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Register a new userNon-contact electrical detection of intrinsic local charge and internal electric field at nanointerfaces
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A nanoscale non-contact electrical measurement has been developed based on Auger electron spectroscopy. This approach used the speciality of Auger electron, which is self-generated and free from external influences, to overcome the technical limitations of conventional measurements. The detections of the intrinsic local charge and internal electric field for nanostructured materials were achieved with resolution below 10 nm. As an example, the electrical properties at the GaN/AlGaN/GaN nanointerfaces were characterized. The concentration of the intrinsic polarization sheet charges embedded in GaN/AlGaN nanointerfacial layers were accurately detected to be -4.4 e/nm^2. The mapping of internal electric field across the nanointerface revealed the actual energy band configuration at the early stage of the formation of two-dimensional electron gas.
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Two-dimensional materials offer a novel platform for the development of future quantum technologies. However, the electrical characterisation of topological insulating states, non-local resistance and bandgap tuning in atomically-thin materials, can be strongly affected by spurious signals arising from the measuring electronics. Common-mode voltages, dielectric leakage in the coaxial cables and the limited input impedance of alternate-current amplifiers can mask the true nature of such high-impedance states. Here, we present an optical isolator circuit which grants access to such states by electrically decoupling the current-injection from the voltage-sensing circuitry. We benchmark our apparatus against two state-of-the-art measurements: the non-local resistance of a graphene Hall bar and the transfer characteristic of a WS2 field-effect transistor. Our system allows the quick characterisation of novel insulating states in two-dimensional materials with potential applications in future quantum technologies.
Resistive plate chamber (RPC) is one of the state-of-the-art particle detection technology for the High Energy Physics (HEP) experiments. The basic operating mechanism of an RPC involves ionization of gas due to the passage of charged particles followed by electron transport , avalanche, and subsequent electromagnetic induction on readout strips due to the movement of the electrons and ions. Especially during streamer mode of operation, the electric field applied to the RPC can get significantly modified due to the presence of large number of electrons and ions. In this study, we have worked on dominant issues related to the estimation of electric field due to the space charge arising out of the presence of electrons, ions within an RPC. For this purpose we have considered two approaches: representation of the space charge cloud as (a) a collection of ring charges, and (b) as a collection of line charges. The results from these different methods have been compared with results available in the literature.
Nano/micro-scale mechanical properties of multiferroic materials can be controlled by the external magnetic or electric field due to the coupling interaction. For the first time, a modularized multi-field nanoindentation apparatus for carrying out testing on materials in external magnetostatic/electrostatic field is constructed. Technical issues, such as the application of magnetic/electric field and the processes to diminish the interference between external fields and the other parts of the apparatus, are addressed. Tests on calibration specimen indicate the feasibility of the apparatus. The load-displacement curves of ferromagnetic, ferroelectric and magnetoelectric materials in the presence/absence of external fields reveal the small-scale magnetomechanical and electromechanical coupling, showing as the Delta-E and Delta-H effects, i.e. the magnetic/electric field induced changes in the apparent elastic modulus and indentation hardness.
The spin-polarized surface states in topological insulators offer unique transport characteristics which make them distinguishable from trivial conductors. Due to the topological protection, these states are gapless over the whole surface of the material. Here, we detect the surface states in the topological insulator BiSbTeSe$_{2}$ by electrical means using a non-local transport configuration. We unambiguously probe the spin-momentum locking of the topologically protected surface states by spin-sensitive electrical read-out using ferromagnetic Co/Al$_2$O$_3$ electrodes. We show that the non-local measurement allows to probe the surface currents flowing along the whole surface, i.e. from the top along the side to the bottom surface and back to the top surface along the opposite side. This is in contrast to local transport configurations where only the surface states of the one face being in contact to the electrodes can be measured. Our results furthermore exclude the contribution of the bulk to the non-local transport at low temperatures. Increasing the temperature, on the other hand, increases the interaction between bulk and surface states, which shortens the non-local current path along the surface and hence leads to a complete disappearance of the non-local signal at around 20 K. All this demonstrates that the non-local signal at low temperatures is solely due to the topologically protected surface states.
The interface between graphene and the ferroelectric superlattice $mathrm{PbTiO_3/SrTiO_3}$ (PTO/STO) is studied. Tuning the transition temperature through the PTO/STO volume fraction minimizes the adsorbates at the graphene-ferroelectric interface, allowing robust ferroelectric hysteresis to be demonstrated. Intrinsic charge traps from the ferroelectric surface defects can adversely affect the graphene channel hysteresis, and can be controlled by careful sample processing, enabling systematic study of the charge trapping mechanism.
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