Spray printing of organic semiconducting single crystals.

Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.

Simultaneous Tunable Selection and Self-Assembly of Si Nanowires from Heterogeneous Feedstock.

Semiconducting nanowires (NWs) are becoming essential nanobuilding blocks for advanced devices from sensors to energy harvesters, however their full technology penetration requires large scale materials synthesis together with efficient NW assembly methods. We demonstrate a scalable one-step solution process for the direct selection, collection, and ordered assembly of silicon NWs with desired electrical properties from a poly disperse collection of NWs obtained from a supercritical fluid-liquid-solid growth process. Dielectrophoresis (DEP) combined with impedance spectroscopy provides a selection mechanism at high signal frequencies (>500 kHz) to isolate NWs with the highest conductivity and lowest defect density. The technique allows simultaneous control of five key parameters in NW assembly: selection of electrical properties, control of NW length, placement in predefined electrode areas, highly preferential orientation along the device channel, and control of NWs deposition density from few to hundreds per device. Direct correlation between DEP signal frequency and deposited NWs conductivity is confirmed by field-effect transistor and conducting AFM data. Fabricated NW transistor devices demonstrate excellent performance with up to 1.6 mA current, 10(6)-10(7) on/off ratio and hole mobility of 50 cm(2) V(-1) s(-1).

Precise Characterisation of Molecular Orientation in a Single Crystal Field-Effect Transistor Using Polarised Raman Spectroscopy.

Charge transport in organic semiconductors is strongly dependent on the molecular orientation and packing, such that manipulation of this molecular packing is a proven technique for enhancing the charge mobility in organic transistors. However, quantitative measurements of molecular orientation in micrometre-scale structures are experimentally challenging. Several research groups have suggested polarised Raman spectroscopy as a suitable technique for these measurements and have been able to partially characterise molecular orientations using one or two orientation parameters. Here we demonstrate a new approach that allows quantitative measurements of molecular orientations in terms of three parameters, offering the complete characterisation of a three-dimensional orientation. We apply this new method to organic semiconductor molecules in a single crystal field-effect transistor in order to correlate the measured orientation with charge carrier mobility measurements. This approach offers the opportunity for micrometre resolution (diffraction limited) spatial mapping of molecular orientation using bench-top apparatus, enabling a rational approach towards controlling this orientation to achieve optimum device performance.