Excitation Of N2 Research Articles

Effects of Gas-Flow-Rate Ratio on Electrical Characteristics and Fowler-Nordheim Stress Resistance of Si Oxynitride Grown with Helicon-Wave-Excited N2–Ar plasma

The effects of the gas-flow-rate ratio on the electrical characteristics and the Fowler-Nordheim (FN) current stress resistance were investigated for Si oxynitride grown with helicon-wave excited (HWP) N2–Ar plasma. The flow-rate ratio of N2 [N2/(N2+Ar)] was varied from 100% (N2 only) to 60%. The X-ray photoelectron spectroscopic data (XPS) indicated that uniform Si oxynitride (probably Si2N2O) was formed through the entire film thickness when the N2 gas-flow-rate ratio was 100% (N2 only), though a small amount of Si suboxide was included. The capacitance–voltage (C–V) measurements revealed that the interface-state density was the lowest in this flow-rate ratio case, as the grown layer was postannealed at moderate temperatures (300–500°C). Fowler-Nordheim current injection was performed using the metal/Si-oxynitride/Si capacitors thus fabricated. The shift of the threshold voltage was the lowest for the sample grown without Ar mixing. It was smaller than that for the thermal Si oxide (SiO2) grown at 900°C. The results of FN current stress resistance experiments were explained in terms of the surface plasmon and avalanche breakdown models.

Effect of short-time helicon-wave excited N2–Ar plasma treatment on the interface characteristic of GaAs

The short-time helicon-wave excited N2–Ar plasma treatments of n-type GaAs (100) substrates were performed in order to investigate the effect of these treatments on the interface characteristics of GaAs and to explore a possibility of a robust surface passivation of GaAs. X-ray photoelectron spectroscopic measurements indicated formation of GaN at the insulative-layer GaAs interface. The current-density–voltage (J–V) characteristics of the Schottky or tunnel metal–insulator–semiconductor diodes were measured before and after the plasma treatment. The analysis of these data suggested that the “intrinsic” surface Fermi level pinning near the midgap of the GaAs forbidden band was partially removed and the Fermi level was newly pinned at EC−0.2–0.3 eV (EC: the conduction band edge) after the plasma treatment. This is probably due to generation of high-density plasma-induced donor-like interface states having the energy level (or levels) in this energy region. The reverse leakage current increased with this plasma treatment. However, it decreased after the post-thermal annealing at moderate temperatures (200–500 °C) in N2 ambient. The thermal and air-exposure stability were substantially improved with the plasma treatment. The J–V characteristics did not show any deterioration after air exposure for three months for the plasma-treated samples, whereas these greatly degraded with air exposure for three weeks for the untreated ones.

Effects of helicon-wave excited N2 plasma treatment on Fermi-level pinning in GaAs

GaAs(100) substrate was treated in a helicon-wave excited N2 plasma for short time (5–15 min). Current density–voltage (J–V) characteristics were measured for the Schottky or tunnel metal–insulator–semiconductor diode. The Schottky barrier height obtained from Richardson plot was about 0.3–0.4 eV for the plasma-treated samples independent of the plasma exposure time, while it was about 0.7 eV for the untreated one. The ideality factor and the reverse (leakage) current were much higher for the plasma-treated GaAs than for the untreated ones. The bulk carrier density showed a small decrease near the GaAs surface only for the plasma-treated samples. A very high density of the interface states was observed at EC=0.3–0.4 eV from the analysis of J–V characteristics based on the Horváth’s theory [J. Appl. Phys. 63, 976 (1988)]. These experimental results indicated that the high density of the interface states were generated at the energy of EC=0.3–0.4 eV, probably due to plasma-induced damage, and the surface Fermi level was strongly pinned at this energy position, though the midgap pinning was removed or partially removed due to the plasma treatment. Some possible reasons of this removal of the midgap pinning are also discussed.

CONCENTRATIONS OF ACTIVE SPECIES IN THE FLOWING AFTERGLOW OF A NITROGEN MICROWAVE PLASMA

Measurements of nitrogen atom density, by means of NO chemical titration, along with an evaluation of the densities of some excited species N2(B, v=11), N2(B, v=2), N2(C, v=0), and N2+(B,v=0), by means of a spectroscopic study of some bands of dinitrogen, are achieved along the flowing afterglow of a dinitrogen microwave plasma (2450 MHz) for several pressures. The concentrations obtained are in the following range: [N]∼10+15, [N2(B, 2)]∼10+9–10+10, [N2(B, 11)]∼10+8–10+9, [N2(C, 0)]∼10+6–10+7, [N2+(B,0)]∼10+6-10+8(cm-3). From a kinetic study of the formation and decay of excited and charged species, an estimation of N2(A, v), N2(X, v, and N2+(X) densities can be derived: [N2(A, v)]∼10+12, [N2(X, v≥6)]∼10+15–10+16, [N2(X, v≥12)]∼10+14–10+15, [N2+(X)]∼10+10(cm-3).

Pulsed Fowler–Nordheim current stress resistance of Si oxynitride grown with helicon-wave excited nitrogen–argon plasma

Pulsed Fowler–Nordheim (FN) current stress resistance was investigated for the Si oxynitride grown in the helicon-wave excited N2–Ar plasma. The shift of the gate threshold voltage Vth increased with an increase in the pulse frequency for both polarities of the applied stress voltage. At low frequencies (<1 kHz), the Vth shift was larger for the negative gate-voltage stress than for the positive one. However, as the frequency exceeds about 1 kHz, the Vth shift become much higher for the positive stress than for the negative one. The Vth shift was smaller as the pulse duty ratio was larger. These findings could be explained with the surface–plasmon and avalanche breakdown models combined with the effect of the total amount of the injected carriers to the oxynitride from the Si substrate or the gate electrode. The effect of Ar ion etching during plasma processing on the FN stress resistance was also investigated. The Ar ion etching effect was found to be substantially reduced as the plasma-sheath width was large and Si oxynitride samples were grown under this condition. The mean time to failure was highly improved by the Si oxynitride samples grown under the condition of reduced Ar ion etching effect.

Detection of O(3P2) by Vacuum Ultraviolet Laser Spectroscopy

O atoms in the 3P2 state were detected by vacuum ultraviolet laser-induced fluorescence (VUV LIF) technique. The O(3P2) atoms were produced by the collision between the O atoms in the 1D excited state and collision partner N2. O atoms in the 1D excited state were obtained by photodissociation of N2O at 193 nm laser light. As O(3P2) species has their first transition in the VUV region, the probe laser was used to excite O(2p3Pj) atoms to the O(3s3So) state at 130.212 nm. A four wave difference frequency mixing (2ω1−ω2) process using Kr as nonlinear media was employed to generate 130.212 nm probe laser light.

On the vibrational fine structure in the near-threshold photofragmentation spectrum of the I−⋅CH3I complex: Spectroscopic observation of nonadiabatic effects in electron-molecule scattering

Photofragmentation of the I−⋅CH3I ion-molecule complex is observed to accompany photoexcitation in the vicinity of its electron detachment thresholds. The I− photofragment action spectrum displays a vibrational progression in the ν3 (largely C–I stretching) mode of neutral CH3I, the same mode which is excited upon photodetachment of the complex. The extent of this vibrational activity in the I−⋅CH3I photoelectron spectrum is found to strongly depend on the photodetachment energy, becoming very pronounced as the photon energy approaches the detachment threshold. This indicates that the vibrational features in the photoelectron spectrum arise from non-Franck–Condon effects. These observations of selective excitation of ν3 in both the photoelectron and photofragmentation spectra are correlated to nonadiabatic effects arising from the repulsive state of the CH3I− anion, which is thought to evolve into a resonance near the equilibrium separation of neutral CH3I. The I−⋅CH3I photochemistry is discussed in the context of the mechanisms postulated to govern electron-molecule scattering (i.e., vibrational inelastic and dissociative electron attachment) in bare CH3I. Finally, we cast the scattering mechanism in a spectroscopic picture and suggest that the threshold fragmentation in I−⋅CH3I can be viewed as the predissociation of a transient or virtual dipole-bound electronic state.

Further study on collisional quantum interference effect in energy transfer within CO singlet–triplet mixed states

In our previous study [G-H Sha, J-B. He, B. Jiang, and C-H. Zhang, J. Chem. Phys. 102, 2772 (1995)], a concept of interference phase angle (θST) has been formally introduced to define the coherence effect between singlet and triplet energy transfer channels for mixed states. In this contribution, we have measured θST for various monoatomic (He, Ne, Ar) and diatomic (H2, N2) collision partners at temperatures of 77 K and 470 K. Via a new data processing approach, θST is fitted more accurately than earlier approximations. Our experimental results show that θST increases with the polarizability of monoatomic collision partners, while for diatomic collision partners θST is significantly higher than that for monoatomic ones. θST at 470 K for He and Ne is higher than that of 77 K, while an adverse temperature effect on θST has been found for N2. The influence of intermolecular potential and possible complex formation between excited CO and N2 or H2 has been discussed.

Density functional theory of the collective electronic excitations in NanKn clusters

AbstractThe collective electronic response of NanKn clusters has been studied for some model structures. In their low‐temperature lowest‐energy structure, those clusters have all the K atoms on the surface. The collective oscillation frequencies for clusters with the K atoms segregated to the surface are red‐shifted with respect to the corresponding frequencies for isomers with a very similar underlying skeleton but with the Na atoms segregated to the surface. The collective frequency varies smoothly with respect to the degree of relative segregation. These results may be useful in the analysis of the collective response of large alloy clusters and microcrystals. © 1995 John Wiley & Sons, Inc.

Electron Excitation Function of the N 2 Second Positive System

view Abstract Citations (36) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron Excitation Function of the N 2 Second Positive System Shemansky, D. E. ; Ajello, J. M. ; Kanik, I. Abstract The band strengths of the electron excited N2 (C 3Πu-B 3Πg) second positive system (2PG) have been measured in the middle ultraviolet (MUV) range (280-444 nm). The energy dependence of the (0,0) and (1,0) band cross sections is reported with analytic shape functions for use in model calculations. The excitation functions were measured at low pressure to avoid effects of collisional cascade from higher lying states. At low electron energies (11-15 eV), the resolution and energy spacing of the excitation function measurements were sufficient to reveal the importance of threshold effects from resonance processes. The absolute cross section of the 337.14 nm band has a peak value of 1.11±0.15 × 10-17 cm2 at 14.1 eV. Above 30 eV the cross section decreases with an asymptotic E-2 dependence. A spectral analysis of the 2PG band system at 14 and 20 eV has provided relative excited state vibrational level cross sections. The variation of the electronic transition moment over the wavelength range indicated above, has been derived, and an improved transition probability matrix has been obtained. The rate coefficient for solar photoelectron excitation of the (0,0) band is 9.1 × 10-10 cm-3 s-1 for photoelectrons above 11.0 eV, a factor of ∼1.3 smaller than the previous recommended value. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176319 Bibcode: 1995ApJ...452..472S Keywords: ATMOSPHERIC EFFECTS; EARTH; MOLECULAR DATA; ULTRAVIOLET: GENERAL full text sources ADS |

Non-equilibrium coupled kinetics in stationary N2-O2 discharges

A detailed study of the coupled electron and heavy-particle kinetics in a low-pressure stationary N2-O2 discharge is carried out. The model is based on the self-consistent solutions to the Boltzmann equation coupled to the rate balance equations for the vibrationally excited molecules N2(X1 Sigma g+,v) and O2(X3 Sigma g-,v'), NO(X2 Pi r) molecules and N(4S) and O(3P) atoms. It is shown that the vibrational distribution of N2(X,v) plays a central role in the whole problem, affecting considerably the predicted concentrations of NO molecules and N atoms, whereas the concentration of O atoms is practically independent of both vibrational distributions. In particular, it is shown that, in the case of a rate coefficient of about 10-13 cm3 s-1 for the reaction N2(X,v)+O to NO+N, the N2(X,v) molecules are strongly de-excited by vibrational-translational energy exchange processes associated with N2-N collisions. In contrast, in the case of a higher value for this rate coefficient, the N2(X,v) molecules are efficiently destroyed by this mechanism. The contributions of the different processes to the total production of NO, N and O are evaluated and compared.

Excited ν3 vibrational state of the Ar–HCN and Kr–HCN dimers

Rotational spectra have been observed for an excited vibrational state of the Ar/Kr–HCN dimers in a Balle–Flygare Fourier transform microwave spectrometer with a high temperature nozzle that can be heated to ∼1300 K. The B, DJ, and HJ rotational constants found for the excited parent Ar–HCN isotopic species are 1602.475(3) MHz, 164.2(6) kHz, and 309(5) Hz, and for Kr–HCN they are 1176.4493(3) MHz, 41.7(1) kHz, and 56(1) Hz. The 14N quadrupole interaction χa(J=1) observed in the excited state is −2.824 (−3.239) MHz for Ar(Kr)–HCN, slightly smaller than the −2.844 (−3.268) MHz in the ground state. A substitution analysis based on the C and N isotopic species reveals that the C–N distance rs (CN) increases by ∼0.013 (0.020 Å) on excitation of Ar(Kr)–HCN. A similar analysis for free DC15N gives an increase in rs(CN) upon ν3 excitation of 0.0022 Å. Assignment of the excited state in the dimer as the ν3C–N stretch of the HCN is proposed and discussed.

A BOXCARS investigation of the interspecies V–V energy transfer from highly excited SF6 to N2

The BOXCARS technique was used to investigate the V–V energy transfer between highly excited SF6 and N2. It was found that a Boltzmann population distribution among vibrational levels of N2 is present by 1 μs after laser excitation of SF6 and is maintained during the energy-transfer processes. The maximum energy transferred to N2 increases linearly with the increase of the average number of photons absorbed [Formula: see text] by SF6 in the range [Formula: see text]. The maximum energy transferred to the N2 vibrational levels increases with the partial pressure of SF6 and decreases with the partial pressure of N2. The apparent rate of energy increase in the N2 vibrational levels increases with both partial pressures of SF6 and N2. However, both the rate and the amount of energy transferred to N2 vibrational levels depend more strongly on the partial pressure of SF6 than on the partial pressure of N2. A model calculation produces a reasonable fit to the experimental data.

Alignment in two-step pulsed laser excitation of Rydberg levels in light atoms: The example of sodium.

Aligned atomic Rydberg states of sodium can be prepared using two-step excitation from the ground state by linearly polarized pulsed lasers. Information that is normally inaccessible, e.g., sublevel partial cross sections in charge-transfer experiments, can be obtained when aligned targets are used. The calculations of orbital alignment must carefully allow for fine and hyperfine structure, laser linewidths, pulse widths and delays, sublevel coherences, and other factors. In this paper we derive the orbital alignments and time-averaged d-state sublevel populations for 3 $^{2}$${\mathit{S}}_{1/2}$\ensuremath{\rightarrow}3 $^{2}$${\mathit{P}}_{\mathit{J}1}$\ensuremath{\rightarrow}n $^{2}$D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment ${\mathit{A}}^{(2)}$ and hexadecapole alignment ${\mathit{A}}^{(4)}$, with excitation through either ${\mathit{J}}_{1}$=1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for \ensuremath{\Vert}${\mathit{M}}_{\mathit{L}}$\ensuremath{\Vert}=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.

Interrogating the vibrational relaxation of highly excited polyatomics with time-resolved diode laser spectroscopy: C6H6, C6D6, and C6F6+CO2

The vibrational relaxation of highly excited ground state benzene, benzene d6, and hexafluorobenzene by CO2 has been investigated with high resolution diode laser spectroscopy. The vibrationally hot polyatomics are formed by single photon 248 nm excitation to the S1 state followed by rapid radiationless transitions. It has been found that in all cases less than 1% of the energy initially present in the polyatomics is deposited into the high frequency mode of CO2 (ν3). An investigation of the CO2(0001) nascent rotational distribution under single collision conditions reveals that very little rotational excitation accompanies vibrational energy transfer to the ν3 mode. The CO2(ν3) rotational states can be described by temperatures, Trot, as follows: C6H6, Trot =360±30 K; C6D6, Trot =350±35 K and C6F6, Trot =340±23 K. An estimate of 〈ΔE〉ν3, the mean energy transferred to the CO2 ν3 mode per collision, suggests that as the availability of low frequency modes in the excited molecule increases, less energy is deposited into the high frequency mode of CO2. Finally, evidence is presented suggesting that even at moderate laser fluences, the two-photon ionization of benzene can lead to substantial CO2 ν3 excitation via electron+CO2 inelastic collisions.

Fragment energy and vector correlations in the overtone-pumped dissociation of HN3 X̃ 1A′

NH stretching overtone and combination states in HN3 X̃ 1A′ were excited by IR–visible double resonance pumping and by direct overtone pumping in the range 6ν1 (17 670 cm−1) to 7ν1 (20 070 cm−1). NH fragments in the a 1Δ and X 3Σ− states were detected by laser induced fluorescence with sub-Doppler resolution to determine branching ratios, correlated fragment rotational state and kinetic energy distributions, and fragment vector correlations. The spin-forbidden triplet channel was accessible to all states excited, while the threshold for the singlet channel was determined to lie in the range 18 190 to 18 755 cm−1. The measured energy release places limits on the HN–NN bond energy, and the heights of barriers to reaction. The barrier in the singlet exit channel is at least 540 cm−1. The singlet channel accessed by 7ν1 dissociation is characterized by a Boltzmann-like NH rotational distribution (〈J NH〉≊3.5), highly excited N2 rotations (〈JN2〉 ≥ 20), and total translational energy release peaked away from zero (〈ET〉≊1350 cm−1). Vector correlations and Λ-doublet propensities indicate that nonplanar dissociation processes influence the NH rotations, but become less important for higher NH rotational states. The principal correlations are a strong positive recoil anisotropy (β≊0.6), a weak positive v–J correlation (βvJ≊0.17), and a JNH-dependent Λ-doublet propensity. A model using parent vibrational motion projected onto fragment rotation is suggested to explain these observations. The triplet channel exhibits similar NH and N2 rotational state distributions, with most of the available energy (substantially greater than in the singlet channel) appearing as fragment kinetic energy.

Asymmetry of departing fragment ion in the K-shell excitation of N2.

La distribution angulaire d'ions N + provenant de N 2 stimule par une photoexcitation en couche K, est mesuree a l'aide d'un spectrometre de masse a temps de vol. Une analyse detaillee des spectres TOF montre qu'a 401 eV, transition de resonance de 1 σ u a 2 pμg, le parametre d'asymetrie β est proche de -1. Entre 405 et 410 eV, β presente une variation oscillatoire due aux excitations de l'electron de coeur aux etats de Rydberg. Pour la resonance de forme de type σ u , β est plus grand que 0. Les resultats sont discutes en relation avec les caracteristiques des etats excites en couche K

Close-coupling analysis of electron-impact excitation of Na(4s).

Electron-impact excitation of sodium from the ground state to the 4/sup 2/S state is investigated for impact energies 5eVless than or equal toEless than or equal to100 eV. Configuration-interaction-type wave functions are employed in a close-coupling (CC) approximation to determine the significance of the 3p and 3d intermediate states on the 3s..-->..4s excitation cross section by comparing six-, four-, three-, and two-state CC results (6CC, 4CC, 3CC, and 2CC). Surprisingly, the 2CC and 6CC calculated cross sections are in excellent agreement with each other throughout the energy range investigated, and with measurement at 54.4 eV. At other energies the agreement with experimental integral cross sections is less close. Calculations which couple only the 3p or the 3p and 3d intermediate states such as the present 3CC and 4CC approximations may overestimate significantly the Na(4s) cross sections. The second-Born-approximation analysis leads to incorrect results even at 100 eV.

Infrared diode laser kinetic spectroscopy of the CCD radical ν3 band

Infrared diode laser kinetic spectroscopy was applied to the photodecomposition of the deuterated acetylene at 193 nm to observe the ν3 (C=C stretching) band of the CCD radical. The band origin which was derived from the observed spectrum is 1743.1785 (3) cm−1, in agreement with the result of a previous matrix study. As in the case of CCH, the spin–rotation interaction constant was found to change by as much as 31% upon ν3 excitation, presumably because of the interaction with the lowest excited electronic state. Many lines with lifetimes shorter than those of the ν3 band were observed, but remained to be assigned.

Spacecraft Ram cloud atom exchange and N2 LBH glow

Recently a ram source of N2 Lyman‐BirgeHopfield (LBH) emission has been reported on S3‐4 satellite. An investigation of likely chemical processes responsible has identified a gas phase reaction involving ram atmosphere and the ram‐side cloud of gas leading the satellite. The process produces large quantities of fast N that impinge on low‐altitude spacecraft. Subsequent surface recombination produces excited N2 which results in the emission with predictions of altitude variation similar to that measured by other investigators.