Aligned Phthalocyanine Molecular Nanowires by Graphoepitaxial Self‐Assembly and Their In Situ Integration into Photodetector Arrays

Abstract

Large-scale on-chip integration of organic nanowire-based devices requires the deterministic assembly of organic small molecules into highly-aligned nanowires. In this work, phthalocyanine molecules are self-assembled into horizontally-aligned nanowires after generating parallel hydrophobic nanogrooves on a sapphire surface. In contrast to previous self-oriented inorganic nanowires, these molecular nanowires are separated from their supporting sapphire by an ultrathin amorphous layer, indicating a complete elimination of lattice matching between nanowires and substrates. Therefore, small molecules beyond phthalocyanines hold promise to form aligned nanowires using this graphoepitaxial self-assembly strategy. The excellent alignment and high crystallinity of these nanowires enable the desired in-situ integration of nanowire-based devices without additional postgrowth processing steps. As a proof of concept, self-oriented CuPc nanowires are integrated into photodetector arrays directly on their growth substrate after electrode arrays are transferred onto the nanowires. Compared to previous CuPc photodetectors constructed using other approaches, these detectors exhibit a faster response to the spectrum in the 488-780 nm range (rise and fall times are 0.05-0.43 s and 0.38-2.34 s, respectively) while offering comparable detectivities (2.49 × 10 10 Jones on average). This graphoepitaxial self-assembly offers new opportunities for the aligned growth of organic crystalline nanowires and their large-scale in-situ integration into functional devices.

Physically Unclonable Functions Based on Self‐Oriented Nanowires

“…High magnification SEM observation (Figure 1c; Figure S1, Supporting Information) reveals that these nanowires grow in parallel along the direction defined by the nanogrooves, instead of the symmetric crystallographic orientations of the underlying sapphire. [ 46,48–50 ] The X‐ray diffraction (XRD, Figure S2, Supporting Information) and Raman spectra (Figure S3, Supporting Information) of these nanowires match that of the CuPc powder, hence, no chemical reaction occurs during the vapor deposition process. Figure 1d shows a representative device with 16 × 16 arrays of gold electrodes.…”

“…We first prepared high‐density oriented CuPc nanowires with lengths of 50–150 µm on an annealed M‐plane sapphire surface ( Figure a) by evaporating commercially available CuPc powder at 240 °C. [ 46–48 ] These nanowires are then stored at ambient conditions without special protection (e.g., vacuum or inert gas). Even with high‐velocity gas flow, it is impossible to remove these self‐oriented nanowires from their growth substrate, indicating that these self‐oriented nanowires have a much stronger interaction with their underlying substrate than the commonly reported freestanding nanowires.…”

Deterministic Single-Row-Droplet Catalyst Formation for Uniform Growth Integration of High-Density Silicon Nanowires

“…However, as the gaseous precursor feeding in VLS growth tends to produce vertical bundles of standing SiNWs, they need to be collected, transferred and rearranged into precise locations on planar surface for reliable logic device integration . Though many research efforts have been developed to achieve planar growth of VLS SiNWs, , surface faceted groove-guided planar growth, , or postgrowth rearrangement of them, , a scalable integration of orderly VLS-grown SiNWs on planar surface is still missing.…”

Horizontally Oriented Growth of Highly Conductive MoO2 Nanobelts on Sapphire

“…Up to now, various methods have been proposed for the assembly of 1D nanostructures, such as roll printing strategy, contact printing, dielectrophoretic assembly, nanoscale combing technique, magnetic field alignment, etc . Although these methods have proven successful in large-scale directional arrangement of 1D nanostructures, they have their own drawbacks, such as the tendency to damage nanowires, the limited length of nanowires, etc. − To overcome the drawbacks of postgrowth assembly of 1D nanostructures, a graphoepitaxy technology has been proposed. − This method usually refers to the use of periodic nanofeatures (e.g., nanogrooves or nanosteps) on a substrate surface to achieve directional assembly of atoms or molecules . For example, as early as 1996, Sunamura et al observed the self-organized growth of Ge quantum wires at step edges on Si(100) by its lateral confinement effect .…”

“…They later achieved the guided growth of millimeter-long GaN nanowires along the nanogrooves of the annealed M-plane (101̅0) sapphire . Up to now, the generality of graphoepitaxial growth has been widely demonstrated in the horizontally oriented growth of various 1D inorganic (e.g., ZnTe, ZnSe, ZnO, CdSe, and CdS) or organic (e.g., metal phthalocyanines, Alq3) nanowires on various substrates (such as SiC, quartz, and spinel). − ,,,− …”