Influence of Nanoparticle Surface Functionalization on the Thermal

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Influence of Nanoparticle Surface Functionalization on the Thermal Stability of Colloidal Polystyrene Films Gerd Herzog,*,†,‡ Mottakin M. Abul Kashem,† Gunthard Benecke,†,§ Adeline Buffet,† Rainer Gehrke,† Jan Perlich,† Matthias Schwartzkopf,† Volker Körstgens,⊥ Robert Meier,⊥ Martin A. Niedermeier,⊥ Monika Rawolle,⊥ Matthias A. Ruderer,⊥ Peter Müller-Buschbaum,⊥ Wilfried Wurth,‡ and Stephan V. Roth*,† †

HASYLAB at DESY, Notkestr. 85, D-22607 Hamburg, Germany Department Physik, Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany § Department of Biomaterials, MPI of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany ⊥ Physik-Department, Lehrstuhl für Funktionelle Materialien, TU München, James-Franck-Str. 1, 85748 Garching, Germany ‡

S Supporting Information *

ABSTRACT: The installation of large scale colloidal nanoparticle thin films is of great interest in sensor technology or data storage. Often, such devices are operated at elevated temperatures. In the present study, we investigate the effect of heat treatment on the structure of colloidal thin films of polystyrene (PS) nanoparticles in situ by using the combination of grazing incidence small-angle X-ray scattering (GISAXS) and optical ellipsometry. In addition, the samples are investigated with optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). To install large scale coatings on silicon wafers, spin-coating of colloidal pure PS nanoparticles and carboxylated PS nanoparticles is used. Our results indicate that thermal annealing in the vicinity of the glass transition temperature Tg of pure PS leads to a rapid loss in the ordering of the nanoparticles in spin-coated films. For carboxylated particles, this loss of order is shifted to a higher temperature, which can be useful for applications at elevated temperatures. Our model assumes a softening of the boundaries between the individual colloidal spheres, leading to strong changes in the nanostructure morphology. While the nanostructure changes drastically, the macroscopic morphology remains unaffected by annealing near Tg.

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INTRODUCTION In recent years a lot of research has been done on colloidal nanoparticle crystals and thin films, with respect to production,1−13 a fundamental understanding,14−18 and their application.19,20 The use of colloids as templates prior to subsequent metal deposition21−23 is a promising way to nanostructure polymer/metal thin films. They are used in many technological applications, e.g. solar cells,24,25 anticounterfeiting and biosensors,26 optical components,27,28 high-frequency magnetic components,27 antibacterial coatings,27 organic memory devices,27,29 and organic vapor sensors.27 As the devices making use of polymer nanoparticles are often exposed to elevated temperatures, it is important to know at which temperature the structure of the used polymer nanoparticle thin films changes, if the changes are reversible, and how they possibly influence the application. An irreversible structural change is the coalescence of individual nanoparticles into larger structures and, finally, into a continuous film. The process of polymer film formation has been investigated in depth over the past two decades.30−40 Major reviews have been produced by the group of Winnik,36 and by Keddie and Routh.40 The related process is thought to be consisting of several stages:17,31,33,36,39,41,42 In the first stage, solvent evaporation brings the individual and isolated particles into © XXXX American Chemical Society

close contact. Further evaporation leads to limited particle deformation at the contact points and a coalescence. The third step involves the diffusion of polymer chains across the initial particle borders and results in a decrease in particle definition. The steps two and three depend on several parameters like the glass transition temperature Tg of the polymer, the existence of a core−shell structure, the presence of surfactants,31 and the surface chemistry of the particles and their Coulombic charges which can be pH-dependent.32 Cross-linking of the polymer chains in the core or the shell reduces the chain mobility and particle fusion probability.32 For applications of nanoparticle solutions like painting, coalescence leading to a film formation is desired to occur already at room temperature (RT), and many investigations of the film formation process have been done on polymer latices with Tg at or below RT. However, for the applications mentioned above, stability of the nanoparticles above RT is desired because the nanoparticles need to keep their integrity to stay with well-defined nanostructures. For our investigation, we chose a simple model system, namely silicon substrates coated Received: February 20, 2012 Revised: April 19, 2012

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dx.doi.org/10.1021/la3007348 | Langmuir XXXX, XXX, XXX−XXX

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Figure 1. 3 μm × 3 μm AFM topography images and 3 μm × 3 μm FESEM images of spin-coated samples. (a) AFM image of a spin-PS sample before annealing. (b) AFM image of sample spin-PS at RT after the annealing treatment at 110 °C. Individual nanoparticles are observable in limited regions only as marked with an arrow. (c) SEM image of sample spin-PS at RT after the annealing treatment at 110 °C. Individual nanoparticles are not observable anymore. (d) AFM image of a spin-cPS sample before annealing. (e) AFM image of sample spin-cPS at RT after the annealing treatment at 120 °C. The individual nanoparticles are still visible but seem to be slightly larger. (f) SEM image of sample spin-cPS at RT after the annealing treatment at 120 °C. The individual nanoparticles remain visible.

with polystyrene (PS) nanoparticle thin films. Pure as well as carboxylated PS nanoparticles are investigated. Among the possible coating techniques like dip-coating, spin-coating, spray-coating, or solution-casting,43,44 we focus on spin-coating as it is widely used in industry and research and gives rise to very well-defined thin films.45 The structure of the colloidal polymer thin films is investigated in situ during annealing above the bulk glass transition temperature Tg of PS by GISAXS and ellipsometry. In addition, the samples are examined ex situ by means of optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). FESEM is usually used to image organic films due to its higher contrast. AFM, however, allows for an easy detection of the height. Whereas AFM and FESEM allow for a local analysis of the sample surface, GISAXS46 probes a larger area defined by the footprint of the X-ray beam on the sample surfacein our case 34 μm × 3 mmand therefore guarantees a much better statistical relevance as compared with local probes. An additional advantage of GISAXS is the possibility to examine buried and near-surface structures. With ellipsometry the changes in the polarization of light reflected from the surface are measured to deduce changes in n and kthe real and the imaginary part of the complex refractive indexand in the film thickness. While several aspects of this study have already been examined by others groups, like the surface structure of latex particle films around Tg,35 the role of polymer diffusion during latex film formation,30 or the influence of functionalized surfaces on coalescence,31 we demonstrate the combination of in-situ GISAXS and in-situ imaging ellipsometry to investigate the process of film formation. This novel combination allows for monitoring a region of interest that includes the X-ray beam footprint during the experiment. In this way the influence of temperature on the sample properties

is examined independently by using two complementary methods.

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EXPERIMENTAL SECTION

Sample Preparation. The 18 × 30 mm2 silicon wafers were stored in dichloromethane at RT for 30 min, subsequently put into deionized water at RT for 20 min, cleaned in a basic bath47 consisting of 350 mL of deionized water, 35 mL of 25% ammonia solution, and 25 mL of 35% hydrogen peroxide at 75 °C for 120 min, and subsequently rinsed with deionized water and dried with a nitrogen jet. In detail, two different sample systems were prepared, which we call spin-PS and spin-cPS. Spin-PS samples were prepared by spin-coating 40 μL of a 2.5% aqueous suspension of PS nanoparticles with a nominal diameter of 96 nm (Kisker) on cleaned silicon substrates using a Süss MicroTec DELTA 10TT spin-coater at 4000 rpm for 120 s. For spin-cPS samples, 40 μL of a 5% aqueous suspension of carboxylated PS (cPS) nanoparticles with a nominal diameter of 96 nm (Kisker) was spincoated under the same conditions. Grazing Incidence Small-Angle X-ray Scattering (GISAXS) and Ellipsometry Measurements. GISAXS and ellipsometry measurements were performed at beamline BW448 of the DORIS III storage ring of HASYLAB (DESY, Hamburg, Germany). The wavelength λ = 0.138 nm was used for GISAXS. A surface probe ellipsometric microscope (SPEM) by Accurion GmbH was installed at the beamline so that both GISAXS and ellipsometry measurements were performed in situ.49 For imaging ellipsometry we used a laser beam with a wavelength λLaser = 532 nm impinging on the sample at an angle of incidence Φ0 = 42°. The field of view was 201 μm × 205 μm. The hot plate used for annealing the samples was heated electrically and cooled with compressed air. A 2D detector (MARCCD, 2048 × 2048 pixels, pixel size 79.1 × 79.1 μm2) was used, the sample-todetector distance was 1.982 m, and the angle of incidence αi = 0.37°. For sample spin-cPS, GISAXS and ellipsometry measurements were done at RT, 90 °C, 100 °C, 110 °C, 120 °C, and after cooling the sample to RT. The temperature values were chosen to examine the sample in the vicinity of the bulk glass transition temperature Tg ≈ 100 °C of PS and to compare the nanostructure at RT before and after annealing to investigate the reversibility of the changes in the sample structures. As the first sample hardly changed at 90 °C, we skipped this step and examined sample spin-PS with GISAXS and ellipsometry at B


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Figure 2. GISAXS patterns for sample spin-PS (upper row) and sample spin-cPS (lower row). The arrows highlight the position of the side maxima.

Figure 3. Left: out-of-plane cuts and corresponding fits (black) of sample spin-PS. The side maxima have vanished at 110 °C and do not reappear at room temperature. For clarity, the out-of-plane cuts are shifted along the vertical axis. Right: out-of-plane cuts and corresponding fits (black) of sample spin-cPS. While the side maxima have diminished considerably at 110 °C, they are not visible anymore at 120 °C and do not reappear after cooling. For clarity, the out-of-plane cuts are shifted along the vertical axis.

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RT, 100 °C, 110 °C, and again at RT after cooling the sample. In addition, we did not anneal sample spin-PS at 120 °C because the characteristics of a lateral structure in the GISAXS patterns had already vanished at 110 °C. The ellipsometric data are expressed as Ψ (tan (Ψ) is the relative amplitude ratio) and Δ (relative phase shift) which are related to the Fresnel reflection coefficients Rs and Rp for s- and p-polarized light, respectively. As Hennig et al.50 reported, the coefficients are complex functions of the angle of incidence Φ0, the wavelength λLaser, the optical constants of the substrate Ns, the ambient medium n0 and the layers nj, kj, and of the layer thicknesses dj:50,51

tan(Ψ) exp(iΔ) =

Rp Rs

RESULTS AND DISCUSSION Structure before Annealing. Surface Structure. With high spatial resolution the surface structure is probed with AFM. AFM topographic images of as-prepared spin-PS and spin-cPS samples are shown in Figures 1a and 1d, respectively. Before annealing, the spin-PS sample shows domains of hexagonally ordered nanoparticles as well as less ordered and uncovered areas, which appear due to the nonfully optimized spin-coating conditions. The nonannealed spin-cPS sample seems to be less ordered as compared with its spin-PS counterpart. However, the average surface coverage appears higher and more uniform. As a consequence, the average surface roughness is smaller for the spin-cPS sample as compared with the spin-PS samples. Film Morphology. The film morphology is accessed with GISAXS. The left column of Figure 2 shows 2D GISAXS data measured before annealing of sample spin-PS (upper row) and sample spin-cPS (lower row). In the center of the lower part of each pattern a pronounced intensity maximum, the so-called Yoneda52 peak, is visible. The Yoneda peak is accompanied by several side peaks for the as-prepared samples. To analyze the GISAXS patterns, horizontal line cuts called out-of-plane46,53 cuts extracted from the 2D GISAXS data (see Figure 2) at the Yoneda peak position are used. The term “plane” refers to the plane spanned by the incident beam and the surface normal. These line cuts are shown in Figure 3. For good statistics, the intensity has been integrated over 35 pixels in the qz direction, which corresponds to exit angles ranging from 0.14° to 0.21°.

= F(Φ0 , λLaser , Ns , n0 , nj , kj , dj)

with j = 0, 1, 2 (number of layers). n and k are the real and the imaginary part of the complex refractive index N. AFM, SEM, and Optical Microscopy. The atomic force microscopy (AFM) measurements were performed using an NTMDT NTEGRA Aura and an NT-MDT SOLVER NEXT system. The samples were probed at ambient conditions in air. Several different spots on the samples were probed at different scan sizes. From the AFM data the background was subtracted using standard routines. To obtain SEM images, a Zeiss NVision 40 Gemini field emission SEM was operated at an accelerating voltage of 5 kV and at a low working distance around 3 mm. The same spot on a spin-PS sample was examined with optical microscopy (Keyence VHX-600) before and after annealing. The applied magnification was 500×. C


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0, and air as ambient medium was simulated to get estimates of the index of refraction n and the thickness d of the polymer layer. The data for both samples are shown in Figure 5 on a

In Figure 3, the curves are shifted vertically for better visibility of the individual features. The dotted line indicates the resolution limit of the GISAXS setup.46 The first side maxima observed for both samples before annealing are structure factor signals and indicate a strong lateral ordering of the nanoparticles. The peak in the qy range of 0.06−0.07 nm−1 in reciprocal space corresponds to the particle distance d = 2π/qy ≈ 100 nm in real space. For close-packed spheres, the particle distance is equal to the particle diameter. The other side maxima can be explained by the form factor of a spherical particle as illustrated in Figure 4. The software IsGISAXS54 was

Figure 4. Out-of-plane cut of sample spin-PS (red), form factor of a sphere with a diameter of d = 94 nm (black), and simulation of an outof-plane cut of a layer of spheres with a diameter of d = 94 ± 8 nm (blue).

Figure 5. Simulated refractive index n and polymer layer thickness d of sample spin-PS (upper part) and sample spin-cPS (lower part) during annealing treatment. The data for sample spin-cPS are adjusted for a reduction of the region of interest.

used for a DWBA simulation of a hexagonally ordered layer of PS spheres with a diameter of d = 94 ± 8 nm and a distance of 100 ± 15 nm. A simulated out-of-plane cut at an exit angle 0.175° is shown in Figure 4. The peak positions are in good agreement with the measured data. Structural Changes during and after Annealing. Surface Structure. On a macroscopic length scale the surface structure is probed with optical microscopy. Before and after annealing no structural differences are seen on that scale. An exemplary comparison of optical microscopy images is available in the Supporting Information. Higher resolution information is gained with AFM and FESEM. The topographic AFM images of the annealed samples spin-PS and spin-cPS are shown in Figures 1b and 1e, respectively. Both sample types behave differently. After annealing of sample spin-PS a clear change in the surface structure is seen. Polymer-covered areas of several hundred nanometer size have formed. These areas have an irregular surface shape and are often merged with neighboring areas. The individual nanoparticles are hardly visible anymore. The FESEM image of this sample (Figure 1c) shows the same kind of large scale structures. However, in the case of the annealed spin-cPS sample, the individual nanoparticles are still clearly visible on the AFM image and show only slight deviation in shape from the as-prepared spin-cPS sample. The size has increased as compared to the as-prepared state. On the corresponding FESEM image (Figure 1f) individual nanoparticles remain visible but seem to be partially merged with their neighbors. Film Morphology. An indirect access to the film morphology is gained from ellipsometry measurements, which reveal the optical parameters Δ and Ψ. A model consisting of a silicon substrate with a 1.5 nm silicon dioxide layer, a polymer layer with an extinction coefficient k =

time axis because of the kinetic experiment. The individual changes in temperature are marked with the solid vertical lines. Around the glass transition temperature changes in d and n are visible for both samples. d shows a decrease, while n is increasing (sample spin-PS) or at first decreasing, then increasing (sample spin-cPS) depending on the surface termination of the PS spheres. For spin-PS a strong change occurs at 110 °C while for spin-cPS only small changes are observed at 110 °C, and stronger changes occur at a higher temperature of 120 °C. The occurrence of changes in the optical properties for T ≥ Tg can be explained as follows: First, the samples are covered with spherical nanoparticles and voids in between them filled with air. Because of the voids, the effective index of refraction of the layer is lower than that of bulk PS. During annealing at T ≥ Tg, it seems that the particles are deformed. A higher effective index of refraction and a lower layer thickness can be explained by this process because the deformation seems to lead to less voids. Figure 6 depicts this process qualitatively.

Figure 6. Sketch of the particle deformation at/above Tg indicating subsurface coalescence as proposed by Hu et al.41 D


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Figure 7. Time evolution of the parameters of the Gaussian and Lorentzian functions used for fitting the out-of-plane cuts. (a) Sample spin-PS: ξ0 = 2π/qy,0. (b) Sample spin-PS: AL/AG. (c) Sample spin-PS: ω. (d) Sample spin-cPS: ξ0 = 2π/qy,0. (e) Sample spin-cPS: AL/AG. (f) Sample spin-cPS: ω.

A more detailed information about the film morphology is obtained from the in-situ GISAXS experiment. Figure 2 shows 2D GISAXS data taken before, during, and after annealing of sample spin-PS (upper row) and sample spin-cPS (lower row). Very clearly, annealing changes the nanoscale morphology as the GISAXS data change during the thermal processing. Moreover, the comparison of both sets of GISAXS data shows the same trend as observed with ellipsometry; the change in morphology happens at different onset temperatures. To analyze the changes occurring during annealing more carefully, out-of-plane cuts are extracted from the 2D GISAXS data. These cuts are shown in Figure 3. Again, the cuts have been taken at the Yoneda peak position with an integration as explained before. For clarity, the curves are shifted vertically in Figure 3. The cuts from the 2D GISAXS data of sample spin-PS show strong side peaks at RT and during annealing at 100 °C which indicates a strong lateral order persisting at both temperatures. The strong side peaks vanish at a temperature of 110 °C and do not reappear after cooling the sample back to RT. Obviously, the lateral order is strongly decreased at 110 °C, and the nanostructure is altered irreversibly. Particle deformation and coalescence of particles, or at least, a loss of contrast between the particles during and/or after annealing41 is the reason for this observation. Such behavior is closely connected with the glass transition of the polymer, which might induce mobility of the polymer chains and thus lead to a softening of the boundaries between the individual colloids (Figure 6).

In the case of sample spin-cPS, in the cuts from the 2D GISAXS data the side maxima are still visible at 110 °C but vanish at 120 °C. Moreover, the all over behavior is different. While the first and third side maxima of sample spin-PS show little change at 100 °C, the second side peak has already decreased significantly. For sample spin-cPS, the second side maximum is relatively weak even before annealing. For a more quantitative analysis, the out-of-plane cuts of both samples are fitted with a sum of Gaussian ⎛ ⎛ q ⎞2 ⎞ y g (qy) = A G exp⎜⎜ −⎜ ⎟ ⎟⎟ ⎝ ⎝ 2σ ⎠ ⎠

(1)

and Lorentzian l(qy) =

AL

(

1+4

qy − qy,0 2 | ω|

)

(2)

functions for low qy values and for the side maxima, respectively, to extract peak heights, widths and positions. The temporal development of the fit parameters is plotted in Figure 7. Whereas qy,0 indicates the first Lorentzian’s peak position in reciprocal space, ξ0 = 2π/qy,0 ≈ 100 nm gives a length scale in real space corresponding to a nearest-neighbor distance andin the case of close packingyielding an estimate of the particle diameter. The ratio AL/AG compares the height of the first Lorentzian peak to the height of the Gaussian peak at qy = 0 nm−1. The last parameter ω measures E


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the width of the first Lorentzian peak and is thus a measure of the variance of ξ0. In the initial state, the first Lorentzian peak is fitted to the first visible side maximum identified as the colloid’s structure factor. The central Gaussian peak is fitted to the Yoneda peak which is caused by unresolved large-scale structures. Therefore, as long as the first visible side maximum is strong enough to be identified by the fitting procedure, AL/AG states the ratio of short-range order to unresolved large-scale structures (domains). In later stages, when the side maximum caused by the structure factor has disappeared, the fitting routine moves the Lorentzian toward lower qy values, toward larger-scale unresolved structures. For sample spin-PS, we see fast and irreversible increases in ξ0 and ω accompanied by an irreversibly decreasing AL/AG, a strong change in the polymer layer thickness d and refractive index n, and the vanishing of the side maxima in Figures 2 and 3 at 110 °C, while for sample spin-cPS an irreversible increase in ξ0, a strong change in d, and the vanishing of the side maxima in Figures 2 and 3 occur at 120 °C. The fact that structural changes occur at different temperatures for sample spin-PS and spin-cPS is thus confirmed independently by GISAXS and ellipsometry. Moreover, the AFM and SEM images of sample spin-PS (Figure 1a−c) corroborate that strong structural changes have occurred during annealing at 110 °C for sample spin-PS. In the AFM and SEM images of sample spin-cPS (Figure 1d−f), however, the individual colloids are still visible even after annealing at 120 °C. For AFM images taken at different positions of the sample after annealing at 120 °C, this is not the case. In the GISAXS patterns (Figure 2) for the annealed sample spin-cPS, the structure factor can still be seen in the area above the beam stop. In a previous investigation with colloids having a lower Tg, Hu et al.41 examined a single-layer butyl acrylate latex film with GIUSAXS and AFM and found a Bragg peak corresponding to the particle diameter. Similar to our results, the Bragg peak vanishes when the sample is annealed above Tg, but the particles are still visible on AFM images. This observation is explained with the surface sensitivity of AFM measurements, whereas GIUSAXS can detect buried information like subsurface particle coalescence. This is again comparable with our AFM, SEM, ellipsometry, and GISAXS results and our model of particle deformation. The decrease in particle definition as seen in the AFM image of our spin-PS sample after annealing (Figure 1b) is in agreement with findings by Goudy et al.33 They performed AFM investigations on PS latices of different particle size which were annealed for different times and at different temperatures. While there is no measurable change in the peak-to-peak distance, the peak-to-trough height (the difference in height between the top of a particle and the trough between two adjacent particles) decreases strongly when the sample is annealed above Tg. This is consistent with the vanishing of the side maxima in our GISAXS patterns. They also found out that higher annealing temperatures above Tg cause a faster decrease in the peak-to-trough height and that the peak-to-trough height normalized against the particle size decreases faster for 240 nm particles than for 375 nm particles. The decrease in particle definition of our even smaller 100 nm particles after annealing (Figure 1b) therefore agrees with their findings and can be due to diffusion of polymer chains across particle surfaces. The fact that this does not occur at the same temperature for our spincPS sample can be explained by the hydrophilic carboxyl groups

at the particle surfaces which seem to prevent, or at least slow down, the coalescence of the otherwise hydrophobic PS nanospheres. To observe the wetting behavior of individual PS nanoparticles on silicon wafers before and after annealing, a 0.025% aqueous suspension of 96 nm PS nanoparticles was spin-coated onto silicon wafers cleaned in a basic bath. AFM measurements using an NT-MDT SOLVER NEXT system were performed on a sample as prepared and on a sample annealed like sample spin-PS. Height profiles of nonannealed and annealed nanoparticles in Figure 8 show that, while the particle height

Figure 8. Height profiles of PS nanoparticles on silicon wafers before (black) and after annealing (red). Whereas the height of the nonannealed particle corresponds very well with the nominal nanoparticle size of 96 nm, the height of the annealed particle is about 45 nm. The widths of both particles at the contact line are about 200 and 250 nm.

decreases from 96 nm to about 45 nm during annealing, the particle width increases. This flattening corroborates the decrease in layer thickness observed with ellipsometry and might be due to strong interfacial interaction between PS and silicon wafer. To further investigate the behavior of cPS particles at 110 °C, we performed an in-situ GISAXS experiment in which a silicon substrate covered with 100 nm cPS particles was annealed for more than 1 h at 110 °C. During annealing, the side maxima in the GISAXS data slightly weaken, but after cooling back to RT the side peaks are about as strong as before annealing. Thus, it seems that the cPS particles are only reversibly affected by a temperature treatment at 110 °C for 1 h, and therefore the stability limit seems to be shifted to higher temperatures.

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SUMMARY In our investigation we followed structural changes in PS colloidal thin films during annealing. Our results indicate that structural changes occur when colloidal PS thin films are exposed to temperatures above Tg. The changes are observable at the nanometer scale by using GISAXS and ellipsometry, but no changes at the microscopic scale are observed as confirmed by the optical microscopic measurements. At which temperature these changes occur depends in detail not only on the polymer material of the nanoparticles itself but also on the particles’ outer end groups. While a spin-coated film of pure PS spheres is unstable at 110 °C, a spin-coated film of carboxylated PS spheres proved to be more stable at 110 °C and unstable at 120 °C. Thus, the stability limit can be shifted toward higher temperatures by a proper surface functionalization. This finding will be of use for future application of PS nanoparticle films at higher temperatures. For example, in application as templates F


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(13) Yap, H. P.; Quinn, J. F.; Ng, S. M.; Cho, J.; Caruso, F. Colloid Surface Engineering via Deposition of Multilayered Thin Films from Polyelectrolyte Blend Solutions. Langmuir 2005, 21, 4328−4333. (14) Fernandes, G. E.; Bevan, M. A. Equivalent Temperature and Specific Ion Effects in Macromolecule-Coated Colloid Interactions. Langmuir 2007, 23, 1500−1506. (15) Smith, J. N.; Meadows, J.; Williams, P. A. Adsorption of Polyvinylpyrrolidone onto Polystyrene Latices and the Effect on Colloid Stability. Langmuir 1996, 12, 3773−3778. (16) Men, Y.; Rieger, J.; Roth, S. V.; Gehrke, R.; Kong, X. Non-Affine Structural Evolution of Soft Colloidal Crystalline Latex Films under Stretching as Observed via Synchrotron X-ray Scattering. Langmuir 2006, 22, 8285−8288. (17) Chen, X.; Fischer, S.; Yi, Z.; Boyko, V.; Terrenoire, A.; Reinhold, F.; Rieger, J.; Li, X.; Men, Y. Structural Reorganization of a Polymeric Latex Film During Dry Sintering at Elevated Temperatures. Langmuir 2011, 27, 8458−8463. (18) Zhang, J.; Yi, Z.; Wang, Q.; Liu, Z.; Perlich, J.; Gehrke, R.; Men, Y. Effect of Solvent Annealing on the Tensile Deformation Mechanism of a Colloidal Crystalline Polymeric Latex Film. Langmuir 2011, 27, 12197−12200. (19) Talapin, D. V.; Lee, J.-S.; Kovalenko, M. V.; Shevchenko, E. V. Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 2010, 110, 389−458. (20) Xia, Y.; Gates, B.; Yin, Y.; Lu, Y. Monodispersed Colloidal Spheres: Old Materials with New Applications. Adv. Mater. 2000, 12, 693−713. (21) Frömsdorf, A.; Kornowski, A.; Pütter, S.; Stillrich, H.; Lee, L.-T. Highly Ordered Nanostructured Surfaces Obtained with Silica-Filled Diblock-Copolymer Micelles as Templates. Small 2007, 3 (No.5), 880−889. (22) Siffalovic, P.; Majkova, E.; Chitu, L.; Halahovets, Y.; Jergel, M.; Senderak, R.; Luby, S.; Weis, M.; Satka, A.; Szymański, B.; Stobiecki, F.; Timmann, A.; Roth, S. V. Fabrication and Characterization of Hybrid Tunnel Magnetoresistance Structures with Embedded SelfAssembled Nanoparticle Templates. Acta Phys. Pol., A 2009, 115, 332−335. (23) Dolatshahi-Pirouz, A.; Jensen, T.; Vorup-Jensen, T.; Bech, R.; Chevallier, J.; Besenbacher, F.; Foss, M.; Sutherland, D. S. Synthesis of Functional Nanomaterials via Colloidal Mask Templating and Glancing Angle Deposition (GLAD). Adv. Eng. Mater. 2010, 12, 899−905. (24) Kaune, G.; Ruderer, M. A.; Metwalli, E.; Wang, W.; Couet, S.; Schlage, K.; Röhlsberger, R.; Roth, S. V.; Müller-Buschbaum, P. In Situ GISAXS Study of Gold Film Growth on Conducting Polymer Films. ACS Appl. Mater. Interfaces 2009, 1, 353−360. (25) Kaune, G.; Memesa, M.; Ruderer, M.; Diethert, A.; Roth, S. V.; D’Acunzi, M.; Gutmann, J. S.; Müller-Buschbaum, P. Hierarchically structured titania films prepared by polymer/colloidal templating. ACS Appl. Mater. Interfaces 2009, 1, 2862−2869. (26) Bauer, G.; Hassmann, J.; Walter, H.; Haglmüller, J.; Mayer, C.; Schalkhammer, T. Resonant nanocluster technology−from optical coding and high quality security features to biochips. Nanotechnology 2003, 14, 1289−1311. (27) Faupel, F.; Zaporojtchenko, V.; Strunskus, T.; Elbahri, M. Metal-Polymer Nanocomposites for Functional Applications. Adv. Eng. Mater. 2010, 12, 1117−1190. (28) Pyayt, A. L.; Wiley, B.; Xia, Y.; Chen, A.; Dalton, L. Integration of photonic and silver nanowire plasmonic waveguides. Nat. Nanotechnol. 2008, 3, 660. (29) Yang, Y.; Ma, L.; Wu, J. Organic Thin-Film Memory. MRS Bull. 2004, 29, 833. (30) Zhao, C.-L.; Wang, Y.; Hruska, Z.; Winnik, M. A. Molecular Aspects of Latex Film Formation: An Energy-Transfer Study. Macromolecules 1990, 23, 4082−4087. (31) Chevalier, Y.; Pichot, C.; Graillat, C.; Joanicot, M.; Wong, K.; Maquet, J.; Lindner, P.; Cabane, B. Film formation with latex particles. Colloid Polym. Sci. 1992, 270, 806−821.

for sputter deposition often elevated temperatures are desired for subsequent metal layer nanostructuring.55 The combination of in-situ GISAXS with in-situ ellipsometry proved to be useful to study annealing processes.

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ASSOCIATED CONTENT

* Supporting Information S

An exemplary comparison of optical microscopy images of a spin-PS sample before and after annealing. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (G.H.); [email protected] (S.V.R.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS R.M., V.K., and P.M.-B. thank the Bundesministerium für Bildung und Forschung for financial support (grant 05KS7WO1). M.A.R. acknowledges the financial support by the Bavarian State Ministry of Sciences, Research and Arts for funding this research work through the International Graduate School “Materials Science of Complex Interfaces” (CompInt). Portions of this research were carried out at the light source DORIS III at HASYLAB/DESY. DESY is a member of the Helmholtz Association (HGF). We thank D. Erb for her help with AFM measurements.

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