Nicolas Joffin

Bruno Caillier

Jeannette Dexpert-Ghys

Marc Verelst

Guy Baret

Alain Garcia

Philippe Guillot

Jacques Galy

Robert Mauricot

Sylvie Schamm

Elaboration by spray pyrolysis and characterization in the VUV range of phosphor particles with spherical shape and micronic size

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Introduction

Spray pyrolysis is a promising way of synthesizing spherical shaped and micronic sized particles in a very large range of compositions and applications [1]. We have used this technique to prepare red and green phosphors (Y 2 O 3 : Eu 3+ and Zn 2 SiO 4 : Mn 2+ , respectively) for plasma display panels (PDPs). In this paper, the different methods employed for investigation of the optical properties in the vacuum ultraviolet (VUV) energy range of the prepared powders are described. The intrinsic absorption of the phosphors has been measured by electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM). The luminescence excitation spectra of the samples have been recorded in the proper spectral range and the photoluminescence efficiencies under plasma excitation measured with two different set-ups. The luminescence decays have been analysed and the decay times (measured at I 0 /10) determined. The characteristics of the red and green phosphors from spray pyrolysis (SPR and SPG) have been compared with those of the corresponding commercial phosphors (CPR and CPG). It is one of the objectives of this work to consider in detail the various experimental set-ups, in order to perform a critical analysis of the results.

Experimental

Samples synthesis and structural characterizations

Powder samples were prepared using a laboratory scale spray pyrolysis process that we have described previously [START_REF] Joffin | Synthèse par pyrolyse d'aérosol et caractérisation de luminophores: Y 2 O 3 : Eu 3+ et Zn 2 SiO 4 : Mn 2+ pour applications dans les panneaux à plasma Thèse Institut National Polytechnique Toulouse[END_REF][START_REF] Alavi | Advances in Science and Technology[END_REF]. The piezoelectric pellet frequency was 2.4 MHz, the air flow was maintained constant at 5 litre min -1 , and the drying area was about 100˚C. For the SPR samples, only the composition Y 1.93 Eu 0.07 O 3 (that of the CPR, purchased from Kyokko) has been synthesized. A solution of yttrium and europium nitrates in appropriate proportions was decomposed at 700˚C. The powder was further annealed under air at temperatures from 900˚C to 1400˚C, in order to complete the crystallization of the cubic oxide. Samples with different post-synthesis thermal treatments are denoted hereafter SPR1-3. The resulting powders are made of hollow spheres: an empty core and a polycrystalline shell less than 100 nm thick, as described previously in more detail [START_REF] Joffin | [END_REF]5]. TEM and scanning electron microscopy (SEM) images of SPR3 are shown in figure 1. The variation of the average crystal size has been monitored by x-ray diffraction. The inter-particle agglomeration has been estimated by considering the mean equivalent diameter from the volume of the spheres, D v 50, measured with a Malvern Mastersizer S laser size analyser. The samples SPR1-3 are characterized by the same D v 50 = 2.2 µm and by an increasing average crystal size with heat treatment (table 1).

For the SPG1-4 phosphors Zn 2-2x Mn 2x SiO 4 , samples with x = 0.02-0.05 have been prepared starting from a mixture of zinc and manganese nitrates and of a colloidal silica solution in relevant proportions. The decomposition was performed at 500˚C. The spherical particles at this stage are made of crystallized ZnO and amorphous silica. An additional thermal treatment is then applied in order to complete the formation of the luminescent manganese-doped willemite phase, checked by x-ray diffraction. Simultaneously there is an increase in the crystal size. Unlike what has been observed for Y 2 O 3 : Eu 3+ , the annealing of Zn 2 SiO 4 : Mn 2+ samples induces different variations of D v 50 with temperature when the Mn content is varied [START_REF] Joffin | Synthèse par pyrolyse d'aérosol et caractérisation de luminophores: Y 2 O 3 : Eu 3+ et Zn 2 SiO 4 : Mn 2+ pour applications dans les panneaux à plasma Thèse Institut National Polytechnique Toulouse[END_REF]. In this study, the SPG1-4 samples have been all submitted to the same thermal treatment at 1300˚C for 1 h, and the D v 50 values are gathered in table 2. The morphology of the green phosphors, imaged by TEM or by SEM (figure 2), is different from that of the red phosphor. There is an important open porosity (macroporosity), homogeneously distributed in the spheres, but no core-shell contrast is observed. The CPG was purchased from Nishia, and its formula is Zn 1.92 Mn 0.08 SiO 4 (x = 0.04).

Absorption coefficient measurement by EELS

Quantitative information on optical constants such as the absorption coefficient can be extracted with a good spatial resolution, down to the nanometric range, by performing EELS experiments in a TEM. This information is obtained from exploitation of the low energy-loss domain of the EELS spectrum, which extends over a large spectral domain covering the visible-UV-soft x-rays range.

The measurements were performed on a Philips CM20 TEM operating at 100 kV. The microscope is equipped with a Gatan PEELS spectrometer, the energy resolution (FWHM of the zero-loss peak) and dispersion of which were 0.6 eV and 0.1 eV per channel, respectively. Spectra were acquired in the image mode, and the diameter of the analysed area was a few tens of nanometres. The spectra are corrected for noise and detector gain via the Gatan procedure. The samples analysed were SPR2 and SPG4 (table 3). Undoped willemite, Zn 2 SiO 4 , from spray pyrolysis was investigated, as well as pure cubic C-Y 2 O 3 purchased from Rhodia. The low-loss spectra were processed using home-made software [6,7]. It consists of different stages [START_REF] Egerton | Electron Energy-Loss Spectroscopy in the Electron Microscope 2nd edn[END_REF], pertaining to the extraction of the low-loss function Im(-1/ε(E)) from an experimental spectrum I (E), after which Re(-1/ε(E)) is obtained from the Kramers-Krönig relation, thereby yielding the real part, ε 1 (E), and the imaginary part, ε 2 (E), of the dielectric function. The absolute scale of Im(-1/ε(E)) is obtained by use of the Kramers-Krönig sum rule at zero energy. ε(0) is taken to be the square of the refractive index. The variation of some optical constants with energy or wavelength can then be deduced, such as the refractive index, n, the extinction coefficient, κ, the absorption coefficient, α and the reflectance, R. In this paper, we concentrate on the absorption coefficient.

Experimental set-ups for luminescence characterization

The phosphor powders have been characterized by several means: luminescence excitation spectroscopy (in the UV and VUV ranges) and emission measurements under Hg-lamp or plasma excitation.

The spectroscopy set-up has a SPEX Jobin Yvon (Fluorolog II FL212) spectrofluorimeter. It is coupled with a VTM300 VUV excitation monochromator, equipped with a 200 W D 2 lamp, for the VUV bench. The UV bench is made of a SPEX 1680 double grating monochromator equipped with an XBO W/4 (Suprasil quartz glass) 450 W lamp. The excitation spectrum of sodium salicylate is recorded under the same conditions and is used as a standard to correct the data from the lamp flux and the monochromator response. This procedure is the one generally applied to correct the excitation spectra because the external quantum efficiency of sodium salicylate is constant in the 40-340 nm excitation range [START_REF] Mayolet | Etude des processus d'absorption et de transfert d'énergie au sein de matériaux inorganiques luminescents dans le domaine de l'UV et VUV[END_REF][START_REF] Samson | [END_REF].

The corrected excitation spectrum is then determined as follows: raw excitation spectrum/sodium salicylate spectrum. It has been observed that residual short-wavelength light passes through the VUV monochromator operating in the 210-300 nm range, that may be removed by filtering with a quartz plate. For samples CPi (i = R or G), excitation spectra have been collected without and with the filter. The correction curves F CPi = I filtered /I unfiltered have then been applied to the observations under unfiltered conditions. With this correction, the spectra observed in the 210-300 nm range with the VUV bench match those obtained with the UV bench. The data of the excitation spectra displayed on figure 3 have been recorded with the VUV device between 120 and 275 nm, and with the UV-visible configuration for the range between 275 and 500 nm. The powders have been deposited in one of the compartments of a rotating holder, and gently pressed with a MgF 2 plate to obtain a smooth surface; the sodium salicylate used as a standard is placed in one of the four compartments. The position of the sample holder and the quality and the position of the sample surface relative to the collimation point of the incident light have nonnegligible effects. The reproducibility of the relative intensity measurements is estimated at ±5%. This experimental set-up can be compared with the one already described by Jüstel et al [11]. In their work, there was a dry nitrogen flow around the sample. Moreover, they normalized the intensity in the spectra to the absolute value of light efficiency at 254 nm excitation and the results have been validated using synchrotron radiation experiments. The excitation spectra of this work and those displayed in [11] have a similar shape. On the other hand, in order to work near PDP conditions, we have developed an experimental set-up ('CPAT set-up') to study the emission spectra, relative intensities and transient characteristics of phosphors excited by rare gas discharges. The experimental set-up, as shown in figure 4, consists of a stainless steel chamber filled for this work with Xe at low pressure, typically a few Torr. Under these conditions, the VUV photons are emitted by the resonance states of xenon (147 nm) [START_REF] Caillier | 15th International Conf. on Gas Discharges and their Applications[END_REF]. The discharge is confined between two aluminium electrodes 6 cm in diameter, insulated from the walls by a ceramic. The distance between the electrodes can be tuned between 0.1 and 5.5 cm. Visual observation and spectroscopic measurements are possible through a quartz window at the top of the chamber. A rotating ceramic plate with six compartments can receive five samples and a blank powder (BaSO 4 ) to characterize the plasma and to control the discharge stability. Each compartment is placed successively below the electrodes using a rotary motion. Once the samples are installed, the chamber is evacuated using a standard rotary pump and a turbomolecular pump to 10 -6 Torr. Then the chamber is filled with xenon (5 Torr). The voltage supply is then connected, and the working conditions are: alternative sinus input voltage, voltage range 100-500 V and frequency range 1-2 MHz. The light emitted by the phosphors and that associated with the gas discharge are collected via an optical fibre through the quartz window, connected to an Avantes SD2000 spectrometer with two gratings (500-780 and 775-1020 nm). The near-IR part of the spectra allows us to characterize the xenon emission [START_REF] Ouyang | [END_REF]. The acquisition time is about 1 s for spectrum measurements. The visible part of the gas discharge emissions is measured on the BaSO 4 powder (blank spectrum). Sample emission spectra (displayed in figures 5 and 6) can be obtained by subtracting the blank spectrum from the total spectrum (phosphor sample + discharge). The emission intensity is numerically integrated on the 500-750 nm range of the spectrometer. Measurements to validate the experimental set-up have been done as described in [START_REF] Caillier | 15th International Conf. on Gas Discharges and their Applications[END_REF]. The reproducibility of the relative intensity measurements is ±6.5%. For the decay analysis, the discharge is modulated at 6 Hz (ON for 30 ms, OFF for 136 ms) and the signal is measured using a photodiode (Centronic OSD15-E) coupled to an operational amplifier and an oscilloscope (Tektronix TDS 714L). The blank time response is also systematically subtracted from the sample's response.

Some of the samples have also been measured with another set-up ('DGTec set-up'), closer to PDP working conditions. In this set-up, the vacuum chamber front glass window supports a grating of co-planar electrodes. After evacuation to 10 -6 Torr, a gas mixture, Ne-30%Xe, is introduced at 450 Torr. The discharge is ignited and sustained by a 20-50 kHz and 0-1000 V power supply. The rotating sample holder is vertical; it receives three samples and a reference (Al 2 O 3 ). The luminance is measured through the front window using a Photoreasearch Pritchard 1980B spectrophotometer, after filtering by a photopic filter. The integrated intensity is read for each sample successively, and the measure on the reference powder is subtracted. At this gas pressure, the VUV photons are emitted by the resonance (147 nm) and excimer (173 nm) states of xenon [START_REF] Audray | Euro Display[END_REF].

The relative brightness of the samples under 254 nm excitation has also been measured using a 4 W Vilber Lourmat mercury lamp ('Hg-lamp set-up'), the emitted light is measured by reflection on the sample surface using a Photoresearch Pritchard 1980B spectrophotometer, after filtering by a photopic filter. The scattered incident light measured under the same conditions on the reference Al 2 O 3 is negligible. Results obtained with these set-ups (denoted, respectively, as spectroscopy, Hg lamp, CPAT and DGTec) will be compared in the next sections.

Results

Absorption coefficients

The absorption coefficients measured for the SPR and SPG powders (figure 7) have the same order of magnitude as a function of the wavelength. The curves displayed in the figures correspond to analysis of different grains of the same sample. The values of the absorption coefficient are low near 254 nm compared with those in the plasma domain (147 and 173 nm). They differ by at least one order of magnitude (table 3).

The EELS measurements are not sensitive enough in the high-wavelength domain (over 240 nm) to detect the absorption of the dopant (Eu 3+ or Mn 2+ ), which should appear as a shoulder on the lattice signal (Y 2 O 3 or Zn 2 SiO 4 , respectively) around 250 nm. In fact, in this wavelength domain, the extraction of the EELS signal cannot be precise. The comparison of EELS results with optical ones (extracted from [START_REF] Palik | Handbook of Optical Constants of Solids 2nd edn[END_REF]) in the low-energy domain revealed that the absorption coefficient is higher in the case of EELS. However, this is not the case for the plasma domain, where the two experiments agree well.

Photoluminescence intensities

The excitation spectra of the SPR, SPG series and commercial red and green (CPR, CPG) phosphors are shown in figures 8 and 9. The dotted line represents the limit between the absorption in the charge transfer state of the dopant ion (higher wavelengths) and that in the host lattice (lower wavelengths): it has been drawn at the minima of the curves, 222 nm for Y 2 O 3 : Eu 3+ and 225 nm for Zn 2 SiO 4 : Mn 2+ . The luminescence efficiencies relative to the commercial ×10 ×10 phosphors have been extracted from these spectra at 254 and 147 nm (tables 1 and 2).

At 254 nm excitation, there is a good agreement of the measurements with the two set-ups 'Hg lamp' and 'spectroscopy'. The efficiencies of the SPR samples (table 1) are the same and are equal to 60% of the CPR, whatever the crystal size. This has been assigned in previous works [START_REF] Joffin | [END_REF]5] to (i) the fact that the absorption of the 254 nm radiation is not complete in SPR samples, due to the hollow character of the particles, and (ii) the fact that absorption at 254 nm promotes transitions to the charge transfer state; this electronic state is localized on the europium ions and there is no appreciable diffusion of this energy in the crystals, then there being no effect of the crystal size. The relative efficiencies measured under VUV excitations are quite different from the UV-excited ones. Under plasma excitation CPAT and DGTec in 1), the luminescence efficiencies of the SPR phosphors increase with increasing crystal (figure SPR3 attaining CPR one. The energies of the VUV are just above the fundamental edge of the lattice (figure 7).

Taking the absorption coefficient α = 10 6 cm -1 (table 3), one estimates that 90% of the radiation is absorbed over a 25 nm thickness, that is in the particle's outer shell. The VUV energy migrates in the individual crystals before transferring to the europium ions, which explains the observed increase in emitted light with average crystal size. The intensities measured at 147 nm in the excitation spectra (figure 8) also increase from SPR1 to SPR3, but the variation is less steep than observed with the plasma set-ups and the last sample efficiency is only 80% of the CPR. As discussed in the section later, the origins of these discrepancies are till now not fully understood. The efficiencies of SPG samples at 254 nm excitation amount to 70% of the CPG. There is no appreciable variation with the Mn 2+ percentage between 2% and 5% Mn/(Mn + Zn) (table 2). The morphology of the SPG particles is not the core-shell one observed in SPR (see figures 1 and 2), but the apparent density in these samples also is low (about 1 2 of the theoretical one) and the absorption of the 254 nm radiation is not complete. The absorption in the oxygen to manganese charge transfer state increases with the manganese proportion, but at the same time the emitted visible light is more quenched. As a result, we observe that the light efficiency is constant in the composition range investigated. Other authors [START_REF] Van Der Kolk | [END_REF]17] have observed a maximum efficiency around 5-6% Mn/(Mn + Zn).

The emission of SPG phosphors under VUV excitation decreases steeply with increasing Mn 2+ content (table 2). This general trend has been observed with all three experimental set-ups, but marked differences remain between the measurements. The excitation spectra (figure 9) for SPG1 and SPG2 (Mn/(Mn + Zn) = 2% and 3%, respectively) almost match, and the same is true for SPG3 and SPG4 (Mn/(Mn + Zn) = 4% and 5%, respectively). At the same time, the emission spectra recorded using the CPAT set-up (figure 6) exhibit a more regular decrease from SPG1 to SPG4. It has been reported in the literature (for instance in [START_REF] Van Der Kolk | [END_REF]17]) that the efficiency of the manganese-doped willemite green phosphor under VUV excitation decreases between 1% and 10% Mn/(Mn + Zn), which means that the maximum efficiency occurs at still lower contents. So the same trend is observed here; nevertheless, it is really difficult to compare more precisely the observations made by different groups, because the synthesis conditions, i.e. the powders morphologies, have such a strong influence on the efficiencies observed under VUV radiation and on their variation with doping rate as well, specifically for Zn 2 SiO 4 : Mn 2+ .

Photoluminescence decays

The luminescence decays have been analysed using the CPAT set-up, and the 147 nm excitation pulse duration is 30 ms. The three SPR phosphors exhibit the same decay curves; the decay times τ 10 (measured at 10% of the intensity, I 0 , at the end of the pulse) are all equal to 4 ms, within the error range. The CPR decays more slowly, and τ 10 is 5 ms (table 1).

The τ 10 values measured for SPG powders decrease rapidly from 36 to 12 ms with Mn content increasing from 2% to 5% (table 2). Van der Kolk et al have put forward in [START_REF] Van Der Kolk | [END_REF] the idea that the lifetimes measured under VUV excitation are longer than the ones measured under 254 nm or longer wavelength excitations, indicating that slow relaxation mechanisms affect the Mn luminescence after host lattice excitation. Also, excitation pulses longer than 5 ms induce an increase in the apparent decay times. The value given for 2.5% Mn/(Mn + Zn), τ 10 = 17 ms, has been measured under a microsecond pulse and it is reported that for a 5 ms pulse the apparent τ 10 is 5 ms longer. It turns out to be 22 ms, whereas our values are 36 ms and 29 ms for Mn/(Mn + Zn) = 2% and 3%, respectively. Regarding the samples prepared by spray pyrolysis, the value τ 10 = 7 ms at 5% Mn/(Mn + Zn) has been reported by Kang and Park [18], but the details of experimentation are not given, whereas we measure 12 ms. There is a spreading of the numerical values reported. Besides the uncertainties in the determinations (generally ±10%), important effects are caused by the mechanisms of energy transfer in the host towards the emitting ions, which makes the proper description of the experimental conditions crucial. It may be underlined that CPG and SPG3 phosphors, both with 4% Mn/(Mn + Zn), exhibit quite similar decay functions when recorded under the same conditions (table 3), which is a proof that the mechanisms involved are directly connected to the phosphor composition, and much less influenced by the morphology than the intensity variation.

Discussion

All measurements performed in the UV excitation range with the excitation spectroscopy set-up on the one hand and with Hg-lamp excitation on the other hand are in very good agreement for both series of phosphors. The relative efficiencies measured for excitation in the VUV range agree much less. The possible artefacts originating from the different devices have been considered and as far as possible corrected. One problem of major importance nevertheless remains: the sample preparation for the measurements. It appears that points like the macroscopic surface roughness, or the exact position of the sample with respect to the incident radiation and to the optical set-up, are of major importance when considering high-energy incident radiations. In contrast, the VUV-excited emission decay curves do not suffer from possible nonreproducibility in the sample preparation. The decays are not exponential, and will be characterized, as usual, by τ 10 , which is appropriate for comparing data measured under similar experimental conditions.

All the observations made highlighted the differences between the phosphor responses at 254 nm excitation and at higher energy excitations. At 254 nm excitation, the SPR and SPG phosphors never reach the luminescence efficiencies of the commercial phosphors, CPR and CPG. At VUV excitation, the red phosphor Y 2 O 3 : Eu 3+ prepared by spray pyrolysis and submitted to proper annealing (SPR3) attains the luminescence characteristics of CPR. But the luminescence characteristics of CPG (100% efficiency and τ 10 = 17.5 ms) were not attained simultaneously by one of the SPG samples. The efficiency of SPG1 (Mn/(Mn + Zn) = 2%) is 130% ± 10% that of the commercial phosphor (CPG, Mn/(Mn + Zn) = 4%), and the decay time τ 10 is equal to 36 ms. On the other hand, the same decay time as for CPG, τ 10 = 17.5 ms, is observed with SPG3 (4% Mn/(Mn +Zn)), but the measured efficiency is only 80% ± 10%. It must be mentioned that another group (Kang and Park [18]) claims to have succeeded in obtaining the proper characteristics of spray pyrolysed green phosphors.

Because the natures of the transitions responsible for the absorptions of the two radiations are quite different, the penetration depths of the incident radiations also differ by at least one order of magnitude: 90% of the 254 nm incident radiation is absorbed over 500-2500 nm with the coefficients in table 3, whereas 90% of the VUV radiation is absorbed over 25-50 nm. Bechtel et al [19] have also underlined the fact that the limited size of the volume excited in the phosphor must be taken into account in PDP applications. They estimate the penetration depth of VUV excitation at 100-200 nm. It has been shown in [5] that the core-shell morphology of the spherical particles in spray pyrolysed red phosphors (SPRs) allows us to understand why these powders exhibit a relatively low efficiency at 254 nm excitation, while they attain the CPR efficiency at VUV excitations. The morphology of spray pyrolysed green phosphors (SPGs), with a lot of open porosity at the surface of the spheres, is very probably the cause of the failure to observe 100% efficiency relative to the commercial green phosphor (CPG) of the same composition, even with VUV excitation. The fact that the same decay curves have been recorded for SPG3 and CPG suggests that the luminescence build-up, the concentration quenching and even the quenching at structural or chemical defects are the same in the two samples and are not modified by the surface morphology. Thus we conclude that the porous morphology alters the absorption, and maybe the light scattering of the green phosphors.

Conclusion

We have used the technique of spray pyrolysis to prepare red and green phosphors (Y 2 O 3 : Eu 3+ and Zn 2 SiO 4 : Mn 2+ , respectively) for PDPs. Different techniques have been employed for investigation of the optical properties of the prepared powders, especially in the VUV energy range. Characteristics of the red and green phosphors from spray pyrolysis (SPR and SPG) have been compared with those of the corresponding commercial phosphors (CPR and CPG). Some discrepancies still remain between the observations made with the different set-ups, highlighting the difficulty in quantifying properly the emission efficiencies. The red phosphors prepared by spray pyrolysis and submitted to appropriate annealing attain the luminescence characteristics of the commercial phosphor under plasma excitation and can be proposed for PDP applications, but the characteristics of the commercial green phosphor, its efficiency and decay time, have not been attained simultaneously.

Figure 1 .

 1 Figure 1. (a) SEM and (b) TEM imaging of SPR3 powder.

Figure 2 .

 2 Figure 2. (a) SEM and (b) TEM imaging of SPG3 powder.

Figure 3 .

 3 Figure 3. Excitation spectra of the two phosphors in the whole VUV-UV-visible range.

Figure 4 .

 4 Figure 4. Scheme of the CPAT experimental set-up.

Figure 5 .

 5 Figure 5. Emission spectra of the SPR series compared with the commercial phosphor one under plasma excitation in the CPAT chamber.

Figure 6 .

 6 Figure 6. Emission spectra of the SPG series compared with the commercial phosphor one under plasma excitation in the CPAT chamber.

Figure 7 .

 7 Figure 7. Absorption coefficients extracted from EELS analysis of SPR2 and SPG4 samples.

Figure 8 .

 8 Figure 8. VUV-UV excitation spectra of the red phosphor series.

Figure 9 .

 9 Figure 9. VUV-UV excitation spectra of the green phosphor series.

Table 1 .

 1 Structural characteristics, luminescence efficiencies and decay times of the red phosphors.

		Crystal Particle				Plasma Plasma
		size	diameter,	254 nm	254 nm	147 nm	CPAT	DGTec τ 10
	Sample (nm) D CPR 95 3.5	100	100	100	100	100	5
	SPR1	42	2.2	56	56	63	44	53	3.7
	SPR2	53	2.2	59	59	74	62	85	3.7
	SPR3	85	2.2	58	58	80	91	105	4.3

v 50 (µm) Hg lamp spectroscopy spectroscopy set-up set-up (ms)

Table 2 .

 2 Structural characteristics, luminescence efficiencies and decay times of the green phosphors.

			Particle				Plasma Plasma
		Mn/(Mn + Zn) diameter,	254 nm	254 nm	147 nm	CPAT	DGTec τ 10
	Sample (%)	D v 50 (µm) Hg lamp spectroscopy spectroscopy set-up	set-up	(ms)
	CPG	4	8	100	100	100	100	100	17.5
	SPG1	2	7.8	72	73	100	124	132	36
	SPG2	3	5.2	72	75	100	116	87	29
	SPG3	4	4.8	74	71	75	88	71	17.5
	SPG4	5	4.4	66	70	75	48	49	12

Table 3 .

 3 Mean values of the absorption coefficients for the SPR and SPG powders in the plasma wavelength domain and at 254 nm.

	Absorption
	coefficient		Plasma
	(cm -1 )	254 nm	(147 and 173 nm)
	SPR	5 × 10 4 ± 50% 10 6 ± 5%
	SPG	10 4 ± 50%	0.5 × 10 6 ± 10%

Acknowledgments

This work was supported by the Ministère de la Recherche (RNMP/POSUMIC). The authors wish to thank RHODIA for supplying the lanthanide solution and Thomson Plasma for the measurements under plasma excitation. The SEM images have been taken at the Service de Microscopie Electronique (UPS, Toulouse).


Mélanie Jouitteau

LISTEN TO THE SOUND OF SALIENCE MULTICHANNEL SYNTAX OF Q PARTICLES *

I claim that the linguistic message that realizes syntax is multichannel. The syntax-PF interface is the interface of syntax with all the sensorimotor systems available to humans, including, for oral languages, minimal vocalic productions, intonation, hand movement and body gestures. I show that the realization of syntactic structure consists of (i) segmental oral morphemes, (ii) non-segmental oral morphemes (intonation), and (iii) non-oral morphemes (segmental or not; hand movements, upper body gestures and face movements). In particular, the latter predicts the use of non-oral morphemes in oral languages, since the speakers of oral languages have it available in their sensorimotor system. I focus on the CP domain of oral languages, and show that its functional projections can be realized by either (i), (ii) and (iii). The empirical body of this article concentrates on the multichannel Q particles in French, Atlantic French and British English. * Thanks are due to Johan Rooryck, Milan Rezac and to an anonymous reviewer for useful comments and suggestions. The usual disclaimers apply. 1 The recurrent presupposition seems to be, for the syntax of oral languages, that intonation is not part of PF, despite the contradictions this triggers. As it is difficult to point out unspecified

Introduction

 Chomsky (1995:131)defines PF as "the interface with the sensorimotor systems". The very existence of sign languages demonstrates that sensorimotor systems available to humans are not stricto sensu restricted to the production of phonological material. A terminological problem therefore arises: the Phonological Form in the Minimalist Program is broader than its label assumes (φωνή; voice, noise, sound) and it is common to refer to the phonology of signed languages [START_REF] Brentari | A Prosodic Model of Sign Language Phonology[END_REF]. The minimalist notion of PF has to be understood in such a way as to account for all possible realizations of syntactic structure: oral morphemes, intonation, gestures (hand movements, upper body gestures and face movements), whatever the selected sensorimotor subsystems of realization (henceforth channels). A standard assumption is that a given language selects one channel and keeps to it (henceforth mono-channel hypothesis). The mono-channel hypothesis is seldom formally defined, hardly motivated, and empirically incorrect 1 . Since the 1990's, the field of signed languages has extensively studied the multichannality of the linguistic message (see Aarons 1994:chap.3 and references therein, [START_REF] Bahan | Nonmanual realization of agreement in American Sign Language[END_REF][START_REF] Woll | The Linguistics of British Sign Language, An Introduction[END_REF], Neidle & al. 2000, among others). A bi-channel hypothesis emerges from this field: [START_REF] Sandler | The medium and the message: Prosodic interpretation of linguistic content in Israeli Sign Language[END_REF], [START_REF] Wilbur | Phonological and prosodic layering of nonmanuals in American Sign Language[END_REF], Pfau (2002, under press) and [START_REF] Pfau | Doing it the right way: Wh-movement in Indo-Pakistani Sign Language[END_REF] propose that in signed languages, non-manual marking is to manual marking what intonation is to the oral segmental message in oral languages. I strengthen the claim in (1), which states that the marked case is indeed not multichannality, but the suppression of a given sensorimotor subsystem in a given language.

(1) Full use of available sensorimotor systems is the unmarked case for the human language faculty.

The case of deaf-mute speakers illustrates (1) rather clearly in that they make full use of the available sensorimotor systems -manual and non-manual marking-giving rise to so-called sign languages (see [START_REF] Kegl | Creation through contact: Sign language emergence in sign language change in Nicaragua[END_REF]. Full use of available sensorimotor systems is less clear for oral languages; the standard assumption being that they resort exclusively to oral morphemes. In contrast to this assumption, I pursue the hypothesis that (1) is empirically correct. In particular, I assume that the visual-gestural system can realize functional projections in oral languages. In previous work, I have shown that the lexicon of Atlantic French 2 contains morphemes realized by gestural morphology [START_REF] Jouitteau | Gestures as Expletives, Multichannel Syntax[END_REF]Jouitteau ( , 2005:chap 6:chap 6). The C head in (2) is imposed as an expletive strategy in subject-drop environments and can be realized by any ostensible sound or gesture in the preverbal area. The Q particle in (3) can be realized by a closed set of ostensible gestures (raising of the head, raising of one or both eyebrows, opening movement of the hand). In ( 2) and (3), the crucial assumptions without illustration, I will take a concrete example (chosen only to illustrate the usage of an entire field; let the following authors be assured of the reader's empathy and forgive me for their appearance as the bad example). Roberts and Roussou (1999:11) present a standard typology of the realisations of Q particles. For Colloquial French, they note that in the yes/no question Il a vu Marie? (-he has seen Marie?-), "Q is silent" and "has no PF-realisation". Furthermore, they propose that the "interrogative clause-typing is not grammaticalized and is marked purely by intonation." The contradictions are numerous. In my perspective, Q in this example indeed has a PF-realisation, precisely because it is marked by intonation. I also consider that a rising intonation contour, if it can be shown to realise functional material, is fully grammaticalized. Notice further that my analysis allows for 'really silent' Q particles that do have a PF-realisation: Q particles realised by gestures are certainly silent, but they have a PF realization. Again, the realization of a Q particle by a given gesture shows that it is fully grammaticalized.

2 The paradigm characteristic of Atlantic French is productive along the Atlantic coast, excluding the Breton speaking area. The preverbal gestured morpheme is thus fully a part of grammar. It is also restricted to the preverbal position of matrix sentences, and permits otherwise ungrammatical subject-drop (see [START_REF] Jouitteau | Gestures as Expletives, Multichannel Syntax[END_REF][START_REF] Jouitteau | La syntaxe comparée du Breton[END_REF]. In this article, I concentrate on clause typing realized by intonation or gestures in oral languages, as in (3). The article is organized into four sections. In section 1, I present a brief typology of question marking strategies, and the principal syntactic analyses proposed. I show, following [START_REF] Cheng | Licensing Wh-in-situ[END_REF], that Q particles can be realised by intonational markers. In section 2, I show that gestures can also realise Q particles, and consequently that gestures can realise syntactic functional projections. In section 3, I discuss the implications of my proposal, and sketch the lines of a research program on multichannality. Section 4 concludes.

1.

The least it takes to be a question I illustrate below the different PF alternatives for the formation of questions across languages. The first alternative is the wh movement of an XP into the CP area, as illustrated in (4). The second alternative is to generate a phrasal wh XP in the CP area. This is illustrated for German in (5), where the generated wh XP was is a scope marker, and the questioned element wen raises to the wh specifier of the embedded sentence. The third alternative is a special realization of the C head. In the well-known subject inversion paradigms illustrated in (6), a verbal head raises to C from the IP projection and provides phonological material for the realization of the C head. The interrogative head can also be merged directly in the CP area. This happens in (7) in a Breton yes/no question. This is a crosslinguistic common strategy, i.e. the particle czy in Polish, kö in Finnish, ma in Mandarin Chinese, li in Slavic languages, ki in Bengali, ci in Yiddish, etc. Merge of a Q particle is also the strategy to license in situ questions (Cheng 1991)4 ,5 . In the Chinese example in (8), the wh object is in its canonical (non wh) position and the morphosyntactic identification of the sentence as a question is ensured by the segmental realization of the Q particle ne.

(7) Hag eo gwir an dra-se? (Breton) Q is true the thing-here "Is it true?" (Chinese, Cheng 1991) (8)

Hufei mai-le na-yi-ben-shu ne. Hufei buy-ASP which-one-CL-book Q wh "Which book did Hufei buy ?" Minimal vocalic productions can also realize Merged clause typing particles, as in Child Dutch or English. In the first acquisition stages of wh questions in Dutch, a preverbal /schwa/ identifies the sentence as a question (van Kampen 1997:80 and references therein).

(Child Dutch, van Kampen 1997) (9)

/schwa/ is de badkamer nou bleven? schwa is the bathroom then gone "(dropped-where) is the bathroom then gone?"

To sum up, the range of possible morphological manifestations of the interrogative element is rather varied; the valid generalization for the formation of questions seems to be that a morphosyntactic interrogative element must be realized at least in the CP area. This element is a head X or a phrasal XP. It is generated in situ or derived from the IP domain.

1.1. Implementations [START_REF] Cheng | On the Typology of wh Questions[END_REF]Cheng ( , 1997 :22) :22) proposes that the morphosyntactic identification of a given sentence as an assertion or as a question is obligatory (see also [START_REF] Chomsky | The Minimalist program[END_REF]Lasnik 1977, May 1985). She develops the Clause Typing Hypothesis: for a question to be well-formed, either a wh complementizer appears in the high periphery, or a wh phrase raises to the specifier of the same projection. This accounts for the complementarity of wh + movement strategy vs. the Q + in situ strategy, and obtains the generalization that the languages with wh in situ also have interrogative particles. The same intuition is embodied by proposals like [START_REF] Rizzi | Residual V2 and the wh Criterion[END_REF][START_REF] Rizzi | Residual Verb Second and the Wh-Criterion[END_REF] wh criterion illustrated in (10).

(10)a. A wh operator must be in a specifier-head relation with a wh head.

b. A wh head must be in a specifier-head relation with a wh operator .

The wh criterion differs from the Clause Typing Hypothesis in generalizing wh movement in that said movement also applies in wh in situ languages, but at LF. Is there a minimal material required at PF to identify a question? [START_REF] Platzack | A Visibility Condition for the C domain[END_REF] adds to (10) the Visibility Condition, which states that each CP projection of the CP area must have at least either its specifier or its head phonologically realized, and thus he obtains the generalization of [START_REF] Cheng | On the Typology of wh Questions[END_REF][START_REF] Cheng | On the Typology of wh Questions[END_REF]) that a clause must be typed by the morphosyntactic realization of either a CP specifier or a C head. However, with the proliferation of the CP domain functional projections [START_REF] Rizzi | The Fine Structure of the Left Periphery[END_REF], the Visibility Condition would inaccurately predict a proportional proliferation of realized elements in the CP domain. [START_REF] Vangsnes | The identification of Functional Structures[END_REF][START_REF] Vangsnes | On wh-Questions and V2 across Norwegian Dialects: a survey and some speculations[END_REF] proposes the weaker Identification Condition: adequate material must be realized in the projection of a head for this head to be identified and its properties activated (only identified heads can be interpreted). Under the Identification Condition, the minimum amount of initial sentence material needed for a question to be well formed is a realized element α in the CP area. This α element can be either a head X or a phrasal XP, it can be generated in the CP zone or derived from lower in the structure; the only requirement being that it must be realized in the CP area.

In minimalist developments, a feature-checking relation easily yields the lack of sensitivity to the syntactic X/XP status of the required element. A head, as well as an XP, is a potential satisfier for a feature-checking relation. For example, [START_REF] Miyagawa | The EPP, scrambling, and wh-in-situ[END_REF] postulates an EPP feature on C that has to be erased by either an adjoined Q-head (in wh in situ languages) or a merged specifier (in wh movement languages) 6 . For the purposes of this article, I will adopt the Identification Condition as it elegantly accounts for the minimum material required in the data from (4) to (8). The Identification Condition is falsifiable in questions where no marker at all is realized in the CP area. I will now illustrate cases where only a rising intonation or a rising gesture realizes the question marker in the absence of a segmental morpheme realized by the vocal channel.

Counter-examples (?)

The question marker in ( 11) is realized by an oral Q morpheme that seems at first sight optional 7 . I will argue that ( 11) is no counter-example to the Identification Condition: the optionality vanishes once we take into account the missing dimensions of the data. When the particle Esk or Do does not appear, the sentence is more accurately represented as in ( 12), where ' ' represents the direction of intonation in the entire sentence 8 . ( 11 12). The first one which I will adopt is to suppose that the clause typing information is here provided by intonation because the acceptability of sentences depends on it 9 . The fact that ' ' extends over the entire sentence suggests that it realizes a syntactic element at the edge of the sentence.

The second option is to maintain the mono-channel hypothesis: it is exclusively the segmental oral channel that can realize morphosyntactic wh features. I outline the cost of such an option before I develop the syntactic implementation of my hypothesis in the coming section. The first challenge for the mono-channel hypothesis is to account for the grammaticality of the sentences in (12) in spite of the Identification Condition. This calls for a complete reanalysis of the proposals and generalizations made by the literature 6 See also Roberts & Roussou (1999:9) who propose to mark F* the functional projections whose PF-realization is forced for interface interpretability. 7 The French lexicon contains a morphemic particle 'Esk' formed on 'Est-ce que' (Is-this that…), reanalyzed as a simplex interrogative morpheme. 8 Both Esk and ' ' can occur in the same sentence, as discussed later, see example (16). 9 See also [START_REF] Deguchi | Prosody and Wh questions[END_REF] and [START_REF] Kitagawa | Default Prosody explains Neglected Syntax analysis[END_REF] for similar arguments on different data. Their conclusion is that "syntactic theory can not escape prosody, […] because the acceptability of sentences can depend on them". on question formation since the generalization of [START_REF] Cheng | On the Typology of wh Questions[END_REF]. Moreover, sentences as in ( 12) are far from being exceptional. According to the typological estimations of [START_REF] Ultan | Some general characteristics of interrogative systems[END_REF], the morphosyntactic marking of yes/no questions by a (rising) intonation is the strategy represented by 95% of the languages of the world. If we maintain that intonation cannot achieve the realization of morphosyntactic wh features, the typologically over-represented rising intonation strategy needs an explanation. The second challenge is to motivate the restriction to a given linguistic channel. As seen in the introduction, the linguistic message is multichannel in sign languages. What could thus motivate the assumption that multichannality is not an available option in oral languages? The third challenge lies in the lack of motivation for the specific election of the segmental oral system.

In contrast, I propose that intonation realizes the same morphosyntactic wh features an oral segmental particle does, and that the Identification Condition accurately predicts that (12) illustrates well-formed yes/no questions. I leave the typological over-representation of intonational Q heads unexplained, but the Identification Condition together with (1) accurately predicts this strategy to be available. Intonation can be the unique morphosyntactic trigger for a yes/no question reading. The sentence in (13)a. is obligatorily typed as a question, and the assertion reading is ungrammatical. Consistently, modification of the rising intonation contour leads to the obligatory interpretation of the sentence as an assertion or command, as in (13)b., reinforcing the conclusion that rising intonation was a clause-typing morpheme in (13)a.10 .

(13)a. Ø Tu prends du café sans lait (French) you take DET coffee without milk *"You take coffee without milk."/ √ "Do you take coffee without milk?" b. Ø Tu prends du café sans lait / you take DET coffee without milk √ "You take coffee without milk." / √ "Take coffee without milk." * "Do you take coffee without milk?" Intonation can realize a Q particle even when there is segmental material that could seem to provide clause typing information. The yes/no colloquial French construction in ( 14) is characterized by the tag ou bien (presumably ellipsis), and a rising contour. Clause typing cannot arise from the tag alone: non-rising intonation is rescued in (14)c. by the merge of a segmental Q particle. I conclude that in (14)a.,' ' realizes a Q particle licensing the tag. ( 14 [START_REF] Cheng | Licensing Wh-in-situ[END_REF] in analyzing rising intonation as the realization of a Q particle. Under this hypothesis, the left periphery of the above grammatical questions in French is never empty at the relevant syntactic level. Satisfaction of the Identification Condition is achieved via Merge or Move of either a head or a phrasal XP. The particular choice for the realization of the morphosyntactic wh element depends on the lexical inventory of a given language. I assume that the French has two Q particles (i) a Q morpheme ' ' licensing wh in situ as in ( 15) and (ii), a yes/no Q particle with two allomorphs: esk and rising intonation ' ' 12 . The hypothesis that esk and ' ' are allomorphs of the yes/no Q morpheme is supported by their mutual exclusivity. In ( 16), non-rising intonation is obligatorily sent to the pragmatic module. 11 Atlantic French has in situ questions without an obligatory presuppositional context (contra Chang 1997:42 ). For a similar argument for standard French, and further discussion on the contexts licensing wh in situ, see [START_REF] Butler | Split-DPs, generalized EPP and visibility[END_REF]. Atlantic French contrasts with the variety of French studied by Boeckx (1999b) and Vergnaud and Zubizarreta (2001). [START_REF] Cheng | Licensing Wh-in-situ[END_REF] draw a parallel between in situ questions and yes/no questions in French, both having a Q clause-typing particle realized by intonation, and both being restricted by presuppositional contexts. Atlantic French shows the same parallel: yes/no questions also have no obligatory presuppositional context.

12 In Japanese, existence of a segmental Q head has no bearing on the distribution of a nonsegmental one: the ' ' Q particle is banned from embedded sentences, whereas the segmental ka is not [START_REF] Yoshida | Question Marker Drop in Japanese[END_REF]Yoshida 1996, Hoshi 2004).

The intonational morpheme, whether rising or not, does not rule the sentence out in imposing competition for the same Q site because there is another interpretation available pertaining to pragmatics (aggressiveness or impatience is marked by a falling intonation ' ', depending on factors such as the degree of politeness). In ( 16), the ' ' Q allomorph is banned and ' ' has to be interpreted as a non-syntactic element for the sentence to be fine. I predict that if ' ' had no pragmatic import, the sentence would be out because two Q particles would compete for the same site. I also predict that the sentence is obligatorily interpreted as a yes/no question because esk has no other interpretation available. I will now turn to the third allomorph: the Q particle realized by the visual-gestural channel.

Q particles realized by the gestural channel

The gestural channel also can realize Q particles satisfying the Identification Condition. [START_REF] Jouitteau | Visibility doesn't mean Hearability[END_REF] present two cases of grammatical yes/no questions with an intonation typical of assertions and no oral segmental Q particle. These two cases take from a multichannel transcription of a corpus in spontaneous British English [START_REF] Ferre | Relations entre discours, intonation et gestualité en anglais britannique[END_REF]. In ( 17 The sentence is interpreted as a question and receives an answer from Michelle despite the typically assertive intonation. However, the Identification Condition is not violated since the gestural channel realizes a Q particle in the preverbal position (Zoe's rising head movement). On the opposite hypothesis, where the gestural channel does not provide morphology spelling out functional projections, example ( 17) is a serious counterexample to the Identification Condition. In (18), Zoe and Michelle converse about Michelle's mother having an accent from the north, which Zoe has doubts about. There is neither an oral segmental Q particle nor a rising intonation. Yet the sentence receives an answer.

(18) Zoe:

_________________________[ RAISED EYEBROWS]

Really ? But she used to have an accent . 'Really ? But did she use to have an accent ?' Michelle : Yeah and she still says things now like 'All right pet'.

Zoe raises eyebrows on really and keeps them high during the entire following sentence. The eyebrows fall after the end of the interrogative sentence. I claim that a Q head is realized by the raising eyebrow and satisfies the Identification Condition. On the opposite hypothesis, again, the sentence in ( 18) is a counterexample to the Identification Condition. I conclude, therefore, that the lexicon of British English contains a Q particle whose realization is gestural in nature. The lexicon of French also contains Q particles realized by the gestural channel 13 . This is clearly the case in Atlantic French, where a Q particle licenses exceptional subject-drop [START_REF] Jouitteau | Gestures as Expletives, Multichannel Syntax[END_REF][START_REF] Jouitteau | La syntaxe comparée du Breton[END_REF] 2). Again, we would have to account for the surprising restriction that oral languages limit their morphology to the oral channel since we know from the study of sign languages that gestural morphology is part of the human language faculty. What could prevent oral languages from making use of a realization that (i), we know is available to the speakers and (ii), that we know is available in UG (sign languages)? In (20), I

13 [START_REF] Oiry | Les questions exceptionnelles en français ou <tu penses quoi qui est caché dans l'sac?[END_REF] and [START_REF] Butler | Split-DPs, generalized EPP and visibility[END_REF] independently note occasional non-rising intonation in French in situ questions. Multichannel data is not available in these works, but my hypothesis would be that a gestured Q head has satisfied the Identification Condition.

show that the gestural Q particle triggers obligatory yes/no question reading, particular intonation variations being send to pragmatics.

(Atlantic French) (20) [ CP / / RAISED EYEBROW [ IP Tu prends du café sans lait ? you take DET coffee without milk "Do you take coffee without milk?"/ * "You take coffee without milk." I conclude that the lexicon of French contains a Q morpheme, coming in three allomorphic varieties: (i) a segmental oral allomorph Esk, (ii) a non-segmental oral allomorph (rising intonation contour), and (iii) a non-oral allomorph (rising facial or body movement).

3.

Multichannel Syntax I have shown that oral languages can select different channels of the available sensorimotor systems to realize Q particles required by the Identification Condition. However, if (1) is on the right track, extension of the hypothesis to all functional projections is probably in order. In the CP domain, at least, it is likely that multichannel signs can realize any head. In German for example, the rise-fall contour on a constituent internal to IP is equivalent, in terms of interpretation, to the topicalization of the same constituent (see [START_REF] Krifka | Scope inversion under the rise fall contour in German[END_REF] and references therein). As for FocP, the focus interpretation is crosslinguistically obtained via different channels, morphemic or intonational. The morphemic message can show Merge of a dedicated segmental morphemic marker (Wolof, Swahili) or the Movement of an XP (Celtic languages, German, Hungarian or Basque). Intonation can also realize Focus by either stress (German and most Romance languages) or phrasing (determined by segmental alternations in French, tones in Chinese, and lengthening or absence of shortening in Kimatuumbi, see Féry 2001 and references therein). Each strategy is a PF variant that realizes Foc or SpecFocP in the syntactic structure for interpretability purposes. Independently, we know from everyday experience that this typology has to be extended as to account for the fact that focus on an DP can be achieved via the body-gesture channel: a pointing gesture triggers salience in context. As illustrated in (21), a postverbal object pronoun is illicit except if it is made ostensible (Cardinaletti and Starke 1999:152). Ostension can be realized by (i) contrastive stress intonation or (ii) flat intonation and a pointing gesture. Pointing gestures also typically realize deictic adverbs. In ( 22), I illustrate the analytic [det-noun-deictic adverb] order, with the adverb realized by a pointing gesture ( ). From ( 21) to ( 22), the pointing gesture can be realized with a wide array of face and body gestures (finger, hand, head, eye, etc.) which, however, is not without restrictions (*lips). This restriction depends on the lexicon of each given language: lip pointing realizes deictics in Thai (Anne Kelleher, p.c.)). If the part of PF that realizes syntactic elements by either prosody or gestures becomes visible for syntactic theorizing (as it is for speakers), we will be able to isolate the environments where truly null elements have to be postulated, and consequently be able to measure the crosslinguistic obligatoriness of a PF realization for Focus, Topic, Q particles, wh scope markers, deictics, etc.

Conclusion

If any sensorimotor system available can realize syntactic structure, a new set of fruitful questions arises. In oral languages, is the part of the lexicon realized by gestures more widely shared across oral languages than the part realized by the oral channel (i.e., rising movements for questions)? And if so on what grounds? Is there a difference in modality between functional heads realized by gestures in oral languages and the same functional heads realized by the same signs in sign languages? How come human languages show a global bias toward the oral modality, unless it is excluded by physical impairment? Why do we not find mixed systems, for example oral languages whose verbal lexical inventory or quantifier scope marking would be gestured? I propose to represent the multichannel dimensions of languages as illustrated in table (23) where multichannel productions are the unmarked case. Suppression of a given channel is the byproduct of physical impairment (i.e. deafness, ton-deafness, blindness, facial paralysis) or of voluntary restriction (mono-channel-writing system, whistled languages).

Sign languages

Oral languages oral timing units The global image is that human languages are bi-channel. Following Bouchard (2002:38), two different strategies realize semantic relations in an oral language: Juxtaposition (A and B are ordered temporally next to one another) and Superimposition (B is a modulation superimposed on A). In this sense, intonation in oral languages is thus an effect of superimposition unto the oral Channel 1. I predict that Channel 1 in sign languages also expresses linguistic differentiations by superimposition (according to its availability). Very importantly, the multichannel dimension of the linguistic message calls into question the linearization process: for the moment, our models of linearization are designed as to obtain a mono-linear output which is simply inappropriate to account for the multichannality of the data. Given that two syntactic elements can occur at the same time in two different channels, linearization must be thought of as creating different lines and not just one. What are the rules of multilinearization and are there universals? How to represent the relations between the different syntax realization channels? Can a gestural marker, for example, cliticize on an oral one? Are there syntactic elements that have to be realised in the same line? Why? The fact that multichannality is not the key for the differences between oral and sign languages opens new insights to the inquiry.

(

(

  16) a. / / Esk [ IP tu veux passer en premier? (French) b. / / Do [ IP you wanna go first ?

  ), Zoe asks her partner what were her advantages of working at Mark & Spencer's. Rising head movement extends over the entire sentence, pleading for its syntactic realization in sentence (edge/) initial position. (17) Zoe : _______[ RISING HEAD MOVEMENT] (British English, Ferre 2004) You get big bonuses at Christmas . 'Do you get big bonuses at Christmas ?' Ben got like loads of money at Christmas. Michelle : No cause they got rid of me before I had any rights.

(

  21) J'ai vu Marie puis j'ai vu *elle / ELLE / + elle. (French) I have seen Mary then I have seen her. "I saw Mary then I saw her."

  observation is that if no other ostensible gesture or sound is inserted in the preverbal area, the sentence becomes strongly ungrammatical 3 .

					(Atlantic French)
	(2)	* (SHOULDER RAISING)	pars en février	de toute façon.
		C	Ø leave in February anyway.
		"I leave in February anyway."
	(3)	______________________EYEBROW RAISING__(_____)
		pars en février	de toute façon
		Q Ø leave in February anyway
		"Do you leave in February anyway?"	/ * assertive / * imperative

  . In the grammatical (19)b, (19)c and (19)d, no oral wh morpheme is present, but the linguistic message contains ostensible facial movements. The sentence can only be interpreted as a question. In (19)e, no ostensible facial movement is produced, and consequently, the sentence cannot be interpreted as a question.

	(19) a.	[ CP	/ Esk	[ IP Ø peux finir mon thé ?
	b.	[ CP	/ raised head	[ IP Ø peux finir mon thé ?
	c.	[ CP	/ raised eyebrow [ IP Ø peux finir mon thé ?
	d.	[ CP	/ raised eyebrows [ IP Ø peux finir mon thé ?
	e. * [ CP	/	[ IP Ø peux finir mon thé ?
				(I) can finish my tea
	The Identification Condition rules out (19)e.; reinforcing the conclusion that the
	gestural channel realizes a Q particle in (19)b, (19)c and (19)d. If I am wrong in
	this conclusion and if the gestural channel is not able to realize functional heads
	in oral languages, two major problems arise. First, we have to account for the
	fact that (19)b., (19)c. and (19)d. violate the Identification Condition (see
	problems developed on in section 1.

The dropped subject is identified by a null topic. In 'out of the blue' contexts, the gesture obligatorily steps in for the lack of features in the null topic: the required gesture is thus a pointing gesture and provides the features required for subject identification. SeeJouitteau (2004a[START_REF] Jouitteau | La syntaxe comparée du Breton[END_REF].

[START_REF] Cheng | On the Typology of wh Questions[END_REF][START_REF] Cheng | On the Typology of wh Questions[END_REF] proposes the generalization that all languages which show wh in situ also have interrogative particles. SeeBruening (2004:14) for a contrasting hypothesis that most languages, if not all, have Q particles. In this article, I concentrate on the minimal PF material necessary for a question to be well-formed.

Merge of a wh marker also serves as scope marking in the split-DP constructions of French (i)Combien (de livres) as-tu lu (de livres) (Butler and Mathieu 2005) how.many (of books) have-you read (of books) 'How many books have you read?'

The same phenomena arise in many languages: seeHaspelmath (2001Haspelmath ( :1013) ) for Italian, or[START_REF] Jouitteau | La syntaxe comparée du Breton[END_REF] for Breton, among many others.

Mélanie Jouitteau