Trap states generated at grain boundaries often dominate the charge transport behavior of polycrystalline organic field effect transistors (OFETs). While these grain boundaries can be reduced through careful processing, unfortunately they cannot be completely suppressed. In this work, we introduce an approach that renders the grain boundaries inactive. Diels-Alder chemistry, which selectively reacts at the grain boundaries within organic semiconductor thin films, is utilized to attach a dipole-containing molecule in a localized manner. This induced dipole alters the surface potential, shifting the mean energy within the grain boundary and resulting in significantly enhanced device performance. Conductance increases exceed two orders of magnitude with the increase proportional to the amount of grain boundary reacted. In OFETs, this generated a doubling in charge carrier mobility and a reduction in the threshold voltage. The ability to tune the performance and uniformity of fabricated films, regardless of their initial grain size or conductance, represents a significant advance in post-fabrication optimization.

Metal deposition onto organic materials results in a myriad of issues at the metal-on-organic interface, necessitating a highly adaptable interlayer. A single cysteamine-based monolayer on evaporated tetracene thin films is demonstrated to be highly multifunctional, inhibiting metal penetration and increasing contact wetting for the silver-on-organic interface. Cross sections of the monolayer-coated sample, imaged via transmission electron microscopy, show that silver penetration decreased by up to 40% compared to untreated tetracene. Substantial morphology differences are observed between treated and untreated samples; metal poorly wets untreated samples, forming nanoparticle clusters, while monolayer-coated samples are uniform. Scanning electron microscopy indicates that the monolayers prevent contact discontinuities (hundreds of nanometers in size) that were observed on untreated samples with thin (20 nm) silver contacts. Monolayers do not add any significant barrier to charge transport compared to untreated samples, with conductivity values measured to be near identical. When these are combined with earlier reports of cysteamine improving contact adhesion and durability, monolayers can effectively address most of the issues plaguing metal-on-organic devices.

We characterized the prominent electron transport layer 2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) via single crystal X-ray diffraction, grazing incidence X-ray diffractio...

Anhydride terminated acene thin films were chemically transformed to thiol or carboxylic acid functionalities, groups heretofore incompatible with monolayer reactions. The molecular surface imparts large rate acceleration when imides are formed, while disfavored disulfides can be formed from the thiols. The modified surface imparts improved adhesion to top metal contacts in flexible/bendable applications.

Morphology plays a critical role in determining the properties of solid-state molecular materials, yet fluctuates wildly as these materials undergo reaction. A prototypical system, a vapor-solid Diels-Alder reaction of tetracene and pentacene thin-films, is used to observe the evolution of morphology features as the reaction transitions from surface to bulk. The initial stages of reaction display little topographical change as measured by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and substrates are coated with a uniform layer of product 1-2 molecules thick, as determined by energy-dispersive X-ray (EDX) spectroscopy. The highly textured surfaces of late stage reactions are a result of aggregated products, as identified via EDX spectroscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS); areas of the surface in between product aggregates resemble the initial stages. The mechanism by which products aggregate into surface asperities requires the assistance of a facilitating media - in this case condensed vapor; simple thermally assisted surface diffusion was unable to generate these morphology changes. The combined data indicate that reactions of molecular solids, could be confined to the surface in the absence of condensate of the vapor phase reactant.

The rapid emergence of superbugs, or multi-drug resistant (MDR) organisms, has prompted a search for novel antibiotics, beyond traditional small-molecule therapies. Nanotherapeutics are being investigated as alternatives, and recently superoxide-generating quantum dots (QDs) have been shown as important candidates for selective light-activated therapy, while also potentiating existing antibiotics against MDR superbugs. Their therapeutic action is selective, can be tailored by simply changing their quantum-confined conduction-valence band (CB-VB) positions and alignment with different redox half-reactions-and hence their ability to generate specific radical species in biological media. Here, we show the design of superoxide-generating QDs using optimal QD material and size well-matched to superoxide redox potential, charged ligands to modulate their uptake in cells and selective redox interventions, and core/shell structures to improve their stability for therapeutic action. We show that cadmium telluride (CdTe) QDs with conduction band (CB) position at -0.5 V with respect to Normal Hydrogen Electron (NHE) and visible 2.4 eV bandgap generate a large flux of selective superoxide radicals, thereby demonstrating the effective light-activated therapy. Although the positively charged QDs demonstrate large cellular uptake, they bind indiscriminately to cell surfaces and cause non-selective cell death, while negatively charged and zwitterionic QD ligands reduce the uptake and allow selective therapeutic action via interaction with redox species. The stability of designed QDs in biologically-relevant media increases with the formation of core-shell QD structures, but an appropriate design of core-shell structures is needed to minimize any reduction in charge injection efficiency to adsorbed oxygen molecules (to form superoxide) and maintain similar quantitative generation of tailored redox species, as measured using electron paramagnetic resonance (EPR) spectroscopy and electrochemical impedance spectroscopy (EIS). Using these findings, we demonstrate the rational design of QDs as selective therapeutic to kill more than 99% of a priority class I pathogen, thus providing an effective therapy against MDR superbugs.

The optical properties of β-Y2Si2O7:Pr3+ were studied. Efficient visible-to-UVC upconversion was observed and explained based on intermediate state decay behavior.

A facile solution-phase route for the preparation of AgInSe2 nanocrystals was developed by using silver nitrate, indium stearate, and oleylamine-selenium (OAm-Se) as precursors. The evolution process of the AgInSe2 nanocrystals is discussed in detail and different reaction conditions all have a great impact on the growth and morphology of the nanocrystals. Alloyed AgIn(S1-xSex)2 nanocrystals with controlled composition across the entire range (0 ≤ x ≤ 1) was also successfully prepared by modulating the S/Se reactant mole ratio. X-ray diffraction (XRD), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were used to confirm that the alloyed AgIn(S1-xSex)2 nanocrystals are homogeneous. The UV-vis absorption spectra revealed that the band gap energies of the alloyed AgIn(S1-xSex)2 nanocrystals could be continuously tuned by increasing the Se content.

The morphology of CuInSe2 nanocrystals plays a key role in their functional properties. Achieving controllable morphology is significant for studying their structures and novel properties. Here, CuInSe2 nanocrystals with a trigonal-pyramidal shape have successfully been synthesized by a facile solution-phase method. The nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), etc. The morphological evolution of the CuInSe2 nanocrystals was illustrated by tuning the injection temperature of oleylamine-selenium (OAm-Se). In addition, CuInSe2 nanocrystals with spherical and ellipsoidal shapes were also obtained when copper stearate was used as the copper precursor.

The up-conversion luminescent material for optically written display, NaGdF4: Yb3+,Er3+ up-conversion nanoparticies(UCNPs) were prepared under microwave irradiation. The particle size was about 65 nm and the samples exhibited green (550 nm) fluorescence excited by a 980 nm diode laser. The UCNPs@SiO2-NH, nanocomposites, the size of which was 70 nm, were prepared and conjugated with polyclonal antibidy. Then, the ability of polyclonal antibody fluorescent probes was detected to recognize the expression of tissue inhibitor of metalloproteinases-4(TIMP4) in the endometrial gland cells by immunohistochemistry. The results show that the as-prepared UCNPs have uniform shape and size distribution. The UCNPs @ SiO2-NH2 nanocomposites offer some distinct advantages, such as good distribution and water-solubility, strong and stable upcoversion fluorscence as well as significant auto-fluorescence from biological tissues resting in low signal to background ratio, and are potentially to apply to detect the expression of protein in tissues at 980 nm excitation.

1,5-Bis(3-methylimidazole-2-selone)pentane (Pbis), which belongs to the coordination chemistry of organochalcogenone compounds, was used as a novel Se precursor to purposely synthesize various metal selenide nanostructures. By this method, CdSe, Bi2Se3, ZnSe and PbSe have been successfully prepared and all exhibit relatively uniform size and morphology. High water solubility and good dispersity is achieved by using poly (vinyl pyrrolidone) (PVP) as the capping agent. At the same time, the shape of the metal selenide nanostructures could be controlled by adjusting the experimental conditions. The thermoelectric properties of the Bi2Se3 have also been discussed. It would be expected that Pbis could be more widely used to prepare more metal selenide nanostructures with uniform morphologies, sizes, and remarkable properties.

Lanthanide-doped core-shell upconversion nanocrystals (UCNCs) have tremendous potential for applications in many fields, especially in bio-imaging and medical therapy. As core-shell UCNCs are mostly synthesized in organic solvents, tedious organic-aqueous phase transfer processes are usually needed for their use in bio-applications. Herein, we demonstrate the first example of one-step synthesis of highly luminescent core-shell UCNCs in the "aqueous" phase under mild conditions using innocuous reagents. A microwave-assisted approach allowed for layer-by-layer epitaxial growth of a hydrophilic NaGdF4 shell on NaYF4:Yb, Er cores. During this process, surface defects of the nanocrystals could be gradually passivated by the homogeneous shell deposition, resulting in obvious enhancement in the overall upconversion emission efficiency. In addition, the up-down conversion dual-mode luminescent NaYF4:Yb, Er@NaGdF4:Ce, Ln (Eu, Tb, Sm, Dy) nanocrystals were also synthesized to further validate the successful formation of the core-shell structure. More significantly, based on their superior solubility and stability in water solution, high upconversion efficiency and Gd-doped predominant X-ray absorption, the as-prepared NaYF4:Yb, Er@NaGdF4 core-shell UCNCs exhibited high contrast in in vitro cell imaging and in vivo X-ray computed tomography (CT) imaging, demonstrating great potential as multiplexed luminescent biolabels and CT contrast agents.

A new facile solution method for the synthesis of high quality lead selenide (PbSe) nanocrystals with controllable size and shape was developed. A Pb-stearate complex and oleylamine-selenium (OLA-Se) were used as new precursors to prepare monodispersed nanocrystals instead of the traditional lead oxide (PbO) and trioctylphosphine-selenium (TOPSe). Both of the lead and chalcogenide precursors used in this method are inexpensive and air-stable, which largely reduces the cost of the reaction and simplifies the synthetic process. Five different shapes including quasi-spherical, cubic, octahedral, cuboctahedral and star shaped monodispersed PbSe nanocrystals were obtained, and the particle size can be easily tuned from similar to 18 nm to similar to 50 nm by varying the amount of oleic acid (OA) while keeping the amount of oleylamine (OLA) fixed. Oleic acid based growth orientation and shape evolution mechanism in double stabilizer surfactants was investigated in detail. The etching of PbSe nanocrystals was also observed when they were dispersed in toluene containing excessive amine over time, the etching process of oleylamine occurred on particle surfaces, and a new framework composed of nanorods formed around the nanocrystals. An ITO-PbSe-Al device based on a film of PbSe nanocrystals was constructed. The dark steadystate I-V characteristics of the films before and after ligand exchange revealed a broad prospect for the use of PbSe nanocrystals in light detection and infrared solar cells.

Water-dispersible Re(3+) doped CeF(3) colloidal nanocrystals with well controllable morphology and high crystallinity have been successfully synthesized through a solvothermal process. The TEM images illustrate that the Re(3+) doped CeF(3) nanocrystals are rectangular (or cubic) with a mean diameter of ~10 nm. The excellent dispersibility in some of the polar solvents including water is achieved by using polyethyleneimine as the capping agent. The amine groups of the polymer chains on one hand bind to the nanocrystal surface; on the other hand the free ones could link to functional materials including bio-molecules. The CeF(3) nanocrystals doped with Tb(3+) and Dy(3+) ions show the characteristic emission of Tb(3+ 5)D(4)-(7)F(J) (J = 6-3, with (5)D(4)-(7)F(5) green emission at 542 nm as the strongest one) and Dy(3+ 4)F(9/2)-(6)H(15/2) (blue-green color at 478 nm) and (4)F(9/2)-(6)H(13/2) (yellow color at 571 nm) transitions, respectively. The energy transfer from Ce(3+) to Tb(3+) and Dy(3+) was also investigated in detail. In vitro studies of Re(3+) doped CeF(3) colloidal nanocrystals on HepG2 cells confirm their excellent biological compatibility. The obtained solid CeF(3) : Tb(3+)/PDMS nanocomposites are very stable and flexible and exhibit strong green photoluminescence upon UV excitation.

Monodisperse water-soluble LaF(3):Ln(3+) nanocrystals (NCs) have been successfully fabricated via a fast, facile and environmentally-friendly microwave-assisted modified polyol process with polyvinylpyrrolidone (PVP) as an amphiphilic surfactant. The obtained NCs can be well dispersed in hydrophilic solutions with small sizes in the range of 9-12 nm. The LaF(3):Ln(3+) NCs (Ln = Eu, Nd, Ce, Tb, Yb, Er, Yb, Ho and Yb, Tm) have the unique feature of up-down conversion from visible to NIR emission owing to the ladder-like arranged energy levels of Ln(3+) and in particular, the high efficiency upconversion of the two-photon, obtained from excitation by a continuous 980 nm laser. This investigation focuses on both the up and down conversion fluorescence properties of water-soluble monodisperse crystalline LaF(3):Ln(3+) NCs in such a small size. Furthermore, the three-dimensional PDMS rod-like fluorescence displays and a silica surface modification by a core/shell structure on the obtained NCs can improve the biocompatibility, indicating potential applications in optical 3D devices and as bio-probes.

Visible-light-responsive photonic structures have been prepared in alcohol solvents by using silica-modified PbS colloidal nanocrystal clusters (CNCs) as building blocks. Further modification of the PbS CNCs with a coating of silica allowed the dispersion of the particles into nonaqueous solutions. Repulsive electrostatic and solvation forces contribute to the self-assembly of the PbS@SiO2 spheres. The core-shell par-ticles have optical properties similar to those of CNCs, and they can also be assembled into close-packing films through simple drop-casting on silicon substrates. Embedding droplets of such a PbS@SiO2 colloidal solution in a polymer matrix produced solid composite materials with visible-light-responsive optical properties with potential applications as sensors and optical switches.