed.

Anomalously Low Bond Energy of Surface Oxygen on FeZSM-5 Zeolite

Calorimetric measurements have shown that surface oxygen resulting from N2O decomposition on FeZSM has an anomalously low bond energy, which accounts for some peculiar properties of this oxygen, including its high reactivity.

Proton transfer reactions of C 2H + [rad]2 : the bond energy D0 (C 2HH)

Reactions of C 2H + 2 with a series of molecules having different proton affinities were studied on a selected ion flow tube (SIFT) in order to bracket the proton affinity of the C 2H radical. Reactions with XCN (X = Cl, Br) were particularly relevant and yielded PA (C 2H ) = 175 ± 1 kcal mol −1 at 298 K. A thermochemical cycle leads to the bond energy D 0 (C 2HH) = 123 ± 1 kcal mol −1. Since the proton transfer reactions were studied only in the forward direction, these values were obtained from correlations between the efficiency of proton transfer and the overall reaction thermochemistry. The observation of H atom transfer from C 2H 2 to NH + 3 verifies the rather low bond energy in acetylene.

The pitting corrosion potentials of metals and surface alloys in relation to their solid state cohesion

Recent data on the pitting potentials of metals in chloride ion solutions, as well as on the pitting potentials of surface alloys (prepared by ion implantation) of aluminum in solutions containing chloride ions, are examined in relation to the solid state cohesion of corresponding metals and alloys. Consistent with our previous proposal, it is shown that low metal-metal bond energies, b(M-M), herald less noble pitting potentials both for metals and alloys. These observations are interpreted as a support for the suggestion of Richardson and Wood [1], and, Galvelle et al. [2] that pitting is the active dissolution of the bare metal sites in the micro-fissures and defects of the oxide, under attack by the aggressive anions such as the halide. The oxide itself is concluded to play an inert role and the events postulated by Natishan and coworkers [6] invoking anion adsorption on, and penetration through, the oxide surface to initiate pitting have been found to be less solidly based in experimental facts.

石炭の熱分解による液状成分の生成

The formation of liquid products such as BTX and tar from the pyrolysis of coal was reviewed from a chemical point of view. First, the dissociation of bonds in coal during heat treatment was discussed. Polymethylene and/or oxymethylene bridges play important roles for the tar formation, because of their relatively low bond energies. The radicals produced in the above stage should be stabilized by hydrogen supplied either from other parts of coal molecule or from ambient atmosphere to yield liquid products. The factors which affect the final product yields were discussed. The secondary reaction of primary volatile matter is essential in this respect. The temperature, heating rate, residence time, coal particle size, gas pressure and minerals in coal all influence the secondary reaction. A molecular model of a bituminous coal and the reaction model during pyrolysis were proposed