NL2011849C2

NL2011849C2 - Large pressure range hydrogen sensor.

Info

Publication number: NL2011849C2
Application number: NL2011849A
Authority: NL
Inventors: Christiaan Boelsma; Bernard Dam
Original assignee: Univ Delft Tech
Priority date: 2013-11-27
Filing date: 2013-11-27
Publication date: 2015-06-01
Also published as: WO2015080577A1

Abstract

The present invention relates to a thin-film sensor, to a method for producing a thin-film device, to an alloy for use in an optical sensing layer, to use of an alloy for sensing a chemical species such as hydrogen, to a sensor, to an apparatus for detecting hydrogen, to an electro-magnetic transformer comprising said sensor and to a switching device.

Description

Large pressure range hydrogen sensor

FIELD OF THE INVENTION

The present invention relates to a thin-film device, to a method for producing a thin-film device, to an alloy for hydrogen absorption, to a method for producing a hydrogen absorption alloy, to use of a hydrogen absorption alloy for detecting a chemical species such as hydrogen, to a hydrogen sensor, to an apparatus for detecting hydrogen and to an electro-magnetic transformer comprising said sensor.

BACKGROUND OF THE INVENTION

In a more generic perspective in an economy with hydrogen as a major energy carrier, the development of affordable, reliable, sensitive and selective hydrogen sensors is indispensable. Several types of hydrogen sensors are currently available, which exploit the following detection mechanisms: catalytic, electrochemical, mechanical, optical, acoustic, thermal conductivity, resistance and work function. In principle, Pd-based optical fibre sensors could meet requirements if cross-contamination effect of a Pd surface by oxygen, moisture or carbon monoxide, for example, can be prevented. Such sensors can also be used for detecting hydrogen in other environments. Since hydrogen detection often takes place in an explosive environment, cf. for leak detection or hydrogen-concentration measurements in gas streams, use of optical hydrogen sensors has a major advantage of being intrinsically safe due to the lack of electric leads in a sensing area. In addition known, fibre-optic, Pd-based thin-film hydrogen sensors represent a relatively cheap and reliable solution to this problem since they also allow for continuous sensing via remote hydrogen-gas detection, a key for personal and material safety. However, it is well known that Pd-based sensors have a highly non-linear optical response, depending strongly on the applied hydrogen pressure. A prior art thin-film device comprises a substrate, an active sensing layer whose optical properties change depending on hydrogen content and a protective layer on the active sensing layer.

Such thin-film devices are known from the prior art. As an example, WO2007/126313 discloses a switchable mirror device comprising an active layer, wherein said active layer changes its optical properties upon addition or removal of hydrogen and comprises a hydrogen and oxygen permeable and water impermeable layer, wherein said layer is liquid water impermeable and water vapour permeable and has hydrophobic surface properties .

Thin-film devices of the prior art suffer a number of disadvantages in particular with regards to achieving controlled and reliable absorption of a species such as hydrogen, such as over a broad range of hydrogen pressures. It remains important to have a protective coating of Pd-based hydrogen sensors that does not compromise its favourable properties such as low detection limits and response time, relatively easy and affordable fabrication, low weight and portability, etc .

The present invention therefore relates to a thin-film device and further aspects thereof, which overcomes one or more of the above disadvantages, without compromising functionality and advantages.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more limitations of the thin-film devices of the prior art and at the very least to provide an alternative thereto.

In a first aspect, the invention relates to a thin-film device according to claim 1, comprising the present alloy.

It is noted that the present invention provides controlled and reliable absorption, specifically of hydrogen, over a large range of hydrogen pressures. As the mechanism of absorption is in principle reversible, also controlled and reliable desorption is provided. In an example a means for monitoring a (varying) hydrogen concentration over a large range of pressures is provided. It is noted that the present optical system is much safer to use and to handle compared to e.g. electrical (conducting) sensors, especially in environments where a large electro-magnetic field may be present.

In an example the present thin thin-film device comprises a substrate, an active sensing layer whose optical properties change continuously as a function of hydrogen content, a Pd cap layer to dissociate hydrogen which acts simultaneously as a protective coating for the sensing layer, and a protective layer coating the Pd which protects this cap layer. In the following sections various elements of the present device are further elucidated. A person of skill in the art is able to identify many suitable substrate materials upon which a thin-film device such as the thin-film device of the invention can be constructed. Examples of suitable substrate materials include glass, quartz, indium-tin oxide, etc. The substrate material is preferably optically transparent (more than 95%), at least over a proportion of the visible, UV and/or IR regions of the electromagnetic spectrum (200 nm- 3000 nm). Such provides for use of white light, IR-light, UV-light, a laser with a specific wavelength, and combinations thereof.

As mentioned above, optical sensing layers, with variable optical properties depending on e.g. a hydrogen content of the layer, comprising an alloy, are known in the prior art. In an example of the present invention the sensing layer is the present alloy. The alloy comprises at least a first metal and a second metal. In principle the first, the second, as well as any further metal may be selected from the periodic system of elements. Typically characteristics of a metal are that they may oxidize, may form a cation, may be an electrical conductor, etc. In the present alloy the first and second metal have an equilibrium pressure (Pa) for hydrogen absorption. Such an equilibrium pressure per se can be measured with means known to a person skilled in the art. Typically it is measured at ambient temperature (273 K). In the present alloy the hydrogen equilibrium pressure (Pa)of the first metal is at least 5*103 times as large as the hydrogen equilibrium pressure (Pa)of the second metal, preferably at least 104 times, more preferably at least 5*104 times, even more preferably at least 5*105 times, such as 106-1015 times.

In table 1 various metals and equilibrium pressures (Pa, @273 K)(as calculated/estimated) are given.

Mg 1.1*10°

Ti 6.1*10~15 Zr 1.2*10~23 Hf 1*10~5 Ta 1*10~13

Inventors have discovered that in principle metals having any ratio of pressures can be combined (into alloys). If the ratio is relatively large, e.g. more than 106, it is preferred to introduce a third metal, having with respect to the first and second metal an intermediate hydrogen equilibrium pressure. A few examples of such alloys are: AxByCz, with A being selected from alkaline metals and alkaline earth-metals, preferably from Mg, and Ca, B being selected from Sc, Ti, V, Cr,

Mn, Fe, Co, Ni, Cu and Zn, preferably Sc, Ti and V, and C being selected from Zr, Nb, Ta, Y and Hf with ranges preferably as follows: for z=0: xe [ 0.5-0.95], ye [ 0.05-0.5>, and preferably y:xe [ 0.1-0.9], with the exception of A=Mg and B=Ti; or xe [ 0.4-0.95], ye[0.0-0.6], ze [ 0.5-0.45], and preferably y:xe [ 0.7-0.9] . Examples of suitable alloys are given below.

MgxTiyZrz, MgxVyZrz, MgxScyZrz, MgxNiyZrz, MgxCryZrz, Mgx-CoyZrz, MgxTiyHfz, MgxVyHfz, MgxScyHfz, MgxNiyHfz, MgxCryHfz, MgxCoy-Hfz, MgxTiyTaz, MgxVyTaz, MgxScyTaz, MgxNiyTaz, MgxCryTaz, MgxCoyTaz, MgxTiyNbz, MgxVyNbz, MgxScyNbz, MgxNiyNbz, MgxCryNbz, MgxCoyNbz, Mgx-TiyYz, MgxVyYz, MgxScyYz, MgxNiyYz, MgxCryYz, MgxCoyYz, CaxTiyZrz, CaxVyZrz, CaxScyZrz, CaxNiyZrz, CaxCryZrz, CaxCoyZrz, CaxTiyHfz,

CaxVyHfz, CaxScyHfz, CaxNiyHfz, CaxCryHfz, CaxCoyHfz, CaxTiyTaz,

CaxVyTaz, CaxScyTaz, CaxNiyTaz, CaxCryTaz, CaxCoyTaz, CaxTiyNbz,

CaxVyNbz, CaxScyNbz, CaxNiyNbz, CaxCryNbz, CaxCoyNbz, CaxTiyYz,

CaxVyYz, CaxScyYz, CaxNiyYz, CaxCryYz, and CaxCoyYz, with xe[0.4-0.6], ye[0.2-0.3], ze [ 0.05-0.45], and preferably y:xe[0.7-0.9]. These alloys provide the advantages in particular.

In other words a ratio of first and second hydrogen pressures of more than 106 is possible; in that case it is preferred to use the third metal. Likewise an additional order of magnitude (107) is possible, especially when a fourth metal is used. Likewise detectable pressures may be expanded by including in the alloy a metal having a significant lower, or higher, hydrogen equilibrium pressure, compared to the first and second metal. It is noted that as the equilibrium pressures are taken with respect to one and another, e.g. a pressure of a first and a second metal, it is in principle less relevant by what exact way of measurement individual pressures are determined.

The first metal, having a relatively high hydrogen equilibrium pressure (Pa), may have a first phase with metallic properties at relative low hydrogen pressure and has a second phase with low electrical conducting properties at relative high hydrogen pressure. Metallic properties relate e.g. to electrical conductivity. It is noted that on hydrogenation electronic properties of metals and alloys change. An electrical conducting metal typically has an appreciable density of states at the Fermi level as the conduction band is partially filled. It has been found that on hydrogenation of a metal the Fermi level changes resulting in a small effect on the electrical conductivity and the optical properties. Large optical changes occur if at least one of the metals transforms into a semiconducting or isolating state; if a bandgap opens up.

In an example the first metal may be present in an amount of 10-90 atom % and the second metal in an amount of 10-50 atom %: AxBy with xe [0.5-0.9], and ye[0.1-0.5>; with the exception of A=Mg and B=Ti.

Inventors have identified that it is preferred that the alloy comprises a metal providing the alloy X-ray amorphousness. This metal may relate to a third metal, being different from the first and second metal, or it may be the same as any of the first and second metal. An indication of presence of amorphousness is given by taking an X-ray measurement of an alloy, and identifying presence or absence of amorphousness; for the present alloy presence is required. The identification of presence or absence of X-ray amorphousness is considered an objective determination.

In an example the alloy of the optical sensing layer has a distribution of interstitial sites. The sites being characterized and formed by surrounding atoms of the alloy. In a regular crystal such sites could relate to tetraeder and octaëder sites. Also coordination number and interatomic distance may be taken into account. As the present alloy may be largely amorphous, only in very small domains such regular sites may be observed. Most sites however are even then at least partially distorted. The sites are in principle considered suited for hydrogen absorption. The distribution comprises at least four different (types of) sites, preferably at least 10 different (types of) sites, more preferably at least 100 different (types of) sites, such as at least 103 different sites (types of) /μπι3 (i.e. taken per unit volume) . It is noted that in an amorphous structure any first site may be different from any second site; thus an enormous amount of different sites may be present, such as 104 different sites/μπι3. A difference may further relate to a (slight) variation with respect to hydrogen absorption energy.

An effect of the present alloy is a large gap material forms on hydrogenation of at least one of the constituents, a good (hydrogen) diffusion, and high (optical) dynamics resulting in a wide range of hydrogen pressures that can be detected. In an example MgTi provides 0.5-1 order of detection, whereas adding Zr to the alloy even 3 orders of detection or more are obtained. Inventors provide a sensing material with a large optical contrast over a wide pressure range.

Common examples of the present alloy include Mg-lanthanide hydride layers and magnesium-transition metal alloys such as Mg-Ti alloys. Transmission, reflection and/or absorption of light by the layers changes through addition or removal of hydrogen from the layer. Such changes can be measured. Hydrogen absorbs into the alloy material. The optical sensing layer may be amorphous, and may be in a sequence of layers or layer stacks or in 2- or 3-dimensional domains. It is preferred to use an amorphous layer, as a broader range of e.g. hydrogen absorption pressures is obtained, more preferably an amorphous zircon comprising layer. A catalyst such as in a layer is provided on top of the optical sensing layer, such as coating the optical sensing layer. Examples of such layers include for example Pd-layers. The Pd-layers may comprise pure Pd or mixtures comprising Pd. For example, Ag can be added in a quantity of for example 20-30 mole%. The catalyst may also relate to a complex layer, suited for the present purpose. Such layers serve to facilitate hydrogen absorption by the optical sensing layer.

In an exemplary embodiment, the catalyst layer has a thickness in the range of 1.5-500 nm, preferably 3-100 nm, such as 5-30 nm.

It is noted that a term as "on top" may relate to a sequence of e.g. layers, a first layer coating a second layer, a layer provided on an intermediate layer, the intermediate provided on e.g. the sensing layer, etc. The layer may also partly be on top. In view of the present application such termi- nology is mainly functional of nature.

On top of the optical sensing layer, or where present, on top of the catalyst (layer), a protective layer is provided, the protective layer not limiting functionality of the optical sensing layer, e.g. being permeable to relevant species, optical transparent, etc. and protecting the optical layer. Both the catalyst layer (where present) and the protecting layer are permeable to a species to be measured, such as hydrogen, and are optically transparent, at least over a range of the visible, UV and/or IR regions of the electromagnetic spectrum. An example of a protecting layer from the aforementioned WO2007/126313 is to provide a layer of Teflon. The protective layer is provided to improve the longevity of the thin-film device through preventing deterioration of the catalyst and/or optical sensing layers and improves the handleability of the device through preventing a user from coming into contact with the optical sensing and/or catalyst layers. It is noted that the nature of Teflon and more specific sputtered PTFE makes it in principle difficult to process.

In an example the present device further comprises one or more intermediate layers, wherein the intermediate layer preferably comprises a Period 4 transition metal, such as Ti, even more preferably an alloy of (i) a Period 4 transition metal, such as Ti and (ii) the first metal or second metal.

For instance, when the present alloy (of the optical sensing layer) comprises MgTiZr, the intermediate layer may comprise TiZr; it is preferred to use a same or similar ratio of Ti:Zr in the intermediate layer as in the present alloy, in view of performance of the present device. It is preferred to have at least one intermediate layer between the catalyst and present alloy.

It is preferred to provide two intermediate layers, one between the catalyst and present alloy, and one between the present alloy and substrate.

In an exemplary embodiment, the intermediate layer has a thickness in the range of 1.5-500 nm, preferably 3-100 nm, such as 5-30 nm.

Control and reliability of e.g. hydrogen absorption is further achieved with the thin-film device of the invention by providing an optical sensing layer according to the invention, e.g. comprising a Zr, Hf, Nb, Y, lanthanide or Ta doped alloy, or preferably both. Examples hereof are MgTiZr and ZrTi.

Examples of coating layers are given in the Dutch Patent Application NL2010031, filed December 20, 2012. Details, teachings and examples thereof are incorporated by reference.

Research by the inventors has shown that doping of (i) Group I, or Group II transition metal based layers such as Mg-transition metal alloys e.g. Mg-Ti alloys, or (ii) rare earth-based layers, such as of Mg-lanthanide hydride materials, having optical properties that change depending on hydrogen content, with Zr, Hf, Nb, Y, La or Ta can result in improved sensing properties in terms of the range of analytes, e.g. hydrogen, pressures under which they are able to be operated and under which they provide a related output, such as a change in an optical property e.g. the absorbance, transmission or reflectance of the layer. The present alloys provide in an example for a range of hydrogen pressures between 4*10_1 Pa- 3*103 Pa to be detected accurately. Depending on the present alloy much lower pressures (e.g. 1CT5 Pa) and much higher pressures (e.g. 107 Pa)may be detected. Upon calibration of the curves larger ranges are envisaged. In comparison an optimal crystalline MgTi layer provides 1-2 orders of hydrogen pressure to be detected accurately.

Desirable performance of the thin-film device of the invention in terms of control and reliability of hydrogen absorption can be achieved through either improvement separately or through the combination of improvements. Reliability relates particularly to reliability over time, such as tens of years, and with repeated use.

The invention also relates to a Zr doped Mg-based alloy, optionally comprising Ti, to a method for producing a Zr doped Mg(Ti) alloy, to use of a Zr doped Mg(Ti) alloy for detecting a chemical species such as hydrogen, to a protective layer for shielding an oxygen, moisture, hydrogen sulphide and/or carbon monoxide sensitive surface, to a hydrogen sensor and to an electro-magnetic transformer comprising said hydrogen sensor.

The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In an exemplary embodiment, the optical sensing layer has a Zr, Hf, Nb, Y, La or Ta content in the range of 10 to 40%, preferably 15 to 35%, more preferably 18 to 30%, such as a content of 20%. An example is MgxTiyZrz, z being in the above range, and x,ye[5%-80%]. In an example the alloy comprises 10-40% Zr and 60-90% Mg.

In an alternative also known optical sensing layers, such as a Pd-Au alloy sensing layer may be used in combination, albeit having a smaller dynamic detection range of e.g. hydrogen .

In an exemplary embodiment, the optical sensing layer has a thickness in the range of 1.5-500 nm, such as 10-100 nm.

In an exemplary embodiment, the protective layer has a thickness in the range of 0.02-200 pm, such as 1 pm.

Also a catalyst layer to enhance absorption is present, typically on top of the optical layer, either directly or with one or more intermediate layers.

In a second aspect, the invention relates to the present alloy for use in an optical sensing layer.

In a third aspect, the invention relates to a method of for producing a thin-film device comprising providing a substrate, depositing an optical sensing layer on the substrate, the optical sensing layer comprising the present alloy, depositing a catalyst layer on the optical sensing layer, and providing a protective layer on the catalyst layer.

It has been found experimentally that for a stable performance a device is first cycled a few times, from a relatively low (hydrogen) pressure to a relatively high (hydrogen) pressure, and back. 2-10 cycles are typically sufficient. It is also preferred to cycle at elevated temperature; fewer cycles are required in that case, compared to ambient temperature cycling.

In a fourth aspect, the invention relates to a method for forming the present alloy, such as a Zr doped Mg(Ti) alloy. Suitable techniques include vacuum, PVD, sputter deposition, laser ablation and deposition, and evaporation and deposition.

In a fifth aspect, the invention relates to a use of the present alloy for detecting a chemical species such as hydro gen. It is noted that various methods of the prior art are not reliable, not accurate, expensive, and often not applicable at all, especially in complex and/or harsh environments. Specifically the present invention provides for detection of species, e.g. hydrogen gas species, in oil, such as transformer oil. It is noted that the species are an indirect measurement for the quality and/or status of the transformer as a whole and of sub-functionality thereof, such as transformer oil. As a consequence the quality and status of the transformer can now be monitored continuously.

In a sixth aspect, the invention relates to a sensor comprising the thin-film device of the invention. In a preferred example the sensor is a hydrogen sensor. The sensor may be provided with an optical transmitter, such as an optical fiber. Such provides e.g. as advantage that a measurement can take place at a spatial distance of detection. Even further the invention may relate to a combination of optical sensing layers, such as a stack of layers. Each layer or stack of layers may be optimised to sense a species, such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, etc. Also, a layer or stack of layers may be optimised to determine a species in a first concentration range, and a further layer or stack of layers for determining a species in a second concentration range. Likewise and preferred a combination of various 2-d and 3-D domains may be used. Thereby an enlarged range of concentrations can be determined. Even further the sensor may comprise one or more of the above, e.g. layers for various species and layers for various concentrations of one or more species. Even further, other materials may be used in combination with the present optical layer to extend e.g. a pressure range and to incorporate further species being measurable. An advantage is that the present invention allows for a combination of various optical layers without much extra measures to be taken in order to obtain a functional device.

In a seventh aspect, the invention relates to an electromagnetic transformer comprising the hydrogen sensor of the invention. Therewith behaviour and status of the transformer can be monitored. Even further, an automatic signal may be provided, indicating malfunction or risk of malfunction, based on the hydrogen concentration measurement. The transformer can then be replaced or serviced, as required.

In an eighth aspect the invention relates to an apparatus for detecting hydrogen comprising a sensor, the sensor being located at a longitudinal side of an optical transmitter, the optical transmitter comprising a central transmitting element, such as a quartz core, a transducer layer, preferably having a surface plasmon resonance frequency, an alloy according to the invention, and optionally a protection layer, preferably according to the invention, and a frequency shift detector.

With the optical resonator in combination with the frequency shift detector a resolution in the order of pm is obtained .

The above apparatus relates to a new design of a fiber optic Surface Plasmon Resonance (SPR) sensor using e.g. Palladium as a sensitive layer for hydrogen detection, or likewise an alloy according to the present invention. In an example, a transducer layer is deposited on the outside of a multimode fiber, after removing the optical cladding thereof. In an example the transducer layer is a multilayer stack made of a silver, a silica and the sensing layer (e.g. the alloy, the Pd-alloy and the protective coating). Spectral modulation of light transmitted by the fiber allows detecting the presence of hydrogen in the environment. The sensor is only sensitive to a Transverse Magnetic polarized light and Traverse Electric polarized light can be used therefore as a reference signal. A more reliable response is expected for the fiber SPR hydrogen sensor based on spectral modulation instead of on intensity modulation. The multilayer thickness defines the sensor performance. The silica thickness tunes the resonant wavelength, whereas the Silver and Palladium thickness determine the sensor sensitivity. In an optimal configuration (NA = 0.22, 100 pm core radius and transducer length = 1 cm), a resonant wavelength is shifted over 17.6 nm at a concentration of 4% Hydrogen in Argon for the case of the 35 nm Silver/100 nm Silica/3 nm palladium multilayer. Amongst others the above results are published in two articles of one of the present inventors (Opt. Soc. America, 7 November 2011, Vol. 19, No. S6, ppA1175-1183 and Proc. SPIE, Vol. 8368, pp. 836804-1-12).

The invention will hereafter be further elucidated through the following examples which are exemplary and explan- atory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

FIGURES

Figure 1 is a schematic representation of hydrogen pressure versus hydrogen content.

Figure 2 is a measurement of hydrogen pressure as a function of relative transmittance.

Figure 3 is a measurement of hydrogen pressure as a function of relative transmittance.

Figure 4 shows hydrogen pressures and optical response for various MgTi alloys. DETAILED DESCRIPTION OF FIGURES Figure 1 is a schematic representation of hydrogen pressure (vertical axis) versus hydrogen content and relates to prior art systems. Therein, depending on the temperature of the system, one or more phase may be present, namely an α-phase, a β-phase and a mixed α+β-phase. The hydrogen content can be measured as natural logarithm of a relative transmittance at a given pressure. For such a system a dynamic range is limited, typically to about one order of magnitude hydrogen concentrations (e.g. from 1CT2 to 1CT1 Pa) .

Figure 2 is a measurement of hydrogen pressure (PTU in Pa) as a function of transmittance (ln(T/To) . Therein an example of a present sensor, comprising a quartz substrate of 10x10x1 mm3, a first 10 nm thick Tio.45Zro.55 layer on the substrate, a 80 nm Mgo.51Tio.22Zro.27 sensing layer on the first TiZr layer, a second 10 nm thick Tio.45Zro.55 layer on the sensing layer, and a 10 nm Pd layer on the second TiZr layer, is used to measure hydrogen pressure. It can be seen that it is now possible to measure the hydrogen pressure over approximately 5 orders of magnitude (from 1CT1 Pa to 104 Pa) . It is preferred for best results to perform a few (3-5) cycles from low to high hydrogen concentration and back, at an elevated temperature, to arrive at a "stable" situation wherein behaviour of the present sensor does not change any more over time.

Figure 3 is a measurement of hydrogen pressure (PH2 in Pa) as a function of transmittance (ln(T/To)for Ti and Mg, respectively.

As in figure 2, also results of an example of the present sensor are given. In fig. 3 equilibrium pressures for Mg and Ti are indicated (about 3*102 Pa and 2*10_1 Pa, respectively) . It is noted that likewise an equilibrium pressure of e.g. Zr is found to be about 1CT13 Pa. These respective equilibrium pressure are far apart from one and another. It is considered that for the present sensor X-ray amorphousness is required. Further, it is considered that many energy levels in the present alloy are present. And it is considered that an elastic coupling between levels is present.

Figure 4 shows hydrogen pressures (PPM in mbar (lOOPa)) and optical response for various prior art MgyTii-y alloys. Even the "best" alloy, with y=0.61, provides a sensor with not more than 2 orders of magnitude dynamic range. Also the optical response is relatively small. EXAMPLES Experimental Substrate preparation

Pd thin films with a thickness of 60 nm were deposited at room temperature on quartz substrates in an ultrahigh-vacuum (UHV) DC/RF magnetron sputtering system (base pressure 10~8 mbar, Ar deposition pressure 0.003 mbar).

Alloy thin films of e.g. Mg(Ti)Zr with a thickness of 80 nm were co-deposited in a similar DC magnetron sputter system using quartz substrates. The thin films show a significant (ln(T/T0) >0.5) optical response that is linear over almost 4 orders of magnitudes of hydrogen pressure (from 0.4 Pa to 2000 Pa) at 120°C. On deposition the films are crystalline, which decays on cycling with hydrogen.

Claims

A thin film device for the controlled and reliable absorption of hydrogen comprising: (a) a substrate; (b) an optical detection layer on the substrate wherein the optical detection layer comprises an alloy; (c) a protective layer applied directly or via an adhesive layer to the optical detection layer, and (d) a catalyst layer between the optical detection layer and the protective layer; characterized in that (e) the alloy (b1) comprises at least a first metal and a second metal, the first and second metal having a hydrogen equilibrium pressure (Pa), wherein the hydrogen equilibrium pressure (Pa) of the first metal is at least 5 * 103 times the hydrogen equilibrium pressure (Pa) of the second metal, preferably at least 104 times.

A thin film according to claim 1, (b2), wherein the first metal, with a relatively high hydrogen equilibrium pressure (Pa), a first phase with metallic properties at relatively low hydrogen pressure and a second phase with low electrically conductive properties at has relatively high hydrogen pressure, such as semi-conductive or insulating properties and / or wherein (b3) the alloy contains a metal providing the X-ray amorphous alloy.

A thin film device according to any one of the preceding claims, wherein the alloy of the optical detection layer has a distribution of interstitial sites, the sites being characterized and formed by surrounding atoms of the alloy, the sites being suitable for hydrogen absorption wherein the distribution comprises at least four different locations / μπι3, preferably at least 10 different locations / μπι3, more preferably at least 100 different locations / μπι3, such as at least 103 different locations / μπι3.

A thin film device according to one or more of the preceding claims, further comprising one or more intermediate layers, wherein the intermediate layer preferably comprises a period 4 over transition metal, such as Ti, more preferably an alloy of (i) a period 4 transition metal, such as Ti and (ii) the first metal or second metal.

A thin film device according to one or more of the preceding claims, wherein the alloy is one or more of; (i) a Group I metal, Group II metal, (ii) a period 4 transition metal, and (iii) a rare earth metal, such as Zr, Hf, Nb, Y, La and Ta, such as an Mg doped or MgTi doped alloy.

A thin film according to any one of the preceding claims, wherein the alloy has a Zr, Hf, Nb, Y, La and Ta dopant content in the range of 10 to 40%, preferably 15 to 35%, more preferably 18 to 30%, for example a content of 20%.

A thin film according to any of the preceding claims, wherein the optical detection layer has a thickness in the range of 1.5-500 nm, preferably 10-100 nm, and / or wherein the protective layer has a thickness in has the range of 0, 02-200 μπι.

An alloy for use in an optical detection layer comprising (b1) at least a first metal and a second metal, wherein the first and second metal have a hydrogen equilibrium pressure (Pa), wherein the hydrogen equilibrium pressure (Pa) of the first metal is at least 5 * 103 times the hydrogen equilibrium pressure (Pa) of the second metal, preferably at least 104 times, and optionally (b2), wherein the first metal, with a relatively high hydrogen equilibrium pressure (Pa), is a first phase with metallic has properties with relatively low hydrogen pressure and a second phase with low electrical conductivity properties with relatively high hydrogen pressure, such as semiconductor or insulating properties.

The alloy of claim 8, wherein (b3) the alloy contains a metal providing the X-ray amorphous alloy.

The alloy of claim 8 or 9, wherein the alloy of the optical detection layer has a distribution of interstitial sites, the sites being characterized and formed by surrounding atoms of the alloy, the sites being suitable for hydrogen absorption, the distribution comprises at least four different places / μπι3, preferably at least 10 different places / μπι3, more preferably at least 100 different places / μπι3, such as at least 103 different locations / μπι3.

The alloy of any one of claims 8-10, wherein the alloy is a Zr doped MgTi alloy for use in a thin film device comprising 10-40% Zr, 35-80% Mg and 5-55% Ti, or wherein the alloy 10 -40% Zr and 60-90% Mg.

A method for producing a thin film device comprising providing a substrate, depositing an optical detection layer on the substrate, wherein the optical detection layer comprises an alloy according to any of claims 8-11, depositing a catalyst layer on the optical detection layer, providing a protective layer on the catalyst layer, and optionally adjusting the device 1-10 times cyclically.

Use of an alloy according to any of claims 8 to 11 for detecting a chemical species, such as hydrogen.

A sensor comprising a device according to one or more of claims 1-7, preferably a hydrogen sensor, comprising an optical transmitter, such as an optical fiber, wherein the optical detection layer is located on a top of the optical transmitter and / or wherein the optical detection layer is on a longitudinal side of the optical transmitter.

An electromagnetic transformer comprising a hydrogen sensor according to claim 14.

A device for detecting hydrogen comprising a sensor, the sensor being on a longitudinal side of an optical transmitter, the optical transmitter comprising a central transmitter element, such as a quartz core, a transducer layer, preferably with a surface piasmon resonance frequency, a alloy according to any one of claims 8-11, and optionally a protective layer, and a frequency shift detector.