SUPPORTING INFORMATION. Disposable ATR-IR Crystals from Silicon Wafer: A. Versatile Approach to Surface Infrared. Spectroscopy

Transcription

1 SUPPORTING INFORMATION Disposable ATR-IR Crystals from Silicon Wafer: A Versatile Approach to Surface Infrared Spectroscopy Engin Karabudak1,*, Recep Kas2*, Wojciech Ogieglo3, Damon Rafieian4, Stefan Schlautmann1, R.G.H. Lammertink4, Han (J.G.E.) Gardeniers1, Guido Mul2. 1 Mesoscale Chemical Systems group, 2Photo Catalytic Synthesis Group, Technology Group, 4 3 The Membrane Soft matter, Fluidics and Interfaces, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands; Frensel Equations: ( ) (1) ( ) (2) r is the reflection coefficient, R is reflectance, n1 and n2 the refractive indices of incident and transmitted media, and θi and θt the angles of incidence and refraction.

2 Hand Cut Silicon Wafers: The silicon wafers are cut into desired dimensions simply by using a scriber with a sapphire crystal tip to scratch the wafer from the edge and subsequently-break off pieces by putting a metal wire under the wafer, as shown in Figure SI 1. The silicon wafer is divided into two pieces along the scratch by applying force from both sides of the scratch. By applying this procedure silicon wafer pieces with any desired dimension can be obtained. Scheme SI 1 : Procedure for manual cleaving of silicon wafer ATR-IR spectra of water and the organic compounds isopropyl-alcohol (IPA) and 1,8-diazabicyclo- [5.4.0]undec-7-ene ( DBU) are taken by using these manually cleaved silicon pieces as IREs. Results are shown in Figure SI 1.

3 Absorbance (a.u) Absorbance (a.u) 0.10 a Water Wavenumber (cm -1 ) 0.10 b IPA Wavenumber (cm -1 )

4 Absorbance (a.u) 0.10 c DBU Wavenumber (cm -1 ) Figure SI 1 : ATR-IR spectra of a) water b) IPA c) DBU taken with manually cleaved silicon. The peaks at 3373 cm -1 and and 1641 cm -1 in the spectrum of water are assigned to O-H stretching and bending vibrations. In the spectrum of 2-propanol the broad peak at 3343 cm -1 and the peaks between 3000 cm -1 and 2800 cm -1 are assigned to O-H and C-H stretching vibrations, respectively. The peaks at 1466 cm -1 and 1379 cm -1 are assigned to bending modes of the CH 3 group. The broad peak centered at 1300 cm -1 and the weak peak at 1340 cm -1 are assigned to C-O-H and C-H deformation vibrations, respectively 1. The peaks at 2921 cm -1 and 2850 cm -1 are assigned to stretching of the C-H bonds. The sharp peak at 1616 cm -1 is assigned to stretching of the C=N bond. The peaks below 1500 cm -1 are consecutive vibrations of the whole molecule through bending stretching of the bonds and the positions of the peaks agrees quite well with the literature 2. Preparation of Titania-PVA composite films: Initially 1 gram of commercial TiO 2 -p25 (Aeroxide ) and 10 gram of PVA ((Sigma-Aldrich, average MW: 13,000-23,000, and 87-89% Hydrolyzed) as the steric stabilizer and viscosity enhancer were dissolved in 50 ml of 2-propanol and 50 ml of demi water. Subsequently, the suspension was stirred overnight leading to a high homogeneity. Next, the

5 ph of the suspension was adjusted to 3 by adding acetic acid followed by sonication for 30 minutes prior to spin coating of the silicon pieces, which were previously immersed in nitric acid (99%) for 10 minutes followed by rinsing and drying. Finally the chips were coated by using a spin coater (Laurell ) operating at 2000 rpm for 1 minute. The Si pieces were treated at 120 C in static air, and then two cycles of annealing at 250 C for 20 minutes with a 10 C/minute ramp rate were applied. Finally, the coatings were sintered at 500 C for 2 hours, applying a 2 /minute ramp rate, open to air. The wafers were allowed to cool down in the oven and infrared spectra were recorded after each thermal step. The thickness of the coating was measured by surface profilometry (Metrology VEECO, Dektak 150). The electron microscopy images were taken using a JEOL JSM-5600LV Scanning Electron Microscope (SEM). Preparation of the PS films: Polystyrene thin films (molecular weight g/mol, Sigma Aldrich, also determined with Gel Permeation Chromatography,) were prepared via a spin coating method at 2000 rpm from toluene (Sigma Aldrich) solutions, using concentrations varying between 1 and 5 % (w/w). Each time approximately 0.5 ml of the polymer solution was used to coat the silicon wafer. A M-2000X Spectroscopic Ellipsometer by J.A. Woolam, Co., Inc. was used to measure film thickness with a maximum error of ±2 nm. Optical dispersion of the material was fitted to a well-known Cauchy formula and the wavelength range employed was nm, where polystyrene is transparent. The optical model used took into account the presence of approximately 2 nm of native silicon oxide on the silicon wafer, while the optical dispersion of crystalline silicon was taken from literature 3 All of the prepared films were characterized by a low depolarization factor indicating very uniform thickness, with roughness varying in the order of less than 0.5%. The average refractive index of the prepared films was determined to be ± which is in a very good agreement with literature 3, 4.

6 Intensity (a.u) Infrared spectrum of pure PVA The spectrum of pure PVA, taken from the silicon wafers cut with a dicing machine, is given in Figure SI 2. The peaks at 1249 cm -1 and 1736 cm -1 are assigned to C-O and C=O stretching of acetate groups present in PVA due to incomplete hydrolysis. The band at 1713 cm -1 which can be seen as a shoulder in the pure spectrum of PVA is assigned to carbonyl groups in the polymer in addition to the contribution of the carbonyl group of acetic acid. The peak at 1570 cm -1 is assigned to carbonyl groups of the acetate group due to the presence of sodium acetate and deprotonated acetic acid. The broad band between cm -1 is attributed to O-H stretching modes, related to both TiO 2 surface hydroxyl groups and OH-groups in PVA. The absorption between 3000 and 2800 cm -1 is due to C-H vibrations. The band centered at 1431 cm -1 is assigned to the bending mode of the CH 2 group in PVA. The bands at 1325 cm -1 and 1433 cm -1 are assigned to C-H deformation modes associated with O-H groups and CH 2 deformation vibrations of PVA PVA Wavenumber (cm -1 ) Figure SI 2 : ATR-IR spectrum of PVA Band assignments of PS films

7 Polystyrene was chosen to study the linearity in spectral intensity as a function of thickness, because it is a well-studied macromolecular system frequently employed in fundamental research. It is also known to form very uniform films, down to the ultra-thin range (<100 nm) when spin coated on silicon wafers or glass substrates. Since it is a fully amorphous glassy polymer with an easily accessible glass transition temperature of 373 K, it often serves as a model system for instance in gas sorption 5, nano-confinement 6, mechanical properties 7 or polymer chain conformations 8. In the infrared spectra of the PS films, the bands at 2923 cm -1 and 2951 cm -1 are assigned to the C-H asymmetrical and symmetrical stretching vibrations, respectively. The absorption bands between 3000 cm -1 and 3100 cm -1 result from the C-H stretching modes in the aromatic rings of PS. At lower wavenumbers the sharp bands between 1490 cm -1 and 1600 cm -1 are attributed to the quadrant ring stretching and the C-C stretching in the aromatic ring, respectively. The sharp band at 1453 cm -1 is due to the contribution of semicircle ring stretching and CH 2 deformation. The combination bands of PS can be seen between 1670 cm -1 and 1950 cm -1 which agrees quite well with literature 9. Figure SI 3: SEM image of the titania-pva composite films after sintering at 500 C

8 Figure-SI4: Background spectra of an empty cell and on a KOH etched and straight-edge Si IRE; Full range, i.e. wavenrs cm -1 to 400 cm -1 ; Figure-SI5: ATR-IR spectra of PS thin films with thicknesses of 65 nm, 93 nm, 144 nm, 232 nm, 434 nm. References: 1. Miyata, H.; Kohno, M.; Ono, T.; Ohno, T.; Hatayama, F., Journal of Molecular Catalysis 1990, 63 (2), Karabudak, E.; Mojet, B. L.; Schlautmann, S.; Mul, G.; Gardeniers, H. J. G. E., Analytical Chemistry 2012, 84 (7), Herzinger, C. M.; Johs, B.; McGahan, W. A.; Woollam, J. A.; Paulson, W., J. Appl. Phys. 1998, 83 (6),

9 4. Brandrup, J.; Immergut, E. H.; Grulke, E. A., Polymer handbook. 4th ed.; Wiley: New York, Krimm, S.; Liang, C. Y.; Sutherland, G. B. B. M., Journal of Polymer Science 1956, 22 (101), Smirnov, L. V.; Kulikova, N. P.; Platonova, N. V., Polymer Science U.S.S.R. 1967, 9 (11), Laboratories, S. R., The Infrared spectra atlas of monomers and polymers. Sadtler Research Laboratories: Kumar, R. V.; Koltypin, Y.; Cohen, Y. S.; Cohen, Y.; Aurbach, D.; Palchik, O.; Felner, I.; Gedanken, A., Journal of Materials Chemistry 2000, 10 (5), Foster, G. N.; Row, S. B.; Griskey, R. G., Journal of Applied Polymer Science 1964, 8 (3),