[Show abstract][Hide abstract] ABSTRACT: At atmospheric pressure, anatase TiO2 films with various nano-morphologies have been grown on quartz substrate by non-thermal TiCl4–O2–Ar reactive plasma vapor deposition. High concentration of oxygen vacancies and undercoordinated Ti atoms are incorporated into the crystal lattice of the deposited films, which can be tuned by changing the discharge conditions such as temperature and vapor flow rate. Strong visible luminescence is found for the deposited films, originating from the radiative recombination of trapped electrons due to uncoordinated Ti atoms and oxygen vacancies. To clarify the growth mechanism, an analytical model is proposed to explain the corresponding discharging process. We find the theoretical predictions agree well with experimental results. By effectively adjusting the morphology and lattice crystallinity, we believe this work can provide an expedient and controllable way to fabricate anatase films with interesting optical properties, which can meet the demands of complex practical situations to the maximum degree.
[Show abstract][Hide abstract] ABSTRACT: Pre-stressed multi-layer nanomembranes are rolled-up into a microtube in order to tune the strain applied to the contained coupled GaAs quantum wells. Additional GaAs/AlAs adjusting layers were deposited on the top of the nanomembrane to alter the thickness/stiffness of the to-be-rolled nanomembrane. In this way, microtubes with an adjustable diameter and strain are possible from a single initial grown sample. The internal strain state in the microtube affects the energy levels of the quantum wells and their coupling, which can be probed sensitively by photoluminescence. We measure different strain relaxation in rolled-up nanomembranes which we explain using a gradual change of the longitudinal relaxation as the distance of the nanomembrane from the etching front varies.
No preview · Article · Jan 2013 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: An equilibrium phase diagram for the shape of compressively strained free-hanging films is developed by minimizing the total strain energy. For small strain gradients , the film wrinkles, while for sufficiently large strain gradients, a phase transition from wrinkling to bending occurs. Download CDF player to play the file at http://www.wolfram.com/cdf-player/
[Show abstract][Hide abstract] ABSTRACT: Dynamic curvature control of rolled-up metal nanomembranes by active magnesium layer design is implemented in bio-oriented conditions to realize shape transformation of expansion, shrinking, un-rolling and rerolling. The tube integrated with catalytic Pt layer, proposes a new type of smart drug delivery microsystem.
No preview · Article · Jun 2012 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: The design of catalytic engines powered by chemical fuels is an exciting and emerging field in multidisciplinary scientific communities. Recent progress in nanotechnology has enabled scientists to shrink the size of macroengines down to microscopic, but yet powerful, engines. Since a couple of years ago, we have reported our progress towards the control and application of catalytic microtubular engines powered by the breakdown of hydrogen peroxide fuel which produces a thrust of oxygen bubbles. Efforts were undertaken in our group to prove whether the fabrication of nanoscale jets is possible. Indeed, the smallest jet engine (600 nm in diameter and 1 picogram of weight) was synthesized based on heteroepitaxially grown layers. These nanojets are able to self-propel in hydrogen peroxide solutions and are promising for the realisation of multiple tasks.
No preview · Article · Dec 2011 · The Chemical Record
[Show abstract][Hide abstract] ABSTRACT: ZnO nanoporous films consisting nanocrystals on ITO-coated glass substrates were prolongedly electrodeposited under pulse voltages in zinc nitrate solution at room temperature. Their structures were found to be determined by experimental parameters, especially, the voltage and the deposition time. On the basis of the structural characterization, the growth mechanism was proposed as a combined growth process: the competitive growth between lateral overgrowth and nanovoid formation. The structural evolvement is believed to be due to the decrease of surface potential with deposition time, leading to the formation of a quasi-two-layer structure. The revealed mechanism here could be helpful to understand the growth and corresponding properties of ZnO films as well as their nanostructures.
No preview · Article · Oct 2011 · Fuel and Energy Abstracts
[Show abstract][Hide abstract] ABSTRACT: In this work we study the evolution of roughness in interfaces of HfO2/Al2O3 multilayers by x-ray reflectivity. It was found that, besides the reduced adatom surface mobility during atomic layer deposition, an improvement of the interface quality can be achieved upon the stacking of several layers. Although the low roughness of the initial surface could not be recovered, there was a considerable improvement of surface/interface quality along the deposition process. In particular, variations on the growth temperature were not able to tailor the surface quality, if compared to the stacking process. Finally, transmission electron microscopy analysis has shown that local defects can take place among nearly perfect interfaces. Such effect must be taken into account for nanometer-scale device fabrication.
Full-text · Article · Mar 2011 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Recently a significant amount of attention has been paid towards the development of man-made synthetic catalytic micro- and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self-propelled vehicles have been described. Here the magnetic control of self-propelled catalytic Ti/Fe/Pt rolled-up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films (“nanoplates”). Microbots self-propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275 µm s−1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77 pN when transporting a single 5 µm diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled-up microtubes, their motion can be fully controlled by an external magnetic field.
No preview · Article · Aug 2010 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: A theoretical study has been conducted to explore the mechanics of self-organizing channel networks with dimensions in the submicron range and nanorange. The channels form by the partial release and bond back of prestressed thin films. In the release phase, the film spontaneously buckles into wrinkles of a certain wave-length, followed by a bond-back phase in which the final channel geometry is established through cohesive interface attractions. Results are presented in terms of the channel spacing, height, and width as a function of the film stiffness, thickness, eigenstrain, etch width, and interface energy. We have identified two dimensionless parameters that fully quantify the network assembly, showing excellent agreement with experiments. Our results provide valuable insight for the design of submicron and nanoscale channel networks with specific geometries.
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Aug 2009 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Tubular optical microcavities have been fabricated by releasing prestressed SiO/SiO2 bilayer nanomembranes from polymer sacrificial layers, and their geometrical structure is well controlled by defining the shape of nanomembranes via photolithography. Optical measurements at room temperature demonstrate that resonant modes of microtubular cavities rolled up from circular shapes can be tuned in peak energy and relative intensity along the tube axes compared to those from square patterns. The resonant modes shift to higher energy with decreasing number of tube wall rotations and thickness, which fits well to finite-difference time-domain simulations. Polarization resolved measurements of the resonant modes indicate that their polarization axes are parallel to the tube axis, independent of the polarization of the excitation laser.
[Show abstract][Hide abstract] ABSTRACT: Au/Co/Au trilayers are fabricated by tilted deposition on prestructured polymer sacrificial layers. The metal trilayers are released by selectively dissolving the sacrificial layer and roll-up into microtubes. Magnetization properties are strongly affected by the roll-up process. In addition to a modified shape anisotropy, the magnetostrictive anisotropy due to the anisotropic stress release is reversed. Low temperature measurements support the presence of significant exchange bias in these rolled-up structures.
Full-text · Article · Mar 2009 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: An equilibrium phase diagram for the shape of compressively strained free-hanging films is developed by total strain energy minimization. For small strain gradients Δε, the film wrinkles, while for sufficiently large Δε, a phase transition from wrinkling to bending occurs. We consider competing relaxation mechanisms for free-hanging films, which have rolled up into tube structures, and we provide an upper limit for the maximum achievable number of tube rotations.
[Show abstract][Hide abstract] ABSTRACT: C/β-SiC/Si hybrid microtubes have been fabricated by releasing prestressed C/Si bilayer structures and treating with a postannealing process. Detailed characterization reveals the synthesis of β-SiC via a solid phase reaction at the C/Si interface. Remarkably, the production of β-SiC is promoted in the tube wall by rolled-up bonding of adjacent windings, which increases the area of the C/Si interface by a factor of 2. The Raman spectra acquired from the hybrid microtubes disclose peaks pertaining to the optical phonon modes of β-SiC that exhibit obvious downshifts due to surface effects on the SiC nanoparticles. Moreover, two light emission bands are detected from a hybrid microtube and their origin is discussed based on spectral analyses.
No preview · Article · Jan 2009 · Journal of Applied Physics