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In SPIE Defense, Security, and Sensing, Vol. 8042 (13 May 2011), pp. 80360O-80360O-10, doi:10.1117/12.886347
Abstract
Secondary electron energy distribution (SEED) from Mo, Ni and Pt was measured in helium ion microscope (HeIM) with semispherical retarding potential technique. For all investigated metals the energy position of the SEED maximum and the SEED width in HeIM is found to be noticeably less than in conventional scanning electron microscope and even less than predicted by previous numerical simulations. A simple analytical phenomenological function to describe the SEED shape is suggested. The reasons of the lower energy transfer efficiency in ...
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Abstract
Background: The unique surface sensitivity and the high resolution that can be achieved with helium ion microscopy make it a competitive technique for modern materials characterization. As in other techniques that make use of a charged particle beam, channeling through the crystal structure of the bulk of the material can occur. Results: Here, we demonstrate how this bulk phenomenon affects secondary electron images that predominantly contain surface information. In addition, we will show how it can be used to obtain crystallographic information. ...
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Abstract
Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons. Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light ...
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Abstract
The mechanical properties of nanocrystalline materials are reviewed, with emphasis on their constitutive response and on the fundamental physical mechanisms. In a brief introduction, the most important synthesis methods are presented. A number of aspects of mechanical behavior are discussed, including the deviation from the Hall–Petch slope and possible negative slope, the effect of porosity, the difference between tensile and compressive strength, the limited ductility, the tendency for shear localization, the fatigue and creep responses. The strain-rate sensitivity of FCC metals ...
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Abstract
When a crystal deforms plastically, phenomena such as dislocation storage, multiplication, motion, pinning, and nucleation occur over the submicron-to-nanometer scale. Here we report measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals. We find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes. The results show dramatic size effects at surprisingly large sample dimensions. These results emphasize that at the micrometer scale, one must define both ...
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Abstract
Insights into conducting research and the writing of scientific papers are given by Prof. Whitesides in this short essay. The manuscript and its guidelines has been circulated within the Whitesides' research group since 1989. ...
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(13 Oct 2009)
posted to graphene him lithography oxide silicon
by lawa
on 2012-10-11 15:35:10
Abstract
We report nanoscale patterning of graphene using a helium ion microscope configured for lithography. Helium ion lithography is a direct-write lithography process, comparable to conventional focused ion beam patterning, with no resist or other material contacting the sample surface. In the present application, graphene samples on Si/SiO2 substrates are cut using helium ions, with computer controlled alignment, patterning, and exposure. Once suitable beam doses are determined, sharp edge profiles and clean etching are obtained, with little evident damage or doping to the sample. This technique provides fast lithography compatible ...
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Abstract
We report recent experimental work on electron emission from clean polycrystalline metal surfaces under ion bombardment. We critically discuss existing theories and point out the presently unsolved problems. ...
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Note (first note only)
The abstract from Bethe can be found on page 28/33 point 136. On the Theory of Secondary Emission.
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Abstract
A new and thorough examination of secondary electron (SE) yield as a function of primary energy (EPE) and atomic number Z for the 44 elements in the database1 is made. The principles of the semiempirical universal law for the SE yield are described and a template for Monte Carlo (MC) simulation is produced accordingly. Both universal curve fitting and MC simulation are made for the 44 elements. The resulted maximum SE yield δm, corresponding primary energy $E_ PE^ m$, SE excitation ...
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Abstract
Secondary electron yields depending on work function were measured for 30 species of metal in ultrahigh vacuum by electron and ion bombardment. Secondary electron yields induced by electrons at 10 keV increase with work function, while those by Ar+ ions at 3 keV decrease with increasing work function. The opposite dependencies of secondary electron yields on work function between electron and ion bombardment are discussed on the basis of the different mechanisms of secondary electron emission, i.e., kinetic and potential emission ...
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Abstract
Monte Carlo simulations have been widely used by microscopists for the last few decades. In the beginning it was a tedious and slow process, requiring a high level of computer skills from users and long computational times. Recent progress in the microelectronics industry now provides researchers with affordable desktop computers with clock rates greater than 3 GHz. With this type of computing power routinely available, Monte Carlo simulation is no longer an exclusive or long (overnight) process. The aim of this ...
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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 20, No. 3. (2002), 950, doi:10.1116/1.1472415
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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, Vol. 29, No. 6. (2011), 06F901, doi:10.1116/1.3643752
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(August 2009)
Abstract
The scanning electron microscope (SEM) is a popular instrument used for imaging because of its high resolution images it can generate. However the new scanning helium ion scanning microscope (SHIM) can produce higher resolution and better contrast images than the conventional SEM. In both the microscopes secondary electron (SE) signal is the most widely used imaging mode because of their high yield efficiency and their high spatial resolution. In order to be able to properly evaluate the relative strengths and weaknesses ...
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Abstract
Solution-processed tandem polymer solar cells are demonstrated using stacked perovskite, (TBA,H)Ca2Nb3O10 (CNO), semiconductor nanosheets as an electron transport layer (ETL) within the recombination layers. Two poly(3-hexylthiophene):(6,6)-phenyl-C61-butyric acid methyl ester, P3HT:PCBM, sub-cells connected in series via a CNO-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), Pedot:PSS, recombination layer provide a Voc of 1.02 V. The Voc is less than double that of a single junction due to leakage (dark) current. When TiOx is used as an additional hole-blocking layer within the recombination stack, the Voc is improved to 1.16 ...
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Abstract
The scanning helium ion microscope has been used in transmission mode to investigate both the feasibility of this approach and the utility of the signal content and the image information available. Operating at 40 keV the penetration of the ion beam, and the imaging resolution achieved, in MgO crystals was found to be in good agreement with values predicted by Monte Carlo modeling. The bright-field and annular dark-field signals displayed the anticipated contrasts associated with beam absorption and scattering. In addition, ...
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Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 â July 30, 2009 ...
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Abstract
We show that the different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons and fullerenes can be distinguished by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)–functionalized tip. We found two different contrast mechanisms, which were corroborated by density functional theory calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images ...
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Abstract
Ultrathin films of para-hexaphenyl (6P) were prepared on freshly cleaved and sputter-amorphized mica(001) by physical vapor deposition. Ex situ atomic force microscopy (AFM) revealed a bimodal island size distribution for the films on both surfaces. On freshly cleaved mica long needlelike islands exist, which are surrounded by small crystallites. On the sputter-amorphized substrates, large dendritic islands exist which are again surrounded by small, compact islands. We could prove by thermal desorption spectroscopy that the small islands are the result of adsorbate-induced ...
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posted to 6p afm diffusion growth oxide silicon
by lawa
on 2012-08-29 09:58:10
Abstract
The nucleation and growth of organic molecules is usually discussed in the framework of diffusion limited aggregation (DLA). In this letter we demonstrate for the rod-like organic molecules hexaphenyl (6P) on sputter-modified mica, that under specific experimental conditions the nucleation has to be described by attachment limited aggregation (ALA). The crucial parameter for the growth mode is the roughness of the substrate surface, as induced by ion sputtering. With decreasing surface roughness the diffusion probability of the molecules increases and the ...
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Abstract
Using atomistic computer simulations based on analytical potential and density-functional theory models, we study effects of ion irradiation on graphene. We identify the types and concentrations of defects which appear in graphene under impacts of various ions with energies ranging from tens of electron volts to mega-electron volts. For two-dimensional targets, defects beyond single and double vacancies are formed via in-plane recoils. We demonstrate that the conventional approach based on binary-collision approximation and stochastic algorithms developed for bulk solids cannot be ...
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Abstract
We have used helium ion microscopy to directly track the subsurface diffusion of Pd through a Si stack in a non-invasive manner. The imaging and analysis of semiconductor structures along a direction perpendicular to the substrate is traditionally performed by making cross sections of a sample and viewing those at high magnification in a charged particle beam microscope. Two evident limitations of this approach are the destructive nature of the preparation procedure and the limited amount of information that can be ...
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Abstract
This work focuses on the structural and morphological studies of the evolution of epitaxially grown para-sexiphenyl (p-6P) thin films on freshly cleaved KCl(1 0 0) surfaces. The film growth is varied using growth times between 5 sec and 60 min and substrate temperatures in the range of 80–150 °C. The study is based on a combination of X-ray diffraction to derive structural information on the molecular scale, and atomic force as well as electron microscopy to obtain morphological information. The initial growth orientation of p-6P crystallites ...
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(December 2011)
Abstract
This PhD thesis addresses two major issues: 1) Fabricating nanometer-scale patterns of functional materials, 2) Extending the applicability of soft lithographic processes to a wide range of functional materials on conventional silicon substrates and flexible plastic substrates. This thesis describes novel soft lithographic processes, with which it is possible to fabricate sub-50 nanometer to micrometer length scale patterns of a wide range of functional materials, including metals, nanoparticles, organosilane molecules, nanowires, semiconducting materials and conducting polymers on silicon and flexible plastic substrates. Chapter 2 describes ...
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Abstract
Semiconductor nanostructures – and in particular ensembles of them – are the prerequisites for the ongoing miniaturization in microelectronics. Since lithographic techniques become increasingly expensive and technologically complex, self-organization into quasiperiodic nanostructure arrays is an elegant alternative. Here, strain-induced pattern formation in SiGe/Si(001), ion bombardment induced self-organization of inorganic semiconductors, and crystallite ordering in oligophenylene films are presented as illustrative examples for nanostructure self-organization that is not at all restricted to semiconductor systems. ...
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by Thomas Höfler, Anna M. Track, Peter Pacher, et al.Quan Shen, Heinz-Georg Flesch, Gregor Hlawacek, Georg Koller, Michael G. Ramsey, Robert Schennach, Roland Resel, Christian Teichert, Wolfgang Kern, Gregor Trimmel, Thomas Griesser
Abstract
The photolithographic modification of thin functional silane layers provides a versatile and powerful means of fabricating functionalized patterned surfaces which can be applied for tuning inorganic surface properties and for modern immobilisation techniques. In this contribution we present the synthesis of a new functional trichloro organosilane bearing photoreactive aryl ester groups and its application in thin silane layers on silicon oxide surfaces. Whereas the trichlorosilyl group acts as anchoring unit to the inorganic surface, the aryl ester group undergoes the photo-Fries ...
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(June 2012)
Abstract
New biomaterials are being developed to meet the bone healing needs of patients. When these biomaterials encounter cells in the tissues within the body, their physico-chemical properties (namely their chemical composition and structural properties) will impact the way cells behave and consequently influence the materials? therapeutical capacity. It is known that stem cells can commit to specific lineages depending on the physico-chemical properties of these biomaterials. However, this cross-talk between cells and materials needs to be understood and the contributing signals unraveled. ...
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J. Am. Chem. Soc. In Journal of the American Chemical Society, Vol. 133, No. 24. (23 May 2011), pp. 9208-9211, doi:10.1021/ja2025855
Abstract
The competition between intermolecular interactions and lateral variations in the molecule?substrate interactions has been studied by scanning tunneling microscopy (STM), comparing the phase formation of (sub)monolayers of the organic molecule 2,4?-BTP on buckled graphene/Ru(0001) and Ag(111) oriented thin films on Ru(0001). On the Ag films, the molecules form a densely packed 2D structure, while on graphene/Ru(0001), only the areas between the maxima are populated. The findings are rationalized by a high corrugation in the adsorption potential for 2,4?-BTP molecules on graphene/Ru(0001). ...
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(1979)
Abstract
Silica, the major component of the earth’s solid surface and the constituent of ordinary sand, becomes involved at some point in a great many phases of modern technology and science. It is an essential material in many, if not all, forms of life. Its role in human disease, aging, and health is just beginning to be explored. Here is a comprehensive account of the basic chemistry involved in a wide range of research and development activities, as well as a wealth ...
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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 21, No. 5. (2003), S96, doi:10.1116/1.1600454
Abstract
A review is given of nucleation and growth models as applied to the earliest stages of thin film growth. Rate equations, kinetic Monte Carlo, and level set simulations are described in some detail, with discussion of remaining uncertainties, in particular the functional form of the so-called capture numbers in rate equations. Recent examples are given of sub-monolayer nucleation at surface defects, attachment-limited capture, and Ostwald ripening. The experimental literature is cited, and experiment–theory comparisons are made where possible. Emphasis is given ...
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J. Phys. Chem. B In The Journal of Physical Chemistry B, Vol. 112, No. 26. (30 May 2008), pp. 7816-7820, doi:10.1021/jp711455u
posted to afm dla para-sexiphenyl
by lawa
on 2012-06-08 13:07:00
Abstract
The para-sexiphenyl (p-6P) monolayer film induces weak epitaxy growth (WEG) of disk-like organic semiconductors, and their charge mobilities are increased dramatically to the level of the corresponding single crystals [Wang et al., Adv. Mater. 2007, 19, 2168]. The growth behavior and morphology of p-6P monolayer film play decisive roles on WEG. Here, we investigated the growth behavior of p-6P submonolayer film as a function of the substrate temperature. Its growth exhibited two different mechanisms at high and low substrate temperature. At ...
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Abstract
A review is given of the nucleation and growth processes occurring in thin film formation. Emphasis is given to quantitative nucleation theories and to the role of electron microscopy and surface techniques in providing data to test such theories. The relations between the thermodynamics of adsorption and the kinetics of crystal growth is stressed. Experimental examples are taken from the island growth, layer plus island (or Stranski-Krastanov) and layer growth modes. The shapes of growing crystallites are briefly discussed. ...
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Abstract
We present experimental and theoretical findings on the geometry of polycrystalline para hexaphenyl via Raman scattering. The planarity of the molecule is affected by hydrostatic pressure and temperature. Our studies indicate that the potential energy curve which governs the torsional motion between neighboring phenyl rings is “W” shaped. We determine the activation energy to promote the molecule from a nonplanar to a planar state to be 0.04 eV, in good agreement with our quantum chemical calculations. From the relative intensities of ...
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Abstract
Phenylene oligomers, which are low molecular weight materials of the Ï-conjugated polymer of poly(p-phenylene), PPP, have been examined for their unique electrical and optical properties. Recently, the vacuum-deposited thin films of oligophenylenes were applied to light-emitting diodes (LED), non-linear optical (NLO) devices, etc. In this study, highly crystalline p-sexiphenyl (6P) thin films were prepared on an ionic crystal substrate (potassium chloride, KCl) by using organic molecular beam deposition technique. The crystal structure, molecular orientation and morphology of thin films prepared at ...
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(2001)
Abstract
The structure of a growth or an etch front on a surface is not only a subject of great interest from the practical point of view but also is of fundamental scientific interest. Very often surfaces are created under non-equilibrium conditions such that the morphology is not always smooth. In addition to a detailed description of the characteristics of random rough surfaces, Experimental Methods in the Physical Sciences, Volume 37, Characterization of Amorphous and Crystalline Rough Surface-Principles and Applications will focus ...
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Abstract
It is postulated that steps on crystal surfaces capture atoms diffusing on the surface with certain probabilities and, in addition, that the capture probability depends on the direction from which adsorbed atoms approach the step. A general solution for the time‐dependent step distribution is obtained in terms of these probabilities and an arbitrary initial distribution of an infinite sequence of parallel steps. It is shown that coalescence of steps or stabilization of step spacings can occur as a consequence of assuming ...
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Abstract
The statistics of surface diffusion phenomena are developed for the conditions appropriate to measurements in the field‐ion microscope. Examined in detail are: (1) The effect of boundaries (lattice steps) on the mean‐square displacement in a random walk; (2) the probability density for distances traversed in a two‐dimensional walk along nonorthogonal surface channels; (3) the distribution of distances for random walks in which the number of jumps is subject to fluctuation, as it is in real systems. Both reflecting and adsorbing boundaries ...
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Abstract
Surface diffusion of tungsten adatoms on several smooth, low‐index planes of the tungsten lattice has for the first time been followed by direct observation of individual atoms in the field‐ion microscope. Contrary to expectation, the mobility at room temperature is found to increase in the order (211) > (321) ∼ (110) > (310) ∼ (111). Migrating atoms are reflected at the boundaries of the (110), (211), and (321) planes; on the latter two, motion along atomic rows is favored over diffusion ...
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J. Am. Chem. Soc. In Journal of the American Chemical Society, Vol. 133, No. 9. (10 February 2011), pp. 3056-3062, doi:10.1021/ja109729e
by Clemens Simbrunner, Dmitrii Nabok, Gerardo Hernandez-Sosa, et al.Martin Oehzelt, Tatjana Djuric, Roland Resel, Lorenz Romaner, Peter Puschnig, Claudia Ambrosch-Draxl, Ingo Salzmann, Günther Schwabegger, Irene Watzinger, Helmut Sitter
Abstract
During the last years, self-assembled organic nanostructures have been recognized as a proper fundament for several electrical and optical applications. In particular, phenylenes deposited on muscovite mica have turned out to be an outstanding material combination. They tend to align parallel to each other forming needlelike structures. In that way, they provide the key for macroscopic highly polarized emission, waveguiding, and lasing. The resulting anisotropy has been interpreted so far by an induced dipole originating from the muscovite mica substrate. Based ...
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Abstract
Ionoluminescence (IL) has mainly been used to detect impurities or defects inside synthetic materials. This paper gives a summary of new applications of IL to natural minerals that might be found in ancient pieces of jewellery or decorative artefacts (affreschi, stucchi, mosaics). Some relevant examples of its use for archaeometrical purposes are given to highlight the potential of the technique. Chemical information can be obtained by luminescent characterization of minerals. IL spectra act as digital imprint for elements or defects inside ...
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Abstract
Crystal growth far from thermodynamic equilibrium is nothing but homoepitaxy - thin film growth on a crystalline substrate of the same material. Because of the absence of misfit effects, homoepitaxy is an ideal playground to study growth kinetics in its pure form. Despite its conceptual simplicity, homoepitaxy gives rise to a wide range of patterns. This book explains the formation of such patterns in terms of elementary atomic processes, using the well-studied Pt/Pt(111) system as a reference point and a large ...
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Abstract
We have prepared organic thin-film transistors (OTFTs) featuring pentacene molecules deposited at various substrate temperatures onto either hexamethyldisilazane (HMDS)- or poly(α-methylsyrene) (PαMS)-treated SiO 2 surfaces. As a result, we obtained different grain boundary densities in the conducting channel. Since the surface-modified devices featured similar grain boundary densities in their active layers, but displayed different electrical performances, we suspected that different trap states probably existed at the grain boundaries for the two different kinds of OTFTs. In addition, the surface morphologies ...
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