Sunday 28 October 2007

Irreversible Electrowetting on Thin Fluoropolymer Films

Review article on Electrowetting : from basics to applications
Electrowetting from physorg.com

Electrowetting

http://www.ee.duke.edu/research/microfluidics/

Digital microfluidics is an alternative paradigm for lab-on-a-chip systems based upon micromanipulation of discrete droplets. Microfluidic processing is performed on unit-sized packets of fluid which are transported, stored, mixed, reacted, or analyzed in a discrete manner using a standard set of basic instructions. In analogy to digital microelectronics, these basic instructions can be combined and reused within heirarchical design structures so that complex procedures (e.g. chemical synthesis or biological assays) can be built up step-by-step. And in contrast to continuous-flow microfluidics, digital microfluidics works much the same way as traditional bench-top protocols, only with much smaller volumes and much higher automation. Thus a wide range of established chemistries and protocols can be seamlessly transferred to a nanoliter droplet format.


Research in Dr. Richard Fair's laboratory at Duke University has focused on the use of electrowetting arrays to demonstrate the digital microfluidic concept. Electrowetting is essentially the phenomenon whereby an electric field can modify the wetting behavior of a droplet in contact with an insulated electrode. If an electric field is applied non-uniformly then a surface energy gradient is created which can be used to manipulate a droplet sandwiched between two plates. Electrowetting arrays allow large numbers of droplets to be independently manipulated under direct electrical control without the use of pumps, valves or even fixed channels.






Click on the thumbnail to launch the video. All videos are in mpeg-1 format (*.mpg), 640x480 resolution, and play back in real-time. A fast computer is recommended for accurate playback.

(in above said link - use it for videos )

Nanoelectronics and Liquid state field effect transistors


UC Engineering Research Widens Possibilities for Electronic Devices, NSF-funded engineering research on microfluidics at the University of Cincinnati widens the possibilities on the horizon for electronic devices.
Parting a tiny red sea at the University of Cincinnati: Today’s — and tomorrow’s — sophisticated electronic devices may hinge on our ability to control microdrops of liquid on a surface.
This effect, called electrowetting, controls the contact angle of a liquid on a hydrophobic surface through the use of an electric field.

As recently published in Applied Physics Letters and featured on the cover of the journal, Andrew Steckl’s research on liquid-state-field-effect transistors (LiquiFETs) promises improvements in such things as “lab on a chip” devices. These tiny devices, reminiscent of the “Fantastic Voyage,” can be introduced into the blood stream to monitor the blood’s chemistry. Steckl, a professor in the Department of Electrical and Computer Engineering in the College of Engineering, calls it “liquid logic” — using liquids to make electronic devices instead of solids.

One of the limitations of traditional health care instruments, for example, is that the information contained in the liquid (blood, in this example) must be translated into electrical signals that can be read in some kind of measuring device. Classical methods for this “translation” have used methods based on light and colorimetric measurement, direct optical sensing (using a video camera or detector) or combinations of optical excitation of fluorescent dyes.

Enter the liquid-state-field-effect transistors (LiquiFETs). Steckl and his doctoral student Duk Young Kim have designed and fabricated an electrowetting-based LiquiFET that operates in the liquid stateand can directly convert charge-related information from the fluid into electronic, measurable signals. Such a device could co-exist in human body environment, for example, which is mostly liquid.

This technology could have applications in biology, health sciences and many other areas.

“In microelectronics, we usually think small,” says Steckl. “But there are applications where you have to think large — like big, big flat-panel televisions, with flexible panels perhaps.” Other applications might be for objects that have a peculiar shape, like the curves and corners of an automobile.

Organic Bulk heterojunction solar cells

Polymeric Field Effect Transistors Ph.D thesis from netherland


Charge injection into organic semiconductors

Sunday 21 October 2007

Photovoltaic cell or solar cell animation


An internet resource from http://micro.magnet.fsu.edu/primer/java/solarcell/index.html

which has animation of solar cell working principle

The most common photovoltaic cells employ several layers of doped silicon, the same semiconductor material used to make computer chips. Their function depends upon the movement of charge-carrying entities between successive silicon layers. In pure silicon, when sufficient energy is added (for example, by heating), some electrons in the silicon atoms can break free from their bonds in the crystal, leaving behind a hole in an atom's electronic structure. These freed electrons move about randomly through the solid material searching for another hole with which to combine and release their excess energy. Functioning as free carriers, the electrons are capable of producing an electrical current, although in pure silicon there are so few of them that current levels would be insignificant. However, silicon can be modified by adding specific impurities that will either increase the number of free electrons (n-silicon), or the number of holes (missing electrons; also referred to as p-silicon). Because both holes and electrons are mobile within the fixed silicon crystalline lattice, they can combine to neutralize each other under the influence of an electrical potential. Silicon that has been doped in this manner has sufficient photosensitivity to be useful in photovoltaic applications.

In a typical photovoltaic cell, two layers of doped silicon semiconductor are tightly bonded together (illustrated in Figure 1). One layer is modified to have excess free electrons (termed an n-layer), while the other layer is treated to have an excess of electron holes or vacancies (a p-layer). When the two dissimilar semiconductor layers are joined at a common boundary, the free electrons in the n-layer cross into the p-layer in an attempt to fill the electron holes. The combining of electrons and holes at the p-n junction creates a barrier that makes it increasingly difficult for additional electrons to cross. As the electrical imbalance reaches an equilibrium condition, a fixed electric field results across the boundary separating the two sides.

When light of an appropriate wavelength (and energy) strikes the layered cell and is absorbed, electrons are freed to travel randomly. Electrons close to the boundary (the p-n junction) can be swept across the junction by the fixed field. Because the electrons can easily cross the boundary, but cannot return in the other direction (against the field gradient), a charge imbalance results between the two semiconductor regions. Electrons being swept into the n-layer by the localized effects of the fixed field have a natural tendency to leave the layer in order to correct the charge imbalance. Towards this end, the electrons will follow another path if one is available. By providing an external circuit by which the electrons can return to the other layer, a current flow is produced that will continue as long as light strikes the solar cell. In the construction of a photovoltaic cell, metal contact layers are applied to the outer faces of the two semiconductor layers, and provide a path to the external circuit that connects the two layers. The final result is production of electrical power derived directly from the energy of light.

The voltage produced by solar cells varies with the wavelength of incident light, but typical cells are designed to use the broad spectrum of daylight provided by the sun. The amount of energy produced by the cell is wavelength-dependent with longer wavelengths generating less electricity than shorter wavelengths. Because commonly available cells produce only about as much voltage as a flashlight battery, hundreds or even thousands must be coupled together in order to produce enough electricity for demanding applications. A number of solar-powered automobiles have been built and successfully operated at highway speeds through the use of a large number of solar cells. In 1981, an aircraft known as the Solar Challenger, which was covered with 16,000 solar cells producing over 3,000 watts of power, was flown across the English Channel powered solely by sunlight. Feats such as these inspire interest in expanding the uses of solar power. However, the use of solar cells is still in its infancy, and these energy sources are still largely restricted to powering low demand devices.

Current photovoltaic cells employing the latest advances in doped silicon semiconductors convert a average of 18 percent (reaching a maximum of about 25 percent) of the incident light energy into electricity, compared to about 6 percent for cells produced in the 1950s. In addition to improvements in efficiency, new methods are also being devised to produce cells that are less expensive than those made from single crystal silicon. Such improvements include silicon films that are grown on much less expensive polycrystalline silicon wafers. Amorphous silicon has also been tried with some success, as has the evaporation of thin silicon films onto glass substrates. Materials other than silicon, such as gallium arsenide, cadmium telluride, and copper indium diselenide, are being investigated for their potential benefits in solar cell applications. Recently, titanium dioxide thin films have been developed for potential photovoltaic cell construction. These transparent films are particularly interesting because they can also serve double duty as windows.

Saturday 13 October 2007

VIDEO ECTURES

the following fields of division has video lectures
Arts (19)
Business (15)
Computers (5)
Computer Science (584)
Environment (2)
Science (27)
Society (26)

Video lectures on all subjects

Important blogspot for all general sujects list and science
http://freescienceonline.blogspot.com/2007/09/programming-language-video-lectures.html

http://www.ecse.rpi.edu/Homepages/shivkuma/teaching/video_index.html
(video lectures on Computer Communication Networks,Internet Protocols ,
Broadband and OpticalNetworks)
MIT video lectures link on all Engineering subjects and medicine
http://mitworld.mit.edu/video_index.php

Free streaming audio and video lectures

http://all-streaming-media.com/streaming-audio-and-video-online/free-streaming-audio-video-lectures.htm

Choosing PIC Microcontrollers

Choosing PIC Microcontrollers

When starting a new microcontroller project it's often difficult to decide what sort of microcontroller to use. If you don't have a specific project but want to play with microcontrollers for learning purposes, it's probably best to start with a simple, mid-range device. High-end devices have many complicated modes and large manuals which can be confusing. But moving up to a larger micro from a smaller one is easy. The PIC series is very well designed and uniform throughout the line. This means that learning done on one PIC is easily adapted to a different device.

For new users, the PIC16F627A is highly recommended. It is modern and powerful, but still very easy to use.

For users with specific applications, generally the following criteria should be considered:

  • I/O - How many and what kinds of I/O are required? Be careful when simply counting I/O pins from a specs sheet. Not all I/O pins are the same, and not all of the features can be used at once.
  • Processing Power - Make sure that your application is a reasonable one for a micro. Don't expect to decode MPEG movies on a microcontroller. (at least not in 2006 anyway) As microcontroller projects get more complex, it's often a hard choice between a complicated custom microcontroller project and a small embedded PC or Arm board that can run a full OS. Some applications just work better on a full PC.
  • Storage - Most micros don't have very much RAM and ROM. If you need to store a lot of data, you might need to interface with external memory. Be careful not to underestimate the I/O bandwidth requirements of moving a lot of data around. Sometimes a larger processor is required for memory reasons and not for processing power reasons.

Here are some PIC suggestions:

  • PIC10F200 - The world's smallest microcontroller! Only 6 pins, 4 of which are I/O pins. If you need a little processor for something special, at $1 and the size of a grain of rice this is a great alternative to logic gates for many low-speed applications. A J/K flip-flop can toggle a light on and off, but the PIC10F200 can toggle the light on and off, debounce the switch, and even do dimming... all in software!
  • PIC16F627A - A low cost (<$2) PIC with a lot of power. There are larger version with more memory, but this small PIC has a serial port, timers, PWMs, interrupts, and a good amount of I/O.
  • PIC16F87x - These PICs offer lots of choices of I/O and memory sizes, with the addition of A/D converters and more.
  • PIC18F252/PIC18F2520 - More sophisticated PICs. Still not badly priced at $12 or so, they have much larger memories, and lots of other special features.
  • PIC18F6527/PIC18F8527 - Super massive PICs with tons of I/O, memory and all the peripherals. At $15, these are pricey, and you can't get them in a DIP package. But if you want to do massive I/O, lots of analog inputs, etc. without using external I/O expanders, this is for you. Nearly single cycle access to any I/O pin is really nice for many applications.

Monday 8 October 2007

n-Type doping of organic molecular electronic films

A. Kahn, Princeton University, USA

N-type Doping of Organic Molecular Films

N-type doping of organic materials is difficult because of the low electron affinity (~1.5 – 2.5 eV) of most electron transport materials (ETM) of interest. Dopants must have low ionization energy to transfer an electron to lowest unoccupied molecular orbital (LUMO) of the host, and are thus inherently unstable. Alkali cations are mobile and diffuses through the organic layer. Their small size leads to a fairly tightly bond cation-anion pair with the host molecule, resulting in strong electron localization. Larger, less mobile donors are therefore being pursued. We report here on the use of the strongly reducing molecule bis(cyclopentadienyl)-cobalt(II) (cobaltocene, CoCp2) (ionization energy = 4.0 eV) to n-dope an important ETM, a tris(thieno)hexaazaphenylylene derivative (THAP) [1]. UPS, inverse photoemission, ion scattering, X-ray photoemission and I-V measurements are used to characterize the energetics and transport properties of the doped system. We also describe on-going work using the even stronger reducing molecular agent decamethyl cobaltocene to n-dope phthalocyanines and pentacene.

Antoine Kahn received his Ph.D. in Electrical Engineering and Computer Science from Princeton University in 1978. He joined the Princeton faculty in 1979, and was promoted to the rank of Associate Professor in 1985 and Full Professor in 1991. His research is in the field of semiconductor surfaces and interfaces. Over the past twelve years, he and his group focused on the structural, electronic and chemical properties of surfaces and interfaces of organic molecular and polymer films, and the physics of molecular level alignment across interfaces. He has published over 260 regular and review articles. He is a Fellow of the AVS (1999) and APS (2002).