Four-point probe measurements using current probes with voltage feedback to measure electric potentials

We present a four-point probe resistance measurement technique which uses four equivalent current measuring units, resulting in minimal hardware requirements and corresponding sources of noise. Local sample potentials are measured by a software feedback loop which adjusts the corresponding tip voltage such that no current flows to the sample. The resulting tip voltage is then equivalent to the sample potential at the tip position. We implement this measurement method into a multi-tip scanning tunneling microscope setup such that potentials can also be measured in tunneling contact, allowing in principle truly non-invasive four-probe measurements. The resulting measurement capabilities are demonstrated for BiSbTe$_3$ and Si$(111)-(7\times7)$ samples

Thermoplastic deformation of silicon surfaces induced by ultrashort pulsed lasers in submelting conditions

A hybrid 2D theoretical model is presented to describe thermoplastic deformation effects on silicon surfaces induced by single and multiple ultrashort pulsed laser irradiation in submelting conditions. An approximation of the Boltzmann transport equation is adopted to describe the laser irradiation process. The evolution of the induced deformation field is described initially by adopting the differential equations of dynamic thermoelasticity while the onset of plastic yielding is described by the von Mise's stress. Details of the resulting picometre sized crater, produced by irradiation with a single pulse, are then discussed as a function of the imposed conditions and thresholds for the onset of plasticity are computed. Irradiation with multiple pulses leads to ripple formation of nanometre size that originates from the interference of the incident and a surface scattered wave. It is suggested that ultrafast laser induced surface modification in semiconductors is feasible in submelting conditions, and it may act as a precursor of the incubation effects observed at multiple pulse irradiation of materials surfaces.Comment: To appear in the Journal of Applied Physic

Analytical evaluation of the X-ray scattering contribution to imaging degradation in grazing-incidence X-ray telescopes

The focusing performance of X-ray optics (conveniently expressed in terms of HEW, Half Energy Width) strongly depend on both mirrors deformations and photon scattering caused by the microroughness of reflecting surfaces. In particular, the contribution of X-ray Scattering (XRS) to the HEW of the optic is usually an increasing function H(E) of the photon energy E. Therefore, in future hard X-ray imaging telescopes of the future (SIMBOL-X, NeXT, Constellation-X, XEUS), the X-ray scattering could be the dominant problem since they will operate also in the hard X-ray band (i.e. beyond 10 keV). [...] Several methods were proposed in the past years to estimate the scattering contribution to the HEW, dealing with the surface microroughness expressed in terms of its Power Spectral Density (PSD), on the basis of the well-established theory of X-ray scattering from rough surfaces. We faced that problem on the basis on the same theory, but we tried a new approach: the direct, analytical translation of a given surface roughness PSD into a H(E) trend, and - vice versa - the direct translation of a H(E) requirement into a surface PSD. This PSD represents the maximum tolerable microroughness level in order to meet the H(E) requirement in the energy band of a given X-ray telescope. We have thereby found a new, analytical and widely applicable formalism to compute the XRS contribution to the HEW from the surface PSD, provided that the PSD had been measured in a wide range of spatial frequencies. The inverse problem was also solved, allowing the immediate evaluation of the mirror surface PSD from a measured function H(E). The same formalism allows establishing the maximum allowed PSD of the mirror in order to fulfill a given H(E) requirement. [...]Comment: 10 pages, 6 figures, published in Astronomy & Astrophysics, sect. "Astronomical Instrumentation". In this version, a typo in two equations has been corrected. After the correction, the other results, formulae and conclusions in the paper remain unchange

Electronic structure of indium tungsten oxide alloys and their energy band alignment at the heterojunction to crystalline silicon

The electronic structure of thermally co evaporated indium tungsten oxide films is investigated. The stoichiometry is varied from pure tungsten oxide to pure indium oxide and the band alignment at the indium tungsten oxide crystalline silicon heterointerface is monitored. Using in system photoelectron spectroscopy, optical spectroscopy and surface photovoltage measurements we show that the work function of indium tungsten oxide continuously decreases from 6.3 eV for tungsten oxide to 4.3 eV for indium oxide, with a concomitant decrease of the band bending at the hetero interface to crystalline silicon than indium oxid

RNA secondary structure design

We consider the inverse-folding problem for RNA secondary structures: for a given (pseudo-knot-free) secondary structure find a sequence that has that structure as its ground state. If such a sequence exists, the structure is called designable. We implemented a branch-and-bound algorithm that is able to do an exhaustive search within the sequence space, i.e., gives an exact answer whether such a sequence exists. The bound required by the branch-and-bound algorithm are calculated by a dynamic programming algorithm. We consider different alphabet sizes and an ensemble of random structures, which we want to design. We find that for two letters almost none of these structures are designable. The designability improves for the three-letter case, but still a significant fraction of structures is undesignable. This changes when we look at the natural four-letter case with two pairs of complementary bases: undesignable structures are the exception, although they still exist. Finally, we also study the relation between designability and the algorithmic complexity of the branch-and-bound algorithm. Within the ensemble of structures, a high average degree of undesignability is correlated to a long time to prove that a given structure is (un-)designable. In the four-letter case, where the designability is high everywhere, the algorithmic complexity is highest in the region of naturally occurring RNA.Comment: 11 pages, 10 figure

Nanocrystalline n Type Silicon Front Surface Field Layers From Research to Industry Applications in Silicon Heterojunction Solar Cells

Nanocrystalline silicon and silicon oxide nc Si Ox H layers grown by plasma enhanced chemical vapor deposition PECVD have shown low parasitic absorption and excellent contact properties when implemented as n type front surface field FSF contact in rear junction silicon heterojunction SHJ solar cells [1 3]. In this contribution we present results from the successful process transfer from the lab at PVcomB at the Helmholtz Zentrum Berlin HZB , to the industrial pilot line at Meyer Burger Germany GmbH MBG . Conversion efficiencies gt; 22.5 were demonstrated on SHJ cell 4 cm2 [2, 3]. The excellent cell performance in the lab and the potential to reduce parasitic absorption in the front stack by using nc SiOx H motivated the process transfer from HZB to MBG. Initial cross processing experiments on 244 cm2 wafers showed the benefit of using nc Si H as FSF layer. We here also emphasize the role of the Si texture on a fast nc Si H nucleation. After cross processing experiments a successful transfer of the nc Si H process and fine tuning resulted in a median cell efficiency of 23.4 . This is in the same range as the MGB reference on 244 cm2 cells, noteworthy, at the same throughput. Currently work is ongoing to further improve the optical performance of the cells by adding oxygen CO

\u3ci\u3eDrosophila\u3c/i\u3e Model for Potential Plasticizer Induced Hyperactivity

Plasticizing additives such as phthalates, are known to cause disruptions in human nervous systems linked to neurological disorders, thus with the Drosophila activity monitoring (DAM) system test can be conducted to consider whether the flies are exhibiting hyperactivity (Hlisníková et al., 2021). Drosophila is a useful model for exposure of metabolic compounds followed by general and specific assays of their effects. Our experiments propose a link between exposure to phthalates and hyperactivity between humans that can be investigated with flies as a model for testing hyperactivity (Praveena et al., 2020). The link that is proposed is a cross-sectional study that collected urine samples of children and then scored kids based on attention-deficit/hyperactivity disorder (ADHD) (Kim et al., 2009). The DAM system is a method in which flies are individually monitored for activity during the day and night to notice any differences in general activity, locomotion, and circadian rhythms. The general activities of the flies would be examined alongside a baseline of Drosophila activity, alongside flies induced with glucose to measure any differences in hyperactivity. The addition of glucose is to give a baseline of what hyperactive flies will look like in their sleep cycle and movements in the DAM system We hypothesize a significant increase in hyperactivity in phthalate-exposed flies over both high-glucose and normal flies because phthalates are disrupters in the nervous system, thus may cause signs of hyperactivity when administered to the flies

A note on anti-coordination and social interactions

This note confirms a conjecture of [Bramoull\'{e}, Anti-coordination and social interactions, Games and Economic Behavior, 58, 2007: 30-49]. The problem, which we name the maximum independent cut problem, is a restricted version of the MAX-CUT problem, requiring one side of the cut to be an independent set. We show that the maximum independent cut problem does not admit any polynomial time algorithm with approximation ratio better than $n^{1-\epsilon}$, where $n$ is the number of nodes, and $\epsilon$ arbitrarily small, unless P=NP. For the rather special case where each node has a degree of at most four, the problem is still MAXSNP-hard.Comment: 7 page