Optical transmission spectroscopy of switchable yttrium hydride films

Kremers, M.; Koeman, N.J.; Griessen, R.; Notten, Peter H. L.; Tolboom, R.; Kelly, Paul J.; Duine, Peter A.

doi:10.1103/physrevb.57.4943

Cited by 113 publications

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“…6,7 Recently den Broeder et al 8 presented an optical method to monitor the lateral migration of hydrogen in Y, exploiting the intrinsic concentration dependent optical properties of the Y-H system. 9 Especially the progression of the boundaries separating the various stable hydride phases can easily be detected as discontinuities in the optical contrast.…”

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“…The lateral migration of hydrogen in vanadium away from the Pd-covered region can easily be monitored optically in the Y indicator layer as the various yttrium hydride phases formed at different hydrogen concentrations, exhibit characteristic optical properties. 9,11 For example, the front corresponding to the coexisting ␣ and ␤ phases is clearly identified as a discontinuous change in transmission and reflection. 8 11,12 In the following we call this optical feature the ''␤-front'' or simply the front and its position x f .…”

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Switchable mirrors for visualization and control of hydrogen diffusion in transition metals

et al. 2002

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We show that the switchable mirror material YH x can be used both as an indicator to monitor and as an agent to control hydrogen diffusion in thin films. The applicability of the optical-indicator technique is demonstrated for VH x thin films. The diffusion coefficient is typically 10 Ϫ5 cm 2 /s at concentrations around 0.7 H/V at temperatures between 373 and 473 K. Deposition of a layer of Y on V makes it also possible to tune the effective hydrogen mobility via the V/Y thickness ratio. This can be used for investigation of hydrogen diffusion waves in laterally structured objects. DOI: 10.1103/PhysRevB.66.020101 PACS number͑s͒: 66.30.Ϫh, 68.55.Ln, 68.37.Ϫd, 68.60.Ϫp One of the striking properties of hydrogen in metals is its large mobility. Already at room temperature the H diffusion coefficient can be as high as 10 Ϫ5 cm 2 /s, i.e., a value almost comparable to diffusion in liquids. A review of experimental data and techiques used so far to measure hydrogen diffusivity in bulk samples is given by Alefeld and Völkl. 1 Most of these methods are not applicable to thin films as they are either hampered by the influence of the substrate ͑e.g., in Gorsky effect͒ or by the rather small volume of the film ͑e.g. in quasielastic neutron scattering͒. Consequently, relatively little is known about hydrogen diffusion in thin metallic films and multilayers. The understanding and manipulation of hydrogen transport through films is, however, important for the control and optimization of coatings and thin-film devices such as hydrogen detectors, 2,3 metal-hydride switchable mirrors 4,5 or tunable magnetical elements. 6,7 Recently den Broeder et al. 8 presented an optical method to monitor the lateral migration of hydrogen in Y, exploiting the intrinsic concentration dependent optical properties of the Y-H system. 9 Especially the progression of the boundaries separating the various stable hydride phases can easily be detected as discontinuities in the optical contrast.The main purpose of this communication is to demonstrate that visualization of H diffusion is also possible for hydrogen in opaque transition-metal films. More specifically ͑i͒ we demonstrate the feasibility to use a thin layer of Y as an optical indicator to visualize the lateral H migration in thin films of vanadium, ͑ii͒ we show that the mobility of the phase boundaries in a composite film ͑e.g., V/Y͒ can be tuned through the sample/indicator thickness ratio, and ͑iii͒ we determine quantitatively the H-diffusion coefficient in a vanadium film by means of our optical indicator method.The samples are prepared by means of e-gun evaporation in an ultrahigh vacuum system ͑background pressure Ͻ10 Ϫ9 mbar). A typical sample consists of a V stripe of length Lϭ10 mm, width bϭ1 mm, and thickness 25 nm Ͻd S Ͻ250 nm. Usually 11 stripes of various thickness d S are deposited onto one, polished amorphous quartz substrate. The V stripes are covered with a thin layer of yttrium as an optical indicator for hydrogen diffusion. Indicator thicknesses 10 nm Ͻd I Ͻ50 nm are exa...

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Switchable mirrors for visualization and control of hydrogen diffusion in transition metals

et al. 2002

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“…Electrochemical loading offers a double advantage: the concentration of hydrogen in the film can be controlled accurately, and extremely low pressures can be achieved. 7,8 The adsorbed hydrogen diffuses into the material; the concentration of hydrogen in the film, x, ͑hydrogen/metal atomic ratio͒ is proportional to the charge transferred in the electrochemical reaction. 7 With the galvanostatic intermittent titration technique ͑GITT͒, 9 the equilibrium potential U e , which is measured in open circuit after a current pulse, provides us, via the Nernst equation, with the equivalent hydrogen pressure p H 2 :…”

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Optical switching properties from isotherms of Gd and GdMg hydride mirrors

Vece

Zevenhuizen

Kelly

2002

Applied Physics Letters

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Concentration-pressure isotherms were measured together with the optical transmission in polycrystalline Gd and GdMg thin-film switchable mirrors. Formation plateaus in GdMg alloys, corresponding to gadolinium dihydride and trihydride as well as magnesium dihydride have been found. From these, the formation enthalpies could be calculated. These results show that the GdMg alloys are phase separated. From the onset of the transmission we conclude that the formation of gadolinium trihydride is the final stage in the switching process.

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“…It is a further development of the optical method presented by Den Broeder et al 5 to monitor the lateral migration of hydrogen in Y, exploiting the intrinsic concentration dependent optical properties of the Y-H system. 6 Electromigration studies on thin film YH x samples demonstrated that H in Y behaves like a negatively charged particle, 5,7 opening the possibility to work with electrodiffusion waves. In the presence of a static electric field E a charged particle experiences an additional force, leading to electrodiffusion waves which are solutions of a modified diffusion equation:…”

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confidence: 99%

“…The lateral migration of hydrogen in Y away from the Pdcovered region can easily be monitored optically, as different yttrium-hydride phases are formed at different hydrogen concentrations, exhibiting characteristic optical properties. 6,11 Figure 1 depicts below the schematical sample design two vanadium samples of 50 nm and 100 nm thickness. The images are recorded after an exposure of 3 h in a hydrogen atmosphere of 1 mbar at 473 K. The front separating the ␣ from the ␤ phase is clearly identified from a discontinuous change in reflection.…”

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Generation and detection of H electrodiffusion waves

Remhof

Mechelen

Koeman

et al. 2003

Review of Scientific Instruments

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Hydrogen electrodiffusion waves are forced oscillations of the H concentration within a host metal, driven by an electric field. Simulations show that they suffer less from the drawbacks of ordinary diffusion waves such as heavy damping. H in Y/V bilayers fulfills all the requirements to generate and to detect H electrodiffusion waves. We demonstrate the possibility to spatially modulate the H concentration in a thin V film and to drive H ''pulses'' via an applied electric field. The electric field is also used to control the hydrogen uptake of the sample. We visualize the temporal and spatial evolution of the H distribution in the V film using the switchable mirror material YH x as an optical hydrogen indicator. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1518569͔ Diffusion waves arise from forced oscillations of diffusing particles. Denoting the particle density as c and the diffusivity as D, one-dimensional diffusion waves are mathematically described as solutions of the diffusion equation ͑1͒in which c(x,t) varies as c(0,t)ϭsin( t) at the origin. Examples are oscillating temperature such as the temperature profile of the earth resulting from the seasonal temperature variation 1 or diffuse photon density waves in a turbid medium. 2 Reviews on diffusion waves together with examples of their technological applications have been published by Yodh 3 and by Mandelis. 4 In this article, we describe a simple technique to generate and to visualize hydrogen diffusion waves in thin metallic films. It is a further development of the optical method presented by Den Broeder et al. 5 to monitor the lateral migration of hydrogen in Y, exploiting the intrinsic concentration dependent optical properties of the Y-H system. 6 Electromigration studies on thin film YH x samples demonstrated that H in Y behaves like a negatively charged particle, 5,7 opening the possibility to work with electrodiffusion waves. In the presence of a static electric field E a charged particle experiences an additional force, leading to electrodiffusion waves which are solutions of a modified diffusion equation:where eZ denotes the effective charge of the particle, and is the chemical potential of H in the metal. The prefactor of the linear term of Eq. ͑2͒, ͑3͒has the dimension of a velocity. Electrodiffusion waves may exist at all frequencies and suffer less from damping than ordinary diffusion waves, which typically damp out within one wavelength. In order to investigate diffusion waves, we need to work in a concentration regime in which ͑i͒ the hydrogen concentration can be varied continuous and reversible and ͑ii͒ in which the optical properties depend strongly on the hydrogen concentration. Recently, Van der Molen et al. 8 succeeded in creating a single ''pulse'' of H vacancies within the YH 3Ϫ␦ phase. In the presence of an electric field, the vacancy distribution does not only spread out with time, but also moves with the electric field. For a study of electrodiffusion waves, YH 3Ϫ␦ is not ideal because of its rather small diffusion c...

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Optical transmission spectroscopy of switchable yttrium hydride films

Cited by 113 publications

References 17 publications

Switchable mirrors for visualization and control of hydrogen diffusion in transition metals

Switchable mirrors for visualization and control of hydrogen diffusion in transition metals

Optical switching properties from isotherms of Gd and GdMg hydride mirrors

Generation and detection of H electrodiffusion waves

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