24378 research outputs found
Sort by
Bimodal interfacial charge transfer in quantum dot heterostructures revealed by donor acceptor specific broadband transient absorption spectroscopy
No full textQuantum dot sensitized metal oxide heterostructures offer an attractive platform for harvesting carriers from solar energy. Interfacial charge transfer processes lie at the heart of solar energy conversion using heterostructured nanomaterials, yet they are poorly understood and difficult to study. Here we employ broadband optical transient absorption spectroscopy, spanning a wavelength range that covers both quantum dot donor and metal oxide acceptor band gaps, enabling a selective view of charge transfer across the interface of CdSe sensitized ZnO nanorods. This allows us to reveal a bimodal charge injection mechanism a fast lt;1 ps indirect charge injection pathway populates an optically dark intermediate state, and a direct charge injection pathway on the tens of ps time scale without an observable intermediate state. The bimodal charge injection kinetics are attributed to heterogeneity of ZnO acceptor states. Our results deepen the understanding of the role of donor and acceptor states in heterostructured nanomaterials and pave the way for the rational design and control of charge transfer across complex interfaces and their application in optoelectronic device
Origin of large coercivity in charge ordered lanthanide free magnets
No full textLanthanide based permanent magnets are essential for a wide range of applications, from nanotechnology to industrial engineering. However, the limited availability and escalating costs of rare earth elements have spurred efforts to develop alternative lanthanide free magnets. Low dimensional magnetic oxides, such as Co3BO5 and Co2FeBO5 single crystals space group Pbam , offer a promising solution due to their structural properties and potential for stabilizing charge ordered states. This study investigates the influence of nanodomains on macroscopic coercivity in these materials, revealing that domain wall pinning and high energy barriers significantly impede domain wall motion, resulting in exceptional coercive fields. Notably, Co2FeBO5 exhibits a giant coercive field exceeding 9 Tesla at low temperatures. X ray absorption and single crystal X ray diffraction confirmed the mixed valent character of Co and Fe ions, showing a 3 oxidation state at the M4 sites and 2 at other sites M1, M2, M3 . X ray magnetic circular dichroism XMCD further revealed element selective magnetizations in opposing directions below the N el temperature, indicative of strong antiferromagnetic interactions persisting even in the paramagnetic state. These unprecedented coercivities are attributed to the interaction of alternating magnetic sublattices formed by adjacent ions, influenced by the crystallographic symmetry. By precisely substituting ions at specific crystallographic sites M1 M4 , it is possible to modulate local magnetic anisotropy and establish regions with high energy barriers, effectively enhancing the material s resistance to demagnetization. This targeted optimization of magnetic properties positions these materials as strong candidates for applications demanding stable and robust magnetic performance under challenging condition
A Paraffin Based Photoresin 3D Printing of Paraffin for Encapsulation Free Shape Stabilized Paraffin Based Phase Change Materials
Get PDFHigh resolution structuring of paraffin wax as phase change material is essential for miniaturized applications in thermal actuators, flexible electronics, and sensors, yet requires complex encapsulation methods that limit design freedom and increase costs. A low cost encapsulation free approach is demonstrated for preparing shape stabilized paraffin based phase change materials using digital light processing based 3D printing. In this work, a paraffin loaded photoresin with paraffin concentrations up to 60 wt. in acrylated polymer networks. The printed parts are thermally responsive undergoing a shape stabilized phase change, and exhibits elastic and stretchable properties. Despite the high paraffin loading, the printed parts can be stretched up to 130 in length. Differential scanning calorimetry results show that the highest phase change latent heat of the printed parts can reach 120 J g amp; 8722;1. Cyclic scanning differential calorimetry results show a slight shift in endothermic and exothermic signals indicating no obvious paraffin leakage. Considering that the phase transition of the paraffin in the photoresin at the melting point of paraffin affects the mechanical modulus of the printed parts, a pneumatic actuator is also printed that responds to body temperature. This work contributes a significant step toward a wide range of applications from micro sensors to new interactive soft actuator
Enabling High Throughput Perovskite FET Research by a Customizable Automated FET Measurement Station
Get PDFPerovskite based thin film field effect transistors PeFETs have yet to achieve the full theoretical potential of this promising class of materials. To bridge this gap, it is essential to develop and optimize novel perovskite compositions and fabrication techniques. Given the large variety of potential compounds as well as the manifold of influencing variables such as concentration, temperature, and choice of solvent, a high throughput research approach is critical for efficient exploration and advancement. We present a flexible and customizable process that spans from substrate fabrication to device characterization. This process is enabled by and integrates photolithography for custom patterning, an automated measurement station for FET characterization, and automated data analysis. The automated measurement station is based on a multiplexer, which is connected to five measurement boards. The measurement boards are configured to measure one substrate with four devices each. Allowing the automated measurement of 20 devices with up to 5 different perovskite formulations. Using standardized testing procedures, the raw data is automatically analyzed to get the transfer and output characteristics of the PeFETs as well as key performance parameters like the threshold voltage, subthreshold swing, and the field effect mobility. The result is a systematically organized data pool with easily comparable data for different perovskite compositions or modifications in fabrication condition
HESEB Soft X ray Beamline ID11 L at SESAME Performance and First User Experiments
Get PDFThe ID11 L HESEB Soft X ray beamline and end station significantly enhance soft X ray research capabilities. Operating in an energy range of 90 1800 eV, extendable to 70 2000 eV, the beamline achieves high performance with an energy resolution of E amp; 916;E gt; 8000 and a photon flux of 1010 to 3.4 1012 photons s. Its 500 250 amp; 956;m lt; beam spot size allows for precise measurements, including studies on magnetic materials using variable circular polarization. This paper presents the end station s design, including the receptacle, magnetic sample holder, and ambient pressure capabilities, along with experimental results that demonstrate the beamline s potential for diverse scientific application
Helical spin dynamics in Cu2OSeO3 as measured with small angle neutron scattering
Get PDFThe insulating chiral magnet Cu2OSeO3 exhibits a rich array of low temperature magnetic phenomena, making it a prime candidate for the study of its spin dynamics. Using spin wave small angle neutron scattering SWSANS , we systematically investigated the temperature dependent behavior of the helimagnon excitations in the field polarized phase of Cu2OSeO3. Our measurements, spanning 5?55?K, reveal the temperature evolution of spin wave stiffness and damping constant with unprecedented resolution, facilitated by the insulating nature of Cu2OSeO3. These findings align with theoretical predictions and resolve discrepancies observed in previous studies, emphasizing the enhanced sensitivity of the SWSANS method. The results provide deeper insights into the fundamental magnetic properties of Cu2OSeO3, contributing to a broader understanding of chiral magnet
Identification of metal centered excited states in Cr iii complexes with time resolved L edge X ray spectroscopy
Get PDFNew coordination complexes of 3d metals that possess photoactive metal centered MC excited states are promising targets for optical applications and photocatalysis. Ultrafast spectroscopy plays an important role in elucidating the photophysical mechanisms that underlie photochemical activity. However, it can be difficult to assign transient signals to specific electronic excited states and mechanistic information is often inferred from kinetics. Here it is demonstrated that 3d L edge X ray absorption spectroscopy is highly selective for MC excited states. This is accomplished by probing the 2E spin flip excited state in Cr acac 3 using synchrotron based picosecond time resolved XAS in solution. This excited state of Cr III has the property that its potential is nested with the ground state, which allows for the assessment of purely electronic changes upon excited state formation. Combining the measurements with ligand field and ab initio theory shows that the observed spectral changes between the 4A2 ground state and 2E excited state are due to an intensity redistribution among the core excited multiplets. Extrapolating these results to higher lying MC excited states predicts that Cr L3 edge XAS can distinguish two states separated by amp; 8764;0.1 eV despite the L3 edge resolution being limited by the 0.27 eV lifetime width of the 2p core hole. This highlights the potential of L edge XAS as a sub natural linewidth probe of electronic state identit
Tail Group Engineering in Perfluorophenyl Based Self Assembled Monolayers
No full textWe present a series of custom designed, perfluorophenyl PFP based molecular films on gold, in which the terminal PFP unit, coupled to the thiolate anchoring group via a cystamine linker CA , is additionally decorated with various polar groups R , such as amp; 8722;CF3, amp; 8722;SCF3, amp; 8722;CN, and amp; 8722;CH3. The basic characterization of the series with several complementary experimental tools shows that, on Au 111 , the CA R molecules form self assembled monolayers SAMs with dense packing and high orientation. The structural parameters of these SAMs are nearly independent of R, implying that their work function WF can be exclusively associated with the identity of R. This was indeed the case, with the WF value varying from 5.5 to 5.6 eV for the electron withdrawing amp; 8722;CF3 and amp; 8722;SCF3 groups to amp; 8764;4.9 eV for the electron donating amp; 8722;CH3 group. Surprisingly, the CA CN SAM, bearing electron withdrawing nitrile groups, showed a similar work function as CA CH3 an effect that was observed earlier for other CN terminated aromatic SAMs as well, and is tentatively explained by a redistribution of electron density due to the conjugation of the CN orbitals with the adjacent aromatic ring. This SAM features lower hydrophobicity than the other CA R monolayers, which might be useful to provide a better match to a deposited organic materia
Ultra Dense, Highly Ordered and Thermally Stable Anthracene Monolayers on Ag 111 The Impact of the Anchoring Group
No full textAromatic self assembled monolayers SAMs are commonly used to tune the properties of metal electrodes in organic electronics, with their structural quality and thermal stability being of key importance. As demonstrated before for the gold electrodes, the use of anthracenethiol or selenol SAMs provides template layer which can be used for the growth of organic semiconductors such as pentacene. Here, we show that the use of silver instead of gold and carboxylate instead of thiol selenol allows to fabricate highly ordered anthracene monolayers with unprecedentedly high packing density an area per molecule of amp; 8764;0.226 nm2 , which even exceeds that of anthracene single crystal in the 001 plane an area per molecule of amp; 8764;0.256 nm2 and, for the first time, provides 2D structure commensurate with the pentacene single crystal. Moreover, we show that these modifications lead to a radical improvement in the thermal stability by amp; 8764;100 K of anthracene based SAMs. Consequently, the obtained results open up the possibility of using carboxylate anchored anthracene monolayers on silver as a molecular template for facilitating the growth of high quality anthracene and pentacene films for organic electronic
Reconstructing time of flight detector values of angular streaking using machine learning
Get PDFAngular streaking experiments enable for experimentation in the attosecond regions. However, the deployed time of flight TOF detectors are susceptible to noise and failure. These shortcomings make the outputs of the TOF detectors hard to understand for humans and further processing, such as, for example, the extraction of beam properties. In this article, we present an approach to remove high noise levels and reconstruct up to three failed TOF detectors from an arrangement of 16 TOF detectors. Due to its fast evaluation time, the presented method is applicable online during a running experiment. It is trained with simulation data, and we show the results of denoising and reconstruction of our method on real world experiment dat