
Yay for me! I've highjacked the thread!
I'm actually 35.1 years old, so that`s just more a suggestion.stardust wrote:pubertal bachelor party ?
Did you read how the atomic force microscopy works? It is very interesting.stardust wrote:http://www.physik.uni-regensburg.de/for ... es_e.shtml
Quantummechanical tunneling-effect: When approaching two biased conductors, the current increases exponentially by a factor of 10 for each 0.1nm reduction in distance before they finally make contact.
Cross-section through tip and sample in STM (contour-lines indicate constant charge density)
Because of the sharp increase in tunneling current with decreasing distance, even tips with moderate sharpness yield atomic resolution easily, because the front atom carries the lion´s share of the tunneling current!
Operation with sub-nm amplitudes is thus only possible using very stiff cantilevers (k ≈ 1 kN/m). Traditional silicon cantilevers with such a large stiffness are usually not available, moreover they suffer from two additional disadvantages:
1. The tips of microfabricated Si cantilevers point in a [001]-crystal direction - an unfavorable orientation, see [10].
2. The eigenfrequency of Si-cantilevers varies strongly with temperature (-58 ppm/K). Oscillators with low temperature drift are important in watch technology. Today, most watches utilize quartz tuning forks as time-keeping elements.
Quartz tuning forks for watches are two coupled oscillators, housed in an evacuated metal case. Most of them come with an eigenfrequency f0 = 32 768 = 215 Hz. We build cantilevers from these tuning forks by attaching one prong to a large-mass substrate and mounting a tip to the free prong, creating the 'qPlus-Sensor' [8]. Its eigenfrequency is approximately 20 kHz (depending on the mass of the tip), and the spring constant of our favorite tuning forks (taken from Swatch-watches) is k = 1800 N/m.
The advantages offered by high-stiffness, small-amplitude FM AFM have been demonstrated by experimental imaging of single atoms with "subatomic" resolution, i.e. structures within a single atom related to the orbital charge density have been resolved.
Experimental AFM image of a single atom
http://www.physik.uni-regensburg.de/for ... xm_e.shtml