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Spatially Uniform Shallow Trap Distribution in an Ultrathin Organic Transistor
摘要： In organic electronic materials, charge carrier transport is often limited by disorder-induced trap states very close in energy to the ideal band transport states. We directly view the location and impact of these 'shallow' traps on an ultrathin transistor active layer using Kelvin Probe Force Microscopy. As the transistor turns on, dramatic fluctuations in the surface potential of the active channel suddenly arise due to charge trapping and release processes. Importantly, the spatial distribution of rapid fluctuations in surface potential is uniform throughout the active channel. These facts strongly constrain the microscopic origin of shallow charge traps, and associated efforts to optimize the mobility and noise performance baseline in device applications.
关键词： disorder,charge traps,electrical noise,organic electronics
更新于2025-09-23 15:23:52
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Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach
摘要： The contribution of static and thermal disorder is one of the largest challenges for the accurate determination of the atomic structure from the extended X-ray absorption fine structure (EXAFS). Although there are a number of generally accepted approaches to solve this problem, which are widely used in the EXAFS data analysis, they often provide less accurate results when applied to outer coordination shells around the absorbing atom. In this case, the advanced techniques based on the molecular dynamics and reverse Monte Carlo simulations are known to be more appropriate: their strengths and weaknesses are reviewed here.
关键词： Reverse Monte Carlo,Extended X-ray absorption fine structure (EXAFS),Molecular dynamics,Static and thermal disorder,X-ray absorption spectroscopy
更新于2025-09-23 15:23:52
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Energy disorder and energy level alignment between host and dopant in organic semiconductors
摘要： Energy level alignment between host and dopant molecules plays a critical role in exciton formation and harvesting in light emission zone of organic light-emitting diodes. Understanding the mechanism for predicting energy level alignment is thus important in materials selection for fabricating high-performance organic light-emitting devices. Here we show that host-dopant energy level alignment strongly depends on film thickness and substrate work function by using X-ray and ultraviolet photoemission spectroscopy. Invariant Gaussian density of states fails to explain the experimental data. We speculate that energy disorder in molecules next to the surface dictates the alignment. Ultraviolet photoemission spectroscopy measurements of several archetypical organic semiconductors confirm our speculation. An empirical interface disorder function is derived and used to construct a functional Gaussian density of states to compute host energy levels. Host-dopant energy level alignment is then computed by applying the universal energy alignment rule and is found in excellent agreement with the experimental data.
关键词： Host-dopant systems,Organic semiconductors,Energy level alignment,Photoemission spectroscopy,Energy disorder
更新于2025-09-23 15:23:52
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Unconventional charge and spin-dependent transport properties of a graphene nanoribbon with line-disorder
摘要： Electronic transport with a line (or a few lines) of Anderson-type disorder in a zigzag graphene nanoribbon is investigated in the presence of Rashba spin-orbit interaction. Such line-disorders give rise to a peculiar behavior in both charge as well as spin-polarized transmission in the following sense. In the weak-disorder regime, the charge transport data show Anderson localization up to a certain disorder strength, beyond which the extended states emerge and start dominating over the localized states. These results are the hallmark signature of a selectively disordered (as opposed to bulk disorder) graphene nanoribbon. However, the spin-polarized transport shows a completely contradicting behavior. Further, the structural symmetries are shown to have an important role in the spintronic properties of the nanoribbons. Moreover, the edge-disorder scenario (disorder selectively placed at the edges) seems to hold promise for the spin-filter and switching device applications.
关键词： Anderson localization,spin transport,graphene nanoribbon,line-disorder,Rashba spin-orbit interaction
更新于2025-09-23 15:23:52
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Vacuum-enhanced optical nonlinearities with disordered molecular photoswitches
摘要： It is well known that nonlinear optical signals such as cross-phase modulation can be coherently enhanced in multilevel atomic gases under conditions of electromagnetically induced transparency, but analogous results in solids are challenging to obtain due to natural energetic disorder. We propose a solid-state cavity QED scheme to enable cross-phase modulation between two arbitrarily weak classical fields in the optical domain, using a highly disordered intracavity medium composed of organic molecular photoswitches. Even in the presence of strong energetic and orientational disorder, the unique spectral properties of organic photoswitches can be used to enhance the desired nonlinearity under conditions of vacuum-induced transparency, enabling cross-phase modulation signals that surpass the detection limit imposed by absorption losses. Possible applications of the scheme include integrated all-optical switching with low photon numbers.
关键词： organic photoswitches,cavity QED,vacuum-induced transparency,cross-phase modulation,disorder
更新于2025-09-23 15:23:52
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Ultralow Thermal Conductivity of Turbostratically Disordered MoSe2 Ultra-Thin Films and Implications for Heterostructures
摘要： Films containing 8, 16, 24, 32 and 64 MoSe2 layers were synthesized using the modulated elemental reactants (MER) method. X-ray reflectivity patterns showed that the annealed films were the targeted number of MoSe2 layers thick with atomically smooth interfaces. In-plane x-ray diffraction scans contained only hk0 reflections for crystalline MoSe2 monolayers. Specular x-ray diffraction patterns contained only 00l reflections, also indicating that the hk0 plane of the MoSe2 layers are parallel to the substrate. Both x-ray diffraction and electron microscopy techniques indicated that the hk0 planes are rotationally disordered with respect to one another, with all orientations equally probable for large areas. The rotational disorder between MoSe2 layers is present even when analyzed spots are within 10 nm of one another. Cross-plane thermal conductivities of 0.07 – 0.09 W m-1 K-1 were measured by time domain thermoreflectance, with the thinnest films exhibiting the lowest conductivity. The structural analysis suggests that the ultralow thermal conductivity is a consequence of rotational disorder, which increases the separation between MoSe2 layers. The bonding environment of the Se atoms also becomes significantly distorted from C3v symmetry due to the rotational disorder between layers. This structural disorder efficiently reduces the group velocity of the transverse phonon modes but not that of longitudinal modes. Since rotational disorder between adjacent layers in heterostructures is expected if the constituents have incommensurate lattices, this study indicates that these heterostructures will have very low cross-plane thermal conductivity.
关键词： rotational disorder,heterostructure,TMDs,turbostratic disorder,thermal conductivity,molybdenum diselenide
更新于2025-09-23 15:22:29
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Disorder Control in Crystalline GeSb <sub/>2</sub> Te <sub/>4</sub> and its Impact on Characteristic Length Scales
摘要： Crystalline GeSb2Te4 (GST) is a remarkable material, as it allows to continuously tune the electrical resistance by orders of magnitude without involving a structural phase transition or stoichiometric changes. While well-ordered specimen are metallic, increasing amounts of disorder eventually lead to an insulating state with vanishing conductivity in the 0 K limit, but a similar number of charge carriers. Hence, GST provides ideal grounds to explore the impact of disorder on transport properties. Here, a sputter-deposition process is employed that enables growing biaxially textured GST films with large grain sizes on mica substrates. The resulting films exhibit a systematic variation between metallic and truly insulating specimen upon varying deposition temperature. Transport measurements reveal that their electron mean free path can be altered by a factor of 20, while always remaining more than an order of magnitude smaller than the lateral grain size. This proves unequivocally that grain boundaries play a negligible role for electron scattering, while intra-grain scattering, presumably by disordered vacancies, dominates. These findings underline that the insulating state and the system’s evolution toward metallic conductivity are intrinsic properties of the material.
关键词： metal–insulator transition,electrical properties,phase-change materials,disorder,structural properties
更新于2025-09-23 15:22:29
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Cell death mechanisms in a mouse model of retinal degeneration in Spinocerebellar ataxia 7
摘要： Spino-cerebellar ataxia type 7 (SCA7) is a polyglutamine (polyQ) disorder characterized by neurodegeneration of the brain, cerebellum, and retina caused by a polyglutamine expansion in ataxin 7. The presence of an expanded polyQ tract in a mutant protein is known to induce protein aggregation, cellular stress, toxicity, and finally cell death. However, the consequences of the presence of mutant ataxin7 in the retina and the mechanisms underlying photoreceptor degeneration remain poorly understood. In this study, we show that in a retinal SCA7 mouse model, polyQ ataxin7 induces stress within the retina and activates Muller cells. Moreover, Unfolded Protein Response and autophagy are activated in SCA7 photoreceptors. We have also shown that the photoreceptor death does not involve a caspase-dependent apoptosis but instead involves apoptosis inducing factor (AIF) and Leukocyte Elastase Inhibitor (LEI/L-DNase II). When these two cell death effectors are downregulated by their siRNA, a significant reduction of photoreceptor death is observed. These results highlight the consequences of polyQ protein expression in the retina and the role of caspase-independent pathways involved in photoreceptor cell death.
关键词： retina,toxicity,Spinocerebellar ataxia type 7,caspase-independent cell death,photoreceptors,polyglutamine disorder,autophagy,unfolded protein response
更新于2025-09-23 15:22:29
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Multimodal Approach for Rationalization and Quantification of Structural Disorder in Transition Al 2 O 3
摘要： Transition aluminas form a basis of important catalytic and catalytic support materials due to their unique surface acidity, high temperature structural stability, and their viability for synthesis as high surface area materials. The origin of transition aluminas attractive properties has been extensively studied in the past 50+ years, but despite this effort, there are number of structural, electronic and surface properties that remain poorly understood. The poor understanding stems mostly from the inadequate crystallographic description of transition alumina polymorphs of γ-Al2O3, δ-Al2O3, θ-Al2O3 that evolve as a continuum of metastable structures. This work focuses on rationalization and quantification of structural disorder in Boehmite derived transition aluminas by using a suite of complementary imaging, spectroscopy and quantum calculation techniques. Based on aberration corrected STEM HAADF imaging, it will be shown that the individual polymorphs of δ?Al2O3 and θ-Al2O3 accommodate a significant degree of structural disorder, which leads to loss of crystallographic periodicity. The complexity of this disorder can be rationalized as an atomic scale intergrowth of closely related crystallographic variants. As a part of this work, we present a crystallographic approach based on real space interpretation of projected atomic potential that enabled us to unambiguously derive Al3+ coordination in δ-Al2O3 and θ-Al2O3 from a series of low-index STEM HAADF images. This work lead to a full crystallographic description of the crystallographic variants belonging to δ-Al2O3 and θ-Al2O3 family. To quantify the heterogeneous microstructure of transition aluminas on statistically relevant bases, we employed novel approaches for characterization of structural disorder using XRD and NMR techniques. XRD is one of the most employed methods for crystallographic bulk characterization, but historically it has not been successfully used on transition alumina. It will be shown that the crystallographic polymorphs and their structural disorder can be quantified with the use of recursive algorithms as implemented in DIFFAX and TOPAS XRD simulation packages. To further validate the quantification of structural disordered in transition Al2O3, we also employed complementary NMR spectroscopy, combined with DFT NMR simulation methods. As a part of this talk, we also discuss results from DFT energetic calculations explaining how energetic degeneracy between the number of crystallographic variants leads to structural disorder in transition aluminas.
关键词： DFT,transition aluminas,structural disorder,NMR,XRD,STEM HAADF imaging
更新于2025-09-23 15:21:21
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Scattering of light from disordered photonic structures
摘要： We study theoretically and experimentally the scattering of light from ordered and disordered photonic structures. As an example, we consider a thin slab of a woodpile-type photonic crystal and introduce random fluctuations in the rod orientation, revealing a crossover from the Laue diffraction to the formation of speckle patterns. We observe a nontrivial interplay between order and disorder when the orientational disorder is added only in one direction of the square woodpile structure. Namely, ordered sets of rods produce disordered patterns and, vice versa, disordered sets of rods produce ordered patterns. We explain this effect theoretically and experimentally by the fact that light scatters only from the intersection points of different rods.
关键词： light scattering,Laue diffraction,speckle patterns,photonic structures,disorder
更新于2025-09-23 15:21:21