Isn’t it amazing how much you’ve learned over a lifetime?  Did you ever stop to think how much you’ve forgotton?   The human memory is amazing but certainly not fool-proof.  And yet even a whiff of a certain smell or a glimpse of a certain shape can bring back the memories of something in your past.

Electronic memory is also quite amazing, powering digital cameras and MP3 players.  As nanotechnology takes hold the density of the memory will continue to increase, giving us the power to capture and store nearly everything around us.  As the size shrinks, one challenge will be the testing of memory.  When dealing with nanoscale elements on a memory chip it is critical that the electronic signals be very precise. 

Fudan University in China uses a function generator to send very precise nanosecond pulses to its nanoscale memory devices.   Read more about the application in the Application Example section of the Agilent in Nanotechnology website.  http://nano.tm.agilent.com/index.cgi?CONTENT_ID=1238&User:LANGUAGE=en-US

Chemical sensing will very likely become an important field in the world of nanotechnology.  Chemical sensing plays in important role in our homes as we use carbon dioxide sensors to detect that harmful gas.  Sensors in public arenas are important to warn us of impending danger from toxic spills or terrorist attacks.  Chemical sensors in hospitals and clinics help us prevent disease or warn us of harmful viruses.  Nanotechnology will no doubt improve the sensitivity of chemical sensors making them even more useful for characterizing minute amounts of toxins or finding very early signs of disease.

Carnegie Melon University is building a chemical sensor array using inkjet printing technology.  The printed circuit board is powered with a DC power supply during the testing. To learn more about this chemical sensor - go to Application Examples on the Agilent in Nanotechnology website.

Stimulus and response is common in almost every part of our society.  As parents– a bad behavior by your child (stimulus) results in a punishment from you (response).  A lowering of interest rates (economic stimulus) generally results in a surge in house sales or consumer spending (economic response).  The swallowing of a sleeping pill (stimulus) results in a much needed rest (response).  The same holds true for nanotechnology.

This week I want to highlight three examples of a stimulus-response from our collection of nanotechnology measurement examples found on the nanotechnology website.  http://nano.tm.agilent.com/index.cgi?CONTENT_ID=1361&User:LANGUAGE=en-US

In electronics, we have the Unversity of Groningen in The Netherlands performing a stimulus-response on an organic field effect transistor (FET).  They use a pulse generator to stimulate the FET with an 85V, 10ms pulse and they use a semiconductor analyzer to measure the current/voltage and the capacitance/voltage responses.  Their work is published in the February 2005 edition of Nature Materials.

In life science, Pohang University in South Korea is performing a stimulus-response in electrochemistry.  They are using a function / arbitrary waveform generator to generate a simulated noise signal and use an oscilloscope to measure the peak current from analytes.  Their work is published in the June 2005 edition of Analytical Chemistry. 

In materials science, Georgia Tech is using a combination of instruments to characterize the mechanical properties of carbon nanosprings.  They use an atomic force microscope (AFM) to stimulate the nanospring and a dynamic signal analyzer (DSA) to capture the deflection signal.  They also use a function/arbitrary waveform generator to trigger the DSA with a specfic pulse waveform.  Their work is published in the February 2004 Nano Letters. 

If you have an application that you would like us to highlight on the nanotechnology website, send me an email at grant_drenkow@agilent.com

Today, Agilent begins an applications section of the nanotechnology website.  The new section is a reference of nanotechnology applications showing typical instruments being used in research projects.   Each example gives a brief description of the project, the instruments used, the measurements made, and the device or structure being studied.  It also cites the name of the article, the publication, and the authors if you want to read more about this specific application.  It is divided into chemical, electronics, life sciences, materials, and optical categories for easier reference. 

To see the applications section, go to www.agilent.com/find/nano and click on the Application Examples found on the left side navigation bar under Resources.

 Let me highlight a few of the applications available this week.  If you are interested in carbon nanotubes, check out the chemical section to see how a gas chromatograph is used as a nanotube filter.  For those in electronics, this week’s applications include optical amplifiers tested with an oscilloscope and transistors tested with a semiconductor parameter analyzer.  In life science, genes are being identified with a bioanlyzer.  In in the optical section quantum dots being used as infared photodectors are tested using a semiconductor analyzer to accurately plot their current/voltage (I-V) characteristics.  In the nanomaterials section polymer micelles are characterized with a liquid chromatograph / mass spectrometer.  An LCR meter is used to plot the capacitance/voltage (C-V) curves. 

The applications section will have weekly additions, so visit it frequently.   My thanks to Jeff Harvey, a student at the University of Colorado-Boulder, who help us put together these research summaries.  If you have an application that you would like us to highlight- reply to this blog. 

The Nobel Prize for 2007 goes to Albert Fert and Peter Grunberg for giant magnetoresistance (GMR).  The technology allows one to read very small magnetic differences stored on computer hard drives and convert it to electric current.  It enables hard drive manufacturers to store large amounts of data in a small space.  GMR is a great example of nanoscale measurements enabling breakthroughs in future commercial products. 

 Go to http://nobelprize.org/nobel_prizes/physics/laureates/2007/press.html to read the full report.

I recently attended the SPIE Optics East Conference in Boston. Nanotechnology is having a strong influence on optics. In particular, researchers are looking for a way to increase the efficiency of photovoltaics and solar cells to reduce our dependency on fossil fuel. The National Renewable Energy Laboratory (NREL) in Golden, Colorado recently hosted the Colorado Nanotechnology Alliance. An odd combination? Not really. NREL, a government-funded center, is actively testing a variety of nanotechnology materials, looking for the most efficient way to turn solar energy into electricity. An article just released talks about NREL’s interest in quantum dots to improve the efficiency of photovoltaic material. <Learn More>

Researchers like those at the University of Toronto in Canada have been looking at quantum dots for a number of years. Steven McDonald and his team have been using a semiconductor parameter analyzer to measure the low level voltage and current generated by quantum dots. In an article published in Nature Materials in January 19, 2005 they were measuring currents on the order of 100 nanoamps and voltages of around 5 volts. Semiconductor analyzers like the Agilent B1500A are ideal tools for solar panel and photovoltaic research because of their ability to measure currents down to atto-amps and voltages in the microvolts. Atomic force microscopes are nice complements to the electronic measurements, allowing one to look at the surface of material and the individual quantum dots.

For more information on Agilent’s complete line of nanotechnology - visit the nanotechnology website at www.agilent.com/find/nano

Agilent B1500A Semiconductor Analyzer

If you’re looking for some reference material to put on the wall of your lab - consider Agilent’s new nanotechnology poster call “The Scale of Nanotechnology”.  The poster relates the size of typical objects like human hair, red blood cells, viruses, DNA, and carbon nanotubes to various wavelengths of light and distances in micrometers and nanometers.  It also shows typical instruments that are used for biological, chemical, electrical, and topographical measurements.  Go to the following URL to get a FREE poster.

http://nano.tm.agilent.com/index.cgi?ALIAS=NewsletterPosterRegistration

A recent bridge collapse in Minneapolis, Minnesota has prompted renewed interest in the materials science of critical infrastructures like bridges.  Bridges in the northern regions of the country have been weakened by prolonged exposure to deicing salt that finds its way through the concrete to the steel reinforcing beams causing extensive corrosion.  Cathodic protection, a technique developed in the USA and UK during the second half of the 20th century, is a possible means to protect these bridges.  Who would have thought that electronics could play a role in materials science?   If you would like to read more about this technique, visit the Agilent application note library and download this application note.  http://cp.literature.agilent.com/litweb/pdf/5989-6459EN.pdf

As I talk with university professors doing nanotechnology research, many of them are utilizing electronic test equipment in their research on various nanotechnology structures.  Semiconductor analyzers capable of low level voltage and current measurements are at the top of the list.  Network analyzers with the ability to add stimulus and measure responses in the GHz arena are also popular.  And others are using high precision multimeters, high speed oscilloscopes, RF signal generators, MHz function generators, and high precision power supplies. 

What instruments are you using in your research?  Over the course of the next few weeks I will be highlighting applications that I’ve seen using various types of electronic, chemical analysis, bioanalysis, and microscopy products for nanotechnology research.  Feel free to add your own applications to this blog. 

In my continuing effort to show you the flexibility of an atomic force microscope (AFM) - let’s look at phase imaging.  

Phase Imaging is a powerful, dynamic force technique that can reveal many unique mechanical and chemical properties of a sample at the nanometer scale. In Phase Imaging, an AFM cantilever is oscillated vertically near its mechanical resonance frequency while it is in close proximity to a sample. As the AFM tip comes in very close proximity to the sample surface, the amplitude of the cantilever’s oscillation is reduced. The change in amplitude is measured and is used to track changes in the surface topography and roughness of the sample. Simultaneously, as the AFM tip encounters regions of different composition, a change in phase, relative to the phase of the drive signal, is measured and recorded. This change in phase is very sensitive to variations in material properties, including surface stiffness, elasticity and adhesion. The phase shifts are measured and displayed in a very straightforward manner that facilitates quantitative analysis and interpretation.

Both inorganic and organic materials have been examined with phase imaging. Phase imaging has been found to be particularly useful to map the various components of composite materials, to study variations in composition and contamination in materials, and to measure adhesion, surface hardness and elasticity. It has been applied to thin film studies, the materials sciences, and composite characterization.

Phase Imaging is included with Acoustic AC Mode and MAC Mode. It can be conducted with or without temperature control, in air, in liquid, and even under controlled atmospheres.

Phase Imaging can reveal material properties that can not be observed in surface topography and it can identify properties that might otherwise be obscured by topography. It is a sensitive, quantitative, high lateral resolution AFM method that is often more convenient and gentler than other surface property methods that are based on contact mode operation.

SPM is the acronym of scanning probe microscopy.  An AFM (atomic force microscope) is a subset of SPM. 

STM is the acronym of scanning tunneling microscopy.  STM is a mode of AFM.  So what is it, you ask? 

STM (Scanning Tunneling Microscopy) was invented in 1981 by G. Binnig and H Rohrer who shared the 1986 Nobel Price in Physics for their invention. STM uses a sharp conducting tip and it applies a bias voltage between the tip and the sample. When the tip is brought close to the sample electrons can “tunnel” through the narrow gap either from the sample to the tip or from the tip to the sample, depending on the sign of the bias voltage. This tunneling current changes with tip-to-sample distance, it decays exponentially with the distance, which gives STM its remarkably high precision in positioning the tip (sub-angstrom vertically and atomic resolution laterally). For the electron tunneling to take place, both the sample and the tip must be conductive. Therefore STM cannot be used on insulating materials.

STM can image a sample surface in either constant-current mode or constant-height mode, as shown in the image above. In constant-current mode, in order to keep the tunneling current constant STM uses feedback to adjust the height of the scanner at each measurement point, e.g. when the system senses a tunneling current increase, it adjusts the voltage applied to the piezoelectric scanner so that the scanner lifts the tip and give an increase in the tip-sample distance. The scanner height measured at each location on the sample surface constitutes the topographic image. The constant-current mode is thus generally used to acquire surface height data, its scan speed is limited by the feedback response and thus it takes longer to image an irregular surface at a larger scan size. In constant-height mode, the tip scans at a constant height above the sample and the tunneling current changes due to the topography and the local surface electronic properties of the sample. The current image is a result of measured tunneling current at each location on the sample surface. The constant-height mode can acquire data faster because the system doesn’t have to move the scanner in the vertical direction, so it is most often used for imaging relatively smooth surfaces.

Strictly speaking STM tunneling current is correlated to the surface electronic density of states, i.e., the number of filled or unfilled electron states near the Fermi level, within an energy range determined by the bias voltage. So STM measures constant tunneling probability instead of the physical topography at the surface. STM tunneling spectroscopy, looking at the current-voltage relationship at a constant tip-sample distance or the current-distance relationship at a constant bias voltage, is a useful tool to study the electronic structure and property of a sample surface at the atomic level.