Semiconductor GaN NWs are promising components in next generation nano- and optoelectronic systems. In addition to their direct band gap, they exhibit piezoelectricity, which renders them particularly attractive in energy harvesting applications for self-powered devices. Nanowires are often considered as one-dimensional nanostructures; however, the electromechanical coupling leads to a third rank tensor that for wurtzite crystals (GaN NWs) possesses three independent coefficients, d(33), d(13), and d(15). Therefore, the full piezoelectric characterization of individual GaN NWs requires application of electric fields in different directions and measurements of associated displacements on the order of several picometers. In this Letter, we present an experimental approach based on scanning probe microscopy to directly quantify the three-dimensional piezoelectric response of individual GaN NWs. Experimental results reveal that GaN NWs exhibit strong piezoelectricity in three dimensions, with up to six times the effect in bulk. Based on finite element modeling, this finding has major implication on the design of energy harvesting systems exhibiting unprecedented levels of power density production. The presented method is applicable to other piezoelectric NW materials as well as wires manufactured along different crystallographic orientations.
Transition metal dichalcogenide (TMDC) semiconductors have attracted significant attention because of their rich electronic/photonic properties and importance for fundamental research and novel device applications. These materials provide a unique opportunity to build up high quality and atomically sharp heterostructures because of the nature of weak van der Waals interlayer interactions. The variable electronic properties of TMDCs (e.g., band gap and their alignment) provide a platform for the design of novel electronic and optoelectronic devices. The integration of TMDC heterostructures into the semiconductor industry is presently hindered by limited options in reliable production methods. Many exciting properties and device architectures which have been studied to date are, in large, based on the exfoliation methods of bulk TMDC crystals. These methods are generally more difficult to consider for large scale integration processes, and hence, continued developments of different fabrication strategies are essential for further advancements in this area. In this review, the authors highlight the recent progress in the fabrication of TMDC heterostructures. The authors will review several methods most commonly used to date for controllable heterostructure formation. One of the focuses will be on TMDC heterostructures fabricated by thermal chemical vapor deposition methods which allow for the control over the resulting materials, individual layers and heterostructures. Another focus would be on the techniques for selective growth of TMDCs. The authors will discuss conventional and unconventional fabrication methods and their advantages and drawbacks and will provide some guidance for future improvements. Mask-assisted and mask-free methods will be presented, which include traditional lithographic techniques (photo- or e-beam lithography) and some unconventional methods such as the focus ion beam and the recently developed direct-write patterning approach, which are shown to be promising for the fabrication of quality TMDC heterostructures.
Semiconductor devices continue to press into the nanoscale regime, and new applications have been proposed for which a single dopant atom acts as the functional part of the device 1-3 . Moreover, because shallow donors and acceptors are analogous to hydrogen atoms, experiments on small numbers of dopants have the potential to be a testing ground for fundamental questions of atomic and molecular physics 4,5 . Although dopant properties are well understood with respect to the bulk, the study of configurations of dopants in small numbers is an emerging field 6,7 . Here we present local capacitance measurements of electrons entering silicon donors in a gallium arsenide heterostructure. To the best of our knowledge, this study is the first example of single-electron capacitance spectroscopy carried out directly with a scanning probe tip 8 . The precise position with respect to tip voltage of the observed single-electron peaks varies with the location of the probe, reflecting a random distribution of silicon within the donor plane. In addition, three broad capacitance peaks are observed independent of the probe location, indicating clusters of electrons entering the system at approximately the same voltages. These broad peaks are consistent with the addition energy spectrum of donor molecules, effectively formed by nearest-neighbour pairs of silicon donors.Electron tunnelling spectroscopy through isolated dopants has been observed in transport studies 9,10 . In addition, Geim and coworkers identified resonances due to two closely spaced donors, effectively forming donor molecules 11 . Rather than measuring transport current, our scanning-probe method is essentially a capacitance technique 8,12 . In contrast to the work of Geim et al., the measurements show discernible peaks attributed to successive electrons entering the molecules.Our method is an extension of scanning charge accumulation imaging 12 . Figure 1a shows the experiment schematically. The key component is a metallic tip with an apex of radius ∼ 50 nm, connected directly to a charge sensor, which achieves a sensitivity of 0.01e/ √ H z (ref. 13). For the capacitance spectroscopy measurements reported here, the tip's position is fixed (that is, not scanned) at a distance of ∼1 nm from the sample surface. We then monitor the tip's a.c. charge q tip in response to an a.c. excitation voltage V exc applied to an underlying electrode, as a function of d.c. bias voltage V tip . As detailed in the Methods section, if the quantum system below the tip can accommodate additional charge, the excitation voltage causes it to resonate between the system and the underlying electrode-giving rise to an enhanced capacitance,The first observations of donor-layer capacitance peaks acquired with our method probed a gallium arsenide heterostructure sample grown by molecular beam epitaxy, for which the donor layer was bulk-doped with Si at a density of 10 24 m −3 . To achieve better characterized results that would be more conducive to analysis, we used a GaAs [001] heterostructure...
Antiprotons (p[over]) remain confined in a Penning trap, in sufficient numbers to form antihydrogen (H[over ) atoms via charge exchange, when the radial field of a quadrupole Ioffe trap is added. This first demonstration with p[over] suggests that quadrupole Ioffe traps can be superimposed upon p[over] and e(+) traps to attempt the capture of H[over] atoms as they form, contrary to conclusions of previous analyses.
We present a numerical method to model electric-field-sensitive scanning probe microscopy measurements which allows for a tip of arbitrary shape and invokes image charges to exactly account for a sample dielectric overlayer. The method is applied to calculate the spatial resolution of a subsurface charge accumulation imaging system, achieving reasonable agreement with experiment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.