Institute for Integrative Nanosciences (IIN)
Most recent highlights: | |||||||
 | Spin selective tunneling through SiGe quantum dotsWhen contacting a quantum dot (QD) with normal metallic leads no spin selective tunnel rates are expected. However, low-temperature magneto-transport measurements through individual SiGe self-assembled QDs have now revealed that this assumption is not always true. Indeed, we have observed that spin-selective tunnel rates through individual QDs can be achieved with normal metallic contacts. The surprising spin selectivity arises from the interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. This work was carried out in collaboration with CEA-Grenoble and Yale University. G. Katsaros et al., Phys. Rev. Lett. 107, 246601 (2011) URL PDF | ||||||
 | Lab-in-a-tubeWorking towards creating a fully functional Lab-in-a-tube, we report a method for the precise capturing of embryonic fibroblast mouse cells into rolled-up microtube resonators. The microtubes contain a nanometer-sized gap in their wall which defines a new type of optofluidic sensor, i.e., a flexible split-wall microtube resonator sensor (F-SWμRS), employed as a label-free fully integrative detection tool for individual cells. The sensor action works through peak sharpening and spectral shifts of whispering gallery modes within the microresonators under light illumination. | ||||||
"Starting" and "stopping" microjet enginesThe control over the autonomous motion of artificial nano/micromachines is essential for real biomedical and nanotechnological applications. Consequently, a complete nanomachine should be able to be turned on and off at will. We report the tuning of the propulsion power of catalytic microjets through illumination of a solution by a white-light source. We show that light suppresses the generation of microbubbles, stopping the engines if they are fixed-to or self-propelled above a platinum-patterned surface. The microjets are reactivated by dimming the light source that illuminates the fuel solution.A. A. Solovev et al., Angewandte Chemie International Edition 50, 10875 (2011) URL PDF | |||||||
Magnetic microhelix coil structuresWe design and investigate three-dimensional microhelix coil structures that are radial-, corkscrew-, and hollow-bar-magnetized. The magnetization configurations of the differently magnetized coils are experimentally revealed by probing their specific dynamic response to an external magnetic field. Helix coils offer an opportunity to realize microscale geometries of the magnetic toroidal moment, observed so far only in bulk multiferroic materials.E. J. Smith et al., Physical Review Letters 107, 097204 (2011) URL PDF | |||||||
| | Rolled-up magnetic sensor for in-flow detection of magnetic objectsRolled-up nanotech is used to fabricate magnetic sensor devices, which are directly integrated into fluidic architectures. Strain engineering is applied to roll-up a thin layer stack revealing giant magnetoresistence (GMR). In this way, the rolled-up tube acts as a fluidic channel, while the integrated GMR sensor responds to a magnetic field. In-flow detection of ferromagnetic CrO2 nanoparticles embedded in a biocompatible polymeric hydrogel shell is highlighted. The advantage of rolled-up devices is their integrability into existing on-chip technologies and the ability to combine several functions into a single architecture, possibly leading to a fully operational lab-in-a-tube system.I. Mönch et al., ACS Nano 5, 7436 (2011) URL PDF | ||||||
Superfast motion of catalytic microjet engines at physiological temperatureWe reduced the toxicity of the fuel used to self-propel artificial nanomachines. At physiological temperatures, i.e. 37°C, only very small amounts of H2O2 as fuel is needed to propel the microjets. Under those conditions, Fibroblast cells are viable for more than 1 hour which is highly important for the not-too-distant use of artificial nanomachines in biomedical applications. In addition, at 5% H2O2, the microjets acquire superfast speeds reaching 10 mm sec-1. The dynamics of motion is altered while increasing the speed, i.e. the motion deviates from the linear to curvilinear trajectories which has been theoretically modelled. | |||||||
Hybrid organic/inorganic molecular heterojunctionsWe combine self-assembly and top-down methods to create hybrid junctions consisting of single organic molecular monolayers sandwiched between metal and/or single-crystalline semiconductor nanomembrane based electrodes. The fabrication process is fully integrative and produces a yield loss of less than 5% on-chip. The nanomembrane-based electrodes guarantee a soft yet robust contact to the molecules where the presence of pinholes and other defects becomes almost irrelevant. We also pioneer the fabrication and characterization of semiconductor/molecule/semiconductor tunneling heterojunctions which exhibit a double transition from direct tunneling to field emission and back to direct tunneling, a phenomenon which has not been reported previously. | |||||||
Stretchable magnetoelectronicsWe add a new member to the family of stretchable electronic devices: A flexible and stretchable magnetoelectronic sensor element based on the giant magnetoresistance (GMR) effect. The remarkable performance of the fabricated GMR multilayers upon stretching relies on efficient wrinkling of the GMR films on top of a free-standing rubber membrane. The operation of the device was demonstrated on a proof-of-concept level by attaching it to a curved surface and measuring the sensor's dynamic response to a magnetic field of a rotating magnet. This flexible magnetic sensor opens a straightforward possibility for the integration into existing stretchable electronic systems to realize smart hybrid magnetic and electronic devices with the functionality to sense and to respond to magnetic fields.M. Melzer et al., Nano Letters 11, 2522 (2011) URL PDF | |||||||
Towards remotely controlled intelligent microrobotsIn this tutorial review we describe recent progress on catalytic microtubular engines fabricated by rolled-up nanotech. The control over speed, directionality and interactions of the microengines to perform tasks such as cargo transportation is also discussed. Since rolled-up nanotech on polymers can easily integrate almost any type of inorganic material, huge potential and advanced performance such as high speed, cargo delivery, motion control, and dynamic assembly are foreseen-ultimately promising a practical way to construct versatile and intelligent catalytic tubular microrobots.Y. F. Mei et al., Chemical Society Reviews 40, 2109 (2011) URL PDF This work was highlighted in: derStandard.at (March 8, 2011) URL LiLipuz (March 9, 2011) URL Blick.ch (March 9, 2011) URL | |||||||
Slowing down single photons from quantum dotsNowadays, the vast majority of information is transferred by light in optical fibers. The single elementary particle of light is called a photon. The advantage of single photons is that they can carry and transfer quantum information over very long distances, enabling 100% secure communication, impossible to crack. We have successfully designed a new type of semiconductor material (quantum dots), which emit photons at a frequency that can be combined with rubidium atoms. By guiding the emitted light through the atoms the speed of the photons is reduced to less than 4% of the speed of light in vacuum. The breakthrough can enable the realization of quantum memories - an essential component in quantum information technology. Merging semiconductor and atomic physics in a hybrid interface opens the way to a series of novel experiments and research directions. For instance, quantum memories and quantum repeaters for quantum dot generated photons can now be fabricated. This work was carried out in close collaboration with the Kavli Institute of Nanoscience at Delft University of Technology in the Netherlands.N. Akopian et al., Nature Photonics 5, 230 (2011) URL PDF This work was highlighted in: Nature Photonics, 5, 197 (2011) (March 31, 2011) URL PDF pro-physik.de (March 28, 2011) URL
| |||||||
Guinness World Record® for "Smallest Man-Made Jet Engine""The smallest man-made jet engine measures just 600nm across and weighs 1 picogram. It was produced by Alex A. Solovev, Samuel Sanchez, Yongfeng Mei and Oliver G. Schmidt at the Leibniz Institute for Solid State and Materials Research (IFW Dresden)."This is the text of the official certificate issued by Guinness World Records® beginning of this year (see left side for scanned original). This achievement was highlighted in: Pro-Physik.de (March 8, 2011) URL Die Welt (March 8, 2011) URL Scinexx (March 9, 2011) URL Nanowerk (March 9, 2011) URL | |||||||
Barkhausen Poster Award 2010 goes to IINCongratulations to Michael Melzer, who has been awarded this year's Barkhausen Poster Prize on 4 February 2011!On his poster he described in detail how to fabricate highly sensitive thin films to detect small magnetic fields on rubber substrates. His work paves the way for a technology rapidly moving towards stretchable and flexible magnetoelelctronics. An electronic version of the poster can be found here. The Barkhausen Poster Prize is awarded every year to students and young scientists for their outstanding research and convincing presentation. The award is funded by Materialforschungsverbund Dresden, TU Dresden, European Center for Micro- and Nanoreliability and Fries Research & Technology. | |||||||
Microbots swimming in the flowing streams of microfluidic channelsThe motion of artificial catalytic nanomachines is commonly studied in free bulk solution, which differs significantly from the stream-like channel networks existing in the human body. Here, we demonstrate that catalytic microbots can self-propel in the microchannels of a microfluidics system and transport multiple spherical microparticles into desired locations. We also show for the first time that artificial micromachines can easily swim against strong flowing streams.The integration of “smart and powerful” microbots with microchips will lead to plentiful functions in lab-on-a-chip devices including e.g. efficient and convenient drug or cell separation.S. Sanchez et al., Journal of The American Chemical Society 133, 701 (2011) URL PDF | |||||||
Cardboard rolls on the nanoscaleEverybody knows that cardboard paper can be a highly anisotropic material. You can easily bend or roll it in one direction and it is stiff in the other. If you take a close look you will find that the paper is periodically buckled along one direction. We have now exploited this phenomenon on the nanoscale to define the roll-up direction of ultra-thin membranes on a substrate surface. Given the abundance of fabrication methods to create thin corrugated films (including graphene), our work will help to realize novel 3D tubular nanostructures with well-controlled position, orientation, material composition, and exciting functionalities.P. Cendula et al., Nano Letters 11, 236 (2011) URL PDF | |||||||
Transport of animal cell material by catalytic microbotsAnimal cells can be transported within a fluid in a controllable manner by using artificial microbots. The Ti/Fe/Pt rolled-up catalytic microjet engine (microbot) is guided towards a specific cell, which is moved to a desired location where it is released. The direction of the microbots is easily steered by using an external small magnetic field. This work paves the way to future biomedical applications of artificial micromachines such as curing unhealthy cells or separation of cancer cells.S. Sanchez et al., Chemical Communications 47, 698 (2011) URL PDF This work was highlighted in: Chemistry World (Nov 19, 2010) URL | |||||||
Neuron cells cultured in rolled-up microtubesPrimary mouse motor neurons and immortalised CAD cells, a cell line derived from the central nervous system, can be well cultured on arrays of rolled-up microtubes. In this way, we investigate the influence of topographical surface features on the growth and differentiation behaviour of these cells inside and outside of strongly 2D confined space. Our work opens up a cost-efficient and bio-compatible way of analysing single cell behaviour for various biological applications ranging from neurite protection studies to cell sensor development.S. Schulze et al., Advanced Engineering Materials 12, B558 (2010) URL PDF | |||||||
Rolled-up nanotech for lithium energy storage devicesSelf-wound nanomembranes out of functional multilayers are designed to improve lithium storage performance. The intrinsic strain is relaxed by rolling; the composite components are uniformly dispersed; the micro/nanohierarchical structure assumes a mixed ion/electron conduction network; and conventional nanomembrane deposition techniques allow for various material combinations, suitable to meet different demands of lithium ion batteries. This work represents a further step towards extending the broad range of applications possible through rolled-up nanotech.H.-X. Ji et al., Advanced Materials 22, 4591 (2010) URL PDF | |||||||
Collective behaviour of artifcial autonomous systemsArtificial autonomous systems act as catalytic water striders at the air–liquid interface of hydrogen peroxide solution. Such systems, buoyed by oxygen bubbles, self-propel at the fuel surface by the bubble recoiling mechanism and dynamically self-assemble into patterns due to the meniscus-climbing effect. Artificial systems like these are ideally suited to study the collective behaviour of a large number of individuals, where repelling engine power competes against attractive surface tension. Our results give way to many new approaches to sense environment with swarms of micro-/nanoengineered microtube robots.A. A. Solovev et al., Advanced Materials 22, 4340 (2010) URL PDF This work was highlighted in: Nanowerk.com (Sep 30, 2010) URL MaterialsViews (Nov 10, 2010) URL | |||||||
The DotFET becomes realityOn May 18, 2001 a patent to speed up Si transistors was filed by Schmidt and Eberl (US 6,498,359), which relies on a SiGe dot positioned below the channel of a Si transistor (see left image). The 3D geometry of the dot provides huge amounts of tensile strain to the Si, which decisively affects the band structure and enhances the mobility of electrons in the channel, and thus the performance of the heart of electronics: The Metal Oxide Semiconductor Field Effect Transistor (MOSFET). In a mutual effort funded by the European Union this concept was eventually brought into reality by a consortium of research groups in Delft, Linz, Jülich, Milano, and Dresden.V. Jovanović et al., IEEE Electron Device Letters 31, 1083 (2010) URL PDF | |||||||
How nanostructures healthily cope with stress...Elastic stress is the main driving force for the “birth and fate” of self-assembled quantum dots (QDs). Some of them rapidly grow in size and need to find ways to release the increasing amount of stress. Eventually, beyond a certain critical size, the QD usually relaxes by crystal defect introduction, which is analogous to its “death”. By guiding the formation of QDs on periodically patterned substrates, the QDs are able to cope with the increasing stress by cyclically incorporating large amounts of material from the substrate and corresponding changes of their shape. This allows them to keep growing in size while delaying relaxation mediated by defects.J. J. Zhang et al., Physical Review Letters 105, 166102 (2010) URL PDF | |||||||
Highly efficient locomotion of hybrid biocatalytic microenginesWe have designed a novel hybrid biocatalytic microengine. The engine is based on a catalytic enzyme, catalase, specifically bounded to self-assembled monolayers covering the inside wall of an inorganic rolled-up microtube. This novel approach leads to faster, more powerful, and more efficient microengines requiring much lower concentrations of peroxide fuel. The engine's speed and direction is dynamically controlled by the friction of bubbles attached to the outside wall of the microtube. Our work presents a major step towards engineering micro-/nanorobots which run on biocompatible fuels and which - one day - might well sense their environment biochemically.S. Sanchez et al., Journal of The American Chemical Society 132, 13144 (2010) URL PDF This work was highlighted in: RSC Chemistry World (July 29, 2010) URL Nanowerk.com (Aug 3, 2010) URL ChemViews Magazine (Aug 11, 2010) URL | |||||||
Stretch graphene, get more details...We are continuously expanding the knowledge of how controllable external stresses, as a basic physical technique, modify the properties and unveil interesting physics of nanomaterials. Graphene, a one atom thick carbon sheet, can be studied in more details with our recently developed piezoelectric-actuator based technique. Controllable biaxial stress, which does not change the relative positions of the Dirac cones, is applied to graphene. The key mechanical characteristics of graphene, the Grueneisen parameters, are extracted from Raman spectroscopy. We also observe that the frequency of the 2D peak is not exactly twice that of the D peak, as predicted previously by theory. The appealing feature of our technique is that it allows exerting strain on demand, which promises new opportunities to study the strain-related behaviors of graphene with unprecedented details.F. Ding et al., Nano Letters 10, 3453 (2010) URL PDF | |||||||
Rolled-up mesoscopic Josephson junctionsJosephson junctions are crucial to many areas of high precision science and technology. However, the fabrication of nanoscale Josephson junctions is still tedious and often requires complex preocessing steps such as electron beam lithography with highest resolution. Here, mesoscopic SNS Josephson junctions are developed simply relying on natural metallic film roughnesses, self-assembly and standard optical lithography. We achieve high critical currents, and an IcRn product placing the characteristic frequency in the THz regime. These properties make them interesting candidates for many applications ranging from quantum metrology over THz radiation sensors to flux-qubits.D. J. Thurmer et al., Nano Letters 10, 3704 (2010) URL PDF | |||||||
Photovoltaic effect in ultrathin Si nanomembranesUnder local illumination, ultrathin silicon nanomembranes (SiNMs) on insulator reveal a gate-controlled photovoltaic effect and negative transconductance in Schottky transistors applying both homo- and hetero-contacts. Tiny variations of Schottky barriers between source and drain contacts are responsible for the photovoltaic effect (see the image) and can be enhanced by gate voltage and/or contact design. Our results provide a useful method to disclose contact properties of nanomaterials and open alternative ways for novel nano-optoelectronic devices based on the photovoltaic effect.P. Feng et al., Advanced Materials 22, 3667 (2010) URL PDF | |||||||
Direct laser writing of nanoscale light-emitting diodesWe have fabricated sub-micrometer light emitting diodes (LEDs) in a mesoscopic semiconductor structure by means of a focused laser beam. The local heating produced by the beam allows spatially controlled diffusion of mobile interstitial manganese ions out of a GaMnAs layer towards an underlying quantum well heterostructure. This activates a nanoscale region of the LED to emit light at a bias well below the threshold voltage for emission from the non-annealed regions. The technique,which provides real-time in-situ control of the nanostructures during their formation, may represent an alternative to deep etching for defining narrow current channels in mesoscopic devices.O. Makarovsky et al., Advanced Materials 22, 3176 (2010) URL PDF | |||||||
Magnetic control of tubular catalytic microbotsWe have demonstrated the magnetic control of self-propelled catalytic Ti/Fe/Pt rolled-up microtubes (microbots). The microbots move by ejecting microbubbles, which are produced by a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The particularly easy control over the movement of the microbots by changing the direction of the magnetic field during motion helps to accurately load and deliver cargo at desired places in a fluid. Our microbots show a high propulsion power that allows the selective transport of up to 60 polystyrene microparticles and several thin metallic nanoplates. Our microbots represent an exciting artificial species to be employed for applications such as controllable drug-delivery and cleaning tasks.A. A. Solovev et al., Advanced Functional Materials 20, 2430 (2010) URL PDF This work was highlighted in: Nanowerk.com (Aug 3, 2010) URL | |||||||
Self-wound ultra-compact energy storage elementsWe have demonstrated the self-assembly of ultra-compact energy storage devices based on self-wound three-dimensional hybrid organic/inorganic nanomembranes. Such ultra-compact elements exhibit capacitances per footprint area higher than their state-of-the-art planar counterparts and reach specific energies comparable to supercapacitors. The combination of self-assembled organic monolayers with inorganic capacitor materials leads to elements with small footprints, remarkable performance and properties strongly correlated with the organic materials incorporated. Our results represent a breakthrough for local on-chip energy storage and energy supply for autonomous systems at the micro- and nanoscale.C. C. Bof Bufon et al., Nano Letters 10, 2506 (2010) URL PDF This work was highlighted in: New Scientist Magazine (June 26, 2010) URL smartgrid (June 27, 2010) URL Freie Presse (August 3, 2010) Online Pro-Physik.de (August 4, 2010) URL nanowerk (August 4, 2010) URL Scinexx (August 5, 2010) URL materialgates (August 6, 2010) URL electroniknet.de (August 12, 2010) URL GreenTech Germany (August 17, 2010) URL scienceknowledge.org (September 2, 2010) URL MRS Bulletin News & Analysis (October, 2010) URL | |||||||
Tubular optofluidic sensors for enhanced refractive index sensingOptofluidic microcavities from rolled-up ring resonators with subwavelength wall thicknesses have been fabricated with excellent sensing function. The positions of resonant modes shift significantly when light emission was measured in different surrounding liquids, and thus the sensitivity can be calculated based on experimental observation. A maximum sensitivity of 425 nm/refractive index unit is currently achieved, which is caused by the pronounced propagation of the evanescent field in the surrounding media due to the subwavelength wall thickness design of the sensor. Our optofluidic sensors show high potential for lab-on-a-chip applications, e.g. real-time bio-analytic systems.G. S. Huang et al., ACS Nano 4, 3123 (2010) URL PDF | |||||||
 | Quantum transport through SiGe quantum dotsWe have realized single-hole transistors based on self-assembled SiGe quantum dots. Charge transport measurements reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin-orbit coupling strength with pronounced gate-voltage and magnetic-field dependence. For strongly coupled devices single-hole supercurrent transistors were realized. Our observations render SiGe quantum dots exciting candidates for the development of spin-based devices and the study of new transport regimes. This work was carried out in collaboration with CEA-Grenoble and CNRS-Grenoble.G. Katsaros et al., Nature Nanotechnology 5, 458 (2010) URL PDF | ||||||
 | When Silicon becomes a better thermal insulator than glass…Silicon has a high room temperature thermal conductivity, which is important for efficient heat dissipation in microelectronics. At the same time this circumstance is a road-block for thermoelectric applications (which exploit thermal/electric energy conversion). We have now demonstrated that introducing Ge nanostructures in single-crystalline Si leads to thermal conductivities which are lower than for any other SiGe alloy, amorphous Si and even glass. The perception of "Nano-Si" opens great opportunities towards development of Si compatible on chip cooling or power generation devices. This work was carried out in collaboration with Université Bordeaux-CNRS, CEA-Grenoble, Fraunhofer-IPM, Max-Planck-Institut für Festkörperforschung and The University of California at Santa Cruz.G. Pernot et al., Nature Materials 9, 491 (2010) URL PDF This work was highlighted in: Sächsische Zeitung (June 10, 2010) Online | ||||||
 | First Swiss roll micro-supercapacitorWinding layers into batteries is an industry-standard to manufacture commercial batteries on the macroscale. On the micro- and nanoscale, however, applying external forces to roll-up layers is not possible any more. Here, we engineer strain in ultra-thin layers by deposition, which causes the layers to wind up automatically upon their release from a substrate. We demonstrate a redox Swiss roll micro-supercapacitor consisting of a self-rolled multilayered nanomembrane with an electrochemical active layer at either the outer or inner surface for different proton diffusion paths. The Swiss roll micro-supercapacitor is ideally suited to achieve high performance (e.g. capacity and life time) in a microscale power source and is helpful for studying charge transfer at the electrolyte/electrode interface.H. X. Ji et al., Chemical Communications 46, 3881 (2010) URL PDF This work was highlighted by Chemical Communications as a “Hot article”. | ||||||
Lateral Si quantum dot moleculesSite-controlled SiGe islands which have both large sizes and high Ge fraction are successfully obtained. Finite element method calculations of the strain distribution with the realistic structure reveal that (i) the Si spacer between a pair of islands can act as a lateral quantum dot molecule made of four nearby dots for electrons and (ii) the tensile strain in a Si cap deposited on top of the stack is significantly enhanced with respect to a single layer. This work was carried out in collaboration with the Institute of Semiconductor and Solid State Physics, University Linz.J. Zhang et al., Applied Physics Letters 96, 193101 (2010) URL PDF | |||||||
 | Gewickelte AlleskönnerKleine Röhrchen sind es, die mit einer Vielzahl erstaunlicher Eigenschaften verblüffen. Auf kleinstem Raum lassen sich in ihnen unterschiedlichste Funktionen unterbringen. Das macht sie beispielsweise interessant für elektronische Chips, Mikrosensoren oder die Medizin. Prof. Oliver G. Schmidt und seine Mitarbeiter haben in den letzten Jahren eine Technologie geschaffen, um solche Röhrchen kontrolliert und in nahezu allen Größenordnungen und Materialkombinationen herzustellen. Weitere Anwendungen finden sich in der Energietechnik und Nanorobotik.Sächsische Zeitung, 12. April 2010, S. 7 Online | ||||||
 | Electromechanical tuning of quantum dot emission energiesElastic mechanical strain is a powerful control tool for engineering the electronic states in quantum dots. With a simple electro-mechanical device we apply in-plane biaxial stress to a 200-nm-thick GaAs membrane containing InAs quantum dots. The relative energy levels of the exciton and biexciton states can be tuned to emit photons with exactly the same color. This observation may lead to the implementation of a recently proposed concept for the generation of entangled photon pairs. The strain tuning technique adds a new degree of freedom to the field of semiconductor nanostructures, and may inspire exciting future experiments in other fields.F. Ding et al., Physical Review Letters 104, 067405 (2010) URL PDF | ||||||
 | Metamaterial fiber opticsA metamaterial integration for fiber optics, leading to a dual effect of surface plasmon and classical waveguiding, is presented along with experimental potentiality. We theoretically propose a metamaterial fiber in which, depending on the wavelength (from ultraviolet to infrared) and the particular metamaterial composition, one can transmit information through surface plasmon mediated or classical waveguidance. The metamaterial can be used as the core or cladding of a fiber which allows waveguidance through a subwavelength geometry.E. J. Smith et al., Nano Letters 10, 1 (2010) DOI: 10.1021/nl900550j (2009) URL PDF This work was highlighted in: Nature Photonics 3, 310 (2009) URL PDF www.technologyreview.com (April 17, 2009) URL | ||||||
 | Microtubular jet enginesWe have strain-engineered microtubes traveling as self-propelled catalytic microjet engines along various trajectories with speeds up to ≈ 2 mm s-1 (approximately 50 body lengths per second). The motion of the microjets is generated by gas bubbles thrust out of one opening of the tube. The trajectories of various geometries can be traced by long microbubble tails. A magnetic layer is integrated into the wall of the microjet engine, which allows easy control over the direction of motion by applying external magnetic fields.A. A. Solovev et al., Small 5, 1688 (2009) URL PDF | ||||||
 | Ultrathin AlN/GaN nanomembranesScanning electron micrographs of ultrathin AlN/GaN nanomembranes self-assembled into various geometries such as tubes, spirals, and curved sheets on Si(111). These freestanding structures contain nanopores with sizes from several to tens of nanometers within nanomembranes of 20−35 nm nominal thickness and can find application in molecular separation or artificial blood capillaries.Y. F. Mei et al., ACS Nano 3, 1663 (2009) URL PDF | ||||||
 | Self-assembled quantum dot moleculesSelf-assembled semiconductor quantum dot molecules (QDMs) obtained by epitaxial growth are reviewed. A comprehensive overview of the development and current stage of the research on QDMs composed of vertically (in the growth direction) or laterally (in the growth plane) aligned QDs is provided. The cover shows a 2D photoluminescence intensity map from a self-assembled lateral QDM in an electric field applied along the molecular axis. The coupling of the two QDs is evidenced by intricate spectral line anticrossings, indicated by dotted lines.L. Wang et al., Advanced Materials 21, 2601 (2009) URL PDF | ||||||
 | Ferngesteuerte MikroraketenWir haben winzige Mikroraketen hergestellt, die sich durch ein Magnetfeld fernsteuern lassen. Die Herstellung der Mikroraketen erfolgt durch hauchdünne Schichtsysteme, die sich auf einem Trägersubstrat von selbst zu Mikroröhrchen aufrollen. Nach dem Ablösen der Röhrchen von dem Substrat erzeugen die chemisch aktiven Innenwände eine katalytische Reaktion in einer Flüssigkeit. Die Reaktion führt zur Bildung von Sauerstoffblasen, die aus den Röhrchen ausgestoßen werden, und so für den Vortrieb der Mikrorakete sorgen. Da das aufgerollte Schichtsystem magnetische Materialien enthält, können die Mikroraketen durch ein Magnetfeld ferngesteuert werden. | ||||||
 | Shaped tubular optical microcavitiesWe have fabricated tubular optical microcavities by releasing pre-defined stressed SiO/SiO2 bilayer nanomembranes from polymer sacrificial layers. Optical measurements at room temperature demonstrate that the resonant optical modes can be accurately tuned along the tube axes. The resonant modes shift to higher energies with decreasing number of tube wall rotations and thickness, which is well-described by simulations. Rolled-up tubular optical microcavities can be produced in large periodic arrays on arbitrary substrates and are therefore highly attractive for on-chip integration technologies. G. S. Huang et al., Applied Physics Letters 94, 141901 (2009) URL PDF | ||||||
Advanced quantum dot configurationsWe have presented an overview on approaches currently employed to fabricate advanced quantum dot configurations by epitaxial growth. Absolute position control of self-assembled quantum dots, so-called 'seeded' quantum dot crystals, is achieved by the combination of bottom–up and top–down methods. A promising way to realize quantum dot crystals with controlled spatial and optical properties is described.S. Kiravittaya et al., Reports on Progress in Physics 72, 046502 (2009) URL PDF | |||||||
From wrinkling to rollingWe have explored the change-over from wrinkling to rolling for compressively strained thin solid films. For small strain gradients across the film thickness the layer wrinkles whereas for large strain gradients it rolls up into a nanotube. Our theory provides an upper limit for the maximum achievable rotations of the film and is therefore of uttermost importance for many applications such as on-chip self-wound capacitors and coils.P. Cendula et al., Physical Review B 79, 085429 (2009) URL PDF | |||||||
Cell culturing in single tubes integrated on a Si ChipTransparent oxide rolled-up microtube arrays are realized by the deposition of a pre-stressed oxide layer on patterned photoresist and the subsequent removal of the photoresist. Due to the unique tubular structure and optical transparency, such rolled-up microtubes can serve as well-defined 2D confined cell culture scaffolds. Yeast cells exhibit different growth phenomena in microtubes as the diameter is scaled down. Detailed investigations of individual yeast cells in a single microtube reveal the mechanical interaction between microtubes and the 2D confined cells causing different cellular assemblies. Our appoach is fully compatible to Si technology and might lead to high speed integrated analysis systems of individual cells on a single chip.G. S. Huang et al., Lab on a Chip 9, 263 (2009) DOI: 10.1039/b810419k (2008) URL PDF | |||||||
Strain engineered micro-/nanotubes on polymersA generic approach has been developed to engineer tubular micro-/nanostructures out of many different materials with tunable diameters and lengths by precisely releasing and rolling up functional nanomembranes on polymers. The technology spans across different scientific fields ranging from photonics to biophysics and we demonstrate optical ring resonators, magneto-fluidic sensors, remotely controlled microjets and 2D confined channels for cell growth guiding.Y. F. Mei et al., Advanced Materials 20, 4085 (2008) URL PDFThis work was highlighted in: P.M. Magazine (February 17, 2009) URL Frankfurter Allgemeine Zeitung (November 11, 2008) URL Nanowerk (October 20, 2008) URL Pro Physik (October 20, 2008) URL Bild (August 27, 2008) URL | |||||||