G. de Rosny

Dissociation cross sections of silane and disilane by electron impact

Abstract The total dissociation cross sections for silane and disilane are reported for electron energies above their ionization thresholds up to 110 eV. The measurements are derived from a kinetic analysis of silane and disilane dissociation in a constant-flow multipole dc plasma reactor. The methane dissociation cross section was also measured and found in agreement with published data. Maxima for silane and disilane, occurring around 60 eV, are respectively (1.2±3)×10 −15 cm 2 and (2.6±0.6)× 10 −15 cm 2 . Total ionization cross sections are also measured and above 50 eV the ratios of dissociative ionization to dissociation cross sections are 0.5±0.1 and 0.25±0.10 respectively for silane and disilane. The probability for silane elimination in the disilane fragmentation reaches a maximum of 0.8 at 19 eV and decreases down to 0.5 at 100 eV. Dissociation processes of silane and disilane are discussed in comparison with methane and ethane

Production mechanism and reactivity of the SiH radical in a silane plasma

Abstract SiH free radicals in a dc multipole post-discharge plasma were analyzed using laser-induced fluorescence. The cross section for SiH formation from 40–70 eV electron impact induced dissociation of SiH 4 was measured to be (10 ± 5) × 10 −17 cm 2 . At the instant of its formation in its X 2 Π ground state, the rotational temperature of the SiH radical is 950 K. This temperature subsequently relaxes by collisions with SiH at a collisional relaxation rate k = (9 ± 2) × 10 13 cm 3 /mole s. Quenching of the A 2 Δ electronic state of SiH was found to be negligible below 0.3 Torr. The primary reaction path for destruction of the SiH radical was observed to be via: SiH + SiH 4 → products, k = 2 × 10 12 cm 3 /mole s.

Growth of hydrogenated amorphous silicon due to controlled ion bombardment from a pure silane plasma

The growth process, optical and structural properties of a‐Si:H films deposited from a silane multipole dc discharge are analyzed by real time and spectroscopic ellipsometry, and ir absorption spectroscopy. Films deposited mainly from neutral polymerized species are systematically compared to films deposited from monomeric ionic species at various ion incident energy up to 100‐eV. An increase of ion bombardment energy is shown to favor the formation of high density homogeneous and isotropic films.

Silane dissociation mechanisms and thin film formation in a low pressure multipole dc discharge

A silane plasma is generated by a hot cathode dc discharge in a partially confining multipolar magnetic structure yielding hydrogenated amorphous silicon thin films on the walls. The low‐pressure range (0.1–5 mTorr) allows the analysis of the elementary processes for SiH4 dissociation. At low silane partial pressure the deposition rate remains in the range of 1–10 A/sec, but the contribution of ions to deposition can reach up to 80% in contrast with standard glow discharges.

Experimental comparison of Jψ production by π±, K±, p and p̄ beams at 39.5 GeV/c

Abstract Measurements have been made of relative production cross sections of the J ψ by π±, K±, p and p at 39.5 GeV/c incident on copper. J ψ production rates from π−, K− and p are similar. The J ψ relative particle/anti-particle production cross sections for x>0 are σ(π + ) σ(π − )=(0.87±0.14) , σ(K+)/σ(K−)=(0.85±0.5) and σ( p ) σ( p )=(0.15 ±0.08) . The small p/p cross section ratio disagrees with models of J/ψ production by gluon amalgamation.

Positive and negative ions in silane and disilane multipole discharges

Mass spectra have been obtained for positive and negative ions extracted from a multipole discharge where thin films of hydrogenated amorphous silicon are produced from silane and disilane plasma decomposition. Highly polymerized ions of both signs are observed at high pressure. In silane plasmas, the pressure dependence of the positive ion composition is described according to known reaction schemes. The first steps of negative ion formation and reaction are discussed. Hydrogen depletion of large oligomeric negative ions is attributed to increasing electron affinities from SinH4–5 to SinH0–1. An upper limit for the total reaction rate coefficient, k, for Sin− and SinH− (n = 2 to 6) on SiH4 is found to be ≤5×10−13 cm3 molecule−1 s−1 which is consistent with the similar upper limit for the total reaction rate coefficients for C2− and C2H− on CH4. The influence of increasing discharge currents on the positive and negative ion chemistry is also analyzed.

Photoproduction of ϱ0 and ω on hydrogen at photon energies of 20 to 70 GeV

Abstract We present results on photoproduction of ϱ 0 and ω in the reactions γ p→ π + π − p and γ p→ π + π − π 0 p by tagged photons in the energy ranges 20 to 70 GeV and 20 to 45 GeV, respectively. The production of the ϱ 0 shows dominantly the characteristics of a diffractive process with respect to the E γ and t dependence of the cross section and the spin density matrix. The ϱ 0 photoproduction yields on average over the photon energy range a total cross section of σ ( γ p→ ϱ 0 p) = 9.4±0.1 μ b with an additional systematic error of ±1 μ b, and average slope parameters of the t distribution d σ /d t ≈exp(− b | t | + ct 2 ), of b =9.1±0.1 GeV −2 and c = 3.1 ±±0.2 GeV −4 . The shape of the ϱ 0 peak in the π + π − invariant spectra shows a skewing similar to that observed at lower energies. The photoproduction of ω is also consistent with a diffractive process and has a cross section of σ ( γ p→ ω p) = 1.2± 0.1 μ b with an additional systematic error of ±0.2 μ b. The average slope parameters of the t distribution are b =8.3 ± 1.3 GeV −2 and c = 3.4±2.6 GeV −4 .

The reaction γp → pπ+π−π+π− for photon energies from 25 to 70 GeV

Abstract Measurements of the reaction γ p → p π + π − π + π − are presented, in which π + π − π + π − systems with masses up to 3 GeV are produced from fragmentation of the incident photon. The reaction is dominated by production of the large peak of the ϱ′(1600) meson and, at higher masses ≳2 GeV, y production of jet-like 4 π systems. The ϱ′(1600) meson is produced by a predominantly s -channel helicity conserving mechanism. At higher masses there are also indications of ϱπ peaks, of masses 1.3 GeV (the A 2 meson) and 1.75 GeV, produced with a recoiling π meson by a mechanism consistent with the Deck effect.

Photoproduction of charmed D mesons at γ energies of 40–70 GeV

Inclusive D0 photoproduction is observed in Kπ+π− and K+π−π0. Evidence is presented for an associated (CD) production mechanism. Cross section estimates and limits are given for D and D mesons.

Observation of the ϱ′(1600) in the channel γp→π+π−p☆

Abstract A dipion enhancement of mass 1.59 GeV and width 0.23 GeV is observed in the channel γp→π + π − p. The spin-parity of the enhancement is consistent with being 1 − .