Assessment of Carbon Storage and Biomass on Minelands Reclaimed to Grassland Environments Using Landsat Spectral Indices

This study investigated carbon (C) storage and biomass in grasslands of West Virginia reclaimed surface minesites. Mine-related disturbance and subsequent reclamation may be an important component of C cycling. Biomass and C storage generally increased for the first five years after reclamation, but then declined, suggesting a nonlinear pattern to vegetation recovery. Three 2007 Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus images were used to assess the potential to predict biomass from raw red and near infrared radiance, the tasseled cap transformation (TC), and four vegetation indices [normalized difference vegetation index, enhanced vegetation index (EVI), triangular vegetation index, and the soil adjusted vegetation index]. TC greenness and EVI were most strongly correlated with biomass and illustrate a modest potential for monitoring vegetation recovery in reclaimed minelands. Additionally, a number of regression models that included age since reclamation and spectral indices were statistically significant suggesting a temporal recovery pattern amongst minesites in this study

Compact modeling of organic thin film transistors with solution processed octadecyl substituted tetrabenzotriazaporphyrin as an active layer

Using 70nm thick spin-coated film of newly synthesized octadecyl substituted copper tetrabenzotriazaporphyrin (10CuTBTAP) as an active layer on a highly doped silicon (110) gate electrode substrates, output characteristics and transfer characteristics of bottom-gate bottom-contact organic thin film transistors have been measured at room temperature. A compact model for thin film transistors has been employed as a part of circuit design tool to extract device parameters such as the charge carrier mobility μ, the threshold voltage VT and the contact resistances. Parallel measurements and analysis were performed on similarly constructed devices with a copper phthalocyanine analogue (10CuPc). The results reveal that the 10CuPc layer is relatively more susceptible to trapping degradation near the gate region than a 10CuTBTAP layer, which is significant in order to achieve stability in these transistors. The application of the simple square law in the classical MOS model provides a quicker but approximate interpretation of the transistor performance without providing information on the gate voltage dependence of mobility and the effects of the contact regions. In this comparative study, the analysis of the contact regions is found to be very important for determining the difference in the performance of two transistors

A liquid crystalline copper phthalocyanine derivative for high performance organic thin film transistors

This journal is © The Royal Society of Chemistry 2012Bottom-gate, bottom-contact organic thin film transistors (OTFTs) were fabricated using solvent soluble copper 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine as the active semiconductor layer. The compound was deposited as 70 nm thick spin-coated films onto gold source–drain electrodes supported on octadecyltrichlorosilane treated 250 nm thick SiO2 gate insulators. The performance of the OTFTs was optimised by investigating the effects of vacuum annealing of the films at temperatures between 50 0C and 200 0C, a range that included the thermotropic mesophase of the bulk material. These effects were monitored by ultraviolet-visible absorption spectroscopy, atomic force microscopy and XRD measurements. Device performance was shown to be dependent upon the annealing temperature due to structural changes of the film. Devices heat treated at 100 0C under vacuum (≥10-7 mbar) were found to exhibit the highest field-effect mobility, 0.7 cm2 V^-1 s^-1, with an on–off current modulation ratio of~107, a reduced threshold voltage of 2.0 V and a sub-threshold swing of 1.11 V per decade.UK Technology Strategy Board (Project no: TP/6/EPH/6/S/K2536J) and UK National Measurement System (Project IRD C02 ‘‘Plastic Electronics’’, 2008–2011)

Solution processable lutetium phthalocyanine organic field-effect transistors

Spun films of novel thermotropic liquid crystalline lutetium bisphthalocyanine sandwich complexes substituted with sixteen octyl chains are employed as active organic semiconducting layers in the fabrication of organic field-effect transistors (OFET). When the device is annealed under vacuum at 70 °C, an increase in the field effect mobility in the saturated regime by a factor of five is observed while the threshold voltage is reduced to half the value obtained for as-deposited films. The annealed devices exhibit an increase in on/off ratio by two orders of magnitude. An improvement in performance of OFETs annealed above the crystal to mesophase transition temperature is consistent with atomic force microscopic images indicating increases in grain sizes and decreases in mean surface roughness of the organic bisphthalocyanine films

Development of Superstrate CuInGaSe₂ Thin Film Solar Cells with Low-Cost Electrochemical Route from Nonaqueous Bath

Electrodeposition of Cu­(In,Ga)­Se₂ (CIGS) thin film is an attractive approach for the development of highly efficient low-cost solar cells. This work focuses on the effects of various electrodeposition parameters on the growth and properties of CIGS layers. The films deposited at −0.9 V tend to drive the growth of CIGS favoring (112) crystal orientation, whereas the films deposited at −1.6 V show the orientation along (220)/(204). Interplanar distances corresponding to (112) and (204/220) planes could be observed in the high resolution transmission electron microscopy (HRTEM) images of the respective films, confirming the dependence of the texture on the deposition potential. Films with larger grains could be grown by maintaining higher temperature (130 °C) during the deposition of layers. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Cu⁺, In³⁺, Ga³⁺, and Se^2– valence states in the CIGS layers prepared at −0.9 and −1.6 V. The film deposited at −1.6 V with (220/204) orientation showed high efficiency as compared to the film deposited at −0.9 V with (112) orientation. The observed solar cell parameters, measured under illuminated condition of input power intensity 100 mW/cm², were <i>V</i>_OC = 0.357 V; <i>J</i>_SC = 27 mA/cm², FF = 44, and η = 4.90; and <i>V</i>_OC = 0.460 V, <i>J</i>_SC = 34 mA/cm², FF = 58, and η = 9.07 for the deposition potentials of −0.9 and −1.6 V, respectively<sub>.</sub

High-mobility solution-processed copper phthalocyanine-based organic field-effect transistors

Solution-processed films of 1,4,8,11,15,18,22,25-octakis(hexyl) copper phthalocyanine (CuPc6) were utilized as an active semiconducting layer in the fabrication of organic field-effect transistors (OFETs) in the bottom-gate configurations using chemical vapour deposited silicon dioxide (SiO2) as gate dielectrics. The surface treatment of the gate dielectric with a self-assembled monolayer of octadecyltrichlorosilane (OTS) resulted in values of 4×10−2 cm2 V−1 s−1 and 106 for saturation mobility and on/off current ratio, respectively. This improvement was accompanied by a shift in the threshold voltage from 3 V for untreated devices to -2 V for OTS treated devices. The trap density at the interface between the gate dielectric and semiconductor decreased by about one order of magnitude after the surface treatment. The transistors with the OTS treated gate dielectrics were more stable over a 30-day period in air than untreated ones