The evolution of real-time medical diagnostic tools such as angiography and computer tomography from radiography based on photographic plates was enabled by the development of integrated solid-state ...X-ray photon detectors made from conventional solid-state semiconductors. Recently, for optoelectronic devices operating in the visible and near-infrared spectral regions, solution-processed organic and inorganic semiconductors have also attracted a great deal of attention. Here, we demonstrate a possibility to use such inexpensive semiconductors for the sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH3 NH3 PbI3 ) offers a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms. Solution-processed photodiodes as well as photoconductors are presented, exhibiting high values of X-ray sensitivity (up to 25 μC mGyair-1 cm-3 ) and responsivity (1.9 × 104 carriers/photon), which are commensurate with those obtained by the current solid-state technology.
Abstract
Non-collinear antiferromagnets are revealing many unexpected phenomena and they became crucial for the field of antiferromagnetic spintronics. To visualize and prepare a well-defined domain ...structure is of key importance. The spatial magnetic contrast, however, remains extraordinarily difficult to be observed experimentally. Here, we demonstrate a magnetic imaging technique based on a laser induced local thermal gradient combined with detection of the anomalous Nernst effect. We employ this method in one the most actively studied representatives of this class of materials—Mn
3
Sn. We demonstrate that the observed contrast is of magnetic origin. We further show an algorithm to prepare a well-defined domain pattern at room temperature based on heat assisted recording principle. Our study opens up a prospect to study spintronics phenomena in non-collinear antiferromagnets with spatial resolution.
We report on advanced in-situ magneto-transport measurements in a transmission electron microscope. The approach allows for concurrent magnetic imaging and high resolution structural and chemical ...characterization of the same sample. Proof-of-principle in-situ Hall measurements on presumably undemanding nickel thin films supported by micromagnetic simulations reveal that in samples with non-trivial structures and/or compositions, detailed knowledge of the latter is indispensable for a thorough understanding and reliable interpretation of the magneto-transport data. The proposed in-situ approach is thus expected to contribute to a better understanding of the Hall signatures in more complex magnetic textures.
Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to ...be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180
and 90
domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.
In recent years strain engineering is proposed in chalcogenide superlattices (SLs) to shape in particular the switching functionality for phase change memory applications. This is possible in ...Sb2Te3/GeTe heterostructures leveraging on the peculiar behavior of Sb2Te3, in between covalently bonded and weakly bonded materials. In the present study, the structural and thermoelectric (TE) properties of epitaxial Sb2+xTe3 films are shown, as they represent an intriguing option to expand the horizon of strain engineering in such SLs. Samples with composition between Sb2Te3 and Sb4Te3 are prepared by molecular beam epitaxy. A combination of X‐ray diffraction and Raman spectroscopy, together with dedicated simulations, allows unveiling the structural characteristics of the alloys. A consistent evaluation of the structural disorder characterizing the material is drawn as well as the presence of both Sb2 and Sb4 slabs is detected. A strong link exists among structural and TE properties, the latter having implications also in phase change SLs. A further improvement of the TE performances may be achieved by accurately engineering the intrinsic disorder. The possibility to tune the strain in designed Sb2+xTe3/GeTe SLs by controlling at the nanoscale the 2D character of the Sb2+xTe3 alloys is envisioned.
The precise tuning of the properties of epitaxial Sb2+xTe3 in between those of 2D and 3D materials is established. It paves the way to expand the horizon of strain engineering in phase change memory superlattice structures. The interplay between structural and thermoelectric properties in these alloys is presented.
With the continued maturation of III–V nanowire research, expectations of material quality should be concomitantly raised. Ideally, III–V nanowires integrated on silicon should be entirely free of ...extended planar defects such as twins, stacking faults, or polytypism, position-controlled for convenient device processing, and gold-free for compatibility with standard complementary metal–oxide–semiconductor (CMOS) processing tools. Here we demonstrate large area vertical GaAs x Sb1–x nanowire arrays grown on silicon (111) by molecular beam epitaxy. The nanowires’ complex faceting, pure zinc blende crystal structure, and composition are mapped using characterization techniques both at the nanoscale and in large-area ensembles. We prove unambiguously that these gold-free nanowires are entirely twin-free down to the first bilayer and reveal their three-dimensional composition evolution, paving the way for novel infrared devices integrated directly on the cost-effective Si platform.
The twin distribution in topological insulators Bi2Te3 and Bi2Se3 was imaged by electron backscatter diffraction (EBSD) and scanning X‐ray diffraction microscopy (SXRM). The crystal orientation at ...the surface, determined by EBSD, is correlated with the surface topography, which shows triangular pyramidal features with edges oriented in two different orientations rotated in the surface plane by 60°. The bulk crystal orientation is mapped out using SXRM by measuring the diffracted X‐ray intensity of an asymmetric Bragg peak using a nano‐focused X‐ray beam scanned over the sample. By comparing bulk‐ and surface‐sensitive measurements of the same area, buried twin domains not visible on the surface are identified. The lateral twin domain size is found to increase with the film thickness.
Imaging with surface‐ and bulk‐sensitive electron and X‐ray diffraction based microscopic techniques enabled identification of the twin domain distribution of Bi2Te3 and Bi2Se3 thin films. Correlations between the surface topography and crystal orientation are established.
Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell ...viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.Nanomaterials that form a bioelectronic interface with cells are fascinating tools for controlling cellular behavior. Here, the authors photostimulate single cells with spiky assemblies of semiconducting quinacridone nanocrystals, whose nanoscale needles maximize electronic contact with the cells.
Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce ...a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants.
We present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 ...K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006±0.001 emuT. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2μB), while the local moments of Ni atoms effectively vanish. These results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.
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