On the spectroscopic detection of neutral species in a low-pressure plasma containing boron and hydrogen

Abstract

Spectroscopic studies of microwave discharges in H 2 -Ar-B 2 H 6 gas mixtures (f = 2.45 GHz, P = 1.2-3.5 kW, p = 1-8 mbar) have been performed to improve the possibilities of diagnostics of non-equilibrium, low-pressure plasmas containing boron and hydrogen. For this purpose, UV-VIS optical emission spectroscopy and infrared absorption spectroscopy with tunable diode lasers (TDLAS) have been applied. It is shown that information about neutral species and the gas temperature may be obtained by means of new and modified spectroscopic methods. A method for the determination of the absolute number density of boron atoms from measured relative intensities of the components of the boron resonance doublet (distorted by reabsorption) is proposed and tested for validity. The maximum of the density was found to be 3.8 × 10 11 atoms cm −3 at an admixture of diborane of about 2%. The gas temperature was determined from the intensity distributions in the rotational structure of the emission bands of BH and H 2 and from Doppler broadening of the absorption line profiles of the BH molecule. It was observed that values of the gas temperature obtained from the rotational intensity distributions are in good agreement with those obtained from Doppler widths (T g = 700-1070 K). Based on measurements of the relative line intensities of atomic and molecular hydrogen and the gas temperature, and using a simple excitation-deactivation model, the density of molecular hydrogen was found to be about 40 times higher than the density of atomic hydrogen. It is shown that some absorption lines of boron hydrides (B 2 H 6 , BH 3 and BH) detected by TDLAS may be used for plasma diagnostics.

On the Reaction Kinetics of Chemically Active Molecular Microwave Plasmas

“…Gas temperatures have been measured spectroscopically [7]. The error bars were estimated taking into account the uncertainties in the experimental determination of the gas temperature of 10% and 7% in measured line intensity ratios.…”

Reactivity of Transition-Metal Borylene Complexes: Recent Advances in B–C and B–B Bond Formation via Borylene Ligand Coupling

“…68 In contrast to 2, complex 5 possesses two different terminal borylene ligands, which significantly interact with each other. This is evident in several aspects: (i) the 11 100 Although the detailed mechanism is still unknown, the reaction is likely to proceed via the formation of terminal chloroborylene intermediate [(η 5 -C 5 H 4 CH 3 )(OC) 2 MnBCl] (7) followed by intermolecular coupling with another molecule, which would represent the first example of a borylene−borylene coupling reaction. Calculations have shown that both formation of the proposed terminal chloroborylene intermediate from its bridged borylene precursor and its dimerization are highly exothermic processes and have small reaction barriers.…”

From Carbon Nanostructures to New Photoluminescence Sources: An Overview of New Perspectives and Emerging Applications of Low‐Pressure PECVD

“…This technique has been used for decades to identify the existing species with a high degree of confidence and sensitivity; nevertheless it can barely provide estimations of species concentrations. In order to get reliable relative concentrations from emission data, recent improvements in diagnostics and a more precise knowledge of excitation cross-sections [58,59] have opened new possibilities and alternatives [60,61] to the formerly well-established method of actinometry. Broadband light-emitting sources, such as cyclotron radiation and high resolution laser sources extending from the MW to the VUV region, have stimulated noticeably the use of direct absorption spectroscopic techniques from ground and excited levels to study the electronic, vibrational, and rotational molecular transitions, providing direct and detailed information about absolute concentrations of the detected species and their characteristic temperatures, which may be far from equilibrium and differ for the various energy modes.…”