Measurement of the Surface Recombination Velocity in Organically

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Measurement of the Surface Recombination Velocity in Organically Functionalized Silicon Nanostructures: The Case of Silicon on Insulator Romain Coustel,*,†,|| Quentin Beno^it a la Guillaume,‡ Vincent Calvo,‡ Olivier Renault,§ Lionel Dubois,† Florence Duclairoir,† and Nicolas Pauc‡ †

SCIB, UMR-E CEA/UJF-Grenoble 1, INAC Grenoble F-38054, France SP2M, UMR-E CEA/UJF-Grenoble 1, INAC Grenoble F-38054, France § CEA/LETI/MINATEC/SPCIO, 17 Avenue des Martyrs, Grenoble F-38054, France ‡

ABSTRACT: As an alternative to the traditional surface oxidation of silicon into SiO2, covalently bonded organic monolayer is investigated as a mean to electronically passivate silicon surfaces and applied to the particular case of 2D silicon wells made on silicon on insulator. Functionalization of the silicon surface with a C11-alkyl (Si
C11) chain is achieved and confirmed by X-ray photoelectron spectroscopy (XPS). We use a direct detection of the photoluminescence decay rate of the free carriers generated into the 2D silicon crystal (thickness in the 90
200 nm range) as a marker of the surface quality and find a Si
C11 surface recombination velocity of 61.6 ( 0.9 cm s
1. This type of measurement on such a type of modified Si samples is original and confirms that low surface recombination velocity can be reached when an organic layer is used, illustrating the fact that such a technique is an interesting passivation method. Comparison with hydrogenated Si (Si
H) surface is done. Freshly prepared Si
H surfaces show a better recombination velocity (22.5 ( 0.4 cm s
1) than the Si
C11 surface, but sample aging reverses such a trend. As confirmed by XPS, organic monolayer slows down native silica, and hence carrier trap formation, demonstrating that covalently grafted organic monolayers on Si exhibit satisfying electronic and chemical passivating properties.

1. INTRODUCTION The development of hybrid devices interfacing silicon to molecules has gained a lot of interest over the past 10 years as a route to obtain small devices with new applications. The size of the active element can be dictated by the structure chosen (flat Si crystals,1,2 nanoporous Si,3 Si nanopowder/quantum dots,4 Si nanowires,5 and so forth), and the properties of the device are tuned by the molecule properties (redox compound for charge storage media/nanoelectronics,6 photosensitive compounds for photovoltaics, optical devices, coordination chemistry compounds for sensor, biological systems for nanoelectronics,7 or nanobiotechnology8). In such a field, the interface between the inorganic substrate and the organic compound plays a key role in the device properties and stability over time. This issue is even more problematic when the substrate used becomes very small. For example, Si nanowire properties will be so sensitive to their environment that the quality of their surface will have a big impact on their properties. We can therefore distinguish two interlocked interface problems: the surface state of the object itself and the interface with the organic compound. An efficient technique used to connect molecules to Si substrate is the hydrosilylation reaction that yields Si
C interfacial bonds.9 Such covalent bonding provides an efficient surface passivation1,10 and allows to obtain a surface chemically and electronically passivated that will enhance the stability of the device and improve its operating time. r 2011 American Chemical Society

Hydrogenation upon exposure to HF is also a mean to passivate the Si surface. Such Si
H terminated surface displays a low number of defect sites (recombination centers); however, these surfaces are prone to rapid oxidation and yield SiO2 native oxide layers with a lot of defects. To functionalize Si surface with an alkyl chain presents an interesting alternative as the organic monolayer could respond to both problems by passivating the object surface and acting as a protection layer against uncontrolled oxidation of the substrate. Moreover, such a monolayer offers anchor sites to couple in addition molecules of interest to the surface. A few studies have been conducted to prove and confirm the utility of such a layer for surface passivation and hence for nanodevice fabrication. For example, such passivation behavior of an organic monolayer on Si has been established by photoluminescence measurements for Si surfaces decorated by the means of electrochemical grafting.10
12 Other studies conducted on Si substrate prepared with various methods and modified by hydrosilylation reaction showed a quite low surface trap density using the CV method.13 Similarly, when a Grignard reaction is used to modify the bulk silicon, such a passivating effect has also been shown.14 The aging of Si substrates functionalized with diazonium chemistry has also been reported Received: August 18, 2011 Revised: October 6, 2011 Published: October 08, 2011 22265

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The Journal of Physical Chemistry C showing (notably by combined X-ray photoelectron spectroscopy (XPS) and IR studies) that the organic monolayer presence slows down the reoxidation process.10,15 Recently, Haick et al. conducted experiments on the functionalization of Si nanowires by the mean of a Grignard reaction on an hydrogenated sample. XPS and ToF-SIMS experiments revealed the passivation power of such layers also providing information on the trend between chain length and interface quality.16 To date, only a few studies using optical excitation for measuring the surface recombination velocity (S) have been reported. Among them, measurements of the photoluminescence (PL) integrated intensity of grafted bulk Si samples were made, allowing qualitative estimates of their surface qualities.12 More accurate measurements of S in the case of the very peculiar Diels
Alder reaction between 9,10-phenanthrenequinone with Si(100)-2  1 were presented recently in17 using the photoconductance decay technique. Promising results were obtained as low S were reached (∼150 cm s
1). Recently, Demichel et al.18,19 developed an original optical method to measure the surface recombination velocity at the surface of Si nanostructures. Here, the free carrier recombination lifetime at the wavelength corresponding to the near band edge luminescence of silicon is used as a marker allowing an accurate measurement of S, and thus provides a higher confidence level in measuring S compared with the PL integrated intensity method. In addition, under the experimental conditions, a high and constant density plasma of free carriers is generated, the socalled electron hole liquid (EHL).19 Owing to the incompressibility properties of this condensate, there is no carrier gradient all over the sample depth, more particularly close to the interfaces, thus eliminating the uncertainty in evaluating S for the carrier density under study, a problem which can be encountered in photoconductivity measurements of S in bulk samples. Demichel et al. validated this method on the well-known silicon/silica interface, traditionally used to passivate the silicon surface in the microelectronic industry. These authors report accurate SSiO2/Si values for 2D silicon crystals and silicon nanowires, 36 ( 5 cm s
1 and 20 ( 4 cm s
1, respectively. In the present work, this innovative technique is applied to provide the surface recombination velocity of 2D silicon crystals passivated by an organic monolayer. Silicon on insulator (SOI) samples are used as a crystalline silicon medium with a thickness in the 90
200 nm range. Different interfaces are created in order to settle a comparison between (i) the Si
H or Si
C terminated surfaces and (ii) the aging effect on S for the two interfaces under study. The silicon top-layer is subjected either to a hydrogenation reaction by HF etching or to a hydrosilylation reaction with chloroundecene (C11). In the first step, Si
H superficial bonds are generated, and in the latter case covalent Si
C bonds are obtained between the surface and the C11-alkyl chain. XPS is used to check the chemical state of the surface.

2. EXPERIMENTAL SECTION All chemicals were used as received except 11-chloro-1undecene that was distilled under vacuum and kept under argon. Moreover, prior to its use, in order to remove oxygen contamination the alkene was subjected to a series of 4
6 freeze
thaw cycles. Preparation Protocol. SOI samples are fabricated using the Smart Cut process. The initial stack is made of a Æ100æ 200 nm crystalline silicon slab lying on a 400 nm thick buried oxide layer located on a silicon substrate. As will be mentioned later, in order

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Scheme 1. Protocol for SOI Etching and Hydrogenation Followed by Hydrosilylation with 1-Chloro-1-undecene

to probe the free carrier recombination rate in SOI, getting a set of different thickness SOIs is required. To do so, we start with 200 nm thick SOI samples and perform several cycles of deoxidation (dipping in 48% HF) of the top oxide layer and partial thermal oxidation of the underlying Si layer, resulting in a final oxide
silicon
oxide stack with the desired silicon thickness d. Tuning the thermal oxidation time together with the number of oxidation
deoxidation cycles allowed to obtain samples with d = 196, 162, and 95 nm. Each as prepared SOI sample is initially cleaned by sequential immersion in a trichloroethylene, acetone, isopropanol, and water bath. The upper silica layer is etched in 48% HF solution (5 min). Then, the silicon surface is cleaned in H2SO4/H2O2 solution (3/1, v/v) for 10 min and RCA procedure followed by 3 min dipping into 1% HF aqueous solution. The sample is then subjected to a final rinse with water and dried under a stream of Ar. Grafting Procedure. The hydrogenated sample was immediately immersed in 1-chloro-1-undecene that had been distillated and degassed by freeze
pump
thaw cycles. The reactor was purged with Ar and closed. Hydrosilylation was carried out at 140 C for one night in metallic bath. After the formation of the organic monolayer, the sample was rinsed with n-hexane, THF, isopropanol, and dichloromethane. The grafting process is sketched in Scheme 1. Measurements. XPS spectra were recorded on an S-Probe spectrometer from Surface Science Instruments (SSI), equipped with a microfocused Al Kα source monochromated at 1486.6 eV (spot size 1.7 mm). Photoelectrons were detected by a hemispherical analyzer at an electron emission angle of 65 and pass energy of 150 eV (survey spectra) and 25 eV (core level spectra). For the core-level spectra, the overall energy resolution, resulting from monochromator and electron analyzer bandwidths, was 700 meV. For easier comparison, the core-level spectra presented hereafter were referenced using the Si2p3/2 core-level binding of 99.5 eV characteristic of bulk, lightly doped N-silicon. PL experiments were carried out at low temperature (typically 10 K) in a He circulation cryostat. For continuous wave (cw) PL, laser excitation is provided by the 364 nm line of a cw Ar+ laser, and the signal is recorded by a Jobin Yvon spectrometer equipped with a cooled InGaAs photodiode array. For time-resolved PL, laser excitation is provided by a tripled Nd:YAG pulsed laser emitting at 355 nm with 10 ns pulse width and typical repetition rate of 1 kHz. The PL signal is directed toward a Jobin Yvon monochromator for wavelength selection and recording by a Hamamatsu photomultiplier tube. Temporal reconstruction of the PL decay profile is ensured by a pulse counter plugged to the photomultiplier.

3. RESULTS AND DISCUSSION 3.1. Characterization of the SOI Surface after Hydrogenation and Grafting by the Organic Monolayer. The function-

alized silicon layer is prepared from SOI samples by a two-step process (see Scheme 1). The first one aims at removing the 22266

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Figure 1. Overview (a) and high-resolution Si2p (b) and Cl2s (c) XPS spectra of the fresh and aged Si
C11 and Si
H surfaces.

silicon oxide upper layer and at hydrogenating the Si surface (i.e., producing superficial Si
H bonds). The second step is the grafting of the olefin on the Si
H surface (in the following the obtained surface will be designated by Si
C11). Typical XPS survey scans of the freshly prepared Si
H surface are shown in Figure 1a. Primary peaks are observed at ∼100 eV (Si2p), ∼151 eV (Si2s), ∼285 eV (C1s), and ∼532 eV (O1s). The small C1s peak should be attributed to a hydrocarbon contamination in ambient atmosphere before introduction into the XPS chamber. The Si2p core level XPS spectrum (see Figure 1b) only presents one component located at 99.5 eV assigned to pure Si. No additional component related to oxidized species is observed at higher binding energy, indicating that the amount of oxidized Si atoms on the fresh Si
H surface is below the sensitivity threshold of our equipment (1% ML). The small O1s peak observed in the survey scan of the fresh Si
H surface could arise from a number of sources including physisorbed water and oxygen-containing organic molecule contamination.20 As for fresh Si
H surfaces, the XPS survey scan of the fresh Si
C11 surfaces (Figure 1a) presents Si2p, Si2s, C1s, and O1s peaks. In the literature there are reports of XPS evidence of covalent bonding between short alkyl chains and silicon,21,22 with two split components peaking at ∼285 and ∼284 eV in the C1s region, attributed to C
C and C
Si bonds, respectively. It is worthwhile noting that carbon pollution makes the interpretation of C1s signal difficult on an ex-situ prepared organic monolayer, and that the C
Si component is expected to show a strong attenuation for chloroundecene monolayer. Actually, for long grafted alkyl chains (Cm with m g 10), photoelectrons originating near the monolayer
substrate interface are expected to undergo inelastic scattering in the organic film before reaching the vacuum.22 The literature also mentions the use of the Si2p

Figure 2. PL spectra of the Si
C11, Si
H, and initial SOIs.

region (see Figure 1b) to probe the Si
C bonding state in alkyl functionalized silicon nanocrystals, and assigns a transition located at 101.9 eV to Si
C bonds.23 Our data shows transitions for fresh Si
C11 surfaces at 99.5 eV (elemental silicon Si0) and 102.9 eV. This last value has also to be compared with the levels of silicon in higher oxidation states (Si1+, Si2+, Si3+, and Si4+ at 100.60, 101.40, 102.47, and 103.65 eV, respectively, see for example, ref 24), making this signal a likely signature of a slight oxidation of grafted samples before XPS characterization. Despite direct evidence of C
Si bonding being a difficult task here, we made use of Cl atoms as a spectral marker to provide evidence of the immobilization of our molecule on the Si surface. This is supported by the observation of the Cl2p and Cl2s lines (∼201 and ∼271 eV) recorded on the Si
C11 surfaces (see in Figure 1a,c). As hydrosilylation is extensively described as a robust process, such immobilization can be reasonably interpreted as arising from covalent grafting of the chain. It is worthwhile noting that no bonding between the Cl of the alkyl chain and the silicon surface during the hydrosilylation process occurs as, in a second step, the C
Cl bonds of the obtained monolayer can be used as an anchoring point to couple active compounds to the surface.25 Assuming that the high energy side of the Si2p lines arises only from Si
O bonds, it is possible to evaluate the amount of silicon oxide on Si
C11. The silicon oxide amount is evaluated from a standard procedure.26 In brief, the photoelectron signal from 22267

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The Journal of Physical Chemistry C bulk, pure silicon is attenuated by a uniform oxide layer depending on its thickness, which is then deduced from the ratio of the area of the Si0 and Sin+ peaks, the value of the attenuation length of the Si2p photoelectrons (2.96 nm), and the bulk intensity ratio (0.91); the organic layer attenuates equally both Si0 and Sin+ signals, and then it does not affect the peak intensity ratio. From this calculation, we found that the average oxide layer on Si
C11 surface is only 0.3 nm thick. 3.2. PL Results. Figure 2 presents the PL spectrum of the initial SOI recorded at 10 K. Three main peaks can be identified across the spectral range under study: a main transition centered at 1.08 eV and two weaker peaks at 1.02 and 1.12 eV, respectively. Such bands are observed in ultrapure bulk silicon,27 two-dimensional SiO2/Si/SiO2 quantum wells made on SOI,28,29 and SiO2 passivated silicon nanowires18,30 and result from phonon assisted (transverse optic and longitudinal optic modes at 1.08 eV, transverse acoustic mode at 1.12 eV, and two phonons at 1.02 eV) recombination of electron
hole pairs in a dense and constant density electron hole liquid, with a pair density n0 = 3.2  1018 cm
3. Offsets between the expected indirect band gap energy (1.17 eV at 10 K) and PL lines are explained by the 2-fold contribution of phonons involved in the electron hole (e
h) pair recombination and the rigid shift of the band edges due to the renormalization effect associated with high carrier densities (the exchange and correlation energy of the carriers assembly act as a stabilizing term and lead to an apparent red shift of the band edges). Figure 2 also presents the PL spectrum of the grafted SOI (Si layer = 158 nm, as measured by ellipsometry) for which the top SiO2/Si interface was substituted by a Si
C11 one. Both PL spectra are quite similar. This result indicates qualitatively that the grafted molecules do not induce electronic states which are optically active in the vicinity of the Si band gap and that the grafted interface does not generate a too large density of interface traps compared to the thermal SiO2 one. Indeed, since it is found experimentally that the part of photogenerated carriers that recombine radiatively still remains in the same range after grafting, we can conclude that the number of extra nonradiative recombination channels related to interface traps still remains at a quite reasonable level. This result suggests that the covalently grafted organic layer/Si interface provides an electronic passivation of the Si surface presenting a low carrier recombination rate. It is important to note here that the pump radiation does not reach the silicon substrate since the typical penetration depth of 350 nm radiation in silicon is only typically ∼10 nm. Thus, no extra and parasitic contribution coming from the substrate can be found in the continuous wave (cw) or time-resolved spectra of SOIs. Moreover modified SOI for which the SiO2/Si top layer was substituted by a hydrogenated silicon surface (Si
H) presents also the same PL spectrum (see Figure 2). To go deeper in the analysis of the surface recombination properties of H- or C11-passivated Si surfaces, time-resolved PL experiments are necessary and have been shown to give accurate estimates of the surface recombination velocity18,25 for oxidized SOI and silicon nanowires. In bulk silicon, time-resolved PL of the near band gap (1.08 eV at 10 K) recombination line gives the lifetime of photogenerated free carriers. Since silicon is an indirect band gap semiconductor, high carrier densities can be created even with quite reasonable laser pumping intensities (higher than 1018 cm
3), leading to the overlap of the exciton wave function and to their condensation

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into EHL. The leading recombination mechanism in EHL is the Auger recombination (ehe or ehh Auger recombination events) that is extremely efficient in pure silicon compared with radiative recombination or recombination on traps. The Auger mechanism sets the measured lifetime τvol with typical values in the 200 ns range. The case of nanostructures such as nanowires or SOI is somewhat different. In the latter case, surface plays a predominant role, and the apparent recombination rate r = no/τ has to be modified to take into account the extra nonradiative surface recombination events: r = rvol + rsurf, where rvol = no/τvol is the volume recombination rate, equal to the bulk one, and that is constant whatever the surface state is, and rsurf is the global surface recombination rate. For SOI, this equation can be written19 τ
1 ¼ τ
1 vol þ

ðS1 þ S2 Þ d

ð1Þ

with no(S1 + S2)/d the recombination rate associated with the two interfaces of the SOI of thickness d. Here, S1 is the recombination velocity of the interface between the silicon and the buried oxide, while S2 is the recombination velocity at the grafted or hydrogenated surface. Measuring the e
h lifetime in SOIs with different thicknesses but identical surface states is thus a very convenient way to have access to an accurate estimate of S1 + S2. SOI substrates with different Si layer thickness (d = 92, 160, and 192 nm) have been used and subjected to the same passivation methods (hydrogenation and hydrosilylation), and for each sample PL spectra have been recorded and charge carrier lifetime measurements carried out in order to estimate the surface recombination velocities of Si
H and Si
C11 surfaces. Figure 3 shows the time-resolved PL of the 1.08 eV PL line recorded at 10 K on the three Si
C11 samples. During the first 50 ns a nonexponential decay profile is observed that is due to the relaxation of extremely dense and hot e
h plasma in the very first moments after the end of the intense laser pulse, as described in ref 24 for which the model giving eq 1 does not hold. Beyond this stabilization time, the decay is single exponential, and the e
h liquid may be seen as an homogeneous layer of constant density liquid wetting both interfaces of SOI with its surroundings, with a radius progressively vanishing with the time delay after pulse. One can clearly see in Figure 3 that the thinner the layer is, the faster the decay is. Such behavior is in agreement with eq 1 and shows that the e
h pair lifetime increases with the silicon thickness, as a result of the less pronounced effect of surfaces on the overall lifetime of thick SOIs. Shown in Figure 4 is the effective recombination rate (1/τ) as a function of the inverse of their thickness for each functionalized Si layer. According to eq 1, we find from the linear fit of the data S1 + S2 = SSiO2/Si + SSi
C11. In order to discriminate between the overall surface recombination velocity SSiO2/Si + SSi
C11 and the surface recombination velocity of interest, i.e., SSi
C11, one has to have a separate measurement of the recombination velocity SSiO2/Si. This is obtained by measuring the e
h lifetime in the initial SOIs where both interfaces of the Si layers (d = 95, 162, and 196 nm, respectively) are SiO2/Si. We deduce from measurements performed on this oxidized SOIs that S1= SSiO2/Si = 3.1 ( 0.2 cm s
1, with this value being in good agreement with our previous results.19 Assuming that the grafting process does not alter the value of S1, we find S2 = SSi
C11 = 61.6 ( 0.9 cm s
1. Let us now compare the functionalized silicon surface and the hydrogenated silicon (Si
H) surface properties in term of electronic passivation and chemical passivation. The PL spectrum of the 22268

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Figure 3. Time decays of the 1.08 eV PL line recorded on initial, Si
H, and Si
C11 SOIs (fresh and aged). For Si layer thickness, see legend.

Figure 4. Effective recombination rates of EHL carriers in SOIs are reported as a function of the inverse of the Si layer thickness.

hydrogenated Si layer is identical to the ones obtained on the initial SOIs or on functionalized Si layers. Time decays of the 1.08 eV PL line recorded on hydrogenated Si layers are shown in Figure 3. As for functionalized Si layers, after a 50 ns transition regime, the decays are single exponential. The deduced 1/τ versus 1/d curve is shown in Figure 4, and according to eq 1, we find a surface recombination velocity S2 = SSi
H = 22.5 ( 0.4 cm s
1, making this latter value slightly smaller (and hence better) than for the grafted surfaces. SSi
H and SSi
C11 stay however in the same range and close to the thermal SiO2/Si interfacial recombination velocity which is up to now the best known interface for Si passivation. Grafted organic layer is meant to slow down native silicon oxide formation: Si
C interfacial bonds reduce the kinetics of oxidation, and packed alkyl chains are expected to act as a barrier against oxygen. Despite this positive effect, it is important to note that the chemical surface reactions that yield Si
C bonds do not occur on each Si superficial site for steric hindrance reasons (projected surface area of the alkyl chain and Si orientation to take into account) and that interstitial oxidation can occur. So, the oxidation process is slowed but not removed. Given the above-mentioned arguments on the detrimental effect of the

reoxidation on the electronic passivation and thus on the surface recombination velocity, following S with time gives a direct signature of the chemical passivation properties of the grafted layer compared with the hydrogenated one (here, the term “chemical passivation” refers to the ability of the grafted surface to prevent oxidation of surface sites). To do so, the evolution of the electronic surface passivation was investigated carrying time decay measurements of the 1.08 eV PL line on three months aged Si
H and Si
C11 layers stored in air. As we did for the freshly prepared surfaces, we can extract the surface recombination
1 velocity rates of the aged surfaces: Saged Si
C11 = 208.6 ( 8.5 cm s , aged
1 and SSi
H = 398.5 ( 37.1 cm s . Both velocities increase with time, indicating that surface oxidation occurs on each surface, but in a much weaker ratio for the grafted one (increase of a 3.4 factor) than for the hydrogenated one (increase of a 17.7 factor). This result shows that the grafted layer is not fully permeable to diffused oxygen molecules but offers a very reasonable level of physical protection against reoxidation compared to the hydrogenated case. To confirm our optical measurements, we carried out XPS measurements on the two aged surfaces. The corresponding spectra of three month aged surfaces (Si
H and Si
C11) are shown in Figure 1. The Si2p region of both spectra present a main transition at 99.5 eV attributed to nonoxidized Si. The transitions at higher binding energy (Si
H 103.5 eV; Si
C11 102.9 eV) should be assigned to Si atoms in higher oxidation states (Sin+, n = 1, ..., 4). With the binding energy shift increasing with n, we deduce that the Si
H surface presents Si atoms with a higher oxidation degree than the Si
C11 surface (mostly Si4+ for the aged Si
H surface, whereas for the aged Si
C11 surface, Si3+ states are predominant). Moreover, Sin+ to Si0 peak ratios indicate that the amount of native oxide weakly increases from 0.3 to 0.4 nm for the fresh and the aged Si
C11 surface whereas the increase is from 0.0 to 0.7 nm on the corresponding Si
H surface. The reoxidation process appears much faster on Si
H than on Si
C11, which confirms that our grafted organic layer reduces oxygen diffusion to silicon, and is in agreement with our optical measurements of S.

4. CONCLUSION XPS and PL characterizations indicate that the grafting of alkyl chains on Si surface leads to a low number of recombination centers yielding a sample with a low surface recombination velocity (SSi
C11 = 61.6 ( 0.9 cm s
1) and slows down the 22269

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The Journal of Physical Chemistry C native silicon oxide formation. These results open up a new way to achieve silicon surface passivation as an alternative to the traditional thermal-SiO2/Si interface. They also illustrate and confirm quantitatively the passivating effect of the linker layer that is generally used when sequential immobilization of compounds with functionalities is targeted. Thus, the importance of this intermediate organic layer is clearly proven and supports the research conducted following such a path. Straightforward adaptation of this process to Ge surfaces would allow Ge nanoobject exploitation that is today limited by the instability of the GeO2/Ge interface. Related studies are now in progress.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Phone: 33 4 67 14 91 61. Fax: 33 4 67 14 91 19. )

Present Addresses

IEM, UM2
CC 047 Place Eugene Bataillon 34090 Montpellier Cedex 5, France.

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