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In situ and Real-Time Inspection of Nanoparticle Average Size in Flexible Printed Sensors Meital Segev-Bar, Ben Ukrainsky, Gady Konvalina, and Hossam Haick J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09340 • Publication Date (Web): 13 Nov 2015 Downloaded from http://pubs.acs.org on November 20, 2015

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The Journal of Physical Chemistry

In situ and Real-Time Inspection of Nanoparticle Average Size in Flexible Printed Sensors Meital Segev-Bar, Ben Ukrainsky, Gady Konvalina, and Hossam Haick* Department of Chemical Engineering and Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 3200003, Israel

ABSTRACT: Nanoparticles play an integral part for the production of contact and active sensing layers in the fast developing printed electronic technology on flexible devices. Unfortunately, all currently available techniques for nanoparticle characterization are limited to ex situ and/or off-line processing. Here, we describe a new approach composed of two complementary parts for in situ and real-time estimation of the nanoparticles diameter on flexible substrates. The first part of the approach is based on measurements electrical resistance of the device in response to strain, and correlation of the response with the nanoparticles diameter. The second part takes place only when measuring the electrical resistance is unfeasible. It is based on UV-vis absorption of the device and correlation of the absorption peak with the nanoparticle diameter based on previous calibration data from strain sensitivity. The new approach shows excellent estimations of the nanoparticle diameter (2.5 – 20 nm) on the substrate with the advantages of being on-line, in-situ and inexpensive. In addition, the estimated nanoparticle diameter is in excellent agreement with Atomic Force Microscopy (AFM) measurements. These capabilities are expected to improve the process of “quality control” of the nanoscale-enabled flexible devices, which, till now, has been considered to be one of the most annoying issues that inhibit the commercialization of nanotechnology-based flexible products.

Keywords: Nanoparticle, printing, flexible, in situ, gauge factor.

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INTRODUCTION Technology of printed electronics for fabrication of flexible devices has gained enormous attention owing to large-scale and intuitive fabrication possibilities, and light-weightiness and biocompatibility in their versatile applications.1,2 An important component of these printing technologies relies on metal nanoparticles, which have several advantages, such as: 1) simple synthesis with high controllability over the size, capping ligand and morphology;3-6 2) straightforward integration with or in various devices and/or transduction mechanisms;7-9 and 3) high compatibility with printing techniques, such as the inkjet approach.10 The use of printable gold nanoparticles (GNPs) for fabrication of flexible electronic devices as well as chemical and strain sensors has been well researched.4,7,9,11-21 Several studies have demonstrated the production of metallic (conductive) contacts or connections22-25 by simply sintering and/or annealing printed GNPs at relatively high temperatures.14,18,19,26,27 The sintering process influences the characteristics of the devices, such as electrical resistance and reflectance at temperatures >150°C.28-30 In this regards, we have previously shown that a partial sintering/annealing process can enable combination of pressure sensing and conductive features simultaneously by deliberately controlling the size of agglomerations of multiple GNPs.12 For example, a GNP line that was sintered for a relatively long time (e.g., several minutes at 200°C) produced in a conductive gold line that can readily be used as interconnects. On the other hand, partial sintering (e.g., tens of seconds at 180°C) produced highly sensitive strain sensors with well-controlled sensitivity towards various environmental factors (e.g., temperature and humidity). The tight relationship between the GNP effective size (or agglomeration) and the sensing properties of the resulting sensor mainly needs real-time characterization techniques, and most importantly, this is because small changes in GNP diameter affect electrical resistance, optical properties31 and sensitivity15 of the devices. Unfortunately, all currently available techniques for GNP characterization are limited to ex situ and/or off-line processing, something that limits the characterization of representative examples in the production line, and/or limit the characterization to small representative areas of the device under examination. Examples for conventional GNPs characterization techniques include: •

Electron Microscopy and Atomic Force Microscopy (AFM): These techniques provide an image of the GNPs in an ex situ process. Images are representative of only a small area of the whole film or device, and the procedure is time-consuming, requiring a large number of particles to be measured and special skills.32-34 Also individual GNPs were not detectable in the HR-SEM when dense GNP layers were present.

•

Dynamic light scattering: this technique provides ex situ information on the average size of GNPs dispersed in a solution,35 and is limited to low-concentrations of GNP solution.


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It does not offer direct characterization of the GNPs on flexible devices, which, naturally, present different properties than GNPs in solution. At present, no technique for in situ and real-time characterization of the GNPs size estimation is available. We therefore describe a new approach composed of 2 complementary parts for in situ and real-time estimation of the GNPs diameter on flexible substrates. The first part of the approach is based on measurements electrical resistance of the device in response to strain, and correlation of the response with the GNPs diameter (Figure 1a). The second part takes place only when measuring the electrical resistance is unfeasible. It is based on UV-vis absorption of the device and correlation of the absorption peak with the GNP diameter based on previous calibration data from strain sensitivity.

EXPERIMENTAL METHODS Synthesis of Hexanethiol Encapsulated Gold Nanoparticles Gold(III) chloride trihydrate (HAuCl4·3H2O), tetraoctylammonium bromide (TOAB), sodium borohydride, and hexanethiol (HT) were purchased from Sigma-Aldrich. All reagents were of analytical grade and were used as received. Spherical gold nanoparticles (3−5 nm in diameter) were synthesized as described elsewhere36,37. Briefly, a solution of HAuCl4 was added to a stirred solution of TOAB in toluene. After the solution had been stirred and phase separation had occurred, the lower (aqueous) phase was removed. HT and sodium borohydride were added to the toluene phase. After 3 h on ice, the lower phase was removed and the toluene phase rotary evaporated. After first washing with cold ethanol, the solution was kept at 5°C for 18 h until complete immersion had been achieved. The dark brown precipitate was filtered and washed with ethanol. Printing Nanostructures with Propelled Anti-Pinning Ink Droplet Procedure (PAPID)7 All the devices were printed using PAPID approach. Prior to use, all substrates were cleaned by rinsing in acetone, methanol and 2-propanol, followed by drying in a stream of nitrogen, rinsing in double-distilled water and finally drying in another stream of nitrogen. PAPIDs approach allowed the ink droplets to be laterally actuated while conforming to the geometry of the substrate, producing distinct and controllable deposition patterns. This combination of functions was made possible by the binary solvent composition of our ink; the solvents combination included 0.7 volume percent of toluene and 0.3 volume percent of nonane. Hexanthiol-encapsulated GNPs were dissolved in this solvent mixture to a final concentration of 50 mg/ml. The binary composition induces Marangoni vortices within the ink droplets in the direction opposing droplet spreading. The vortices were produced by surface tension gradients generated by concentration gradients following enhanced evaporation of the more volatile compound near the fluid/substrate contact line. Low velocity (4–8 mm s−1) ink droplets, 1.5 µl, were used to produce a characteristic of micro-rivulet (µ-rivulet). The (µrivulet) was protrudes from the corner and trails the droplet, producing distinct and controllable self3 ACS Paragon Plus Environment


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assembled deposition patterns – for more information, please refer to ref. 7. The process is repeated 56 times to create a conductive thin film of 500 ± 100nm in thickness.

Three-point bending setup Bending experiments used a MARK 10 ESM301 motorized test stand, which could apply a constant strain of 1.5 mm/sec. The stress was applied by an upper beam, the lower beams being supporting beams. The substrate was bent under applied stress/pressure/force, with forces being measured with an Advanced Digital FORCE GAUGE (Mark10, USA).

RESULTS AND DISCUSSION Flexible sensors based on Hexanethiol-encapsulated GNPs (FlexHGS) were fabricated on a flexible substrate. GNPs were deposited on 125 µm thick Kapton sheet patterned with 1 mm spaced electrodes, using the PAPID approach.7 Briefly, a droplet of Hexanethiol-encapsulated GNPs dispersed in a mixture of 2 solvents with different vapor pressures was casted on the patterned substrate. The binary composition of the droplet induces Marangoni vortices within the ink droplets in the direction opposing their spreading. The vortices produced by surface tension gradients generated by concentration gradients following the faster evaporation of the more volatile compound near the fluid/substrate contact line. At the end of this process, a thin film of GNPs (500 ± 100 nm thickness) with an initial resistance of 3.7·±1.4·108 ohm was obtained.7 For more details on the fabrication approach of the FlexHGS please refer to the Experimental Section. The FlexHGS was then sintered at a constant temperature of 150-200°C in defined intervals (60 sec at 150°C to 10 sec at 200°C). For each sintering step, FlexHGS resistance was measured while bending it in a 3-point bending setup (see Experimental Section).14 The electrical resistance was continuously recorded during the bending process and the Gauge Factor (GF; sensitivity of the sensor to strain, defined as the ratio between the sensor response to the strain applied) were measured. In parallel, the UV-vis absorption at 400-800 nm, which gave clear peaks at 540-580 nm, were recorded during the sintering process. Note: When facilitating the PAPID approach for printing GNPs films, non-uniform crosssection was expected. In general, small GNPs will be deposited in the edges creating a discontinuous, nonconductive film, while larger particles will be deposited in the middle creating a conductive, micro-rivulet with small GNP size distribution. It is assumable the resistance and the GF of the FlexHGS are mainly affected by the middle, micro-rivulet regime.

Calculation of the FlexHGS’s Inherent Parameters Consistent with others

9,38

, we found that the adjacent GNPs tend to agglomerate, viz. the effective

diameter of the GNPs increases with temperature.12 This was clear from HR-SEM analysis carried out on substrates coated with GNPs at low surface concentration (Figure 1b). GNPs (right side) had diameters ranging from few nanometers to 25 nm after 240 sec sintering at 150°C, values that were 4 ACS Paragon Plus Environment

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significantly larger than GNPs before sintering (left side) which are only ~3 nm in average diameter. It is noteworthy that sintering at a polymer compatible temperature (common polymer glass transition temperatures range from 70°C for polyethylene terephthalate to 270°C for Polyimide)1,39 is possible because of the small size of nanoparticles.29 The electrical resistance, R,40,41 of GNPs film at each sintering step was measured and related parameters were calculated according to the tunneling and/or hopping mechanism,42 as given in the following equations:9,17,38

= exp ( ) ∙ exp (1)

=

!

(1

! − ! $%)

(2)

where is the tunneling constant, is the interparticle distance, is the activation energy (the energy barrier associated with charging adjacent metal cores)43, &' ( is the characteristic thermal energy, e is the charge of an electron, ) is the permittivity of vacuum, )*+ is the dielectric constant of

the thiolate ligand layer, and ,!2 is the radius of each metal core.

The tunneling constant, for alkenthiols is about 13 nm-1.44,45This constant is usually

calculated by measuring the electrical conductance of GNP devices as a function of the thiol ligand length.46 The interparticles distance, , was determined using equations (1) and (2) as follows. Eleven sensors were sintered for different periods at 3 representative sintring tempertures: 423, 453 and 473 K. The resistance of each sensor was recorded as a function of temperature from between 268 to 303 K, and the activation energy of each sensor was calculated according to Equation 1 ( Figure 1c-g). As expected, FlexHGS that was sintered at a specific temperature for longer time had lower activation energy than FlexHGS sintered for shorter time. For example, at 453 K, the activation energy for tunneling was 73 meV after 30 sec, falling to 18 meV after 120 sec. Since the hopping activation energy is strongly dependent on nanoparticle diameter,47 the results imply that sintering and the consequent GNPs enlargement dominates during heating.48 At 423 °C, there is an exception with the results of sintering times of 360 and 600 sec. This could be attributed to sintering processes that are partially activated at this temperature.28-30 The sintering rate highly depends on the temperature, the GNP size increases much more rapidaly at higher temperatures (as will be further discussed in the text). For that reason, FlexHGS with larger sintering time intervals were measured at low sintering temperature. The change in the interparticle distance, ∆ , was calculated based on the experimental activation energies and Equation 2, as detailed in the SI section 1. It is noteworthy that the initial interparticle distance (before sintering), , needed as a reference for the aforementioned estimations was determined from transmission electron microscopy (TEM) images. Figure 1h shows a representative example of the initial interparticle distance of ~1 nm in Hexanethiol-encapsulated GNP film, in good agreement with other results for alkenthiols.38,41,44 5 ACS Paragon Plus Environment


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Figure 1: (a) Optical image of bended FlexHGS (left side). During sintering nanoparticles tend to agglomerate, and as a result, nanoparticles grow in diameter (right side). (b) HR-SEM images of low concentration GNPs on a Kapton sheet before sintering (left side) and after 240 sec at 150°C (right side). The scale bar = 100 nm. FlexHGSs resistance as was measured in a temperature controlled vacuum chamber for temperatures of 268-303 K for FlexHGSs devices sintered at (c) 423, (d) 453 and (e) 473 K. High linearity of FlexHGSs resistance natural logarithm with temperature-1 is presented (for all linear fits R2>0.99). (f) A table summarizing the calculation of the activation energy Ea based on equation 1. This calculation was based on FlexHGS electrical resistance measurements at temperatures of from 268 to 303 K in a vacuum chamber. The activation energy calculation of FlexHGS before sintering was based on the average value of 3 devices. (g) Calculated activation energy for the FlexHGSs. (h) TEM image of hexanethiol encapsulated GNP before sintering (scale bar: 20 nm). Interparticle spacing was estimated as ~1 nm.


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Estimation of GNP Diameter Based on GF Measurements The responses of FlexHGS to strain is highly depended on the interparticles distance, . For example, when bending the devices, the outer layer is being stretched. For GNPs that are deposited on the outer layer, the interparticle distance between the GNPs will increase, as a consequences, the resistance of the device should dramatically increase. This yields a highly sensitive strain sensors with GF value ranging from 50 to 250,14 making this feature attractive for estimation of GNP diameter. FlexHGS resistance was measured while bending it in a 3-point bending setup (see Experimental Section).14 Changes in resistance (∆R) due to bending over the baseline resistance (Rb) were calculated. The ratio between sensor response and the applied strain e.g., the GF, is represented by the following relationship:38

./ ≡ (, + ) (3) To estimate the GF experimentally, changes in ∆R/Rb of the FlexHGS were measured as a function of the strain at different sintering steps (Figure 2a). Based on Equation 1, we would expect the response of the FlexHGS to strain will be exponential, however, probably due to highly disorder GNPs packing arrangements and relatively small strain range, the response to strain is linear.14 The device response upon sintering at 453 K to strain was highly influenced by the sintering time, the longer times resulted in a dramatic increase in the sensitivity to strain. For example, in the case of FlexHGS subjected to 0.05% strain, unsintered FlexHGS gave a relatively small ∆R/Rb response of ~3%, while the same device after 120 sec at 453 K had a ∆R/Rb response of ~12%. FlexHGS results for sintering processes at other temperatures are presented and discussed in SI, Section 2. Enhanced sensitivity to strain with respect to sintering time could be attributed to the agglomeration of adjacent GNPs,12 which ultimately leads to increase in their effective diameter.9,38 GF could be determined experimentally by a simple calibration curve (Figure 2b), and thus in situ inspection of the GNP average diameter could be estimated using Equation (3). Relying on this approach, the GF of the FlexHGS at different sintering times was calculated from the slopes of the responses vs. the strain. Figure 2b and Figure S1 of the SI, show GF is linearly dependent on the sintering time. When aiming for a certain GF, the temperature has a significant effect on the sintering time of FlexHGS, meaning that shorter sintering times are required at higher temperatures. For example, at 160°C, GF ~150 is achievable after 200 sec (Figure S1b). On the other hand, a similar GF can be reached after only 20 sec at 200 0C (Figure S1f). These results indicate that the GF can be easily tuned by the sintering temperature and time. By using Equations 1-3, the diameter, ,, of the GNPs in the FlexHGS was calculated and is used as the right axis in Figure 2b (the calculations of and have been detailed above). These results indicate that GNP diameter can be directly estimated by measuring the GF of a flexible device that does not require expensive equipment and is applicable for any such device that has electrical contacts.



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The kinetics of sintering (i.e., the time needed to get to a predefined effective diameter of GNPs at a specific sintering) can be understood using the Ostwald ripening model, in which the sintering rate is proportional to an exponent of the temperature-1.49,50 The slope of the change in the GNP diameter versus the change in the sintering time was calculated for all temperatures based on the experimental graphs that were obtained from GF measurements as a function of sintering time and equation 3 (Figures 2b and S1). For instance, at 150 °C GNP diameter tends to grow at a rate of 0.18 Å per sec. The growth rates at higher temperatures were much faster, for instance, the rate was 3.4 Å per sec at 200 °C (~19 times faster). In agreement with the rate calculation results, The GF of FlexHGS after 10 sec sintering is ~115, and the GF of FlexHGS after 190 sec of sintering at 150 °C is similar (Figure S1). Thus it can be assumed that the microstructure of the devices is similar. The logarithm of the growth rate is given as a function of the temperature-1 in Figure 2c. It can be concluded that there is high linear correlation between GNP diameter growth rate and temperature-1. The graph can be used as a calibration curve for FlexHGS growth rates. Thus, when a particular average GNP diameter is needed, the working temperature and sintering time can be determined from the calibration curve. The chosen parameters (e.g., sintering temperature and sintering time) can meet fabrication requirements, like the suitable temperature for a substrate or production times.12,30 A correlation was found between the FlexHGS electrical resistance and the calculated diameter for all tested temperatures (Figure 2d). Thus, for the sensor configuration (e.g., 1 mm spacing) when the measured electrical resistance of FlexHGS is ~170 MΩ, the GNP average diameter is probably ~5 nm, but when the electrical resistance of a similar device is ~17 MΩ, the vale will probably be ~15 nm. These results indicate that, once a calibration curve is created, the GNP diameter can be estimated by simply measuring the resistance of a sensor. Inherent FlexHGS parameters can be established based on previous studies and temperature sweeps (Figure 1). Once established, these parameters can be used for any similar device for real-time estimation of GNP diameter. The GF is a direct indication for the GNP diameter, there being a straightforward correlation between the GF and the GNP diameter. A relatively high GF will indicate large nanoparticles and a small GF will indicate relatively small nanoparticles, as can be concluded from Figure 2b and equation 3. For example, an initial GF of ~50 was used to calculate the initial GNP diameter of ~2.5±0.2, which is in good agreement with the GNP diameter from TEM images (Figure 1h). A GF of ~243 was used to calculate a GNP diameter of ~16.6±0.9. When calculating and experimenting with different temperatures and sintering times, a general indication of changes in the GNP diameter is directly related to the in situ device resistance. In addition, the GF measurements are highly repeatable as each measurement was repeated three times with small deviations as can be concluded from error bars in Figure 2b. Figures 2c and d can be consulted for choosing appropriate sintering times and temperatures.


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Figure 2: (a) Response of FlexHGS to strain at different sintering times at 180°C, which has been calculated as the difference between the initial sensor resistance and the resistance during bending, ∆R, normalized by the initial sensor resistance, Rb. The optical image presents the bended sensor under the 3-point bending setup. (b) The GF (left axis) and the calculated diameter (right axis) of FlexHGS as a function of the sintering time for a sintering temperature of 180°C. The symbols and the error bars stand for the average and the standard deviation of 3 measurements (R2=0.98). (c) Logarithm of the change in the GNP diameter with sintering times vs. the temperature-1 (R2=0.99). (d) Logarithm of the sensors resistance vs. the calculated diameter at 6 different sintering temperatures.

Estimation of GNP Diameter Based on UV-vis Measurements For some applications, measuring the electrical resistance of a device during bending is not always feasible. In these cases, an alternative approach has been developed in which GNP size and sintering rate can be assessed by UV-vis measurements.31,33,51 Since for printed electronics it is possible to use transparent or semitransparent sheets14 (instead of Si in conventional microelectronic technologies), the absorption of GNPs can be measured directly on the substrate, thereby establishing an accurate and real-time approach. This helps in preliminarily establishing the correlation between the electrical measurement abovementioned and the UV-vis absorption peak and similar sintering conditions, as described below. Examination of this hypothesis was conducted with hexanethiol GNP films printed with PAPID approach in the same manner to the FlexHGS devices mentioned earlier in the text.



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Figure 3a shows the UV-vis spectra of GNPs film on a Kapton sheet. The spectra were taken at representative intervals during sintering process at 180 °C. The spectra had red shifts with increasing sintering time, which are correlated with GNPs enlargement.31 The UV-vis spectra's peak (λmax) was calculated and shown as a function of sintering time (Figure 3b). The red shift can be interpreted to a linear increase of λmax with sintering time. Similar results were obtained for sintering at other temperatures (see SI, Section 4). In a similar manner to Figure 2c, the slope of λmax as a function of sintering time was calculated for all temperatures recorded. The change in UV-vis spectra's peak, λmax, is plotted against temperature-1 (Figure 3c). The rate of change is analogous to the rate of change in the GNP diameter, calculated based on the GF analysis. Thus, by this analogy, GNP diameter can be determined based on the absorption spectra. λmax and GNP diameter were correlated by comparing the results at similar sintering times (Figure 3d, blue x). A comparative study was done on similar GNPs in solution using heat treatment.52 The mother solution and additional 2 grown fraction of GNPs were examined by TEM (Figure 3 e-g). The GNP diameter in a solution (calculated based on TEM images) was also linearly correlated with λmax; however, the slopes were dramatically different between the absorption of GNPs in solution to GNPs on a flexible substrate. These results were expected since surface plasmon resonance (SPR) is highly influenced by GNP concentration and surrounding media.53 Thus, GNP with similar size and shape will have different SPR peak in a solution and on a substrate. The results emphasizes that properties (such as GNP diameter) need to be estimated in situ.


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Figure 3: (a) Absorption spectra of GNPs film on a 125um Kapton sheet taken at representative times during sintering at 180°C. (b) The wavelength for which the absorption was maximal (λmax) was calculated based on UV-vis measurements of 2 different samples that were sintered in a similar process and the same time intervals. The X symbol represents the average, and the error bars stand for the STDEV of the 2 sample measurements, R2=0.80. (c) Rate of change of λmax (blue circles) and GNP diameter (GF) (black X) as a function of sintering temperature-1. (d) GNP diameter as a function of λmax for GNPs in a solution, calculated based on TEM images, R2=0.99 (red circles), and for GNPs film on a Kapton sheet, calculated based on the measured GF at representative times during sintering at 180°C, R2=0.99 (blue X). TEM images of hexanethiol encapsulated GNPs (upper panel) and the diameter histograms (lower panel) for solution with λmax of (e) 533 nm (f) 545 nm (g) 580 nm. Scale bar = 5 nm.



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AFM measurements of GNP Diameter and Comparison to Theoretical Calculations Comparing the estimated diameter calculated using the above mentioned technique was performed with AFM. For that purpose, GNP film was printed on a Kapton substrate using PAPID approach as described before. This sample was then sintered for 300 sec at 160 °C. The sample was tested in the AFM at several locations along the GNP film. Indeed, as expected, the edges of the GNP film contained smaller discontinues particles in comparison to that in the middle of the film, however, since electrons are most likely to travel along the minimal resistance pathway, the edges of the film are not expected to contribute to the resistance of the device nor to the characteristic GF. As can be seen in Figure 4, GNPs showed clear borderlines. Whereas the lateral resolution of the AFM is limited due to the tip size, the height resolution can be employed in order to measure the particles diameter. GNP diameter analysis was conducted based on eight AFM scan in the middle of the film (scan size: 500 nm x 500 nm). The GNPs have sphere-like shape, so the basic assumption was that the GNP radius can be measured by measuring the profile height between the borderline to the center of a particle (as can be seen in the profile line in Figure 4a). This measurement was conducted for over 100 borderlines. The measured GNP diameter (the radius multiplies by 2) is presented in Figure 4b. The average diameter is 12.3±4.6 nm. The UV-vis absorption peak measured for this sample was 560 nm. Based on the sintering time, temperature and the measured absorption peak, the estimated GNP diameter would be ~ 13 nm. This results lies in excellent agreement with the theoretical calculation, highlighting the efficiency of the suggested inspection method.

Figure 4: (a) AFM scan of GNP film printed on a Kapton substrate using PAPID approach. (b) Histogram of the profile height between the borderline (multiplied by 2) to the center of a particle for over 100 borderlines.


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CONCLUSIONS We describe a new methodology for the estimation of GNP size, which is both, simple and does not require expensive equipment, nor is time-consuming. For many flexible GNPs (and other types of nanoparticles) devices, the approach can be used for real-time in situ estimation of nanoparticle size. In addition, This method can also be applied to different types of sintering (e.g., laser pulse,28 chemical30,32) since the main mechanism of particle growth remains similar, making this method applicable for the next generation of low temperatures sintering processes.39 The main advantages include: in situ (during fabrication steps) monitoring of GNP size, applicability for flexible electronic devices (via electrical resistance measurements), and also for optical devices (via UV-vis absorption measurements). The main disadvantage is that the results include only an average GNP size without size distribution data. In addition, these methods might meet problem when the top layer is not homogenous at macro scale.

CORRESPONDING AUTHOR: * H. Haick. Email: [email protected]

ACKNOWLEDGMENTS We acknowledge the financial support of Phase-I (grant ID: OPP1058560) and the Phase-II (grant ID: OPP1109493) Grand Challenges Explorations award of the Bill & Melinda Gates Foundation.

SUPPORTING INFORMATION: Calculation of FlexHGS’s Inherent Parameters; FlexHGS results for sintering at 150 to 200°C; UVvis Absorption of GNPs on Kapton Sheet. This material is available free of charge via the Internet at http://pubs.acs.org.

COMPETING FINANCIAL INTERESTS The authors declare no competing financial interests.



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REFERENCES (1) Khan, S.; Dahiya, R.; Lorenzelli, L. Technologies for Printing Sensors and Electronics Over Large Flexible Substrates: A Review. IEEE Sensors J. 2015, 15, 3164 - 3185. (2)Kim, D.-H.; Ghaffari, R.; Lu, N.; Rogers, J. A. Flexible and Stretchable Electronics for Biointegrated Devices. Annu. Rev. Biomed. Eng. 2012, 14, 113-128. (3) Segev-Bar, M.; Shuster, G.; Haick, H. Effect of Perforation on the Sensing Properties of Monolayer-Capped Metallic Nanoparticle Films. J. Phys. Chem. C 2012, 116, 15361-15368. (4) Haick, H. Chemical Sensors Based on Molecularly Modified Metallic Nanoparticles. J. Phys. D: Appl. Phys. 2007, 40, 7173. (5) Dovgolevsky, E.; Konvalina, G.; U., T.; Haick, H. Monolayer-Capped Cubic Platinum Nanoparticles for Sensing Nonpolar Analytes in Highly Humid Atmospheres. J. Phys. Chem. C 2010, 114, 14042-14049 (6) Dovgolevsky, E.; Tisch, U.; Haick, H. Chemically Sensitive Resistors Based on MonolayerCapped Cubic Nanoparticles: Towards Configurable Nanoporous Sensors. Small 2009, 5, 1158-1161. (7) Konvalina, G.; Leshansky, A.; Haick, H. Printing Nanostructures with a Propelled Anti‐Pinning Ink Droplet. Adv. Funct. Mater. 2015, 25, 2411-2419. (8) Kahn, N.; Lavie, O.; Paz, M.; Segev, Y.; Haick, H. Dynamic Nanoparticle-Based Flexible Sensors: Diagnosis of Ovarian Carcinoma from Exhaled Breath. Nano Lett. 2015, 15, 7023-7028. (9) Segev-Bar, M.; Haick, H. Flexible Sensors Based on Nanoparticles. ACS Nano 2013, 7, 83668378. (10) Singh, M.; Haverinen, H. M.; Dhagat, P.; Jabbour, G. E. Inkjet Printing—Process and Its Applications. Adv. Mater. 2010, 22, 673-685. (11) Zhao, W.; Luo, J.; Shan, S.; Lombardi, J. P.; Xu, Y.; Cartwright, K.; Lu, S.; Poliks, M.; Zhong, C. J. Nanoparticle‐Structured Highly Sensitive and Anisotropic Gauge Sensors. Small 2015, 16, 4509-4516. (12) Segev-Bar, M.; Konvalina, G.; Haick, H. High‐Resolution Unpixelated Smart Patches with Antiparallel Thickness Gradients of Nanoparticles. Adv. Mater. 2015, 27, 1779-1784. (13) Nakhleh, M. K.; Broza, Y. Y.; Haick, H. Monolayer-Capped Gold Nanoparticles for Disease Detection from Breath. Nanomedicine 2014, 9, 1991-2002. (14) Segev-Bar, M.; Landman, A.; Nir-Shapira, M.; Shuster, G.; Haick, H. Tunable Touch Sensor and Combined Sensing Platform: Toward Nanoparticle-based Electronic Skin. ACS Appl. Mater. Interfaces 2013, 5, 5531-5541. (15) Sangeetha, N. M.; Decorde, N.; Viallet, B.; Viau, G.; Ressier, L. Nanoparticle-Based Strain Gauges Fabricated by Convective Self Assembly: Strain Sensitivity and Hysteresis with Respect to Nanoparticle Sizes. J. Phys. Chem. C 2013, 117, 1935-1940. (16) Konvalina, G.; Haick, H. The Effect of Humidity on Nanoparticle-Based Chemiresistors: A Comparison Between Synthetic and Real-World Samples. ACS Appl. Mater. Interfaces 2012, 4, 317325. (17) Farcau, C.; Sangeetha, N. M.; Decorde, N.; Astilean, S.; Ressier, L. Microarrays of Gold Nanoparticle Clusters Fabricated by Stop&Go Convective Self-Assembly for SERS-based Sensor Chips. Nanoscale 2012, 4, 7870-7877. (18) Olichwer, N.; Leib, E. W.; Halfar, A. H.; Petrov, A.; Vossmeyer, T. Cross-Linked Gold Nanoparticles on Polyethylene: Resistive Responses to Tensile Strain and Vapors. ACS Appl. Mater. Interfaces 2012, 4, 6151-6161. (19) Yin, J.; Hu, P.; Luo, J.; Wang, L.; Cohen, M. F.; Zhong, C.-J. Molecularly Mediated Thin Film Assembly of Nanoparticles on Flexible Devices: Electrical Conductivity versus Device Strains in Different Gas/Vapor Environment. ACS Nano 2011, 5, 6516-6526. (20) Shuster, G.; Gallimidi, Z.; Reiss, A. H.; Dovgolevsky, E.; Billan, S.; Abdah-Bortnyak, R.; Kuten, A.; Engel, A.; Shiban, A.; Tisch, U. Classification of Breast Cancer Precursors Through Exhaled Breath. Breast Cancer Res. Treat. 2011, 126, 791-796. (21) Vishinkin, R.; Haick, H. Nanoscale Sensor Technologies for Disease Detection via Volatolomics. Small 2015, DOI: 10.1002/smll.201501904. (22) Haick, H.; Niitsoo, O.; Ghabboun, J.; Cahen, D. Electrical Contacts to Organic Molecular Films by Metal Evaporation: Effect of Contacting Details. J. Phys. Chem. C 2007, 111, 2318-2329. 14 ACS Paragon Plus Environment

Page 14 of 17

Page 15 of 17

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(23) Haick, H.; Ghabboun, J.; Niitsoo, O.; Cohen, H.; Cahen, D.; Vilan, A.; Hwang, J.; Wan, A.; Amy, F.; Kahn, A. Effect of Molecular Binding to Semiconductor on a Metal/ Molecule/Semiconductor Junction Behavior. J. Phys. Chem. B. 2005, 109, 9622-9630. (24) Haick, H.; Ghabboun, J.; Cahen, D. Pd versus Au as Evaporated Metal Contacts to Molecules. Appl. Phys. Lett. 2005, 86, 042113/1-042113/3. (25) Haick, H.; Ambrico, M.; Ghabboun, J.; Ligonzo, T.; Cahen, D. Contacting Organic Molecules by Metal Evaporation. Phys. Chem. Chem. Phys. 2004, 6, 4538-4541. (26) Wang, L.; Luo, J.; Yin, J.; Zhang, H.; Wu, J.; Shi, X.; Crew, E.; Xu, Z.; Rendeng, Q.; Lu, S. Flexible Chemiresistor Sensors: Thin Film Assemblies of Nanoparticles on a Polyethylene Terephthalate Substrate. J. Mater. Chem. 2010, 20, 907-915. (27) Farcau, C.; Sangeetha, N. M.; Moreira, H.; Viallet, B.; Grisolia, J.; Ciuculescu-Pradines, D.; Ressier, L. High-Sensitivity Strain Gauge Based on a Single Wire of Gold Nanoparticles Fabricated by Stop-and-Go Convective Self-Assembly. ACS Nano 2011, 5, 7137-7143. (28) Ko, S. H.; Pan, H.; Grigoropoulos, C. P.; Luscombe, C. K.; Fréchet, J. M. J.; Poulikakos, D. AllInkjet-Printed Flexible Electronics Fabrication on a Polymer Substrate by Low-Temperature HighResolution Selective Laser Sintering of Metal Nanoparticles. Nanotechnol. 2007, 18, 345202. (29) Ko, S. H.; Park, I.; Pan, H.; Grigoropoulos, C. P.; Pisano, A. P.; Luscombe, C. K.; Fréchet, J. M. J. Direct Nanoimprinting of Metal Nanoparticles for Nanoscale Electronics Fabrication. Nano Lett. 2007, 7, 1869-1877. (30) Coutts, M. J.; Cortie, M. B.; Ford, M. J.; McDonagh, A. M. Rapid and Controllable Sintering of Gold Nanoparticle Inks at Room Temperature Using a Chemical Agent. J. Phys. Chem. C 2009, 113, 1325-1328. (31) Jain, P. K.; Lee, K. S.; El-Sayed, I. H.; El-Sayed, M. A. Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine. J. Phys. Chem. B 2006, 110, 7238-7248. (32) Magdassi, S.; Grouchko, M.; Berezin, O.; Kamyshny, A. Triggering the Sintering of Silver Nanoparticles at Room Temperature. ACS Nano 2010, 4, 1943-1948. (33) Martínez, J. C.; Chequer, N. A.; González, J. L.; Cordova, T. Alternative Metodology for Gold Nanoparticles Diameter Characterization Using PCA Technique and UV-VIS Spectrophotometry. Nanosci. Nanotechnol. 2012, 2, 184-189. (34) Baalousha, M.; Ju‐Nam, Y.; Cole, P. A.; Gaiser, B.; Fernandes, T. F.; Hriljac, J. A.; Jepson, M. A.; Stone, V.; Tyler, C. R.; Lead, J. R. Characterization of Cerium Oxide Nanoparticles—Part 1: Size Measurements. Environ. Toxicol. Chem. 2012, 31, 983-993. (35) Domingos, R. F.; Baalousha, M. A.; Ju-Nam, Y.; Reid, M. M.; Tufenkji, N.; Lead, J. R.; Leppard, G. G.; Wilkinson, K. J. Characterizing Manufactured Nanoparticles in the Environment: Multimethod Determination of Particle Sizes. Environ. Sci. Technol. 2009, 43, 7277-7284. (36) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. Synthesis of Thiol-Derivatised Gold Nanoparticles in a Two-Phase Liquid–Liquid System. J. Chem. Soc. Chem. Commun. 1994, 801-802. (37) Hostetler, M. J.; Wingate, J. E.; Zhong, C.-J.; Harris, J. E.; Vachet, R. W.; Clark, M. R.; Londono, J. D.; Green, S. J.; Stokes, J. J.; Wignall, G. D. Alkanethiolate Gold Cluster Molecules with Core Diameters from 1.5 to 5.2 nm: Core and Monolayer Properties as a Function of Core Size. Langmuir 1998, 14, 17-30. (38) Herrmann, J.; Müller, K.-H.; Reda, T.; Baxter, G. R.; Raguse, B.; De Groot, G. J. J. B.; Chai, R.; Roberts, M.; Wieczorek, L. Nanoparticle Films as Sensitive Strain Gauges. Appl. Phys. Lett. 2007, 91, 183105. (39) Nathan, A.; Ahnood, A.; Cole, M. T.; Lee, S.; Suzuki, Y.; Hiralal, P.; Bonaccorso, F.; Hasan, T.; Garcia-Gancedo, L.; Dyadyusha, A. Flexible Electronics: The Next Ubiquitous Platform. Proc. IEEE 2012, 100, 1486-1517. (40) Schmid, G.; Simon, U. Gold Nanoparticles: Assembly and Electrical Properties in 1–3 Dimensions. Chem. Commun. 2005, 697-710. (41) Franke, M. E.; Koplin, T. J.; Simon, U. Metal and Metal Oxide Nanoparticles in Chemiresistors: Does the Nanoscale Matter? Small 2006, 2, 36-50.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(42) Ye, C.; Li, M.; Xue, M.; Shen, W.; Cao, T.; Song, Y.; Jiang, L. Flexible Au Nanoparticle Arrays Induced Metal-Enhanced Fluorescence Towards Pressure Sensors. J. Mater. Chem. 2011, 21, 52345237. (43) Steinecker, W. H.; Rowe, M. P.; Zellers, E. T. Model of Vapor-Induced Resistivity Changes in Gold−Thiolate Monolayer-Protected Nanoparticle Sensor Films. Anal. Chem. 2007, 79, 4977-4986. (44) Holmlin, R. E.; Haag, R.; Chabinyc, M. L.; Ismagilov, R. F.; Cohen, A. E.; Terfort, A.; Rampi, M. A.; Whitesides, G. M. Electron Transport Through Thin Organic Films in Metal−Insulator−Metal Junctions Based on Self-Assembled Monolayers. J. Am. Chem. Soc. 2001, 123, 5075-5085. (45) Raguse, B.; Barton, C. S.; Müller, K.-H.; Chow, E.; Wieczorek, L. Gold Nanoparticle Chemiresistor Sensors in Aqueous Solution: Comparison of Hydrophobic and Hydrophilic Nanoparticle Films. J. Phys. Chem. C 2009, 113, 15390-15397. (46) Wuelfing, W. P.; Green, S. J.; Pietron, J. J.; Cliffel, D. E.; Murray, R. W. Electronic Conductivity of Solid-State, Mixed-Valent, Monolayer-Protected Au Clusters. J. Am. Chem. Soc. 2000, 122, 11465-11472. (47) Yajadda, M. M. A.; Levchenko, I.; Han, Z. J.; Ostrikov, K. Hierarchical Multilevel Arrays of Self-Assembled Gold Nanoparticles: Control of Resistivity-Temperature Dependence. Appl. Phys. Lett. 2010, 97, 163109. (48) Chen, Y.; Palmer, R. E.; Wilcoxon, J. P. Sintering of Passivated Gold Nanoparticles under the Electron Beam. Langmuir 2006, 22, 2851-2855. (49) Yang, F.; Chen, M. S.; Goodman, D. W. Sintering of Au Particles Supported on TiO2(110) during CO Oxidation. J. Phys. Chem. C 2008, 113, 254-260. (50) Perelaer, J.; Smith, P. J.; Mager, D.; Soltman, D.; Volkman, S. K.; Subramanian, V.; Korvink, J. G.; Schubert, U. S. Printed Electronics: The Challenges Involved in Printing Devices, Interconnects, and Contacts Based on Inorganic Materials. J. Mater. Chem. 2010, 20, 8446-8453. (51) Haiss, W.; Thanh, N. T. K.; Aveyard, J.; Fernig, D. G. Determination of Size and Concentration of Gold Nanoparticles from UV−Vis Spectra. Anal. Chem. 2007, 79, 4215-4221. (52) Teranishi, T.; Hasegawa, S.; Shimizu, T.; Miyake, M. Heat-Induced Size Evolution of Gold Nanoparticles in the Solid State. Adv. Mater. 2001, 13, 1699. (53) Jain, P. K.; Huang, X.; El-Sayed, I. H.; El-Sayed, M. A. Review of Some Interesting Surface Plasmon Resonance-enhanced Properties of Noble Metal Nanoparticles and Their Applications to Biosystems. Plasmonics 2007, 2, 107-118.


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