This is the submitted version of the article: Alexandros El Sachat, Jean Spièce, Charalambos Evangeli, Alexander James Robson, Martin Kreuzer, Maria R. Rodríguez-Laguna, Emigdio Chavez, Marianna Sledzinska, Clivia M. Sotomayor Torres, Oleg V. Kolosov, Francesc Alzina. Nanoscale Mapping of Thermal and Mechanical Properties of Bare and Metal-Covered Self-Assembled Block Copolymer Thin Films. Acs Applied Polymer Materials, (2020). 2. : 487 - . 10.1021/acsapm.9b00924. Available at: https://dx.doi.org/10.1021/acsapm.9b00924 Nanoscale mapping of thermal and mechanical properties of bare and metal-covered self-assembled block copolymer thin films Alexandros El Sachat,*, †, # Jean Spièce,‡ Charalambos Evangeli,‡, ¶ Alexander James Robson,‡ Martin Kreuzer,†,⊥ Maria R. Rodríguez-Laguna,† Emigdio Chavez,† Marianna Sledzinska,† Clivia M. Sotomayor Torres,†, § Oleg V. Kolosov,‡ Francesc Alzina† † Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain. ‡ Physics Department and Materials Science Institute, Lancaster University, Lancaster, LA1 4YB, United Kingdom § ICREA, Passeig Lluis Companys 23, 08010 Barcelona, Spain. KEYWORDS: Block copolymers, self-assembly, thermal and mechanical mapping, thermal conductivity, scanning probe microscopy 1 ABSTRACT We report on the structural, mechanical and thermal analysis of 40 nm thick polystyrene-block- poly (ethylene oxide) (PS-b-PEO) block copolymer (BCP) films coated with evaporated chromium layers of different thicknesses (1, 2 and 5 nm). Solvent annealing processes allow the structural control of the BCP films morphology by re-arranging the position of the PEO cylinders parallel to the substrate plane. High-vacuum scanning thermal microscopy and ultrasonic force microscopy measurements performed in ambient pressure revealed that the nanometer thick metal coated layers strongly influence the heat dissipation in the BCP films and the local surface stiffness of the individual BCP domains, respectively. The measured tip-sample effective thermal resistance decreases from 6.1×107 to 2.5×107 KW-1 with increasing Cr film thickness. In addition, scanning probe microscopy measurements allow the thermal and mechanical mapping of the two segregated polymer domains (PEO-PS) of sub-50 nm characteristic sizes, with sub-15 nm thermal spatial resolution. The results revealed the effect of the surface morphology of the BCP and the incorporation of the metal film on the nanoscale thermal properties and volume self-assembly on the mechanical properties. The findings from this study provide insight in the formation of high aspect ratio BCP-metal structures with the more established applications in lithography. In addition, knowledge on the thermal and mechanical properties at the nanoscale is required in emergent applications, such as thermal management, where the BCP is part of the final structure or device. 2 1. Introduction Block copolymers (BCPs) composed of two or more chemically distinct, incompatible blocks are well-known to regularly self-assemble into various ordered nanostructures over macroscopic areas. In thin films, the domain structure is dependent on the interfaces energies (for example, air-BCP and BCP-substrate) and the film thickness, in addition to the other known parameters like composition and molecular weight. The control of the orientation in BCP thin films can be achieved by different approaches including surface modification, solvent annealing, temperature gradient, mechanical and electrical fields, etc.1-4 BCPs are suitable for a number of nanotechnologies on account of the tunability of their size, shape, and composition.5 Different etch contrast between blocks allows the selective removal of one block and the use of the remaining one as a mask for pattern transfer into a functional material.6 Hard-mask approaches can be introduced into the nanofabrication process when high- aspect ratio structures have to be realized,7-11 such as conductive nanowires and semiconductor nanopillars. Alternatively, the remaining pattern can be employed as a sacrificial soft template structure. Functional materials are then introduced into the pore spaces of sacrificial templates by deposition, followed by removal of the template and generating the desired nanostructure.12-14 The patterning process can be repeated to produce a stack of 2D patterns, which can be constituted of the same or different materials, morphologies and orientations.15 Such block copolymer self-assembly methods have been implemented to pattern microelectronic circuit elements on the nanometre length scale (e.g. high density hard drivers,16 memory semiconductor capacitors17 and magnetic films18). Furthermore, BCP (PS-b-PEO) films composed of selectively localized metal nanoparticles recently have been used as transparent patterned electrodes19 in organic thin film transistors. 3 Beyond the generation of templates for lithography, the applications of BCPs are expanding to other fields exploiting their functional properties.20-21 However, there is a need to find complementary properties available from inorganic materials in many cases to enhance existing properties or impart novel functionalities to BCPs.22-23 Various applications require the deposition of the inorganic materials on the surface of the BCP, instead of incorporating the inorganic materials into the phases of the BCP.24 The selective decoration of evaporated metals has been reported, where nanoparticles and continuous films form by aggregation in the polymer.10-11, 25-31 This provides a route for the metallization of templates; however, it is required to get more insight on the factors and parameters involved in the process. Metallization in the form of thin films can also be used to improve the heat dissipation in polymer containing active nanoelectronic and optoelectronic devices, where the high thermal resistance of these materials prevents an efficient extraction and may cause the degradation of the organic material.32 The measurement of the thermal conductance of such polymer based structures is very important as the polymer layer, polymer-metal or polymer-semiconductor interface can act as a heat barrier in the nanostructure. In addition, the knowledge of heat resistance and thermal stability of self-assembled nanostructures is crucial to define an upper temperature limit for the use of polymers on devices (e.g. to avoid overheating).33 The possibility given by nanostructuring polymers for further tuning its low thermal conductivity and combining them with efficient heat conductive materials, opens new prospects in the control of heat transport for applications in thermal management. Contrary to homopolymers, however, thermal transport in such polymer based systems has been barely explored. George et al.34 reported thermal transport measurements on BCP films containing PS and Poly (methyl methacrylate) (PMMA) polymers (PS-b-PMMA). They found 4 that neither the film thickness nor the block’s phase separation influenced the effective thermal conductivity of the BCP, obtaining values consistent with the bulk homopolymer values. The authors, however, used an optical diffraction-limited spatial resolution (~300 nm) technique that is not sufficient to characterize individual BCP blocks only a few nanometres in size. At such highly localized length scales heat transport is affected by interfaces, boundaries and contacts, thus the thermal imaging of individual BCP blocks is of high importance. Furthermore, the mechanical property is arguably the weakest (both figuratively and literally) point of the polymer in the nanostructure applications, essentially defining the stability of polymer nanostructure in contact with the nano-patterned metal, especially for polymers structures with high aspect ratios. For instance, in self-assembled structures the presence of a much stiffer block greatly affects microphase separation.35 In addition, previous works predicted that as the stiffness of one of the blocks is significantly increased, new intermolecular interactions can be introduced,36-37 influencing the macroscopic structure of the BCP film and thus the nature of thermodynamically stable microphases. In particular, in thin films, these effects can cause significant deviations from the predicted bulk BCP structure and needs to be investigated. Consequently, the nanomechanical mapping of individual phases of the BCP structures is essential to investigate such effects. The characterization of such complex structures at the nanoscale is crucial for further understanding the morphology-property relationship and the connection between the properties of the constituent components and the structure in the mesoscale. Electron microscopies can simultaneously provide structure characterization and chemical composition. Moreover, Atomic Force Microscopy (AFM)-based techniques, such as Ultrasonic Force Microscopy (UFM) and Scanning Thermal Microscopy (SThM), allow the nanoscale characterization of materials 5 beyond their surface topography and provide surface nanomechanical38 and thermal39 properties imaging, respectively. In this work, we investigated the effect of microphase separation in BCP films on the aggregation of an evaporated metal. Particularly, we studied two different morphologies of these films, which were used as templates for metal coating. The primary BCP morphology consists of vertically oriented PEO cylinders within a PS matrix, which can be transformed in a morphology with in-plane oriented PEO cylindrical domains embedded in a PS matrix by solvent exposure. Structural and chemical characterization was primarily performed in order to gain insight into the morphology of the heterogeneous structures. Then, we studied the thermal and mechanical properties of the resulting BCP films and the effect of the incorporation of evaporated metal films. The surface imaging and measurements of nanoscale physical properties of these structures, which also revealed sub-surface detection and imaging, were performed by SThM and UFM. The complexity and size scale of the samples represents a challenge to the performance of Scanning Probe Microscopy (SPM) for both spatial resolution and probe sensitivity. Moreover, the thermal and mechanical response of the heterogeneous structure reflects the complexity of their morphology, i.e., surfaces, interfaces and film thickness, along with the intrinsic properties of the forming materials. 2. Results and Discussion Fabrication and structural analysis of BCP templates. A 1% (w/w) solution of PS-b- PEO diblock copolymer in toluene with molecular weights of 𝑀𝑛, PS = 102 kgmol−1 and 𝑀𝑛, PEO = 34 kgmol−1 was dispersed into a Si substrate, and spin-coated at 4000 RPM for 60 sec. The Si substrates were cleaned in ethanol, toluene and acetone prior to use. The microphase separation 6 of the BCP film by self-assembly resulted in the formation of vertically oriented PEO cylinders showing a hexagonal arrangement embedded in a PS matrix, as seen in previous works using similar methodology.27, 40-41 Schematic of the morphology of the bare BCP film is shown in Figure 1a. Then, we proceeded to deposit Cr on a first set of as prepared BCP templates by using electron beam evaporation and targeting Cr layers with different nominal thicknesses (1, 2 and 5 nm). Figures 1c-f show Scanning Electron Microscopy (SEM) images of the surface of the bare (0 nm Cr) and the three metal decorated BCP samples, respectively (1st set of samples). The surface of the bare BCP film shows the presence of cylindrical domains (dark color in SEM) with average radius and average spacing between them of r = 15 ± 2 nm and D = 25 ± 2 nm, respectively. The composition of the cylinders was further verified after performing the thermal and mechanical measurements, by selectively etching the PEO block of the bare BCP film with an oxygen plasma.40-41 (see Figures S2a, b in the Electronic Supplementary Information (ESI)). The PS matrix is higher than the PEO cylinders by a difference of 5 ± 1 nm in average. After the evaporation of Cr on the non-etched samples, the oriented polymer template is still distinguishable, indicating a preferential metal coverage. This observation will be further confirmed by transmission electron microscopy (TEM) measurements. The RMS surface roughness of the BCP films decreases from 3 to 2 nm with increasing Cr layer thickness as estimated from AFM topography images (Figure S3 in the ESI). A second set of as prepared BCP templates was processed by solvent annealing in mixed chloroform and toluene atmosphere for 2 hours. The selective wetting of the minor block of the BCP (hydrophilic PEO) resulted in the alignment of the PEO cylinders parallel to the substrate 7 plane, as has been shown elsewhere.40 Particularly, the local segregation of the different polymer blocks of PS-b-PEO thin films through a solvent annealing process has been studied in previous works.40-41 A schematic illustration of the morphology of the resulting BCP template is shown in Figure 1b. The rate of the structural conversion is time and film thickness dependent and, since the PS and PEO blocks are highly immiscible, the microphase separation occurs at relatively high solvent concentrations.27, 41 Figures 1g shows a SEM image of the solvent annealed BCP film. The brighter color in the SEM images corresponds to the PS matrix while the PEO cylindrical domains are expected to be rearranged horizontally to the film, and embedded in the PS matrix.40, 42 Then, similarly to the previous set of samples, Cr layers with nominal thicknesses of 2 and 5 nm were evaporated on the surface of the BCP template by electron beam evaporation (see Figures 1h, l, 2nd set of samples). To study the morphology and chemical composition of the BCP templates, we performed transmission electron microscopy (TEM), energy dispersive x-ray (EDX) and electron energy- loss spectroscopy (EELS) measurements. TEM measurements are shown in Figure 1 while EDX and EELS measurements are presented in the ESI (Figure S4). In Figures 1j, k, l we show cross- section TEM images of the BCP templates with nominal Cr coatings of 1, 2 and 5 nm, respectively (see 1st set of samples). The resulting BCP film thickness was measured 39 2 nm. The Cr film is seen to deposit preferentially on the PS matrix, forming islands that grow laterally as the evaporation time increases.The selectivity of Cr is not complete, but a slower kinetics of the growth-coalescence process on PEO cylinders than in the PS matrix results in a partial coverage of the PEO cylinders.43 The different metal deposition on the two BCP blocks can be seen with higher resolution in STEM mode. In the ESI we show the BCP template with 2 nm thick Cr (1st set of samples) in STEM mode (Figure S4a) and, with higher magnification at the 8 framed area, in Figure S4b. From these images, we observe that the metal layer (see brighter regions in Figure S4b) is preferentially formed on the PS surface. However, the EDX spectrum taken along the line indicated in Figure S4b confirmed the presence of Cr atoms within the PEO domains as well (see Figure S4c). High-resolution TEM images of the solvent annealed BCP templates (2nd set of samples) with nominal 2 and 5 nm thick Cr layers are shown in Figures 1m, n, respectively. From the TEM images we observe that there is no selectivity in the deposition of the Cr layer, i.e., a homogeneous Cr layer is evident all along the sample surface. Figure S4d shows the selected area for the composition analysis (orange box) in the BCP template with 2 nm Cr layer. Figures S4e, f show the EELS composition maps for chromium and oxygen elements, respectively. As already seen in the TEM images, Figure S4e shows that the Cr layer is homogeneously distributed on top of the BCP surface. Oxygen content (brighter regions in Figure S4f) is clearly detected at the substrate-BCP interface and at the Cr layer. The former is attributed to the native SiO2 film formed on top of the Si substrate and the latter reveals the oxidized Cr. 9 Figure 1. (a), (b) Schematics of the BCP films morphology. (c) SEM image of the fabricated microphase separated BCP film on Si substrate, and (d), (e), (f) Top view SEM images of the BCP templates with nominal Cr coatings of 1, 2 and 5 nm (first set of samples), respectively. The darker regions are the PEO domains that were degraded while the lighter regions correspond to the PS matrix. (g) SEM image of the BCP film after the solvent annealing, showing the modified morphology; (h), (i) Solvent annealed BCP templates with 2 and 5 nm Cr layers, respectively. (j), (k), (l) cross-section TEM images of the BCP templates with nominal Cr coatings of 1, 2 and 5 nm, respectively; (m), (n) cross-section TEM images of the solvent annealed BCP templates with 2 and 5 nm Cr, respectively. From the TEM measurements it is clear that the metal deposition in the two sets of samples has distinctive morphologies. While there is a weak preference of Cr for the matrix surface over cylinders in the 1st set of samples, in contrast, it fully covers the whole surface of the 2nd set of 10 samples. The uniform metal coverage in the 2nd set of samples suggests surface homogeneity and further supports the description of the parallel oriented cylinders embedded in a PS matrix. A full PS surface is favored as air-PS interface minimizes the energy of the system.44 In addition, the surface of the 2nd set of samples was activated (solvent annealed) prior to metal deposition, thus expected to exhibit enhanced metal adhesion.45-47 The presence of additional functional groups after the solvent annealing may interact with the evaporated Cr atoms creating the homogeneous Cr layer on the BCP surface with uniform thickness. Although the morphology of the metal deposition on the different BCP templates is a necessary information to interpret the thermal and mechanical measurements presented below, further investigation of the basic physical mechanisms of metal film formation on BCP surfaces is beyond the subject of this work. A better understanding of the wetting behavior of metal films on solid substrates and their growth kinetics can be found elsewhere.48-49 Thermal analysis of the BCP templates. Next, we study heat transport between a SThM microscope tip and the fabricated BCP films. Measurements were performed in specialized high vacuum SThM (10-7 mbar).50 Using a doped-Si probe with an integrated resistive heater close to the tip (Figure 3b), operating in active mode (described in ESI), we measured variations of the tip-sample effective thermal resistance in all the BCP samples. More details about the experimental setup and the quantification of the thermal resistance can be found elsewhere.51 First we study individual regions of the BCP films. In Figure 2 we present topography and thermal images of the bare BCP templates obtained by simultaneous mapping the local variations in height (Figures 2a, c) and tip-sample thermal resistance (Figures 2b, d). The high-resolution thermal image of the BCP template with the vertical cylinder morphology (Figure 2b) shows thermal contrast between the PS matrix and the PEO cylindrical domains, where the hexagonal 11 arrangement of the latter is visible. The PEO cylinders appears darker than the PS matrix in the thermal image, i.e. lower thermal resistance, indicating an increased tip-sample heat transfer when the tip is in contact with the PEO domains. In particular, from the 40 nm long thermal resistance line profile (white dashed line in Figure 2b), we observe that as the tip is moving from the PS matrix towards the PEO cylinders, the thermal resistance decreases approximately 0.04 MK/W (see Figure 2e). The same trend has been observed in the full 1st set of samples, as shown in the ESI (Figure S5). Similarly, in the BCP film with the embedded horizontal cylinders (Figure 2d), the thermal map shows darker contrast in the depressions than the higher level PS matrix. From the 100 nm long thermal resistance line profile along the white dashed line of Figure 2d, we found that as the tip is moving from the higher level PS matrix towards the depressions, the thermal resistance decreases approximately 0.12 MK/W (see Figure 2f). Note that in this case the tip is continuously in contact with the PS matrix while the embedded PEO cylinders cannot be directly probed. Since the two constituent polymers have similar intrinsic thermal conductivities, the origin of the thermal contrast between the PS matrix and PEO vertical cylinders (see Figure 2b), could be related to a topography artifact. However, by analysing the topography and thermal resistance profiles of Figures 2e,f we show that the thermal spatial resolution in our measurements (sub-15 nm range) is sufficient to resolve features with sizes similar to the PEO vertical cylinders. In particular, the thermal lateral resolution is extracted by comparing the slope of the acquired thermal resistance signal, when the tip is moving at the interface between the PS matrix and PEO cylinders, with the corresponding topography, taking the full width at half maximum as a resolution criterion (see line profiles in ESI), as has been applied in previous SThM 12 measurements52. Therefore, the change of the thermal resistance signal, when the tip is moving from the PS matrix to the PEO cylinders, is not related to the geometrical change of the contact area, mostly ruling out the effect of topography artifacts. Figure 2. (a), (c) Topography and (b), (d) thermal resistance maps of the bare BCP films formed by vertical (1st set, Figures 2a, b) and horizontal cylinders (2nd set, Figures 2c, d). (e), (f) Topography (black data points) and thermal resistance profiles (red data points) along the white dashed lines of Figures 2a, c and Figures 2b, d, respectively. Open symbols in Figure 2e correspond to data points from Figures 2a, b and solid symbols in Figure 2f correspond to data points from Figures 2c, d. Once topographic artifacts are discarded, a simple explanation of the thermal contrast in the images would be the small difference between the thermal conductivities of the PS and PEO constituent polymers. However, a complete interpretation needs to take into account the heat spreading into the substrate that, consequently, affects the tip-sample heat transfer. As the BCP 13 film shows a marked surface topography with the vertical PEO cylinders forming surface depressions, it introduces a film thickness modulation, which results, accordingly, in a thermal conductance and thermal contrast change because of different distance between the heater and substrate. The fact that we observe a larger thermal resistance decrease in the depressions in the 2nd set of samples, where larger changes in height are observed (see Figure 2e), further supports the interpretation of a thickness-dependent substrate effect causing the thermal contrast. We have performed point contact measurements, where the SThM tip is brought in- and out- of contact with the sample at randomly chosen positions on the BCP samples surfaces in order to obtain more insightful and quantitative measurements of the effect of deposited Cr on the effective thermal resistance between the tip and the samples. Each point contact measurement gives us the heat flux variation caused by the difference in tip-sample temperature. Then, an averaged effective thermal resistance Rts is obtained for each BCP sample by taking the mean value of the point measurements. In general, for a given sample, Rts can be expressed as a sum of three different thermal resistances: 𝑅 𝑅 𝑅 𝑅 (1) where Rt is the thermal resistance of the SThM conical tip, Rc the thermal interface resistance between tip and the sample in contact (thermal contact resistance) and Rspr the thermal spreading resistance within the sample (see schematic in Figure 3a). Particularly, when the probe is in contact with the sample, the heat generated in the SThM heater can only transfer to two heat sinks: the probe cantilever and the sample. By monitoring the change in probe excess temperature (ΔT=Tprobe - T0) out (ΔTnc) and in contact (ΔTc), we measure the effective thermal resistance Rts between the tip and the sample. Rts is given by the following equation: 14 𝑅 𝑅 1 (2) where Rp is the probe thermal resistance, which is measured during the probe calibration procedure (see ESI) and was found Rp = 8.7×104 KW-1. In Figure 3c we show the effective thermal resistance as a function of the Cr thickness in the 1st set of BCP samples (black stars). It corresponds to the mean value Rts of the measurements taken at each sample and the error bars the dispersion found in the measurements. Note that we measured negligible differences in Rts between the 1st and the 2nd set of samples. The measurements show that by increasing the Cr layer thickness on the BCP films, the thermal resistance, Rts, decreases, thus, the heat transfer from the tip to the sample increases. We have implemented a model to account for the previous point contact measurements and gain more quantitative information regarding the heat transport in the Cr/BCP/Si system. Provided that the point contact measurements were performed at random positions, we have assumed that we can model the BCP film as an equivalent homogeneous layer with effective properties, which can be modelled as the weighted average of the properties of each block. Details of the heat transport model can be found in the ESI. The blue dashed curve in Figure 3c shows the calculated thermal resistance values. 15 Figure 3. (a) Schematic of the probe-sample thermal resistance model and (b) SEM image of the Si-doped SThM probe. A tip of a nanoscopic radius curvature ((5−10) nm) with a pyramidal shape is mounted on top of the resistive element. (c) The tip-sample thermal resistance variations of the 1st set of samples as a function of the Cr thickness (black stars) and the two layers on substrate analytical model (blue spheres). The error for the Cr thickness is ± 0.5 nm. The inset graph in Figure 3c shows the percentage of the thermal resistance variations between PS and PEO in the BCP films with the vertical (green spheres) and horizontal (blue spheres) cylinders, respectively. Furthermore, by analysing the thermal images and taking into account Rt and the power generated in the probe, we estimated the percentage of the thermal resistance variations when the tip is on a surface depression (RPEO) and on the top-most of the surface (RPS) (see inset graph in Figure 3c). Note that these values include the error derived by topography related changes of the tip-sample contact geometry and film thickness modulations. Although the percentage variation decreases for both sets of samples with increasing the Cr and giving a similar trend, the values are larger in the case of the 2nd set of samples. Considering the small tip apex of the thermal 16 probe, it is reasonable to assume that the tip-sample thermal exchange is localized at the point contact. Particularly, in high vacuum experimental conditions the heat transfer through the liquid meniscus and air is eliminated and, neglecting the conductance due to radiation, the dominant heat transfer mechanism is the conduction due to the mechanical contact of the probe with the sample. Here, the heat source size is comparable to the thickness of the Cr layer and the influence of the Cr layer, with a thermal conductivity one order of magnitude larger than the thermal conductivity of the block copolymers, dominates over the substrate. Therefore, the increase of the Cr layer enhances heat dissipation or conductance within the sample giving the trend seen in Figure 3c. In addition, the decrease of the thermal resistance seen in the measurement on the sample with 1 nm Cr layer compared to the measurement on the bare sample indicates that the heat spreading due to the presence of the metal dominates over the Cr-BCP interface thermal resistance. Finally, the effect of the substrate can also be detected when the thermal resistance is measured in different positions of the same sample. This is the case of thermal resistance line profiles in Figure 2e where the variation of the thermal resistance from the top most of the sample surface to the surface depression is a factor of three larger in the case of the sample with horizontally orientated cylinders. It reflects a commensurate variation in the relative height between the top-most of the surface and the surface depression (as seen in the topographic line profile in Figure 2e), which translates to the relative distance between the top-most of the surface 60" \o "Petersen, 1979 #201" ADDIN EN.CITE Petersen197920111 Holes in 1 Square Centimeter. Science 1997, 276 (5317), 1401-1404. 24 (7) Cheng, J. Y.; Ross, C. A.; Chan, V. Z.-H.; Thomas, E. L.; Lammertink, R. G. H.; Vancso, G. J. Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography. Adv. Mater. 2001, 13 (15), 1174-1178. (8) Ghoshal, T.; Senthamaraikannan, R.; Shaw, M. T.; Holmes, J. D.; Morris, M. A. “In situ” hard mask materials: a new methodology for creation of vertical silicon nanopillar and nanowire arrays. Nanoscale 2012, 4 (24), 7743-7750. (9) Lim, J.; Wang, H.-T.; Tang, J.; Andrews, S. C.; So, H.; Lee, J.; Lee, D. H.; Russell, T. P.; Yang, P. Simultaneous Thermoelectric Property Measurement and Incoherent Phonon Transport in Holey Silicon. ACS Nano 2016, 10 (1), 124-132. (10) Minelli, C.; Hinderling, C.; Heinzelmann, H.; Pugin, R.; Liley, M. Micrometer-Long Gold Nanowires Fabricated Using Block Copolymer Templates. Langmuir 2005, 21 (16), 7080-7082. (11) Ghoshal, T.; Maity, T.; Senthamaraikannan, R.; Shaw, M. T.; Carolan, P.; Holmes, J. D.; Roy, S.; Morris, M. A. Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application. Sci. Rep. 2013, 3, 2772-2772. (12) Guarini, K. W.; Black, C. T.; Milkove, K. R.; Sandstrom, R. L. Nanoscale patterning using self-assembled polymers for semiconductor applications. J. Vac. Sci. Technol. B Microelectron Nanometer Struct. Process Meas. Phenom. 2001, 19 (6), 2784-2788. (13) Hong, A. J.; Liu, C.-C.; Wang, Y.; Kim, J.; Xiu, F.; Ji, S.; Zou, J.; Nealey, P. F.; Wang, K. L. Metal Nanodot Memory by Self-Assembled Block Copolymer Lift-Off. Nano Lett. 2010, 10 (1), 224-229. (14) Cummins, C.; Ghoshal, T.; Holmes, J. D.; Morris, M. A. Strategies for Inorganic Incorporation using Neat Block Copolymer Thin Films for Etch Mask Function and Nanotechnological Application. Adv. Mater. 2016, 28 (27), 5586-5618. (15) Jin, C.; Olsen, B. C.; Wu, N. L. Y.; Luber, E. J.; Buriak, J. M. Sequential Nanopatterned Block Copolymer Self-Assembly on Surfaces. Langmuir 2016, 32 (23), 5890-5898. (16) Black, C. T. In Integration of self assembly for semiconductor microelectronics, Proceedings of the IEEE 2005 Custom Integrated Circuits Conference, 2005., 21-21 Sept. 2005; 2005; pp 87-91. (17) Black, C. T.; Guarini, K. W.; Milkove, K. R.; Baker, S. M.; Russell, T. P.; Tuominen, M. T. Integration of self-assembled diblock copolymers for semiconductor capacitor fabrication. Appl. Phy. Lett. 2001, 79 (3), 409-411. (18) Naito, K.; Hieda, H.; Sakurai, M.; Kamata, Y.; Asakawa, K. In 2.5-inch disk patterned media prepared by an artificially assisted self-assembling method, 2002 IEEE International Magnetics Conference (INTERMAG), 28 April-2 May 2002; 2002; p AB10. (19) Ben-Sasson, A. J.; Tessler, N. Unraveling the Physics of Vertical Organic Field Effect Transistors through Nanoscale Engineering of a Self-Assembled Transparent Electrode. Nano Lett. 2012, 12 (9), 4729-4733. (20) Segalman, R. A.; McCulloch, B.; Kirmayer, S.; Urban, J. J. Block Copolymers for Organic Optoelectronics. Macromolecules 2009, 42 (23), 9205-9216. (21) Lee, Y.; Gomez, E. D. Challenges and Opportunities in the Development of Conjugated Block Copolymers for Photovoltaics. Macromolecules 2015, 48 (20), 7385-7395. (22) Sarkar, B.; Alexandridis, P. Block copolymer–nanoparticle composites: Structure, functional properties, and processing. Prog. Polym. Sci. 2015, 40, 33-62. (23) Stefik, M.; Guldin, S.; Vignolini, S.; Wiesner, U.; Steiner, U. Block copolymer self- assembly for nanophotonics. Chem. Soc. Rev. 2015, 44 (15), 5076-5091. 25 (24) Xia, S.; Song, L.; Chen, W.; Körstgens, V.; Opel, M.; Schwartzkopf, M.; Roth, S. V.; Müller-Buschbaum, P. Printed Thin Diblock Copolymer Films with Dense Magnetic Nanostructure. ACS Applied Materials & Interfaces 2019, 11 (24), 21935-21945. (25) Morkved, T. L.; Wiltzius, P.; Jaeger, H. M.; Grier, D. G.; Witten, T. A. Mesoscopic self‐ assembly of gold islands on diblock‐copolymer films. Appl. Phys. Lett. 1994, 64 (4), 422-424. (26) Lopes, W. A.; Jaeger, H. M. Hierarchical self-assembly of metal nanostructures on diblock copolymer scaffolds. Nature 2001, 414, 735. (27) Kreuzer, M.; Simão, C.; Diaz, A.; Sotomayor Torres, C. M. Formation of Titanium Nanostructures on Block Copolymer Templates with Varying Molecular Weights. Macromolecules 2014, 47 (24), 8691-8699. (28) Erb, D. J.; Schlage, K.; Röhlsberger, R. Uniform metal nanostructures with long-range order via three-step hierarchical self-assembly. Sci. Adv. 2015, 1 (10), e1500751. (29) Zou, W.; Cai, X.; Li, J.; Dai, X.; Zhang, H.; Zhou, A.; Li, J.; Song, L.; Iyoda, T. Selective deposition on block copolymer film by thermal evaporation of silver. Surf. Coat. Tech. 2012, 206 (22), 4634-4638. (30) Gensch, M.; Schwartzkopf, M.; Ohm, W.; Brett, C. J.; Pandit, P.; Vayalil, S. K.; Bießmann, L.; Kreuzer, L. P.; Drewes, J.; Polonskyi, O.; Strunskus, T.; Faupel, F.; Stierle, A.; Müller- Buschbaum, P.; Roth, S. V. Correlating Nanostructure, Optical and Electronic Properties of Nanogranular Silver Layers during Polymer-Template-Assisted Sputter Deposition. ACS Applied Materials & Interfaces 2019, 11 (32), 29416-29426. (31) Roth, S. V.; Santoro, G.; Risch, J. F. H.; Yu, S.; Schwartzkopf, M.; Boese, T.; Döhrmann, R.; Zhang, P.; Besner, B.; Bremer, P.; Rukser, D.; Rübhausen, M. A.; Terrill, N. J.; Staniec, P. A.; Yao, Y.; Metwalli, E.; Müller-Buschbaum, P. Patterned Diblock Co-Polymer Thin Films as Templates for Advanced Anisotropic Metal Nanostructures. ACS Applied Materials & Interfaces 2015, 7 (23), 12470-12477. (32) Zhang, W.; Wu, Z.; Dong, J.; Yan, X.; Gao, W.; Ma, R.; Hou, X. Heat Dissipation Properties of Thin-Film Encapsulation by Insertion of a Metal Thin Film for Organic Light- Emitting Diodes. Phys. Status Solidi A 2018, 215 (23), 1800326. (33) Dolbin, I. V.; Burya, A. I.; Kozlov, G. V. The structure and thermal stability of polymer materials: A fractal model. High Temperature 2007, 45 (3), 313-316. (34) George, M. C.; Rodriguez, M. A.; Kent, M. S.; Brennecka, G. L.; Hopkins, P. E. Thermal Conductivity of Self-Assembling Symmetric Block Copolymer Thin Films of Polystyrene- Block-Poly(methyl methacrylate). J. Heat Trans. 2015, 138 (2), 024505-024505-5. (35) Chen, J. T.; Thomas, E. L.; Ober, C. K.; Hwang, S. S. Zigzag Morphology of a Poly(styrene-b-hexyl isocyanate) Rod-Coil Block Copolymer. Macromolecules 1995, 28 (5), 1688-1697. (36) Pryamitsyn, V.; Ganesan, V. Self-assembly of rod–coil block copolymers. J. Chem. Phys. 2004, 120 (12), 5824-5838. (37) Reenders, M.; ten Brinke, G. Compositional and Orientational Ordering in Rod−Coil Diblock Copolymer Melts. Macromolecules 2002, 35 (8), 3266-3280. (38) Zauscher, S.; Parlak, Z.; Tu, Q. Mapping the Stiffness of Nanomaterials and Thin Films by Acoustic AFM Techniques: Datasheet from ꞏ Volume : "Handbook of Nanomaterials Properties" in SpringerMaterials (https://dx.doi.org/10.1007/978-3-642-31107-9_40), Springer-Verlag Berlin Heidelberg. (39) Jeong, W.; Hur, S.; Meyhofer, E.; Reddy, P. Scanning Probe Microscopy for Thermal Transport Measurements. Nanosc. Microsc. Therm. 2015, 19 (4), 279-302. 26 (40) Mokarian-Tabari, P.; Collins, T. W.; Holmes, J. D.; Morris, M. A. Cyclical “Flipping” of Morphology in Block Copolymer Thin Films. ACS Nano 2011, 5 (6), 4617-4623. (41) Xu, J.; Hong, S. W.; Gu, W.; Lee, K. Y.; Kuo, D. S.; Xiao, S.; Russell, T. P. Fabrication of Silicon Oxide Nanodots with an Areal Density Beyond 1 Teradots Inch−2. Adv. Mater. 2011, 23 (48), 5755-5761. (42) Neto, C.; James, M.; Telford, A. M. On the Composition of the Top Layer of Microphase Separated Thin PS-PEO Films. Macromolecules 2009, 42 (13), 4801-4808. (43) Metwalli, E.; Körstgens, V.; Schlage, K.; Meier, R.; Kaune, G.; Buffet, A.; Couet, S.; Roth, S. V.; Röhlsberger, R.; Müller-Buschbaum, P. Cobalt Nanoparticles Growth on a Block Copolymer Thin Film: A Time-Resolved GISAXS Study. Langmuir 2013, 29 (21), 6331-6340. (44) Farrell, R. A.; Fitzgerald, T. G.; Borah, D.; Holmes, J. D.; Morris, M. A. Chemical interactions and their role in the microphase separation of block copolymer thin films. Int. J. Mol. Sci. 2009, 10 (9), 3671-3712. (45) Wu, S.; Kang, E. T.; Neoh, K. G.; Han, H. S.; Tan, K. L. Surface Modification of Poly(tetrafluoroethylene) Films by Graft Copolymerization for Adhesion Improvement with Evaporated Copper. Macromolecules 1999, 32 (1), 186-193. (46) Dutschke, A.; Diegelmann, C.; Löbmann, P. Nucleation and Growth of TiO2 Thin Films on Modified Polystyrene Surfaces. Chem. Mater. 2003, 15 (18), 3501-3506. (47) Ochoa-Putman, C.; Vaidya, U. K. Mechanisms of interfacial adhesion in metal–polymer composites – Effect of chemical treatment. Composites Part A: Applied Science and Manufacturing 2011, 42 (8), 906-915. (48) Schwartzkopf, M.; Buffet, A.; Körstgens, V.; Metwalli, E.; Schlage, K.; Benecke, G.; Perlich, J.; Rawolle, M.; Rothkirch, A.; Heidmann, B.; Herzog, G.; Müller-Buschbaum, P.; Röhlsberger, R.; Gehrke, R.; Stribeck, N.; Roth, S. V. From atoms to layers: in situ gold cluster growth kinetics during sputter deposition. Nanoscale 2013, 5 (11), 5053-5062. (49) Schwartzkopf, M.; Santoro, G.; Brett, C. J.; Rothkirch, A.; Polonskyi, O.; Hinz, A.; Metwalli, E.; Yao, Y.; Strunskus, T.; Faupel, F.; Müller-Buschbaum, P.; Roth, S. V. Real-Time Monitoring of Morphology and Optical Properties during Sputter Deposition for Tailoring Metal–Polymer Interfaces. ACS Applied Materials & Interfaces 2015, 7 (24), 13547-13556. (50) Pumarol, M. E.; Rosamond, M. C.; Tovee, P.; Petty, M. C.; Zeze, D. A.; Falko, V.; Kolosov, O. V. Direct Nanoscale Imaging of Ballistic and Diffusive Thermal Transport in Graphene Nanostructures. Nano Lett. 2012, 12 (6), 2906-2911. (51) Tovee, P.; Pumarol, M.; Zeze, D.; Kjoller, K.; Kolosov, O. Nanoscale spatial resolution probes for scanning thermal microscopy of solid state materials. J. Appl. Phys. 2012, 112 (11), 114317. (52) El Sachat, A.; Köenemann, F.; Menges, F.; Del Corro, E.; Garrido, J. A.; Sotomayor Torres, C. M.; Alzina, F.; Gotsmann, B. Crossover from ballistic to diffusive thermal transport in suspended graphene membranes. 2D Materials 2019, 6 (2), 025034. (53) Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V. Ultrasound induced lubricity in microscopic contact. Appl. Phys. Lett. 1997, 71 (9), 1177-1179. (54) Kolosov, O.; Briggs, A. Ultrasonic Force Microscopies. In Acoustic Scanning Probe Microscopy; Marinello, F.; Passeri, D.; Savio, E., Eds.; Springer Berlin Heidelberg: Berlin, Heidelberg, 2013; pp 261-292. (55) Bosse, J. L.; Timofeeva, M.; Tovee, P. D.; Robinson, B. J.; Huey, B. D.; Kolosov, O. V. Nanothermal characterization of amorphous and crystalline phases in chalcogenide thin films with scanning thermal microscopy. J. Appl. Phys. 2014, 116 (13), 134904. 27 (56) Briscoe, B. J.; Fiori, L.; Pelillo, E. Nano-indentation of polymeric surfaces. J. Phys. D Appl. Phys. 1998, 31 (19), 2395. (57) Lubarsky, G. V.; Davidson, M. R.; Bradley, R. H. Elastic modulus, oxidation depth and adhesion force of surface modified polystyrene studied by AFM and XPS. Surf. Sci. 2004, 558 (1), 135-144. (58) Franco, D.; Pasqualantonio, P.; Nicholas, D. K.; Oleg, V. K. Subsurface imaging of two- dimensional materials at the nanoscale. Nanotechnology 2017, 28 (8), 085706. (59) Nie, H. Y.; Motomatsu, M.; Mizutani, W.; Tokumoto, H. Local modification of elastic properties of polystyrene–polyethyleneoxide blend surfaces. J. Vac. Sci. Technol. B 1995, 13 (3), 1163-1166. (60) Petersen, K. E.; Guarnieri, C. R. Young’s modulus measurements of thin films using micromechanics. J. Appl. Phys. 1979, 50 (11), 6761-6766. (61) Lahoche, L.; Lorman, V.; Rochal, S. B.; Roelandt, J. M. Effect of the Ordering of Metal/Oxide Interface on the Thermomechanical Behaviour of High Temperature Oxidized Metal Films. Mater. Sci. Forum 1997, 251-254, 459-466. (62) Gan, Y. X. Effect of interface structure on mechanical properties of advanced composite materials. Int J Mol Sci 2009, 10 (12), 5115-5134. (63) Ciprari, D.; Jacob, K.; Tannenbaum, R. Characterization of Polymer Nanocomposite Interphase and Its Impact on Mechanical Properties. Macromolecules 2006, 39 (19), 6565-6573. (64) Amarandei, G.; O’Dwyer, C.; Arshak, A.; Thiele, U.; Steiner, U.; Corcoran, D. Effect of Au Nanoparticle Spatial Distribution on the Stability of Thin Polymer Films. Langmuir 2013, 29 (22), 6706-6714. (65) Torrisi, V.; Ruffino, F. J. C. Metal-polymer nanocomposites:(Co-) evaporation/(Co) sputtering approaches and electrical properties. Coatings 2015, 5 (3), 378-424. (66) Burkstrand, J. M. Formation of metal–oxygen–polymer complexes on polystyrene with nickel and chromium. J. Vac. Sci. Technol. A. 1979, 16 (4), 1072-1074. (67) Friedrich, J. F.; Koprinarov, I.; Giebler, R.; Lippitz, A.; Unger, W. E. S. Reactions and Intermediates at the Metal-Polymer Interface as Observed by XPS and NEXAFS Spectroscopy. J. Adhes. 1999, 71 (2-3), 297-321. (68) Kovacs, G.; Vincett, P. J. J. o. C.; Science, I. Formation and thermodynamic stability of a novel class of useful materials: Close-packed monolayers of submicron monodisperse spheres just below a polymer surface. J. Colloid Interface Sci. 1982, 90 (2), 335-351. (69) Kovacs, G.; Vincett, P. J. T. S. F. Subsurface particle monolayer and film formation in softenable substrates: Techniques and thermodynamic criteria. Thin Solid Films 1984, 111 (1), 65-81. (70) Briggs, A.; Kolosov, O. Acoustic Microscopy: Second Edition, 2010; p 1-384. TOC GRAPHIC 28 29