Understanding Anisotropic Plasma Etching of Two-Dimensional Polystyrene Opals for Advanced Materials Fabrication

Anisotropic deformation of polystyrene particles in an oxygenated (O₂/Ar) plasma is observed for radio frequency (rf) plasma and inductively coupled plasma (ICP). A facile model based on a ratio of completely isotropic and completely anisotropic etching is presented to describe the anisotropy of the etching process and is implemented to determine the height of the spheroid-shaped polystyrene particles. In our systems, we find the plasma etching to be 54% isotropic in the rf plasma and 79% isotropic in the ICP. With this model, the maximum material deposition thickness for nanofabrication with plasma-etched nanosphere lithography or colloid lithography can be predicted. Moreover, the etching of polystyrene particles in an oxygenated plasma is investigated versus the etching time, gas flow, gas composition, temperature, substrate material, and particle size. The results of this study allow precise shape tuning during the fabrication of nanostructured surfaces with size-dependent properties for bionic, medical, and photonic applications

An Approach to Fabrication of Metal Nanoring Arrays

Fabrication of tailored nanomaterials with desired structure and properties is the greatest challenge of modern nanotechnology. Herein, we describe a wet chemical method for the preparation of large area metal nanoring arrays. This method is based on self-assembly of polystyrene sphere template on a flat substrate and wicking/reducing metal precursor into the interstices between the template and the substrate. In this article, platinum, gold, and copper nanorings were fabricated by applying 505 nm polystyrene spheres onto highly oriented pyrolytic graphite (HOPG) and Si(100) substrates, followed by reducing the templated metal salt with NaBH4. AFM images reveal formation of arrays of metal nanorings comprising metal nanoparticles with the average ring height of 5.7 ± 0.8 nm and diameter of 167.3 ± 8.9 nm. XPS confirms that these structures are metallic

Control of Packing Order of Self-Assembled Monolayers of Magnetite Nanoparticles with and without SiO₂ Coating by Microwave Irradiation

A close packed layer of Fe3O4 and SiO2-coated Fe3O4 nanoparticles can be assembled on silicon and glass substrates modified with polyelectrolytes following the principle of the layer-by-layer self-assembly (Science 1997, 277, 1232). Microwave (MW) treatment of the poly(dimethyldiallylammonium chloride) layer prior to the nanoparticle adsorption results in substantial reduction of the surface roughness of the particulate films. This effect is attributed to reduction of the length of partially desorbed segments of macromolecules protruding into the aqueous phase at a distance of about 70 nm as estimated from force−distance curves. Aggregation of nanoparticles on these segments is responsible for a relatively high degree of disorder in layer-by-layer self-assembled films. A brief MW exposure results in cross-linking of polyelectrolyte chains. This substantially reduces the number of loose segments, and improves 2D packing of nanoparticles. For optimized conditions, the rms roughness, R, of magnetite self-assembled films can be as low as 1.5−3.5 nm. For silica-coated magnetite, initial R of adsorbed films is typically 10−14 nm. It can be reduced to 5.5 nm following the MW treatment of the polyelectrolyte; however, this does not completely prevent the formation of multiparticle 3D aggregates. Further reduction of R to 3.5 nm can be achieved by a brief ultrasonication of the nanoparticulate film, which removes weakly attached particles

Spontaneous Transformation of CdTe Nanoparticles into Angled Te Nanocrystals: From Particles and Rods to Checkmarks, X-Marks, and Other Unusual Shapes

CdTe nanoparticles spontaneously transform into the branched Te nanocrystals with the unique, highly anisotropic shape of checkmarks after partial removal of the stabilizers of l-cysteine. The Te checkmarks are made in a relatively high yield and uniformity; the length of the arms is ca. 150 nm, whereas the angle between the arms is 74°. Subsequent growth of the particle yields mothlike nanocrystals retaining geometrical anisotropy. Unlike the previous synthesis methods of branched nanocrystals, they are formed via a merger of individual rod-shaped crystallites. High-energy crystal faces on their apexes act as the sticky points causing the particles to join in the ends. This is the first demonstration of spontaneous transformation of binary semiconductor particles into highly anisotropic nanocolloids in an angled conformation. The end reactivity of starting Te rods can be used both for bottom-up fabrication of nanoscale electronics and relatively safe and nontoxic method of synthesis of Te-based optical and other materials

Nanorainbows: Graded Semiconductor Films from Quantum Dots

Nanorainbows:  Graded Semiconductor Films from Quantum Dot

One-Pot Synthesis of One-Dimensional Multijunction Semiconductor Nanochains from Cu_1.94S, CdS, and ZnS for Photocatalytic Hydrogen Generation

Chains of alternating semiconductor nanocrystals are complex nanostructures that can offer control over photogenerated charge carriers dynamics and quantized electronic states. We develop a simple one-pot colloidal synthesis of complex Cu1.94S-CdS and Cu1.94S-ZnS nanochains exploiting an equilibrium driving ion exchange mechanism. The chain length of the heterostructures can be tuned using a concentration dependent cation exchange mechanism controlled by the precursor concentrations, which enables the synthesis of monodisperse and uniform Cu1.94S-CdS-Cu1.94S nanochains featuring three epitaxial junctions. These seamless junctions enable efficient separation of photogenerated charge carriers, which can be harvested for photocatalytic applications. We demonstrate the superior photocatalytic activity of these noble metal free materials through solar hydrogen generation at a hydrogen evolution rate of 22.01 mmol g–1 h–1, which is 1.5-fold that of Pt/CdS heterostructure photocatalyst particles

Vortex creation without stirring in coupled ring resonators with gain and loss

We present study of the dynamics of two ring waveguide structure with space dependent coupling, linear gain and nonlinear absorption - the system that can be implemented in polariton condensates, optical waveguides, and nanocavities. We show that by turning on and off local coupling between rings one can selectively generate permanent vortex in one of the rings. We find that due to the modulation instability it is also possible to observe several complex nonlinear phenomena, including spontaneous symmetry breaking, stable inhomogeneous states with interesting structure of currents flowing between rings, generation of stable symmetric and asymmetric circular flows with various vorticities, etc. The latter can be created in pairs (for relatively narrow coupling length) or as single vortex in one of the channels, that is later alternating between channels

Magnetic Colloidosomes Derived from Nanoparticle Interfacial Self-Assembly

Based on the interfacial self-assembly of magnetite nanoparticles, we demonstrate the formation of colloidosomes with shells predominantly composed of monolayers of liquid-like, close-packed nanoparticles. The gelation of aqueous phase with agarose leads to robust and water-dispersible nanoparticle colloidosomes, allowing encapsulation of various water soluble materials. The cutoff of the nanoparticle colloidosomes obtained is primarily defined by the nanoparticle size. This controllable permeability should be of great importance for the encapsulation application

Magnetic measurements of the IONPs and silk/ iron oxide spheres (EMS2/IONP).

A) Zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves for IONPs (upper) and EMS2/IONP spheres (bottom); B) Hysteresis loops at T = 5 and 300 K for IONPs (upper) and EMS2/IONP (bottom) spheres.</p

SEM images and EDXS quantitative results of selected elements of MS1, MS1/IONP spheres, MS2, MS2/IONP spheres, EMS2, and EMS2/IONP spheres.

A) Spheres were prepared by mixing 2 M potassium phosphate at pH 8 with the indicated version of silk (2.5 mg/mL) in the presence or absence of iron oxide nanoparticles (5 mg/mL). B) EMS2 and EMS2/IONP spheres were formed by mixing 2 M potassium phosphate at pH 8 with a silk solution (1 mg/mL) in the presence or absence of the iron oxide nanoparticles (5 mg/mL); scale bar– 4 μm.</p