Thick Junction Research Articles

Further morphological evidence on South African earliest Homo lower postcanine dentition: Enamel thickness and enamel dentine junction

The appearance of the earliest members of the genus Homo in South Africa represents a key event in human evolution. Although enamel thickness and enamel dentine junction (EDJ) morphology preserve important information about hominin systematics and dietary adaptation, these features have not been sufficiently studied with regard to early Homo. We used micro-CT to compare enamel thickness and EDJ morphology among the mandibular postcanine dentitions of South African early hominins (N = 30) and extant Homo sapiens (N = 26), with special reference to early members of the genus Homo. We found that South African early Homo shows a similar enamel thickness distribution pattern to modern humans, although three-dimensional average and relative enamel thicknesses do not distinguish australopiths, early Homo, and modern humans particularly well. Based on enamel thickness distributions, our study suggests that a dietary shift occurred between australopiths and the origin of the Homo lineage. We also observed that South African early Homo postcanine EDJ combined primitive traits seen in australopith molars with derived features observed in modern human premolars. Our results confirm that some dental morphological patterns in later Homo actually occurred early in the Homo lineage, and highlight the taxonomic value of premolar EDJ morphology in hominin species.

Defect engineering of the electronic transport through cuprous oxide interlayers.

The electronic transport through Au–(Cu2O)n–Au junctions is investigated using first-principles calculations and the nonequilibrium Green’s function method. The effect of varying the thickness (i.e., n) is studied as well as that of point defects and anion substitution. For all Cu2O thicknesses the conductance is more enhanced by bulk-like (in contrast to near-interface) defects, with the exception of O vacancies and Cl substitutional defects. A similar transmission behavior results from Cu deficiency and N substitution, as well as from Cl substitution and N interstitials for thick Cu2O junctions. In agreement with recent experimental observations, it is found that N and Cl doping enhances the conductance. A Frenkel defect, i.e., a superposition of an O interstitial and O substitutional defect, leads to a remarkably high conductance. From the analysis of the defect formation energies, Cu vacancies are found to be particularly stable, in agreement with earlier experimental and theoretical work.

Improving resolution in quantum subnanometre-gap tip-enhanced Raman nanoimaging.

Two-dimensional (2D) materials beyond graphene such as transition metal dichalcogenides (TMDs) have unique mechanical, optical and electronic properties with promising applications in flexible devices, catalysis and sensing. Optical imaging of TMDs using photoluminescence and Raman spectroscopy can reveal the effects of structure, strain, doping, edge states, and surface functionalization from materials to bioscience. However, Raman signals are inherently weak and so far have been limited in spatial resolution in TMDs to a few hundred nanometres which is much larger than the intrinsic scale of these effects. Here we overcome the diffraction limit by using resonant tip-enhanced Raman scattering (TERS) of few-layer MoS2, and obtain nanoscale optical images with ~20 nm spatial resolution. This becomes possible due to electric field enhancement in an optimized subnanometre-gap resonant tip-substrate configuration. We investigate the limits of signal enhancement by varying the tip-sample gap with sub-Angstrom precision and observe a quantum quenching behavior, as well as a Schottky-Ohmic transition, for subnanometre gaps, which enable surface mapping based on this new contrast mechanism. This quantum regime of plasmonic gap-mode enhancement with a few nanometre thick MoS2 junction may be used for designing new quantum optoelectronic devices and sensors with a wide range of applications.

Homogenization of a semilinear variational inequality in a thick multi-level junction

We consider a semilinear variation inequality in a thick multi-level junction $\Omega_{\varepsilon}$ , which is the union of a domain $\Omega_{0}$ (the junction’s body) and a large number of thin cylinders. The thin cylinders are divided into m classes depending on the geometrical characteristics and the semilinear perturbed boundary conditions of the Signorini type given on their lateral surfaces. In addition, the thin cylinders from each class are ε-periodically alternated along some manifold on the boundary of the junction’s body. The purpose is to study the asymptotic behavior of the solution $u_{\varepsilon}$ of this variation inequality as $\varepsilon\to0$ , i.e. when the number of the thin cylinders from each class infinitely increases and their thickness tends to zero. The passage to the limit is accompanied by special intensity factors $\{ \varepsilon^{\alpha_{k}}\}_{k=1}^{m}$ in the boundary conditions. We establish two qualitatively different cases in the asymptotic behavior of the solution depending on the value of parameters $\{{\alpha_{k}}\}_{k=1}^{m}$ . For each case we prove a convergence theorem. As a consequence, we see that $u_{\varepsilon}$ converges (as $\varepsilon\to0$ ) to the solution of the corresponding nonstandard homogenized problem and show that the semilinear boundary conditions are transformed in the limiting variational inequalities in the region that is filled up by the thin cylinders from each class.

Changes in Fundus Autofluorescence after Anti-vascular Endothelial Growth Factor According to the Type of Choroidal Neovascularization in Age-related Macular Degeneration.

PurposeTo describe the changes of fundus autofluorescence (FAF) in patients with age-related macular degeneration before and after intravitreal injection of anti-vascular endothelial growth factor according to the type of choroidal neovascularization (CNV) and to evaluate the correlation of FAF with spectral domain optical coherence tomography (SD-OCT) parameters and vision.MethodsThis was a retrospective study. Twenty-one treatment-naïve patients with neovascular age-related macular degeneration were included. Study eyes were divided into two groups according to the type of CNV. Fourteen eyes were type 1 CNV and seven eyes were type 2 CNV. All eyes underwent a complete ophthalmologic examination, including an assessment of best-corrected visual acuity, SD-OCT, fluorescein angiography, and FAF imaging, before and 3 months after intravitreal anti-vascular endothelial growth factor injection. Gray scales of FAF image for CNV areas, delineated as in fluorescein angiography, were analyzed using the ImageJ program, which were adjusted by comparison with normal background areas. Correlation of changes in FAF with changes in SD-OCT parameters, including CNV thickness, photoreceptor inner and outer segment junction disruption length, external limiting membrane disruption length, central macular thickness, subretinal fluid, and intraretinal fluid were analyzed.ResultsEyes with both type 1 and type 2 CNV showed reduced FAF before treatment. The mean gray scales (%) of type 1 and type 2 CNV were 52.20% and 42.55%, respectively. The background values were 106.72 and 96.86. After treatment, the mean gray scales (%) of type 1 CNV and type 2 CNV were changed to 57.61% (p = 0.005) and 57.93% (p = 0.008), respectively. After treatment, CNV thickness, central macular thickness, and inner and outer segment junction disruption length were decreased while FAF increased.ConclusionsFAF was noted to be reduced in eyes with newly diagnosed wet age-related macular degeneration, but increased after anti-vascular endothelial growth factor therapy regardless of CNV lesion type.

Electro-Optics of Conventional and Inverted Thick Junction Organic Solar Cells

Bulk heterojunctions continue to be the dominant architecture for solution processed organic solar cells. In general, photoactive films on the order of 100 nm thickness have delivered the highest power conversion efficiencies. However, it is becoming increasingly apparent that thicker junctions are needed for high yield, high throughput, low cost manufacturing of commercial organic solar cells. Very few organic semiconductors are suitable for maintaining optimal efficiencies in cells with thicker junctions. This paradigm is beginning to shift with the recent high mobility donor polymers, where electrically inverted thick heterojunction structures deliver impressive efficiencies. The inverted architecture seems to be an essential feature of these solar cells. The reason for this has yet to be explained, and in this work, we address this question. We present analytical simulations and experimental evidence showing how the charge generation and extraction physics is significantly different in thin and thick ...

Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions.

We investigate electron tunneling through atomically thin layers of hexagonal boron nitride (hBN). Metal (Cr/Au) and semimetal (graphite) counter-electrodes are employed. While the direct tunneling resistance increases nearly exponentially with barrier thickness as expected, the thicker junctions also exhibit clear signatures of Coulomb blockade, including strong suppression of the tunnel current around zero bias and step-like features in the current at larger biases. The voltage separation of these steps suggests that single-electron charging of nanometer-scale defects in the hBN barrier layer are responsible for these signatures. We find that annealing the metal-hBN-metal junctions removes these defects and the Coulomb blockade signatures in the tunneling current.

Eigenvibrations of thick cascade junctions with `very heavy' concentrated masses

We study small-parameter asymptotics of eigenelements of a boundary-value problem for the Laplace operator in a thick cascade junction with concentrated masses. There are five qualitatively different cases in the asymptotic behaviour of eigenvalues and eigenfunctions as the small parameter tends to zero (`light', `intermediate', `slightly heavy', `intermediate heavy' and `very heavy' concentrated masses). We study the influence of concentrated masses on the asymptotics of eigenvibrations in the last two cases. We construct the leading terms of asymptotic expansions for eigenfunctions and eigenvalues and rigorously justify them by appropriate asymptotic estimates. We also find new types of high-frequency eigenvibrations.

Domain wall network as QCD vacuum and the chromomagnetic trap formation under extreme conditions

The ensemble of Euclidean gluon field configurations represented by the domain wall network is considered. A single domain wall is given by the sine-Gordon kink for the angle between chromomagnetic and chromoelectric components of the gauge field. The domain wall separates the regions with self-dual and anti-self-dual fields. The network of the domain wall defects is introduced as a combination of multiplicative and additive superpositions of kinks. The character of the spectrum and eigenmodes of color-charged fluctuations in the presence of the domain wall network is discussed. The concept of the confinement-deconfinement transition in terms of the ensemble of domain wall networks is outlined. Conditions for the formation of thick domain wall junction during heavy ion collisions are discussed, and the spectrum of color charged quasiparticles inside the trap is evaluated. An important observation is the existence of the critical size $L_c$ of the trap stable against gluon tachyonic modes, which means that deconfinement can occur only in a finite region of space-time in principle. The size $L_c$ is related to the value of gluon condensate $\langle g^2F^2\rangle$.

In vivo precision of digital topological skeletonization based individual trabecula segmentation (ITS) analysis of trabecular microstructure at the distal radius and tibia by HR-pQCT

Trabecular plate and rod microstructure plays a dominant role in the apparent mechanical properties of trabecular bone. With high-resolution computed tomography (CT) images, digital topological analysis (DTA) including skeletonization and topological classification was applied to transform the trabecular three-dimensional (3D) network into surface and curve skeletons. Using the DTA-based topological analysis and a new reconstruction/recovery scheme, individual trabecula segmentation (ITS) was developed to segment individual trabecular plates and rods and quantify the trabecular plate- and rod-related morphological parameters. High-resolution peripheral quantitative computed tomography (HR-pQCT) is an emerging in vivo imaging technique to visualize 3D bone microstructure. Based on HR-pQCT images, ITS was applied to various HR-pQCT datasets to examine trabecular plate- and rod-related microstructure and has demonstrated great potential in cross-sectional and longitudinal clinical applications. However, the reproducibility of ITS has not been fully determined. The aim of the current study is to quantify the precision errors of ITS plate-rod microstructural parameters. In addition, we utilized three different frequently used contour techniques to separate trabecular and cortical bone and to evaluate their effects on ITS measurements.Overall, good reproducibility was found for the standard HR-pQCT parameters with precision errors for volumetric BMD and bone size between 0.2% and 2.0%, and trabecular bone microstructure between 4.9% and 6.7% at the radius and tibia. High reproducibility was also achieved for ITS measurements using all three different contour techniques. For example, using automatic contour technology, low precision errors were found for plate and rod trabecular number (pTb.N, rTb.N, 0.9% and 3.6%), plate and rod trabecular thickness (pTb.Th, rTb.Th, 0.6% and 1.7%), plate trabecular surface (pTb.S, 3.4%), rod trabecular length (rTb.ℓ, 0.8%), and plate-plate junction density (P-P Junc.D, 2.3%) at the tibia. The precision errors at the radius were similar to those at the tibia. In addition, precision errors were affected by the contour techniques. At the tibia, the precision error by the manual contour method was significantly different from automatic and standard contour methods for pTb.N, rTb.N and rTb.Th. Precision error using the manual contour method was also significantly different from the standard contour method for rod trabecular number (rTb.N), rod trabecular thickness (rTb.Th), rod-rod and plate-rod junction densities (R-R Junc.D and P-R Junc.D) at the tibia. At the radius, the precision error was similar between the three different contour methods. Image quality was also found to significantly affect the ITS reproducibility. We concluded that ITS parameters are highly reproducible, giving assurance that future cross-sectional and longitudinal clinical HR-pQCT studies are feasible in the context of limited sample sizes.

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes.

Spectrally selective light detection is vital for full-colour and near-infrared (NIR) imaging and machine vision. This is not possible with traditional broadband-absorbing inorganic semiconductors without input filtering, and is yet to be achieved for narrowband absorbing organic semiconductors. We demonstrate the first sub-100 nm full-width-at-half-maximum visible-blind red and NIR photodetectors with state-of-the-art performance across critical response metrics. These devices are based on organic photodiodes with optically thick junctions. Paradoxically, we use broadband-absorbing organic semiconductors and utilize the electro-optical properties of the junction to create the narrowest NIR-band photoresponses yet demonstrated. In this context, these photodiodes outperform the encumbent technology (input filtered inorganic semiconductor diodes) and emerging technologies such as narrow absorber organic semiconductors or quantum nanocrystals. The design concept allows for response tuning and is generic for other spectral windows. Furthermore, it is material-agnostic and applicable to other disordered and polycrystalline semiconductors.

A surface plasmon enabled liquid-junction photovoltaic cell.

Plasmonic nanosystems have recently been shown to be capable of functioning as photovoltaics and of carrying out redox photochemistry, purportedly using the energetic electrons and holes created following plasmonic decay as charge carriers. Although such devices currently have low efficiency, they already manifest a number of favorable characteristics, such as their tunability over the entire solar spectrum and a remarkable resistance to photocorrosion. Here, we report a plasmonic photovoltaic using a 25 μm thick electrolytic liquid junction which supports the iodide/triiodide (I-/I3-) redox couple. The device produces photocurrent densities in excess of 40 μA cm(-2), an open circuit voltage (Voc) of ∼0.24 V and a fill factor of ∼0.5 using AM 1.5 G solar radiation at 100 mW cm(-2). The photocurrent and the power conversion efficiency are primarily limited by the low light absorption in the 2-D gold nanoparticle arrays. The use of a liquid junction greatly reduces dielectric breakdown in the oxide layers utilized, which must be very thin for optimal performance, leading to a great improvement in the long-term stability of the cell's performance.

Eigenvibrations of thick cascade junctions with ‘very heavy’ concentrated masses

Изучаются асимптотики по малому параметру собственных элементов краевой задачи для оператора Лапласа в густом каскадном соединении с концентрированными массами. Существует пять качественно различных случаев в асимптотическом поведении собственных значений и собственных функций при стремлении малого параметра к нулю ("легкие", "промежуточные", "слегка тяжелые", "умеренно тяжелые" и "сверхтяжелые" концентрированные массы). Изучается влияние концентрированных масс на асимптотики собственных колебаний в последних двух случаях. Строятся ведущие члены асимптотических разложений как для собственных функций, так и для собственных значений, которые строго обосновываются при помощи соответствующих асимптотических оценок. Более того, найдены новые типы высокочастотных собственных колебаний. Библиография: 41 наименование.

Asymptotic approximation for the solution to a semi-linear parabolic problem in a thick junction with the branched structure

We consider a semi-linear parabolic problem in a thick junction Ωε, which is the union of a domain Ω0 and a lot of joined thin trees situated ε-periodically along some manifold on the boundary of Ω0. The trees have finite number of branching levels. The following nonlinear Robin boundary condition ∂νvε+εαiμ(t,x2,vε)=εβgε is given on the boundaries of the branches from the i-th branching layer; {αi} and β are real parameters. The asymptotic analysis of this problem is made as ε→0, i.e., when the number of the thin trees infinitely increases and their thickness vanishes. In particular, the corresponding homogenized problem is found and the existence and uniqueness of its solution in an anisotropic Sobolev space of multi-sheeted functions is proved. We construct the asymptotic approximation for the solution vε and prove the corresponding asymptotic estimate in the space C([0,T];L2(Ωε))∩L2(0,T;H1(Ωε)), which shows the influence of the parameters {αi} and β on the asymptotic behavior of the solution.

Front Cover: Thick junction broadband organic photodiodes (Laser Photonics Rev. 8(6)/2014)

Front Cover: Thick junction broadband organic photodiodes (Laser Photonics Rev. 8(6)/2014)

Efficient, Large Area, and Thick Junction Polymer Solar Cells with Balanced Mobilities and Low Defect Densities

The high power conversion efficiencies (PCEs) of laboratory‐scale polymer‐based organic solar cells are yet to translate to large area modules because of a number of factors including the relatively large sheet resistance of available transparent conducting electrodes (TCEs), and the high defect densities associated with thin organic semiconductor junctions. The TCE problem limits device architectures to narrow connected strips (<1 cm) causing serious fabrication difficulties and extra costs. Thin junctions are required because of poor charge transport (imbalanced mobilities) in the constituent organic semiconductors. These issues are addressed using a combination of approaches to create thick junctions conformally coated on low sheet resistance metal grid TCEs. An essential feature of these thick junctions is balanced carrier mobilities, which affords high fill factors and efficient carrier extraction. Conformal coating is achieved by promoting enhanced intermolecular interactions in the coating solution using a high molecular weight polymeric semiconductor and appropriate solvent system. This combination of balanced mobilities, conformal coating and metallic grid TCEs is a simple and generic approach to the fabrication of defect‐free large area organic solar cells (OSCs). The approach is demonstrated with 25 cm2 monolithic devices possessing aperture‐corrected power conversion efficiencies of 5% and fill factors exceeding 0.5.

Thick junction broadband organic photodiodes

AbstractInorganic semiconductor‐based broadband photodetectors are ubiquitous in imaging technologies such as digital cameras and photometers. Herein a broadband organic photodiode (OPD) that has performance metrics comparable or superior to inorganic photodiodes over the same spectral range is reported. The photodiode with an active layer comprised of a poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)]:[6,6]‐phenyl‐C71‐butyric acid methyl ester bulk heterojunction blend had a dark current < 1 nA/cm2, specific detectivity of ∼1013 Jones, reverse bias −3 dB frequency response of 100 kHz to 1 MHz, and state‐of‐the‐art Linear Dynamic Range for organic photodiodes of nine orders of magnitude (180 dB). The key to these performance metrics was the use of a thick junction (700 nm), which flattened the spectral response, reduced the dark current and decreased performance variations. The strategy also provides a route to large area defect free “monolithic” structures for low noise integrated photo‐sensing, position determination, or contact, non‐focal imaging.

Crossover from diffusive to tunneling regime in NbN/DyN/NbN ferromagnetic semiconductor tunnel junctions

We have investigated NbN-DyN-NbN junctions with 1 to 10 nm thick DyN barriers. A crossover from diffusive (hopping) to tunneling-type transport was found in these junctions as the DyN thickness is reduced below $\ensuremath{\sim}$4 nm. We have also made a detailed study of magnetic and electrical properties of thicker DyN thin films deposited under similar conditions; DyN films were found to be ferromagnetic with ${T}_{\text{Curie}}\ensuremath{\sim}35\ifmmode\pm\else\textpm\fi{}5$ K. Electrical transport of the junctions with $\ensuremath{\sim}$10 nm DyN was understood in terms of Shklovskii-Efros (SE)-type variable range hopping (VRH) at low temperature between 90 and 35 K. We estimated localization length $\ensuremath{\xi}=5.6$ nm in this temperature range. Temperature dependence of resistance was found to deviate from SE-VRH below 35 K along with large suppression of resistance with magnetic field. This is correlated with onset of magnetism below 35 K. Large butterfly-shaped MR up to $\ensuremath{\sim}$40$%$ was found for the $\ensuremath{\sim}$10 nm thick DyN junction at 2 K. In the tunneling regime, barrier height of the tunnel junction was estimated $\ensuremath{\sim}$50 meV from the Simmons model. Signatures of spin filtering was found in temperature dependence of resistance in tunnel junction with $\ensuremath{\sim}$3 nm thick DyN. Cooper pair tunneling in these junctions below ${T}_{C}$ ($\ensuremath{\sim}$10.8 K) of NbN was understood according to S-I-S tunneling current model. We found coherent tunneling of Cooper pairs through a $\ensuremath{\sim}$1 nm thick DyN tunnel barrier with critical current ${I}_{C}\ensuremath{\sim}12$ $\ensuremath{\mu}$A. The critical current also showed modulation with magnetic field.

High-frequency cell vibrations and spatial skin effect in thick cascade junction with heavy concentrated masses

We study the asymptotic behavior of eigenvalues and eigenfunctions of the Laplacian in a 2D thick cascade junction with heavy concentrated masses. We present two-term asymptotic approximations, as ε→0, for the eigenelements in the case of “slightly heavy”, “moderate heavy”, and “super heavy” concentrated masses. Asymptotics of high-frequency cell-vibrations are found as well.

Spatial‐skin effect for eigenvibrations of a thick cascade junction with ‘heavy’ concentrated masses

A spectral problem for the Laplace operator in a thick cascade junction with concentrated masses is considered. This cascade junction consists of the junction's body and a great number of ϵ‐alternating thin rods belonging to two classes. One class consists of rods of finite length, and the second one consists of rods of small length of order . The density of the junction is of order on the rods from the second class and outside of them. The asymptotic behavior of eigenvalues and eigenfunctions of this problem is studied as ϵ → 0. There exist five qualitatively different cases in the asymptotic behavior of eigenmagnitudes as ϵ → 0, namely the case of ‘light’ concentrated (α ∈ (0,1)), ‘middle’ concentrated (α = 1), and ‘heavy’ concentrated masses (α ∈ (1, + ∞ )) that we divide into ‘slightly heavy’ concentrated (α ∈ (1,2)), ‘intermediate heavy’ concentrated (α = 2), and ‘very heavy’ concentrated masses (α > 2). In the paper, we study in detail the influence of the concentrated masses on the asymptotic behavior if α ∈ (1,2). We construct the leading terms of asymptotic expansions both for the eigenvalues and eigenfunctions and prove the corresponding asymptotic estimates. Copyright © 2013 John Wiley & Sons, Ltd.