1D nanostructures, characterized by their extremely small lateral size, large surface-to-volume ratio, and quantum confinement effect, hold tremendous potential to build next-generation electronic circuits, sensors with high sensitivity and reaction rate, and even new devices operating on quantummechanical principles. [1][2][3] Polymers are intrinsic 1D nanostructures with well-defined and versatile structures and compositions. The lateral size of a polymer chain is generally below 10 nm, which is the limit of current lithographic technology and is also the critical size at which quantum-mechanical effects can become prominent. [2,4,5] DNA is by far the most extensively studied polymer as 1D nanomaterial due to its high aspect ratio, base-pairing capability, designable base sequence, chemical modifiability, and intriguing electronic properties.[6] It has been used as a template to prepare various types of functional nanowires by conjugation of a broad range of materials such as metals, [2,7] conducting polymers, [8] nanoparticles, [9,10] fluorophores, [11] and single-walled carbon nanotubes. [12] In addition to DNA, functional polymers such as conducting polymers hold potential to be directly used as 1D nanometer-sized building blocks to construct novel devices such as molecular circuits. Polymer chains generally adopt a coiled conformation in a solvent. In order to form 1D nanostructures and integrate them into a functional system, these coils need to be stretched and patterned into appropriate architectures. Examples of such architectures are suspended DNA-templated nanowire pairs in a quantum interference device [2] and crossbar arrays as address decoders.[13] Molecular combing and its derivatives are a set of methods capable of uncoiling, aligning, and immobilizing single molecules or nanowires utilizing the surface tension of water, but they are limited in the precise control of length and location of the stretched molecules over a large area. [14] Arrays of polymeric nanofibers can also be generated by electrospinning on a rotating substrate [15] or mechanical drawing, [16] but the electrospinning method cannot position the nanofibers precisely and the fibers produced by the mechanical drawing are over 50 nm in diameter. We developed a molecular-combing-based approach able to generate a highly ordered array of short (5-10 lm) and long (up to 1 mm) nanowires composed of stretched DNA molecules through dewetting of a DNA solution on a poly(dimethyl siloxane) (PDMS) stamp containing microwells on the surface. [17] In this paper,we report the use of a different type of surface features, micropillars, to generate arrays of DNA nanowires up to 1 cm in length, less than 10 nm in lateral size, and covering an area of up to 1 cm × 1 cm. We have also extended this method to several other polymers and demonstrated functionalization of these nanowires with small molecules and nanoparticles. As schematically shown in Figure 1, the generation of the polymer 1D nanowires was easily achieved by gently placing a PDMS stamp ...
ing sphere [28] purged with flowing nitrogen and the sample was excited at 325 nm and excitation power of 0.2 mW. Photoluminescence transient decays were measured by a time-correlated singlephoton counting (TCSPC) system. Excitation was at~390 nm from a pulsed laser diode (Picoquant) giving 10 pJ pulse ±1. The apparatus response function was~350 ps (full width at half maximum) on its fastest scale. All measurements were performed at room temperature. Films were kept in a vacuum of < 10 ±3 mbar during measurements. The decay kinetics were fitted by a sum of exponential functions: I(t) = A 1 exp(±t/s 1 ) + A 2 exp(±t/s 2 ) with A and s as the pre-exponential factor and excited state lifetime respectively. The quality of the fits was confirmed by random distribution of the residuals.For EL characterization OLEDs were prepared by spin-coating the electroluminescent layers, consisting of 20 wt.-% of each dendrimer blended into CBP, onto transparent indium tin oxide (ITO) anodes (20 X/square) that had been oxygen-plasma treated in an Emitech K1050X plasma unit. The solution concentration was 20 mg mL ±1 in chloroform and the spin speed 2000 rpm for 1 min. The films formed were of good quality as determined by optical microscopy and surface profilometry. After spin-coating, the samples were placed into a high vacuum chamber and an electron transport layer (ETL) and cathode materials were sequentially evaporated. The electron transport layer was 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI), and was evaporated at 0.05 nm s ±1, and the cathode comprised lithium fluoride (0.4 nm), calcium (12 nm), and aluminum (50 nm) layers evaporated at 0.5 nm s ±1 . Electrical and optical measurements of all OLED devices were made under high vacuum (10 ±5 mbar) at room temperature. The effective area of each emitting diode was 6 mm 2 . The EL spectra were recorded with an Oriel MS125 Spectrograph coupled to a CCD detector (spectral resolution~1 nm). Current±voltage and brightness±voltage analyses were performed using a Keithley 2400 Source meter and a Keithley 2000 meter (employing a calibrated silicon photodiode), respectively. Luminance was also measured using a calibrated Minolta LS-100 luminance meter. External quantum efficiencies were calculated from the luminance, current density, and emission spectrum of each device assuming Lambertian emission.
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