Individual Sublayers Research Articles

(Keynote) Epitaxial Si/SiGe Multi-Stacks: From Stacked Nano-Sheet to Fork-Sheet and CFET Devices

After a short description of the evolution of metal-oxide-semiconductor (MOS) device architectures and the corresponding requirements on epitaxial growth processes, the manuscript describes the material properties of complicated Si/SiGe multi-layer stacks used for complementary field effect transistor (CFET) devices. They contain two different Ge concentrations and have been grown using conventional process gases. A relatively high growth temperature is used to obtain acceptable Si and SiGe growth rates. Still island growth has been suppressed for Ge concentrations up to 40%. Excellent structural and optical material properties of the Si/SiGe multi-layer stack will be reported, with up to 3 + 3 Si channels in the top and bottom part of the stack, respectively. The absence/presence of lattice defects has been verified by room temperature photoluminescence measurements. Photoluminescence measurements at low temperatures are used to study band-to-band luminescence from individual sub-layers and to illustrate the optical material quality of the CFET stack.

Modification of magnetoelectric properties of thin film composite multiferroics of Fe10Ni90/PVDF type with using nanostructured Fe10Ni90 layer

In this work, we study the effectiveness of using nanostructuring of a magnetostrictive Fe10Ni90 layer in a film composite multiferroic of the [Fe10Ni90/Cu]p/Fe10Ni90/PVDF type in order to obtain the maximum magnetoelectric effect (ME) while maintaining the high magnetosensitivity characteristic of thin Fe10Ni90 films. In this case, such nanostructuring parameters as the number of periods p and the thickness LFeNi of the Fe–Ni sublayers were varied. The analysis of the dependences of the ME coefficient αE on the indicated parameters carried out in this work made it possible to identify the optimal configuration of the multiferroic. Thus, the work shows that in the non-resonant mode the highest ME coupling coefficient (αE = 4.2 V/cm∙Oe) is achieved for a structure with p = 4 and LFeNi = 200 nm in a saturation field of ∼50 Oe, and a close to linear change in αE is realized in the field range 6–15 Oe. At the same time, this structure retains a low coercive field Hc ∼ 4–5 Oe and pronounced uniaxial magnetic anisotropy in the film plane. These facts indicate the absence in the magnetic component of the multiferroic structure of an undesirable “supercritical” magnetic state, which appears in unstructured Fe10Ni90 films with equivalent thicknesses of the ferromagnetic layer and sharply worsens its magnetosensitivity. Thus, in the case of a homogeneous magnetic layer, the thickness of which is equivalent to the total thickness of the magnetic phase of a nanostructured multiferroic (1000 nm), a significantly lower value of αE = 1.6 V/cm∙Oe is achieved. The totality of the data obtained indicates the validity of using the nanostructuring method when optimizing the properties of film composite multiferroics. A detailed analysis of the dependences αE(p) and αE (LFeNi) together with the results of computer modeling made it possible to determine the main factors influencing the value of αE. In particular, it is shown that an increase in αE is primarily caused by an increase in the total volume of the magnetostrictive phase in the composite, as well as a weakening of the damping effect of the substrate, which occurs with an increase in the number of periods and the thickness of individual sublayers in the structure.

Quasi-1D Moiré superlattices in self-twisted two-allotropic antimonene heterostructures.

Two-dimensional heterostructures, characterized by a twist angle between individual sublayers, offer unique and tunable properties distinct from standalone layers. These structures typically introduce a realm of exotic quantum phenomena due to the appearance of new, long range periodicities associated with Moiré superlattices. Using molecular beam epitaxy, we demonstrate the growth of bi-allotropic 2D-Sb heterostructures on a W(110) substrate composed of twisted α (α-Sb) and β (β-Sb) phases of antimonene. Due to the relatively weak interaction between sublayers, the twist angle is intrinsically determined for each heterostructure, revealing its inherent self-twisted nature. The different atomic lattice symmetries of both allotropes lead to the formation of distinctive quasi-1D Moiré superlattices, while the random nature of the twist angle allows for a wide modulation of the Moiré potential landscape. The observed Moiré patterns on β-Sb/α-Sb heterostructures were compared with a simple model, revealing satisfactory agreement with the experiments and strongly validating the formation of self-twisted β-Sb/α-Sb heterostructures. The samples were characterized in situ using low energy electron microscopy and diffraction techniques providing a real-time tracking of the growth process and insight into the atomic structure of the synthesized nanostructures.

Multimethod cross-sectional characterization approaching the limits of diamond monophase multilayers

Chemical vapour deposited diamond draws significant scientific interest due to its wide range of mechanical and functional properties, which can be easily tuned by the applied deposition conditions. Here, hot filament chemical vapour deposition was used to synthesize four monophase multilayer diamond thin films with individual layer thickness down to ∼ 300 nm. Extensive structural characterization by scanning electron microscopy and Raman spectroscopy on the cross-section confirmed the different diamond morphologies originating from the different applied process parameters of the individual sublayers, where Raman spectroscopy could give a clear distinction between nano- and microcrystalline diamond down to a layer thickness of ∼ 1 μm. Cross-sectional X-ray nanodiffraction identified exclusively the diamond crystal structure throughout the cross-section of the multilayered diamond thin films. Cross-sectional phase and FWHM analysis allowed to discriminate between the diamond morphologies down to ∼ 500 nm, thus identifying the limitations of monophase diamond multilayers. While the microcrystalline diamond sublayers all exhibit pronounced structural gradients expressed in (i) increasing intensity of the 111 Debye-Scherrer ring, (ii) ⟨110⟩ fibre texture, and periodic variations of (iii) grain size and (iv) residual stress, the nanocrystalline diamond sublayers showed no pronounced cross-sectional variations. In summary, the experimental results provide insights into the cross-sectional evolution of microstructure and residual stress and the limitations of monophase multilayered diamond thin films.

Beyond Conventional Charge Density Wave for Strongly Enhanced 2D Superconductivity in 1H-TaS2 Superlattices.

Noncentrosymmetric transition metal dichalcogenide (TMD) monolayers offer a fertile platform for exploring unconventional Ising superconductivity (SC) and charge density waves (CDWs). However, the vulnerability of isolated monolayers to structural disorder and environmental oxidation often degrade their electronic coherence. Herein, an alternative approach is reported for fabricating stable and intrinsic monolayers of 1H-TaS2 sandwiched between SnS blocks in a (SnS)1.15TaS2 van der Waals (vdW) superlattice. The SnS block layers not only decouple individual 1H-TaS2 sublayers to endow them with monolayer-like electronic characteristics, but also protect the 1H-TaS2 layers from electronic degradation. The results reveal the characteristic 3 × 3 CDW order in 1H-TaS2 sublayers associated with electronic rearrangement in the low-lying sulfur p band, which uncovers a previously undiscovered CDW mechanism rather than the conventional Fermi surface-related framework. Additionally, the (SnS)1.15TaS2 superlattice exhibits a strongly enhanced Ising-like SC with a layer-independent Tc of ≈3.0 K, comparable to that of the isolated monolayer 1H-TaS2 sample, presumably attributed to their monolayer-like characteristics and retained Fermi states. These results provide new insights into the long-debated CDW order and enhanced SC of monolayer 1H-TaS2, establishing bulk vdW superlattices as promising platforms for investigating exotic collective quantum phases in the 2D limit.

Reliability-oriented segmentation of sublayers in geologically uncertain substrate: A case study of the Żelazny Most TSF

In this study, a new approach is proposed for the stability analysis of tailings storage facility (TSF) dams. Given the considerable scale of such objects, te correct identification of geotechnical layers for computational models and the determination of reliable parameters can present significant challenges. Therefore, the investigation focuses on distinguishing additional sublayers within a geological substratum to enhance the credibility of stability assessment. The procedure of sublayer separation is directly based on soil parameters derived from geotechnical tests and it aims at reducing the variability in the parameters of individual sublayers. Specifically, the segmentation technique known as the Gaussian mixture model (GMM) is employed for this purpose. Subsequently, the spatial arrangement of sublayers within the finite element model domain is identified using the kriging technique. Utilizing Monte Carlo simulations statistical distribution of factor of safety (FOS) is obtained for the structure. Finally, the stability is assessed using the Cornell reliability index. The application of this developed methodology is demonstrated through a case study of the Żelazny Most TSF. Additional sublayers are identified in Neogene clays constituting the dominant layer beneath the facility. In total, six different segmentation variants are proposed and their performance is evaluated. The results show that the segmentation of additional sublayers produces a clear reduction in the scatter of the FOS. Consequently, the estimated simplified reliability index surpasses that of the case, which does not involve the separation of additional layers.

Effects of thickness ratio on phase structures, mechanical properties, and wear behaviors of CrN/ZrB2 bilayer films

CrN/ZrB2 bilayer films leveraging the wear resistance of CrN and the mechanical properties of ZrB2 were successfully produced and characterized. DC magnetron sputtering was used to deposit CrN/ZrB2 bilayer films with a thickness of approximately 1 μm and various ZrB2/CrN sublayer thickness ratios (TZrB2/TCrN = 10.85, 5.78, 4.50, 2.29, and 1.04). The thickness ratio was controlled by adjusting the deposition times of the individual sublayers. The effects of thickness ratio on the films' phase structures, mechanical properties, and wear resistance were investigated. The ZrB2 sublayer initially formed with a nanocrystalline structure; as its thickness increased, its texture became (001). As the thickness of the CrN sublayer increased, the CrN (111) reflection became more dominant, and the hardness of the CrN/ZrB2 bilayer films decreased from 19.8 to 11.6 GPa. In the CrN/ZrB2 bilayer films, the CrN sublayer was softer than the harder ZrB2 sublayer; specifically, the wear rate of the monolithic ZrB2 film was 6.45 × 10−5 mm3/N·m. This hardness enabled the bilayer films to exhibit excellent wear resistance with wear rates of 1.04–1.68 × 10−6 mm3/N·m. The wear behaviors of the CrN/ZrB2 bilayer films were classified into two tribological mechanisms in accordance with wear track observations. For the samples with high TZrB2/TCrN ratios, the shear mechanism dominated the wear behavior and resulted in the formation of a transfer layer on the worn surface. By contrast, the samples with low TZrB2/TCrN ratios had a ploughing mechanism in which a deformed track was generated on the surface.

A computational approach to predict and enhance the sensitivity of X-ray resonant magnetic reflectometry to the magnetic behavior of deeply buried interfaces

In the present work a computational approach is applied to model and predict the results of X-ray resonant magnetic reflectometry – a non-destructive synchrotron-based technique to probe chemical composition, crystallographic environment and magnetization in multilayer epitaxial heterostructures with nanoscale depth resolution. The discussed 2D mapping approach is a step forward with respect to conventional resonant X-ray reflectometry and consists of collecting a fine step array of reflected intensity as a function of grazing angle and photon energy across the absorption edge of a particular chemical element. With the use of circularly polarized photons the method can be extended to magnetic systems to produce a map of dichroic reflectance directly related to the magnetization profile of the heterostructure. Studying the magnetic field dependence of dichroic reflectance maps can provide valuable information on the magnetization reversal of individual sublayers of a multilayer heterostructure. In the present paper modeling is performed for a bilayer system mimicking the behavior of a 30 nm ɛ-Fe2O3 thin film that is known to exhibit a pronounced two-component magnetic hysteresis. A technique to find optimal energy/angle combinations in order to sense magnetization of individual sublayers is proposed. Also discussed is the advantage of heavy-element capping, which leads to a substantial increase of the dichroic intensity oscillation contrast in the pre-edge region where the sensitivity to the magnetic behavior of the deeply buried interfaces is most pronounced.

Structure and mechanical properties of TiCN-ZrCN multilayer coatings

The present study is focused on the design, deposition and characterization of nanoscale multilayer TiCN/ZrCN coatings obtained by cathodic-arc PVD technique. The multilayer coatings with the bilayer period’s thickness of 12 nm, 20 nm and 32 nm were deposited on stainless steel and high-speed steel substrates at temperature of 320°C in a mixture of N2 and CH4 gases. Scanning electron microscopy equipped with energy dispersive x-ray spectroscopy, was employed to investigate the top surface morphology, cross-sectional morphology, bilayer thickness and structure of the coatings. Mechanical properties were investigated via Calotester, Nanoindentation tester, Scratch tester and Tribometer. The SEM/EDS cross-sectional analysis revealed a columnar morphology and well expressed multi-layered periodic structure. All the multilayer samples demonstrated an increase in hardness and well fracture resistance ability in comparison to TiCN and ZrCN monolayer coatings. The highest nanohardness of 41GPa and better wear resistance for the coatings with bilayer period of 12 nm was determined. The results of the study show that a reduction in the thickness of the individual sub-layers has a significant impact on the mechanical properties of the coatings.

Histochemical and biochemical analysis of collagen content in formalin-fixed, paraffin embedded colonic samples

Collagen is the most abundant structural protein and extracellular matrix component in mammals. In the colon, collagen fibres reside in all the major sublayers; namely, the mucosa, submucosa, muscularis externa and the serosa. Methods to quantify collagen content in formalin-fixed, paraffin-embedded (FFPE) stained sections are required and image analysis offers a technique by which the spatial distribution and localisation of collagen fibres can be easily measured. This laboratory protocol was developed from established techniques using FFPE colon. Human colonic samples embedded transversally in paraffin wax were serially sectioned and stained with either Masson's trichrome (MT) or Picrosirius red (PSR). Quantitation estimation of collagen content in each sublayer was performed via ImageJ processing. Hydroxyproline content was quantified using a rapid and sensitive assay in sectioned tissue. Either MT or PSR staining followed by morphometric image analysis via ImageJ provided equally appreciable quantitative results. Moreso, analysis of hydroxyproline content in our samples indicate that this protocol could be useful in retrospective studies for FFPE samples. This laboratory protocol provides a systematic and reproducible method that can be utilized to accurately assess collagen content in individual sublayers of the colonic wall as well as detection of overall hydroxyproline content in FFPE specimens.

Processing and Properties of Sintered W/Steel Composites for the First Wall of Future Fusion Reactor

Functionally graded tungsten/steel composites are attractive to be used as an interlayer to join tungsten (W) and steel for the first wall of future fusion reactor to reduce the thermally induced stresses arising from the different coefficient of thermal expansion (CTE) of W and steel. W/steel composites, with three W contents: 25, 50 and 75 vol% W, will serve as individual sublayers of this functionally graded material. Therefore, the present work exploits an emerging sintering technique, field-assisted sintering technology, to produce these composites. Firstly, a systematic parameter study was conducted aiming to reduce the residual porosity to a minimum while keeping the formation of intermetallic phases at the W/steel interface at a low level. The optimized composites 25, 50 and 75 vol% W achieved a relative density of 99%, 99% and 96%, respectively. Secondly, mechanical tests at elevated temperatures reveal that these composites are ductile above 300 °C, which is the minimum operating temperature of the first wall. Lastly, the measured CTE, specific heat capacity and thermal conductivity were consistent with the theoretically expected values.

Vibrational Analysis of Hydration-Layer Water around Ubiquitin, Unpeeled Layer by Layer: Molecular-Dynamics Perceptions.

Classical molecular-dynamics simulations have been performed to examine the interplay between ubiquitin and its hydration-water sub-layers, chiefly from a vibrational-mode and IR viewpoint-where we analyse individual sub-layers characteristics. The vibrational Density of States (VDOS) revealed that the first solvation sub-shell indicates a confined character therein. For layers of increasing distance from the surface, the adoption of greater bulk-like spectral behaviour was evident, suggesting that vibrational harmonisation to bulk occurs within 6-7 Å of the surface.

Graded Inconel-stainless steel multi-material structure by inter- and intralayer variation of metal alloys

Additively manufactured multi-metal hybrid structures can be designed as functionally graded materials providing an optimized response at specific positions for particular applications. In this study, liquid dispersed metal powder bed fusion is used to synthesize a multi-metal structure based on Inconel 625 (IN625) and stainless steel 316L (S316L) stainless steel regions, built on a S316L base plate. Both alloys alternate several times along the build direction as well as within the individual sublayers. The multi-metal sample was investigated by optical microscopy, scanning electron microscopy, microhardness measurements, nanoindentation and energy-dispersive X-ray spectroscopy. Cross-sectional synchrotron X-ray micro-diffraction 2D mapping was carried out at the high-energy material science beamline of the storage ring PETRAIII in Hamburg. Sharp morphological S316L-to-IN625 interfaces along the sample's build direction are observed on the micro- and nanoscale. A gradual phase transition encompassing about 1 mm is revealed in the transverse direction. Mechanical properties change gradually following abrupt or smooth phase transitions between the alloys where a higher strength is determined for the superalloy. The two-dimensional distribution of phases can be assessed indirectly as S316L and IN625 in this multi-metal sample possess a <110> and a <100> fiber crystallographic texture, respectively. Tensile residual stresses of ∼900 and ∼800 MPa in build direction and perpendicular to it, respectively, are evaluated from measured residual X-ray elastic strains. Generally, the study indicates possibilities and limitations of liquid dispersed metal powder bed fusion for additive manufacturing of functionally graded materials with unique synergetic properties and contributes to the understanding of optimization of structurally and functionally advanced composites.

Microstructural and micro-mechanical investigation of cathodic arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness

Modifying the architecture of multilayer hard coatings allows to adjust the mechanical properties of these materials for a given application. Within this work, the effect of the bilayer thickness (Λ) and the individual sublayer thickness ratio on the microstructure and mechanical properties of ZrN/TiN multilayer coatings was investigated. Multilayer coatings with Λ of 570, 320 and 35 nm were deposited by cathodic arc evaporation and compared to TiN and ZrN single-layer coatings. The microstructure was investigated by X-ray diffraction (XRD) and scanning electron microscopy. All coatings exhibit a single phase face-centred cubic structure and a predominant (111) texture. A columnar structure was observed for all coatings and grain growth extending beyond the ZrN/TiN interfaces was evident in all multilayers. For all coatings, compressive residual stresses were determined by XRD using the sin 2 ψ method, where the multilayer sample with the largest Λ exhibited the highest compressive residual stress of −1.7 ± 0.2 GPa. Lower compressive residual stresses could be correlated with decreasing Λ and decreasing ZrN:TiN thickness ratio. Nanoindentation experiments as well as micro-mechanical bending tests were conducted to assess the mechanical properties of the coatings. The ZrN/TiN multilayer sample with Λ of 35 nm showed the highest hardness of 28.0 ± 1.1 GPa. This value is similar to the TiN single-layer and higher compared to the ZrN single-layer, which exhibited a hardness of 27.9 ± 1.4 GPa and 25.8 ± 1.3 GPa, respectively. While the ZrN single-layer showed the highest fracture toughness, the ZrN/TiN multilayer samples were identified as the mechanically stiffest and strongest of the investigated coatings, since they exhibited a higher fracture stress compared to the single-layer coatings. The obtained results allow to optimise the architecture of ZrN/TiN multilayer coatings yielding the desired coating properties for application in the cutting industry. • Arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness Λ • Smaller Λ leads to grain refinement and more pronounced (111) texture. • Multilayer coating with lowest Λ exhibits the highest hardness. • Highest fracture toughness for ZrN single-layer coating • Improved fracture stress for multilayers compared to single-layers

Comprehensive characterization and evaluation of deep shales from Wufeng-Longmaxi Formation by LF-NMR technology

Marine deep shale gas represents the main target of future shale gas development in China. In order to identify the key parametric characteristics of deep shales, a comprehensive test method and application study was carried out based on LF-NMR technology. The results show that the NMR T 2 spectrum of shales varied considerably in different states. A new NMR porosity and water saturation test method based on three-time measurements was established. The relative error between corrected NMR and water immersion porosity is reduced from 49.97% to 6.66%, while that between corrected NMR and weighing water saturation is reduced from 32.15% to 6.85%. By testing key parameters such as free water quantity, adsorbed water quantity, and average adsorption thickness, the NMR surface relaxivity of shale is determined and used to transform NMR T 2 spectrum into pore size distribution. The NMR T 2 spectra of individual sublayers also differ significantly. In order to quantitatively describe the distribution of spectral peaks, a new reservoir evaluation parameter, T 2 geometric mean value ( T 2g ), is proposed. Larger T 2g values signify larger pores, broader average pore size distribution, and higher fluid mobility. With this parameter, qualitative description of pore size distribution can be transformed into quantitative characterization. When evaluating shale gas reservoirs, it is important to use multiple key parameters, among which NMR test results are an important indicator. LF-NMR testing is uniquely superior over other test methods as one or more NMR tests can provide abundant parametric information. The presented comprehensive NMR test method offers useful theoretical references for furthering the development and application of this technology in shale gas research. • A three-time NMR test method was proposed for all the basic parameters determination. • NMR surface relaxivity was determined and negatively correlated with TOC. • Parameter T 2g was proposed to quantitatively describe the spectrum peak location and pore size. • One or more NMR tests can provide abundant parametric information for shale evaluation.

Shaking-Induced Sublayer Vertical Strains of Saturated Sands Estimated from Partially Drained Dynamic Centrifuge Tests

Earthquake-induced free-field settlement of coarse-grained soils has historically been assessed using laboratory element tests under drained or undrained conditions. However, in saturated sands, dynamic centrifuge and 1g shaking table tests illustrate that excess porewater pressure generation/dissipation and settlement occur simultaneously during shaking under partially drained conditions. The average vertical strains computed from measured surface settlements in these tests neglect (1) the impact of effective stress on compressibility and (2) settlements that occur in denser and potentially nonliquefiable sands present in the centrifuge models. Here, the authors employ a simple procedure that uses measured porewater pressure and surface settlement time histories from partially drained centrifuge and 1g shaking table tests to properly distribute vertical strain throughout the coarse-grained soil profiles, thereby incorporating variations of effective stress and relative density on vertical strain. The vertical strains are resolved into a shaking-induced component and a post-shaking reconsolidation component, and the procedure yields computed surface settlement time histories that reasonably match the rate and magnitude of measured settlements both during and after shaking. Using this procedure, we interpreted 151 individual (sublayer) estimates of vertical strain from 34 shaking events applied in dynamic centrifuge and 1g shaking table tests. Combined with the sublayer shaking intensities, the 151 vertical strain values constitute a new database that can be used to develop shaking-induced settlement correlations for realistic partially drained conditions.

Infrared photo-induced force microscopy unveils nanoscale features of Norway spruce fibre wall

Infrared photo-induced force microscopy (IR PiFM) was applied for imaging ultrathin sections of Norway spruce (Picea abies) at 800–1885 cm−1 with varying scanning steps from 0.6 to 30 nm. Cell wall sublayers were visualized in the low-resolution mode based on differences in their chemical composition. The spectra from the individual sublayers demonstrated differences in the orientation of cellulose elementary fibrils (EFs) and in the content and structure of lignin. The high-resolution images revealed 5–20 nm wide lignin-free areas in the S1 layer. Full spectra collected from a non-lignified spot and at a short distance apart from it verified an abrupt change in the lignin content and the presence of tangentially oriented EFs. Line scans across the lignin-free areas corresponded to a spatial resolution of ≤ 5 nm. The ability of IR PiFM to resolve structures based on their chemical composition differentiates it from transmission electron microscopy that can reach a similar spatial resolution in imaging ultrathin wood sections. In comparison with Raman imaging, IR PiFM can acquire chemical images with ≥ 50 times higher spatial resolution. IR PiFM is also a surface-sensitive technique that is important for reaching the high spatial resolution in anisotropic samples like the cell wall. All these features make IR PiFM a highly promising technique for analyzing the recalcitrant nature of lignocellulosic biomass for its conversion into various materials and chemicals.Graphic abstract

Terahertz spectroscopy analysis of human corneal sublayers.

.Significance: Corneal diseases is a major cause of reversible blindness in the world. Monitoring the progression of human corneal edema or corneal scarring to prevent the disease entering into the end stage is crucial.Aim: We present a method for sensing human corneal composition at different depths, namely focused on the epithelium and stromal layer, using high-sensitivity terahertz (THz) broadband spectroscopy.Approach: From the proposed methodology, the THz temporal and absorption spectra of human corneas at different edema stages have been studied. THz wave signals were collected from the direct reflection and four other collection points along the THz wave propagation direction as reviewed from the simulation THz electrical field.Result: Our results show that the epithelium layer acts as a good barrier to maintain hydration level of the stroma, and the quality of the epithelium can be used to predict the level of corneal swelling in corneal edema. At the detection points near to the incident point, the THz frequency spectra demonstrated interference oscillation behavior. At the final edema observing time, results showed that the epithelium lose its barrier properties. The intactness of the epithelium can be used to predict the edema severity in the final stage. When the detection points are further away from the incident point, the THz spectra are believed to contain information from stromal layer. Stromal absorption spectra demonstrated correlation with optical coherence tomography thickness results.Conclusion: The hydration concentration from stromal layer was further quantitatively calculated. At the end of the experiment, all the corneal hydration levels reach to the same value which shows that the edema hydration has reached maximum saturation. The information of individual sublayers of the cornea is obtained by characterizing noninvasively with the use of THz spectroscopy. To our knowledge, this is the first report of using THz for noninvasive characterization of sublayers of the cornea.

Direct formation of interlayer exciton in two-dimensional van der Waals heterostructures.

In atomically thin two-dimensional van der Waals (2D vdW) heterostructures, spatially separated interlayer excitons play an important role in the optoelectronic performance and show great potential for the exploration of many-body quantum phenomena. A commonly accepted formation mode for interlayer excitons is via a two-step intralayer exciton transfer mechanism, namely, photo-excited intralayer excitons are initially generated in individual sublayers, and photogenerated electrons and holes are then separated into opposite sublayers based on the type-II band alignment. Herein, we expand the concept of interlayer exciton formation and reveal that bright interlayer excitons can be generated in one step by direct interlayer photoexcitation in 2D vdW heterostructures that have strong interlayer coupling and a short photoexcitation channel. First-principles and many-body perturbation theory calculations demonstrate that indium selenide/antimonene and indium selenide/black phosphorus heterostructures are two promising systems that show an exceptionally large interlayer transition probability (>500 Debye2). This study enriches the understanding of interlayer exciton formation and provides a new avenue to acquiring strong interlayer excitons in artificial 2D vdW heterostructures.

Analysis of retinal sublayer thicknesses and rates of change in ABCA4-associated Stargardt disease

Stargardt disease, the most common inherited macular dystrophy, is characterized by vision loss due to central retinal atrophy. Although clinical trials for Stargardt are currently underway, the disease is typically slowly progressive, and objective, imaging-based biomarkers are critically needed. In this retrospective, observational study, we characterize the thicknesses of individual retinal sublayers by macular optical coherence tomography (OCT) in a large cohort of patients with molecularly-confirmed, ABCA4-associated Stargardt disease (STGD1) relative to normal controls. Automated segmentation of retinal sublayers was performed with manual correction as needed, and thicknesses in various macular regions were compared using mixed effects models. Relative to controls (42 eyes, 40 patients), STGD1 patients (107 eyes, 63 patients) had slight thickening of the nerve fiber layer and retinal pigment epithelium-Bruch’s membrane, with thinning in other sublayers, especially the outer nuclear layer (ONL) (p < 0.0015). When comparing the rate of retinal sublayer thickness change over time (mean follow-up 3.9 years for STGD1, 2.5 years for controls), STGD1 retinas thinned faster than controls in the outer retina (ONL to photoreceptor outer segments). OCT-based retinal sublayer thickness measurements are feasible in STGD1 patients and may provide objective measures of disease progression or treatment response.