Ultrastrong Anchoring on the Periodic Atomic Grooves of Black Phosphorus

Abstract

the range of aligned molecules may be limited to those possessing strong π-π interactions with 2D materials. [19][20][21] In this regard, grooved surfaces can provide a powerful approach, because the anchoring energy and anchoring direction of their patterned surface can be artificially designed by controlling the direction, amplitude, and period of the patterned substrate according to Berreman's theory. [22][23][24] Despite the success achieved with aligning lyotropic chromonic liquid crystals (LC) by introducing patterned surfaces with high aspect ratio, [22] the anchoring energy of the grooved surfaces used in these attempts is still low for anchoring of various soft materials such as polymeric materials and dendrimers. This limitation is due to the restriction of the surface anchoring energy of the patterned surface to above 20 nm by the resolution of current lithographic techniques. [22][23][24] Here, we demonstrate for the first time that black phosphorus (BP) with atomic-scale grooves and a puckered honeycomb structure of adjacent phosphorus atoms enables alignment of a wide range of soft materials, including thermotropic LCs such as 4-cyano-4′-alkylbiphenyl (nCB) and 4-cyano-4′-alkyloxybiphenyl (nOCB), the lyotropic LC sunset yellow (SSY), and fluorinated dendrimers. Especially, SSY and dendrimer molecules are difficult to align through known surfaceanchoring techniques. We found that the planar direction of the aligned soft materials is fixed in a single direction, following the direction of the atomic grooves of BP. This result is attributed to the regular and atomic-scale grooves of BP with height of 2 Å and period of 4.33 Å. [26] These induce an ultrastrong azimuthal anchoring energy of soft materials, ≈0.235 N m −1 (for 5CB), which is two orders of magnitude higher than that of previously reported anchoring methods. Thus, our surface-anchoring technology represents a new approach for aligning a wide range of soft materials using well-designed atomic-scale grooves of BP. Such an approach can be used in various methods for realizing high-performance optoelectronic devices and biotechnological applications.The overall procedure for aligning various soft materials on the BP surface is illustrated in Figure 1. Briefly, BP flakes were exfoliated through a mechanical method using commercial 3M tape and then transferred onto SiO 2 /Si substrates for polarized optical microscopy (POM) observations and onto a Si nitride (SiN) grid for transmission electron microscopy (TEM) observations (Figure 1a). [27] The BP substrate was coated with various soft materials, namely, nCB, nOCB, SSY, and fluorinated dendrimer, by either spin-coating or a sandwiched-cell or solution-casting method, depending on the materials and observation tools (for specific experimental conditions, see the Experimental Section; Figure 1b). Thermotropic nCBs, nOCBs, and lyotropic SSY were used because the anchoring behavior of Controlling the molecular orientation of soft materials is one of the most important issues in physical and materials ...

Black Phosphorus Rediscovered: From Bulk Material to Monolayers

“…Thedegradation caused by air and water in the case of BP has become an issue paralleled only by the concerns of metallic and oxidation debris in the preparation of carbon nanomaterials. [104] requisite to retain the intrinsic material properties of BP and advance its applications. [48,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84] Other authors have taken advantage of this stability issue and proposed using BP in humidity sensors (Section 4.3).…”

“…[102] Bulk BP appears to be stable over aprolonged period of time under ambient conditions. [104] Kim et al point out that the planar anchoring of the aligned soft materials is fixed in one direction, which the authors attributed to the regular atomic-scale grooves of BP inducing an ultrastrong azimuthal anchoring energy of the soft materials (ca. [17,90,103] It was recently demonstrated that the puckered honeycomb structure of BP enables the controlled alignment of awide range of soft materials,including rodlike molecules and even dendrimers ( Figure 1D).…”

“…[93] [100] D) Mechanismso falignment of various soft materials on the atomic grooves of BP. [104] requisite to retain the intrinsic material properties of BP and advance its applications. [82,[89][90][91][92][93]95] Some of the materials reported for BP passivation include Al 2 O 3 , [70,91,96] TiO 2 , [73] titanium sulfonate ligand (TiL 4 ), [75] and aryl diazonium moieties.…”

“…[17,90,103] It was recently demonstrated that the puckered honeycomb structure of BP enables the controlled alignment of awide range of soft materials,including rodlike molecules and even dendrimers ( Figure 1D). [104] Kim et al point out that the planar anchoring of the aligned soft materials is fixed in one direction, which the authors attributed to the regular atomic-scale grooves of BP inducing an ultrastrong azimuthal anchoring energy of the soft materials (ca. 0.235 Nm À1 ).…”

Enhanced Cytosolic Delivery and Release of CRISPR/Cas9 by Black Phosphorus Nanosheets for Genome Editing

“…[11] As an allotrope of elemental phosphorus,B Ps possess excellent element biocompatibility and degrade to nontoxic phosphite/phosphate ions under physiological conditions. [12] BPs with atomic thickness and a2Dpuckered honeycomb structure [13] provide very high surface-to-volume ratios among various nanomaterials.Furthermore,the periodic atomic grooves on surfaces of BPs provide ideal anchoring sites for proteins [14] and soft linear materials, [15] indicating their potentials in loading and delivery of biomolecules.B Ps-based approaches have thus been employed in numerous biomedical applications. [16] However,t he applications of BPs in cytosolic delivery of bioactive macromolecules have not yet been reported.…”