Correlation length exponent ν for long linear DNA molecules was determined by direct measurement of the average end-to-end distance as a function of the contour length s by means of atomic force microscopy (AFM). Linear DNA, up to 48'502 base pairs (bp), was irreversibly deposited from a solution onto silanized mica and imaged in air. Under the adsorption conditions used, the DNA is trapped onto the surface without any two-dimensional equilibration. The measured exponent is ν = 0.589 ± 0.006, in agreement with the theoretical 3D value of ν = 0.5880 ± 0.0010.The persistence length ℓ p of DNA was estimated to be 44±3 nm, in agreement with the literature values. The distribution of the end-to-end distances for a given contour length s and the exponents characterizing the distribution were determined for different s. For s smaller or comparable to ℓ p , a delta function like distribution was observed, while for larger s, a probability distribution of the type x d−1 x g e −bx δ was observed with g = 0.33±0.22 and δ = 2.58±0.76. These values are compared to the theoretical exponents for Self-Avoiding Walk (SAW): namely g = γ−1 ν and δ = (1 − ν) −1 . So for d = 2, g ≈ 0.44 and δ = 4, while for d = 3, g ≈ 0.33 and δ ≈ 2.5. The derived entropic exponent γ is γ = 1.194 ± 0.129. The present data indicate that the DNA behaves on large length scales like a 3 dimensional SAW.

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Atomic force microscopy (AFM) investigations of living cells provide new information in both biology and medicine. However, slow cell dynamics and the need for statistically significant sample sizes mean that data collection can be an extremely lengthy process. We address this problem by parallelizing AFM experiments using a two-dimensional cantilever array, instead of a single cantilever. We have developed an instrument able to operate a two-dimensional cantilever array, to perform topographical and mechanical investigations in both air and liquid. Deflection readout for all cantilevers of the probe array is performed in parallel and online by interferometry. Probe arrays were microfabricated in silicon nitride. Proof-of-concept has been demonstrated by analyzing the topography of hard surfaces and fixed cells in parallel, and by performing parallel force spectroscopy on living cells. These results open new research opportunities in cell biology by measuring the adhesion and elastic properties of a large number of cells. Both properties are essential parameters for research in metastatic cancer development.

In order to simulate the performance of the present day state-of-the-art multijunction solar cells in its entirety, an integrated electrical-optical model has been developed. The one-dimensional ab initio electrical model for the analysis of the transport properties of such devices can handle a very general semiconductor device structure where the material properties vary with position and the gap state properties with position and energy. The original semi-empirical optical model used takes into account both specular interference effects, and diffused reflectances and transmittances due to interface roughness. The latter are derived from angular-resolved photometric measurements and used as input parameters to the numerical programme. Comparison of the illuminated current density-voltage (J-V) characteristics, calculated on the basis of (a) a simple exponential absorption law and (b) the optical model, reveals an increase of ˜1 mA cm−2 in the short-circuit current and ˜8% in the cell conversion efficiency for case (b). Also the long wavelength quantum efficiency (QE) shows a marked improvement, while the blue QE decreases since proper account is taken of the absorption in the transparent conducting oxide and reflection from the device. The combined model is being applied to simulate the characteristics of wideband-gap-emitter-layer solar cells deposited in a three chamber conventional glow discharge reactor onto (i) highly textured SnO2 and (ii) weakly textured indium tin oxide substrates. The cells have been characterised experimentally by J-V and QE measurements. Preliminary results indicate that the integrated model matches the experimental J-V and QE data with a more realistic set of material parameters as compared to case (a).