Z Zhou Qing

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

rotational temperature of the excited state H 2~d 2 P u) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher- a system of H 2 . The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to . 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the plasma: ~1! Langmuir probe measurements ~T e .1.4 eV!, ~2! appearance of the Fulcher-a system of H 2 ~excitation potential DE513.87 eV!, ~3! low rotational temperature ~T rot .260 K! of the excited H 2 ~d 3 P u ) molecules, ~4! local excitation in the plasma of Ar I~DE515.45 eV!, and Ar II~DE519.68 eV! spectral lines, ~5! local excitation in the plasma of He I~DE523.07 eV and DE524.04 eV! spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the ~1‐1.4!310 20 m 23 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%‐13%.

On expanding recombining plasma for fast deposition of a-Si:H thin films

A high-density expanding recombining plasma is investigated for deposition of a-Si:H thin films. The deposition method allows high growth rates and it relies on separation of plasma production in a high-pressure thermal arc, and transport of fragments of injected SiH4 monomer to the substrate. Some characteristics of the plasma are discussed together with an explanation of the dominant chemical kinetics, which proceed mainly through heavy-particle interactions. The deposition results indeed show very high growth rates from 2-30 nm s-1 on areas of 30 cm2. The properties of the layers are characterized by measuring their refractive index (in the range 3.1-3.8) and bandgap 1.2-1.5 eV). Analysis of the oxygen content in the deposited films shows oxidation of the samples in air, which is probably associated with the microstructure of the layers.

The role of hydrogen during plasma beam deposition of amorphous thin films

Abstract The influence of wall-associated H 2 molecules and other hydrogen-containing monomers on the degree of ionization in the expanding thermal plasma used for the fast plasma beam deposition of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated silicon (a-Si:H) was determined. Deposition models are discussed with emphasis on the specific role of the ion during deposition. The connection between the role of atomic hydrogen and the degree of ionization in the plasma beam deposition of a-C:H and a-Si:H is addressed.

Experimental characterization of a hydrogen/argon cascaded arc plasma source

A H2 /Ar cascaded arc plasma source has been experimentally characterized by determination of the efficiency, the electric field, and the pressure gradient of the arc. The results show that the efficiency of a H2/Ar cascaded arc drops when the hydrogen flow rate is increased. The electron temperature in the argon cascaded arc has been derived to be in the range 9000–12 500 K. For a hydrogen arc, the mass dissociation degree of hydrogen molecules has been derived to be above 60%.

Rotational and gas temperatures in a surface conversion negative ion source

The Fulcher band emission spectrum is used to determine rotational temperatures in the FOMSCE plasma setup. The measured temperatures are found to vary from 500 to 700 K, whereas usually in this kind of plasmas they are very close to room temperature. In this paper the interpretation of the spectra will be discussed. The influence of some plasma settings on the measured temperature will be presented.

Fundamentals and application of an expanding hydrogen low-pressure plasma jet

Abstract The absolute density of atomic hydrogen excited states in two different regimes of a magnetized expanding plasma is determined using emission and absorption spectroscopy. First evidence has been found for the presence of high densities of negative ions in the “atomic” (recombining) regime of an expanding hydrogen plasma. Several clear observations of the presence of “hot” electrons have been made in the “molecular” (ionizing) regime of the expanding plasma. For both regimes the absolute density of atomic hydrogen in the ground state and the degree of plasma dissociation have been determined.

Optical Diagnostics for High Electron Density Plasmas

Nowadays high electron density plasmas are, beside their fundamental interest, widely used for many applications, e.g., light sources and plasma processing. The well known examples of high electron density plasmas can be found among the class of thermal plasmas as, e.g., the Inductively Coupled Plasma (ICP) and the Wall Stabilized Cascaded Arc (WSCA). Usually the pressure of the plasma is high, i.e., sub atmospheric to atmospheric. Other examples are the plasmas generated in tokamaks for fusion purposes and the recently exploited plasmas for etching and deposition devices such as the Electron Cyclotron Resonance plasmas. For the plasmas mentioned, the electron density is typical in the range of 1018 to 1023 m−3, and the electron velocity distribution is close to a Maxwellian velocity distribution.

Hot Electrons in an Expanding Magnetized Hydrogen Plasma

The rotational temperature of hydrogen molecular excited state H2(d 3IIu)has been determined by analyzing the relative intensity distribution of the rotational spectral lines of the Fulcher-α system of H2. A strong hydrogen molecular spectrum, and an estimated low rotational temperature of H2(d 3IIu) molecules (260 K) indicate that in the molecular regime of an expanding hydrogen plasma the electronic quantum state H2(d 3IIu) (excitation potential ΔE = 13.87 eV) is excited by a direct electron impact from the ground electronic state H2(X 1∑sk+/g). The gas temperature in the plasma is twice the value of the rotational temperature, i.e. approximately 520 K.

Active actinometry on a cold hydrogen afterglow

Summary form only given. A new method of actinometry has developed to characterize the cold afterglow of an expanding thermal plasma source in hydrogen. A small electrode is placed in the afterglow to generate a local low-frequency (100-500 kHz) plasma. In this plasma fast electrons are created that can excite particles from the ground state to visible light emitting levels. The atomic Balmer /spl alpha/ line and the molecular Fulcher band are used to determine the atomic and molecular abundances of the plasma. The power input from the low frequency discharge is kept low enough to assure that the plasma composition and the gas temperature are not significantly influenced. Active actinometry thus offers a method to sample the composition and the ground state molecular populations of the flowing afterglow plasma. The method has been successfully applied under plasma conditions with a low electron temperature (< 0.2 eV) and a low electron density (< 10/sup 17/ m/sup -3/).

Thermal discharges: experiments and diagnostics

In plasma processing commonly a distinction is made between low pressure (or low (ion) temperature) plasmas and thermal plasmas1. The transition between these two classes is gradual. Plasmas cover a wide spectrum in electron density (1015/m3–1023/m3) and ionization degree (10−7–1). In low pressure plasmas2 as RF—discharges the ionization degree is usually small and these plasmas are characterized by an abundance of molecular fragments and large ambipolar fields. The high electron density thermal plasmas have a high ionization degree and nearly full dissociation and a high heavy particle temperature. In this paper we will focuss on these plasmas.