Effect of controlled O2 impurities on N2 afterglows of RF discharges

강남준,이민욱,André Ricard,오수기 한국물리학회 2012 Current Applied Physics Vol.12 No.6

A RF capacitive flowing discharge and post-discharge are experimentally studied in N2 gas and N2-(10-4-10-2)O2 gas mixtures by using the optical emission spectroscopy at a pressure of 8 Torr, a flow rate of 1 slm and a transmitted RF power of 100W. In these conditions the flowing discharge is distinguished by early and late afterglow. It is shown that the early afterglow is very sensitive to small quantity of O2. The band emissions from N2+(B) and N2(B,y') decreased sharply in the early afterglow when O2 is introduced before the plasma. By using simple gas kinetics for pseudo-stationary conditions in the afterglows, N2+ +O2 charge transfer and N2(a') quenching by O2 play key roles in the afterglow. The charge transfers and quenching reactions are amplified when O-atoms are produced in the plasma. It is also observed that the O-atoms are produced in the early afterglow when O2 is introduced after the plasma.

Discharge source-dependent variation in the densities of active species in the flowing afterglows of N2 RF and UHF plasmas

Andre Ricard,Jean-Philippe Sarrette,전병욱,김유권 한국물리학회 2017 Current Applied Physics Vol.17 No.7

With a potential application to surface modification of oxide materials in mind, active species in RF and microwave (UHF) N2 afterglows were analyzed in our newly designed flowing reactors. For both plasma systems, discharge of N2 was generated in a long quartz tube with a small diameter (dia. 5e6 mm) and then was directly injected into a chamber with a large diameter of 15e20 cm. The discharge condition was set to be similar between the two systems; the gas pressure, flow rate and the applied power were 6 Torr, 0.6 slm and 100W, respectively. Under this condition, the residence time at the chamber inlet was (1e3) x 10『3 s. The RF and UHF afterglows were formed in the chamber with luminous jets from the end of the discharge tube. However, we found that the densities of active species were quite sourcedependent; N and N2(A) densities were higher in UHF than in RF in spite of more O-atoms impurity. The origin of such difference is also attributed to the inherent difference in the nature of excitation between the two plasma sources; RF is more vibrational and is longer than UHF.

Quantitative evaluation of the densities of active species of N2 in the afterglow of Ar-embedded N2 RF plasma

Andre Ricard,오수기,장중희,김유권 한국물리학회 2015 Current Applied Physics Vol.15 No.11

The N2 and Ar-20%N2 RF plasmas and afterglows have been generated in a quartz tube under a flowing condition maintained at 6e8 Torr and a flow rate of 0.5e0.6 slm. The detailed emission characteristics of active species have been analyzed by emission spectroscopy. Under such conditions, the plasma rotational temperature increases from 400 to 800 K with increasing RF powers from 50 to 130 W, while the characteristic vibrational temperature remains at about 104 K. The densities of active species (N, N2(A), N2(X, v > 13) and Nþ 2 ) in the afterglow are measured to be in the order of ~1015, ~1011, ~1014 and ~1010 cm3, respectively. In addition, the following characteristics of the afterglows are noted: First, the same densities of the active species can be obtained at lower RF powers (20-50 W) for Ar-20%N2 than for pure N2 which requires higher RF powers (50-100 W). Second, the ionization degree of N+ 2 =N2 in the plasma increases readily to a saturation value at a lower RF power of 50 W for Ar-20%N2, whereas in the afterglow, the absolute density of Nþ 2 is further reduced below 109 cm-3.

Characteristics of RF and microwave N₂ plasmas and afterglows and their application to nitrogen doping into anatase TiO₂ nanocrystals

Byungwook JEON,Andre RICARD,Jean-Philippe SARRETTE,Yu Kwon KIM 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

The role of active species in the N₂ and N₂-H₂ RF afterglows on selective surface nitriding of ALD-grown TiO₂ films

Wang, Yunfei,Ricard, Andre,Sarrette, Jean-Philippe,Kim, Ansoon,Kim, Yu Kwon Elsevier Sequoia 2017 Surface & coatings technology Vol.324 No.-

<P><B>Abstract</B></P> <P>We find that surface modification characteristics of TiO<SUB>2</SUB> using N<SUB>2</SUB> RF plasma are strongly dependent on the detailed composition of active species in the plasma and the afterglows. The surface nitriding of ALD-grown TiO<SUB>2</SUB> films in pure N<SUB>2</SUB> RF afterglows at room temperature (RT) is found to be more effective in the late afterglows than in the early afterglows. Adding a small fraction of H<SUB>2</SUB> in N<SUB>2</SUB> results in suppression of surface nitriding, suggesting that the change in the composition of the active species in the afterglows by H<SUB>2</SUB> is the origin to the suppressed nitriding performance. Here, we present our analysis on the surface chemical composition after the plasma modification as well as the densities of excited species such as N atoms, N<SUB>2</SUB>(A) and N<SUB>2</SUB>(X, <I>v</I>) metastable molecules and N<SUB>2</SUB> <SUP>+</SUP> ions in the afterglows of RF N<SUB>2</SUB> and N<SUB>2</SUB>–H<SUB>2</SUB> (<5%) at different positions along the downstream by emission spectroscopy. The early afterglow of N<SUB>2</SUB> changes from a pink to a late afterglow where the N+N recombination is the dominant process with the introduction of H<SUB>2</SUB>. The roles of active species such as N–atoms and N<SUB>2</SUB> <SUP>+</SUP> ions on TiO<SUB>2</SUB> surface nitriding are found to oppose to each other. We find that N atoms enhance the surface nitriding, while N<SUB>2</SUB> <SUP>+</SUP> ions are likely to deplete the surface-bound N species.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Surface nitriding of TiO<SUB>2</SUB> in the N<SUB>2</SUB> RF afterglow at RT is strongly dependent on the active species densities. </LI> <LI> High density of neutral N atoms plays a beneficial role in the surface nitriding of TiO<SUB>2</SUB>. </LI> <LI> The vibrationally excited N<SUB>2</SUB> and N<SUB>2</SUB> <SUP>+</SUP> species play a negative role in the surface nitriding performance. </LI> </UL> </P>

Determination of Absolute Nitrogen Atom Density in Ar-N_2 ICP Discharge

강남준,오수기,Freddy Gaboriau,Andre Ricard 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.5

The absolute N atom density in low pressure Ar-N_2 inductively coupled plasma (ICP) is numerically studied with simple gas kinetic model using measured electron temperature and electron density. In the calculation we found the charge transfer between Ar^+ and N_2 is the dominant source of N atoms at higher pressure. The calculated results are compared with measured values using two-photon absorption laser-induced fluorescence (TALIF). We observed that at 200 mTorr N atom density decreases as the N_2 mixing ratio raises, while it is proportional to the N_2 at 20 mTorr.

A study on selective surface nitridation of TiO₂ nanocrystals in the afterglows of N₂ and N₂-O₂ microwave plasmas

Jeon, Byungwook,Kim, Ansoon,Ricard, André,Sarrette, Jean-Philippe,Yu, Xiaomei,Kim, Yu Kwon Elsevier BV * North-Holland 2018 Applied Surface Science Vol.432 No.2

<P><B>Abstract</B></P> <P>Surface-selective chemical modification of anatase TiO<SUB>2</SUB> nanocrystals is performed in the post-discharge region of N<SUB>2</SUB> microwave plasma and the chemical bonding states of surface nitrogen species are carefully evaluated using X-ray photoemission spectroscopy (XPS). It is found that the surface treatments in the afterglows induce the formation of stable nitrogen species at or near the surface of TiO<SUB>2</SUB>. Interestingly, the detailed bonding structure varies strongly depending on the afterglow condition. In pure N<SUB>2</SUB> afterglows, various N species with a direct TiN bond are formed on the surface, while the use of N<SUB>2</SUB>-O<SUB>2</SUB> mixtures induces the formation of additional oxidized species of NO<SUB>3</SUB> <SUP>−</SUP> on the surface. This is attributed to the high concentrations of O or NO in the afterglows of N<SUB>2</SUB>-O<SUB>2</SUB> plasmas. The incorporation of substitutional N species in the subsurface is also achieved after a prolonged exposure in the early afterglow with a high density of N<SUB>2</SUB> <SUP>+</SUP> species. Our results show that the exposure condition can be controlled for a selective chemical modification of TiO<SUB>2</SUB> surface for the control of surface properties in various applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Selective surface nitridation of TiO<SUB>2</SUB> is performed in the afterglows of N<SUB>2</SUB> plasma. </LI> <LI> The bonding states of N vary depending on the active species in the afterglows. </LI> <LI> The O and/or NO species are responsible for the formation of nitrate on TiO<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Experimental study of Ar and Ar–N₂ afterglow in a pulse-modulated ICP discharge: observation of highly excited Ar(6d) afterpeak emission

Kang, Namjun,Britun, Nikolay,Oh, Soo-ghee,Gaboriau, Freddy,Ricard, André Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.11

<P>In an argon ICP RF discharge modulated by 1 kHz square pulses, strong emission at 549.6 nm (corresponding to the upper level Ar(6d)) was observed about 100 µs after the pulse termination in the afterglow. This emission exceeds by a factor of as much as five the duty-on cycle intensity. With simple kinetic considerations, we assigned this emission to the Penning pooling ionization of argon metastable atoms leading to the formation of <img SRC='http://ej.iop.org/images/0022-3727/42/11/112001/jphysd311174in001.gif' ALIGN='MIDDLE' ALT='{\rm Ar}_{2}^{+} '/> in the afterglow followed by electron–ion recombination producing highly excited argon atoms Ar(6d). With the addition of 1% N<SUB>2</SUB> into Ar, the emission at 549.6 nm completely disappeared in the afterglow. This disappearance could be explained by excitation transfer between Ar metastable atoms and nitrogen molecules leading to the emission of the second positive system of N<SUB>2.</SUB>.</P>