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Electrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms
We demonstrate the first wavelength-tunable electrically pumped source of nonclassical light that can emit photons with wavelength in resonance with the D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel GaAs single-quantum-dot light-emitting diode (LED) onto a piezoelectric actuator. By feeding the emitted photons into a 75 mm long cell containing warm 87Rb vapor, we observe slow-light with a temporal delay of up to 3.4 ns. In view of the possibility of using 87Rb atomic vapors as quantum memories, this work makes an important step toward the realization of hybrid-quantum systems for future quantum networks.
Deposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands
The chemisorption of magnetically bistable transition metal complexes on planar surfaces has recently attracted increased scientific interest due to its potential application in various fields, including molecular spintronics. In this work, the synthesis of mixed-ligand complexes of the type [NiII2L(L’)](ClO4), where L represents a 24-membered macrocyclic hexaazadithiophenolate ligand and L’ is a ω-mercapto-carboxylato ligand (L’ = HS(CH2)5CO2− (6), HS(CH2)10CO2− (7), or HS(C6H4)2CO2− (8)), and their ability to adsorb on gold surfaces is reported. Besides elemental analysis, IR spectroscopy, electrospray ionization mass spectrometry (ESIMS), UV–vis spectroscopy, and X-ray crystallography (for 6 and 7), the compounds were also studied by temperature-dependent magnetic susceptibility measurements (for 7 and 8) and (broken symmetry) density functional theory (DFT) calculations. An S = 2 ground state is demonstrated by temperature-dependent susceptibility and magnetization measurements, achieved by ferromagnetic coupling between the spins of the Ni(II) ions in 7 (J = +22.3 cm−1) and 8 (J = +20.8 cm−1; H = −2JS1S2). The reactivity of complexes 6–8 is reminiscent of that of pure thiolato ligands, which readily chemisorb on Au surfaces as verified by contact angle, atomic force microscopy (AFM) and spectroscopic ellipsometry measurements. The large [Ni2L] tail groups, however, prevent the packing and self-assembly of the hydrocarbon chains. The smaller film thickness of 7 is attributed to the specific coordination mode of the coligand. Results of preliminary transport measurements utilizing rolled-up devices are also reported.
Precise Localization and Control of Catalytic Janus Micromotors Using Weak Magnetic Fields
We experimentally demonstrate the precise localization of spherical Pt-Silica Janus micromotors (diameter 5 μm) under the influence of controlled magnetic fields. First, we control the motion of the Janus micromotors in two-dimensional (2D) space. The control system achieves precise localization within an average region-of-convergence of 7 μm. Second, we show that these micromotors provide sufficient propulsion force, allowing them to overcome drag and gravitational forces and move both downwards and upwards. This propulsion is studied by moving the micromotors in three-dimensional (3D) space. The micromotors move downwards and upwards at average speeds of 19.1 μm/s and 9.8 μm/s, respectively. Moreover, our closed-loop control system achieves localization in 3D space within an average region-of-convergence of 6.3 μm in diameter. The precise motion control and localization of the Janus micromotors in 2D and 3D spaces provides broad possibilities for nanotechnology applications.
Impedimetric Microfluidic Sensor-in-a-Tube for Label-Free Immune Cell Analysis
Analytical platforms based on impedance spectroscopy are promising for non-invasive and label-free analysis of single cells as well as of their extracellular matrix, being essential to understand cell function in the presence of certain diseases. Here, an innovative rolled-up impedimetric microfulidic sensor, called sensor-in-a-tube, is introduced for the simultaneous analysis of single human monocytes CD14+ and their extracellular medium upon liposaccharides (LPS)-mediated activation. In particular, rolled-up platinum microelectrodes are integrated within for the static and dynamic (in-flow) detection of cells and their surrounding medium (containing expressed cytokines) over an excitation frequency range from 102 to 5 × 106 Hz. The correspondence between cell activation stages and the electrical properties of the cell surrounding medium have been detected by electrical impedance spectroscopy in dynamic mode without employing electrode surface functionalization or labeling. The designed sensor-in-a-tube platform is shown as a sensitive and reliable tool for precise single cell analysis toward immune-deficient diseases diagnosis.
(Metallo)porphyrins for potential materials science applications
The bottom-up approach to replace existing devices by molecular-based systems is a subject that attracts permanently increasing interest. Molecular-based devices offer not only to miniaturize the device further, but also to benefit from advanced functionalities of deposited molecules. Furthermore, the molecules itself can be tailored to allow via their self-assembly the potential fabrication of devices with an application potential, which is still unforeseeable at this time. Herein, we review efforts to use discrete (metallo)porphyrins for the formation of (sub)monolayers by surface-confined polymerization, of monolayers formed by supramolecular recognition and of thin films formed by sublimation techniques. Selected physical properties of these systems are reported as well. The application potential of those ensembles of (metallo)porphyrins in materials science is discussed.
Active Matrix Flexible Sensory Systems: Materials, Design, Fabrication, and Integration
A variety of modern applications including soft robotics, prosthetics, and health monitoring devices that cover electronic skins (e-skins), wearables as well as implants have been developed within the last two decades to bridge the gap between artificial and biological systems. During this development, high-density integration of various sensing modalities into flexible electronic devices becomes vitally important to improve the perception and interaction of the human bodies and robotic appliances with external environment. As a key component in flexible electronics, the flexible thin-film transistors (TFTs) have seen significant advances, allowing for building flexible active matrices. The flexible active matrices have been integrated with distributed arrays of sensing elements, enabling the detection of signals over a large area. The integration of sensors within pixels of flexible active matrices has brought the application scenarios to a higher level of sophistication with many advanced functionalities. Herein, recent progress in the active matrix flexible sensory systems is reviewed. The materials used to construct the semiconductor channels, the dielectric layers, and the flexible substrates for the active matrices are summarized. The pixel designs and fabrication strategies for the active matrix flexible sensory systems are briefly discussed. The applications of the flexible sensory systems are exemplified by reviewing pressure sensors, temperature sensors, photodetectors, magnetic sensors, and biosignal sensors. At the end, the recent development is summarized and the vision on the further advances of flexible active matrix sensory systems is provided.
Charge transport in organic nanocrystal diodes based on rolled-up robust nanomembrane contacts
The investigation of charge transport in organic nanocrystals is essential to understand nanoscale physical properties of organic systems and the development of novel organic nanodevices. In this work, we fabricate organic nanocrystal diodes contacted by rolled-up robust nanomembranes. The organic nanocrystals consist of vanadyl phthalocyanine and copper hexadecafluorophthalocyanine heterojunctions. The temperature dependent charge transport through organic nanocrystals was investigated to reveal the transport properties of ohmic and space-charge-limited current under different conditions, for instance, temperature and bias
Synthesis, spectroscopic characterization and thermogravimetric analysis of two series of substituted (metallo)tetraphenylporphyrins
Subsequent treatment of H2TPP(CO2H)4 (tetra(p-carboxylic acid phenyl)porphyrin, 1) with an excess of oxalyl chloride and HNR2 afforded H2TPP(C(O)NR2)4 (R = Me, 2; iPr, 3) with yields exceeding 80%. The porphyrins 2 and 3 could be converted to the corresponding metalloporphyrins MTPP(C(O)NR2)4 (R = Me/iPr for M = Zn (2a, 3a); Cu (2b, 3b); Ni (2c, 3c); Co (2d, 3d)) by the addition of 3 equiv of anhydrous MCl2 (M = Zn, Cu, Ni, Co) to dimethylformamide solutions of 2 and 3 at elevated temperatures. Metalloporphyrins 2a–d and 3a–d were obtained in yields exceeding 60% and have been, as well as 2 and 3, characterized by elemental analysis, electrospray ionization mass spectrometry (ESIMS) and IR and UV–vis spectroscopy. Porphyrins 2, 2a–d and 3, 3a–d are not suitable for organic molecular beam deposition (OMBD), which is attributed to their comparatively low thermal stability as determined by thermogravimetric analysis (TG) of selected representatives.
Tuning the magneto-optical response of TbPc2 single molecule magnets by the choice of the substrate
In this work, we investigated the magneto-optical response of thin films of TbPc2 on substrates which are relevant for (spin) organic field effect transistors (SiO2) or vertical spin valves (Co) in order to explore the possibility of implementing TbPc2 in magneto-electronic devices, the functionality of which includes optical reading. The optical and magneto-optical properties of TbPc2 thin films prepared by organic molecular beam deposition (OMBD) on silicon substrates covered with native oxide were investigated by variable angle spectroscopic ellipsometry (VASE) and magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. The magneto-optical activity of the TbPc2 films can be significantly enhanced by one to two orders of magnitude upon changing the molecular orientation (from nearly standing molecules on SiO2/Si substrates to nearly lying molecules on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) templated SiO2/Si substrates) or by using metallic ferromagnetic substrates (Co).
Imperceptible Supercapacitors with High Area-Specific Capacitance
Imperceptible electronics will make next-generation healthcare and biomedical systems thinner, lighter, and more flexible. While other components are thoroughly investigated, imperceptible energy storage devices lag behind because the decrease of thickness impairs the area-specific energy density. Imperceptible supercapacitors with high area-specific capacitance based on reduced graphene oxide/polyaniline (RGO/PANI) composite electrodes and polyvinyl alcohol (PVA)/H2SO4 gel electrolyte are reported. Two strategies to realize a supercapacitor with a total device thickness of 5 µm—including substrate, electrode, and electrolyte—and an area-specific capacitance of 36 mF cm−2 simultaneously are implemented. First, the void volume of the RGO/PANI electrodes through mechanical compression is reduced, which decreases the thickness by 83% while retaining 89% of the capacitance. Second, the PVA-to-H2SO4 mass ratio is decreased to 1:4.5, which improves the ion conductivity by 5000% compared to the commonly used PVA/H2SO4 gel. Both advantages enable a 2 µm-thick gel electrolyte for planar interdigital supercapacitors. The impressive electromechanical stability of the imperceptible supercapacitors by wrinkling the substrate to produce folds with radii of 6 µm or less is demonstrated. The supercapacitors will be meaningful energy storage modules for future self-powered imperceptible electronics.