Optical thin-film hydrogen sensing material based on tantalum or other group v element alloy

Abstract

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

Claims

1. A tuneable hydrogen sensing device allowing controlled and reliable, hysteresis free, measurement of an amount of hydrogen comprising: a hydrogen sensing material (12), the hydrogen sensing material comprising an alloy M.sub.1-yA.sub.x B.sub.z, wherein y=x+z, and wherein z0, wherein the metal M is selected from Group V elements, and at least one alloying element A being selected from elements with a cubic unit cell, and combinations thereof, wherein hydrogenation of the sensing material is tuneable by changing an amount x of the at least one alloying element in the alloy M.sub.1-yA.sub.xB.sub.z, wherein the at least one alloying element A is present in an amount of x=0.01-35 atom %; and a hydrogen sensing material read-out system (20), wherein the read-out system is selected from optical read-out systems, dielectric read-out systems, electro-magnetic read-out systems, an electrical voltage detector, an electrical resistance detector, and a transistor, and combinations thereof.

2. The tuneable hydrogen sensing device according to claim 1, wherein the hydrogen sensing material is provided as one of a thin layer, a part of a thin layer, nanoparticles, microparticles, a patterned nanosheet, a nanowire, and a combination thereof.

3. The tuneable hydrogen sensing device according to claim 1, wherein the hydrogen sensing material is provided as one of on a substrate (10), on an adhesion layer (11) which is provided on the substrate (10), is incorporated in an embedding material, is incorporated in a fibre (16), is deposited on a fibre (16), and a combination thereof.

4. The tuneable hydrogen sensing device according to claim 1, wherein the metal M is selected from V, Nb, Ta, and alloys thereof, and wherein the hydrogen sensing material has one of a thickness and a cross-section in the range of 1.5-2000 nm.

5. The tuneable hydrogen sensing device according to claim 1, wherein the hydrogen sensing material further comprises at least one second alloying element B.sub.z, wherein B is selected from metals Pd, Ni, Pt, Ru, Rh, and combinations thereof, wherein hydrogenation of the sensing material is tuneable by changing an amount z of the at least one second alloying element in the alloy M.sub.1-yA.sub.xB.sub.z, wherein the at least one alloying element B is present in an amount of 0.01-5 atom %.

6. The tuneable hydrogen sensing device according to claim 1, further comprising (14) a capping layer between the hydrogen sensing material and a protective layer, wherein the capping layer comprises at least one of Pd, Pt, Ag, Au, Ni, Cu, Ru, and Rh, and wherein the capping layer has a thickness in the range of 1.5-2000 nm.

7. The tuneable hydrogen sensing device according to claim 1, further comprising (15) a protective layer provided on the sensing material, wherein the protective layer comprises a polymer.

8. The tuneable hydrogen sensing device according to claim 1, comprising at least one intermediate layer (11, 13), and wherein the intermediate layer (11, 13) each individually is selected from Ti, Cr, Au, and a combination thereof, and wherein the intermediate layer (11, 13) each individually has a thickness in the range of 1.5-400 nm.

9. The tuneable hydrogen sensing device according to claim 1, wherein the hydrogenation of the sensing material is tuneable from 10.sup.1 Pa (0.001 mbar)-10.sup.8 Pa (1,000,000 mbar), at a temperature of 301K.

10. The tuneable hydrogen sensing device according to claim 6, wherein a/the protective layer and a/the capping layer are combined.

11. The tuneable hydrogen sensing device according to claim 1, wherein a concentration of the at least one alloying element A in the optical sensing layer varies continuously from 0.01 atom % to a maximum atom %, wherein the maximum atom % A is in a range from 10-35 atom %.

12. The tuneable hydrogen sensing device according to claim 1, comprising at least one optical sensing layer, each layer comprising a sensing material.

13. The tuneable hydrogen sensing device according to claim 1, comprising at least two sensing material domains, each domain comprising a different sensing material, wherein the domain has a size of 0.01-10.sup.8 m.sup.2.

14. The tuneable hydrogen sensing device according to claim 1, wherein the device is for use in combination with photons with a wavelength in a range of 200-1200 nm.

15. The tuneable hydrogen sensing device according to claim 1, wherein the sensing material and capping layer exhibit optical interference at at least one given frequency.

16. A sensor comprising at least one device of claim 1, comprising an optical transmitter, wherein the sensing layer is located at a top of the optical transmitter and wherein the sensing layer is located at a longitudinal side of the optical transmitter.

17. A device comprising a sensor according to claim 16 for monitoring one of a hydrogen pressure and a hydrogen concentration, wherein the device is selected from an electro-magnetic transformer, a hydrogen storage device, and a battery.

18. An apparatus for detecting hydrogen comprising a sensor with a sensing material, the sensor being located at one of a longitudinal side of an optical transmitter, and a top side of an optical transmitter, the optical transmitter comprising a central transmitting element, wherein the central transmitting element is a quartz core, a tuneable hydrogen sensing material according to claim 1, the hydrogen sensing material comprising an alloy M.sub.1-yA.sub.x B.sub.z, wherein y=x+z, and wherein z0, wherein the metal M is selected from Group V elements, and at least one alloying element A being selected from elements with a cubic unit cell, and combinations thereof, wherein hydrogenation of the sensing material is tuneable by changing an amount x of the at least one alloying element in the alloy M.sub.1-yA.sub.x B.sub.z, wherein the at least one alloying element A is present in an amount of x=0.01-35 atom %, and a spectrometer.

19. The tuneable hydrogen sensing device according to claim 1, wherein the at least one alloying element A is selected from Pd, Ni, Pt, Ru, Rh, and combinations thereof.

Description

FIGURES

(1) FIG. 1 shows a schematic set-up of the present device.

(2) FIG. 2 shows a stack of layers, comprising a substrate 10, a sensing layer 12, an optional capping layer 14, and an optional protection layer 15.

(3) FIG. 3: Ex-situ XRD results of the 40 nm Ta.sub.1-yPd.sub.y thin films with a 4 nm Ti adhesion layer and capped with a 10 nm Pd layer after exposure of the thin films to hydrogen and measured in air.

(4) FIG. 4a-c: Partial hydrogen pressure and temperature dependence of the optical transmission T of 40 nm Ta.sub.1-yPd.sub.y sensing layers measured relative to the optical transmission of the as-prepared state (T prep).

(5) FIGS. 5a-c show changes of the green light optical transmission T of the 40 nm Ta.sub.1-yRu.sub.y sensing layers. The optical transmission is measured as a function of time and relative to the transmission of the as-prepared film (T prep). The film was exposed at T=28 C. to various increasing and decreasing pressure steps of (a) 1.510.sup.1PH.sub.21.010.sup.+2 Pa, (b) 210.sup.+2PH.sub.2410.sup.+5 Pa, and c) 5.510.sup.+3PH.sub.21.010.sup.+6 Pa. The dashed lines indicate levels of the same transmission (top panel) and pressure (bot-tom panel).

(6) FIG. 6 shows the partial hydrogen pressure dependence of the green light optical transmission T of the 40 nm Ta.sub.1-yRu.sub.z sensing layers measured relative to the optical transmission of the as-prepared state (T prep) at 28 C. Each data-point corresponds to the optical transmission after exposing the film for at least 20 min to a constant pressure of P.sub.H2=10.sup.1-10.sup.+6 Pa, where the closed data points correspond to increasing pressure steps, and the open ones to decreasing pressure steps.

(7) FIG. 7a,b: Stability of a 40 nm Ta.sub.0.88Pd.sub.0.12 thin film with a 4 nm Ti adhesion layer capped with a 10 nm Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 layer that is covered with a 30 nm PTFE layer.

(8) FIG. 8a-c: Adsorption kinetics of a 40 nm Ta.sub.0.88Pd.sub.0.12 thin film with a 4 nm Ti adhesion layer capped with a 10 nm Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 layer that is covered with a 30 nm PTFE layer.

(9) FIG. 9a-b: Comparison of adsorption kinetics between a 40 nm Ta and a 40 nm Ta.sub.0.88Pd.sub.0.12 thin film that both have a 4 nm Ti adhesion layer and are capped with a 10 nm Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 layer at T=28 C.

DETAILED DESCRIPTION OF FIGURES

(10) In the figures: 1 tunable hydrogen sensing device 10 substrate/support 11 optional substrate-sensing layer adhesion material 12 hydrogen sensing material 13 optional capping layer-sensing layer adhesion material 14 capping layer 15 protection layer 16 optical fiber 17 cladding of fiber 18 hydrogen sensing material read-out system 22 splitter 23 CCD camera

EXPERIMENTAL

(11) 1.1 Sample Preparation

(12) The Ta.sub.1-yPd.sub.y samples are composed of a 4 nm titanium adhesion layer, a 40 nm Ta.sub.1-yPd.sub.y layer and a 10 nm cap layer to catalyze the hydrogen dissociation and re-combination reaction and prevent the film from oxidation. As a cap layer, we have both used a Pd and a Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 covered with a 30 nm PTFE layer to reduce response times. The layers are deposited on 10*10 mm.sup.2 quartz substrates (thickness of 0.5 mm and surface roughness <0.4 nm) in 0.3 Pa of Ar by magnetron sputtering in n ultrahigh vacuum chamber (AJA Int.) with a base pressure of 10.sup.10 Pa. PTFE was deposited by radiofrequency magnetron sputtering in 0.5 Pa of Ar. The Ta target was pre-sputtered for at least 240 min to avoid possible contamination from the tantalum oxide and nitride layers at the surface of the target. We note that for commercial manufacturing one can use alloy targets, and that alloys of Ta.sub.1-yPd.sub.y are, even at low concentrations of Pd, not susceptible to nitration and oxidation. This is one of the advantages of the present material over single-element sensing materials.

(13) 1.2 Structural Measurements

(14) Ex-situ X-ray diffraction (XRD) measurements were per-formed with a Bruker D8 Discover in combination with a Cu X-ray source. In-situ XRD measurements were performed with a Bruker D8 Advance in combination with a Co X-ray source and an Anton Paar XRK 900 reactor chamber.

(15) 1.3 Optical Measurements

(16) The white-light optical transmission of the Pd-capped samples were measured using hydrogenography with a Sony DXC-390P three charge-coupled device (3CCD) color video camera and a maximum acquisition frequency of 0.5 Hz. The partial hydrogen pressures of 10.sup.1<PH.sub.2<10.sup.+6 Pa are obtained by using 0.1%, 4% and 100% H.sub.2 in Ar gas mixtures. The measurements on the Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 PTFE capped samples were performed using a similar set-up in which the 3CCD camera was re-placed by an Imaging Source 1/2.5 Aptina CMOS 25921944 pixel monochrome camera with an Edmunds Optics 55-906 lens.

(17) 2. Structural Measurements

(18) FIG. 3 shows ex-situ XRD results of the 40 nm Ta.sub.1-yPd.sub.y thin films with a 4 nm Ti adhesion layer and capped with a 10 nm Pd layer after exposure of the thin films to hydrogen and measured in air. FIG. 3(a) shows diffractograms of the Ta.sub.1-yPd.sub.y thin films. In this figure, the continuous lines represent fits of two pseudo-Voigt functions to the experimental data. In FIG. 3(b) Rocking curves of the Ta.sub.1-yPd.sub.y thin films around the Ta.sub.1-yPd.sub.y <110> peak are shown. FIG. 3(c) shows the Pd doping dependence of the d.sub.110-spacing in Ta.sub.1-yPd.sub.y. FIG. 3(d) displays the Pd doping dependence of the total intensity of the <110> diffraction peak in Ta.sub.1-yPd.sub.y in which the effect of both the changing amplitude and width are incorporated. The intensity is scaled to the intensity of the Ta sample. In this figure, the dashed lines serve as guides to the eye.

(19) Inventors also employ in-situ XRD to study the structural response of Ta.sub.1-yPd.sub.y to hydrogen. The objective of these measurements is to determine whether the various ordered and disordered cubic and orthorhombic phases found in bulk TaH.sub.h for various values of h are present at low temperatures (e.g. below the critical temperature of Tc=61 C.) in the present Ta.sub.1-yPd.sub.y nanosized thin films. If this would have been the case, it would make the thin films unsuitable for room-temperature hydrogen sensing as a result of the sizable hysteresis involved in the first-order transitions between these various phases.

(20) 3. Optical Response of the Sensing Material

(21) For a material to be suitable for optical hydrogen sensing, the optical properties should change considerably and uniformly with the application of a hydrogen pressure. To evaluate this, inventors perform white-light optical transmission measurements of the Pd-capped Ta.sub.1-yPd.sub.y thin films by stepwise exposing the film to a series of increasing and decreasing hydrogen pressures between 10.sup.1<PH.sub.2<10.sup.+6 Pa. It is noted that Ta.sub.0.5Pd.sub.0.5 does not show any optical response in the investigated pressure range and provides similar adhesion conditions, ensuring that the optical response of the Pd layer mimics the one on top of the film of interest.

(22) The levels of transmission are well-defined and stable for a given partial hydrogen pressure, and, importantly, free of any hysteresis: the optical transmission is, in accordance with the in-situ XRD measurements, the same after increasing and decreasing pressure steps.

(23) The optical transmission measurements are summarized in FIG. 4. It shows the measurements performed for different pressures between 1.0 10.sup.1<PH.sub.2<1.0 10.sup.+6 Pa, for different Pd concentrations of 0.0y0.36, and for 28, 60, 90 and 120 C. In this figure, the pressure-transmission-isotherms (PTIs) are plotted, where each closed data-point corresponds to the optical transmission obtained after exposing the film for at least one hour to a constant pressure after an increase in pressure, and the open points to decreasing pressure steps.

(24) The optical transmission measurements are summarized in FIG. 4. It shows the measurements performed for different pressures between 1.0 10.sup.1<PH.sub.2<1.0 10.sup.+6 Pa, for different Pd concentrations of 0.0y0.36, and for 28, 60, 90 and 120 C. In this figure, the pressure-transmission-isotherms (PTIs) are plotted, where each closed data-point corresponds to the optical transmission obtained after exposing the film for at least one hour to a constant pressure after an increase in pressure, and the open points to decreasing pressure steps. The right axis indicates h in Ta.sub.1-yPd.sub.yH.sub.h as based on the scaling between the optical response and the hydrogen content obtained using in-situ neutron reflectometry measurements. Additional optical measurements on a Ta.sub.1-yRu.sub.y sensing layer are provided in FIGS. 5 and 6.

(25) For safety as well as other applications a short response time of a hydrogen sensor is crucial, especially for hydrogen pressures close to the explosive limit in air of 4%. Inventors performed room temperature response time measurements for the Ta.sub.0.88Pd.sub.0.12 sample capped with a 10 nm Pd.sub.0.6Au.sub.0.35Cu.sub.0.05 layer that is covered with a 30 nm PTFE layer which are shown in FIG. 8-9). While other thin film materials re-ported so far often have the disadvantage that the response times are especially at room temperature too long for most applications, the room temperature response time of the 40 nm Ta.sub.0.88Pd.sub.0.12 based thin film is smaller than 1 s in the entire pressure window of PH.sub.2=10.sup.+2<PH.sub.2<10.sup.+5 (measured e.g. at 250 Pa, 420 Pa, 1180 Pa, 3340 Pa, 5630 Pa, 10000 Pa, 15000 Pa, and 47000 Pa. This corresponds to a hydrogen concentration range of 0.1 to 100% under ambient conditions. As shown in FIG. 9, the introduction of Pd in Ta enhances the kinetics. In fact, these response times are shorter than other hydrogen sensors including those based on metal-hydride nanoparticles.

(26) Another requirement to hydrogen sensors is good reproducibility and long-term stability. To illustrate the stability of the sensor response, inventors exposed the thin film to 310 cycles of hydrogen between PH.sub.2=1.0 and 4.0 10.sup.+3 Pa at T=28 C. FIG. 7 demonstrates that no change is behavior or response was observed.