Microbubbles (MBs) are routinely used as contrast agents for ultrasound imaging. The use of ultrasound in combination with MBs has also attracted attention as a method to enhance drug delivery. We ...have developed a technology platform incorporating multiple functionalities, including imaging and therapy in a single system consisting of MBs stabilized by polyethylene glycol (PEG)-coated polymeric nanoparticles (NPs). The NPs, containing lipophilic drugs and/or contrast agents, are composed of the widely used poly(butyl cyanoacrylate) (PBCA) polymer and prepared in a single step. MBs stabilized by these NPs are subsequently prepared by self-assembly of NPs at the MB air-liquid interface. Here we show that these MBs can act as contrast agents for conventional ultrasound imaging. Successful encapsulation of iron oxide NPs inside the PBCA NPs is demonstrated, potentially enabling the NP-MBs to be used as magnetic resonance imaging (MRI) and/or molecular ultrasound imaging contrast agents. By precise tuning of the applied ultrasound pulse, the MBs burst and the NPs constituting the shell are released. This could result in increased local deposit of NPs into target tissue, providing improved therapy and imaging contrast compared with freely distributed NPs.
A complex set of transport spectroscopy data on a clean single‐wall carbon nanotube device in high magnetic fields is presented. At zero axial field, the device displays in hole conduction with ...increasingly negative gate voltage a fast transition toward high contact transparency and eventually Fabry–Pérot interference of conductance. When increasing the axial field component up to B∥=17 T, the contact transparency and the overall conductance are reduced all the way to Coulomb blockade, clearly displaying the subsequent charging with the first ten holes. The continuous transition between the transport regimes is dominated by a rich spectrum of Kondo‐like resonances, with distinct features in the stability diagrams.
At low temperatures, carbon nanotubes can act as ballistic conductors and electron waveguides, but also near‐perfect traps for artificial atom‐like bound electronic states. Herein, measurements that tune the conductance all the way between these extremes are presented, using a magnetic field only and keeping the charge constant. Coulomb oscillations are directly connected to Fabry–Pérot like interference patterns.
We investigate the electronic properties of a graphene and α-ruthenium trichloride (α-RuCl3) heterostructure using a combination of experimental techniques. α-RuCl3 is a Mott insulator and a Kitaev ...material. Its combination with graphene has gained increasing attention due to its potential applicability in novel optoelectronic devices. By using a combination of spatially resolved photoemission spectroscopy and low-energy electron microscopy, we are able to provide a direct visualization of the massive charge transfer from graphene to α-RuCl3, which can modify the electronic properties of both materials, leading to novel electronic phenomena at their interface. A measurement of the spatially resolved work function allows for a direct estimate of the interface dipole between graphene and α-RuCl3. Their strong coupling could lead to new ways of manipulating electronic properties of a two-dimensional heterojunction. Understanding the electronic properties of this structure is pivotal for designing next generation low-power optoelectronics devices.
Chiral magnetic domains are topological spin textures in which the Dzyaloshinskii–Moriya interaction assigns a given chirality to the domain walls. Notably, despite rapid progress in chiral magnetic ...research, one fundamental issue that remains unclear is how the chirality of chiral magnetic domains change as a magnetic field deforms the spin texture. Using spin‐polarized low energy electron microscopy, the evolution of Fe/Ni chiral magnetic stripe domains are investigated in single‐crystalline Fe/Ni/Cu/Co/Cu(001) multilayers in which the interlayer magnetic coupling between the Co and Fe/Ni films serves as an in‐plane magnetic field. Contrary to theoretical works, it is found that the chirality of the Néel walls results in a parallel alignment of the magnetic stripes with the in‐plane magnetic field direction. The transformation of chiral Néel walls into achiral Bloch walls can be precisely controlled by tuning the Cu spacer layer thickness. In addition, the domain wall exhibits a spontaneous asymmetry within the in‐plane magnetic field, leading to an unbalanced chirality between the left‐handed and right‐handed Bloch walls. These new results foster a better understanding of the chiral domain properties within a magnetic field.
Combining the high‐resolution spin‐polarized low energy electron microscopy and designed (Fe/Ni)/Cu/Co/Cu(001) multilayers, the study reveals the complete evolution of chiral magnetic domain walls within an in‐plane magnetic field. The in‐plane magnetic field aligns the chiral stripes parallel to the field direction and leads to a spontaneous asymmetry of the achiral Bloch walls within a magnetic field.
Chiral magnetic domain walls are of great interest because lifting the energetic degeneracy of left- and right-handed spin textures in magnetic domain walls enables fast current-driven domain wall ...propagation. Although two types of magnetic domain walls are known to exist in magnetic thin films, Bloch- and Néel-walls, up to now the stabilization of homochirality was restricted to Néel-type domain walls. Since the driving mechanism of thin-film magnetic chirality, the interfacial Dzyaloshinskii-Moriya interaction, is thought to vanish in Bloch-type walls, homochiral Bloch walls have remained elusive. Here we use real-space imaging of the spin texture in iron/nickel bilayers on tungsten to show that chiral domain walls of mixed Bloch-type and Néel-type can indeed be stabilized by adding uniaxial strain in the presence of interfacial Dzyaloshinskii-Moriya interaction. Our findings introduce Bloch-type chirality as a new spin texture, which may open up new opportunities to design spin-orbitronics devices.
•Atomic steps locally induce perpendicular magnetic anisotropy in magnetic thin-films.•Annealing temperature of Cu(001) promotes or suppresses step bunch growth.•Images of domain structure taken near ...spin reorientation transition with spin-polarized low energy electron microscopy.•Induced anisotropy potentially originating from substrate morphology and directionality of physical vapor deposition flux.
Using spin-polarized low energy electron microscopy (SPLEEM), we observed surface step bunch induced perpendicular magnetic anisotropy in Fe/Ni bilayers grown on Cu(001) single crystal as well as in Ni/Co/Pd trilayers grown on W(110) crystal. On Cu(100) the formation of step bunches can be stimulated or suppressed by high- or low-temperature annealing cycles, respectively. SPLEEM images resolving the three dimensional magnetization vector in the Fe/Ni films grown on step bunched Cu(100) reveal an additional perpendicular magnetic anisotropy in regions near step bunches. In contrast, no extra perpendicular magnetic anisotropy is observed on low-temperature annealed Cu(100) featuring single-atom height step arrays. Additional investigation of Ni/Co/Pd trilayers on W(110) reveals the influence of step bunch orientation on magnetic anisotropy. Our observations may lead to opportunities for tailoring or patterning anisotropy in magnetic thin-films by controlling film morphology.
Magnetic materials offer an opportunity to overcome the scalability and energy consumption limits affecting the semiconductor industry. New computational device architectures, such as low-power solid ...state magnetic logic and memory-in-logic devices, have been proposed which rely on the unique properties of magnetic materials. Magnetic skyrmions, topologically protected quasi-particles, are at the core of many of the newly proposed spintronic devices. Many different materials systems have been shown hosting ferromagnetic skyrmions at room temperature. However, a magnetic field is a key ingredient to stabilize skyrmions, and this is not desirable for applications, due to the poor scalability of active components generating magnetic fields. Here we report the observation of ferromagnetic skyrmions at room temperature and zero magnetic field, stabilized through interlayer exchange coupling (IEC) between a reference magnet and a free magnet. Most importantly, by tuning the strength of the IEC, we are able to tune the skyrmion size and areal density. Our findings are relevant to the development of skyrmion-based spintronic devices suitable for general-use applications which go beyond modern nanoelectronics.
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