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K. Kohlhaas

Other affiliations: University of South Carolina
Bio: K. Kohlhaas is an academic researcher from Northwestern University. The author has contributed to research in topics: Nanowire & Resonance. The author has an hindex of 6, co-authored 11 publications receiving 11416 citations. Previous affiliations of K. Kohlhaas include University of South Carolina.

Papers
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Journal ArticleDOI
TL;DR: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005 shows the importance of knowing the carrier and removal status of Na6(CO3)(SO4) in the determination of Na2SO4 levels.
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

9 citations

Journal ArticleDOI
TL;DR: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005 shows the importance of knowing the carrier and removal status of Na6(CO3)(SO4) in the determination of Na2SO4 levels.
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005
01 Jan 2006
TL;DR: In this paper, a method for detecting nanocracks through mechanical resonance and tensile testing of boron nanowires is proposed. But it is not possible to know whether nanocacks alone were responsible for the frequency shifts.
Abstract: Resonance and tensile tests of boron nanowires are reported and discussed assuming the presence of nanocracks. From the measured resonant frequency shift a procedure to localize the nanocrack and quantify its depth is proposed. The nanocrack depth is expected to strongly influence the failure stress and its position can be assumed to be at the fractured cross-section: thus nanocrack depth and position might be independently deduced by resonance and tensile tests. Introduction In recent years nanostructures such as nanotubes and nanowires have attracted great attention due to the promise of applications in sensing, materials reinforcement and micro/nano-electromechanical systems. Both the mechanical resonance method and the tensile testing method are two methods used to study the mechanical properties of nanostructures. The mechanical resonance method has been used to study the mechanical properties of onedimensional nanostructures such as carbon nanotubes, nanowires and nanobelts [1-4]. The uniaxial tensile test is the most popular method for bulk material mechanical property characterization, and it has been adapted for use in mechanics measurements of nanostructures such as carbon nanotubes [5]. Crystalline boron (B) nanowires (NWs) have been synthesized recently with the chemical vapor deposition (CVD) method [6]. We have experimentally investigated their dynamical resonance (i) and mechanical strength (ii) [7]. Both of these independent methods suggest the possible presence of nanocracks in the tested B NWs. Nanocrack detection can in principle be achieved by analytical calculations quantifying crack position and depth. The mechanical resonances of cantilevered B NWs were excited and the resonance peak frequencies measured. Shifts in the natural frequencies were observed, suggesting the possibility of the presence of nanocracks; other possible shift causes, such as intrinsic NW curvature, non-ideal clamps, presence of spurious masses, coating layer, large displacements, etc., have been discussed elsewhere [8]. Assuming the existence of a nanocrack, analytical calculations were obtained to quantify its depth and position based on the measured frequency shifts. A newly developed rapid electron beam induced deposition (EBID) method [9] was used to clamp the B NWs and test them in tension inside an SEM with a home-built nanomanipulator. High-resolution SEM images were acquired at each loading step, and two independent methods of analysis of each image were used to obtain the corresponding tensile load. The B NW geometries were measured by TEM after the tests. The stress vs strain, Young’s modulus, and tensile strength of the B NWs were obtained through data analysis. The strength measurements strongly suggest the presence of nanocracks in the B NWs. Assuming the existence of a nanocrack, placed at the fracture section, its depth can be quantified by applying Quantized Fracture Mechanics [10] starting from the measured fracture strengths. The possibility of detecting nanocracks through mechanical resonance and tensile testing of nanostructures is thus exemplified, even though it is not possible to know whether nanocracks alone were responsible for the frequency shifts [8]. The challenge on the experimental side in the future will be ensuring that other contributors to shifts in mechanical resonance are not present or have sufficiently different functional dependence, such that the nanocrack contribution, if present, can perhaps be “uncovered”. Frequency shift and strength reduction due to the presence of a nanocrack Mechanical resonance can be induced in nanowires when the frequency of the applied force approaches their resonant frequency. According to simple beam theory, the n mode mechanical resonance frequency fn of a clampedfree uniform beam is given by: A I E L f b n n ρ π β 2 2
Book ChapterDOI
01 Jan 2006
TL;DR: In this paper, the authors focused on characterizing the mechanical properties of these novel 1D nanostructures, such as nanotubes and nanowires, and applied them in sensing and materials reinforcement.
Abstract: One-dimensional (1D) nanostructures such as nanotubes and nanowires have attracted considerable attention in recent years due to their promise of applications in sensing and materials reinforcement. Over the past decade various 1D nanostructures has been synthesized. To develop applications with these nanostructures, it is important to first understand their fundamental properties. Our work focused on characterizing the mechanical properties of these novel 1D nanostructures.

Cited by
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Journal ArticleDOI
TL;DR: Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena can now be mimicked and tested in table-top experiments.
Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

35,293 citations

Journal ArticleDOI
01 Jun 2007-Carbon
TL;DR: In this paper, a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high surface area carbon material which consists of thin graphene-based sheets.

12,756 citations

Journal ArticleDOI
TL;DR: This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material.
Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

10,126 citations

Journal ArticleDOI
05 Feb 2009-Nature
TL;DR: The direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers is reported, and two different methods of patterning the films and transferring them to arbitrary substrates are presented, implying that the quality of graphene grown by chemical vapours is as high as mechanically cleaved graphene.
Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

10,033 citations

Journal ArticleDOI
TL;DR: An overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

8,919 citations