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Laser induced functionalization of organo/carbon interfaces for selective adsorption of Au nanoparticles in micro-sized domains Martin Schade, Steffen Franzka, and Nils Hartmann Langmuir, Just Accepted Manuscript • Publication Date (Web): 21 Apr 2017 Downloaded from http://pubs.acs.org on April 23, 2017

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Laser induced functionalization of organo/carbon interfaces for selective adsorption of Au nanoparticles in micro-sized domains Martin Schade,1-2 Steffen Franzka,2-3 Nils Hartmann1-3,1

1 2

Fakultät für Chemie, Universität Duisburg-Essen, 45117 Essen, Germany

Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, 47057 Duisburg, Germany 3

Interdisciplinary Center for Analytics on the Nanoscale (ICAN), Universität Duisburg-Essen, 47057 Duisburg, Germany

Abstract: Laser microprocessing of highly oriented pyrolytic graphite (HOPG) in conjunction with chemical functionalization routines are used to fabricate functional micro-sized domains. Infrared and Auger electron spectroscopy, contact angle measurements and electron microscopy are used for characterization of laserfabricated structures. HOPG samples are coated with alkylsiloxane monolayers. Laser-induced bromination of coated HOPG samples in gaseous bromine is carried out using a microfocused laser beam at a wavelength of 514 nm and 1/e2 laser spot diameter of about 2 µm. Subsequent azidation and amination results in functional domains with sizes in the range of 1.2 µm to 40 µm and more. At low laser powers and irradiation times fully functionalized circular-shaped structures are formed. At high laser powers and irradiation times laser processing results in decomposition of the organic monolayer and substrate in the center of the structures yielding donutshaped structures. After laser processing and chemical transformation Au nanoparticles are selectively adsorbed onto the functional domains. This provides an opportunity to build up functional nanoparticles micro-arrays on carbon-based materials, e. g. for applications in sensing and electrocatalysis. *

Corresponding author, Phone: +49 203 379 8033, Fax: +49 203 379 8159, E-mail: [email protected]

ACS Paragon Plus Environment

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1. Introduction Graphite is the most stable allotrope of carbon under standard conditions and has a long history of industrial and commercial applications, both as bulk material and as additive in composites, e. g. for electrode materials in batteries and fuel cells.1-3 Moreover, in the last decades related carbon nanomaterials such as graphene attracted considerable attention due to their electronic, mechanical and thermal properties.4-5 Generally, the peculiar properties make sp2 carbon nanomaterials highly interesting for applications in electronics and sensors. The use of graphene in various electronic components, for example, has already been demonstrated.6-7 Also graphene-base electrochemical sensors have been developed.8-9 Chemical functionalization offers an opportunity to tailor the electronic properties of sp2 carbon nanomaterials.10 Lee et al., for example, followed a promising approach based on coating routines employing organic self-assembled monolayers (SAMs).11 The application of SAMs in organic electronics as active materials or insulators has also been shown in several previous contributions.12-13 The preparation of SAMs with laterally alternating chemical terminations on sp2 carbon materials is beneficial for engineering of complex surface structures with applications in

a

broad

variety

of

applications

including

electronics,

sensorics

and

electrocatalysis. Here we present a laser patterning technique for direct chemical functionalization of alkylsiloxane monolayers on highly oriented pyrolytic graphite (HOPG) samples. HOPG is a well-defined model system for bulk graphite. It is also commonly used as basic material in the preparation of graphene via exfoliation. In this respect it represents an important reference system. Laser patterning of ultrathin organic coatings has attracted significant attention in the last decade.14-29 Apart from the unique properties of SAMs and their prospects in micro- and nanofabrication, the general interest of these studies originates from the powerful technical features of laser patterning techniques, which makes them an indispensible tool in many fundamental studies and various technical and medical applications.30-32 Sequential patterning techniques employing focused laser beams provide fast writing speeds and a high flexibility.24-28 Also, parallel processing of large-areas has been demonstrated using micro lens arrays and interference patterns.18-20 More recent efforts addressed nanopatterning of organic monolayers,


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e. g. taking advantage of nonlinear effects resulting from multiphoton absorption processes or photothermally induced reactions.24-28 The high thermal and chemical stability of silane-based SAMs offer unique opportunities in laser fabrication of nanostructured chemical patterns and architectures.27-28 Photothermal micro- and nanoprocessing of alkylsiloxane monolayers, for example, has been demonstrated using ordinary microfocused CW lasers at wavelength in the visible range.28 Minimum structure sizes are below 100 nm.27 The approach described in this contribution is based on our previous work focusing on photothermal bromination of alkylsiloxane SAMs on silicon substrates using a microfocused laser beam at a wavelength λ = 514 nm.14-15 Bromination opens up an avenue towards various chemical functionalities via wet chemical transformation in order to engineer surface properties such as the wettability and the chemical affinity,15 e. g. to selectively couple nanoscopic building blocks, such as noble metal nanoparticles,33 and build up micro-arrays for applications in sensing and electrocatalysis.

2. Experimental section For all experiments HOPG purchased from MaTecK in ZYA quality (size 10 mm x 10 mm, thickness 1 mm, mosaic spread 0.4°± 0.1°) is used. Thin samples are cleaved carefully with a scalpel from the original HOPG block. Subsequently, the upper layers of the samples are removed using a scotch tape to get a uniform surface. Finally the samples are cleaned via successive dipping in ethanol and toluene (both pa. VWR Prolabo) and dried in a stream of high purity argon (5.0, Air Liquide). For coating with octadecylsiloxane (ODS) monolayers the samples are put in a commercial low-pressure plasma device (Femto QLS with a 40 kHz microwave generator, Diener) for oxygen plasma treatment. Experimental parameters are optimized in order to ensure activation of samples but avoid significant decomposition of the surface (plasma power of 5 W, exposure time of 6 s, oxygen pressure of 0.5 mbar).34-36 Immediately after plasma treatment the samples are introduced in a glove box under argon atmosphere and immersed into a freshly prepared 2.5 mM solution of n-octadecyltrichlorosilane (OTS, ABCR-Chemicals) in


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dried toluene. After 24 h at 4°C the samples are removed and subsequently rinsed with toluene and ethanol and dried in a stream of high purity argon. For laser experiments the coated samples are placed in a reaction cell in front of a laser window (BK7 glass with anti-reflective coating for 514 nm). After evacuating down to a pressure of about 10-3 mbar over night, the cell is filled with bromine gas up to a pressure of about 30 mbar. Liquid bromine (p.a., Acros Organics) is used as source for the gaseous bromine. Then the reaction cell is integrated in an optical setup for laser induced bromination (Figure 1). All patterning experiments are carried out at room temperature. The optical setup consists of an Ar+-laser (Innova 90, Coherent) operating at λ = 514 nm, an acousto-optical tunable filter (AOTF), a standard microscope objective (Achromat, 10x, 0,25 NA, ∞/0, Zeiss) and three stepper motor stages (MT65, Micos) on which the reaction cell and the microscope objective are mounted. The laser beam is focused with the microscope objective through the laser window of the reaction cell onto the sample surface. The measured 1/e2 laser spot diameter reached in the focal plane in this way is 2 µm. For measurement of the focal laser spot diameter a commercial CCD camera system is used (Spiricon, Laserbeam diagnostics SP6204). Note, the detector array of the CCD camera has a pixel size of 4 µm x 4 µm. A microscope objective (PL 160x / 0.95 ∞/0, Leitz) has been used to image the focused beam onto the camera detector array. This expands the measurement range of the camera to include smaller beams, which could not be ordinarily measured due to the pixel size of the detector array. For calibration a stage micrometer (20/100, 5 µm, LOMO) has been employed. The resolution in this configuration is 0.05 µm/pixel. Laser power (P) and irradiation time (τ) are controlled with the AOTF. Generally, processing with this laser setup can be carried out either in pulse-mode operation or in continuous-mode operation. In this work pulse-mode operation is used. The sample is moved in the focal plane to predefined positions. Once a given position is reached, the AOTF is used to generate a single laser pulse at a certain laser power (50-800 mW) and a selected irradiation time (0.01-20 ms). Repeating this procedure multiple times allows one to fabricate patterns and screen the laser parameters. Wet chemical transformation of the locally brominated areas is achieved in a two-


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step procedure: azidation by substitution with sodium azide (> 99.5%, Sigma Aldrich) in N,N-dimethylformamide (DMF, > 99%, AppliChem) followed by reduction of the azide groups with lithium aluminum hydride (> 97%, Sigma Aldrich) in diethylether (p.a., Fisher Scientific) yielding amine groups.15 Gold nanoparticles (Au NP) with an average particle size of 16 nm produced via the citrate method are used for selective adsorption onto the amine-terminated areas.33 For this purpose, the samples are immersed into a Au NP solution with a total gold concentration of about 10 mg L-1 for 30 min. Sample characterization is carried out via scanning Auger electron spectroscopy (AES) using a PHI 660 from Physical Electronics for chemical analysis. The PHI 660 is also used for structural analysis via scanning electron microscopy (SEM). Further SEM analysis is performed using an ESEM Quanta 400 from FEI. For analysis the outer diameter of laser-fabricated structures in SEM images has been determined using the image processing software of IGOR pro 6 from WaveMetrics. Infrared reflection absorption spectroscopy (IRRAS) measurements are carried out with a Vertex 70 from Bruker with p-polarised light at an angle of incidence of 80° with respect to the surface normal. Static contact angle measurements are performed with a commercial contact angle goniometer, SURFTENS universal goniometer from OEG, and ultrapure water (18.2 MΩ) from a Millipore system each time taking a droplet volume of 10 µL.

3. Results and discussion For illustration, an overview of the functionalization procedure is shown in Figure 2. At first HOPG samples are coated with an ODS monolayer. The coating is characterized by contact angle and IRRAS measurements (Figure 3). IRRAS spectra of the ODS-coated HOPG surface show two intense peaks at 2852 cm-1 and 2921 cm-1 corresponding to the symmetric, vs(CH2), and antisymmetric, vas(CH2), stretching vibrations of the CH2-groups of the alkyl chains in the ODS monolayer. In addition, at 2958 cm-1 a weak peak corresponding to the antisymmetric CH3 vibration, vas(CH3), is visible (Figure 3a).37 Note, no asymmetric peak distortions as expected because of the semimetallic character of HOPG are evident in these data.38 In contrast to the ODS-coated samples, CH stretching absorptions are hardly


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discernible on uncoated HOPG samples. ODS-coated HOPG samples show a static water contact angle of Θs = 107°±5°, which is in reasonable agreement with literature values of ODS-monolayers on surface-oxidized silicon samples.39 For comparison, the static water contact angle of an uncoated, freshly cleaned HOPG sample is 80°±5° (Figure 3b-c).40 In conclusion, both, contact angle and IRRAS data point to a densely packed, ordered organic monolayer on the HOPG substrate.41-42 The IRRAS data provides no information on the nature of the bonding between the ODS-monolayer and the substrate. On glass and oxidic surfaces, alkylsiloxane monolayers are known to couple to the substrate via siloxane bridges, which form during monolayer growth.43-44 At first alkylsilanes are hydrolyzed to alkylsilanols. Subsequently, siloxane bridges are formed in a condensation reaction between alkylsilanol species and surface hydroxyl groups.44 Oxygen plasma treatment of HOPG and sp2 carbon nanomaterials is known to result in oxygen-containing surface functionalities, including epoxy groups, carbonyl groups and hydroxyl groups.34-36 Hence, the formation of siloxane bridges appears possible. Alkylsiloxane monolayers, however, also form on substrates, which are virtually devoid of hydroxyl groups if these substrates are hydrophilized before coating, e. g. on gold surfaces activated via UV-ozone exposure.45-46 This commonly is attributed to lateral crosslinking of alkylsilanol species on an ultrathin water layer, which is present on the surface of the hydrophilized substrate.44-46 Only few, if any, siloxane bridges between the monolayer and the substrate are formed in this case. Local bromination of the alkyl chains is carried out via laser induced microprocessing in a reaction cell with bromine gas atmosphere at a bromine pressure of about 30 mbar (Figure 2). In order to allow for selective adsorption of Au NPs onto the laser-functionalized domains, post-functionalization routines are employed.15 In the first step, bromine groups are quantitatively substituted by azide groups via substitution in a solution of sodium azide. In the second step, the azide groups then are reduced with lithium aluminum hydride to amine groups. In the third step, the aminated areas are covered by selective adsorption of citrate stabilized Au NPs. This also allows for convenient characterization of the laser-fabricated structures using SEM. Figure 4 shows AES data of every step of the chemical transformation and


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decoration procedure. For this purpose, a dense dot pattern has been fabricated at a laser power of P = 750 mW, an irradiation time of  = 15 ms, a distance of 25 µm between the dots. Subsequently this pattern has been further functionalized and decorated with Au NPs as described above. After every step, an area of 61 µm x 46 µm including 4 dots of the pattern has been analyzed using AES. In addition an area of the same size outside of the pattern has been analyzed for reference. Note, that AES is a surface-sensitive technique, which provides information on the first few nanometers of the surface layers of the sample.47-48 The uncoated HOPG sample only shows a C KLL peak at 338 eV. After coating with ODS, an additional O KLL peak at 516 eV and a Si LVV peak at 88 eV appear in the Auger electron spectrum. Note, the spectra taken outside of the pattern after every functionalization step are all similar to the spectrum taken after ODS-coating. This means that the chemical transformation discussed in the following is limited to the laser processed areas. After laser induced bromination a Br LMM peak at 1394 eV becomes visible in the spectrum. Note, that the signal-to-noise ratio in this spectrum is higher than in the other spectra. The C-Br bond is very sensitive to high electron currents.49 Hence the standard measurement parameters had to be adjusted in order to minimize damage and get a good signal intensity. This affects the overall quality of the spectrum. Adopting the measurement parameters, however, allows one to verify local bromination. After wet chemical substitution of the bromine groups with azide groups, the bromine peak disappears in the Auger electron spectrum. Instead a N KLL peak at 388 eV appears indicating the successful formation of azide groups in the investigated area. After reduction with lithium aluminum hydride the spectrum essentially remains unchanged. In agreement with lower nitrogen content, however, the intensity of the nitrogen peak decreases slightly. For selective nanoparticles adsorption onto the aminated areas the samples are immersed in a solution of citrate stabilised Au NPs. After selective adsorption of Au NPs, the Auger electron spectrum of the decorated area show Au MNN peaks at 2024 eV and 2110 eV. Note, all other peaks decrease in intensity, which points to dense decoration of the aminated area with Au NPs. Altogether, the AES results demonstrate successful laser induced bromination, chemical post-functionalization and selective nanoparticles adsorption. Further measurements using scanning AES are carried out in order to obtain laterally resolved AES data, i. e. chemical maps. For this purpose, local areas are


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brominated via laser microprocessing at P = 450 mW and τ = 1 ms, functionalized and covered with Au NPs. Figure 5 shows single laser-fabricated dots after azidation, amination and selective Au NPs adsorption. Note, no data after bromination is shown. Chemical mapping requires long measurement times of 10 h and more. Therefore the investigated areas are exposed to high electron dosages. This results in complete damage of the C-Br bonds, so that detection of bromine is not feasible. For analysis of the azidated and aminated areas, the N KLL peak at 382 eV has been chosen. The nitrogen map after azidation shows a low concentration of nitrogen in the center of the dot structure (Figure 5a). In adjacent areas around this inner structure a high concentration of nitrogen is visible as a bright ring with a diameter of about 8 µm. The chemical map after amination generally is very similar. The overall signal intensity of nitrogen, though, is much weaker (Figure 5b). This is very much expected if one compares the ratio of the number of nitrogen atoms in the azide and amine groups of 3:1. For chemical mapping of the structure coated with Au NPs the Au MNN peak at 2015 eV has been chosen (Figure 5c). In addition a SEM image of the investigated area is shown (Figure 5d). Overall these results show that laser microprocessing in gaseous bromine allows one to brominate and further functionalize microscopic areas. Moreover, all the structures and chemical maps in Figure 5a-d are of the same size and shape. In particular the N and Au structures in the chemical maps of the N KLL peak and Au MNN peak in Figure 5a-c are of the same size and shape as the structure shown in the SEM image. Hence, the dependence of the size and shape of the laser-fabricated structures can conveniently be carried out using SEM. SEM images of laser-functionalized and subsequently Au NPs coated structures are shown in Figure 6. Laser microprocessing is carried out at a constant laser power and distinct irradiation times. As evident, both the size and the shape of the laser-functionalized areas strongly depend on the laser parameters. Generally, two types of structures are observed. At low irradiation times fully functionalized micronsized domains are formed. The Au NPs form sharply confined circular-shaped structures. At a given laser power the diameter of these structures increases with increasing irradiation time. At high irradiation times, donut-shaped structures are formed. These structures show an inner region with significantly lower Au NPs coverage surrounded by an outer area with high Au NPs coverage. The diameter of


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the inner region is nearly constant irrespective of the laser irradiation time. The chemical maps in Figure 5a and b show a low nitrogen content in these areas and hence suggest that decomposition of the organic monolayer and the HOPG substrate takes place during laser processing. In contrast, the diameter of the outer area with high Au NPs coverage increases with increasing irradiation time. Figure 7a-b show plots of the outer diameters of the laser-fabricated structures at varying laser powers between 50 and 800 mW and irradiation times between 0.01 and 20 ms. The data has been obtained by analysis of SEM images as those, e. g., shown in Figure 6. Note, processing at high laser powers and long irradiation times, e.g., at P = 800 mW and τ > 2 ms, result in structures with diameters > 45 µm. These structures strongly overlap in the chosen laser pattern forming large areas homogeneously covered with Au NPs. Hence, no diameters of such structures are shown. Generally, at high laser powers and irradiation times donut-shaped structures with increasing outer diameter are observed (open symbols in Figure 7a-b). Outer diameters reach values well above 40 µm. Note, this is more then ten times bigger than the laser spot size of about 2 µm used for microprocessing. Note, fully covered circular-shaped structures in the experiments described here are observed only at low laser powers and irradiation times. It is, of course, well expect that large fully covered circular-shaped structures can be fabricated at larger laser spot sizes and lower intensities. Of particular interest, however, is the fabrication of small structures.24-27 This generally requires tightly focusing optics yielding small laser spot diameters. For this reason more detailed experiments at low laser powers in the range between 50 mW and 200 mW and short irradiation times between 0.05 ms and 2 ms are carried out revealing minimum structure sizes and the transition between fully covered circular-shaped and the donut-shaped structures (full symbols in Figure 7a-b). The smallest structure, that is obtained in these experiments, exhibits a diameter of d = 1.2 µm at a laser parameter set of P = 150 mW and τ = 0.05 ms. Note, even smaller structures are formed at lower laser powers and irradiation times, respectively. Generally, however, laser processing at these parameters results in irregular structures with inhomogeneous coverage of Au NPs. Clearly, a minimum structure size of d = 1.2 µm is significantly smaller than the laser spot diameter of 2 µm used here. This suggests a photothermal


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functionalization

process

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in

laser-induced

bromination

of

octadecylsiloxane monolayers on surface-oxidized silicon substrates (cf. Figure 2).1415

Generally, in photothermal patterning a microfocused laser is used in order to

locally heat the substrate surface and initiate thermally activated reactions.27 At irradiation times in the milli-/microsecond range, a stationary temperature profile is established. Because of the activated reaction the overall laser induced process exhibits a nonlinear dependence on the laser intensity. At high activation energies fabrication of nanostructures is feasible.24-27 In the case of surface-limited processes, e. g. considering photothermal decomposition of alkylsiloxane monolayers, the experimental data can be plotted in an Arrhenius-type diagram, ln(τ) vs. 1/T, where T represents the temperature reached at the edge of the structures as calculated on the basis of the underlying heat conduction equation.27 In the Arrhenius-type diagram all data collapse on a single line, which allows one to determine the activation energy as the key scaling parameter. In contrast, photothermal bromination of alkylsiloxane monolayers, considered here, is a complicated process depending on reactions, which take place in the gas phase and on the surface of the coated substrate (Figure 2).15 The reaction is initiated via photolysis of bromine molecules. The bromine atoms generated in this process rapidly diffuse in the gas phase over length scale of > 100 µm on a millisecond time scale. At short irradiation times the reaction between the photogenerated bromine atoms and the alkylsiloxane monolayer remains confined to the laser irradiated areas, where high temperatures are reached. The activation energy of this reaction, though, is comparatively low.15,50 Hence monolayer bromination also slowly proceeds at room temperature resulting in large brominated areas. Because of the complicated nature of the overall bromination reaction a simple analysis of the data on the basis of an Arrhenius-type diagram as reported for photothermal decomposition of alkylsiloxane monolayers is not feasible.

4. Conclusion A laser-assisted functionalization procedure for the fabrication of functional microsized domains on graphite is demonstrated. Depending on the laser parameters domain sizes vary in the range of 1-40 µm. Post-functionalization routines are


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chosen in order to selectively bind Au NPs. The procedure, however, is very flexible and can be adopted to bind a variety of other functionalities and nanoscopic components. This allows one to fabricate micro-arrays on carbon-based materials, e. g. for application as electrodes in sensing and electrocatalysis. The approach also is considered as a starting point to build up micro- and nanometer sized surface architectures on graphene-coated substrates or composites containing sp2 carbon nanomaterials, e. g. exploiting near-field techniques.

Acknowledgments Financial funding by the European Union and the Ministry of Innovation, Science and Research of the State of North Rhine-Westphalia in Germany (NETZ, Objective 2 Programme: European Regional Development Fund, ERDF) is gratefully acknowledged.


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(21) Rhinow, D.; Hampp, N. A. Patterned self-assembled monolayers of alkanethiols on copper nanomembranes by submerged laser ablation. Appl. Phys. A 2012, 107, 755-759. (22) Zhang, M. Y.; Shadnam, M. R.; Amirfazli, A. Direct laser patterning of selfassembled monolayer using elliptical laser beams: A theoretical parametric study. Opt. Laser Technol. 2011, 43, 1377-1384. (23) Belgardt, C.; Blaudeck, T.; von Borczykowski, C.; Graaf, H. Self-assembly of ordered colloidal nanoparticle films in few-micron wide laser-desorbed lines of octadecylsiloxane monolayers on silicon oxide surfaces. Adv. Eng. Mater. 2014, 16, 1090-1097. (24) Scheres, L.; Klingebiel, B.; ter Maat, J.; Giesbers, M.; de Jong, H.; Hartmann, N.; Zuilhof, H. Micro- and nanopatterns of functional organic monolayers on oxide-free silicon prepared by laser-induced photothermal desorption. Small 2010, 6, 1918-1926. (25) Klingebiel, B.; Scheres, L.; Franzka, S.; Zuilhof, H.; Hartmann, N. Photothermal micro- and nanopatterning of organo/silicon interfaces. Langmuir 2010, 26, 6826-6831. (26) Hartmann, N.; Franzka, S.; Koch, J.; Ostendorf, A.; Chichkov, B. N. Subwavelength patterning of alkylsiloxane monolayers via nonlinear processing with single femtosecond laser pulses. Appl. Phys. Lett. 2008, 92, 223111-1 223111-3. (27) Mathieu, M.; Hartmann, N.; Sub-wavelength patterning of organic monolayers via nonlinear processing with continuous-wave lasers. New J. Phys. 2010, 12, 125017-1 - 125017-21. (28) Hartmann, N.; Balgar, T.; Bautista, R.; Franzka, S. Direct laser patterning of octadecylsiloxane monolayers on surface-oxidized silicon substrates: indications for a phothothermal excitation mechanism. Surf. Sci. 2006, 600, 4034-4038. (29) Mathieu, M.; Schunk, D.; Franzka, S.; Mayer, C.; Hasselbrink; E.; Hartmann, N. Direct laser patterning of soft matter: photothermal processing of multilayered phospholipid films with nanoscale precision. Small 2009, 5, 2099-2104. (30) Bäuerle, D. Laser processing and chemistry, 4th ed., Springer, Berlin, 2011.


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(31) Chong, T. C.; Hong, M. H.; Shi, L. P. Laser precision engineering: from microfabrication to nanoprocessing. Laser & Photon. Rev. 2010, 4, 123-143. (32) Ali, M.; Wagner, T.; Shakoor, M.; Molian, P. A. Review of laser nanomachining. Laser Appl. 2008, 20, 169-184. (33) Bhat, R. R.; Fischer, D. A.; Genzer, J. Fabricating planar nanoparticle assemblies with number density gradients. Langmuir 2002, 18, 5640-5643. (34) Shin, Y. J.; Wang, Y.; Huang, H.; Kalon, G.; Wee, A. T.; Shen, Z.; Bhatia, C. S.; Yang, H. Surface-energy engineering of graphene. Langmuir 2010, 26, 37983802. (35) Nourbakhsh, A.; Cantoro, M.; Klekachev, A. V.; Pourtois, G.; Vosch, T.; Hofkens, J.; van der Veen, M. H.; Heyns, M. M.; De Gendt, S.; Sels, B. F. Single layer vs bilayer graphene: a comparative study of the effects of oxygen plasma treatment on their electronic and optical properties. J. Phys. Chem. C 2011, 115, 16619–16624. (36) Ashraf, A.; Wu, Y.; Wang, M. C.; Aluru, N. R.; Dastgheib, S. A.; Nam, S. W. Spectroscopic investigation of the wettability of multilayer graphene using highly ordered pyrolytic graphite as a model material. Langmuir 2014, 30, 1282712836. (37) Brunner, H.; Mayer, U.; Hoffmann, H. External reflection infrared spectroscopy of anisotropic adsorbate layers on dielectric substrates. Appl. Spectrosc. 1997, 51, 209-217. (38) Leitner, T.; Kattner, J.; Hoffmann, H. Infrared reflection spectroscopy of thin films on highly oriented pyrolytic graphite, Appl. Spectrosc. 2003, 57, 15021509. (39) Inoue, A.; Ishida, T.; Choi, N.; Mizutani, W.; Tokumoto, H. Nanometer-scale patterning of self-assembled monolayer films on native silicon oxide. Appl. Phys. Lett. 1998, 73, 1976-1978. (40) Wu, C.-J.; Li, Y.-F.; Woon, W.-Y.; Sheng, Y.-J.; Tsao, H.-K. Contact angle hysteresis on graphene surfaces and hysteresis-free behavior on oil-infused graphite surfaces. Appl. Surf. Sci. 2016, 385, 153-161. (41) Hoffmann, H.; Mayer, U.; Krischanitz, A. Structure of alkylsiloxane monolayers


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on silicon surfaces investigated by external reflection infrared spectroscopy. Langmuir 1995, 11, 1304-1312. (42) Sieval, A. B.; Demirel, A. L.; Nissink, J. W. M.; Linford, M. R.; Van Der Maas, J. H.; De Jeu, W. H.; Zuilhof, H.; Sudhölter, E. J. R. Highly stable Si-C linked functionalized monolayers on the silicon (100) surface. Langmuir 1998, 14, 1759-1768. (43) Onclin, S.; Ravoo, B. J.; Reinhoudt, D. N. Engineering silicon oxide surfaces using self-assembled monolayers. Angew. Chem., Int. Ed. 2005, 44, 62826304. (44) Sagiv, J.. Organized monolayers by adsorption. 1. Formation and structure of oleophobic mixed monolayers on solid surfaces. J. Am. Chem. Soc. 1980, 102, 92-98. (45) Allara, D. L.; Parikh, A. N.; Rondelez, F. Evidence for a unique chain organization in long chain silane monolayers deposited on two widely different solid substrates. Langmuir 1995,11, 2357-2360. (46) Vallant, T.; Brunner, H.; Kattner, J.; Mayer, U.; Hoffmann, H.; Leitner T.; Friedbacher, G.; Schügerl, G.; Svagera, R.; Ebel M. Monolayer-controlled deposition of silicon oxide films on gold, silicon and mica substrates by roomtemperature adsorption and oxidation of alkylsiloxane monolayers. J. Phys. Chem. B 2000, 104, 5309-5317. (47) Briggs, D.; Seah, M. P. Practical surface analysis: by Auger and X-ray photoelectron spectroscopy, Wiley, New York, 1983. (48) Hedberg, C. L. (Ed.) Handbook of Auger electron spectroscopy, Physical Electronics, Eden Prairie, 1995. (49) Moon, J. H.; La, Y.-H.; Shim, J. Y.; Hong, B. J.; Kim, K. J.; Kang, T.-H.; Kim, B.; Kang, H.; Park, J. W. Selective cleavage of the carbon−halide bond in substituted benzaldimine monolayers by synchrotron soft X-ray: anomalously large cleavage rate of the carbon−bromide bond. Langmuir 2000, 16, 29812984. (50) Thaler, W. A.; In Methods in free-radical chemistry, Huysser, E. S., Ed.; M. Dekker: New York, 1969, 121–225.


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Figure captions Figure 1: Schematic drawing of the experimental laser set-up (AOTF: Acousto-optical tunable filter). Figure 2: Schematic presentation of the experimental approach: laser-induced bromination and post-functionalization of alkylsiloxane monolayers on HOPG followed by selective adsorption of Au NPs. Figure 3: Characterization of the ODS monolayer on HOPG via a) IRRASspectroscopy, b) and c) water contact angle measurements. Figure 4: Auger electron spectra (bottom to top) of cleaned HOPG samples, after coating with ODS monolayers, after laser induced bromination, after azidation, after amination and after selective adsorption of Au NPs. Laser parameters for microprocessing are: P = 750 mW ,  = 15 ms, distance between dots: 25 µm. For spectral analysis an area of 61 µm x 46 µm is scanned. Figure 5: Chemical maps and SEM image of dot patterns: a) after azidation (N KLL at 382 eV), b) after amination (N KLL at 382 eV), c) after selective adsorption of Au NPs ( Au MNN transition at 2015 eV, d) SEM image of the same area as shown in c). Dot patterns are fabricated at P = 450 mW, τ = 1 ms and a bromine pressure of 30 mbar. Figure 6: SEM images of dot patterns fabricated at different irradiation times: a) 0.01 ms, b) 0.05 ms, c) 0.1 ms, d) 0.2 ms, e) 0.4 ms, f) 0.6 ms. All patterns are processed at a laser power of P = 600 mW and a bromine pressure of 28 mbar. After laser processing and functionalization, selective adsorption of Au NPs has been carried out. Figure 7: Diagrams displaying the dependence of the outer diameters of laserfabricated dots after laser-induced bromination of the ODS monolayer, subsequent post-functionalization and selective adsorption of Au NPs: a) fabricated at laser powers between 350 and 800 mW, b) fabricated at laser powers between 50 and 200 mW. All dots are created at a bromine pressure of 30 mbar. Open symbols indicate donut-shaped structures with an inner region void of Au NPs. Full symbols indicate circular-shaped structures, which are fully covered with Au-NPs. Lines are to guide the


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eyes only.


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Figure 1


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Figure 2


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Figure 3


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Figure 4


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Figure 5


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Figure 6


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Figure 7


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