Parameters Affecting Interfacial Assembly and Alignment of Nanotubes.

Tangential flow interfacial self-assembly (TaFISA) is a promising scalable technique enabling uniformly aligned carbon nanotubes for high-performance semiconductor electronics. In this process, flow is utilized to induce global alignment in two-dimensional nematic carbon nanotube assemblies trapped at a liquid/liquid interface, and these assemblies are subsequently deposited on target substrates. Here, we present an observational study of experimental parameters that affect the interfacial assembly and subsequent aligned nanotube deposition. We specifically study the water contact angle (WCA) of the substrate, nanotube ink composition, and water subphase and examine their effects on liquid crystal defects, overall and local alignment, and nanotube bunching or crowding. By varying the substrate chemical functionalization, we determine that highly aligned, densely packed, individualized nanotubes deposit only at relatively small WCA between 35 and 65°. At WCA (< 10°), high nanotube bunching or crowding occurs, and the film is nonuniform, while aligned deposition ceases to occur at higher WCA (>65°). We find that the best alignment, with minimal liquid crystal defects, occurs when the polymer-wrapped nanotubes are dispersed in chloroform at a low (0.6:1) wrapper polymer to nanotube ratio. We also demonstrate that modifying the water subphase through the addition of glycerol not only improves overall alignment and reduces liquid crystal defects but also increases local nanotube bunching. These observations provide important guidance for the implementation of TaFISA and its use toward creating technologies based on aligned semiconducting carbon nanotubes.

Novel En Face OCT-Based Closure Patterns in Idiopathic Macular Holes.

PURPOSE: To determine the postoperative en face OCT pattern of closure in idiopathic macular holes (MHs). DESIGN: Retrospective, multicentric, observational study. PARTICIPANTS: Patients aged > 18 years with a diagnosis of idiopathic MH, with well documented en face OCT images. METHODS: Baseline characteristics and preoperative OCT and en face OCT parameters like horizontal and vertical minimum linear diameter (MLD), horizontal and vertical basal hole diameter (BHD), hole height, acircularity index, and hole orientation were measured. MAIN OUTCOME MEASURE: The type of hole closure on en face OCT, and a comparison of baseline parameters and final visual acuity among the en face closure types. RESULTS: A total of 64 eyes of 62 patients (24 men and 40 women) with a mean age of 63.8 ± 12.4 years. The median duration of symptoms was 3 months (interquartile range, 1.75-10.5). The eyes had a mean baseline visual acuity of 0.97 ± 0.46 logarithm of minimum angle of resolution (logMAR). The baseline horizontal MLD was 591.7 ± 219.4 µm and the vertical MLD was 552.9 ± 198.2 µm. Baseline horizontal and vertical BHD were 1240.3 ± 521.1 µm and 1142.1 ± 478.1 µm, respectively. The mean hole height was 394.8 ± 123.2 µm. Two different patterns were noted on en face OCT: round, or linear. A total of 38 eyes had a round/centripetal closure and 26 eyes had a linear closure (17 eyes had a horizontal closure, 7 eyes had an oblique closure, while 2 eyes had a vertical closure). The mean final visual acuity was 0.80 ± 0.43 logMAR (Snellen equivalent of 20/125). Eyes with linear closure (0.76 ± 0.23 logMAR) had a significantly (P = 0.03) better visual acuity than the round closure group (1.07 ± 0.28 logMAR), only in eyes with horizontal MLD of > 650 µm, but not when other MLD cut-offs were used. CONCLUSION: We describe 2 different patterns of hole closure (linear and round) on en face OCT. Further studies will be required to determine its functional significance. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Graphene nanoribbons initiated from molecularly derived seeds.

Semiconducting graphene nanoribbons are promising materials for nanoelectronics but are held back by synthesis challenges. Here we report that molecular-scale carbon seeds can be exploited to initiate the chemical vapor deposition (CVD) synthesis of graphene to generate one-dimensional graphene nanoribbons narrower than 5 nm when coupled with growth phenomena that selectively extend seeds along a single direction. This concept is demonstrated by subliming graphene-like polycyclic aromatic hydrocarbon molecules onto a Ge(001) catalyst surface and then anisotropically evolving size-controlled nanoribbons from the seeds along [Formula: see text] of Ge(001) via CH4 CVD. Armchair nanoribbons with mean normalized standard deviation as small as 11% (3 times smaller than nanoribbons nucleated without seeds), aspect ratio as large as 30, and width as narrow as 2.6 nm (tunable via CH4 exposure time) are realized. Two populations of nanoribbons are compared in field-effect transistors (FETs), with off-current differing by 150 times because of the nanoribbons' different widths.

Chemical and topographical patterns combined with solution shear for selective-area deposition of highly-aligned semiconducting carbon nanotubes.

Selective deposition of semiconducting carbon nanotubes (s-CNTs) into densely packed, aligned arrays of individualized s-CNTs is necessary to realize their potential in semiconductor electronics. We report the combination of chemical contrast patterns, topography, and pre-alignment of s-CNTs via shear to achieve selective-area deposition of aligned arrays of s-CNTs. Alternate stripes of surfaces favorable and unfavorable to s-CNT adsorption were patterned with widths varying from 2000 nm down to 100 nm. Addition of topography to the chemical contrast patterns combined with shear enabled the selective-area deposition of arrays of quasi-aligned s-CNTs (∼14°) even in patterns that are wider than the length of individual nanotubes (>500 nm). When the width of the chemical and topographical contrast patterns is less than the length of individual nanotubes (<500 nm), confinement effects become dominant enabling the selective-area deposition of much more tightly aligned s-CNTs (∼7°). At a trench width of 100 nm, we demonstrate the lowest standard deviation in alignment degree of 7.6 ± 0.3° at a deposition shear rate of 4600 s-1, while maintaining an individualized s-CNT density greater than 30 CNTs µm-1. Chemical contrast alone enables selective-area deposition, but chemical contrast in addition to topography enables more effective selective-area deposition and stronger confinement effects, with the advantage of removal of nanotubes deposited in spurious areas via selective lift-off of the topographical features. These findings provide a methodology that is inherently scalable, and a means to deposit spatially selective, aligned s-CNT arrays for next-generation semiconducting devices.