Ar HCl Research Articles

Effect of plasma surface treatment on embedded n-contact for GaN-based blue light-emitting diodes grown on Si substrate

Unlike the finger-like n-contact that is prepared after the wafer bonding and the N-polar GaN surface roughening for GaN-based vertical structure light-emitting diodes (LEDs) grown on Si substrates, the embedded via-like n-contact is formed prior to the wafer bonding. The high temperature process of the wafer bonding often causes the electrical characteristics of the via-like embedded n-contact to degrade. In this paper, we study in detail the effect of plasma treatment of the n-GaN surface on the forward voltage of GaN-based LED grown on Si substrate. It is shown that with no plasma treatment on the n-GaN surface, the forward voltage (at 350 mA) of the 1.1 mm1.1 mm chip with a highly reflective electrode of Cr (1.1 nm)/Al is 3.43 V, which is 0.28 V higher than that of the chip with a pure Cr-based electrode. The LED forward voltages for both kinds of n-contacts can be reduced by an O2 plasma treatment on the n-GaN surface. But the LED forward voltage with a Cr/Al-based electrode is still 0.14 V higher than that of the chips with a pure Cr-based electrode. However, after an Ar plasma treatment on the n-GaN surface, the LED forward voltage with a Cr/Al-based electrode is reduced to 2.92 V, which is equal to that of the chip with a pure Cr-based electrode. The process window of the n-GaN surface after the Ar plasma treatment is broader. X-ray photoelectron spectroscopy is used to help elucidate the mechanism. It is found that Ar plasma treatment can increase the concentration of N-vacancies (VN) at the n-GaN surface. VN acts as donors, and higher VN helps improve the thermal stability of n-contact because it alleviates the degradation of the n-contact characteristics caused by the high temperature wafer bonding process. It is also found that the O content increases slightly after the Ar plasma treatment and HCl cleaning. The O atoms are mainly present in the dielectric GaOx film before the Ar plasma treatment and the HCl cleaning, and they exist almost equivalently in the conductive GaOxN1-x film and the dielectric GaOx film after Ar treatment and HCl cleaning. The conductive GaOxN1-x film and the VN donors formed during the plasma treatment can reduce the contact resistance and the LED forward voltage.

New potential energy surface and rovibrational spectra of Ar⋯HCl complex: An ab initio study

Two new ab initio IPESs were calculated at the RCCSD(T) level of theory employing aug-cc-pVXZ-33211(X=T and Q) basis set for Ar–HCl complex. Supermolecular approach was used to calculate the interaction energies considering counterpoise correction for the basis sets superposition error (BSSE). The calculated interaction energies were analytically fitted to an analytical potential model. Both fitted potentials show a global and local minimum related to the linear Ar⋯H–Cl and Ar⋯Cl–H configuration, respectively which agree with the developed empirical potentials reported in literature. The interaction second virial coefficients and the rotational–vibrational spectroscopic properties of Ar⋯HCl complex were obtained using the fitted potentials and compared with the available experimental data and the previous works in literature.

Determination of As and in mineral waters by fast sequential continuous flow hydride generation atomic absorption spectrometry.

In this study, a novel analytical method which consists of a combination of Fast Sequential Flame Atomic Absorption Spectrometry (FS-FAAS) and Continuous Flow Hydride Generation Atomic Absorption Spectrometry (CF-HGAAS) is proposed. The method developed was employed for the sequential determination of As and Sb at sub-μg L-1 levels in bottled mineral waters. A strong enhancement in the analytical throughput was obtained when compared with the traditional mono-element CF-HGAAS with a quartz tube atomizer (QTA). Variables which would affect the method performance such as Ar flow rate, HCl and NaBH4 concentrations as well as delay and integration time were optimized. A flame atomic absorption spectrometer working in fast sequential mode was used in all experiments. After just 20 s of read delay, As and Sb were sequentially determined in 6 s (3 s each element). A 26-2 fractional factorial design was employed for studies of potential interferents with transition metals that could be present in mineral water samples. Limits of detection obtained for As and Sb were 0.15 and 0.14 μg L-1, respectively. The accuracy of the proposed method was checked by the use of 2 certified reference materials: Trace elements in water (NIST 1643e) and Trace metals in drinking water (HPS TMDW). Good agreement between certified and found concentrations was observed. Finally, As and Sb were determined in commercial bottled mineral water samples. Adequate sensitivity, high throughput and minimization of reagents and sample consumption are the attractive features of this new method.

Accurate calculation of core-electron binding energies: multireference perturbation treatment.

Multireference perturbation theory (MRPT) with multiconfigurational self-consistent field (MCSCF) reference functions is applied to the calculations of core-electron binding energies (CEBEs) of atoms and molecules. Orbital relaxations in a core-ionized state and electron correlation are both taken into account in a conventional MCSCF-MRPT procedure. In the MCSCF calculation, the target core ionized state is directly optimized as an excited state and this treatment can completely prevent a variational collapse. Multireference Moller-Plesset perturbation theory and multiconfigurational self-consistent field reference quasidegenerated perturbation theory were used to treat electron correlation. The present method quite accurately reproduced the 1s CEBEs of CH4, NH3, H2O, and FH; the average deviation from the experimental data is 0.11 eV using Ahlrichs' VTZ basis set. The C 1s and O 1s CEBEs of formic acid and acetic acid were calculated and the results are consistent with the bonding characters of the atoms in these molecules. The present procedure can also be applied to CEBEs of higher angular momentum orbitals by including spin-orbit coupling. The calculated CEBEs of Ar 2p, HCl 2p, Kr 3d, and HBr 3d are in reasonable agreement with the available experimental values. In the calculation of the 3d CEBEs, a relativistic correction significantly improves the agreements. The effect of polarization functions is also discussed.

Infrared Q-branch absorption and rotationally-hindered species in liquids

We show the interesting sensitivity of infrared Q-branch absorption of HCl in liquid Ar to anisotropic solute–solvent interaction potentials. Comparing the differences among potentials with the different simulated absorption profiles they yield to, it is feasible to extract well-founded conclusions on the main mechanisms contributing to absorption on the Q-branch region. Moreover, it is shown that the well-known Ar–HCl stable quasilinear configuration at low densities is to some extent preserved in the liquid phase. The sizes and orientations of these traces of complexes in the liquid resemble those of van der Waals complexes in low-density gases. Finally, we analyze the meaning of the observed rotational hindering of the molecular probe and its influence on the shape of near-infrared spectra.

Quantum/classical studies of O(3P)+Ar⋅HCl collision dynamics

The dynamics of the O(3P)+HCl and Ar–HCl reactions is investigated using a multiple configuration quantum/classical approach. In this work the dynamics of the hydrogen atom is propagated quantum mechanically in the three Cartesian coordinates of the atom, while the dynamics of the other atoms is propagated classically, in a center-of-mass frame. It is found that the introduction of the argon atom affects the reaction probability through two mechanisms. For nearly collinear O+Ar–HCl collisions, the argon atom blocks the transition state for the O+HCl reaction and inhibits the reaction. On the other hand when the collision geometry is such that the oxygen atom does not collide with the argon atom, the reaction probability is increased. These results are analyzed in terms of the shape of the ground state Ar–HCl wave function. The energy transfer dynamics from the oxygen atom and to the argon atom is also investigated.

Wave packet study of the Ar–HBr photolysis: Stereodynamical effects

The ultraviolet photolysis of Ar–HBr(v=1) is studied through wave packet dynamics simulations, focusing on the fragmentation pathway Ar–HBr +ℏω→H+Ar–Br. Photolysis starts from two initial states of Ar–HBr(v=1) with a different angular shape, namely the ground and the first excited van der Waals (vdW) states, corresponding to the Ar–H–Br and Ar–Br–H isomers, respectively. It is found that the yield of Ar–Br radical products is substantially higher for the initial excited vdW state of the cluster, where H dissociation is less hindered. In addition, the yield of radical formation is much higher in the Ar–HBr(v=1) photolysis than that previously found in the Ar–HCl(v=0) case, even for the ground vdW state, where the initial angular distribution of both clusters is similar. Another unexpected difference is that Ar–HCl(v=0) photolysis exhibits strong manifestations of quantum interference, while these effects are much weaker in Ar–HBr(v=1). A lower probability of the first collision between the recoiling hydrogen and the Ar atom in the case of Ar–HBr(v=1), due to geometrical differences between its initial state and that of Ar–HCl(v=0), is suggested to explain the different photolysis behavior of both clusters. The implications of the present findings in the photolysis of other related precursor clusters are discussed.

Least-squares mass-dependence molecular structures for selected weakly bound intermolecular clusters

The applicability of the recently proposed method of Watson et al. [J. Mol. Spectrosc. 196 (1999) 102] to the determination of geometries of weakly bound clusters was tested. The method delivers equilibrium–quality structural parameters from highly precise fits to only the ground state rotational constants and very encouraging results were obtained for several families of clusters: Rg–HX, N 2 –HX, H 2 O –HX, and Ar 2 HX . Considerable improvement in standard deviations of least-squares fits of geometry relative to ground state fits was obtained. In cases where corroborating information concerning the values of equilibrium geometrical parameters was available, those were found to be reproduced successfully, in particular for Ar–HF, Ar–HCl, H 2 O –HF, and H 2 O –HCl. The long established large amplitude structural averaging correction for complexed hydrogen halides, based on a quadrupolar averaging angle, was found to be a well-defined term in the parameterisation of vibration–rotation contributions to the ground state moments of inertia. However, it is one of several mutually canceling terms and is not necessarily a dominating term in the vibration–rotation contribution. A computer code for such calculations is made available.

An alternative phase-space distribution to sample initial conditions for classical dynamics simulations

Abstract A new quantum-type phase-space distribution is proposed in order to sample initial conditions for classical trajectory simulations. The phase-space distribution is obtained as the modulus of a quantum phase-space state of the system, defined as the direct product of the coordinate and momentum representations of the quantum initial state. The distribution is tested by sampling initial conditions which reproduce the initial state of the Ar–HCl cluster prepared by ultraviolet excitation, and by simulating the photodissociation dynamics by classical trajectories. The results are compared with those of a wave packet calculation, and with a classical simulation using an initial phase-space distribution recently suggested. A better agreement is found between the classical and the quantum predictions with the present phase-space distribution, as compared with the previous one. This improvement is attributed to the fact that the phase-space distribution propagated classically in this work resembles more closely the shape of the wave packet propagated quantum mechanically.

Clusters containing open-shell molecules. II. Equilibrium structures of ArnOH Van der Waals clusters (X2Π, n=1 to 15)

The equilibrium and low-lying isomeric structures of ArnOH (X2Π) clusters for n=1 to 15 are investigated by simulated annealing calculations. Potential energy surfaces are obtained by a pairwise-additive approach, taking into account the open-shell nature of OH X2Π and including spin-orbit coupling. It is found that the spin-orbit coupling suppresses the Jahn–Teller effect, and many of the clusters have high-symmetry structures (Cnν with n>2) which would be forbidden in the absence of spin-orbit coupling. The structures are generally similar to those previously found for the closed-shell systems ArnHF and ArnHCl, but different from those for the open-shell systems ArnNO and ArnCH. This is because Ar–OH (X2Π), like Ar–HF and Ar–HCl but unlike Ar–NO and Ar–CH, has a near-linear equilibrium structure. ArnOH clusters for n up to 6 have all Ar atoms in a single shell around OH. In the clusters with n=7 to 9, OH is under a pentagonal pyramid formed by six Ar atoms, while the others bind to its exterior, away from OH. For n=10 to 12, the minimum-energy structures have OH inside an Arn cage, which is essentially icosahedral for n=12 but has vacancies for n=10 and 11. For n>12, the extra Ar atoms begin to form a second solvation shell. The global minimum of ArnOH may be constructed from the minimum-energy structure of Arn+1 by replacing one Ar atom with OH.

The Ar–HCl potential energy surface from a global map-facilitated inversion of state-to-state rotationally resolved differential scattering cross sections and rovibrational spectral data

A recently developed global, nonlinear map-facilitated quantum inversion procedure is used to obtain the interaction potential for Ar–HCl(v=0) based on the rotationally resolved state-to-state inelastic cross sections of Lorenz, Westley, and Chandler [Phys. Chem. Chem. Phys. 2, 481 (2000)] as well as rovibrational spectral data. The algorithm adopted here makes use of nonlinear potential→observable maps to reveal the complete family of surfaces that reproduce the observed scattering and spectral data to within its experimental error. A nonlinear analysis is performed on the error propagation from the measured data to the recovered family of potentials. The family of potentials extracted from the inversion data is compared to the Hutson H6(4,3,0) surface [Phys. Chem. 96, 4237 (1992)], which was unable to fully account for the inelastic scattering data [Phys. Chem. Chem. Phys. 2, 481 (2000)]. There is excellent agreement with H6(4,3,0) in the attractive well, where Hutson’s surface is considered most reliable. There is also good long-range agreement. However, it is shown that H6(4,3,0) predicts too soft a wall for the linear Ar–HCl configuration and significantly too steep a wall for linear Ar–ClH. These differences account for the systematically backscattered inelastic cross sections computed using the H6(4,3,0) surface. The new, nonlinear inversion results provide a global Ar–HCl interaction potential with reliable error bars that are consistent with all of the experimental data.

Erratum: “An energy-resolved study of the partial fragmentation dynamics of Ar–HCl into H+Ar–Cl after ultraviolet photodissociation” [J. Chem. Phys. 112, 4983 (2000)

Erratum: “An energy-resolved study of the partial fragmentation dynamics of Ar–HCl into H+Ar–Cl after ultraviolet photodissociation” [J. Chem. Phys. <b>112</b>, 4983 (2000)

On the importance of an accurate representation of the initial state of the system in classical dynamics simulations

A definition of a quantum-type phase-space distribution is proposed in order to represent the initial state of the system in a classical dynamics simulation. The central idea is to define an initial quantum phase-space state of the system as the direct product of the coordinate and momentum representations of the quantum initial state. The phase-space distribution is then obtained as the square modulus of this phase-space state. The resulting phase-space distribution closely resembles the quantum nature of the system initial state. The initial conditions are sampled with the distribution, using a grid technique in phase space. With this type of sampling the distribution of initial conditions reproduces more faithfully the shape of the original phase-space distribution. The method is applied to generate initial conditions describing the three-dimensional state of the Ar–HCl cluster prepared by ultraviolet excitation. The photodissociation dynamics is simulated by classical trajectories, and the results are compared with those of a wave packet calculation. The classical and quantum descriptions are found in good agreement for those dynamical events less subject to quantum effects. The classical result fails to reproduce the quantum mechanical one for the more strongly quantum features of the dynamics. The properties and applicability of the phase-space distribution and the sampling technique proposed are discussed.

An energy-resolved study of the partial fragmentation dynamics of Ar–HCl into H+Ar–Cl after ultraviolet photodissociation

The UV photolysis of Ar–HCl is simulated by an exact wave packet calculation. Partial fragmentation of the cluster into H and Ar–Cl fragments is studied by projecting out the asymptotic wave packet onto the product states, at several excitation energies in the range of the Ar–HCl absorption spectrum. The partial fragmentation pathway is found to dominate the photolysis process at very low excitation energies, and to be intense also at high energies. At medium excitation energies the other competing fragmentation pathway, namely total fragmentation into H, Ar, and Cl, dominates almost completely the photodissociation dynamics. The relative intensity of the two fragmentation pathways depends on the extent to which the hydrogen is initially blocked by Ar and Cl. The Ar–Cl radicals are produced with high rotational and low vibrational excitation at most of the Ar–HCl energies studied. The internal energy distributions of Ar–Cl show remarkable differences in shape depending on the regions of the absorption spectrum which are excited. This effect can be exploited to control both the efficiency of Ar–Cl generation and the internal excitation of the radical prepared, by changing the excitation energy of the parent cluster.

Preparation and probing of Ar–Cl radical complexes from UV photodissociation of the Ar–HCl cluster

Photodissociation of Ar–HCl is simulated by exact wavepacket calculations. The asymptotic wavepacket is projected out onto the product states corresponding to several excitation energies of Ar–HCl. A high relative efficiency of Ar–Cl formation is found at low and high cluster excitation energies. The ro-vibrational state distribution of the Ar–Cl radical formed is reflected in the kinetic-energy distribution of the H fragment. Photolysis of Ar–HCl then appears as an efficient method for preparing Ar–Cl radicals, simultaneously probing their final state distribution.

A test of the accuracy of the partially-separable time-dependent self-consistent-field approach

The accuracy of the time-dependent self-consistent-field (TDSCF) approach assuming partial factorization of the total wave packet is tested against an exact treatment, when applied to calculate asymptotic properties. The test is carried out in the framework of a three-dimensional simulation of the Ar–HCl UV photodissociation dynamics. All the partially-separable TDSCF ansatzs possible for this problem are investigated. The quality of the TDSCF results is found to be strongly dependent on the specific partially-separable ansatzs applied. In general, the TDSCF predictions are in very good (even quantitative) agreement with the exact ones for magnitudes associated with direct photodissociation dynamics, and are qualitative in the case of indirect photodissociation. The deviation of the TDSCF results from the exact dynamics is interpreted in terms of an error operator defined as the difference between the exact and the TDSCF Hamiltonians. The analysis of this operator also explains the different accuracy of the partially-separable ansatzs investigated. Based on this analysis, a simple procedure is suggested to estimate the relative average quality of the different TDSCF ansatzs.

Photodissociation of Ar–HCl: An energy-resolved study of the dynamics of total fragmentation into H+Ar+Cl

UV photolysis of Ar–HCl is simulated by means of an exact wave packet treatment in three dimensions. The focus of the work is on the mechanism of indirect dissociation of the hydrogen atom, which leads to total fragmentation of Ar–HCl into H, Ar, and Cl. The results predict for this photodissociation path a probability of about 13% of the photolysis process. The remaining probability would be associated with direct photodissociation of the H fragment. Kinetic-energy distributions of the hydrogen fragments produced by indirect photodissociation are calculated for different excitation energies of Ar–HCl. The distributions reflect a pronounced structure of peaks associated with broad and overlapping resonances of the system. The resonance structure is present in the whole energy range covered by the absorption spectrum. Hydrogen atoms initially populating the resonances can dissociate from the cluster extensively cooled down, after several collisions with Ar and Cl. A mechanism is suggested for the fragmentation process due to indirect photodissociation, which involves successive jumps of the hydrogen to lower-energy resonances, induced by the collisions. A classical collisional model is proposed to rationalize qualitatively the fragmentation dynamics.

Photodissociation of HCl adsorbed on the surface of an Ar12 cluster: Nonadiabatic molecular dynamics simulations

The photodissociation of HCl adsorbed on the surface of an Ar12 cluster is studied by semiclassical molecular dynamics simulations, using a surface-hopping approach for the nonadiabatic transitions. The DIM method is used to construct the 12 potential energy surfaces that are involved, and the nonadiabatic couplings. The results are compared with previous studies on HCl embedded inside Ar clusters and on the triatomic Ar–HCl cluster. The main findings are the following: (1) There is a yield of about 1% for recombination onto the ground electronic state of HCl, roughly the same as for HCl embedded inside Ar12. (2) Photodissociation lifetimes much longer than for Ar–HCl are found. (3) The kinetic energy distribution of the H atom shows large energy transfer to the cluster, greater than in the case of HCl in the embedded geometry in (Ar)12HCl. (4) An interesting mechanism leads to the formation of some fraction of very “hot” Cl atoms. (5) About 10% of the Cl is left trapped in (Ar)mCl clusters. (6) The branching ratio P1/2:P3/2 for the Cl atoms that leave the cluster shows electronic cooling compared to the isolated HCl molecule case. The results throw light on the role of local geometry in photodissociation/recombination processes, and in particular on the mechanisms pertinent in the case of surface-adsorbed species. The nature of the results, showing strong cage effects at the surface geometries is to a large extent a consequence of the encapsulation of the H atom, obtained for the structure of the (Ar)12HCl cluster.

Effects of complex formation on reactions of oxygen with HCl and Ar–HCl

Classical trajectory simulations are used to investigate reactions of HCl and Ar–HCl with atomic oxygen in its ground and first excited states. We focus on the effects of complex formation on reaction cross sections and product state distributions over a range of collision energies. At low collision energies, the argon atom inhibits the formation of the H–O–Cl collision complex and lowers the reaction cross sections. At higher collision energies, the argon atom removes energy from the collision complex, thereby lowering the effective collision energy and increasing the cross sections for reaction. In general, the product state distributions, resulting from reactions of complexes, are shifted to lower energies than the product state distributions of corresponding O+HCl reactions.

Electronic structure of Ne–H–Cl and Ne–Cl–H using the G1, G2 and MP4 methods

The potential energy surface for the Ne–HCl Van der Waals complex is calculated using fourth-order Møller–Plesset perturbation theory (MP4) employing both 6-311G **, cc-pVDZ and AUG-cc-pVDZ basis sets. The global minimum occurs at the linear Ne–H–Cl configuration. The binding energy of the linear Ne–H–Cl and Ne–Cl–H configurations has also been calculated using G1, G2 and MP4 methods. The G1 and G2 methods cannot predict the relative stability of the complexes, since the difference in the calculated binding energies is small. In all the calculations, the binding energy of the Ne–H–Cl and Ne–Cl–H complex is low compared to that of the Ar–HCl Van der Waals complex for which D e=2.096 kJ/mol.