Dr Nikolaos Kostopoulos

Mathias Miranda Vieira

Louis Godeffroy

Dr Jérôme Médard

Dr Catherine Combellas

Jean-Francois Lemineur

Dr Frederic Kanoufi
email: frederic.kanoufi@u-paris.fr

Jean-Marc Noël
email: jean-marc.noel@cnrs.fr

Dr Hubert Girault

Dr J.-F Lemineur

J.-M Noël

Tuning the electrode activity to expose transformational and electrocatalytic characteristics of individual nanoparticles by nanoimpact electrochemistry

Nanoimpact electrochemistry

(NIE) is a straightforward analytical technique to study at high throughput the reactivity of single Nanoparticles (NPs) colliding with a biased UltraMicroElectrode (UME). As NIE can reveal both NP size and catalytic activity, this strategy can be employed to establish relationships between these two NP descriptors. Herein, it is shown that the electrode material is crucial for visualizing simultaneously electro-catalytic processes and NP transformation, that can size the NPs. UMEs made of gold (Au) or glassy carbon (GC), were employed to study the reduction of AgBr NPs and the electrocatalytic activity of the resulting Ag NPs for the oxygen reduction reaction (ORR). With Au UME, only the transformation process is probed, allowing a quantitative analysis of the overpotential effect on the reduction dynamic of the AgBr NPs. When a GC UME is employed, the AgBr NPs reduction and subsequent ORR activity can be quantified for the very same NPs.

Introduction

Nanoimpact electrochemistry (NIE), which was introduced more than a decade ago, [1,2] constitutes a straightforward analytical technique to study, at high throughput, single nano-objects and particularly nanoparticles (NPs). [3][4][5][6][7][8][9] In most cases, such experiments are carried out using an ultramicroelectrode (UME) immersed in a suspension of colloidal NPs. The analysis of the current spikes (shape and amplitude) arising from the collisions of individual NPs with the biased UME allows extracting valuable information about the colloidal system under investigation. On the one hand, the NIE approach was employed to characterize NP transformation or dissolution processes. In the latter case, the electrochemical transients which are generally current spikes provide dynamic sizing [10] of the different populations [11] of NPs during their contact with the electrode surface. This allows deciphering several mechanistic aspects, [4,12] such as demonstrating the role of the potential applied to the electrode on the transformation rate, [12] the possible occurrence of multistep reactions during NP transformation, [13][14][15][16][17][18][19] as well as the importance of electrostatic forces, [20,21] electrolyte concentration, [22] NPs-electrode interactions [11,23] or NPs motion. [18,19,24] On the other hand, NIE was employed to determine the electrocatalytic activity of individual NPs. Many electrocatalytic reactions have been inspected including the oxygen evolution, [25,26] or reduction, [27,28] hydrogen evolution, [29][30][31][32][33] or oxidation, [34] hydrogen peroxide oxidation [35] and reduction, [36] and hydrazine oxidation reactions. [37][38][39] Besides, these reactions were inspected at a variety of NPs such as metals (Pd, [29] Pt, [27,30,34,36,37,39] Au, [30,31] ), metal oxides (CoFe2O4, [25] IrOx, [35] Pt@TiO2 [28] , Ni(OH)2 [40] ) or carbon materials. [24,41,42] The electrocatalytic activity of a NP is detected by an abrupt increase of the current, the height of which reflects the electrocatalytic efficiency, the dynamics (passivation, etc…) [30] at the single NP level, [29] or the NP active area. [38] Herein, we take advantage of a transformation/electrocatalytic NIE strategy, previously employed to study the transformation of Ag NPs to Ag2O followed by their electrocatalytic activity for the OER. [26] We selected AgBr NPs as a model system that represent easy to use precursors of metal Ag NPs, widely studied by NIE. [4] Indeed, Ag NPs can be readily obtained by the reduction of AgBr NPs (Equation 1) and display a good electrocatalytic activity for the ORR in neutral pH aqueous media (equation 2). [43] In particular, following Sepunaru's recent work, [32] the collisions of NPs were recorded at different electrode materials (catalytically inactive or active). Even if most NIE studies are performed at catalytically inactive electrodes in order to inspect the catalytic activity of the NP, Sepunaru demonstrated that the catalytic activity of the NPs was annihilated at catalytically active electrodes as no electrochemical collisions was detected. By varying the activity of the electrode, deeper mechanistic insights were reached regarding the electrocatalysis at the NP. [32] Herein, we will use a catalytically active electrode (Au UME) to suppress the catalytic response of the NPs and therefore to study their redox transformation (Scheme 1a). Alternatively, a catalytically inactive electrode (C UME) will allow probing both the transformation and the electrocatalytic activity of the NPs (Scheme 1b).

Results and Discussion

Firstly, the electrocatalytic properties of the electrode materials for the ORR were inspected and compared to that of Ag. Figure 1a shows the linear sweep voltammograms recorded at Au, Ag and C UMEs, in aerated electrolytic solutions. All UMEs show a reductive wave characteristic of the ORR, but with overpotentials increasing in the order Au < Ag < C. Since Ag has intermediate electrocatalytic activity compared to Au and C, it is pertinent investigating the reduction of AgBr NPs on both Au and Glassy carbon (GC) UMEs. Before apprehending the reductive behavior of AgBr NPs at the single level by NIE experiments, a large ensemble of NPs immobilized on an UME was studied. Figure 1b presents the cyclic voltammogram recorded at the Au UME modified with dropcasted AgBr NPs. On the forward reductive scan, a first cathodic peak at -0.32V (associated to a backward reoxidation at -0.20V) is assigned to the reduction of AgBr to Ag (equation 1). The backward reoxidation peak corresponds to the reoxidation of Ag to AgBr, owing to the 0.1M Br -containing electrolyte. This system is followed by the ORR reaction indicating that the AgBr to Ag conversion occurs at potentials ~ 0.3V more positive than the ORR and that both electrochemical reactions (AgBr to Ag conversion and ORR) can be decomposed when analysing the system at different electrode potentials. Then the AgBr NPs electrochemical behaviour is investigated at the single NP level by immersing Au or C UMEs in a freshly prepared colloidal suspension of AgBr NPs (protocol detailed in the experimental section) diluted 10 times.

The current transients recorded at the Au UME at various potentials ranging from -0.6 to -1.5 V vs FcMeOH are shown in Figure 2a. All transients display current spikes, such as the one presented in the inset of Figure 2b which was recorded at -0.9 V vs FcMeOH. Other examples provided in Figure S1 show the same behaviour. According to Figure 1b, within this potential range, those spikes can be confidently attributed to the reduction of AgBr to Ag (equation 1). One can also observe in Figure 2c and 2d an increase of the individual current spikes' amplitude when the UME potential becomes more negative, whereas the spikes' duration decreases. Similar effect reported previsouly while inceasing the overpotential of Ag NPs oxidation, [12] was attributed to the increase of the transformation kinetic of NPs with the overpotential. Applying more negative potentials is also accompanied by a continuous increase of the impact frequency until -1.4 V vs FcMeOH as shown in Figure S2. This could be due to electrochemically driven phoretic processes (favoured at increased electrochemical current, here more negative potentials), resulting in an apparent acceleration and preconcentration of the NPs in the vicinity of the electrode. [44] However, despite changes in characteristic amplitude and duration the total charge of the spikes remains statistically the same in the entire potential range, as shown in Figure 2e, attesting that the same NP population are probed at the different electrode potentials. Considering that the ORR is catalyzed preferentially on the electrocatalytically active Au surface, this likely means that this ORR reaction is prevented at the NPs' surface so that the current spikes observed solely correspond to the reduction of the AgBr NPs to Ag [17] according to equation 1. This is corroborated by the quasi-steady-state background current, ibg Au recorded during the NIE. As the potential applied at the Au UME decreases, ibg Au becomes more negative, following a sigmoidal evolution similar to that of the voltammogram of Figure 1a, with a similar apparent half-wave potential E 0 The current transients recorded at the C UME for the same range of potentials (-0.6 V to -1.5 V vs FcMeOH) are provided in Figure S3. As observed with the Au UME and illustrated in Figures S3 andS4, when the C UME potential becomes more negative the current spikes' amplitude and frequency increase, their duration decrease whereas the global charge remains the same. By analogy, these current spikes can be attributed to the conversion of the AgBr NPs into Ag NPs. However, looking carefully at all the transients of Figure S3, specific features can be observed within a range of EC UME from -0.6 V to -1.0 V vs FcMeOH. As exemplified in the transient of Figure 3b for a potential of -0.9 V, the 'conversion' current spikes (Figure 3c) are eventually followed by current steps (Figure 3d). The upside-down histogram of Figure 3a represents the probability to observe a current step right after a 'conversion' current spike at the C UME with a limit of detection of ~ 10 pA and for a number of analyzed current spikes N>20 for each potential. On one hand, the probability of observing such current step event after the conversion increases from -0.6 V and reaches a maximum of ~85% at -0.9 V. The Figure 3a (Black curve) also displays the evolution with potential of the background current, ibg C at the C UME extracted from Figure S3. It shows that within the range -0.6 V to -0.9 V the background ORR current recorded at the C UME remains very low. However, since Ag is able to catalyse the ORR within this range of potential (based on the voltammogram at the Ag UME, Figure 1a), the current steps are attributed to the electrocatalytic ORR into H2O or H2O2 (Equation 2 or 3, respectively) at the justelectrochemically converted Ag NPs. [27] Interestingly, the 'catalytic' steps probability increase when increasing the overpotential from -0.6 to -0.9 V, following the electrocatalytic activity of the Ag UME: the more negative the potential, the higher the ORR activity at the electrochemically generated Ag NPs. This observation is in line with those reported previously for the oxidation of Ag to Ag2O followed by the OER. [26] For E C UME <-0.9 V the abrupt decrease of the probability is associated to the increase of ibg recorded at the C UME (Figure 3a, black curve) that give an apparent half-wave potential for the ORR of E 0 app C UME ~ -0.95 V vs FcMeOH consistent with the voltammogram of Figure 1a. It ends up with the complete disappearance of the current steps at E C UME < -1.1 V (see for instance in Figure S4 at -1.2 V) a potential corresponding to the current plateau of the ORR at the C UME. At this potential value, the Ag NPs are electrogenerated at the UME in a region devoid of O2, preventing the observation (actually decreasing the extent) of ORR at the catalytic Ag NP. In this potential region, the individual current spikes observed on the chronoamperometric traces are similar to those observed on the Au UME (Figure S1). This suggests that when the ORR is taking place at the C UME, only the AgBr NP reductive conversion to Ag, Equation 1, is detected by the NIE, the C UME acting as a reactive electrode. [32] Since the NIE experiments performed using the Au UME were free of electrocatalytic behavior, they were further employed to investigate the potential dependence of the AgBr NPs' conversion process. A statistical analysis of all the current spikes was performed at each potential. The charge Qp of each spike associated to this conversion is used to estimate the size of the NP colliding the UME. The apparent electrochemical radius, rEC, of the AgBr NP is extracted from equation 4: (4) with M and ρ the molar mass and density of AgBr, respectively, F the Faraday constant. The values of the equivalent radius, rEC Au, for all Au UME potentials are plotted along its corresponding conversion duration, Δt, in Figure 4a. As previously reported for mixtures of AgX NPs (X=Br or Cl) [17] rEC Au varies linearly with Δt. Herein, this holds true for each UME potential (each color in Figure 4a) with an increase of the slope when the potential decreases. Examples of such linear relationships are detailed in Figure S5. This observation is associated with the shortening of the peak duration with decreasing the UME potential. As shown in Figure 2c, Δt decreases from 50-60 ms at -0.6 V down to <20 ms at -1.5 V. This suggests that the kinetics of AgBr reduction depends on its overpotential. This is consistent with previous observations reported for the reverse reaction i.e., the oxidation of Ag NPs to AgCl NPs. [25] Noteworthy, the linear variation of Δt with NP size questions a diffusion-limited transformation process which would predict a parabolic evolution, Δt = rEC 2 /DAg+. [17] Moreover, for a 100 nm diameter AgBr NP with DAg+ ~ 10 -11 cm 2 .s -1 (which is the diffusion coefficient of Ag + within solid AgBr [45] ), the diffusionlimited conversion process would take Δt ≈ 2.5 s. This duration is about two orders of magnitude higher than the ones observed in the present study. Additionally, a limitation by the diffusion of Br - can be ruled out since with a DBr-in AgBr one order of magnitude lower than in solution (DBr-~ 6x10 -7 cm 2 .s -1 ) [46] one would expect Δt in the order of the µs. Altogether, this suggests that for such large NPs, the AgBr conversion is not limited by the sole diffusion of ions in the ionic crystal matrix. It was previously shown that the NP transformation could be modeled as the formation of a new solid (metallic Ag) phase expanding at the expense of the AgBr phase. [17,47] The conversion is suggested to occur at the moving boundary between the Ag and the AgBr phases. The observations in the present study, introduce a new kinetic regime for such interfacial conversion equivalent to the hopping of an electron (eAg -) from reduced Agred sites to adjacent unreduced AgBr sites within the NP. [17,47] Herein, this is schematized by equation 5.

(5) The conversion dynamics is then characterized by both the diffusion of ions in the ionic solid phase and the hopping rate constant kex (in s -1 ) depicting equation 5. A COMSOL model of this situation, previously presented, [17,47] confirmed the linear relationship between the conversion duration, Δt, and the NP radius, rEC and Δt following the analytical expression given by equation 6.

(

) 6
with rEC expressed in nm, DAg+ in cm 2 .s -1 , kex in s -1 and Δt in s.

The evolution of kex with the UME potential, (Figure 4b) shows that kex increases with the potential up to a limit kex,max ~ 6x10 4 s - 1 at E C UME = -1.3 V vs FcMeOH. This value is one order of magnitude lower than the highest interatomic exchange diffusion limit kex,lim ~ 6x10 5 s -1 determined from the Smoluchovsky theory (Equation 7): (7) with NA the Avogadro number and a = 3.5 Å, the interatomic distance in the AgBr crystal. It is noteworthy that if one assumes that the maximum value estimated experimentally corresponds to the Schmoluchovsky diffusion limit (Equation 7), then equating the expression of kex,lim with that for the evaluation of kex,max, respectively from Equations 6 and 7, yields a diffusion of ions in the AgBr crystal of the order of DAg+ ~3.10 -12 cm².s -1 . This value is in reasonable agreement with the literature one. It further highlights that the high temporal resolution of NIE allows inspecting diffusion-limited hopping mechanism in solid NPs.

Finally, the electrocatalytic activity for the ORR at the reduced AgBr NPs was quantitatively investigated using the C UME. A series of spikes followed by a current step recorded at -0.9 V vs FcMeOH at a GC UME extracted from Figure 3b and others were analyzed. The transients recorded at this specific potential present the highest probability to observe an electrocatalytic current step after a current spike (Figure 3a). Each current step, istep was then related to the charge of the preceding current spike Qp, as illustrated in Figure 3c and 3d, respectively. The current spikes often occur through multiple spike events as shown in Figure 3d, within a < 50 ms range. Such behavior is characteristic of a reduction proceeding through multiple NPelectrode contact events as observed for other Ag-based NPs. [13][14][15][16][17][18][19] In a first approach, the multiple current spikes were considered as a unique transformation process, from which the NP radius rEC C was evaluated using Equation 4, and the current step considered as the electrocatalytic activity for the ORR. This approximation is further supported by the fact that the spike charges are statistically similar to those observed when the electrocatalytic activity of the NPs is hindered i.e., (1) on the catalytically active Au UME whatever its polarization, or (2) at the C UME for EC UME <-1.1 V vs FcMeOH (Figure S3). Figure 4c shows the plot of istep versus rEC for a statistically representative number of events. Assuming that the ORR activity of the NPs is limited by the mass transfer of O2, the current step should be directly proportional to the electrochemical radius, rEC following equation 8: [38,39,48] where n=3.3 is the number of electrons exchanged for the ORR at Ag, [43] F is the Faradaic constant, DO2 ~ 2x10 -5 cm 2 .s -1 is the diffusion coefficient for O2 in water, Δ[O2] = [O2] ∞ -[O2]NP is the concentration difference between the bulk solution and the NP surface, which is at maximum ~0.25 mM in air-saturated aqueous solution.

On the other hand, a kinetic limitation from the ORR, with a rate constant kORR, at the NP surface would be described by a quadratic Butler-Volmer expression:

Combined with the mass transfer arrival of O2 at the NP, from Equation 8, one would expect the ORR electrocatalysis current follows Equation 10: (10) This equation should allow analyzing the ORR kinetic at the single NP and apprehend kinetic vs mass transfer competition with NP size.

Along with the scatter plot in Figure 4d are provided the maximal mass-transfer limited linear trend (Equation 8) and two kinetically-limited trends evaluated, using Equation 10, for kORR = 0.3 and 1 cm s -1 respectively. Noteworthy, the upper-limit mass-transfer regime was evaluated considering that ~ 20% of O2 is consumed by the C UME (extracted from ibg c at -0.9 V vs FcMeOH in Figure 3a). It means that the NP would probe at best an apparent bulk concentration Δ[O2] = ∞ = 0.2 mM. Despite the scatter in the data which might be explained by the disparity of the NPs catalytic efficiency the current steps are within the predicted mass-transfer and kinetic currents. It suggests that the ORR kinetic at the Ag NPs is higher than 0.3 cm s -1 . The scatter in the data could further suggest a size effect on the ORR kinetics with increasing activity when the NP size decreases.

Conclusion

The nanoimpact electrochemistry (NIE) approach was implemented to shed light on the reduction of AgBr NPs to Ag on gold and carbon ultramicroelectrodes. On both electrodes, typical current spikes of AgBr NPs reduction to Ag NP were observed, whereas specifically on the C UME for a potential window between -0.6 V to -1.0 V, the AgBr NPs transformation was accompanied by current steps. The latter, attributed to the electrocatalytic ORR at individual electrogenerated Ag NPs, exhibit the highest probability of occurrence at -0.9 V. Conversely, when the ORR takes place at the surface of the catalytically active Au UME, a gradient of the molecular reactant's concentration is imposed in the vicinity of the UME, hindering the catalytic reaction at the Ag NPs. Hence, for NPs less active than the UME itself (here Ag < Au), electrocatalysis of the ORR at the NP cannot be detected whatever the potential applied at the UME. By hindering the ORR at the NP, the dynamics of the reductive conversion of AgBr NPs to Ag was analyzed. The reduction is characterized by a hopping mechanism, associated to an advancing Ag/AgBr boundary within the NP during its conversion. The hopping electron transfer rate constant within the AgBr NPs increases with a more cathodic potential until it reaches a limit at -1.2 V, suggesting a further limitation of the reduction process. In addition, by employing a C UME, the ORR activity extracted from the current steps was compared to the NPs' size defined from the corresponding current spikes. The trends observed suggest ORR in a mixed control by mass transfer and ORR activity with a lower-bound electrocatalysis rate of 0.3cm s -1 .. This double NIE approach opens the way towards the determination of sizeactivity relationships that was recently reported as a possible explanation for heterogeneous electrocatalytic activities of Pd NPs during NIE experiments. [29] Experimental Section

AgBr NPs synthesis

Analytical grade chemicals were obtained from Sigma-Aldrich and were used without further purification. Solutions were prepared with ultrapure water with a resistivity higher than 18.2 MΩ.cm. AgBr NPs were synthesized according to a previously described procedure [17,47] with minor changes. 1 mL of KBr solution (0.5 M) was mixed with 98 mL of cetyltrimethylammonium bromide solution (2 mM). Then, 1 mL of AgNO3 solution (0.5 M) was added dropwise and under constant stirring to form a 100 mL stock solution. The mixture was further stirred at room temperature for 3 h and became cloudy and white. The colloidal solution was stored under light protection at 4 °C until use in NIE. The AgBr NPs were analysed by SEM-EDX (Figure S6) using a Gemini 360 SEM from Zeiss coupled to an energy-dispersive X-ray detector from Oxford Instruments. The acceleration voltage was equal to 8 kV. For EDX analysis, the microscope aperture size was expanded from 30 to 60 µm. EDX data were processed using the Aztec software. The size distribution of the NPs determined from the SEM images is in fairly good agreement with the one extracted from the NIE experiments performed at the C UME (Figure S6).

UME preparation

Homemade UMEs were designed using borosilicate glass capillaries (Sutter instruments, Novato, California) with outer and inner diameters of 1.0 and 0.5 mm, respectively. 25 µm diameter gold wires or 7µm carbon fiber (99.99%, Goodfellow, Cambridge Ltd, Huntingdon, England) were inserted into the capillaries and sealed with a laser pipette puller (Sutter Instruments, Model PC-10, London, UK). The UMEs were then polished with aluminum oxide tape (3 µm from Precision Surfaces International, Houston, Texas, USA).

NIE experiments

The stochastic EC collisions of NPs were recorded in a 2-electrode system using either the C or the Au UME as the working electrode and a Pt wire as both counter and pseudo-reference electrode. Current transients were recorded at 10 kHz bandwidth with a low noise current amplifier (Element eONE) and the 10 times diluted solution of AgBr NPs freshly synthesized. Noteworthy, the NIE experiments with the Au UME were performed with another batch of slightly larger AgBr NPs synthesized using the same procedure described above. To ensure a reliable comparison between the C and Au UME, all the potential values were referenced versus FcMeOH internal reference by adding into the solution 1mM FcMeOH from Sigma-Aldrich after the NIE experiments (Figure S7).

Scheme 1 .

 1 Scheme 1. NIE mechanism occurring at a) the Au UME and b) the C UME.

Figure 1 .

 1 Figure 1. a) Normalized linear sweep voltammograms on gold (yellow trace), silver (grey line), and carbon (black line) UMEs. b) Cyclic voltammogram of Au UME modified with dropcasted AgBr NPs. All measurements are recorded vs FcMeOH in air saturated aqueous solutions of 0.1 M KBr at 50 mV/s.

  app Au UME ~ -0.75 V vs FcMeOH as shown in Figure 3a. The evolution of ibg Au with the Au UME potential therefore corresponds to the extent of the ORR occurring at the Au UME during the NIE experiments.

Figure 2 .

 2 Figure 2. a) Transients of NIE experiments in a colloidal suspension of AgBr NPs occurring on gold UME in air saturated aqueous mixtures containing 0.1 M KCl, recorded from -0.6 V to -1.5 V vs FcMeOH, every 100 mV and b) zoom of the chronoamperogram recorded at -0.9 V vs FcMeOH. Evolution of the c) duration, d) amplitude and e) charge, Qp, (peak area) for the current spikes extracted from Figure 2a.

Figure 3 .

 3 Figure 3. a) background currents, ibg, recorded at various potential (from -0.6 V to -1.5 V vs FcMeOH) on a 25 µm Au UME (yellow) and a 7 µm GC UME (black) immersed in a solution of AgBr NPs diluted 10 times and histogram showing .the probability to observe current steps after the current spikes at each potential b) Transient recorded at -0.9 V vs FcMeOH at a GC UME in a solution of AgBr NPs diluted 10 times and c) zoom of a single AgBr NP reduction spike and d) its corresponding current step characteristic of the ORR at reduced AgBr to Ag NPs.

Figure 4 . 1 (

 41 Figure 4. a) Electrochemical radius of the NPs, extracted from Qp, plotted versus their duration, with best linear trendline for each potential from which b) hoping rate constant, kex, extracted for each Au UME potential (details in text). c) current steps plotted versus their corresponding electrochemical NP radius (rEC) extracted from transients of Figure3band others recorded at -0.9V at the C UME with the trendlines for the upper-limit mass-transfer regime (blue) and for kinetic limitation from the ORR with kORR = 0.3 cm.s -1 (red) and 1 cm.s -1

Acknowledgements ((optional))

We thank CNRS, the ANR JCJC program (PIRaNa project, ANR-20-CE42-0001) and the Emergence call from the Université de Paris within the Investissement d'Avenir program under reference ANR-18-IDEX-0001 for financial support. We also thank the Ile-de-France region and IDEX for financial support of the AFM-Beam-Rex platform Keywords: Nanoimpact electrochemistry • Single Nanoparticle • electrocatalysis • Size-activity relationship • oxygen reduction reaction


T Chevolleau
email: thierry.chevolleau@cea.fr

N Posseme

T David

R Bouyssou

et al.. Etching Process Scalability J Ducote

F Bailly

Maxime Darnon

M El Kodadi

M Besacier

C Licitra

M El Kodadi

M Guillermet

A Ostrovsky

C Verove

O Joubert

Etching Process Scalability and Challenges for ULK Materials

Introduction

For the next technological generations of integrated circuits (32 nm and below), the integration of copper/porous low-k in interconnects is one of the key point for device performance, process manufacturability and future scalability. For the interconnection fabrication, dual-damascene patterning is performed by etching trenches and vias into porous SiOCH dielectrics (p-SiOCH). Controlling the profiles of the etched structures and minimizing plasma-induced damages of the p-SiOCH materials are the two main concerns. For the patterning of p-SiOCH, two hard mask strategies (metallic and organic masks) have been developed and implemented over the last decade [1]. These two masking strategies have both advantages and drawbacks in patterning of dual damascene structures. For monitoring the p-SiOCH modifications, many studies have been performed to characterize the modification on blanket wafers which mimic the modification of the bottom of the trenches in dual damascene structures [2]. Few studies have been performed on patterned structures to determine the sidewall modifications while this information is critical and more relevant.

In this work, we address the main patterning issues associated with both masking strategies in terms of profile control. We will also focus on the sidewall modifications induced by the plasma processes using new or optimized characterizations such as scatterometric porosimetry (SP), infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS).

Experimental

Patterning of single damascene structures (trenches) is performed in a capacitive plasma reactor (CCP) and an inductively coupled plasma reactor (ICP). In this work, the titanium nitride (TiN) hard mask is deposited by physical vapour deposition (PVD) while the organic mask is a spin coated carbon based mask. The dielectric stack is as follows (figure 1): a SiCN layer, a porous SiOCH film (k < 2.5, porosity < 30 %) and a SiO 2 capping layer. The two types of mask are deposited on the dielectric stack. For the TiN mask, a bottom antireflective coating is spin coated on the TiN layer prior the 193 nm lithography (figure 1). For the organic mask, a silicon containing layer (Si-ARC) is spin coated on the organic hard mask prior 193 nm lithography. This layer is used as a bottom antireflective coating and also to transfer the photoresist patterns into the organic mask. After patterning the damascene structures, the sidewall modifications have been characterized by SP, FTIR and XPS [3]. FTIR can determine the loss of methyl from the porous SiOCH sidewalls while XPS gives the composition of the sidewall surface (within 10 nm probing). The scatterometric porosimetry (SP) is a new technique which has been designed specifically for monitoring the porous SiOCH sidewall damages. This technique is a combination of scatterometry and ellipsometric porosimetry. A SP measurement with water as solvent can provide the thickness of the hydrophilic damaged layer on the sidewalls while a measurement with methanol as solvent determines the porosity of the dielectric lines and the permeation of the surface of the sidewalls.

Results and discussion

Etching process scalability versus masking strategies

The etching process scalability of both masking strategies has been compared with single damascene structures (M1 level).

The organic masking strategy

The Si-ARC material is etched using fluorocarbon based plasmas and the Si-ARC patterns are transferred into the organic mask with reducing based plasmas (NH 3 or N 2 /H 2 ). Straight profiles can be obtained in the organic mask. After the organic mask opening, the SiO 2 , porous SiOCH and SiCN layers are etched in fluorocarbon based plasmas. Straight profiles with a slight bow can be achieved (figure 2). It is worth mentioning that all the etching steps are performed in the CCP reactor. However profile distortions are observed for trench dimensions lower than 30 nm as shown in figure 2. The profile distortions are mainly attributed to pattern flop over of the organic mask or dielectric during the etching of the dielectric layers. One of the possible ways to avoid pattern flop over, is to both improve the mechanical properties of the mask and the porous dielectric materials [4]. Other studies have proposed to use UV cure after organic layer openings or optimized p-SiOCH etch chemistries [4,5]. In addition, the organic masking strategy involves a stripping step using either oxidizing chemistries or reducing chemistries to remove the remaining organic mask after dielectric patterning. Such strip processes generate sidewall damages of porous SiOCH trenches. However, patterning of sub-50 nm p-SiOCH trenches can lead to severe profile distortions attributed to the undulations of the dielectric lines (figure 3). This phenomenon, so called wiggling, is explained by the compressive residual stress into the TiN mask (>2 GPa) and the low elastic properties of the porous dielectrics (young modulus < 7 Gpa). Experiments and mechanical simulations show that undulations originate from buckling of the porous dielectric lines which allows the release of the strain energy initially stored in the TiN layer. Based on these simulations, the use of a low residual stress TiN (< 1GPa) will allow achieving trench dimensions down to 30 nm. With the TiN masking strategy, the formation of post etch residues has been evidenced after patterning of porous SiOCH (figure 4). The presence of Ti based residues prevents a conformal copper deposition inducing via and line opens and consequently yields loss (figure 4). The growth of such residues (metallic salt) is air exposure time dependent and results from complex chemical reactions between the fluorocarbon covered TiN surfaces and air moisture [START_REF] Posseme | Proceeding of IITC[END_REF]. One of the solutions to prevent the residue formation is the implementation of post etching plasma treatments (PET) using reducing chemistries (figure 4). With H 2 and NH 3 based plasma treatments, the residue formation is limited by partially removing fluorine species on the TiN mask. With the CH 4 based plasma treatment, the residue formation is stopped by the presence of a thin carbon passivation layer on the top of the TiN mask which probably prevents the complex mechanisms of reaction between fluorine species and air moisture. Using either the organic mask or the metallic mask, trenches dimension down to 50 nm can be achieved. However profile distortions are expected for sub-50 nm trenches mainly due to mechanical limitations in both cases. For the TiN masking strategy, the development of a layer with a low residual compressive stress is required while it is necessary to improve the mechanical properties of the mask and the porous dielectric for the organic masking strategy. Other emerging issues are the line edge roughness of the porous SiOCH structures which may affect the electrical performances and the reliability of the interconnections [START_REF] Soda | [END_REF].

Plasma induced porous SiOCH sidewall modification

Porous SiOCH materials are very sensitive to fluorocarbon etching plasmas, stripping plasmas and post etching plasma treatments. After etching (POR) and the different post etching plasma treatments (NH 3 , CH 4 , H 2 , and O 2 ), the thickness of the hydrophilic layer formed on the porous SiOCH sidewalls has been estimated thanks to the decoration technique (HF dip) and SP measurements with water (figure 5). First, we observe that the thickness measurements are similar with both techniques. Second, the hydrophilic layer thickness is higher after the O 2 or NH 3 plasmas (20 nm thick) than after etching (10 nm thick) while the thickness of the hydrophilic layer is lower after the CH 4 or H 2 plasmas (below 5 nm thick). This lower thickness can be explained either by a lateral etching of the hydrophilic layer or by creation of a more hydrophobic damaged layer. The adsorption kinetics of methanol into the patterned structures have been determined by SP. Figure 6 shows that the porosity of the porous dielectric lines remains the same as the pristine material after exposure to any plasmas investigated in this study. However the surface permeation is slightly lower after etching than after the different plasma treatments. XPS analyses (figure 7) indicate the presence of a fluorocarbon layer on the porous SiOCH sidewalls after etching. This layer is partially removed after the different plasma treatments. Therefore the difference in terms of kinetic of methanol adsorption between the etching and the plasma treatments can be mainly explained by the fluorocarbon layer on the porous SiOCH sidewalls which tends to slow down the methanol adsorption. Based on these results, the damages of the porous SiOCH sidewalls are unavoidable after plasma exposure. Indeed a hydrophilic layer is present on the porous SiOCH sidewalls which affects the RC value and reliability of the interconnections. One of the emerging solutions is to restore the hydrophobic properties of the modified layer using, for instance, silylation based processes [8].

Conclusion

The etching scalability of porous SiOCH patterning is not related to conventional profile issues such as tapered or bowed profiles. The scaling down to 50 nm can lead to severe profile distortion due to mechanical constraints (wiggling phenomenon with metallic mask and pattern flop over with organic mask). In the damascene structure fabrication, the plasma process induces damages of the porous SiOCH sidewalls. Therefore the characterization of sidewall damages is mandatory in order to explore new solutions to minimize or restore the modified hydrophilic layers.

Figure 1 :

 1 Figure 1: stacks with (a) the metallic masking strategy and (b) the organic masking strategy

  (a) Trench profiles (pitch 70/70 nm) with the organic mask and (b) patterns flop over of the organic mask for narrow dielectric lines (< 30 nm) The metallic hard mask strategy After the BARC opening step, the photoresist patterns are transferred into the TiN mask using a Cl 2 based chemistry. The remaining photoresist is removed using an O 2 plasma. All the etching steps are performed in the ICP reactor. After the TiN opening steps, the SiO 2 , porous SiOCH and SiCN are etched using fluorocarbon based plasmas in the CCP reactor. Straight profiles with a slight bow are obtained (figure3).

Figure 3 :

 3 Figure 3: (a) Trench profiles (pitch 70/70 nm) with (a) the metallic mask and (b) wiggling phenomenon of dielectric lines (< 50 nm)

Figure 4 :

 4 Figure 4: Effect of the different post etching plasma treatments on the line and via yields. Top SEM CD view after etching (POR) and after etching and the different post etching plasmas

Figure 5 :

 5 Figure 5: Thickness of the hydrophilic layer of the porous SiOCH sidewalls after etching and different post etching plasmas (estimation of the thickness by SP measurements in blue and with the SEM using the decoration technique in green)

Figure 6 :

 6 Figure 6: Kinetic of methanol adsorption after etching (POR) and different post etching plasma treatments (PET).

Figure 7 :

 7 Figure 7: Surface composition of porous SiOCH sidewalls after etching (POR) and different post etching plasma treatments.


A Khogeer
email: akhogeer@chu-grenoble.fr

C Thuillier

J.-L Descotes

J.-J Rambeaud

J.-A Long

G Fiard

stress urinary incontinence after surgical cystocele repair by mesh implantation using a vaginal approach Évolution des patientes avec ou sans incontinence urinaire à l'effort préopératoire après une cure chirurgicale de cystocèle par voie vaginale avec une implantation prothétique

Introduction

Pelvic organ prolapse (POP) and urinary incontinence (UI) are two common complaints in women and up to 20% of females may undergo surgery for either condition by the age of 85years [START_REF] Olsen | Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence[END_REF][START_REF] Boyles | Procedures for pelvic organ prolapse in the United States, 1979-1997[END_REF]. POP and UI may occur together in up to 80% of women with pelvic floor dysfunction [START_REF] Bai | Relationship between stress urinary incontinence and pelvic organ prolapse[END_REF][START_REF] Maher | Surgical management of pelvic organ prolapse in women: the updates summary version Cochrane review[END_REF]. In 40-50% of women with POP, stress urinary incontinence (SUI) may occur preoperatively due to related pathophysiological mechanisms [START_REF] Dietz | Bladder neck mobility is a heritable trait[END_REF][START_REF] Chen | Elastolytic activity in women with stress urinary incontinence and pelvic organ prolapse[END_REF]. However there is no direct link between POP and SUI and their frequent association is complex with many unknown factors. The two conditions are reported to share some risk factors including age, obesity and injury during labour [START_REF] Bump | Epidemiology and natural history of pelvic floor dysfunction[END_REF]. De novo SUI is defined as SUI that only occurs after the reduction of a coexisting prolapse [START_REF] Haylen | An International Uro gynecological Association (IUGA) / International Continence Society (ICS) joint report on the terminology for female pelvic organ prolapse (POP)[END_REF]. This type of SUI is hidden and does not become apparent until the prolapse is reduced either in the clinic or after surgical repair. It is considered to be one of the causes of distress after POP repair and in non-informed patients it can be perceived as a surgical complication.

The aetiology of de novo SUI is not fully understood and it has been suggested that it is caused by mechanical pressure created by the prolapse beneath the urethra [START_REF] Long | Urodynamic comparison of continent and incontinent women with severe uterovaginal prolapse[END_REF][START_REF] Myers | The effect of posterior wall support defects on urodynamic indices in stress urinary incontinence[END_REF]. This effect may disappear when the prolapse is treated, hence de novo SUI. The reported incidence of de novo SUI varies between 2% and 43% and the risk increases in patients with previous occult SUI [START_REF] Lo | Predictors for de novo stress urinary incontinence following extensive pelvic reconstructive surgery[END_REF][START_REF] Kleeman | The ability of history and a negative cough stress test to detect occult stress incontinence in patients undergoing surgical repair of advanced pelvic organ prolapse[END_REF][START_REF] Alas | De novo stress urinary incontinence after pelvic organ prolapse surgery in women without occult incontinence[END_REF][START_REF] Lensen | Urinary incontinence after surgery for pelvic organ prolapse[END_REF]. Few data have focussed on de novo SUI in women without preoperative occult SUI and most studies only report the postoperative evolution of pre-existing SUI. It has been shown that preoperative SUI can be cured by POP surgery in 27% of cases [START_REF] Borstad | Surgical strategies for women with pelvic organ prolapse and urinary stress incontinence[END_REF].

Because there is no identifiable relationship between SUI and POP, the treatment strategies for the two conditions are distinct. The surgical approach can be transvaginal, laparoscopic, or open. Non-surgical management can initially be proposed as an option.

However, many patients look for definitive treatment in order to resolve their POP symptoms.

The choice of procedure depends on the surgeon's training and experience, resulting in significant practice variations.

For two decades, the use of synthetic nonabsorbable mesh has reduced the risk of prolapse recurrence in comparison with native tissue repair [START_REF] Mettu | Evidence-based outcomes for mesh-based surgery for pelvic organ prolapse[END_REF]. The second generation Uphold LITE system (Boston Scientific, MA, USA) is a prefabricated mesh kit that decreases biomaterial load in order to avoid mesh-related complications and to provide an enhanced facility for apical suspension [START_REF] Altman | Pelvic organ prolapse repair using the Uphold Vaginal Support System: a 1-year multicenter study[END_REF]. Following recent alerts regarding transvaginal mesh repair, this technique has currently been suspended in all centres.

The primary aim of this descriptive study was to evaluate SUI in the perioperative period of mesh repair surgery in patients with and without previous SUI, including the rate of later interventions for SUI. The role of physiotherapy in cases of persistent or de novo SUI was also evaluated. This report shares our experience and determines the short-term outcomes of POP repair using the Uphold LITE system.

Material and methods

Study design and patients

This retrospective, descriptive study included all women with symptomatic prolapse who underwent cystocele repair with the Uphold LITE system in our department between July 2016 and April 2019. All women were operated on by a single surgeon. A total of 36 patients were identified as a retrospective cohort representing actual clinical data.

All patients complaining of a symptomatic per vaginal mass were examined in the outpatient clinic to confirm the diagnosis of cystocele. Clinical assessment of the prolapse was done using the Baden-Walker half way scoring system which consists of four grades: grade 0 (no prolapse), grade 1 (halfway to hymen), grade 2 (reaching to hymen), grade 3 (halfway past hymen), grade 4 (maximum descent) [START_REF] Baden | The vaginal profile[END_REF]. The study included all patients with symptomatic anterior wall prolapse. Clinical evaluation of SUI was performed using the cough stress test (CST) before and after manual reduction of the prolapse to detect occult SUI.

The CST was performed in the clinic with the patient in various positions (standing, semi-supine or lithotomy) with the urinary bladder in semi-repletion (patients were asked to fill their bladder before the consultation). The patient was then asked to cough many times and the urethra was observed for synchronous urinary leakage. The urodynamic study was not performed systematically as a routine examination in either the pre-or post-operative period but was reserved for cases with complicated UI (mixed or severe UI, post-SUI surgery, etc.).

All selected patients gave their informed consent for only prolapse surgery without any concomitant intervention(s) (e.g. hysterectomy, rectocele repair, etc.) and without associated incontinence repair, even if present preoperatively. All patients were informed orally and were able to refuse participation in this study.

Surgical procedure

All surgical procedures were performed under general anaesthesia. Prophylactic intravenous antibiotics were administered prior to surgery (2 g amoxicillin/clavulanic acid). The vaginal approach prolapse repair was performed by insertion of an Uphold LITE vaginal support system with a Capio Device (Boston Scientific, MA, USA) as described by Letouzey et al. [START_REF] Letouzey | Utero-vaginal suspension using bilateral vaginal anterior sacrospinous fixation with mesh: intermediate results of a cohort study[END_REF]. Two to three simple interrupted sutures (Prolene ® 3.0) were inserted at the distal portion of the mesh and vaginal mucosa below the neck of bladder to stabilize the mesh for better support. Four to six simple interrupted sutures (Monosyn ® 3.0) were inserted at the right and left paravaginal fascia and urethrovesical junction. Vaginal packing was continued for 24 h post-surgery and patients received 1 day of urethral catheterization. Post-void residual (PVR) volume was checked routinely after removal of the catheter using a bladder scan (Verathon Inc., Bothell, WA, USA).

Data collection

Preoperative data including medical history and physical examination results were recorded.

Demographic data including: age, number of births, history of previous prolapse, incontinence repairs and comorbidities (diabetes, obesity, cardiovascular disease or anticoagulants) were collected. Data were collected preoperatively, peri-and postoperatively before discharge and at outpatient visits 1 month, 3 months and 12 months post-surgery. All perioperative data were recorded: type of intervention and approach, coding system (French CCAM), associated surgery for SUI, type of anaesthesia given, type of mesh used, operative time, adverse events, complications, catheterization and hospital duration including all late discharges. The database was checked to eliminate duplicates or missing data.

Postoperative follow-up

Postoperative clinical follow-up was performed by the same surgeon for all patients except for those who were followed by their primary urologist in other centres (the follow-up reports for these patients were transmitted to our centre). Physical examination of the surgical site was done at each follow-up consultation. The evolution of preoperative SUI and persistence of SUI after prolapse repair were assessed, including an evaluation of the incidence of de novo SUI in patients without preoperative SUI. An interval of 3 months post-surgery was allowed before confirming de novo SUI. The presence of either persistent or de novo postoperative SUI was assessed objectively using the CST.

All patients with either persistent or de novo SUI following POP repair underwent physiotherapy sessions with a review of their efficacy and orientation to surgical SUI treatment using a mid-urethral sling (MUS), either with tension-free vaginal tape (TVT) or transobturator tape (TOT) in cases of physiotherapy failure. The Marshall test, which consists of placing the index and second finger on either side of bladder neck to support the proximal urethra with a relatively full bladder, was used to determine whether the urine loss was caused by urethral hypermobility. The indication for MUS insertion was dependent on persistence of SUI after physiotherapy and a positive Marshal test associated with a positive CST.

Outcome criteria

The primary outcome measure was SUI pre-, peri-and post-POP surgery in patients with and without previous SUI, including the rate of later interventions for SUI. The secondary aim was to evaluate our experience and determine the short-term outcomes of POP repair using the Uphold LITE system.

Statistical analysis

The incidence of de novo SUI was calculated as the number of patients with de novo SUI over the total number of patients without preoperative occult SUI and the incidence of persistent SUI was calculated as the number of patients with persistent SUI over the number of patients with previously documented SUI.

Excel (Microsoft office 2019) and JMP software were used for the statistical analyses of descriptive and clinical data.

Results

Thirty-six patients were included. The demographic data for these patients are shown in Table 1. Mean operative time was 41 ± 12 min, intraoperative blood loss was negligible, mean duration of hospitalization was 1 day, duration of urinary catheterization was 1 day (surgeon's preference) and mean PVR was 76 ± 107 ml. Three bladder injuries occurred during surgery (8.3%), all managed with 1 week of catheterization. There was no incidence of other organ injury. There were two cases of acute postoperative urinary retention (5.5%), which is defined as the inability to completely or partially empty the bladder. All patients were able to urinate successfully after reinsertion of the catheter and 2 days after removal of the catheter, as confirmed by a bladder scan (Table 2).

Out of the 36 patients, 12 (33.3%) women were diagnosed with preoperative SUI using the CST; SUI was either obvious or unmasked after manual cystocele reduction. After only POP repair, SUI resolved in six of these women (50%) and persisted in six (50%); these were confirmed with the CST. Physiotherapy sessions were proposed for all patients with persistent SUI with reported improvement in three patients (50%) without further relapse or subsequent incontinence surgery at time of this report. All patients confirmed their actual physiotherapy participation with a mean number of five physiotherapy sessions. Failure of physiotherapy was affirmed in the other three cases (50%) who were later treated by MUS surgery, either with TVT or TOT depending on the surgeon's preference.

Of the 24 women (66.6%) without previous SUI, six (25%) reported the presence of de novo postoperative SUI at the 3 month follow-up visit; these were all confirmed with a CST. One of these cases (16.6%) was treated successfully by physiotherapy without any later complaints and a MUS was inserted for the other five patients (83.3%) (Fig. 1). The risk of having persistent postoperative SUI in patients with preoperative SUI was 50%. Conversely, the risk of developing de novo postoperative SUI in patients without pre-existing SUI was 25%. Patients with preoperative SUI were therefore twice as likely to have persistent SUI postoperatively as patients without preoperative SUI (RR=2.0 [95% CI: 0.8175-4.8928]; p=0.128).

Eight of our 36 patients (22.2%) underwent MUS insertion post POP repair, either with TVT or TOT. Five (62.5%) of these slings were inserted in patients with de novo SUI and three (37.5%) in patients with persistent preoperative SUI. No SUI recurrence was reported or found clinically after 1 year of follow-up post-MUS insertion.

Regarding physiotherapy, the risk of failure of physiotherapy was 50% in patients with persistent SUI and 83.3% in patients with de novo SUI. All patients presenting with postoperative SUI were followed for 1 year with no patient lost to follow-up. At the time of this report, there were no reported cases of mesh exposure or infection and no case of mesh removal or redo. Two patients underwent subsequent surgery for POP relapse (5.5%) by laparoscopic sacro-suspension (Table 3).

Discussion

The close relationship between POP and UI requires optimal preoperative assessment to predict the probability of developing de novo postoperative SUI or persistent SUI after prolapse repair. Discussion with the patient explaining all possible postoperative outcomes can be helpful and beneficial to select the most appropriate management strategy. This information will play an important role in assuring patients, in order to avoid miss perception of these symptoms as a surgical complication. Assessment should include a full clinical examination with a CST before and after bedside manual prolapse reduction, including an evaluation of the severity of incontinence if present and, preferably, done by the patient. The aim of a CST is to recreate the patient's UI to establish the diagnosis of SUI and to assess the results of SUI treatment. The International Continence Society's (ICS) definition of SUI does not include the CST and this test is generally associated with a lack of standardisation.

Therefore, the ICS uniform-CST recommendations indicate the main elements to meet with this test (bladder volume, number of coughs and leakage detection) and for its interpretation [START_REF] Guralnick | ICS Educational Module: Cough stress test in the evaluation of female urinary incontinence: Introducing the ICS-Uniform Cough Stress Test[END_REF]. The American Urological Association recommends a preoperative urodynamic assessment with reduced prolapse in women with stage ≥II cystocele to evaluate occult SUI [START_REF] Winters | Urodynamic studies in adults: AUA/SUFU guideline[END_REF]. Watchful waiting with possible postoperative physiotherapy can be offered to patients with preoperative SUI; the delay and number of physiotherapy sessions should be defined as should the delay required to confirm physiotherapy failure. Postoperative visits can also easily detect the occurrence of de novo SUI and these patients can be directly offered a MUS or, alternatively, a trial of physiotherapy depending on the severity of incontinence and the patient's wishes. The delay to the diagnosis of de novo SUI should also be defined and standardized. The choice of suitable post-POP SUI repair is individualized for each patient depending on the surgeon's experience and preference. In our centre, we offer MUS for all cases of post POP SUI after failure of physiotherapy in fit and willing patients either with TOT or TVT slings. The insertion of a MUS depends on a positive CST associated with a positive Marshall test. No incontinence relapse has been reported in any of our patients at the follow-up visits at the time of writing.

Controversy exists on the advantages of primary prevention using a combined repair approach with anti-incontinence procedures at the primary POP repair. This combined repair may reduce the risk of postoperative SUI in patients with preoperative occult SUI [START_REF] Groutz | Tension-free vaginal tape (TVT) for the treatment of occult stress urinary incontinence in women undergoing prolapse repair: a prospective study of 100 consecutive cases[END_REF] and reduce de novo SUI by about 15% [START_REF] Haessler | Reevaluating occult incontinence[END_REF]. However, combined repair is associated with an increased risk of complications whereas POP repair alone is sufficient to resolve about 27% of patients with SUI [START_REF] Wei | A midurethral sling to reduce incontinence after vaginal prolapse repair[END_REF]. Furthermore, this combined repair can increase short-term voiding difficulties and adverse events [START_REF] Van Der Ploeg | Prolapse surgery with or without stress incontinence surgery for pelvic organ prolapse: a systematic review and meta-analysis of randomised trials[END_REF], although fewer cases report persistent SUI after this combination according to the 2013 Cochrane review. Some recent studies have offered combined treatment for patients with high-risk predictors of SUI with continence rates of 95% with no lower urinary tract symptoms or complication differences compared to prolapse repair only [START_REF] Lo | Prophylactic midurethral sling insertion during transvaginal pelvic reconstructive surgery for advanced prolapse patients with high-risk predictors of postoperative de novo stress urinary incontinence[END_REF]. However, the risks and benefits of this combination are unclear especially in patients who were previously continent. In particular, there are ethical concerns regarding increased morbidity compared to the morbidity associated with the problem requiring correction. The management protocol for this group of patients with high-risk predictive factors for de novo SUI remains unclear at present and therefore a shared decision-making process between the clinician and patient must occur. Surgical treatment of symptomatic prolapse is the gold standard and the abdominal approach is proposed for sexually and physically active patients. The vaginal approach is reserved for older patients with comorbidities and when the abdominal approach is not feasible (i.e. multi-operated abdomen). This technique using the vaginal approach allows easier access to prolapsed organs, a shorter operative time with faster recovery and better cosmetic results (i.e. no obvious scar). Our experiences with this technique found satisfactory results in terms of primary prolapse repair and in the early or delayed complication rate reflected by patients' satisfaction. All of our patients were operated on by a surgeon experienced in prolapse repair either via the abdominal or vaginal approach. Nonetheless, as widely known, these types of surgery require a long learning curve.

Application of a mesh is associated with a number of complications including a risk of exposure and infection. In 2011, the US Food and Drug Administration alerted patients and health professionals to the complications of transvaginal placement of these meshes. A review of the surgical treatment of POP by the Cochrane Library concluded that there was insufficient evidence for superior success rates with vaginal mesh surgery and alerted practitioners and patients to the complications associated with meshes, especially a deterioration in sexual function compared to laparoscopic sacro-suspension (LS) [START_REF] Maher | Transvaginal mesh or grafts compared with native tissue repair for vaginal prolapse[END_REF][START_REF]Urogynecologic surgical mesh implants[END_REF].

However, according to a recent French study, both techniques have similar functional and success rates. LS is safer than transvaginal mesh (TVM) and should be considered as a valuable primary surgical option [START_REF] Lucot | Safety of vaginal mesh surgery versus laparoscopic mesh sacropexy for cystocele repair: results of the prosthetic pelvic floor repair randomized controlled trial[END_REF]. On the other hand, LS has an extensive learning curve and long operative time compared to TVM [START_REF] Richter | Pelvic organ prolapse-vaginal and laparoscopic mesh: the evidence[END_REF] and this approach is not feasible for all cases due to interfering patient or technical factors. The need for a vaginal approach should be proposed to these patients. As a result of these alerts and the following suspension of TVM POP repair, native tissue POP repair may be the solution when transvaginal repair is required.

Our study focussed on the evolution of SUI in patients with and without preoperative SUI and SUI evolution after POP repair, and how to manage these variables either by surgery or observation and physiotherapy. In our experience, the technique using synthetic mesh (Uphold) and bilateral sacrospinous fixation via the vaginal approach seems reproducible and is associated with only mild complications with a high rate of satisfaction and acceptable objective and subjective cure rates 1 year post-surgery.

The main limitation to our study is the small cohort; this is reflected in the statistical significance of our results. Some pre-and postoperative data for the patients were missing particularly regarding functional information such as the severity of incontinence if present either pre-or post-POP repair, before and after physiotherapy, and after physiotherapy failure motivating MUS insertion. This information should be provided by the patients themselves using validated surveys or questionnaires to review their satisfaction rather than verbal subjective assessment. In addition, there was no pre-and postoperative urodynamic study, which is mandatory for patients presenting with POP associated with urinary symptoms [START_REF] Normand | Clinical practice guidelines: synthesis of the guidelines for the surgical treatment of primary pelvic organ prolapse in women by the AFU, CNGOF, SIFUD-PP, SNFCP, and SCGP[END_REF].

These types of assessment are beneficial to evaluate patient comfort after prolapse reduction, to compare POP associated symptoms before and after surgery and finally to evaluate the efficacy of the Uphold LITE system.

Conclusion

Prolapse repair surgery by sacrospinous fixation of Uphold LITE can resolve up to 50% of cases of pre-existing SUI and 50% of cases can be improved by physiotherapy. Postoperative de novo SUI was noted in 25% of patients requiring subsequent repair with a MUS in the majority of cases. The risk of having persistent SUI is more likely when there is preoperative SUI compared to patients without preoperative SUI. Prospective, comparative and long-term data are required to confirm these results.

Fig. 1 .

 1 Fig. 1. Flow diagram of study population at inclusion and follow-up.

Funding

This study had no funding source.


Emmanuel Paradis
email: emmanuel.paradis@ird.fr

A review of computer tools for prediction of ecosystems and populations: We need more open-source software

Keywords: biodiversity, ecosystem, forecasting, modelling, software

Computer programs have taken an important role in the prediction of future ecological trajectories. This study reviewed the existing computer programs that aim to predict future trajectories of ecosystems, biological populations, or ecological systems. Overall, 106 programs were examined. A rich set of programs exist and most of them are free. A substantial proportion (43%) are distributed open source. A majority (57%) of these programs took some form of uncertainty into account, although not always in a rigorous way. Programs considering uncertainty were preferentially implemented in a standard compiled language (C/Fortran) or a statistical language (R). The vast majority of the programs were delivered with recent, sometimes extensive, documentation. None of the reviewed programs used an open-source collaborative framework. Two points require future attention from developers of software for ecological prediction: greater care in the implementation of uncertainty, particularly with appropriate statistical methods, and adoption of an open-source, collaborative framework.

"Prediction is very difficult, especially about the future." (https://quoteinvestigator.com/2013/10/20/nopredict/)

Introduction

Computer programs and software systems have taken an increasingly important role in predicting the future trajectories of ecosystems and natural populations.

The increasing impact of human activities on ecosystems has increased the need for predicting their consequences (positive or negative). In 2016, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) published a report on modelling and scenarios of biodiversity and ecoystem services stating, among other things, that "Scenarios and models can contribute significantly to policy support, even though several barriers have impeded their widespread use to date." (IPBES, 2016, p. xii). However, a number of weaknesses in the use of models were pointed out in this report. For example, "Currently available scenarios [. . . ] do not fully address the needs of Platform assessments due to incomplete consideration of relevant drivers, policy goals and intervention options [. . . ]". Another important point in this IPBES report relates to uncertainty of preditions: "Uncertainty associated with models is often poorly evaluated and reported in published studies, which may lead to serious misconceptions" (p. xxvi).

Computer simulations are a central part of assessing future responses of ecosystems or natural populations that face environmental changes [START_REF] Botkin | Forecasting the effects of global warming on biodiversity[END_REF][START_REF] Dawson | Beyond predictions: biodiversity conservation in a changing climate[END_REF][START_REF] Bonnot | Dynamic-landscape metapopulation models predict complex response of wildlife populations to climate and landscape change[END_REF][START_REF] Dijak | Revision and application of the LINKAGES model to simulate forest growth in central hardwood landscapes in response to climate change[END_REF]. Some specific applications of simulations include predicting future biodiversity responses to climate changes [START_REF] Trisurat | Projecting land-use change and its consequences for biodiversity in northern Thailand[END_REF][START_REF] Trisurat | Assessing potential effects of land use and climate change on mammal distributions in northern Thailand[END_REF][START_REF] Staudinger | Biodiversity in a changing climate: a synthesis of current and projected trends in the US[END_REF][START_REF] Mantyka-Pringle | Understanding and predicting the combined effects of climate change and land-use change on freshwater macroinvertebrates and fish[END_REF][START_REF] Baltensperger | Predicted shifts in small mammal distributions and biodiversity in the altered future environment of Alaska: an open access data and machine learning perspective[END_REF], mapping ecosystem services [START_REF] Kong | Mapping ecosystem service bundles to detect distinct types of multifunctionality within the diverse landscape of the Yangtze River Basin, China[END_REF], life-cycle assessment [START_REF] Chaplin-Kramer | Life cycle assessment needs predictive spatial modelling for biodiversity and ecosystem services[END_REF], food security (Mason-D 'Croz et al., 2016), or future land use [START_REF] Lehsten | Disentangling the effects of land-use change, climate and CO 2 on projected future European habitat types[END_REF][START_REF] Requena-Mullor | Remote-sensing based approach to forecast habitat quality under climate change scenarios[END_REF]. Some attention has been paid on the development and validation of conceptual frameworks used to predict future trajectories of ecosystems [START_REF] Drielsma | The Biodiversity Forecasting Toolkit: answering the 'how much', 'what', and 'where' of planning for biodiversity persistence[END_REF][START_REF] Oliver | The pitfalls of ecological forecasting[END_REF]Zasada et al., 2017b). However, it is not clear how "best practices" in the development and implementation of these computer programs can be enhanced to improve predictions as well as policy recommendations [START_REF] Newman | Review of literature on decision support systems for natural hazard risk reduction: current status and future research directions[END_REF]Zasada et al., 2017a). For instance, IPBES (2016, p. 61) emphasized the lack of repeatability of approaches such as strategic environmental assessments.

Clearly, computer programs have an important role to play here since uncertainty assessment is typically based on computer-intensive methods.

The rise of open source software and worldwide networks such as the Internet has been a formidable stimulus for the development and spread of computer resources. For instance, scientific fields such as bioinformatics have now adopted a "free and open source software" (FOSS) model for the publication of computer programs. Furthermore, the availability of freely distributed computer programs is a requirement for publication in journals such as Bioinformatics, BMC Bioinformatics, or Methods in Ecology and Evolution. FOSS is not only about the price of the computer programs, but also about portability, repeatability, and open knowledge [START_REF] Wheeler | Why open source software / free software (OSS/FS, FLOSS, or FOSS)? Look at the numbers[END_REF].

The following definitions are used in this paper: an 'ecological system' is a set of interacting living entities that also interact with their environment which can itself be composed of living and/or non-living entities. An 'ecosystem' is an ecological system that is restriced to a geographically defined area (e.g., a lake, a forest). A 'biological population' is an ecological system whose entities are individuals belonging to the same species so their interactions are directed by some specific activities (e.g., mating, feeding). An ecological system is characterized by a number of variables (e.g., nutrients, species richness, number of individuals, age structure). 'Prediction' aims at finding the predicted values of these variables in the future.

In this paper, I report the results of an investigation of the availability of computer programs aimed at predicting the future trajectories of ecosystems, ecological systems, or biological populations. The main objectives were firstly to provide a global picture of the "software ecosystem" [START_REF] Manikas | Revisiting software ecosystems research: a longitudinal literature study[END_REF] available for ecological prediction, and secondly to identify the issues that require attention to improve this 'ecosystem' following the statements from IPBES. Some suggestions on future directions are given at the end of this paper.

Methods

Computer programs aimed at prediction of ecosystems, ecological systems, or biological populations were searched using Internet search engines and the literature. The programs selected for further analysis were those available for download or purchase. The programs available for purchase were considered to answer some of the questions below but were not purchased. All the investigated programs were downloaded and checked for some features.

Programs were selected on the basis that they provide tools, models, or approaches that can be directly related to prediction of ecosystems, populations, or other ecological systems. Programs dedicated to human health or epidemiology were excluded. Specifically, the following questions were addressed for each program:

1. What is (are) the computer language(s) used to implement the program? 8. Is a manual available? If yes, how many pages? 9. Is there a support for users? 10. Is there a mailing/discussion list? These questions were defined before investigating the programs; however, the way they were addressed was adjusted during the study. Considering the large number of programs found that meet the above criteria, it was not practically possible to run and test all of them. The answers to questions 1 and 3-7 were searched by reading the documentation or the general presentation of the program (e.g., section "About" of a web page). Questions 2 and 8-10 were answered by looking at the web pages of the program. Further information to answer questions 1, 3, and 8 were found by inspecting the downloaded programs. Questions 2 and 3 are not independent and are related to the distribution licence of the programs. However, the licence under which a computer program is distributed is a complex issue as illustrated by the many existing free licences (e.g., https: //en.wikipedia.org/wiki/Free_and_open-source_software).

Furthermore, a program can be published under several licences or its licencing status can change through time (e.g., https://www.r-project.org/Licenses/). Although this is clearly an important isssue, it was out of the scope of the present study which considered only the availability of source code. Questions 3 and 4 were connected since some programs are distributed simply as source code and not as compiled executables for one or several specific OSs, so 'source code' was a separate category when answering question 4. In order to be more specific, if any form of source or computer code was available, then the program was considered as 'open source' (question 3), whereas if a program was packaged only with its source code, then it was considered as 'source code' (question 4). Thus, a program could be 'open source' while not being distributed as 'source code' (whereas a program classified as 'source code' is necessarily 'open source'). The distinction between these two categories stems from the fact 'source code' programs are often independent of the OS. In order to answer question 6, the programs that model a specific system (e.g., diffusion of pollutants) or consider a specific geographical area were classified as specialist. Programs that consider or model a system which can be considered generic (e.g., a biological population, a watershed) were classified as generalist. Question 6 stems from the importance of being able to use the outputs of a program for further downstream analyses with other program(s), for instance, for uncertainty assessment, or graphical display. Question 7 was answered 'Yes' if the documentation mentioned uncertainty explicitly, or the approach described in the documentation was probabilistic.

All data analyses and graphics presented below were done with R version 3.6.0 (R Core Team, 2019); the R code is available in the Supplementary Information.

Results

A large number of Web pages and resources were found. A substantial number of programs were described "in development" or "coming soon". Other programs were listed on some Web pages but could not be located or downloaded. These "orphaned" or "lost" programs were not counted precisely.

In the end of the search, 106 computer programs were found and examined (Table S1).

The majority of the programs selected for this study (59 or 56%) were distributed by a US federal agency (main domain of the web site URL ending with .gov, .mil, or .us). These included 24 programs by the Environmental Protection Agency (EPA), 15 by the US Forest Service (USFS), 11 by the US Army Corps of Engineers (USACE), three by the US Department of Agriculture (USDA), and three by the US Geological Service (USGS). Almost all programs were distributed on dedicated web pages: only two were distributed on GitHub and two others on R-Forge.

One hundred and two programs (96%) were available free, some of them after registration, three were available as commercial products, and one was available as a free demo version.

For 34 programs (32%), it was not possible to find the computer programming language or platform used for implementation. For 24 programs (23%), a standard compiled language C or Fortran (or one of their variants or dialects: F77, F90, C++, or C#) was used (Fig. 1). Eleven programs were implemented in Excel, six in R, six in Python, six as ArGIS modules, four in Java, one in Julia, and one in Delphi. Six programs were modules of commercial programs (e.g., SAS, Matlab). Finally, seven programs were available as Web forms through Internet and not available for download.

Forty-six programs (43%) were available as open-source, 33 (31%) were distributed only as compiled applications and their sources were not available, one was available as open-source subject to collaboration, and four were commercially distributed. The open-source status of the remaining 22 programs (21%) could not be determined (Fig. 2).

For the analysis of OSs, the programs coded in Excel or in Java were considered as source code because a wide range of office applications can run Excel spreadsheets on most OSs, and there are many Java environments on most OSs as well. The vast majority of programs were available as applications running under Windows (73 or 69%), or even only for this OS (55 or 52%; Fig. 3).

Twenty-nine (27%) programs were distributed as source-code, and exclusively in this form for 22 of them (mainly as Excel code and secondarily as R programs which are OS-independent). Only one program was available only for Linux, and none of them were distributed as MacOS application. Additionally, one program run under 16-bit MS-DOS, and the running OS of two programs was not found.

A majority of programs (47 or 44%) output their results as text files, either only (37 or 35%) or in association with other formats (GIS or HDF5; Fig. 4). Six programs output their results in various file formats (labelled as "many" on Fig. 4). Seventeen programs (16%) did not output files, 13 output Excel files, and two output results in files that cannot be interfaced with other software (PDF reports or private format). Finally, the output format could not be determined for 13 programs (12%). The vast majority of the programs (71 or 67%) were specialist. There seemed to be an association between this variable and the programming language used: programs coded in Excel or as Web forms were all specialist, whereas the generalist ones were more represented among the programs implements in C/Fortran, R, or under a commercial platform (Fig. 5). No association with other variables were apparent.

Uncertainty was a feature in 60 (57%) programs, while this could not be found in six of the 106 (6%). There was a very significant association between this variable and whether a program is specialist or generalist: among the 35 generalist programs, 30 took uncertainty into account, whereas 30 specialist programs did out of 71 (Fisher's exact test: P < 0.0001; this test excluded the six programs where handling of uncertainty was unknown). There was also an association with the programing language: programs taking uncertainty into account were implemented in C/Fortran, R (all four of them) or with commercial programs (also all four of them; Fig. 6). On the other hand, programs in Python, Excel, or available as Web forms did not mostly consider uncertainty.

A manual in PDF format was available for 71 programs (67%), in HTML for 18 (17%), as an on-line wiki for three, and no manual or documentation was found for 12 of them (11%; Fig. 7). The mean number of pages of the manuals in PDF format was 234 (SD = 346, median = 104, min = 6, max = 2262). Most of the available documentation was recent: 55 (52%) were dated after January 1, 2016, and six were produced in 2020 (Fig. 8). The oldest manual was dated September 1994, and six manuals were dated before 2001.

Support to users was offered on the Web pages for 76 (72%) of the programs, non-free support was proposed for one program, and no apparent support was observed for the remaining 29 programs. A mailing list was found for 20 programs (19%). There was no apparent association between these two variables and the previously analysed ones.

Discussion

The present study leads to draw an overall positive picture of software for ecosystem prediction: a remarkable diversity of free programs are available, their associated documentations are generally of good quality (sometimes very extensive), and a good percentage (43%) are also distributed open-source.

Another significantly positive feature is that a majority of programs output their results in file formats which are easily read by other software, considering that Excel files can be open by many other programs (see for instance the R-package 'readxl'; [START_REF] Wickham | A conceptual model to integrate the regional context in landscape policy, management and contribution to rural development: literature review and European case study evidence[END_REF].

Remarkably, US federal agencies took a major part of the programs considered here. This highlights several points. First, this emphasises the importance of public agencies in making available to the public the research work on ecosystems and biodiversity. Second, a substantial number of these programs were published before 2000, so that they constitute an important archive for researchers and students. Even if the distributed programs are only available as executables running on "vintage" OS, the associated documentation, often containing the model description, details on the algorithms, and references to the literature, is a very useful source of information. Third, most of these programs are distributed as Windows executables which explain, at least partly, the predominance of this OS.

Uncertainty was considered in a majority of programs (57%). Unfortunately, it was not possible to assess for the present study whether uncertainty is correctly implemented in these programs. For instance, some manuals state that uncertainty can be taken into account by changing the input parameters of the program. This is a crude approach which could be useful in some situations (e.g., if the predictions are not changed substantially by the different input parameter values) but that could lead to difficulties in interpreting the results if the predictions differ with respect to the input parameter values. A more rigorous approach would be to weigh the outputs by the likelihood of the input values. There is a vast literature on this topic, especially oriented towards the use of Bayesian methods [START_REF] Hoeting | Bayesian model averaging: a tutorial (with discussion)[END_REF][START_REF] Clyde | Model uncertainty[END_REF].

Uncertainty is a difficult topic that often requires computationally intensive methods and/or sophisticated statistical techniques [START_REF] Draper | Assessment and propagation of model uncertainty (with discussion)[END_REF][START_REF] Evans | Methods for approximating integrals in statistics with special emphasis on Bayesian integration problems[END_REF][START_REF] Efron | Computer age statistical inference[END_REF]. Even if some of these methods are complicated to implement, weighting outputs by the likelihood of the input values seems as a bare minimum to take uncertainty into account. From a practical point of view, it is important for programs to include the possibility to save their outputs in a format which can be read and write by the vast majority of software (typically text). Parallel computing will also certainly attract more attention in the future in order to implement such intensive computing tasks.

Interestingly, parallel programming is available in the major languages observed in this study (C, C++, Fortran, R, Python).

It is interesting to note that the programs considering uncertainty were preferentially implemented in compiled languages (C/Fortran) or in a statistical language (R). This highlights the need to use a performing computer language to implement uncertainty. Moreover, these languages are widely used, free, and efficient implementations (e.g., the GCC compilers) are available to all users. It It is regrettable that the computer programs for ecosystem prediction do not currently benefit of this free service.

Open source is not only about the price of the software, it also makes possible to develop code in a more transparent and efficient manner with two major side-effects: scalability and integration. The latter feature is of particular importance for ecosystem prediction. Indeed, predicting future ecosystem trajectories, or some of its characteristics such as ecosystem services, often requires the integration of different components [START_REF] Titeux | Biodiversity scenarios neglect future land-use changes[END_REF][START_REF] Di Minin | Integrating biodiversity, ecosystem services and socio-economic data to identify priority areas and landowners for conservation actions at the national scale[END_REF]. Open software makes integration of different components much easier than closed systems [START_REF] Wheeler | Why open source software / free software (OSS/FS, FLOSS, or FOSS)? Look at the numbers[END_REF]. In this perspective, the integration of spatial data, for instance land use and land cover data, is a predominant feature or many studies attempting to predict changes in ecosystems or biodiversity [START_REF] Titeux | Biodiversity scenarios neglect future land-use changes[END_REF][START_REF] Bonnot | Dynamic-landscape metapopulation models predict complex response of wildlife populations to climate and landscape change[END_REF][START_REF] Chaplin-Kramer | Life cycle assessment needs predictive spatial modelling for biodiversity and ecosystem services[END_REF]. [START_REF] Newman | Review of literature on decision support systems for natural hazard risk reduction: current status and future research directions[END_REF] reviewed 101 papers on decision support systems and found that most effort has been placed on assessing areas of risk and economic consequences of direct losses, whereas less effort has been placed on assessing risk-reduction options. These authors listed a series of recommendations for future research. Although, they did not mention explicitly the development of better software, this is clearly an area that deserves to be considered as carefully as others. As rightly stated by these authors, impacts of natural hazards are likely to increase significantly in the future, so that more rigorous predictions of environmental changes are becoming more and more crucial. Zasada et al. (2017b) performed a review of 60 European projects aiming at developing decision support systems, and found that 88% of them were available after two years and only 61% after eight years. Furthermore, only 50% of these tools are being updated after the end of the project. Interestingly, only a small portion of these tools (3.4%) were available as downloadable programs, and a minority (31%) were integrated with other tools. No mention of either "source code" or "open source" is made in this study.

GIS data, an open binary format (e.g., GeoTIFF or netCDF for more complex data structures) should be preferred to simple text files.

The main criterion for guiding decisions in an open-source software development project should always be quality over quantity. Releasing a lot of computer code that it is not operational, that has not been tested or documentated is very likely to be a waste of resources.

2.

  Is the program freely distributed? 3. Is the source code of the program available? 4. What operating systems (OSs) are supported? 5. What is the main output file format? 6. Is it a specialist or a generalist program? 7. Does the program consider uncertainty?

Figure 1 :

 1 Figure1: Frequencies of computer language implementation of 106 computer programs for ecosystem prediction.

Figure 2 :

 2 Figure 2: Frequencies of open-source features of 106 computer programs for ecosystem prediction.

Figure 3 :

 3 Figure 3: Venn diagram of the supported operating systems for 96 programs (the ten excluded programs from this diagram are: seven Web forms, one MS-DOS program, and two with unknown OS).

Figure 4 :

 4 Figure 4: Formats of the output files.

Figure 5 :

 5 Figure5: Mosaic plot of the contingency between whether a program is specialist or generalist and its programming language implementation. The widths of the rectangles are proportional to the frequencies of the different categories.

Figure 6 :Figure 7 :

 67 Figure6: Mosaic plot of the contingency between whether a program considers uncertainty and its programming language implementation. The widths of the rectangles are proportional to the frequencies of the different categories.

Figure 8 :

 8 Figure 8: Histogram of the dates of the manuals associated with 85 computer programs for ecosystem prediction.

  appears therefore that considering uncertainty in a program devoted to ecosystem prediction has several benefitial effects: it not only increases its usefulness and relevance for prediction but it also increases its likelihood to use an efficient, open source implementation.Open source is not yet a prominent feature of software for ecosystem prediction. However, the above observations are encouraging: the programs that take uncertainty into account are more likely to be implemented in a language commonly associated with open source. Interestingly, a number of programs (7) distributed for Windows are also available as source code. This emphasises that open source is independent of the OS. On the other hand, the software for ecosystem prediction clearly lag behind other scientific fields in terms of code sharing: only two programs are currently distributed on GitHub, a platform for code sharing used by dozens of thousands of developers and currently hosting more than 100 million repositories. Quite illustrative of this sympton, none of the R packages reviewed here are distributed on the Comprehensive R Archive Network (CRAN) which is the standard Internet repository of R packages. The more than 15,000 packages currently on CRAN are checked daily to ensure that they can be installed and run correctly on most common operating systems (currently: Linux, Windows, MacOS X, and Solaris).

Acknowledgements

I am thankful to four anonymous reviewers for their very constructive comments. This is publication ISEM 202x-xxx. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conclusion and Recommendations

The present study agrees with some statements from IPBES, notably: "There are large gaps in the availability of data for constructing and testing scenarios and models, and significant barriers to data sharing remain." (IPBES, 2016, p. xxvii).

Such statements clearly call for significant improvements of the 'software ecosystem' for ecosystem prediction. In addition to the recommendations from IPBES, I wish to formulate a few recommendations.

1. Open source: this feature is coming into wider acceptance in many scientific fields, including ecosystem prediction. However, open source should be considered in the wider context of portability so that software can be installed and run on as many computing platforms as possible. In this perspective, the computer languages R, C, and Fortran (and the dialects of these last two) appear as best choices to implement software for ecosystem and biodiversity prediction. There are free implementations for all common OSs of these languages. Furthermore, they make possible high-performance computing, and there already exist a wide range of tools in these languages to handle the data commonly encountered in ecosystem modelling (see for instance the package rgdal for reading GIS data in a wide range of formats [START_REF] Bivand | rgdal: bindings for the 'Geospatial' Data Abstraction Library[END_REF].

2. Uncertainty: there is need to have more rigorous implementation of uncertainty in ecosystem predictive modelling. The statement that "different input parameter values" can be tested is not generally a valid approach, and should be avoided. Statistical techniques such as weighted integration should be considered more widely.

3. Output file formats: greater care should be taken on output formats. Even if using the standard text output files, a number of difficulties may be encountered, typically related to encoding, text layout, or file sizes. For

Supplementary Information

Table S1: URLs of the 106 programs.