Ciencia y Tecnología, 31(1): 26-37, 2015 
ISSN: 0378-0524 

DIRECT FUNCTIONALIZATION OF Mn12-(METHACRYLATE) CLUSTERS ON 
Si(100): SURFACE CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES  
 

Marisol Ledezma-Gairaud,1,2 Thomas Moehl3, Mavis L. Montero∗1,2 and Leslie W. Pineda,∗1,2 

 

 

1Centro de Electroquímica y Energía Química, CELEQ, Universidad de Costa Rica, San José, Costa Rica 
2Escuela de Química, Universidad de Costa Rica, San José, Costa Rica 

3Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Ecole Polytechique Fédérale de 
Lausanne, CH-1015 Lausanne, Switzerland 

 
Received June 2015; accepted May 2015 

 
Abstract 

 
The reaction of H–terminated Si(100) with methacrylate–substituted manganese carboxylate 
clusters [Mn12O12{CH2C(CH3)COO}16(H2O)4], [Mn12–(methacrylate)] via hydrosilylation 
afforded Mn12–(methacrylate)−Si(100). The chemically modified surface was studied with an 
atomic force microscope (AFM), X–ray photoelectron spectra (XPS), a cyclic voltammeter 
(CV) and electrochemical impedance spectra (EIS). XPS show several Mn and Si electronic 
signatures that indicate the tailoring of Mn12–(methacrylate) on the surface. The CV plot of 
Mn12–(methacrylate)−Si(100) has two irreversible cathodic waves at −0.76 and −0.44 V, 
assigned to Mn(IV)/Mn(III) and Mn(III)/Mn(II) processes. The calculated charge at –0.44 V 
was 3.14 x 10–5 C cm–2. An equivalent-circuit model was proposed based on EIS data and 
element circuit analysis. EIS show that the electronic and structural features of Mn12–
(methacrylate) on a surface greatly influence the electron transfer.  
 

Resumen 
 

La reacción de Si(100)−H con grupos carboxilato del clúster 
[Mn12O12{CH2C(CH3)COO}16(H2O)4], [Mn12- (metacrilato)] a través de la química de 
hidrosililación, proporciona el Mn12-(metacrilato)− Si(100). La superficie modificada 
químicamente se estudió mediante microscopía de fuerza atómica (AFM), espectroscopia de 
fotoelectrones de rayos X (XPS), voltametría cíclica (CV), y la espectroscopia de impedancia 
electroquímica (EIS). Los espectros XPS muestran características electrónicas del Mn y del Si 
que indican la incorporación del Mn12-(metacrilato) en la superficie. El gráfico CV de Mn12-
(metacrilato)−Si (100) tiene dos ondas catódicas irreversibles en −0.76 y −0.44 V, que pueden 
ser asignadas a procesos redox Mn(IV)/ Mn(III) y Mn(III)/Mn(II ). La carga calculada a −0,44 
V es 3,14 x 10-5 C cm-2. Un modelo de circuito equivalente se propuso con base en los datos 
de la EIS y el análisis de elementos del circuito. Las características electrónicas y 
estructurales del Mn12-(metacrilato) en la superficie influyen en gran medida en la 
transferencia de electrones como se muestra por EIS.  
 
Key words: Silicon(100), Mn12 cluster, cyclic voltammetry, X–ray photoelectron spectra 
(XPS), electrochemical impedance spectra (EIS). 
 
Palabras clave: Silicio (100), complejo Mn12, voltametría cíclica, Espectroscopía 
fotoelectrónica de Rayos-X (XPS), Espectroscopía de impedancia electroquímica (EIS). 

 
 
 
 
 

																																																													

* Corresponding author: leslie.pineda@ucr.ac.cr 



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I. INTRODUCTION 
 

Modified surfaces of silicon are currently of great interest because several electronic 
components (e.g., rectifiers, junctions, switches, transistors, sensors etc.) rely on silicon 
semiconductor technology [1−6]. Related to these applications, various chemical protocols to attain 
novel surface properties have been reported, for instance, covalent functionalization under thermal 
conditions, electrochemical process, hydrosilylation catalysis, or photochemical reactions with 
alkenes, Grignard reagents or aldehydes [7–12]. In this vein, molecularly based devices integrating 
organic and inorganic hybrid interfaces might greatly enhance the properties and performance of 
semiconductors [13, 3]. Of particular interest are single–molecule magnets (SMM) that function as 
individual nanoscale magnetic particles; for instance, [Mn12O12(O2CR)16(H2O)4] (R = Me, denoted as 
Mn12–(OAc); Et, Ph) stores magnetic information based on a hysteresis cycle under cryogenic 
conditions [4,14]. This cluster is composed of a central Mn4(IV)O4 cubane and peripherical Mn(III) 
ions; the oxidation state of the latter is associated with a high–spin (d4) electronic configuration that 
typically causes an elongation of manganese bonds known as a Jahn−Teller (JT) distortion (S1, 
Supplementary Information). Mn atoms in Mn12 clusters are active in oxidation and reduction, as 
demonstrated by electrochemical measurements in solution [14]. The integration of Mn12 clusters 
onto Si wafers has been accomplished mostly through a step-wise method requiring surface 
prefunctionalization with chemical groups that provide specific docking sites; the reports [12, 13] 
neglect any electrochemical characterization of the surface. 
To study their integration as a source of novel electronic properties coupled to silicon, we reported 
the tailoring of copper(II) bimetallic complexes on Si(100) [16]; the electronic and structural 
features of the coordination complex led to the formation of multilayers using linking molecules to 
anchor additional molecules. The immobilized copper atoms are electroactive, showing well 
defined redox states. In the case of the Mn12 cluster, its coordination chemistry might also render 
prospective applications as units for information storage on a molecular scale, given the multiple 
stable discrete oxidation states in the molecule. In this work, we investigated the direct grafting of 
Mn12–(methacrylate) onto a silicon surface rather than through a step-wise method requiring a 
ligand displacement to assemble Mn12–(methacrylate)−Si(100). Such a surface array is substantially 
nearer the silicon substrate, and in theory would allow for a more robust and facile electron 
transfer.  To this end, the elemental composition of the surface was characterized with an atomic-
force microscope (AFM) and X–ray photoelectron spectra (XPS); the electrochemical properties and 
charge transfer at the interface of the electrolyte/Mn12–(methacrylate)–Si(100) electrode/Si structure 
were investigated with a cyclic voltammeter (CV) and electrochemical impedance spectra (EIS) 
[17].  
 
II. Experiments 
 
General:  

All chemical and solvents were used as received; all preparation and manipulations were 
performed under aerobic conditions, except as otherwise noted. The substrates were n–type Si(100) 
(Ultrasil Corporation, 0.001–0.002 ohm cm−1). [Mn12O12{CH2C(CH3)COO}16 

(H2O)4]⋅4CH2C(CH3)COOH⋅CH2Cl2, (Mn12–(methacrylate) was synthesized as described elsewhere 
[18]. 
 
 
 



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H–terminated Si(100) surface preparation, (Si–H) 
Si(100) wafers (1x1 cm2) were cleaned in an ultrasonic bath using solvents toluene, acetone, 

isopropanol and water for 10 min each. The wafers were dried in a stream of flowing dinitrogen. 
Si(100) pieces were then oxidized at high frequency for 5 min (each wafer side) in a plasma cleaner 
(Harrick PDC–32G), followed by dipping in an aqueous solution of HF (1%) for 3 min, and dried in 
a stream of dinitrogen. 

 
Mn12–(methacrylate) clusters on Si(100), Mn12–(methacrylate)−Si(100) 

H–terminated Si(100) was soaked in a solution of Mn12–(methacrylate) and benzoyl 
peroxide (BPO) in dichloromethane (CH2Cl2) (1.0 mmol L–1) at 60 °C for 1 h under dinitrogen 
protection. The substrates were washed twice with CH2Cl2 in an ultrasonic bath for 10 min, and 
dried under flowing dinitrogen. 
 
Surface characterization 

An AFM (Veeco, Nanoscope IIId Digital Instruments, Santa Barbara, CA) was operated in 
the tapping mode; the images were analyzed using software (NanoScope). The root-mean-square 
(rms) result for each substrate was calculated for at least three samples and in three areas. 
CV was performed with a potentiostat (Autolab PGSTAT10) and a conventional three–electrode 
system; all measurements were undertaken near 23 oC. The reference electrode was constructed on 
sealing a Ag/AgCl wire into a glass tube with a solution of KCl (3 mol L–1). The CV of Mn12–
(methacrylate) clusters was measured at scan rate 0.100 V s–1, in a solution of NBu4ClO4 in 
acetonitrile (0.25 mol L–1). The CV of Mn12–(methacrylate)−Si(100) were measured with a n–type 
Si(100) working electrode (1 cm x 1 cm) in an enclosed and grounded Faraday cage. A small area of 
the working electrode was wetted with the electrolyte to maintain a small overall area of 
measurement; this practice ensured that the RC time coefficient of the electrochemical cell was 
sufficiently small that rapid kinetic events were accurately measured. A bare silver wire served as 
the counter/reference electrode; this electrode was prepared on sonicating Ag wire in aqueous NH3 
(7.0 mol L–1), rinsing it in deionized water and ethanol, and sonicating it in dichloromethane. The 
prepared wire was placed inside a polypropylene disposable pipet tip (10 µL) containing an 
electrolyte solution (KCl, 3 mol L–1, ca. 5 µL). The working electrode was mounted on a Cu plate 
with a Ga–In eutectic to provide electrical contact through the back side of the wafer. A 
polypropylene micropipette tip, containing an Ag counter/reference electrode was filled with the 
electrolyte solution [19] (S2, Supplementary Information). 
EIS were measured with a potentiostat/frequency analyzer (Autolab PGSTAT10). The AC voltage 
amplitude was 10 mV; the voltage frequencies used for EIS measurements ranged from 20 kHz to 
0.100 Hz. The applied potential was −0.47 V vs. Ag/AgCl. Integration durations were set such that 
at least five cycles were analyzed at each point during each 1 s. 
XPS were recorded (Thermo K–Alpha) with monochromated X–rays (12 kV, 6 mA), spot size 400 
µm and takeoff angle 90° relative to the surface, with a typical duration 2−7 min in total of 
exposure per spot (typically three spots) to minimize beam damage. The binding energy was 
calibrated on centering the C 1s signal at 285 eV. Surveys were effected with pass energy 200 eV 
whereas high-resolution spectra were acquired with pass energy 50 eV. Typical pressures during 
analysis were less than 10− 8 Torr. 
 
 
 
 



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III. RESULTS AND DISCUSSION 
 

Our synthetic approach directly onto the silicon surface took advantage of functionalization 
with the dodecamanganese cluster via hydrosilylation chemistry. The reaction path occurs 
presumably through homolytic cleavage of benzoyl peroxide to form two benzoyloxy radicals, 
which further decompose to carbon dioxide and aryl radical [20, 21] (Figure 1). The latter species 
abstracts a hydrogen atom from Si−H groups resulting in silicon radicals on the surface that 
rapidly undergo nucleophilic addition through unsaturated bonds [11, 20, 21].  

 

FIGURE 1. Reaction path for the preparation of Mn12–(methacrylate)−Si(100). 

AFM topographic characterization 
Both roughness and topographic traits of Mn12–(methacrylate)−Si(100) were measured with 

an AFM operated in tapping mode. The 3D profile of the surface shows several protruding 
features following functionalization with Mn12–(methacrylate) (Figure 2), which differs from an 
AFM image of hydrogen–terminated silicon featuring a flat surface (S3, Supplementary 
Information). 

 
 

 

 
 

FIGURE 2. Tapping−mode AFM images of Mn12–(methacrylate)−Si(100): (a) 3D image; (b) roughness. 
 

The topography of Mn12–(methacrylate)−Si(100) (average statistical roughness, Ra = 0.90 
nm) indicates larger roughness than of a hydride-terminated Si surface (Ra = 0.30 nm), and 

(a) (b) 



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correlates well with the vertically maximal extension of carboxylate substituents bound in an axial 
position at Mn(III) ions, as shown by X–ray crystallographic data for Mn12−(methacrylate): 1.04 nm, 
and Mn12–OAc: 0.8 nm [21]. The root-mean-square roughness amplitude (1.28 nm) was greater 
than for a H–terminated Si surface (0.10 nm).  
XPS results 

Given that Mn(III) ions produce JT elongations, this effect can be thoroughly assessed with 
XPS analysis that allow assignment of binding energies [22, 23]. Table 1 summarizes the signals for 
the elements present on the functionalized surface from a XPS survey (S4, Supplementary 
Information). 
 

TABLE 1. Binding energies obtained from X–ray photoelectron spectra of Mn12–(methacrylate)−Si(100) 
 

 assignment binding energy /eV 

Mn2p 2p½ 653.9 

 2p3/2 642 

C1s C–Si 285.2 

 O–C=O 292.9 

 CH3, CH2 286.9 and 288.7 

O1s COO–  532.5 

 Mn–O 530 

Si2p 2p3/2 99.7 

 2p½ 100.4 

 
The XPS of Mn12–(methacrylate)−Si(100) has two lines at 653.9 and 642 eV, which are 

assigned to Mn 2p signals corresponding to excitation of 2p½ and 2p3/2, respectively. The main 
feature (experimental data) centred at 642 eV shows two components at 642.1 and 644.7 eV on 
deconvolution of the Mn 2p feature, ascribed to oxidation states Mn(III) and Mn(IV), respectively 
(Figure 3). The intensity ratio of Mn(III)/Mn(IV) signals is approximately 2, in accordance with the 
ratio Mn(III)/Mn(IV) for the molecular core. 



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FIGURE 3. High-resolution XPS of the Mn 2p region in Mn12–(methacrylate)−Si(100). 

 
The Si 2p region is a reliable indicator of grafting on the surface. The XPS survey displays 

well resolved Si 2p3/2 / Si 2p½ spin-orbit doublets of elemental silicon (99.7 and 100.4 eV). A line at 
103.3 eV is attributed to oxidized Si, likely due to some free Si−H bonds (umbrella effect on 
grafting bulky molecules such as Mn12 clusters), so that they become oxidized by adsorbed water 
and atmospheric adventitious trace O2 (during or after reaction) (S5, Supplementary Information). 
This observation might explain why the O 1s XPS ratio is somewhat greater than expected, 3:1, 
from 32 oxygen atoms in methacrylate molecules, 4 oxygen atoms from H2O molecules (532.5 eV), 
12 oxygen atoms from the Mn12O12 core (530 eV). The C region exhibits four components, shown on 
deconvolution of the principal C 1s line (285 eV) 285.2 eV, (C–Si) 292.9 eV, (O–C=O) 286.9 eV and 
288.7 eV (aliphatic backbone) [24] (S6, Supplementary Information). 

If the Mn12–(methacrylate) clusters were all spatially oriented with the Mn12 core parallel to 
the surface through the JT axis, one would expect a correlation between the orientation of Mn12–
(methacrylate)–Si(100) through the Si 2p and Mn 2p XPS data. This correlation is obtainable with 
simple calculations and the following structural parameters: a) Si(100) lattice parameter a = 5.42 Å 
and Mn12–(methacrylate) cluster diameter about 16.93 Å; b) on assuming an entirely Si(100) surface 
as tightly packed implying binding of only one carbon atom to the Si(100) surface, exclusion of 
overlap between molecules, and area ratios of maximum extent for each molecule. The resulting 
monolayer area ratio of covered to not covered is about 0.64, so that each Mn12–(methacrylate) 
cluster blocks 24 Si sites.ç 
 
Electrochemical measurements  

The CV plot of Mn12–(methacrylate) in acetonitrile has several cathodic and anodic waves 
matching those reported for [Mn12O12(O2CR)16(H2O)4], (R = Me, Et, Ph) (Figure 4). 



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FIGURE 4. Cyclic voltammogram of Mn12–(methacrylate) using Ag/AgCl as reference electrode in NBu4ClO4 
(0.25 mol L –1) in acetonitrile, scan rate 0.100 V s–1. 

The following reactions summarize the electron transfers proposed to occur in solution at 
the Mn12O12 core [25, 26] (1). 

 
[Mn12O12]+  [Mn12O12]  [Mn12O12]– → [Mn12O12]2– → [Mn12O12]3–                    (1) 

 
The transformations involving oxidation and three subsequent reductions are likely centred 

at the outer Mn(III) and cubane Mn(IV) ions, respectively. The thermodynamic preference for 
reduction of Mn(III) to Mn(II) over Mn(IV) to Mn(III) indicates that the latter process leaves 
unaffected the cubane Mn(IV), as it is inhibited because of the large reorganization energy. As the 
Mn(IV) ions are each bound to five hard O2− ions, they favor higher oxidation states, which disfavor 
reduction to Mn(III). If the reduction to Mn(III) ion occurred, it would generate a JT distortion 
causing strain in the rigid Mn(IV) cubane. Conversely, little perturbation of the Mn12O12 core on 
reduction of an outer Mn(III) ion is observed [14]. To acquire an understanding of the reactivity of 
the functionalized silicon surfaces, we initially tested a cell (S2, Supplementary Information) with 
dropping CH2Cl2 (electric permittivity, εo = 8.93), acetonitrile (MeCN, electric permittivity, εo = 37.5) 
and tetrahydrofuran (THF, electric permittivity, εo = 7.58), but the drop required to effect a contact 
between the working electrode (surface as prepared) and the Ag counter/reference electrode failed 
to form, likely because of the similar chemical affinities of these solvents with the surface nature 
upon functionalization. Additionally, CH2Cl2 and MeCN readily evaporate during measurement 
with the working electrode. With THF as solvent, the functionalization decomposes to native Si 
oxide, shown by XPS survey signals of oxygen atoms (S7, Supplementary Information). In contrast, 
in an aqueous medium both the shape and stability of the drop (H2O electric permittivity, εo = 80.1) 
significantly improved the electrochemical experiments. The CV of Mn12–(methacrylate)−Si(100) 
has two cathodic signals at −0.76 and −0.44 V, with no matching oxidative signals, indicating 
chemical irreversibility (Figure 5). These signals are tentatively assigned to processes 
Mn(IV)/Mn(III) and Mn(III)/Mn(II) [25, 26]. The calculated charge at –0.44 V is 3.14 x 10–5 C cm–2.  
 



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Ciencia y Tecnología, 31(1): 26-37, 2015- ISSN: 0378-0524 33	

 
FIGURE 5. Cyclic voltammograms of Mn12−methacrylate−Si(100) with a piece of n–type Si semiconductor as 

working electrode in KCl (3 mol L–1) at varied rates of potential scan. 
 

Although CV measurements were implemented in water that might be counterproductive 
because of prospective corrosion of the surface, Mn12–(methacrylate)−Si(100) underwent no 
apparent surface decomposition, as demonstrated with varied scan rates, indicating robustness of 
Si−C and the metal core (Figure 5). Furthermore, blank experiments performed with non–
hydrogen− and hydrogen–terminated Si(100) electrodes under similar conditions of measurement 
used for Mn12–(methacrylate)−Si(100) (S8, Supplementary Information) were devoid of cathodic or 
anodic waves over the entire potential sweep.  

Electrochemical impedance is generally measured on applying a sinusoidal AC 
perturbation of potential over the applied base potential. This perturbation involves a wide 
frequency range to probe the various elements and their time coefficients in an investigated system 
[27, 28, 17, 29]. EIS of Mn12–(methacrylate)−Si(100) were performed with AC modulation and 
frequency range 20 kHz to 0.100 Hz. The Nyquist plots (Figure 5) were fitted to an equivalent 
circuit model used by Creager et al. [30]. Using ideal elements in the equivalent circuits for 
electrochemical systems presents difficulties in processing the data because of the non–linearity of 
real systems; for that reason, constant–phase elements (CPE) are used in proposed equivalent 
circuits [27]. The equivalent-circuit model includes a series resistance (resistance of both the 
electrolyte solution and the series resistance from cables and contacts, RSOL), the double–layer 
capacitance (Helmholtz capacitance, CDL), and charge transfer or polarization resistance (RCT), and 
adsorption pseudocapacitance (CAD). The double–layer capacitance is in parallel with the charge-
transfer resistance (Inset, Figure 6). RSOL comprises the resistance between the reference electrode 
and the Mn12–modified silicon electrode and the resistance arising from cables and contacts. 
Importantly, to minimize the variation of RSOL for every measurement, the position of the two 
electrodes and the distance between the two electrodes were maintained constant; the preliminary 
results are listed in Table 2. The Nyquist plot for Mn12–(methacrylate)−Si(100) is a semicircle of 
which the value on the real axis (in–phase impedance) at the high-frequency intercept yields RSOL 
(24.9 Ω). The value on the real axis at the other (low-frequency) intercept is the sum of the 
polarization resistance and the solution resistance; the diameter of the semicircle is hence equal to 
the polarization resistance (348 kΩ), and for hydrogen–modified Si is 150 kΩ. RCT is larger for 



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Mn12−modified than for H−Si(100) because the film thickness increased upon Mn12 tailoring, which 
has a large reorganization energy and a sluggish electron transfer (Figure 6). For non-hydrogen- 
terminated Si, the insulating native oxide causes electron transfer to be slow, which produces an 
electrical resistivity several orders of magnitude greater than for functionalized Si. The capacitive 
double−layer (660 nF) of Mn12−(methacrylate)−Si(100) is larger than of H–terminated Si (129 pF) 
(S9, Supplementary Information). To calculate the electron–transfer rate coefficient of Mn12–
(methacrylate)−Si(100) we used the following equations (2−5) [30, 31], 
 

𝐶!" =  (𝐶 𝐴) 𝐴       (2) 
 

𝐶!" =  (𝐹
!𝐴Γ)

4𝑅𝑇        (3) 

 

𝑅!" =  2𝑅𝑇 (𝐹!𝐴Γ𝑘!")
       (4) 

 
in which CDL denotes the double–layer capacitance, C/A is the double–layer capacitance per unit 
area, A is the electrode area, Γ is the coverage of electroactive species per unit area, CAD is the 
adsorption pseudocapacitance, RCT is the charge–transfer resistance; the remaining quantities have 
their conventional significance. The rate coefficient for electron transfer is obtained with equation 
(5).   
 

𝑘!" = !
(! !!" !!")

      (5) 
 

 

 
 

Figure 5. Nyquist plot of Mn12–(methacrylate)−Si(100). The red circle (solid line) represents 
experimental data; the dotted lines correspond to the fit. The inset shows the equivalent circuit 

model. 
 



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kET (2.6 x 10−2 s–1) for Mn12–(methacrylate)−Si(100) indicates a slow electron transfer, which might be 
attributed to electronic and structural limiting factors. In related systems, the rates of electron 
transfer in ferrocene–containing alkanethiolate monolayers on gold electrodes are about 9 −13 s−1, 
and for zinc(II) porphyrins over Si on the order of 104 s−1 [30, 29].  
 
 

Table 2. Best fitted equivalent-circuit parameters to impedance data in the complex plane at the 
potential maximum for Mn12–(methacrylate)−Si(100). 

Rsol / Ω CDL / nF RCT / kΩ CAD / µF kET / s–1 

24.9 660 348 55 0.026 

 
IV. CONCLUSION 

 
We demonstrate the facile and direct chemisorption of Mn12–(methacrylate) onto H−Si(100) 
through covalent Si−C bonds to form Mn12–(methacrylate)−Si(100) as described with AFM, XPS 
and electrochemical data. Mn12–(methacrylate)−Si(100) is electrochemically active, highlighting the 
advantages of transition elements on a surface. CV and EIS findings indicate that Mn12–
(methacrylate) on a surface has inherent electronic and structural features that cause slow electron 
transfer. Future work in this area will focus on anchoring clusters of less nuclearity and varied core 
geometry such as Mn6.  

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ACKNOWLEDGEMENTS 

Project Nº 115–B1–168 from the Vicerrectoría de Investigación, Centro de Electroquímica y 
Energía Química (CELEQ), and Escuela de Química, Universidad de Costa Rica provided support 
of this work. 

We thank M.Sc. Alejandra Sánchez and Dr. Sergio A. Paniagua at Georgia Institute of 
Technology, USA, for recording XPS, Dr. Daniel Azofeifa (CICIMA) and M.Sc. Roberto Urcuyo 
(CELEQ) for fruitful discussion. 
 

 



DIRECT FUNCTIONALIZATION OF Mn12-(METHACRYLATE) CLUSTERS ON Si(100)	

Ciencia y Tecnología, 31(1): 26-37, 2015- ISSN: 0378-0524 37	

SUPLEMENTARY INFORMATION 

Drawing of Mn12–OAc structure, electrochemical cell setup, AFM image of hydrogen–
terminated silicon, survey XPS of Mn12–modified silicon, high-resolution XPS of O 1s, C 1s and O 
1s regions (reaction in THF) in Mn12–(methacrylate)−Si(100), cyclic voltammogram of non-
hydrogen terminated n–type Si(100) electrode, and Nyquist plots of passivated H−Si(100) electrode 
are available in the Supplementary Information.