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Isaac Balberg

Bio: Isaac Balberg is an academic researcher from The Racah Institute of Physics. The author has contributed to research in topics: Silicon & Percolation. The author has an hindex of 44, co-authored 244 publications receiving 8359 citations. Previous affiliations of Isaac Balberg include Hebrew University of Jerusalem & Princeton University.


Papers
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Journal ArticleDOI
Abstract: The general relationship between the percolation threshold of systems of various objects and the excluded volume associated with these objects is discussed. In particular, we derive the average excluded area and the average excluded volume associated with two- and three-dimensional randomly oriented objects. The results yield predictions for the dependencies, of the percolation critical concentration of various kinds of "sticks," on the stick aspect ratio and the anisotropy of the stick orientation distribution. Comparison of the present results with available Monte Carlo data shows that the percolation threshold of the sticks is described by the above dependencies. On the other hand, the numerical values of the excluded area and the excluded volume are not dimensional invariants as suggested in the literature, but rather depend on the randomness of the stick orientations. The usefulness of the present results for percolation-threshold problems in the continuum is discussed. In particular, it is shown that the excluded area and the excluded volume give the number of bonds per object ${B}_{c}$ when the objects are all the same size. In the case where there is a distribution of object sizes, the proper average of the excluded area or volume is a dimensional invariant while ${B}_{c}$ is not.

817 citations

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TL;DR: In this paper, it was shown that hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device-quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament.
Abstract: Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

464 citations

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TL;DR: In this article, a simple model based on interparticle tunneling conduction and a percolative network is shown to imply a diverging distribution of high resistors in the system.
Abstract: A simple model based on interparticle tunneling conduction and a percolative network is shown to imply a diverging distribution of high resistors in the system. This distribution is expected to yield a nonuniversal behavior of the electrical conductivity. An experimental study of carbon black--polymer composites seems to confirm this expectation, as well as explaining why a nonuniversal behavior has not been observed in previous experimental studies on such composites.

452 citations

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TL;DR: In this paper, the authors reported the dependence of the percolation threshold of the three-dimensional sticks systems on aspect ratio and macroscopic anisotropy, and determined the excluded volume of the sticks.
Abstract: We report the dependence of the percolation threshold of the three-dimensional sticks systems on aspect ratio and on macroscopic anisotropy. This Monte Carlo study is the first determination of percolation thresholds for randomly oriented objects in three-space. The results show that the above dependence is determined by the excluded volume of the sticks. However, the total excluded volume of randomly oriented objects is lower than that of the same objects in parallel alignment.

397 citations

Journal ArticleDOI
TL;DR: In this paper, a Monte Carlo study of the percolation threshold in two-dimensional systems of conducting sticks was carried out and it was shown that in the case of random alignments, the anisotropy dependence of the conductivity is determined by both the percoation threshold and the critical exponent.
Abstract: We report here a Monte Carlo study of the percolation threshold in two-dimensional systems of conducting sticks. This is an extension of the work of Pike and Seager, who have considered only the isotropic sample of randomly-oriented---, equal-length---sticks system. Our study is concerned with the dependence of the percolation threshold on the macroscopic anisotropy of systems in which there is a preferred orientation of the sticks ensemble, as well as on the distribution of the sticks' lengths. In particular, we studied systems in which the orientation is determined by random alignments within a given interval or in which the alignments are normally distributed around a given direction. Similarly, for the sticks' lengths we have studied systems of equal lengths, of normally distributed lengths, and of log-normally distributed lengths. The results have shown that the percolation threshold always increases with the macroscopic anisotropy. Extrapolation of the results, from those of the finite sticks ensembles used to the infinite ensemble case, has indicated that in the infinite ensemble the percolation threshold is isotropic. It is found that the broader the stick-length distribution, the lower the mean of the distribution needed for the onset of percolation. Application of the present results for the evaluation of the conductivity indicates that the anisotropy dependence of the conductivity in systems of conducting fibers is determined by both the anisotropy dependence of the percolation threshold and the anisotropy dependence of the critical exponent. If (as found experimentally) a practically infinite two-dimensional system has a conductivity anisotropy, it must be attributed to the anisotropy in the latter parameter.

323 citations


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Journal ArticleDOI
TL;DR: The renormalization group theory has been applied to a variety of dynamic critical phenomena, such as the phase separation of a symmetric binary fluid as mentioned in this paper, and it has been shown that it can explain available experimental data at the critical point of pure fluids, and binary mixtures, and at many magnetic phase transitions.
Abstract: An introductory review of the central ideas in the modern theory of dynamic critical phenomena is followed by a more detailed account of recent developments in the field. The concepts of the conventional theory, mode-coupling, scaling, universality, and the renormalization group are introduced and are illustrated in the context of a simple example---the phase separation of a symmetric binary fluid. The renormalization group is then developed in some detail, and applied to a variety of systems. The main dynamic universality classes are identified and characterized. It is found that the mode-coupling and renormalization group theories successfully explain available experimental data at the critical point of pure fluids, and binary mixtures, and at many magnetic phase transitions, but that a number of discrepancies exist with data at the superfluid transition of $^{4}\mathrm{He}$.

4,980 citations

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TL;DR: This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.
Abstract: Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.

3,452 citations

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TL;DR: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area, and when incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading.
Abstract: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...

2,979 citations

Journal ArticleDOI
07 Jan 2011-Polymer
TL;DR: A survey of the literature on polymer nanocomposites with graphene-based fillers including recent work using graphite nanoplatelet fillers is presented in this article, along with methods for dispersing these materials in various polymer matrices.

2,782 citations

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TL;DR: There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion.

2,114 citations