Microwell‐Directed Self‐Assembly of Vertical Nanowire Arrays

Abstract

Vertical arrays of anisotropic particles are desired for many applications including solar cells, battery electrodes, and lasers. Partially etched nano­wires (PENs) are hybrid silica nanotube/nanowires with partial metallic cores. These particles spontaneously form vertical arrays in which on average 70% of the particles are oriented perpendicular to the underlying substrate. Here, we perform PEN self‐assembly on lithographically prepared substrates patterned with square microwells having dimensions comparable to the length of the particles. Particle self‐assembly is observed both in the microwells and on the intervening surfaces. PENs both directly deposit into a well and diffuse across the surface between microwells until falling into a well. Assembly occurs as the local concentration of PENs in a well increases by these two mechanisms. Microwells provide a way to control array location on a surface and improve standing percentages up to 100% when the edge dimensions are decreased to a size approximately equal to the nanowire length. Micro­wells also protect against array disruption during sample drying.

Reconfigurable Positioning of Vertically-Oriented Nanowires Around Topographical Features in an AC Electric Field

“…Vertically oriented nanowires, with long axes perpendicular to a substrate, are straightforward to produce during synthesis by growth or etching from a substrate, ,, but such structures have been less-studied for self-assembly of pre-existing nanowires from solution. Approaches to vertical nanowire assembly have included controlled drying, particle designs that take advantage of gravity and interparticle forces, substrate patterning with microwells smaller than the nanowire length, and applied magnetic or electric fields. ,− Of these, strategies based on applied electric field are particularly versatile in terms of particle size and composition while also offering the possibility of dynamic reconfigurability by changing the applied field conditions. We therefore chose to take advantage of applied electric fields in the work described here.…”

Self‐Assembled Binary Mixtures of Partially Etched Nanowires

“…In horizontal assemblies, PEN core patterns lead to variations in VDW attractions along the particle length, which influences their relative orientations . PENs with metal cores at one end and large terminal etched segments adopt vertical orientations (metal core down) that maximize VDW attractions between adjacent particles …”

“…Understanding how interactions of similar and dissimilar particles affects assembly outcomes will enable "by design" production of multicomponent structures for desired applications.We have previously introduced partially etched nanowires (PENs) as a model system to understand the interparticle forces that drive assembly of shape-and composition-anisotropic particles. [19][20][21][22] PENs are hybrid nanotube/nanowire particles, generally ≈300 nm diameter, and ranging from 2 to 12 µm length, consisting of a silica shell and a partial metal core. [19][20][21][22] Like solid nanowires of similar dimensions, PENs sediment from aqueous suspension under the action of gravity, leading to high surface concentrations on an underlying substrate.…”

“…[19][20][21][22] PENs are hybrid nanotube/nanowire particles, generally ≈300 nm diameter, and ranging from 2 to 12 µm length, consisting of a silica shell and a partial metal core. [19][20][21][22] Like solid nanowires of similar dimensions, PENs sediment from aqueous suspension under the action of gravity, leading to high surface concentrations on an underlying substrate. There, electrostatic repulsions from the silica shell and VDW attractions from the metal core lead to assemblies in which particle long axes are either parallel or perpendicular to the surface depending on PEN core patterns.…”

“…[ 19,20 ] PENs with metal cores at one end and large terminal etched segments adopt vertical orientations (metal core down) that maximize VDW attractions between adjacent particles. [20][21][22] Here, we report binary co-assemblies of PENs with different core compositions and introduce PENs with non-Au core metals (Pt, Rh). We took advantage of the diversity of PEN…”