ABSTRACT
A huge challenge is to control the nucleation of crystallites/aggregates in the solution during polymer film formation to generate desired structures. In this work, we investigate crystallization of P(NDI2OD-T2), a donor-acceptor polymer semiconductor, with controlled solution flow along the contact line between the drying film and solution through a seesaw-like pivoting of samples during polymer drying. By controlling the pivoting frequency/amplitude, various types of line patterns can be observed: (I) an array of fishbone-like stripes oriented in the film-growth direction; (II) the pinning-depinning of contact line (PDCL)-mechanism-defined patterned wires along the contact line; and (III) periodic twined crystalline line pattern oriented in the direction of the contact line. The rich variety of pattern formation observed is attributed to the distinctiveness of the donor-acceptor conjugated polymer structure. The result measured from thin-film transistors made of the generated films/structures showed that the charge mobility of P(NDI2OD-T2) does not change much with the film morphology, which supports recent controversy over the charge-transportation mechanism of some donor-acceptor polymer semiconductors.
ABSTRACT
Nanoparticle polymer composites have enabled material multifunctionalities that are difficult to obtain otherwise. A simple modification to a commercially available resin system enables a universal methodology to embed nanoparticles in resins via spatial, temporal, thermal, concentration, and chemical control parameters. Changes in nanoparticle density distribution are exploited to demonstrate dynamic optical and electronic properties that can be processed on-demand, without the need for expensive equipment or cleanroom facilities. This strategy provides access to the control of optical (cooperative plasmonic effects), electronic (insulator to a conductor), and chemical parameters (multimetal patterning). Using the same composite resin system, the followings are fabricated: i) diffraction gratings with tuneable diffraction efficiencies (10-78% diffraction efficiencies), ii) organic electrochemical transistors with a low drive voltage, and iii) embedded electrodes in confined spaces for potential diagnostic applications.
ABSTRACT
An accommodation-free displays, also known as Maxwellian displays, keep the displayed image sharp regardless of the viewer's focal distance. However, they typically suffer from a small eye-box and limited effective field of view (FOV) which requires careful alignment before a viewer can see the image. This paper presents a high-quality accommodation-free head mounted display (aHMD) based on pixel beam scanning for direct image forming on retina. It has an enlarged eye-box and FOV for easy viewing by replicating the viewing points with an array of beam splitters. A prototype aHMD is built using this concept, which shows high definition, low colour aberration 3D augmented reality (AR) images with an FOV of 36°. The advantage of the proposed design over other head mounted display (HMD) architectures is that, due to the narrow, collimated pixel beams, the high image quality is unaffected by changes in eye accommodation, and the approach to enlarge the eye-box is scalable. Most importantly, such an aHMD can deliver realistic three-dimensional (3D) viewing perception with no vergence-accommodation conflict (VAC). It is found that viewing the accommodation-free 3D images with the aHMD presented in this work is comfortable for viewers and does not cause the nausea or eyestrain side effects commonly associated with conventional stereoscopic 3D or HMD displays, even for all day use.
