Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

With the aim of understanding the relationships between organic small molecule field-effect transistors （FETs） and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly （3-hexylthiophene） （RR-P3HT） field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies （average size and average roughness） of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit.

Evolution of domain structure in Fe_(3)GeTe_(2)

Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism.Here,we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe_(3)GeTe_(2)(FGT)with a thickness range of 11.2-112 nm.Three types of domain structures and their corresponding hysteresis loops can be obtained.The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness,which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields.These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness.Our finding not only enriches the fundamental magnetism,but also paves a way towards spintronics based on 2D magnet.

Fabrication and Characterization of Solar Cells Made of p-CuO/n-Si Hetero Junctions

Cupric oxide（CuO） is considered to be a promising material for photovoltaie applications. In this paper, p-CuO/n-Si junction solar cells were obtained by thermal oxidation of metallic copper films deposited on n-Si substrates at 400 ℃ for 5 h. X-ray diffraction patterns show that the as-prepared films are CuO with monoelinic crystalline structure. Hall effect measurement results show that CuO films are p-type conduction. A direct band-gap of -1.57 eV for the CuO film is deduced from UV-Vis absorbance spectra. Solar cells of Cu/p-CuO/n-Si/Al structure show that its photovoltaic behavior has a much wider spectrum response width compared with that of Si solar cells. In addition, the photocurrent of CuO/n-Si junction is investigated as a function of CuO film thickness, and it is found that the critical thickness for CuO on Si is about 250 nm.

Negative Phase Time Effectin Potential-Well Passing

The properties of phase time taken for particles to pass through a quantum potential well are investigated. It is found in a 1 dimensional quantum mechanical problem that the phase time is negative when the incident energy and the thickness of potential well satisfy certain conditions. Similar results are also found in a 2 dimensional fully relativistic optical analog. It is shown that the expression of the la teral shift of transmitted optical waves is similar to that of the phase time in the 1 dimensional quantum mechanical problem. The phase time in the 2 dimensional optical problem is also shown to be negative under certain conditions.

Thickness Dependence of Doping Level in Conducting Polymer Films:the Optical Contrast Optimization in Electrochromism as a Case Study

Doping plays an essential role in the properties of conducting polymers.Film thickness not only has a direct influence on their photoelectric properties,but also affects the doping ability,which may lead to the decline of capacitance and electrochromic properties caused by incomplete doping.Therefore,it is essential to study the quantitative relationship between doping level and film thickness in application.Herein,empirical formula between doping level and thickness was obtained by studying the spectroelectrochemistry behaviors of two different electrochromic materials,poly(N,N'-bis(3,5-(2-thienyl)-phenyl)-1,6,7,12-tetrachloroperylene-3,4,9,10-perylenetetracarboxylic diimide)(poly(Th-Cl-PBI))and poly(3,4-ethylenedioxythiophene)(PEDOT).The doping level is verified to be correlated to the reciprocal of the 3^(rd)power of film thickness.Experimental results fit these formulas very well,giving correlation coefficient R^(2)higher than 0.99.The optical contrast prediction of these two electrochromic materials is also used to verify this relationship formula.For the first time,we quantitatively connect these two important parameters of conducting polymers,doping level and thickness.

Layer Thickness-Dependent Hardness and Strain Rate Sensitivity of Cu–Al/Al Nanostructured Multilayers

Cu-Al/Al nanostructured metallic multilayers with Al layer thickness hAl varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing hAl down to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu-Al monolithic thin films. The strain rate sensitivity （SRS, m）, however, decreased monotonically with reducing hAl. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu-Al nanolayers dominated at hAl≤ 20 nm, while the crystalline Al nanolayers dominated at hAl 〉 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with hAl. In addition, the hAFdependent hardness and SRS were quanti- tatively modeled in light of the strengthening mechanisms at different length scales.

Surface roughness modulated resistivity in copper thin films

The surfaces of metallic thin films are never flat. The resistivity in thin films is very different from that in bulk because of the unavoidable rough surfaces. In this study, we apply a quantum-mechanical method to study the resistivity in metallic thin films.The resulting resistivity formula for metallic thin films merely involves two parameters: bulk relaxation time and surface roughness. We use the formula to fit a large number of experimental data sets for copper thin films obtained using different growing methods. With an additional tuning parameter for calibrating the film thickness, the quantum formula can provide a universal fitting to most data with a satisfactory precision, regardless of their growing methods or data source.