Spiral Growth and Step Edge Barriers

The growth of spiral mounds containing a screw dislocation is compared to the growth of wedding cakes by two-dimensional nucleation. Using phase field simulations and homoepitaxial growth experiments on the Pt(111) surface we show that both structures attain the same characteristic large scale shape when a significant step edge barrier suppresses interlayer transport. The higher vertical growth rate observed for the spiral mounds on Pt(111) reflects the different incorporation mechanisms for atoms in the top region and can be formally represented by an enhanced apparent step edge barrier.Comment: 11 pages, 4 figures, partly in colo

Surface characterization of epitaxial Cu-rich CuInSe2 absorbers

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient conditions before and after potassium cyanide (KCN) etching. In both cases, we do not see any substantial contrast in the surface potential data; furthermore, after the KCN etching we observed outgrowths with a height around 2nm over the sample surface. On the other hand, the KPFM measurements under ultra-high vacuum conditions show a work function dependence according to the surface orientation of the Cu-rich CuInSe 2 crystal. Our results show the possibility to increase the efficiency of epitaxial Cu-rich CuInSe 2 by growing the materials in the appropriated surface orientation where the variations in work function are reduced

The impact of Kelvin probe force microscopy operation modes and environment on grain boundary band bending in perovskite and Cu(In,Ga)Se2 solar cells

An in-depth understanding of the electronic properties of grain boundaries (GB) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that amplitude modulation AM-KPFM, which is by far the most common KPFM measurement mode, is not suitable to measure workfunction variations at GBs on rough samples, such as Cu(In,Ga)Se2 and CH3NH3PbI3. This is a direct consequence of a change in the cantilever-sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation FM-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers

Competition of terrace and step-edge sputtering under oblique-incidence ion impact on a stepped Pt(111) surface

Using molecular-dynamics simulation, we study the sputtering of a Pt(111) surface under oblique and glancing incidence 5 keV Ar ions. For incidence angles larger than a critical angle theta(c), the projectile is reflected off the surface and the sputter yield is zero. We discuss the azimuth dependence of the critical angle theta(c) with the help of the surface corrugation felt by the impinging ion. If a step exists on the surface, sputtering occurs also for glancing incidence theta > theta(c). We demonstrate that for realistic step densities, the total sputtering of a stepped surface may be sizable even at glancing incidence. (C) 2009 Elsevier B.V. All rights reserved

Step-edge sputtering through grazing incidence ions investigated by scanning tunneling microscopy and molecular dynamics simulations

Scanning tunneling microscopy is used to quantify step-edge sputtering of Pt(111) at 550 K by grazing incidence ion bombardment with 5 keV Ar(+) ions. For bombardment conditions causing negligible erosion on terraces, damage features associated with step bombardment allow us to visualize step retraction and thus to quantify the step-edge sputtering yield. An alternative method for step-edge yield determination, which is applicable under more general conditions, is the analysis of the concentration of ascending steps together with the removed amount as a function of ion fluence. Interestingly, the azimuthal direction of the impinging ions with respect to the surface significantly changes the sputtering yield at step edges. This change is attributed to the orientation dependence of subsurface channeling. Atomistic insight into step-edge sputtering and its azimuthal dependence is given by molecular dynamics simulations of ion impacts at 0 and 550 K. The simulations also demonstrate a strong dependence of the step-edge sputtering yield on temperature

Influence of a single adatom on sputtering at grazing incidence - A molecular-dynamics case study of 5 keV Ar impact on Pt (111)

Grazing incidence ion impact on a flat terrace lets the projectile reflect specularly off the surface, leading to little or no damage production or sputtering. The presence of isolated surface defects may change this behaviour drastically. We investigate this phenomenon for the specific case of 5 keV Ar ions impinging at 83 degrees towards the surface normal onto the Pt (111) surface. Molecular-dynamics simulations allow to study the influence of isolated adatoms in detail. The scattering of the projectile from the adatom can redirect the projectile, or let the adatom recoil, such that either of them deposits considerable energy in the target surface, leading to abundant damage production and sputtering. Two distinct collision zones are identified: (i) When the projectile hits the surface in front of the adatom, it may collide with the adatom indirectly (after being specularly reflected off the surface); (ii) alternatively, it may hit the adatom directly. We quantify our results by measuring the zone of influence (congruent to 13 angstrom(2)) around the adatom, into which the projectile must hit in order to collide with the adatom, and by the sputter cross section of roughly 110 angstrom(2). The data compare well with previous simulation results of sputtering from an atomically rough surface. (C) 2008 Elsevier B.V. All rights reserved

Sputtering at grazing ion incidence: Influence of adatom islands

When energetic ions impinge at grazing incidence onto an atomically flat terrace, they will not sputter. However, when adatom islands (containing N atoms) are deposited on the surface, they induce sputtering. We investigate this effect for the specific case of 83 degrees-incident 5 keV Ar ions on a Pt (111) surface by means of molecular-dynamics simulation and experiment. We find that-for constant coverage Theta-the sputter yield has a maximum at island sizes of N congruent to 10-20. A detailed picture explaining the decline of the sputter yield toward larger and smaller island sizes is worked out. Our simulation results are compared with dedicated sputtering experiments, in which a coverage 0.09 of Pt adatoms are deposited onto the Pt (111) surface and form islands with a broad distribution around a most probable size of N congruent to 20

Assessment of the risk of an accident at the turner's workplace

Статья посвящена оценке риска возникновения несчастного случая на рабочем месте токаря. Показана статистическая информация о количестве несчастных случаев людей на производстве. Приведены наиболее травмоопасные виды экономической деятельности. Определены опасности и возможные причины их возникновения на рабочем месте токаря. По построенному дереву причин и результатам опросных листов рассчитана вероятность опасного события. На основе наиболее вероятных причин предложены мероприятия для их устранения.The article is devoted to the assessment of the risk of an accident at the turner's workplace. Shows statistical information on the number of accidents at work. The most traumatic types of economic activities are presented. The dangers and possible causes of their occurrence at the turner's workplace are determined. Based on the constructed tree of reasons and the results of questionnairesthe probability of a dangerous event was calculated. Based on the most probable causesmeasures are proposed to eliminate them