Institute for Integrative Nanosciences (IIN)

Most recent highlights:

		Photovoltaic effect in ultrathin Si nanomembranes Under 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 diodes We 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 microbots We 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

		Highly efficient locomotion of hybrid biocatalytic microengines We 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 DOI: 10.1021/ja104362r (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

		Self-wound ultra-compact energy storage elements We 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 Freie Presse (August 3, 2010) Online Pro-Physik.de (August 4, 2010) URL electroniknet.de (August 12, 2010) URL

		Tubular optofluidic sensors for enhanced refractive index sensing Optofluidic 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 dots We 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-supercapacitor Winding 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 molecules Site-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 Alleskönner Kleine 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 energies Elastic 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 optics A 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

		Towards tunable indistinguishable photons from distant quantum dots In this work, we present steps towards the realization of quantum interference between two photons emitted from two independent QDs. The exciton energies of two nearby GaAs QDs located into spatially separated cavities are brought into resonance and overlapped at a beam splitter. Despite the fact that the short dephasing time of the selected QDs prevents us to observe quantum interference between the two photons, the approach could be applied to other QDs emitting transform-limited single photons. M. Benyoucef et al., Applied Physics Letters 95, 261908 (2009) URL PDF This work was highlighted in: Nature Materials 9, 94 (2010) URL PDF

		Epitaxial quantum dots in stretchable optical microcavities Arrays of GaAs microring optical resonators with embedded quantum dots are placed on top of piezoelectric actuators, which allow the microcavities to be reversibly “stretched” or “squeezed” by applying relatively large biaxial stresses at low temperatures. The emission energy of both QDs and optical modes red- or blue- shift depending on the strain sign, with the QD emission shifting more rapidly than the optical mode with applied strain. Remarkably, excitonic emissions from different QDs are observed to shift at different rates, implying that this technique can be used to bring spatially separated excitons into resonance. T. Zander et al., Optics Express 17, 22452 (2009) URL PDF

		Giant persistent photoconductivity in Si nanomembranes This paper reports the observation of giant persistent photoconductivity from rough Si nanomembranes. When exposed to light, the current in Si nanomembranes is enhanced by roughly 3 orders of magnitude and can persist for days at a high conductive state after the light is switched off. An applied gate voltage can tune the persistent photocurrent and accelerate the response to light. By analyzing the band structure of the devices and the surfaces through various coatings, we attribute the observed effect to the rough surfaces of the nanomembranes, where light activates localised charge carriers. P. Feng et al., Nano Letters 9, 3453 (2009) URL PDF

		Rolled-up hyperlens An investigation of the material makeup and surrounding medium of an optical rolled-up hyperlens is presented. A working spectral range of the hyperlens for different material combinations is studied along with an examination of hyperlens immersion, which suppresses the diffraction of waves exiting the lens due to impedance matching, leading to a higher intensity output. This hyperlens immersion technique can be implemented into cell culture and molecular analysis. E. J. Smith et al., Applied Physics Letters 95, 083104 (2009) URL PDF E. J. Smith et al., Applied Physics Letters 96, 019902 (2010) URL PDF

		Tuneable electronic shell structure of GaAs quantum dots Self-assembled quantum dots (QDs) usually form on top of a thin planar wetting layer (WL), whose properties can be hardly tuned independently from those of the QDs. We now studied QDs for which the WL thickness can be arbitrarily controlled. For fixed QD shape, a systematic decrease in the energy separation between ground and excited states of QDs is observed when the WL thickness is increased. This rather surprising phenomenon can be seen as a cross talk between QD vertical and lateral confinement potential. L. Wang et al., Physical Review B 80, 085309 (2009) URL PDF This work is chosen as PRB Editors' suggestion.

		Microtubular jet engines We 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 nanomembranes Scanning 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 molecules Self-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

		Spectral tunability of microtube resonators on glass The tunability of optical resonant modes of spiral microtube cavities, rolled-up from square patterned SiO/SiO₂ thin nanomembranes on glass substrates, is demonstrated experimentally by coating the tube walls by atomic layer deposition. Transverse-electric modes are observed for Al₂O₃ coatings thicker than approximately 20 nm, as revealed by linear polarization analysis of the emitted light. Such fine tunability, which is essential for realizing optical microdevices, brings a better understanding of the resonant modes in microtubular cavities, suggesting that the microtubes could be used in potential applications for on-chip components like filters and sensors. V. A. Bolaños Quiñones et al., Optics Letters 34, 2345 (2009) URL PDF

		Ferngesteuerte Mikroraketen Wir 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. Oliver G. Schmidt, Spektrum der Wissenschaft, S.16, Juli 2009 URL Oliver G. Schmidt, Welt der Physik 16.05.2009 URL

		Shaped tubular optical microcavities We 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 configurations We 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 rolling We 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

		New planar hybrid heterostructures and superlattices We have invented an entirely new approach to create hybrid material layer stacks, which cannot be produced by any other technology. Hybrid layers are rolled up into a multi-winding tube on a substrate surface, and subsequently pressed down into a planar geometry. This leads to a hybrid superlattice out of single crystalline semiconductors and polycrystalline metals. T. Zander et al., Applied Physics Letters 94, 053102 (2009) URL PDF

		First single photon source on silicon substrate Single quantum emitters have become an emerging area of fundamental research during the last years, driven by the need for nonclassical light sources delivering single-photons on demand for future implementation in the field of quantum information processing. In this work, we demonstrate for the first time triggered single-photon emission from a single quantum dot grown on Si substrate. Our findings show that it is feasible to fabricate high quality indistinguishable single-photon sources aiming at compatibiltiy with Silicon ultra large scale integration technologies. M. Benyoucef et al., Nano Letters 9, 304 (2009) DOI: 10.1021/nl802948a (2008) URL PDF

		First magnetic rolled-up microtubes demonstrated Magnetic rolled-up microtubes are fabricated for the first time, and their hysteresis curves are measured. The tubes consist of semiconductor/magnetic radial superlattices rolled up from a thin solid hybrid material film. The magnetic properties reflect the change of symmetry adopted by the film, once it forms into a cylindrical structure. C. Deneke et al., Nanotechnology 20, 045703 (2009) DOI: 10.1088/0957-4484/20/4/045703 (2008) URL PDF C. Deneke et al., Physica Status Solidi C 5, 2704 (2008) URL PDF

		Cell culturing in single tubes integrated on a Si Chip Transparent 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 polymers A 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 PDF This 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

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Institute for Integrative Nanosciences (IIN)

Most recent highlights:

Photovoltaic effect in ultrathin Si nanomembranes

Direct laser writing of nanoscale light-emitting diodes

Magnetic control of tubular catalytic microbots

Highly efficient locomotion of hybrid biocatalytic microengines

Self-wound ultra-compact energy storage elements

Tubular optofluidic sensors for enhanced refractive index sensing

Quantum transport through SiGe quantum dots

When Silicon becomes a better thermal insulator than glass…

First Swiss roll micro-supercapacitor

Lateral Si quantum dot molecules

Gewickelte Alleskönner

Electromechanical tuning of quantum dot emission energies

Metamaterial fiber optics

Towards tunable indistinguishable photons from distant quantum dots

Epitaxial quantum dots in stretchable optical microcavities

Giant persistent photoconductivity in Si nanomembranes

Rolled-up hyperlens

Tuneable electronic shell structure of GaAs quantum dots

Microtubular jet engines

Ultrathin AlN/GaN nanomembranes

Self-assembled quantum dot molecules

Spectral tunability of microtube resonators on glass

Ferngesteuerte Mikroraketen

Shaped tubular optical microcavities

Advanced quantum dot configurations

From wrinkling to rolling

New planar hybrid heterostructures and superlattices

First single photon source on silicon substrate

First magnetic rolled-up microtubes demonstrated

Cell culturing in single tubes integrated on a Si Chip

Strain engineered micro-/nanotubes on polymers