Plasma homo- and copolymerizations of tetrafluoroethylene and chlorotrifluoroethylene

The plasma homo- and copolymerizations of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE) in a capacitively coupled tubular reactor (TR) with external electrodes were studied by means of microgravimetry and FT-IR and XPS analyses. The deposition rates for CTFE/TFE plasma copolymers, as well as the ratios of IR absorbances at 1180 and 1225 cm⁻¹, and the XPS-derived Cl/C and F/C ratios, varied regularly with mol % CTFE in the feed, all of which results were dependent upon the rf power at which the plasma copolymerizations were conducted. The deposition rates for the plasma homopolymers of TFE (PPTFE) and CTFE (PPTCFE) depended markedly on rf power (W) and monomer molar flow rate (F). The F/C ratio for PPTFE was nearly independent of the composite parameter,W/FM (whereM is the monomer molecular weight), while for PPCTFE, the F/C ratio decreased significantly and the Cl/C ratio increased slightly with increase inW/FM. The percentage of carbon as CF₃ was 20–24% in PPTFE and 7–14% in PPCTFE. Plots of deposition rate versusW/FM for PPTFE and PPCTFE obtained in a TR differed considerably from corresponding plots in the literature for the same homopolymers prepared in a glass-cross or bell-jar reactor.     

Comparisons of glow discharge polymerization between hexamethyldisilazane and trimethylsilyldimethylamine

Glow discharge polymerization between hexamethyldisilazane (HMDSZ) and trimethylsilyldimethylamine (TMSDMA) was compared by means of infrared spectroscopy and ESCA analysis. Infrared spectra pointed out differences in chemical structure between the polymers prepared from the two monomers, although the two polymers were mainly composed of resembling units such as Si? CH₃, Si? CH₂, Si? H, Si? O? Si, and Si? O? C groups: (i) The polymers prepared from TMSDMA contained N → O group, but the polymers from HMDSZ did not contain this group. (ii) Influences of the W/FM parameter (W is the input energy of rf power, F the flow rate of the monomer, and M the molecular weight of the monomer) appeared on decreasing the C? N group and increasing the C?O group in the TMSDMA system, but little influence appeared in the HMDSZ system. ESCA spectra (C_1s, Si_2p, and N_1s core levels) supported the differences between the two polymers elucidated by infrared spectroscopy, and pointed out differences in susceptibility of the Si? N bond to plasma: The N? Si sequence of TMSDMA was completely ruptured in discharge to yield polymers, and the Si? NH? Si sequence of HMDSZ remained in considerable amount.     

Effect of heating on dissociation of water vapor in high-frequency plasmas and formation of hydrogen peroxide in a cold trap downstream of the plasma

At low flow rates (0.7–2.8 mmol hr^–1) and long residence times (2.3–8.5 s) nearly 60% of the input water vapor was decomposed by a 13.56-MHz rf discharge. Downstream of the discharge a trap cooled by liquid nitrogen collected nearly constant yields of H₂O₂. The decomposition is representable by the equation 2H₂O=H₂O₂+H₂. The overall rate of decomposition was found to depend on the absorbed power density. Heating the rf plasma and its spatial afterglow from 25 to 600°C did not significantly change the percent decomposition of H₂O and the formation of H₂O₂. Above 600°C, however, a continuous decrease in H₂O₂ yield was observed with increasing temperature, and this was associated with the increasing formation of H₂O from the dissociated products such as highly excited OH radicals which otherwise produce the precursors of H₂O₂. The same heating effects were observed in the case of the spatial afterglow of a 2.45-GHz microwave cavity discharge in water vapor under essentially similar conditions. It appears that at the high temperatures the reaction OH+OHH₂O+O is favored over the reaction O+OHO₂+H. This limits the formation of O₂ and consequently decreases the H₂O₂ yield.     

Characterization of the Active Species in the Afterglow of a Nitrogen and Helium Atmospheric-Pressure Plasma

The concentrations of the neutral active species in the afterglow of a nitrogen and helium atmospheric-pressure plasma have been determined by optical emission and absorption spectroscopy and by numerical modeling. For operation with 10 Torr N₂ and 750 Torr He, at 15.5 W/cm³ rf power, 30.4 L/min flow rate, and a neutral temperature of 50°C, the plasma produced 4.8×10¹⁵ cm^–3 of ground state nitrogen atoms, N(⁴S), 2.1×10¹³ cm^–3 of N₂(A³_u), 1.2×10¹² cm^–3 of N₂(B³_g), and 3.2×10⁹ cm^–3 of N₂(C³_u). The concentration of nitrogen atoms and metastable state nitrogen molecules, N₂(A), increased gradually with the rf power and the nitrogen partial pressure. Both the model and experiments indicate that ground-state nitrogen atoms are the dominant active species in the afterglow beyond 2.0 ms.     

Feasibility of improvement in analytical performance in laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) by addition of nitrogen to the argon plasma

Addition of nitrogen to an argon ICP in LA-ICP-MS has been found to increase sensitivity and consequently reduce oxide to metal ratios (MO⁺/M⁺) for the reference elements Ce and Th. Addition of about 1% v/v N₂ to the coolant flow increased sensitivity, reducing MO⁺/M⁺ ratios from about 0.6% to about 0.2%. Addition of about 12% N₂ to the cell flow had a similar effect, being greatest at a higher forward rf plasma power (1700 W). The increased sensitivity may be useful in practical analyses; N₂ consumption is very small.     

Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

We present novel measurements of the refractive index, density and integrated band strengths of mid-infrared features of solid N₂O at 16 K and of NO₂ and N₂O₄ in two frozen NO₂:N₂O₄ mixtures deposited at 16 and 60 K. The refractive index and density measurements were performed also for frozen O₂ deposited at 16 K. In this case, the integrated band strength values could not be determined since O₂ is a homonuclear molecule and therefore its fundamental mode is not infrared active. The solid samples were analysed by infrared spectroscopy in the 8000÷800 cm⁻¹ range. The sample thickness was measured by the interference curve obtained using a He–Ne laser operating at 543 nm. The refractive index at this laser wavelength was obtained, by numerical methods, from the measured amplitude of the interference curve. The density values were obtained using the Lorentz–Lorenz relation. Integrated band strength values were then obtained by a linear fit of the integrated band intensities plotted versus column density values. The astrophysical relevance of these novel measurements is briefly discussed.     

An Iron Catalytic Probe for Determination of the O-atom Density in an Ar/O2 Afterglow

An iron fiber optics catalytic probe has been constructed and applied for the real-time measuring of the O-atom density in an Ar/O₂ afterglow. The recombination coefficient for the heterogeneous surface recombination of O atoms on the oxidized iron foil was measured at different temperatures between 400 and 950 K. The coefficient was found to be constant in the entire range of experimental conditions and had a value of 0.41 ± 0.12. The iron fiber optics catalytic probe has an advantage over the classical nickel fiber optics catalytic probe: the probe signal is higher for the iron probe due to a higher recombination coefficient thus causing an easier real-time monitoring of the O-atom density. The O-atom density was measured in an afterglow of microwave plasma created at different discharge powers up to 300 W, at a constant Ar flow rate of 1000 sccm/min and at different oxygen flow rates between 50 and 300 sccm/min. The O-atom density was found to be dependent on oxygen flow. At low oxygen flow rates up to 100 sccm/min, a saturation of the O-atom density was obtained at a certain discharge power, while at high oxygen flow rate the O-atom density kept increasing with the increasing power. The results were explained by gas phase and surface phenomena.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. I. Zinc nitrate in water

Raman and infrared line parameters of Zn(NO₃)₂-H₂O systems ranging from dilute solutions (25°C) to ionic liquids of low water content (75°C) are reported. At 25°C the solutions contain a very low concentration of inner sphere [Zn(ONO₂)(H₂O)₅]⁺, outer sphere [Zn(H₂O)₆]²⁺[NO₃]^–, Zn(H₂O) ₆ ²⁺ , and NO ₃ ^– (aq.). In the ionic liquids the ion triplet also exists. Manifestations of a change from the octahedral coordination of zinc to tetrahedral coordination when the water content is very low include the appearance of a 285 cm^–1 band from the zinc nitrate bond and a shift to higher frequencies of the band from zinc-water.     

Optical Emission Spectroscopy of Abnormal Glow Region in Nitrogen Plasma

Optical emission spectroscopy of the active species in N₂ plasma is carried out to investigate their concentration as a function of discharge parameters such as filling pressure (2.0–7.0 mbar), source power (100–200 W) and gas flow rate (50–300 mg/min). The primary motivation of this work is to obtain reliable information about the concentration of the active species of N₂ plasma, which play an important role in plasma surface nitriding processes. Emission intensity from the selected electronic excited states of molecular and atomic species is evaluated as a function of discharge parameters to investigate their concentration. The emission intensity ratio I(N₂⁺)/I(N₂) and I(N⁺)/I(N) of the electronic transitions is also evaluated as a function of discharge parameters to investigate the relative dependence of their concentrations. It is observed that the concentration of the active species of N₂ plasma is strongly affected by the filling pressure and source power whereas flow rate has no significant effect. An increased occurrence of N₂⁺ molecular ions in comparison with N₂ molecules, and N⁺ ions in comparison with N atoms is observed with source power whereas decreased occurrence of N₂⁺ molecular ions in comparison with N₂ molecules, and N⁺ ions in comparison with N atoms is observed with the rise in filling pressure.     

A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N₂) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.     

Surface modifications of PET in argon atmospheric pressure plasma: Gas flow rate effect

The correlation between plasma optical properties and the treated polyethylene terephthalate (PET) surface characteristics have been studied at various Ar flow rate. The rotational T_rot and vibrational T_vib temperatures of APPJ were determined from SPS emission band. The pristine and plasma-treated PET surfaces were characterized by several techniques including X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy, contact angle (CA), and atomic force microscope (AFM). The CA decreased rapidly in the flow rate range 1–3 L/min and weakly dependent as flow rate > 3 L/min. XPS results showed that C 1s % of plasma-treated PET surfaces decreases and has a minimum for samples treated at 3–4 L/min, while O 1s has a maximum at the same flow rate range. The carbon C 1s peak of pristine and plasma treated PET samples resolved into five subcomponents: C–C, C–O, C=O, O–C=O, and π–π bonds with variable percentage ratio accordance to the plasma gas flow rate. Raman data revealed a partial loss in the crystallinity of the treated PET samples and also confirm the incremental of C–O band at Ar flow rate of 3 L/min. AFM images showed that the surface roughness of treated PET films increases as Ar flow rate increases.     

Molecular adsorption and the chemistry of plasma-deposited thin organic films: Deposition of oligomers of ethylene glycol

Weakly ionized, radio-frequency, glow-discharge plasmas formed from methyl ether or the vapors of a series of dimethyl oligo(ethylene glycol) precursors (general formula: H-(CH₂OCH₂)_n-H;n=1 to 4) were used to deposit organic thin films on polytetrafluoroethylene. X-ray photoelecton spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) of the thin films were used to infer the importance of adsorption of molecular species from the plasma onto the surface of the growing, organic film during deposition. Films were prepared by plasma deposition of each precursor at similar deposition conditions (i.e., equal plasma power (W), precursor flow rate (F), and deposition duration), and at conditions such that the specific energy (energy/mass) of the discharge (assumed to be constrained byW/FM, whereM=molecular weight of the precursor) was constant. At constantW/FM conditions, two levels of plasma power (and, hence, twoFM levels) and three substrate temperatures were examined. By controlling the energy of the discharge (W/FM) and the substrate temperature, these experiments enabled the study of effects of the size and the vapor pressure of the precursor on the film chemistry. The atomic % of oxygen in the film surface, estimated by XPS, and the intensity of theC-O peak in the XPS C_ls spectra of the films, were used as indicators of the degree of incorporation of precursor moieties into the plasma-deposited films. Analysis of films by SIMS suggested that these two measures obtained from XPS were good indicators of the degree of retention in the deposited films of functional groups from the precursors. The XPS and SIMS data suggest that adsorption of intact precursor molecules or fragments of precursor molecules during deposition can have a significant effect on film chemistry. Plasma deposition of low vapor pressure precursors provides a convenient way of producing thin films with predictable chemistry and a high level of retention of functional groups from the precursor.     

Mass spectrometric study of SF6-N2 plasma during etching of silicon and tungsten

The reaction products in the SF₆-N₂ mixture rf plasma during reactive ion etching of Si and W have been measured by a mass spectrometric method. Two kinds of cathode materials were used in this work; they were stainless steel for the Si etching, and SiO₂ for the W etching. The main products detected in the etching experiments of Si and W included SF₄, SF₂, SO₂, SOF₂, SOF₄, SO₂F₂, NSF, NF₃, N₂F₄, N_xS_y, NO₂, and SiF₄. In the W etching with the SiO₂ cathode, additional S₂F₂, N₂O, and WF₆ molecules were also obtained. The formation reactions about the novel NSF compound and the sulfur oxyfuorides were discussed.     

Radial distribution measurement of SiH* in a low-pressure silane plasma

The radial emission intensity distribution of SiH^* (A²,v=0) over the substrate of a low-pressure silane plasma was investigated for various substrate temperatures (T _s=20–320°C). Measured lateral intensities were converted to radial emission coefficients using an Abel inversion. The intensity near the center of the substrate was found to increase withT _s and yielded an activation energyE _a of 1.1 kcal/mole. This result is consistent with the value ofE _a determined by laser-induced flourescence measurements obtained previously. Radially resolved emission data obtained by varying the operating parameters of rf power, gas flow rate, silane/argon mixing rate, and total gas pressure provide a useful means of determining the conditions necessary to generate a uniform plasma.     

Effects of Pressure and Electrode Length on the Abatement of N<Subscript>2</Subscript>O and CF<Subscript>4</Subscript> in a Low-Pressure Plasma Reactor

The emission of greenhouse gases, such as N₂O and fluorinated gases, has been increasingly regulated in the semiconductor industry. Pressure effects on the abatement of N₂O and CF₄ were investigated in a low-pressure plasma reactor by using Fourier transform infrared (FTIR) spectroscopy. The destruction and removal efficiency (DRE) of N₂O and CF₄ was significantly lowered below 0.2 Torr. When the pressure was increased, the DRE of CF₄ with H₂O as the reactant gas increased continuously, but that with O₂ or without any reactant gas first increased and then decreased. A larger electrode length yielded a higher DRE of N₂O and CF₄, especially at lower pressures. To understand this phenomenon, the electrical waveforms for the discharge in N₂O were analyzed in conjunction with its optical emission profiles, and the rotational temperatures for different electrode lengths were compared using the N₂ ⁺ ion band (λ = 391.4 nm). They provided insights into the mechanism involved in terms of plasma property and gas residence time.     

Atmospheric pressure,radio frequency,parallel plate capacitively coupled plasma—excitation temperatures and analytical figures of merit

Electronic excitation (T_exc) and rotational (T_rot) temperatures were determined for a parallel plate capacitively coupled rf plasma operating at atmospheric pressure. T_exc was calculated from the slope of the Boltzmann plot using Fe and He as the thermometric species and Pb excitation temperature was calculated using the two line method. Over a power range from 100 W to 250 W, excitation temperatures are 3255–3900 K for He, 3540–4500 K for Pb, and 4300–4890 K for Fe. The rotational temperature was measured using both OH and N₂⁺ molecular spectra and the values are in the range of 828–911 K and 845–956 K respectively over a power range of 75–275 W. Signal-to-noise ratios, signal-to-background ratios, and absolute detection limit for lead (0.33 ng) and silver (24 pg) are also reported.     

Study of the equilibrium of formation of arsenic(iii) lacunar heteropolytungstates by Raman spectroscopy

The formation of lacunar heteropolyanions (HPA): [AsW₉O₃₃]^9–, [As₂W₁₉O₆₇(H₂O)]^14–, and [As₂W₂₀O₆₈(H₂O)]^10– in aqueous solutions was investigated by Raman spectroscopy at [Na₂HAsO₃]₀ = 0.1, [Na₂WO₄]₀ = 0.9 mol L^–1 and pH 9.4–1.6. The [AsW₉O₃₃]^9– HPA is characterized by the most intense band ns (W=O) at 948 cm^–1 retaining its position in the pH range from 8.9 to 7.5. Under these conditions, the equilibrium constant of [AsW₉O₃₃]^9– formation from H₂AsO₃ ^– and WO₄ ^2– ions was estimated (logK = 87.0±1.0). The asymmetrical band at 952 cm^–1 corresponding to H_x[As₂W₁₉O₆₇(H₂O)]^(14–x)– shifts to 960 cm^–1 as the pH decreases from 6.5 to 5.5, which is due to the change in HPA protonation. The [As₂W₂₀O₆₈(H₂O)]^10– HPA is formed at pH 3.1—1.6; it is characterized by a band at 972 cm^–1.     

Determination of C-atom density downstream an Ar-CH4 rf plasma torch

Nitrogen, oxygen, and carbon atoms have been detected by optical emission spectroscopy in a common flowing post-discharge of an Ar-x CH₄ rf plasma torch and an Ar-2%N₂ microwave discharge. Gas temperature as determined from CN and N₂ rotational svstems is 3200 ± 200 K in the rf torch and 700 ± 100 K in the post-discharge at a time 3 X10^–2 s after the rf plasma torch. From the intensities of the N₂ 1st positive system, of NO, and of CN violet hands, the atom densities have been determined as 2 X 10¹⁶ cm³ for N, 10¹⁵ cm³ for O, and 6 X 10¹² cm³ for C in the post-discharge at p=650 torr, with 10³ of CH₄ in the Ar torch.     

Rotational structure in the infrared spectra of carbon dioxide and nitrous oxide dimers

High-resolution infrared predissociation spectra have been measured for dilute mixtures of CO₂ and N₂O in helium. Rotational fine structure is clearly resolved for both (CO₂)₂ and (N₂O)₂, the linewidths being instrument-limited. This establishes that predissociation lifetimes are longer than approximately 50 ns.     

Glow discharge polymerization of tetramethylsilane investigated by infrared spectroscopy and ESCA

The influence of operating conditions (W/FM parameter: W input energy of rf power; F flow rate of monomer; M molecular weight of monomer) on glow discharge polymerization of tetramethylsilane (TMS) was investigated by infrared spectroscopy and ESCA. Elemental analyses showed that the compositions of the polymers formed strongly depended on the level of the W/FM parameter, i.e., whether the W/FM value was more or less than 190 MJ/kg. The infrared spectra indicated that these polymers were composed of Si? H, Si? O, Si? C, Si? CH₃, and Si? CH₂ groups, and that there was no significant difference in structural features between polymers prepared at W/FM parameters of more or less than 190 MJ/kg. ESCA spectra (C_1s and Si_2p core-level spectra) showed that the polymers included carbonized carbon, aliphatic carbon Si? C, C? O, Si? O, and SiO₂ species, and that the sum of carbonized and aliphatic carbons reached more than 50%. Raising the W/FM value increased the formation of the carbonized carbon but did not influence the formation of Si units such as Si? C and Si? O groups. From this evidence the rupture of Si? CH₃ bonds in the polymer forming process is emphasized. The magnitude of the W/FM parameter may be related to the detachment of hydrogen from the aliphatic carbon units.