Boron films produced by high energy Pulsed Laser Deposition

Dellasega, David; Russo, Valeria; Pezzoli, Andrea; Conti, Claudia; Lecis, N.; Besozzi, Edoardo; Beghi, M.; Bottani, C. E.; Passoni, M.

doi:10.1016/j.matdes.2017.08.025

Cited by 34 publications

(21 citation statements)

References 51 publications

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“…Yet the film material is not elastically identical to nanocrystalline graphite: in fact the values of B (and, consequently, ν) are significantly different. Similar problems are discussed in [33].…”

Section: Films Grown By a Focused Beammentioning

confidence: 65%

Brillouin scattering of phonons in complex materials

Bottani

Fioretto

2018

Advances in Physics: X

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Initially, the theory of propagation of long-wavelength acoustic phonons and Brillouin scattering of laser light in condensed matter is concisely summarized. Then, the case of two relevant classes of complex materials in which Brillouin scattering can be measured is reviewed. First, in lowdensity, low-dimensional, disordered materials, the crossover between confinement and propagation is discussed on the basis of experimental findings. Moreover, the possibility of measuring the local mechanical properties of these materials at the mesoscale by Brillouin scattering is critically discussed. Second the application of Brillouin scattering to biological materials, a rather hot topic, is presented. The acoustic waves and their phonons Though the traditional ways to measure the mechanical properties of materials and, in particular, the elastic constants, are based on quasi-static deformation processes (e.g. the tensile test to measure the Young modulus), many important methods are acoustic in nature or make use of acoustic phenomena (ultrasound

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Section: Films Grown By a Focused Beammentioning

confidence: 65%

Brillouin scattering of phonons in complex materials

Bottani

Fioretto

2018

Advances in Physics: X

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“…The thermomechanical characterization is performed exploiting Brillouin spectroscopy (BS) and the substrate curvature method (SC). The coupling of these two techniques has been shown to be a powerful tool for the characterization of nanostructured films, providing a broad, non destructive characterization of the samples [23,24,25]. In particular, when transparent oxide coatings are investigated, BS can be able to derive, through the detection of surface and bulk acoustic waves, all the elastic moduli of the films (i.e.…”

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confidence: 99%

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

et al. 2019

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Metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films, deposited by Pulsed Laser Deposition, are characterized. The correlation is investigated between morphology, composition, and structure, measured by various techniques, and the mechanical properties, characterized by Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is correlated to the oxygen content and the mass density. The elastic moduli decrease as the mass density decreases and the oxygen-tungsten ratio increases. A plateau region is observed around the transition between the metal-like (conductive and opaque) films and the oxide ones (non conductive and transparent). The compressive residual stresses, moderate stiffness and high local ductility of compact amorphous tungsten-oxide films are interesting for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (8.9 · 10 −6 K −1 ), being strictly correlated to the amorphous structure and stoichiometry of the films. Upon thermal treatments the coatings show a quite low relaxation temperature of 450 K. Starting from 670 K, they crystallize into the γ monoclinic phase of WO 3 , the stiffness increasing by about 70%. The measured thermomechanical properties provide a guidance for the design of devices which include a tungsten based layer, in order to assure their mechanical integrity. mitigating or favoring crack formation. Similarly, in high temperature applications, a significant mismatch between the coefficients of thermal expansion of the coating and of the substrate can induce high interface stresses, with possible coating delamination and device failure. More specifically, in an electrochromic system the W oxide film is part of a complex multilayer system: it is deposited on a transparent conductor, like ITO, and faces the electrolyte, solid or liquid, containing the ions responsible of the electrochromic effect, and can be subject to various and very different stress states [15]. Moreover, in some applications (e.g. solar-cells, thermophotovoltaic) tungsten oxide coatings operate at temperatures above room temperature [16]; this could induce phase transition or recrystallization, with a consequent variation of the as-deposited properties. Although the thermomechanical properties of tungsten based coatings can be crucial for the design of devices which exploit them, relatively fewer studies have investigated the relationship between their nanostructure, composition and mechanical properties [17,18,19]. The goal of this work is to achieve a more comprehensive understanding of the effects of structure, morphology and chemical composition on the thermomechanical properties of different systems of amorphous W-O and WO x coatings, providing useful results for the design of devices. We investigate amorphous films characterized by different oxygen/tungsten ratios and morphologies. To produce them we selected the Pulsed Laser Deposition (PLD) technique, which allows a significant versatility in tailoring the str...

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“…4) A potential application of boron films is as protective coatings, since they exhibit high hardness and low brittleness; in addition, the boron surface is oxidized when exposed to ambient air, producing a hydroxide layer that can act as a solid lubricant. 5) Despite this, thin films of pure boron have seldom been used as high hardness coatings owing to the technological difficulties in producing homogeneous and crystalline films. 6) Boron is a difficult material to work with because of the variety of systems in which it crystallizes and the diversity of morphologies that can be obtained with it.…”

Section: Introductionmentioning

confidence: 99%

“…7) Boron exhibits four main allotropes that are arranged in a framework of icosahedral motifs (B12): 8) -rhombohedral, where the B12 motifs are present on the edges of the cell; -rhombohedral, where the B12 icosahedra are positioned at the vertices of the rhombohedral unit cell; -orthorhombic phase, with a rocksalt type arrangement; and the amorphous phase, in which the long-range order is lost, but the short-range order of the B12 icosahedra is retained. 5) Single crystals of -boron can be prepared from a boron-platinum melt at high pressures (6)(7)(8)(9)(10)(11) and temperatures. 9) Boron films have been prepared by several methods, including plasma-assisted CVD of boron trichloride 10,11) and diborane; 12) laser ablation; 5) magnetron sputtering; 13) pyrolysis; 12) and thermionic vacuum arc.…”

Section: Introductionmentioning

confidence: 99%

Hot Filament Chemical Vapor Deposition of Crystalline Boron Films

Soto¹

2019

J. Korean Ceram. Soc

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This article reports on the conditions required for the growth of crystalline boron films on silicon substrates by hot filament chemical vapor deposition method. The reactive gas was 3% diborane diluted in hydrogen. The films were characterized by optical, electronic, and atomic force microscopies; x-ray diffraction; and energy dispersive, electron energy loss, Raman, x-ray photoelectron, and Auger spectroscopies. The parameters that affect the morphologies of the films have been investigated. It was concluded that faceted crystals are produced at low B 2 H 6 flows and working pressures below 200 mT. -boron is produced between 530 and 600°C. Deposition outside this range produces thin films with a wide variety of morphologies. This result indicates that the films crystallize through a process called "abnormal or discontinuous grain growth." It is assumed that this is due to the anisotropic surfaces of boron allotropes.

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Boron films produced by high energy Pulsed Laser Deposition

Cited by 34 publications

References 51 publications

Brillouin scattering of phonons in complex materials

Brillouin scattering of phonons in complex materials

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

Hot Filament Chemical Vapor Deposition of Crystalline Boron Films

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