Organic Molecular Crystal Engineering via Organic Vapor-Liquid-Solid Deposition

Control over the size, shape, topology, orientation, and crystallographic phase of organic molecular materials is critical for a wide array of applications ranging from optoelectronics to pharmaceutical development. Herein, we demonstrate a relatively low-cost approach for fabricating single crystals with controlled sizes, shapes, microscale periodic features, preferred orientations and specific molecular packing modes. These features allow for the fabrication of intricate arrangements of single crystals for incorporation into complex device architectures, and potentially the endowment of tailored optical, electronic, thermal, and mechanical properties onto these materials. Patterning is achieved by utilizing an organic-vapor-liquid-solid (OVLS) deposition scheme paired with traditional photolithography methods. The OVLS approach involves spin coating a layer of a low vapor pressure solvent onto a substrate in order to drive up the critical nucleus size required for crystal nucleation, resulting in large grain sizes. This substrate is placed above a hot plate with the organic material to be sublimed. Our results show that millimeter-scale, ultrathin, planar organic molecular crystals can be grown on patterned substrates with rudimentary equipment (hot plate, spin coater, photoresist, photomask, UV source). We show that this technique is not only compatible with organic semiconductors, but also other organic molecular crystals such as pharmaceuticals

Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.

The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products

(i)chromatographic Methods For Solute Descriptor Determinations (ii)ruthenium Substrate-Catalyzed Growth Of Nickel Nitride Thin Films By Atomic Layer Deposition

Determination of distribution levels of environmentally important compounds in various environmental compartments is a major procedure in many fields including environmental risk assessment, food and drug safety, and the perfumery industry. Models for direct estimation of environmental properties were developed using gas chromatography and liquid-liquid partitioning. The developed models were used to derive descriptor values for environmentally important organic compounds. The accuracy of the developed models and descriptor values were demonstrated by the application to the estimation of standard environmental properties and by comparison with experimental solute property values. Quantitative structure property relationships were constructed for totally organic biphasic partition systems of different polarity containing ethanolamine as the base solvent. The models demonstrate high accuracy and are of good statistical quality. The descriptor space for the determination of the hydrogen bond acidity descriptor was enhanced by the characterization of ethanolamine based partition systems. Models with high statistical quality were also developed for the totally organic biphasic partition systems containing triethylamine as a counter solvent. The triethylamine-formamide system was identified as a suitable system to supplement the currently available totally organic biphasic systems for the determination of the hydrogen bond basicity descriptor. Descriptor values for polycyclic aromatic hydrocarbons were determined using totally organic biphasic systems and gas and liquid chromatography methods. These descriptors were validated using theoretical models, standard environmental models, and by comparison with experimentally determined values. The descriptor values are homogeneous and accurate as a group. Therefore, the research work reported herein will enable the accurate measurement of solute properties for the estimation of environmental properties. A substrate-dependent catalytic thermal ALD process was developed to address the low reactivity of precursors in atomic layer deposition processes. The developed process can be used to obtain smooth, high purity thin films at low deposition temperatures, and also for the deposition of materials which were found challenging so far using thermal and energy enhanced atomic layer deposition methods. Substrate-dependent catalytic thermal ALD technique can be conveniently used for the commercial production of thin-film materials. The deposition of pure, uniform and conformal nickel nitride thin films were demonstrated using Ni(OCHMeCH2NMe2)2 precursor, and anhydrous hydrazine in a two-step process, and Ni(OCHMeCH2NMe2)2 precursor, formic acid, and anhydrous hydrazine in a three-step process on ruthenium substrates. Films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The ALD window for the two-step process was observed between 140 and 180 °C with a growth rate of 0.25 Å/cycle. The ALD window for the three-step process was observed between 120 and 180 °C with a growth rate of 0.35Å/cycle. Atomic force microscopy measurements demonstrated smooth thin films for the two-step process which was ~0.25 nm for 25 nm thick films deposited between 120-180 °C. The surface roughness of films varied between 0.38-4.4 nm for 35 nm thick films deposited by three-step process between 120-180 °C

Gaseous flux and distribution of polycyclic aromatic hydrocarbons across the air-water interface of southern Chesapeake Bay

Gaseous fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air-water interface of Southern Chesapeake Bay were calculated for the period January 1994 through May 1995 using a modified two-film model. Additionally, the distributions of PAHs between the vapor and aerosol phase in the atmosphere, and between the freely dissolved and suspended particulate phase in the water column were investigated. Net instantaneous gaseous fluxes of PAHs were determined to vary in direction and magnitude both spatially and temporally across the air-water interface of Southern Chesapeake Bay at four sites ranging from remote to urban and highly industrialized. The magnitude of gas exchange fluxes was of the same order as wet and dry atmospheric depositional fluxes. Spatial variations in gaseous fluxes resulted from differences in the air-water concentration gradients between sites. Temporal variations in gas exchange fluxes resulted from seasonal changes in both water temperatures and vapor concentrations. Atmospheric PAH vapor concentrations increased exponentially with temperature at the non-rural sites suggesting volatilization from contaminated surfaces (soils, roads, vegetation) during warmer weather; whereas, PAH vapor concentrations at the rural site decreased with time. All sites experienced increased loadings of particulate-associated PAHs during winter. Mean total atmospheric PAH concentrations ranged from 7.87 ng/m&\sp3& at a rural (Haven Beach) site to 92.8 ng/m&\sp3& at an urban (Elizabeth River) site. Plots of the logarithm of the particle-vapor partitioning coefficient (C&\rm\sb{lcub}p{rcub}/TSP\sp\* C\sb{lcub}v{rcub})& versus inverse temperature indicate different particle characteristics or atmospheric partitioning processes at the urban and rural sites. Three methods (gas sparging, semipermeable membrane devices, filtration with sorption of the dissolved contaminant fraction to XAD-2 resin) for determining freely dissolved contaminant concentrations in estuarine waters were investigated. Mean total PAH concentrations in surface waters ranged from 24.2 ng/l at a mainstem bay site to 91.1 ng/l at the industrialized Elizabeth River site. Dissolved-particulate partitioning of PAHs approximated equilibrium theory at all sites and sampling periods. The results of this study support the hypothesis that gas exchange is a major transport process affecting concentrations and exposure levels of PAHs in the southern Chesapeake Bay Region

Organic Single-Crystal Field-Effect Transistors

We present an overview of recent studies of the charge transport in the field effect transistors on the surface of single crystals of organic low-molecular-weight materials. We first discuss in detail the technological progress that has made these investigations possible. Particular attention is devoted to the growth and characterization of single crystals of organic materials and to different techniques that have been developed for device fabrication. We then concentrate on the measurements of the electrical characteristics. In most cases, these characteristics are highly reproducible and demonstrate the quality of the single crystal transistors. Particularly noticeable are the small sub-threshold slope, the non-monotonic temperature dependence of the mobility, and its weak dependence on the gate voltage. In the best rubrene transistors, room-temperature values of $\mu$ as high as 15 cm$^2$/Vs have been observed. This represents an order-of-magnitude increase with respect to the highest mobility previously reported for organic thin film transistors. In addition, the highest-quality single-crystal devices exhibit a significant anisotropy of the conduction properties with respect to the crystallographic direction. These observations indicate that the field effect transistors fabricated on single crystals are suitable for the study of the \textit{intrinsic} electronic properties of organic molecular semiconductors. We conclude by indicating some directions in which near-future work should focus to progress further in this rapidly evolving area of research.Comment: Review article, to appear in special issue of Phys. Stat. Sol. on organic semiconductor

Reconstructing historical trends of polycyclic aromatic hydrocarbon deposition in a remote area of Spain using herbarium moss material

Herbarium mosses from 1879-1881, 1973-1975 and 2006-2007 were used to investigate the historical changes of atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) at a remote site located in Northern Spain. Natural abundance of nitrogen and carbon isotopes was also measured in order to assess the evolution of emissions from anthropogenic sources. Nitrogen concentrations, 13C, 13N and PAH levels were significantly higher in 19th century samples with respect to the present century samples. Moreover, PAH distribution varied over the centuries, following a tendency of light PAH enrichment. The carbon, nitrogen and PAH levels measured in the mosses tally with the historic evolution of anthropogenic emissions in the area, mainly influenced by changes of economic activities, domestic heating and road traffic density. Mosses provided by herbaria seem to offer the possibility to study long-term temporal evolution of atmospheric PAH deposition

Depletion of gaseous polycyclic aromatic hydrocarbons by a forest canopy

Rapid uptake of gaseous polycyclic aromatic hydrocarbons (PAHs) by a forest canopy was observed at Borden in Southern Ontario, Canada during bud break in early spring 2003. High volume air samples were taken on 12 individual days at three different heights (44.4, 29.1, and 16.7 m) on a scaffolding tower and on the forest floor below the canopy (1.5 m). Concentrations of PAHs were positively correlated to ambient temperature, resulting from relatively warm and polluted air masses passing over the Eastern United States and Toronto prior to arriving at the sampling site. An analysis of vertical profiles and gas/particle partitioning of the PAHs showed that gaseous PAHs established a concentration gradient with height, whereas levels of particulate PAHs were relatively uniform, implying that only the uptake of gaseous PAHs by the forest canopy was sufficiently rapid to be observed. Specifically, the gaseous concentrations of intermediate PAHs, such as phenanthrene, anthracene, and pyrene, during budburst and leaf emergence were reduced within and above the canopy. When a gradient was observed, the percentage of PAHs on particles increased at the elevations experiencing a decrease in gas phase concentrations. The uptake of intermediate PAHs by the canopy also led to significant differences in gaseous PAH composition with height. These results are the most direct evidence yet of the filter effect of forest canopies for gaseous PAHs in early spring. PAH deposition fluxes and dry gaseous deposition velocities to the forest canopy were estimated from the concentration gradients

Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-matter Interactions

Van der Waals (vdW) solids, as a new type of artificial materials that consist of alternating layers bonded by weak interactions, have shed light on fascinating optoelectronic device concepts. As a result, a large variety of vdW devices have been engineered via layer-by-layer stacking of two-dimensional materials, although shadowed by the difficulties of fabrication. Alternatively, direct growth of vdW solids has proven as a scalable and swift way, highlighted by the successful synthesis of graphene/h-BN and transition metal dichalcogenides (TMDs) vertical heterostructures from controlled vapor deposition. Here, we realize high-quality organic and inorganic vdW solids, using methylammonium lead halide (CH3NH3PbI3) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids behave dramatically different in light emission. Our studies demonstrate that h-BN monolayer is a great complement to organic perovskite for preserving its original optical properties. As a result, organic/h-BN vdW solid arrays are patterned for red light emitting. This work paves the way for designing unprecedented vdW solids with great potential for a wide spectrum of applications in optoelectronics

Atmospheric deposition of chlorinated and brominated polycyclic aromatic hydrocarbons in central Europe analyzed by GC-MS/MS

Chlorinated and brominated polycyclic aromatic hydrocarbons (ClPAHs and BrPAHs) are persistent organic pollutants that are ubiquitous in the atmospheric environment. The sources, fate, and sinks in the atmosphere of these substances are largely unknown. One of the reasons is the lack of widely accessible analytical instrumentation. In this study, a new analytical method for ClPAHs and BrPAHs using gas-chromatography coupled with triple quadrupole mass spectrometry is presented. The method was applied to determine ClPAHs and BrPAHs in total deposition samples collected at two sites in central Europe. Deposition fluxes of ClPAHs and BrPAHs ranged 580 (272-962) and 494 (161-936) pg m(-2) day(-1), respectively, at a regional background site, Kosetice, and 547 (351-724) and 449 (202-758) pg m(-2) day(-1), respectively, at a semi-urban site, Praha-Libus. These fluxes are similar to those of PCBs and more than 2 orders of magnitude lower than those of the parent PAHs in the region. Seasonal variations of the deposition fluxes of these halogenated PAHs were found with maxima in summer and autumn, and minima in winter at Kosetice, but vice versa at Praha-Libus. The distribution of ClPAHs and BrPAHs between the particulate and dissolved phases in deposition samples suggests higher degradability of particulate BrFlt/Pyr and BrBaA than of the corresponding ClPAHs. A number of congeners were detected for the first time in the atmospheric environment

Benchmarking the SPARC software program for estimating solubilities of naphthalene and anthracene in organic solvents

The SPARC software program was benchmarked for calculating the solubilities of two representative polyaromatic hydrocarbons (PAHs), naphthalene and anthracene, in a range of organic solvents at various temperatures. Although SPARC was able to reasonably approximate the solubilities of naphthalene in some organic solvents, gross errors were obtained for other solvents. For anthracene, poor prediction performance was observed in all solvents considered. Overall, the results suggest that SPARC is currently not suitable for accurately predicting the solubilities of representative PAHs relevant for the petroleum sector in various organic solvents