Selective Deposition Of Nanoparticles Research Articles

Exploiting Heteroaggregation to Quantify the Contact Angle of Charged Colloids at Interfaces

We exploit the aggregation between oppositely charged particles to visualize and quantify the equilibrium position of charged colloidal particles at the fluid-water interface. A dispersion of commercially available charge-stabilized nanoparticles was used as the aqueous phase to create oil-water and air-water interfaces. The colloidal particles whose charge was opposite that of the nanoparticles in the aqueous phase were deposited at the chosen fluid-water interface. Heteroaggregation, i.e., aggregation between oppositely charged particles, leads to the deposition of nanoparticles onto the larger particle located at the interface; however, this only occurs on the surface of the particle in contact with the aqueous phase. This selective deposition of nanoparticles on the surfaces of the particles exposed to water enables the distinct visualization of the circular three-phase contact line around the particles positioned at the fluid-water interface. Since the electrostatic association between the nanoparticles and the colloids at interfaces is strong, the nanoparticle assembly on the larger particles is preserved even after being transferred to solid substrates via dip-coating. This facilitates the easy visualization of the contact line by electron microscopy and the determination of the equilibrium contact angle of colloidal particles (θ) at the fluid-water interface. The suitability of the method is demonstrated by the measurement of the three-phase contact angle of positively and negatively charged polystyrene particles located at fluid-water interfaces by considering particles with sizes varying from 220 nm to 8.71 μm. The study highlights the effect of the size ratio between the nanoparticles in the aqueous phase and the colloidal particles on the accuracy of the measurement of θ.

Controlled Assembly of Block Copolymer Coated Nanoparticles in 2D Arrays.

The defined assembly of nanoparticles (NPs) in polymer matrices is an important prerequisite for next-generation functional materials. A promising approach to control NP positions in polymer matrices at the nanometer scale is the use of block copolymers. It allows the selective deposition of NPs in nanodomains, but the final defined and ordered positioning of the NPs within the domains has not been possible. This can now be achieved by coating NPs with block copolymers. The self-assembly of block copolymer-coated NPs directly leads to ordered microdomains containing ordered NP arrays with exactly one NP per unit cell. By variation of the grafting density, the inter-nanoparticle distance can be controlled from direct NP surface contact to surface separations of several nanometers, determined by the thickness of the polymer shell. The method can be applied to a wide variety of block copolymers and NPs and is thus suitable for a broad range of applications.

Controlled Assembly of Block Copolymer Coated Nanoparticles in 2D Arrays

AbstractThe defined assembly of nanoparticles (NPs) in polymer matrices is an important prerequisite for next‐generation functional materials. A promising approach to control NP positions in polymer matrices at the nanometer scale is the use of block copolymers. It allows the selective deposition of NPs in nanodomains, but the final defined and ordered positioning of the NPs within the domains has not been possible. This can now be achieved by coating NPs with block copolymers. The self‐assembly of block copolymer‐coated NPs directly leads to ordered microdomains containing ordered NP arrays with exactly one NP per unit cell. By variation of the grafting density, the inter‐nanoparticle distance can be controlled from direct NP surface contact to surface separations of several nanometers, determined by the thickness of the polymer shell. The method can be applied to a wide variety of block copolymers and NPs and is thus suitable for a broad range of applications.

Simulation of conditions for fabrication of optical nanowaveguides in the form of chains of spherical metal nanoparticles by electrostatic functionalization of the process substrate

A method is proposed for electrostatic functionalization of substrates used to prepare ordered structures composed of closely spaced plasmon-resonant nanoparticles. The method ensures selective deposition of nanoparticles from the bulk of a colloidal system onto the substrates. This method is based on placing a metal nanotemplate of a required configuration at the opposite side of a substrate, with an electric potential being applied to the template. A mathematical model is developed to ensure that the system parameters responsible for the deposition of metal nanoparticles into ordered single-domain structures on the substrate from a bulk sol in a nonuniform electric field generated by the nanotemplate correspond to the real experimental conditions. Since the degree of imperfection of the synthesized chains governs the applicability of these structures to transmission of the optical excitation at the frequency of the surface plasmon of the particles, the dependence of the degree of imperfection on the physicochemical and electrical parameters of the system is studied using the Brownian-dynamics model. The calculations of the spectral and transmission properties of nanowaveguides of this type are exemplified.

Selective growth of Au nanoparticles on PZT substrates by using a photochemical reaction

We report the surface distribution of Au nanoparticles (NPs) grown on polarity-patterned ferroelectrics by using photochemical-reaction deposition. Polycrystalline lead zirconate titanate (PZT) was used as a ferroelectric substrate. The local polarization orientation on the surface was patterned by using atomic force microscopy (AFM). The Au NPs were grown by ultraviolet (UV) light exposure of the polarity-patterned PZT substrates while immersed in Au salt solutions. The wavelength dependence of the deposition of the NPs was investigated using UV band pass filters. The dimensions and the surface distribution of the NPs were measured by using AFM. For UV light without a filter, more NPs were formed on the +z polarity region than on the other regions. However, for UV light with wavelengths of 315 nm and 365 nm, we observed the selective deposition of NPs on +z polar domains. The NPs on the +z polar domains were denser and larger than those on the other non-polar regions. The average size of the NPs was ∼30 nm and the number density was ∼22/µm2. In addition, the electron affinity of the PZT was found to be ∼3.0 eV from scanning Kelvin probe microscopy measurements of the PZT film surface with the deposition of Au NPs. This study suggests the possibility of controlling the sizes and the positions of Au NPs on a surface by optimizing the UV wavelength and polarity patterning of the ferroelectrics.

Growth of carbon nanotubes through selective deposition of nanoparticles

This paper describes the selective growth of a high density of Carbon NanoTubes (CNTs) (up to 2.5 1011 CNT cm−2) in nanometric (140 to 300 nm) holes etched in silicon dioxide (vias). The method involves (i) the electrografting of a thin layer of poly(hydroxyethyl methacrylate) (polyHEMA) at the Si bottom of the SiO2 vias; (ii) independent synthesis of nanometric iron oxide nanoparticles (NP) by the polyol method, the NPs being capped by diethylene glycol (DEG); (iii) HF cleaning of the SiO2 structure; (iv) selective deposition of the NPs on the polyHEMA layer at the bottom of the vias; (v) burn-off of the polymer; (vi) Chemical Vapour Deposition (CVD) growth of the CNTs. The success of the experiment is based on the fine tuning of the selective interactions between the capping of the NPs and the polymer deposited exclusively at the bottom of the vias.

Single-electron transistors made by chemical patterning of silicon dioxide substrates and selective deposition of gold nanoparticles

We describe a method to pattern SiO2 surfaces with colloidal gold nanoparticles by e-beam lithography and selective nanoparticle deposition. The simple technique allows us to deposit nanoparticles in continuous straight lines, just one nanoparticle wide and many nanoparticles long. We contact the prepositioned nanoparticles with metal leads to form single electron transistors. The Coulomb blockade pattern surprisingly does not show the parasitic “offset charges” at low temperatures, indicating relatively little surface contamination.