The importance of three-body processes to reaction kinetics at atmospheric pressures--I: Archetype reactions of He species with N2

This paper concerns a reexamination of the significance of three-body effects that enhance the reaction rates for energy transfer and for ion-molecule reactions that occur in atmospheric pressures of inert gas diluent, even in the absence of any formation of product clusters. The archetype case of the reactions of the energy-storing species of helium with molecular nitrogen has been studied in two different preionized discharge systems capable of operation to 6 atm pressure. Earlier results suggesting the critical importance to kinetic modeling of three-body channels were confirmed in this work. The termolecular rate coefficient for the particular reaction He+2+ N2+ He was concluded to be13.1 times 10^{-30}cm⁶/s with no evidence of saturation up to pressures of 6.0 atm. Effective rates of reaction were observed to be increased by this channel to a value three times in excess of the Langevin rate that has been traditionally considered to be an upper limit on the overall rate of reaction. The close conformity to the oldere-beam results in this test case implies that the general conclusion of those studies must be seriously considered. In 95 percent of the cases of the reactions of inert gas ions with other species diluted in inert gases at atmospheric pressures it must be expected that rates can greatly exceed the traditional bimolecular values and can even exceed the Langevin rates by substantial amounts.     

Subnanosecond multi-gigawatt CO2 laser

A semiconductor switching technique has been utilized to produce 30-300 ps variable duration CO₂ laser pulses of 0.5-MW peak power. Eight passes through a 1.2-m long, UV-preionized, 3-atm TE CO₂ amplifier raise the output laser peak power to the 10¹⁰ W level. Sampling the amplifier gain in linear and saturated regimes using CO₂ laser radiation ranging from CW to 30 ps pulse length permits comparison with computer modeling of picosecond CO₂ pulse amplification. The potential for further peak power scaling of picosecond molecular lasers is discussed     

Impact of nitrogen (N2+) implantation intopolysilicon gate on thermal stability of cobalt silicide formed onpolysilicon gate

A novel process which uses N₂⁺ implantation into polysilicon gates to suppress the agglomeration of CoSi₂ in polycide gated MOS devices is presented. The thermal stability of CoSi₂/polysilicon stacked layers can be dramatically improved by using N₂⁺ implantation into polysilicon. The sheet resistance of the samples without N₂⁺ implantation starts to increase after 875°C RTA for 30 s, while the sheet resistance of CoSi₂ film is not increased at all after 950 and 1000°C RTA for 30 s if the dose of nitrogen is increased up to 2×10¹⁵ cm^-2 and 6×10¹⁵ cm², respectively, and TEM photographs show that the agglomeration of CoSi₂ film is completely suppressed. It is found that the transformation to CoSi₂ from CoSi is impeded by N₂⁺ implantation such that the grain size of CoSi₂ with N₂⁺ implantation is much smaller than that without N₂⁺ implantation. As a result, the thermal stability of CoSi₂ is significantly improved by N₂⁺ implantation into polysilicon     

Suppression of cobalt silicide agglomeration using nitrogen(N2+) implantation

In this paper, the effects of nitrogen coimplantation with boron into p⁺-poly gate in PMOSFETs on the agglomeration effects of CoSi₂ are studied. The thermal stability of CoSi₂/poly-Si stacked layers can be significantly improved by using nitrogen implantation. Samples with 40-nm cobalt silicide (CoSi ₂) on 210-nm poly-Si implanted by 2×10¹⁵/cm ² N₂⁺ are thermally stable above 950°C for 30 s in N₂ ambient. If the dose of nitrogen is increased up to 6×10¹⁵/cm², the sheet resistance of CoSi₂ film is not increased at all, and TEM photographs show that the agglomeration of CoSi₂ film is completely suppressed     

Electrical properties of Si p+-n junctions for sub-0.25μm CMOS fabricated by Ga FIB implantation

p⁺-n junction diodes for sub-0.25-μm CMOS circuits were fabricated using focused ion beam (FIB) Ga implantation into n-Si (100) substrates with background doping of N_b=(5-10)×10 ¹⁵ and N_b⁺=(1-10)×10¹⁷ cm^-3. Implant energy was varied from 2 to 50 keV at doses ranging from 1×10¹³ to 1×10¹⁵ cm^-2 with different scan speeds. Rapid thermal annealing (RTA) was performed at either 600 °C or 700°C for 30 s. Diodes fabricated on N_b⁺ with 10-keV Ga⁺ exhibited a leakage current (^I_R) 100× smaller than those fabricated with 50-keV Ga⁺. Tunneling was determined to be the major current transport mechanism for the diodes fabricated on N_b⁺ substrates. An optimal condition for I_R on N_b⁺ substrates was obtained at 15 keV/1×10¹⁵ cm^-2. Diodes annealed at 600°C were found to have an I_R 1000× smaller than those annealed at 700°C. I-V characteristics of diodes fabricated on N_b substrates with low-energy Ga⁺ showed no implant energy dependence. I-V characteristics were also measured as a function of temperature from 25 to 200°C. For diodes implanted with 15-keV Ga ⁺, the cross-over temperatures between I_diff and I_g-r occurred at 106°C for N_b ⁺ and at 91°C for N_b substrates     

RF excitation of a flowing gas CO2 waveguide laser

Investigation of an RF excited CO₂ waveguide laser in flowing gas operation is reported. Power extraction of 0.8 W/cm with an efficiency of 10.3% has been achieved. Using W.W. Rigrod's analysis (1965), values of the small-signal gain α₀ and saturation parameter I_s have been determined for different excitation levels and for different pressures of the amplifying medium. The parameters α₀ and I_s, have been determined as 0.6%/cm and 10.4 kW/cm ², respectively, at 125 torr and 100 W/cm³ RF loading power. These values are close to those reported for sealed-off RF CO₂ waveguide lasers with xenon added to the gas mixture     

Optically pumped NH3 as a high-gain amplifier forCO2 laser radiation

Optically pumped high-pressure mixtures of NH₃ in N₂ are shown to be efficient broadband amplifiers of pulsed CO₂ radiation. In a dilute NH₃ mixture at 6 atm a single-pass gain of 150 (21.8 dB) was measured for the 10P(34) CO₂ transition. Gain was observed in NH₃ at pressures as high as 10 atm. Experimental measurements were made for a range of wavelengths in the 10.7 μm region, and the results compared with calculations based on a rate-equation model     

A novel self-aligned TiN formation by N2+implantation during two-step annealing Ti-salicidation for submicrometerCMOS technology application

A new technology of self-aligned TiN/TiSi₂ formation using N₂⁺ implantation during two-step annealing Ti-salicidation process has been developed. The formation of TiN was confirmed by RBS analysis. The leakage currents of n⁺/p junction diodes fabricated using this technology were measured to investigate the phenomena of Al spiking into Si-substrate. The measured reverse-bias leakage current of diode per unit junction area with Al/TiN/TiSi₂ contact is 1.2 nA/cm² at -5 V, which is less than all of reported data. Also it can sustain the annealing process for 30 min at 500°C. Thus, TiN formed with this technology process is suggested as a very effective barrier layer between TiSi₂ and Al for submicron CMOS technology applications     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

FM mode-locked high-pressure CW RF-excited CO2 waveguidelaser

The authors report the results from a study of a FM mode-locked continuous-wave (CW) RF-excited CO₂ waveguide laser operated at 0.25-2 atm gas pressures. It is shown that electrooptic FM modulations can be efficiently used to mode lock a CW CO₂ laser. The combination of a high gas pressure and a high modulation frequency makes it possible to generate pulses which are substantially shorter than those previously reported for CW mode-locked CO₂ lasers. A theoretical approach is used for simulation of the FM mode-locked laser. The experimental pulses of a few hundred picoseconds FWHM are considerably shorter than previously reported for CW mode-locked CO₂ lasers. The experimental results are compared with the results of numerical calculations using a frequency domain simulation model     

Hot electron energy relaxation via acoustic phonon emission in GaAs/Al0.24Ga0.76As single and multiple quantum wells

The energy relaxation associated with acoustic phonons has been investigated in a series of modulation doped GaAs/AlGaAs single and multiple quantum wells grown by molecular beam epitaxy, using the hot electron Shubnikov — de Haas effect. The power loss is shown to be proportional to (T_e² − T_L²) for electron temperatures 2.2K < T_e < 8K and proportional to (T_e³ − T_L³) for 8K < T_e < 20K. The energy loss rates due to acoustic phonon scattering via both deformation potential coupling and piezoelectric coupling have been calculated. The total energy loss rate as a function of electron temperature is compared with the experimental results. Good agreement is obtained for 2.2K < T_e < 8K. Above 8K the energy loss rate is seen to rise above the predicted values, indicating the onset of an extra energy relaxation mechanism. The application of a high electric field (E = 3kV/cm) at low lattice temperatures is shown to induce persistent parallel conduction and a subsequent reduction of the low field well mobility.     

Continuously tunable high-pressure CO2 laser forspectroscopic studies on trace gases

A high-pressure CO₂ laser with unique characteristics in terms of continuous tunability and emission bandwidth is presented. It is operated at a pressure of 11.5 bar and transversely excited by short, high-voltage pulses generated by a double LC inversion circuit. Auxiliary discharges parallel to the electrodes provide a sufficient free-electron density through UV ionization of the laser gas mixture. The laser resonator consists of a near-grazing-incidence grating setup in which the grating is positioned at a large incidence angle of 77°. A theoretical model for the calculation of the emission bandwidth is presented and its predictions are compared to direct measurements and show excellent agreement. The achieved very narrow bandwidth of 0.018 cm^-1 constitutes the ultimate wavelength resolution of any detection system using this laser as radiation source. It allows the resolution of any fine structure in the spectra of absorbing gases at atmospheric pressure. Continuous tunability has been achieved over 76 cm^-1 between 932 cm^-1 and 1088 cm ^-1 with minimum pulse energies in excess of 10 mJ. The narrow bandwidth precludes the occurrence of mode-pulling effects so that the laser exhibits a linear wavelength tuning behavior throughout the entire emission range. The calibration of the laser wavelength is performed by photoacoustic measurements on low pressure CO₂ gas. An absolute accuracy of ±10^-2 cm^-1 is achieved. A great potential improvement in detection selectivity can thus be expected from a scheme with the high-pressure CO₂ laser as radiation source     

New short-wavelength laser emissions from optically pumped 13CD3OD

We report the discovery of 15 new laser emissions from ¹³ CD₃OD when optically pumped with a CW CO₂ laser. The wavelengths of these lines, ranging from 57.5 to 135.2 μm, are reported along with their polarization relative to the CO₂ pump laser, operating pressure and relative intensity. A three-laser heterodyne system was then used to measure the frequencies of 12 optically pumped laser emissions from this methanol isotope. These emissions range from 65.7 to 151.8 μm and are reported with fractional uncertainties up to 2·10^-7     

LiCaAlF6:Cr3+: a promising new solid-statelaser material

LiCaAlF₆:Cr³⁺ (Cr³⁺:LiCAF) exhibits an intrinsic (extrapolated maximum) slope efficiency of 67%. For comparison, the intrinsic slope efficiencies of BeAl₂O ₄:Cr³⁺ (alexandrite), Na₃Ga₂Li₃F₁₂:Cr³⁺ and ScBO₃:Cr³⁺ were found to be 65, 28, and 26%, respectively. The tuning range of LiCaAlF₆:Cr³⁺ was determined to be at least 720-840 nm. The conventional spectroscopic properties, such as the absorption, emission, and emission lifetimes as a function of temperature, are reported as well     

New CO2 laser lines in the 11-μm wavelength region:new hot bands

Nineteen new laser lines in the 11-μm wavelength region have been observed in CW oscillation from a CO₂ laser with a high-Q, high-resolution cavity at a higher than usual current density. The frequency of each line has been measured using heterodyne frequency measurement techniques. Analysis of the frequencies shows that 15 lines are rotation-vibration transitions of the 01¹2-[11¹1,03¹1]_I band (the first sequence hot band) of the CO₂ molecule and four lines belong to the rotation-vibration transitions of the 02²1-[12 ²0, 04²0]_I band of CO₂     

New direct optical pump schemes for multiatmosphere CO2and N2O lasers

Nine schemes for direct optical pumping of multiatmosphere CO₂ and N₂O lasers at pump wavelengths in the 1.4-3.6-μm region are discussed. Most of these wavelengths can be generated by solid-state lasers, which are more attractive pump sources than the chemical lasers (HBr, HF) used previously to pump high-pressure CO₂ and N₂O lasers. Including previously studied pump schemes, there are altogether 14 possible pump transitions in CO ₂ and N₂O in the 1.4-4.5-μm region. Numerical laser simulations are carried out to compare all of these pump schemes. Assuming 10 J/cm² pump energy in a pulse of 100 ns FWHM, and 5% output coupling as the only resonator loss, the calculated energy conversion efficiencies are in the range of 6-40%. The pump thresholds are in the range of 0.1-3.1 J/cm²     

Diagnostics of TM010-mode microwave cavity discharges inCO2-N2-He laser gas mixtures. I. Measurement ofdielectric constant

Plasma parameters in the microwave discharged CO₂ laser gas mixtures of CO₂-N₂-He=0.9/2.5/20 at 25 Torr obtained using the perturbation method for a TM₀₁₀-mode cylindrical resonant cavity were examined. From the changes in resonant frequencies and Q values of the cavity, dielectric constant of the discharged plasma under the condition of RF to laser output power conversion ratio of 14% at mass flow rate of 4.2 kg/h was determined to be nearly 0.96-0.01j. It was also obtained from the dielectric constants of the plasma that electron number density, the electron temperature, and discharge parameters (E/n) were (0.3-3)×10¹⁵m^-3, 0.5-2.7 eV, and (0.5-2)×10^-15 Vcm², respectively     

Frequency stabilization of the sequence-band CO2 laserusing the 4.3-μm fluorescence method

The saturated 1.3-μm fluorescence stabilization method is applied to the 00⁰2-[10⁰1, 02⁰1]_I,II sequence band CO₂ laser transitions. For this purpose, the 4.3-μm fluorescence is observed using an external longitudinal CO₂ absorption cell heated to 300°C. The dependence of the frequency stability upon the gas temperature and pressure in the cell as well as laser parameters have been carried out in absolute frequency scale with the help of a two-channel heterodyne system. Under optimal conditions, the standard deviation of the beat note frequency between sequence band and regular band lasers for 30 s averaging time is less than 20 kHz, and the long-term stability and reproducibility is achieved at about 10 kHz     

Gain measurement and upconversion analysis in Tm3+, Ho3+ co-doped alumino-zirco-fluoride glass

The small signal gain coefficients were measured in Tm³⁺,Ho³⁺ co-doped alumino-zirco-fluoride glass. A gain of 15%/cm at 2.05 μm was obtained for pump power density of 42 kW/cm². The temperature increase of the glass was found to be more than 150 K with this pump power, which was estimated from a comparison between fluorescence intensities of Tm^{3+ 3} F₄-³H₆ and Ho^{3+ 5} I₇-⁵I₈. An upconversion rate constant of 12.5×10^-17 cm³ sec^-1 from a coupled (Tm^{3+ 3}F₄, Ho^{3+ 5}I₇) level to a coupled (Tm^{3+ 3}H₅, Ho^{3+ 5}I₆) level was determined by fitting the experimentally obtained gain coefficients to the calculated one which takes into consideration any temperature increase     

Observation of a large number of new laser lines from12CD3F gas optically pumped with a continuouslytunable high-pressure pulsed CO2 laser

An observation is reported of a large number of new laser lines from ¹²CD₃F gas optically pumped with a continuously tunable high-pressure pulsed CO₂ laser. Making use of the coincidence of the 10 μm P and R branches of CO₂ with the v₃ and v₆ vibrational-rotational absorption bands of ¹²CD₃F, 180 laser lines were found in the wavenumber range between 8 and 55 cm^-1, all of them yet unknown; these lines are studied for characteristic properties of laser action. All laser lines are assigned as pure rotational transitions in the vibrational excited or ground states