Method for dispersing nanoparticles and methods for producing nanoparticle thin films by using the same
Methods for producing nanoparticle thin films are disclosed. According to one of the methods, a nanoparticle thin film is produced by modifying the surface of nanoparticles to allow the nanoparticles to be charged, controlling an electrostatic attractive force between the charged nanoparticles and a substrate and a repulsive force between the individual nanoparticles by a variation in pH to control the number density of the nanoparticles arranged on the substrate.
1. A method for producing a nanoparticle thin film, comprising:
modifying the surface of nanoparticles to form surface-modified particles;
wherein the surface of the nanoparticles are electrically charged by exchanging nonpolar capping molecules on the surface of the nanoparticles for charged materials;
dispersing the surface-modified nanoparticles in a buffer solution and removing nanoparticle aggregates therefrom;
after the removal of the nanoparticle aggregates, dispersing the surface-modified nanoparticles in a solvent to form a nanoparticle dispersion;
adjusting the pH of the nanoparticle dispersion to a range of 7 to 9 to form a pH controlled nanoparticle dispersion; and
arranging the nanoparticles contained in the pH-controlled nanoparticle dispersion on a substrate bearing a charge opposite to those of the surface modified nanoparticle by dip coating to utilize a capillary force, thereby forming a nanoparticle monolayer on the substrate, wherein the buffer solution is tris(hydroxymethyl)aminomethane buffer.
2. The method according to claim 1 , wherein the surface modification is performed at a reaction temperature of about 25 to about 200° C. for about 0.5 to about 10 hours.
3. The method according to claim 1 , wherein the charged material is selected from the group consisting of compounds having an amino group, a carboxylic group, a mercapto group and a phosphine group and having negative or positive charge.
4. The method according to claim 1 , wherein before being dispersed in the buffer solution, the surface modified nanoparticles are dried in ambient air or under vacuum.
5. The method according to claim 1 , wherein the nanoparticles are negatively charged, the buffer solution has a pH greater than 7, and the substrate is positively charged.
6. The method according to claim 1 , wherein the substrate is pretreated by washing the substrate and adsorbing a functional group on the surface of the washed substrate.
7. The method according to claim 6 , wherein the substrate is pretreated to have a coating of polyallylamine hydrochloride.
8. The method according to claim 1 , wherein the nanoparticles are selected from the group consisting of Group II-IV compound semiconductor particles, Group III-V compound semiconductor particles, Group IV-VI compound semiconductor particles, Group IV compound semiconductor particles, metal particles, magnetic particles, metal oxide nanoparticles and a combination comprising at least one of the foregoing particles.
9. The method according to claim 1 , wherein the pH of the nanoparticle dispersion is adjusted to a range of about 7 to about 8.
10. The method according to claim 1 , wherein the solvent is selected from the group consisting of water, polar solvents, and a tris buffer solution.