Introduction to the Microtherm Lab
This group was the first in the world to develop the ability to simultaneously deposit thermal energy and measure temperature changes on a sub-micron scale. This has led to revolutionary combinations of microscopy with thermal, spectroscopic and chemical analysis, which provide unique data on the mesoscale properties of materials.
For example, the novel use of temperature modulation on a micron scale enables depth discrimination, provides a dramatically improved signal to noise ratio and allows one to distinguish between reversible and irreversible transitions in polymers.
The spectroscopic facility is being used in two major collaborative projects (for details, please click on the Microthermal Analysis banner on the right, then click "Spectroscopy", then "PTMS"). So far in the first of these, pre-malignant cells in breast, prostate and cervical tissues have been characterised, and a summary of the completed EPSRC project may be seen at the EPSRC Project Summary.
The second project, recently awarded half a million pounds by BBSRC/EPSRC, aims to develop a technique which will enable researchers to accurately identify adult stem cells in the human body - opening up the possibility of new treatments for life-threatening diseases.
These techniques have now been adopted by more than 100 groups world-wide, both in industry and academia, to tackle hitherto insoluble problems in physics, chemistry, biology and material science.
By being the first to identify a new generic scanning probe technique, this group has been able to file three successful patents since 1995. The suite of six scanning probe microscopes is funded by EPSRC, JREI and by royalties from a highly innovative "Micro-thermal analysis" instrument, launched in March 1998.
Visit the individual research groups by clicking on their respective banner on the nightsky menu on the right.
How a scanning probe microscope works:
With classical optical microscopy, clearly there is and the limit to the spatial resolution set by the wavelength of the light used. In electron microscopy, the beam can degrade the sample through radiation damage or heating, and image contrast can be poor.
In each of the rapidly expanding number of new varieties of scanning probe microscopy (SPM), a probe or tip scans the sample surface (in some cases without making contact), and is used to obtain a continuous series of measurements of some particular physical quantity.
Corresponding to each point on the surface, the image contrast on a video monitor is determined by this measured value. In general, there is no need for special sample preparation procedures, and no vacuum is required.
The key concept in SPM is that of near-field microscopy, in which the spatial resolution is no longer diffraction-limited by the wavelength of any optical, electron or acoustic radiation. There are various varieties of SPM:
Atomic force microscopy (AFM)
In AFM, the force between probe and sample is measured.Virtually any solid surface may be imaged, in some cases at sub-nanometre resolution. An optical sensor detects the quasi-static or “d.c.” deflection of the force sensor or probe, consisting of a cantilever beam, of suitable spring constant,that carries the sharp tip.
A feedback loop adjusts an actuator (known as the “z- piezo” element), which controls the height of the tip above the sample surface (denoted by z ), so as to maintain the force (and hence the probe / sample separation) constant. The voltage needed to achieve this is used for imaging.
The basic idea of the scanning involves an electronic raster signal which tells the piezoelectric scanner (or “piezo”) to move either the sample or the probe, so as to scan in the plane of the sample surface. The usual type of AFM probe is a silicon nitride pyramid, whose square base measures, say, 5 microns square, with aspect ratio 1:1 and tip radius ca. 100 nm.
There are many other varieties of SPM. As the basis of micro-thermal analysis, scanning thermal microscopy is of special value: see microtherm1/imaging.htm.
