Today, in our Application Note series, we are covering Scanning Thermal Microscopy (SThM) - an atomic force microscopy (AFM) imaging mode that maps changes in thermal conductivity across a sample's surface. Similar to other modes that measure material properties, SThM data is acquired simultaneously with topographic data. The SThM mode is made possible by replacing the standard contact mode cantilever with a nanofabricated thermal probe with a resistive element near the apex of the probe tip. This resistor is incorporated into one leg of a Wheatstone bridge circuit, which allows the system to monitor resistance. This resistance correlates with temperature at the end of the probe, and the Wheatstone bridge may be configured to either monitor the temperature of a sample or to qualitatively map the thermal conductivity of the sample.
The folks at the European NanoHand project, whose nanogripper design we have covered in a previous Nanowerk Spotlight, seem to have loved playing with their plastic toy kits as kids. At least that's the impression you get when watching their latest video explaining their proof-of-principle study of scanning probe tips defined by planar nanolithography and integrated with AFM probes using nanomanipulation. They have prefabricated nanoscale needles, to be picked up by nanogrippers inside a scanning electron microscope. They then use these nanobits as ultralong tips in atomic force microscopes. The researchers call the needles 'nanobits' because they are a reminder of drill bits - you can have a library of different nanobits and then pick the one you want, and mount it where you want it.
Ferroelectric domain patterns attract increasing attention owing to their potential for integrated optical and novel electronic applications. Lately, Piezoresponse Force Microscopy (PFM) has become a standard technique for the investigation of such domain patterns due to the high lateral resolution of only about 10 nm even - so no specific sample preparation is needed. In addition, due to the frequency modulated PFM technique for recording ferroelectric domains, topography and domain patterns can be recorded simultaneously and independently. Piezoresponse force microscopy is based on the deformation of the sample due to the converse piezoelectric effect. Generally, all scanning force microscopes are suited for PFM operation as long as they allow application of voltages to the tip and separate readout of the cantilever movement.
A Japanese-UK research team has now demonstrated that cryoEM image analysis may be exploited to obtain structural information of sufficient resolution to reveal the absolute three-dimensional (3D) configuration of a designed DNA nanostructure. With their technique they have obtained structural information at sufficient resolution to visualize the DNA helix and reveal the absolute stereochemistry of a self-assembled DNA tetrahedron. Each edge is a 7 nm, 20 base pair duplex, and the edges are connected covalently through single unpaired adenosine nucleotides, making it a rigid, triangulated structure that could serve as a building block for larger 3D structures or as a molecular cage. This DNA tetrahedron is the smallest 3D nanostructure made by DNA self-assembly.
It its more than 25 years of existence, Scanning Tunneling Microscopy has predominantly brought us extremely detailed images of matter at the molecular and atomic level. The Scanning Tunneling Microscope (STM) is a non-optical microscope that scans an electrical probe over a surface to be imaged to detect a weak electric current flowing between the tip and the surface. It allows scientists to visualize regions of high electron density and hence infer the position of individual atoms and molecules on the surface of a lattice. Now, researchers in Japan have managed to partially sequence a single DNA molecule with a STM - a significant step towards the realization of electronic-based single-molecule DNA sequencing.
The Atomic Force Microscope (AFM) is a key tool for nanotechnology. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Increasingly, the AFM is also becoming a tool for nanofabrication. Relatively new is the use of AFM in cell biology. Researchers in Switzerland have now demonstrated novel cell biology applications using hollow force-controlled AFM cantilevers - a new device they have called FluidFM.
A major concern in microbiology is to determine whether a bacterium is dead or alive. This crucial question has major consequences in food industry, water supply or health care. While culture-based tests can determine whether bacteria can proliferate and form colonies, these tests are time-consuming and work poorly with certain slow-growing or non-culturable bacteria. They are not suitable for applications where real-time results are needed, e.g. in industrial manufacturing or food processing. A team of scientists in France has now discovered that living and dead cells can be discriminated with a nanotechnology technique on the basis of their cell wall nanomechanical properties.
For the past 20+ years, the atomic force microscope has been one of the most important tools to visualize nanoscale objects where conventional optics cannot resolve them due to the wave nature of light. One limiting factor of conventional AFM operation is the speed at which images can be acquired. Over the past five years, researchers have been developing a high-speed AFM capable of video-rate image capture. An AFM with this ability enables nanoscale processes to be observed in real-time, rather than capturing only snap-shots in time. An obvious application of this instrument is to modify the sample surface while observing changes in the surface topography. Successful demonstration of this would indicate the potential for a new generation of fabrication tools. Scientists have now done exactly that.