Description:FIELD OF THE INVENTION
[0001] The present disclosure relates generally to the field of nanotechnology. Particularly, the present disclosure provides a confined-dewetting method for synthesis of metal nanoparticles. The metal nanoparticles of the present invention can open up new possibilities for applications in various industries such as biomedicine, chemistry, nanotechnology and materials science.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] US10155248B2 discloses improved dewetting methods and improved patterned articles produced using such methods.
[0004] PL205140B1 discloses a sputter coated article with improved mechanical durability and/or thermal stability by sputtering at least one Ag inclusive layer in an atmosphere including at least O2 gas.
[0005] US9909203B2 discloses a method for fabrication of metal film with nanoapertures. The method includes the steps of providing a nanopatterned template including a plurality of nanostructures, depositing of the metal film onto the nanopatterned template, and thermally induced dewetting of the metal film to define the nanoapertures in the metal film by diffusion and reflow of the metal film.
[0006] US8685858B2 discloses formation of metal nanospheres and microspheres. The method comprising: adjusting a deposition rate for depositing a metal film on a substrate, wherein the deposition rate controls a density of future formed dots on a surface of the substrate; annealing the metal film to form dots from the metal film that adhere to the substrate and include the density; and detching the substrate using the dots as an etch mask to form pillars in the substrate.
[0007] CN109119332B discloses a method for preparing a patterned ordered bimetal nanoparticle array by adopting an annealing method, which utilizes two treatment methods of laser interference ablation and metal film annealing, firstly utilizes laser interference to ablate a periodic trans-scale micro/nano structure pattern on a silicon wafer, and sputters and deposits a double-layer metal film with a specific thickness on the silicon substrate, and utilizes the anti-wetting characteristic of the metal film on the surface of the patterned silicon substrate in the annealing process to realize the self-assembly of metal nanoparticle templating, thereby obtaining the ordered bimetal nanoparticle array consistent with the laser interference pattern.
[0008] CN114507846A discloses a preparation method of an SERS substrate with silver nanoparticles loaded on the surface.
[0009] US10179952B2 discloses a method of patterning a thin film deposited on a substrate comprising applying a moving focused field of thermal energy to the thin film deposited on the substrate; and dewetting the thin film from the substrate.
[00010] Present technology commonly uses thermal dewetting of metal thin films for making metal nanoparticles. However, this technique produces random size nanoparticles with a large variation in the interparticle spacing. Most applications require control over size and spacing of these nanoparticles. So the main problem is, how to control the dewetting process in order to increase the monodispersity and getting high density nanoparticle with small interparticle separation. There are some ways to guide the dewetting process, but those need sophisticated patterning of the substrates, which requires complex and expensive lithography technique. Even when using these techniques, it is often difficult to control the particle sizes and achieve close arrangements over a large area. Substrates decorated with metal nanoparticles, featuring a well-defined size distribution and small interparticle separation, are required for numerous applications such as localized surface plasmon and surface-enhanced Raman scattering-based sensors, hydrophobic and anti-icing surfaces, antireflective coatings, photochemical reactions, and catalysis. Plasmonic nanoparticles having interparticle gap less than 5 nm show coupled plasmon absorbance, which finds important application in various sensors like DNA sensor.
[00011] Thus, there is need to address these issues as mentioned in the above and to develop a method of synthesis of metal nanoparticles.

OBJECTSOF THE INVENTION
[00012] An object of the present disclosure is to provide a confined-dewetting method for synthesis of metal nanoparticles.
[00013] Another object of the present disclosure is to provide a method for synthesis of high-density and low-dispersity metal nanoparticles.
[00014] Yet another object of the present disclosure is to provide an easy, scalable, cost effective low thermal budget synthesis of metal nanoparticles.

SUMMARYOF THE INVENTION
[00015] The present disclosure relates generally to the field of nanotechnology. Particularly, the present disclosure provides a confined-dewetting method for synthesis of metal nanoparticles.
[00016] An aspect of the present disclosure provides a confined-dewetting method for synthesis of metal nanoparticles comprising: a) depositing a thin metal film on a substrate to form a metal film coated substrate; b) placing the metal film coated substrate in a thermal conducting container followed by adding a liquid form of polymer to obtain a polymer containing metal film coated substrate; c) heating the polymer containing metal film coated substrate under condition to grow nanoparticle and converts the liquid form of polymer to solid polymer film; and d) removing the solid polymer film to obtain a metal nanoparticle.
[00017] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS
[00018] The following drawings form part of the present specification and are included to further illustrate aspects of the present invention. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[00019] Figure 1 illustrates a schematic of the process of preparing metal nanoparticle (here silver is taken as an example) via dewetting method. (a) shows the conventional dewetting method and (b) shows present metal film dewetting method in the presence of PDMS.
[00020] Figure 2 illustrates SEM images of silver nanoparticles formed by heating 20 nm Ag film deposited on a micro textured Silicon substrate and heated at 250 °C for 30 min in (a) absence of PDMS and (b) presence of PDMS. Scale bar for both the images is 200 nm. The particle size distribution histograms are shown in (c).
[00021] Figure 3 illustrates EDAX spectra show the presence of silver in the nanoparticles-decorated, micro-textured silicon substrate formed through the dewetting of a silver film in the presence of PDMS. Inset shows the place where EDAX was done.
[00022] Figure 4 illustrates XRD of the Ag nanoparticle on glass slide, prepared using dewetting of 10nm Ag film in the presence of PDMS. The upper and lower curve shows the raw and background corrected data respectively.
[00023] Figure 5 illustrates Optical images of glass slide with 10nm Ag film (right side slide). The glass slide in the middle was covered with nanoparticles prepared by thermal dewetting of 10 nm Ag film without PDMS, and the left side slide was made in the presence of PDMS.
[00024] Figure 6 illustrates UV-Vis absorbance spectra of nanoparticles prepared with and without PDMS on glass substrates.
[00025] Figure 7 illustrates UV-Vis spectra at various positions of the substrate showing good uniformity of the nanoparticles, synthesized using PDMS, over the substrate.
[00026] Figure 8 illustrates UV-Vis spectra taken at three different times show the stability of the nanoparticle decorated (synthesized using PDMS) substrate even when they kept in ambient.
[00027] Figure 9 illustrates Surface enhanced Raman scattering (SERS) spectra of 1-4 Benzenedithiol (BDT) taken on different substrates. In (a) 1pM BDT was added on glass substrates covered with silver nanoparticles fabricated without PDMS. No detectable signal was observed in this case. On a plane glass slide, detectable signal was observed for 10 mM BDT as shown in (b) (multiplied by a factor of 3 for clarity). Clear peaks of 1pM DBT is observed (shown in (c)) when added on a glass substrate covered with Ag nanoparticles, fabricated with PDMS. On the same substrate, data for 100 pM was shown in (d). The data in (d) was divided by a factor of 5. For all the substrates 20µl DBT in Ethanol solution were added on the 1x1 cm2 size substrate.
[00028] Figure 10 illustrates comparison of surface enhanced Raman scattering (SERS) spectra of Benzenedithiol (BDT) taken on three different substrates and different concentrations. On a plane glass slide, detectable signal was observed (black line) for 10 mM BDT (data multiplied by a factor of 10 for clarity). To observe clear peaks of BDT on glass substrate covered with Ag nanoparticles, fabricated without PDMS, 10 µM concentration needed. The glass substrate covered with Ag nanoparticles, fabricated in the presence of PDMS, 100 pM BDT showed significantly large signal. 20 µL BDT solution was spread on 1x1 cm2 size substrates in all three cases.
[00029] Figure 11 illustrates Reproducibility of the SERS spectra on a glass substrate covered with Ag nanoparticles, fabricated by dewetting Ag film in the presence of PDMS is shown. BDT was taken as the probe molecule. 20µL of 100 pM BDT was spread on a 1x1 cm2 size substrate. Total 49 spectra were shown.

DETAILED DESCRIPTION OF THE INVENTION
[00030] The embodiments herein and the various features and advantageous details thereof are explained more comprehensively with reference to the non-limiting embodiments that are detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[00031] Unless otherwise specified, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skills in the art to which this invention belongs. By means of further guidance, term definitions may be included to better appreciate the teaching of the present invention.
[00032] As used in the description herein, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00033] As used herein, the terms “comprise”, “comprises”, “comprising”, “include”, “includes”, and “including” are meant to be non- limiting, i.e., other steps and other ingredients which do not affect the end of result can be added. The above terms encompass the terms “consisting of” and “consisting essentially of”.
[00034] As used herein, the terms “blend”, and “mixture” are all intended to be used interchangeably.
[00035] The terms “weight percent”, “vol-%”, “percent by weight”, “% by weight”, and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, “percent”, “%”, and the like are intended to be synonymous with “weight percent”, “vol-%”, etc.
[00036] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about”. Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[00037] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[00038] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[00039] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[00040] The present disclosure relates generally to the field of nanotechnology. Particularly, the present disclosure provides a confined-dewetting method for synthesis of metal nanoparticles.
[00041] The present disclosure is on the premise of a surprising discovery that when the dewetting of metal film in confined environment (specially using PDMS) to produce high density and low dispersity metal nanoparticles having strong surface plasmon resonance (SPR) absorption in the visible range. The observed effect is unexpected and surprising.
[00042] The development of high density nanoparticles with sub-10 nm interparticle spacing through the confined dewetting method with PDMS is a breakthrough that has not been reported before. This innovative approach allows for the production of exceptionally dense nanoparticles with precise control and minimal polydispersity, resulting in a remarkably stable product. Moreover, this method is adaptable to a wide range of substrates, and yields a distinct and well-defined LSPR signal. This advancement holds immense importance for the field of nanotechnology, as it opens up new possibilities for applications in various industries such as biomedicine, chemistry, and materials science.
[00043] An aspect of the present disclosure provides a confined-dewetting method for synthesis of metal nanoparticles comprising: a) depositing a thin metal film on a substrate to form a metal film coated substrate; b) placing the metal film coated substrate in a thermal conducting container followed by adding a liquid form of polymer to obtain a polymer containing metal film coated substrate; c) heating the polymer containing metal film coated substrate under condition to grow nanoparticle and converts the liquid form of polymer to solid polymer film; and d) removing the solid polymer film to obtain a metal nanoparticle.
[00044] In an embodiment, the metal is selected from a group consisting of Ag, Au, Cu and combination thereof. Any type of material that dewets by heating can be used in the present invention. Preferably, the metal is Ag, Au and Ag-Au mixture.
[00045] In an embodiment, the thin metal film has a thickness in the range of 5 to 20 nm. Preferably, the thin metal film has a thickness of 10 nm.
[00046] In an embodiment, the polymer is selected from a group consisting of PDMS and other polymers, like silicone, polyimide, that solidifies and survives at or above dewetting temperature of the coating material can also be used in the present invention. Preferably, the polymer is PDMS.
[00047] In an embodiment, the polymer layer has a thickness in the range of 1 µm to 10 mm. Preferably, the polymer layer has a thickness of 8 mm.
[00048] In an embodiment, the substrate is selected from silicon substrate, SiO2 coated silicon substrate, glass substrate, microtextured substrates and curved substrates. A substrate that survive at the dewetting temperature of the metal can be used in the present invention. Preferably, the substrate is siliconsubstrate, SiO2 coated siliconsubstrate and glass substrate. The substrate is not limited to any particular geometry substrate. The substrate geometry is selected from plane, curved or textured substrate.
[00049] In an embodiment, the condition includes temperature in the range of 200 °C to 450 °C for a period in the range of 5 to 30 min. Temperature is not limited to any particular heating rate. It has been observed that the nanoparticle formation successful carried out at temperature as low as 250°C. The maximum heating time required at the lowest temperature (250°C) is less than 30 minutes. At 450°C, 5 minutes is sufficient. PDMS has been utilized as the polymer, which imposes an upper temperature limit of 450°C. Thus, depending on the type of metal film and its thickness it can be done at as low as 200 °C in the present invention. Upper temperature will be limited by the stability of the polymer used.
[00050] In an embodiment, the method further comprises coating of multiple thin films on the substrate. The present invention is not only limited to coating of one type of material.
[00051] Figure 1 shows a schematic of the process of preparing silver metal nanoparticle via dewetting method. Figure 1 (a) shows the conventional dewetting method and Figure 1 (b) shows the metal film dewetting method in the presence of PDMS as per the present invention. Here, PDMS provides the confined environment.
[00052] The present disclosure first deposited metal films on substrates using physical vapor deposition. The thickness of the metal films can range from few nanometers to few tens of nanometer. The choice of substrate can be wide, the present invention has used plane substrates like silicon, SiO2 coated silicon, glass substrate, microtextured substrates, curved substrates etc. In some substrates, more than one type of metal film like silver and gold film are also deposited. Then, these substrates are placed on a high thermal conducting container (generally made of aluminum) and added PDMS in liquid form into it. The amount of PDMS is controlled in such a way that after the solidification (due to heat treatment), the PDMS layer ranges from one micron to few millimeters on top of the metal film coated substrates. The container then placed on a heater and heated for 5 to 30 mins depending on the temperature. The temperature ranging from 200oC to 450oC. It has been found that the metal thin films heated in absence of PDMS give random size and large spacing metal nanoparticle after dewetting. On the other hand, samples heated in the presence of PDMS produced low dispersity metal nanoparticle having small interparticle separation. Metal nanoparticles produced in both the ways, show plasmonic activity. The surface plasmon resonance peak in case of nanoparticle made without PDMS layer, is relatively broad and the overall absorbance is low. Whereas the nanoparticle made in the presence of PDMS show narrow absorbance peak and the amplitude is much higher. When the prepared metal nanoparticles are used for surface enhanced Raman scattering (SERS) study, it has been found that the signal is several orders of magnitude higher compared to the non-PDMS nanoparticles. In the present invention, the enhancement factor of 1010(ten Billion) is obtained using 1-4 Benzenedithiol (BDT) as probe molecule for substrate decorated with silver nanoparticles made in the presence of PDMS.
[00053] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

EXAMPLES
[00054] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1
[00055] The present invention provides a confined-dewetting method for synthesis of metal nanoparticles as shown in Figure 1 (b). A thin Ag film was deposited on a micro textured silicon substrate/glass to form Ag film coated substrate. The Ag film coated substrate was placed on a thermal conducting container made of aluminum. A liquid form of PDMS was added on the Ag film which was heated in the range of 200 °C to 450 °C for a period of 5 min to 30 min. The formation of Ag nanoparticle was started simultaneously with the conversion of the liquid form of PDMS to solid PDMS film. The solid PDMS film was removed to obtain Ag nanoparticle. Similarly, Ag nanoparticles were also prepared without PDMS for comparison purpose.
[00056] Characterization of the prepared Ag nanoparticles was carried out by SEM analysis as shown in Figure 2. SEM images of prepared silver nanoparticles formed by heating 20nm Ag film deposited on a micro textured Silicon substrate and heated at 250oC for 30 min in Figure 2(a) absence of PDMS and Figure 2(b) presence of PDMS. Scale bar for both the images is 200 nm. Figure 2(c) showed the size distribution histograms for both type of particles. The metal thin films heated in absence of PDMS gave random size and large spacing metal nanoparticle after dewetting. On the other hand, samples heated in the presence of PDMS produced low dispersity metal nanoparticle having small interparticle separation. This particle size distribution indicates advantage of the present invention with the regular dewetting method.
[00057] Further, elemental analysis was also carried out as shown in Figure 3. EDAX spectra in Figure 3 showed the presence of silver in the nanoparticles-decorated, micro-textured silicon substrate formed through the dewetting of a silver film in the presence of PDMS. Inset shows the place where EDAX was done.XRD of the Ag nanoparticle on glass slide as shown in Figure 4, prepared using dewetting of 10nm Ag film in the presence of PDMS. The upper and lower curve shows the raw and background corrected data respectively.
[00058] Figure 5 showed optical images of glass slide with 10 nm Ag film (right side slide). The glass slide in the middle was covered with nanoparticles prepared by thermal dewetting of 10 nm Ag film without PDMS, and the left side slide was made in the presence of PDMS.
[00059] Figure 6: UV-Vis absorbance spectra of nanoparticles prepared with and without PDMS on glass substrates. Absorbance peak is much narrower and stronger than the sample where dewetting is done without PDMS. The peak position of samples with PDMS is found to be at the lower wavelength range which also signifies the smaller size of the nanoparticles in the presence of PDMS. Thus, the surface plasmon resonance peak in case of nanoparticle made without PDMS layer, is relatively broad and the overall absorbance is low. Whereas the nanoparticle made in the presence of PDMS showed narrow absorbance peak and the amplitude is much higher.
[00060] UV-Vis spectra at various positions (position 1, position 2 and position 3) of the substrate showing good uniformity of the nanoparticles over the substrate in presence of PDMS as shown in Figure 7. The peak position does not show any noticeable shift from one position to another.
[00061] Stability testing of the prepared Ag nanoparticle in present of PDMS was carried out as shown in Figure 8. UV-Vis spectra taken at three different times (for Day 1, Day 3 and Day 7) showed the stability of the substrate even when they kept in ambient. The peak position did not show any noticeable shift or change in intensity, indicating good stability of the nanoparticles.
[00062] Surface enhanced Raman scattering (SERS) spectra of 1-4 Benzenedithiol (BDT) taken on different substrates as shown in Figure 9. In Figure 9 (a), 1pM BDT was added on glass substrates covered with silver nanoparticles fabricated without PDMS. No detectable signal was observed in this case. On a plane glass slide, detectable signal was observed for 10 mM BDT as shown in Figure 9 (b) (multiplied by a factor of 3 for clarity). Clear peaks of 1pM BDT is observed (shown in Figure 9 (c)) when added on a glass substrate covered with Ag nanoparticles, fabricated with PDMS. On the same substrate, data for 100 pM was shown in Figure 9 (d). The data in Figure 9 (d) was divided by a factor of 5. For all the substrates 20?l BDT in Ethanol solution were added on the 1x1 cm2 size substrate.
[00063] Comparison of surface enhanced Raman scattering (SERS) spectra of Benzenedithiol (BDT) taken on three different substrates and different concentrations as shown in Figure 10. On a plane glass slide, detectable signal was observed (black line) for 10 mM BDT (data multiplied by a factor of 10 for clarity). To observe clear peaks of BDT on glass substrate covered with Ag nanoparticles, fabricated without PDMS, 10?M concentration needed. 20 ?L of 100 pM BDT was spread on 1x1 cm2 size substrates in all three cases. The glass substrate covered with Ag nanoparticles, fabricated in the presence of PDMS, showed significantly large signal.
[00064] Reproducibility of the SERS spectra on a glass substrate covered with Ag nanoparticles, fabricated by dewetting Ag film in the presence of PDMS is shown in Figure 11. BDT was taken as the probe molecule. 20 ?L of 100 pM BDT was spread on a 1x1 cm2 size substrate. Total 49 spectra were shown in Figure 11.
[00065] In the surface enhanced Raman scattering (SERS) study, it has been found that the signal is several orders of magnitude higher compared to the non-PDMS nanoparticles. The enhancement factor of 1010(ten Billion) was achieved using 1-4 Benzenedithiol (BDT) as probe molecule for substrate decorated with silver nanoparticles made in the presence of PDMS.

ADVANTAGES OF THE PRESENT INVENTION
[00066] The present disclosure developed a novel technique where a thin metal film is dewetted in confined environment. A polymer is used for creating a confined environment. The polymer solidifies as the metal film is heated for dewetting and both the process take place simultaneously. The thickness of metal film and the thickness of the initial polymer control the size, density and spacing of the nanoparticles. Using this technique of dewetting of metal thin films in confined environment, the present invention produces metal nanoparticles of very high density and low dispersity with few nanometer interparticle spacing.
, Claims:1. A confined-dewetting method for synthesis of metal nanoparticles comprising:
a) depositing a thin metal film on a substrate to form a metal film coated substrate;
b) placing the metal film coated substrate in a thermal conducting container followed by adding a liquid form of polymer to obtain a polymer containing metal film coated substrate;
c) heating the polymer containing metal film coated substrate under condition to grow nanoparticle and converts the liquid form of polymer to solid polymer film; and
d) removing the solid polymer film to obtain a metal nanoparticle.

2. The method as claimed in claim 1, wherein the metal is selected from a group consisting of Ag, Au, Cu and combination thereof.

3. The method as claimed in claim 1, wherein the thin metal film has a thickness in the range of 5 to 20 nm.

4. The method as claimed in claim 1, wherein the polymer is selected from a group consisting of PDMS, silicones, polyimide and combination thereof.

5. The method as claimed in claim 1, wherein the polymer layer has a thickness in the range of 1 µm to 10 mm.

6. The method as claimed in claim 1, wherein the substrate is selected from silicon substrate, SiO2 coated silicon substrate, glass substrate, microtextured substrates and curved substrates.

7. The method as claimed in claim 1, wherein the substrate geometry is selected from plane, curved or textured substrate.
8. The method as claimed in claim 1, wherein the condition includes temperature in the range of 200 °C to 450 °C for a period in the range of 5 to 30 min.

9. The method as claimed in claim 1, wherein the metal nanoparticle has interparticle spacing in the range of 1 nm to 10 nm.

10. The method as claimed in claim 1, wherein the method further comprises coating of multiple thin films on the substrate.