PL217816B1 - Method for coating the surface with nanoparticles - Google Patents

Abstract

The material is immersed in a solution containing nanoparticles covered with a charged organic or polymer layer and salt. The solution contains exclusively particles with same-sign charges. The specifically mentioned coated surfaces are glass, indium tin oxide (ITO), silicon and gallium arsenide. The specifically mentioned nanoparticles are gold (Au), silver (Ag), platinum (Pt), palladium (Pd), cadmium chalcogenide (cadmium sulphide CdS, cadmium selenide CdSe, cadmium telluride CdTe), indium phosphide (InP), lead sulphide (PbS), indium arsenide (InAs) and zinc oxide (ZnO), and core shell particles with an outer layer of CdSe, zinc sulphide (ZnS) or zinc selenide (ZnSe). The immersion process may be repeated.

Description

The subject of the invention is a method of coating the surface of a material with nanoparticles. The method is used, among others for coating materials such as glass, indium oxide doped with tin oxide (ITO), silicon and other semiconductors.

Nanoparticles - particles of elements and chemical compounds whose, by convention, at least one of the dimensions does not exceed 100 nm - are characterized by chemical and physical properties that differ from those of these substances in a less comminuted form. Due to the high surface energy, nanoparticles must be secured against aggregation by means of a monolayer of organic molecules or polymers. The particles forming such protective layers may contain in their structure functional groups introduced in order to provide the nanoparticles covered by them with appropriate physical, biological properties or allowing chemical reactions to be carried out on their surface.

Along with the development of methods for obtaining nanoparticles and a better understanding of their properties, attempts are made to use their properties for practical purposes, including in such areas of life as medicine, catalysis, construction of detectors or obtaining energy from renewable sources. To make this possible, in some cases it is necessary to arrange the nanoparticles into two- and three-dimensional structures.

Plane structures - two-dimensional - consisting of or containing nanoparticles of metal (Au, Ag, Pd, Pt, Cu) or semiconductor (CdS, CdSe) arouse interest because of their potential practical importance in the construction of solar cells, LSPR or SERS detectors , electronics, corrosion protection, heterogeneous catalysis, anti-reflective coatings, displays and cell adhesion substrates.

Currently, several methods of obtaining such coatings are known. These are electrodeposition, the Langmuir-Blodgett technique, the spin-coating or casting technique, and the sol-gel technique.

All of these methods have one or several disadvantages such as requiring expensive equipment, being used for a narrow set of surfaces or only covering flat surfaces or small size surfaces. Therefore, it is important to search for methods that allow to cover large areas quickly and cheaply and / or with developed topography.

The present invention relates to a method of coating the surface of materials with nanoparticles. This coating takes place by dipping the surface to be coated in a mixture of nanoparticles coated with a positively charged organic layer, for example 11-mercaptoundecyltrimethylammonium chloride (TMA), and salt. The surface is then rinsed with water, optionally in organic solvents, e.g. methanol, and dried.

In the recently published invention application No. US 2009/0098366 A1 and the publication [Smoukov S.K., Bishop K.J.M., Kowalczyk B., Kalsin A.M., Grzybowski B.A .; Journal of the American Chemical Society, 50 (129), 15623-15630] describes a similar method for surface coating with nanoparticles. However, in this method it is necessary to use a properly prepared mixture consisting of two types of nanoparticles; coated with TMA, which gives them a positive charge, and coated with 11-mercaptoundecanoic acid (MUA), which gives them a negative charge at high pH. The method according to the invention differs in that only solutions of positively charged nanoparticles are used.

According to the invention, a method of coating a surface of a material with nanoparticles, comprising the step of immersing said surface in a solution comprising a mixture of nanoparticles coated with a charged organic or polymer layer and a salt, characterized in that said solution comprises only uniformly charged particles and the concentration of said salt in said solution is from 0.01 mol / l to 2.0 mol / l.

In one embodiment of the invention, said surface is positively charged and said solution contains only negatively charged particles.

According to the invention, said solution is an aqueous solution.

In another embodiment of the invention, said solution is a non-aqueous solution, preferably a methanol solution.

According to the invention, said salt is an inorganic salt.

Alternatively, said salt is an organic salt, preferably the salt is a salt of a carboxylic acid.

PL 217 816 B1

Preferably, said nanoparticles have a size from 1 nm to 100 nm.

In another embodiment of the invention, said surface is negatively charged and said solution contains only positively charged particles.

According to the invention, said nanoparticles are metallic nanoparticles, preferably selected from the group consisting of Au, Ag, Pt, Pd.

Alternatively, said nanoparticles are semiconductor nanoparticles, preferably selected from the group consisting of CdS, CdSe, CdTe, InP, PbS, InAs, ZnO.

In yet another preferred embodiment of the invention, said nanoparticles are core-shell bi- or multicomponent nanoparticles with a top layer preferably consisting of CdSe, ZnS, ZnSe.

In particular, according to the invention, said nanoparticles may be CdTe / CdSe, CdSe / ZnS or CdSe / ZnSe nanoparticles.

Preferably, said nanoparticles are coated with a positively charged layer of 11-mercaptoundecyltrimethylamine chloride, TMA.

Preferably, the surface to be coated is a surface selected from glass, tin-doped indium oxide, ITO, silicon, gallium arsenide, or other semiconductors.

Preferably the duration of a single dip is from 10 seconds to 60 minutes, preferably from 15 seconds to 10 minutes.

According to the invention, said dipping step is repeated.

Preferably, the number of repetitions is from 2 to 10.

The invention will now be illustrated in more detail in the preferred embodiments with reference to the accompanying drawings in which:

Fig. 1 shows a photo of glass plates immersed once (1), twice (2), three times (3) and five times (4) for one minute in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l,

Fig. 2 shows the measured absorbances of glass plates immersed in solutions with a nanoparticle concentration of 0.15 mgAu / ml and a NaCl concentration of 0, 0.001, 0.01, 0.1, 0.5, 2, 4 or 6 mol / l, in depending on the number of dives. The duration of each dive was 1 minute. After each immersion, the plates were rinsed in water, methanol, dried and its absorbance was measured,

Fig. 3 shows the measured absorbances of glass plates immersed in solutions with a nanoparticle concentration of 0.15 mgAu / ml depending on the salt concentration. The plates were immersed five times for 1 minute (a) or eight times for 1 minute (b). After each dipping, the plates were rinsed in water, methanol and dried. At a salt concentration close to 1 mol / l, nanoparticles fall out of the solution, which prevents the measurement,

Fig. 4 shows the measured absorbances of glass plates immersed in solutions with a nanoparticle concentration of 0.15 mgAu / ml and salt: (a) KSCN, (b) Na2CO3, (c) NaCl, (d) sodium acetate, (e) NaNO3 or ( (f) 2 mol / l sodium potassium tartrate. The single dip time was 1 minute. After each immersion, the plates were rinsed in water, methanol and dried,

Fig. 5 shows graphs of the dependence of the degree of surface coverage on the total immersion time in the nanoparticle solution for three different nanoparticle concentrations: 0.15 (a), 0.075 (b), 0.015 mgAu / ml (c) and NaCl concentration 2 mol / l

Fig. 6 shows a photo of an ITO plate immersed once for 5 minutes in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l,

Fig. 7 shows a photo of a silicon wafer immersed five times for a period of 5 minutes in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l,

Fig. 8 shows a picture of a silicon wafer immersed five times for 5 minutes in a solution with a nanoparticle concentration of 0.15 mgAu / ml and 2 mol / l NaCl, and then kept in oxygen plasma for 4 minutes.

The method is used to coat materials with negatively charged surfaces, in particular glass, ITO, silicon, gallium arsenide and other semiconductors. ITO is the abbreviation commonly used for tin-doped indium oxide.

The method of the invention uses metallic nanoparticles, including Au, Ag, Pt, Pd, and or semiconductor nanoparticles, including CdS, CdSe, CdTe, InP, PbS, InAs, ZnO, bi and multicomponent.

PL 217 816 B1 core-shell with a top layer, e.g. of CdSe, ZnS, ZnSe, such as e.g. CdTe / CdSe, CdSe / ZnS, CdSe / ZnSe covered with a positively charged organic or polymer layer or mixtures of such nanoparticles.

The method uses nanoparticles with a size from 1 nm to 100 nm.

In the method according to the invention, it is advantageous to clean the surface to be covered by rinsing in order to achieve a greater degree of coverage. This variant is illustrated by example 2.

In the method of the invention, solutions of organic and inorganic salts are used in any concentration, it being preferred to use concentrations in the range of 0.01 to 2 mol / l to achieve maximum coverage. As can be seen from Figures 2 and 3, the maximum absorbance corresponding to the maximum degree of coverage was obtained for a salt concentration of 0.1 mol / l after eight one-minute dips. Under these conditions, further dips do not lead to an increase in coverage. Depending on the nature of the salt and the concentration of the nanoparticles, under certain conditions, aggregation and / or precipitation of the nanoparticles from the mixture may occur. Such a phenomenon took place in Example 4 at a NaCl concentration of about 1 mol / L, so that the corresponding absorbance was not measured, Fig. 3. In this case, surface coating is impossible. As can be seen from example 4, the salt concentration should then be lowered or increased.

The type of salt used has an influence on the degree of coverage achieved. Among the tested salts, the densest coverage was obtained using salts of carboxylic acids - Fig. 4.

In the method according to the invention, the rate of surface coating with nanoparticles increases with increasing concentration of nanoparticles, as shown in Fig. 5.

In the method according to the invention, it is possible to achieve surface concentrations arbitrarily lower than the maximum by reducing the concentration of nanoparticles, reducing the salt concentration and reducing the number of dips of the surface to be coated in the nanoparticle solution.

The change in the degree of coverage with time, during the dive, is satisfactorily described by the equation:

d <I> (t) / dt = (0> _max - <I>) Kc, where <I> (t) is the degree of coverage, 0> _max is the maximum degree of coverage,

K - proportionality coefficient, c - concentration of nanoparticles. In the above equation, the process of adsorption of nanoparticles to the substrate surface is irreversible. The irreversibility of the adsorption process is the conclusion that after washing the plate its degree of coverage - measured on the basis of absorbance - does not change.

The organic layer on the surface of nanoparticles, after completing the surface coating process, can be removed by chemical methods or with oxygen plasma, which may lead to local aggregation of nanoparticles - example 8.

The coatings obtained are sufficiently mechanically stable to be transported, stored, covered with liquids and heated above room temperature. The method according to the invention always achieves a single layer of nanoparticles. The formation of two and multilayer structures on the coated materials was not found.

Additionally, as stated by the authors [Tretiakov K.V., Bishop K.J.M., Kowalczyk B., Jaiswal A., Poggi M.A., Grzybowski B.A .; Journal of Physical Chemistry A, 16 (113), 3799-3803] the cooperative proportion of positive and negatively charged particles leads to heterogeneity in the nano-level coverage - formation on the surface of structures containing several nanoparticles, because the negatively and positively charged particles attract electrostatically. In the described method, the lack of such a cooperative effect allows to obtain surfaces covered with single nanoparticles.

Materials and equipment

Glass plates were bought from Roth, silicon wafers from the Institute of Electronic Materials Technology in Warsaw. The surfaces were cut to size by hand, on site. The tests used glass cut into 10.5 mm wide strips, which makes it possible to place them vertically in the spectrophotometer cell. Chemical reagents were purchased from Sigma-Aldrich and solvents from Chempur. All experiments used 15 milli-pore water. UV-Vis spectra were recorded on a Shimadzu spectrophotometer. The application was made in polypropylene tubes (Sarstedt) with a capacity of 15 ml. Photos of semiconductor surfaces covered with nanoparticles were taken with the Zeiss scanning electron microscope (SEM) at the Institute of Physics of the Polish Academy of Sciences and the Institute of High Pressure Physics of the Polish Academy of Sciences.

PL 217 816 B1

Experimental part

Silicon, gallium arsenide, gallium nitride and ITO were washed with 20% nitric acid, water, acetone, and methanol immediately before use. The glass was washed with pyranium (a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a ratio of 3: 1), acetone and methanol.

Gold nanoparticle solution with radii of 3.06 ± 0.55 nm was obtained according to the literature procedure [Jana NR, Peng GX, Journal of the American Chemical Society, 47 (125), 14280-14281]. The nanoparticles contained in 10 g of this solution were covered with N, N chloride, N-trimethyl (11-mercaptoundecyl) ammonium (TMA) [Kalsin AM, Fialkowski M., Paszewski M., Smoukov SK, Bishop KJM, Grzybowski BA, Science, 5772 (312), 420-424], giving the nanoparticle a positive charge and dissolved in 50 ml of water to obtain a solution with a gold concentration of 0.6 mg / g solution, hereinafter referred to as stock solution.

Mixtures of nanoparticles and salts with appropriate concentrations of components were prepared from nanoparticle stock solutions, salts or their standard concentrated solutions and water, with the nanoparticle solution always being added last.

The plate of coated material was immersed vertically into 4 ml of the mixture of nanoparticles and salts in a 15 ml test tube for a specified time. Then, the plate was rinsed in a beaker containing 300 ml of water and dried by placing it vertically on blotting paper so that the surface of the test was in contact with the substrate only with its lower edge. An additional rinse in an organic solvent such as methanol, acetone or tetrahydrofuran speeds up drying without affecting the coverage density. Drying technique influences the pattern that nanoparticles sometimes form on a surface, but this has not been systematically studied. The coated surfaces were examined by spectrophotometric (glass) or SEM scanning electron microscopy (ITO, gallium arsenide and silicon).

The influence of conditions on the coverage of materials was tested on glass. It was assumed that the surface concentration of nanoparticles is directly proportional to the measured absorbance of the platelets. It was also assumed that the observed shift of the absorption maximum position towards longer wavelengths (from 525 nm to 550 nm) did not affect the value of the extinction coefficient.

Embodiments of the Invention

Example 1. Visual presentation of the invention.

By the method according to the invention, glass plates were immersed in a solution with a concentration of nanoparticles

0.15 mgAu / ml and NaCl 2 mol / l. Fig. 1 shows a photograph of the surface of these plates immersed once (1), twice (2), three times (3) and five times (4) for a period of one minute. The picture shows an increase in the intensity of the red color originating from nanoparticles, resulting from the increasing degree of coverage of the glass surface with the number of dips.

Example 2. Effect of surface cleaning on the degree of coverage.

According to the method of the invention, four glass plates were immersed in four solutions, respectively, with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l. The first plate was submerged four times for 60 minutes, the others ten times for 15, 5 and 1 minutes. The absorbances of the coated plates were 0.12, 0.26, 0.2 and 0.19, respectively. This example shows that, in order to achieve a high degree of coverage, it is preferable to dip the surfaces for a suitable time, ranging from 1 to 15 minutes, but also to clean the surface by rinsing between successive dips. In the absence of rinsing, even extending the dipping time does not lead to the maximum possible coverage.

Example 3. Effect of salt concentration on the degree of coverage.

In the method according to the invention, glass plates were immersed in solutions with a concentration of nanoparticles of 0.15 mgAu / ml and various concentrations of NaCl. The single dip time was 1 minute. Fig. 2 shows the change in absorbance of glass plates with increasing number of dips in solutions with salt concentration ranging from zero to 6 mol / l. The data shows that there is an optimal salt concentration of about 0.1 mol / L, which is the fastest where the degree of coverage is achieved. At lower and higher salt concentrations, this process is slower or absent, as shown in the next example.

Example 4. Effect of salt concentration on the degree of coverage.

In the method according to the invention, glass plates were immersed in solutions with a concentration of nanoparticles of 0.15 mgAu / ml and various concentrations of NaCl. The single dip time was 1 minute. Fig. 3 shows the change in absorbance of glass plates dipped 5 times (a) or 8 times (b) depending on the concentration of NaCl in the solution. The data show that the salt concentration in the solution has a decisive influence on the coating process. It is fastest at a concentration of about 0.1 mol / l. In these wa6

In these circumstances, at a concentration of NaCl close to 1 mol / l, the aggregation and loss of nanoparticles from the solution occurs, which makes it impossible to cover the surface.

Example 5. Effect of salt type on the degree of coverage.

Using the method according to the invention, glass plates were immersed in solutions with a concentration of nanoparticles of 0.15 mgAu / ml and of the tested salts 2 mol / l. The single dip time was 1 minute. Fig. 4 shows the changes in absorbance of glass plates with an increase in the number of dips in solutions containing nanoparticles at a concentration of 0.15 mgAu / ml and salts: KSCN, Na2CO3, NaCl, sodium acetate, NaNO3, KNaC4H4O6 (potassium sodium tartrate) at a concentration of 2 mol / l. The data show that the type of salt can affect the degree of coverage. The use of KSCN or Na2CO3 is disadvantageous.

Example 6. Effect of nanoparticle concentration on the degree of coverage.

By the method according to the invention, glass plates were immersed in solutions with a nanoparticle concentration of 0.15 (a), 0.075 (b) and 0.015 mgAu / ml (c) and NaCl 2 mol / l. The results are shown in Fig. 5. The example shows that the surface coverage rate, a, is proportional to the concentration of nanoparticles in the solution. The experiment was performed in such a way that the appropriate number of solution samples was prepared for each concentration of nanoparticles. The glass plate was immersed for 1 to 5 minutes, rinsed, dried, the absorbance was measured, then immersed in a new sample of the appropriate solution. For each concentration of nanoparticles, the measurements were repeated three times. The chart shows averaged data. Functions of the formula <I> (t) = 0> _max - exp [-at] were added to the experimental data, where <I> (t) is the degree of surface coverage after the immersion time t, Φ ^ - the maximum degree of coverage, and - is a constant expressing the rate of adsorption of nanoparticles on the surface. The total residence time, t, of the samples in the solutions is marked on the horizontal axis. It turned out that the constant a is proportional to the concentration of nanoparticles in the solution, a = Kc, where K is a constant and c is the concentration of nanoparticles.

P r z k ł a d 7. ITO coating.

Using the method according to the invention, the ITO plate was immersed for 5 minutes in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l. Fig. 6 shows a scanning electron microscope photo of the obtained surface. The example shows that ITO can be coated with nanoparticles by the method of the invention. The lower coverage density compared to Example 8 is mainly due to the lower number of dips.

Example 8. Coating of silicon.

In the method according to the invention, the silicon wafer was immersed five times in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l. The single immersion time was 5 minutes. Fig. 7 shows a scanning electron microscope photo of the obtained surface. The example shows that silicon can be coated with nanoparticles by the method according to the invention.

Example 9. Coating of silicon. The influence of oxygen plasma on the covered surfaces.

In the method according to the invention, the silicon wafer was immersed five times in a solution with a nanoparticle concentration of 0.15 mgAu / ml and NaCl 2 mol / l. Single immersion time was 5 minutes. After coating with nanoparticles, the surfaces were cleaned in oxygen plasma for 4 minutes and then rinsed in water and methanol. Fig. 8 shows a scanning electron microscope photograph of the obtained surface. The better contrast of the photo compared to Example 8 indicates that the non-conductive organic layer has been removed from the nanoparticles. Due to its removal, the nanoparticles were partially aggregated locally.

Claims (19)

A method of coating a surface of a material with nanoparticles, comprising the step of dipping said surface in a solution containing a mixture of nanoparticles coated with a charged organic or polymer layer and salt, characterized in that said solution comprises only uniformly charged particles and the concentration of said salt in said solution is from 0.01 mol / l to 2.0 mol / l. 2. The method according to p. The method of claim 1, wherein said surface is positively charged and said solution comprises only negatively charged particles. 3. The method according to p. 3. The method as claimed in claim 1 or 2, characterized in that said solution is an aqueous solution. 4. The method according to p. 3. The method as claimed in claim 1 or 2, characterized in that said solution is a non-aqueous solution. PL 217 816 B1 5. The method according to p. 4. The process of claim 4, wherein said solution is a methanol solution. 6. The method according to any one of the preceding claims, characterized in that said salt is an inorganic salt. 7. A method according to any one of claims 1 to 7 1-5, characterized in that said salt is an organic salt. 8. The method according to p. 7. The method of claim 7, wherein said salt is a carboxylic acid salt. 9. The method according to any one of the preceding claims, characterized in that said nanoparticles have a size from 1 nm to 100 nm. 10. A method according to any one of claims 1 to 10 The method of claim 1 or 3 to 9, characterized in that said surface is negatively charged and said solution contains only positively charged particles. 11. The method according to p. 10. The method of claim 10, characterized in that said nanoparticles are metallic nanoparticles, preferably selected from the group consisting of Au, Ag, Pt, Pd. 12. The method according to p. 10. The method of claim 10, characterized in that said nanoparticles are semiconductor nanoparticles, preferably selected from the group consisting of CdS, CdSe, CdTe, InP, PbS, InAs, ZnO. 13. The method according to p. The method of claim 10, characterized in that said nanoparticles are core-shell bi- or multicomponent nanoparticles with a top layer preferably consisting of CdSe, ZnS, ZnSe. 14. The method according to p. The method of claim 13, characterized in that said nanoparticles are CdTe / CdSe, CdSe / ZnS or CdSe / ZnSe nanoparticles. 15. A method according to any one of claims 1 to 15 A method according to any of the claims 10 to 14, characterized in that said nanoparticles are coated with a positively charged layer of 11-mercaptoundecyltrimethylamine chloride, TMA. 16. A method according to any one of claims 1 to 16 The process according to 10-15, characterized in that the surface to be coated is a surface selected from glass, tin-doped indium oxide, ITO, silicon, gallium arsenide or other semiconductors. 17. A method according to any one of the preceding claims 1 to 16, characterized in that the duration of a single dip is from 10 seconds to 60 minutes, preferably from 15 seconds to 10 minutes. 18. A method according to any one of the preceding claims 1 to 17, characterized in that said dipping step is repeated. 19. The method according to p. The method of claim 18, wherein the number of repeats is from 2 to 10.