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Materials Today: Proceedings
We have shown that when the conductive tip of an AFM bends a straight, vertical nanowire, a strain field is established, with the stretched surface showing positive strain and the compressed surface showing negative strain. As the tip scans over the top of the zinc oxide nanowires, we observe many peaks in the corresponding voltage output image for each contact position. The idea came first, but we needed experimental support.
Just before Christmas , I designed an experiment to visualize directly the voltage output of a large wire under optical and AFM microscopy. My student and I did the experiments, and one evening in late December, we were rewarded with several videos that directly proved my model. The next day I worked with Jinhui Song in my office to edit the movie.
Then we sent the paper to Science for publication. To be useful in practical applications, our nanogenerator needs to contain an array of nano-wires, all of them continuously generating electricity that can be collected and delivered to a device. And the energy to be converted into electricity has to come in the form of a wave or vibration from the environment so the nano-generator can operate independently and wirelessly. We have developed a novel design that addresses these requirements.
The next challenge was to increase the power of the nanogenerator. Three objectives have to be achieved: eliminate the use of the AFM, make many nanowires generate electricity simultaneously and continuously, and excite the nanowires in an indirect wave, such as an ultrasonic wave. I came out with a new design using a ridged electrode to replace the AFM tips and presented the idea to my postdoctoral assistant, Xudong Wang. It took him about four months of experiments before compiling the first group of data. The signal was rather small. From May to October we focused on the optimum packaging of the nanogenerator to enhance its output.
By the end of the year we realized that the nanogenerator could at last be reported to the scientific community. Our experimental setup provided the first demonstration of continuous direct current produced by a piezoelectric nanogenerator.
Advanced materials, components & processes for integrated autonomous micro-power sources
Coating the electrode with platinum both enhances its conductivity and causes it to act like a diode that allows current to flow in only one direction, from metal to semiconductor. The electrode is placed above the nanowire array at a controlled distance and can be moved laterally so that it bends the nanowires from side to side.
Thanks to its surface ridges, the electrode acts like an array of aligned microscope tips. Flexible Future Since January we have been fully involved in improving our nanogenerator. The ceramic or semiconductor substrates that we initially used for growing zinc oxide nanowires are hard and brittle, for instance, making them unsuitable for applications that require a foldable or flexible power source, such as biosensors implanted in muscles or joints, or power generators built into shoes.
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Here is where conductive polymers can provide a substrate that is likely to be biocompatible. In experiments we discovered that many available flexible plastic substrates are suitable for growing the zinc oxide nanowire arrays, which ultimately could find applications in portable and flexible electronics.
Because of the flexibility of the substrate, the nanowire surface profile was wavy, causing some missed contacts. We believe that providing suitable bonding strength between the nanowires and substrate as well as optimizing the wire spacing will be important in increasing discharge efficiency. Although our approach has demonstrated the principle of the nanogenerator, we must drastically improve its performance to make it practical.
All the nanowires must generate electricity simultaneously and continuously, and all the electricity must be effectively collected and distributed. A large-scale method for growing zinc oxide nanowires can be cost-effective because it does not require expensive high-temperature manufacturing processes. Hurdles that lie ahead in our research include learning how to grow perfectly uniform arrays of nanowires that all produce electricity and how to extend their working life. The dynamics of motion is altered while increasing the speed, i. Sanchez et al. In this tutorial review we describe recent progress on catalytic microtubular engines fabricated by rolled-up nanotech.
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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. Mei et al.
Guide Energy Autonomous Micro and Nano Systems
It was produced by Alex A. The 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. Animal cells can be transported within a fluid in a controllable manner by using artificial microbots.
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. Artificial 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.
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.
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. 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. Wir haben winzige Mikroraketen hergestellt, die sich durch ein Magnetfeld fernsteuern lassen.
Oliver G. Schmidt, Spektrum der Wissenschaft, S. Schmidt, Welt der Physik 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. Office Kristina Krummer office-iin at ifw-dresden. Micro-autonomous systems.