Low-stress thin film multilayers

Abstract

The present disclosure relates to a low-stress thin film comprising a number of bilayers, wherein a bilayer comprises a first layer comprising M, and a second layer comprising X; and wherein at least one of the first layer and the second layer comprises at least one of 11B4C, 10B4C, B4C, 11B, 10B, B and C. The present disclosure 5 also relates to use and a method of producing said low-stress thin film.

Description

[0001] STRESS

[0002] Technical field of the invention

[0003] The present invention relates to a low-stress thin film, use thereof and a method of producing said low-stress thin film.

[0004] Background art

[0005] Metal-based thin film multilayers typically consist of alternating layers of different materials, such as of different metals or of metal and dielectric materials, stacked on a substrate. Each layer often has a thickness on the nanometre scale, and the properties of the overall structure can be tailored by varying the materials and thicknesses of individual layers. These multilayer systems often provide enhanced functionality over single-layer films by exploiting the interactions between different layers, making them vital in advanced technologies across optics, magnetism and energy system. Therefore, metal-based thin film multilayers, such as Fe, Co and / or Ni-based thin film multilayers, are thus used for numerous applications, including inter alia for optical coatings, magnetic storage devices, mirrors and optics, superlattices, and energy and environmental applications.

[0006] However, stress in metal-based thin film multilayers is a common issue that arises during the deposition process and over time, cause several problems in the thin film, including delamination, cracking, and deformation. As a result, stress either completely destroys the film's functionality or leads to performance degradation. The stress is typically increased with an increase in the thin film thickness.

[0007] Managing stress in metal-based thin film multilayers is crucial for ensuring their stability and longevity in applications. Accordingly, there is a need for an improved material with reduced stress therein.

[0008] Summary of the invention

[0009] An object of the present disclosure is to provide new materials which seek to mitigate, alleviate, or eliminate the above-identified deficiencies in the art and disadvantages singly or in any combination. For this and other objects which will be evident from this disclosure, the present invention provides, according to a first aspect, a low-stress thin film comprising a number of bilayers, wherein a bilayer comprises a first layer comprising M and a second layer comprising X; and wherein at least one of the first layer and the second layer comprises at least one of11B4C,10B4C, B4C,11B,10B, B and C.

[0010] According to a second aspect, there is provided use of a low-stress thin film according to the first aspect for one or more of neutron optics, such as polarizing neutron optics, neutron detectors, magnetic sensors, data storage units, such as hard disc drives (HDDs), giant magnetoresistance (GMR) read heads, magnetoresistive random access memory (MRAMs), magnetic recording media, ferromagnetic resonance devices, ferromagnetic resonance (FMR) devices, spintronic devices.

[0011] According to a third aspect, there is provided a method of producing a neutron-reflective and neutron-polarizing bilayer according the first aspect or a multilayer according to the second aspect, wherein the method comprises the steps of: mixing Fe with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a first mixture; mixing X with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a second mixture; the method further comprises the steps of: depositing the first mixture on a substrate such that a first layer is formed, followed by depositing the second mixture on the first layer such that a second layer is formed; or depositing the second mixture on a substrate such that a second layer is formed, followed by depositing the first mixture on the second layer such that a first layer is formed.

[0012] Other objects and advantages will become apparent to those skilled in the art from a review of the ensuing detailed description, which proceeds with reference to the following illustrative drawings, and the attendant claims. The steps of any process disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0013] Preferred embodiments and further aspects are defined in the appended claims, listed embodiments and throughout the application text.

[0014] Brief description of the drawings

[0015] The above and other aspects of the present invention will now be described in more detail, with reference to the appended figures. The figures are not necessarily to scale, and generally only show parts that are necessary in order to elucidate the inventive concept, wherein other parts may be omitted or merely suggested.

[0016] Fig. 1A illustrates multilayers according to the present disclosure, including a multilayer with supermirror geometry comprising depth-graded layer thickness distribution, and a multilayer with multilayer mirror geometry comprising periodic repetition of the layer thicknesses. Fig. 1B illustrates the tensile stress present in the Fe / Cr sample, which can cause substrate curvature, cracking, or delamination during or after deposition (left) and the stress-free condition in the Fe(B4C) / Cr(B4C) sample, resulting in a flat and stable film surface (right).

[0017] Fig. 2 illustrates systems which can perform the method for producing a bilayer or a multilayer according to the present disclosure. Fig. 2a illustrates a system for producing said bilayer or said multilayer using magnetron sputtering. Fig.

[0018] 2b illustrates a system for producing said bilayer or said multilayer using ion beam sputtering.

[0019] Fig. 3 shows wafer curvature measurements of Fe / Si and Fe / Si + B4C (Fig. 3a) and Fe / Cr and Fe / Cr + B4C (Fig. 3b), as well as corresponding quantification of stress of Fe / Si and Fe / Si + B4C (Fig. 3c) and Fe / Cr and Fe / Cr + B4C (Fig. 3d) using the Stoney's equation with linear fits.

[0020] Fig. 4 shows vibrating sample magnetometry on 25 multilayer samples according to the present disclosure. Fig. 4a-4e show the magnetic hysteresis curves for the series of Λ = 300, 100, 50, 30 and 25 Å, respectively. Fig. 4f shows saturated magnetization as a function of concentration. Fig. 4g shows coercivity as a function of concentration. Fig. 4h shows saturated magnetization as a function of period thickness going from large period down to small period. Fig. 4i shows coercivity as a function of period thickness going from large period towards smaller periods. Fig. 4j shows Fe / Si +B4C with 0 and 2.5 % from Fig. 4d in a field range between -6000 and 6000 Oe.

[0021] Fig. 5 shows schematics of the concentration of11B4C for the various period thicknesses according to the present disclosure.

[0022] Fig. 6 shows schematics of hysteresis control using multilayers according to the present disclosure. Fig. 6a shows the control of saturated magnetization using B4C. Fig. 6b depicts the control of coercivity with B4C. Fig. 6c shows the possibility of controlling between FM and AFM coupled magnetic layers using different concentrations of B4C.

[0023] Detailed description

[0024] Metal-based thin film multilayers are engineered structures which are widely used in technology. Multilayer thin films can for example consist of a layer of material A on top of a substrate, whereafter a layer of material B is on top of A, and then this layering of A and B is repeated. However, a structuring of A / B / C or A / B / C / D or any other combination of different layers with or without repetitions is also possible. Such multilayered structures are needed for mirror optics for X-rays and neutrons, magnetic sensors, and data storage. The materials used in the multilayers are carefully selected based on their individual properties, and the thickness of each layer can be adjusted to achieved desired results. This results in an overall structure that can exhibit properties not found in any of the constituent materials alone. These thin films thus offer several advantages over single-layer films, including enhanced mechanical strength, improved thermal stability, and unique optical, magnetic or electronic properties that arise from the interaction between the individual layers therein.

[0025] While metal-based thin film multilayers offer numerous benefits, their fabrication and performance are not without challenges. One major issue is stress within the layers. In general, stresses in thin films, such as Fe-based multilayer thin films, are typically caused by e.g., crystallinity and interface imperfections.

[0026] Compressive or tensile stress causes strong forces causing tears, cracks, shattering and / or delamination of the films, completely destroying their functionality. Such forces are strong enough to cause these issues as soon as the films are fabricated and taken out from the vacuum chamber into the ambiance. Sometimes the film may survive but gets damaged during transport or usage. Generally, the thicker the film, the higher the internal stress. Therefore, metal-based thin film multilayers with reduced stress therein are required.

[0027] The present invention provides, according to a first aspect, a low-stress thin film comprising a number of bilayers, wherein a bilayer comprises a first layer comprising M and a second layer comprising X; and wherein at least one of the first layer and the second layer comprises at least one of11B4C,10B4C, B4C,11B,10B, B and C.

[0028] The inventors have realized that this thin film advantageously achieves sufficient amorphization in each bilayer of the thin film such that a significant reduction of stress is provided.

[0029] Therefore, the present invention provides the above-mentioned advantages using the additive, the at least one of11B4C,10B4C, B4C,11B,10B, B and C, which is sufficient to provide a satisfactory amorphization of the at least one of the first layer and the second layer, and therefore enables reduction of stress in the bilayer and the thin film thereof.

[0030] In an embodiment, M may be a metal. In some embodiments, M may be a magnetic metal. In certain embodiments, M may be selected from one or more of Fe, Co and Ni. In a preferred embodiment, M may be Fe.

[0031] In an embodiment, the maximal concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be determined by the formula: 0.045 · Λ + 1.545 + (2.000 + 0.016 · Λ) volume %, wherein Λ is the thickness of the bilayer in Ångström, Å. In certain embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be at least 1 volume %. In a preferred embodiment, the maximal concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be determined by the formula: 0.045 · Λ + 1.545 + (2.000 + 0.016 · Λ) volume %, wherein Λ is the thickness of the bilayer in Ångström, Å, and the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be at least 1 volume %.

[0032] In an embodiment, the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer may be determined by the formula: 0.045 · Λ + 1.545 ± (2.000 + 0.016 · Λ) volume %, wherein Λ is the thickness of the bilayer in Ångström, Å. Specifically, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer is in a range from (0.045 · Λ + 1.545 -(2.000 + 0.016 · Λ)) volume % and up to (0.045 · Λ + 1.545 + (2.000 + 0.016 · Λ)) volume %, wherein Λ is the thickness of the bilayer in Ångström, Å. In certain embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be at least 1 volume %. In a preferred embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be determined by the formula: 0.045 · Λ + 1.545 ± (2.000 + 0.016 · Λ) volume %, wherein Λ is the thickness of the bilayer in Ångström, Å, such that the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer is in a range from (0.045 · Λ + 1.545 -(2.000 + 0.016 · Λ)) volume % and up to (0.045 · Λ + 1.545 + (2.000 + 0.016 · Λ)) volume %, and the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C in the at least one of the first layer and the second layer may be at least 1 volume %.

[0033] In an embodiment, the bilayer may be at least partly amorphous, such as at least one of the first layer and the second layer may be partly amorphous. In an embodiment, the bilayer may be amorphous, such as at least one of the first layer and the second layer may be amorphous.

[0034] In an embodiment, the first layer may comprise the at least one of11B4C,10B4C, B4C,11B,10B, B and C. In an embodiment, the first layer may be at least partly amorphous. In an embodiment, the first layer may be amorphous. In an embodiment, both of the first layer and the second layer may comprise the at least one of11B4C,10B4C, B4C,11B,10B, B and C. In this case, both layers may be partly amorphous. In an embodiment, both layers may be amorphous. In certain embodiments, the first layer and the second layer may comprise different concentrations of the at least one of11B4C,10B4C, B4C,11B,10B, B and C. In some embodiments, the first layer and the second layer may comprise the same concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C.

[0035] In an embodiment, the thickness, Λ, of the bilayer may be between 1 Å and 500 Å. In some embodiments, the thickness, Λ, of the bilayer may be between 20 Å and 500 Å.

[0036] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be up to 34 volume % for the bilayer having the thickness, Λ, up to 500 Å, such as up to 22 volume % for the bilayer having the thickness, Λ, up to 300 Å.

[0037] In a preferred embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be at least 2.5 volume % for the bilayer having the thickness, Λ, up to 100 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, Λ, up to 50 Å, such as the thickness, Λ, between 15 Å and 50 Å. In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 4.0 volume % for the bilayer having the thickness, Λ, of 10 Å. In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 4.5 volume % for the bilayer having the thickness, Λ, of 20 Å. In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, Λ, of 25 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 2.5 volume % or 5.0 volume % for the bilayer having the thickness, Λ, of 25 Å.

[0038] In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, Λ, of 30 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 2.5 volume % or 5.0 volume % for the bilayer having the thickness, Λ, of 30 Å.

[0039] In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, Λ, up to 50 Å, such as the thickness, Λ, of 50 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 2.5 volume % or 5.0 volume % for the bilayer having the thickness, Λ, of 50 Å.

[0040] In certain embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 10 volume % for the bilayer having the thickness, Λ, between 60 Å and 100 Å. In some embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 2.5 volume % and 9.5 volume %, for the bilayer having the thickness, Λ, of 100 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 2.5 volume % or 5.0 volume % for the bilayer having the thickness, Λ, of 100 Å.

[0041] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be at least 3.0 volume % for the bilayer having the thickness, Λ, between 110 Å and 200 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 3.0 volume % and 16 volume % for the bilayer having the thickness, Λ, between 110 Å and 200 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 4.0 volume % and 12.5 volume % for the bilayer having the thickness, Λ, of 150 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 5.5 volume % and 15.5 volume %, for the bilayer having the thickness, Λ, of 200 Å.

[0042] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be at least 6.0 volume % for the bilayer having the thickness, Λ, between 210 Å and 300 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 6.0 volume % and 22 volume % for the bilayer having the thickness, Λ, between 210 Å and 300 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 7.0 volume % and 18.5 volume % for the bilayer having the thickness, Λ, of 250 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 8.5 volume % and 21.5 volume %, for the bilayer having the thickness, Λ, of 300 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 10 volume %, 15 volume % or 20 volume % for the bilayer having the thickness, Λ, of 300 Å.

[0043] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be at least 8.5 volume % for the bilayer having the thickness, Λ, between 310 Å and 400 Å. In certain embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 8.5 volume % and 28 volume % for the bilayer having the thickness, Λ, between 310 Å and 400 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 10.0 volume % and 24.5 volume % for the bilayer having the thickness, Λ, of 350 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 11.5 volume % and 27.5 volume % for the bilayer having the thickness, Λ, of 400 Å.

[0044] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be at least 11.5 volume % for the bilayer having the thickness, Λ, between 410 Å and 500 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 11.5 volume % and 34 volume % for the bilayer having the thickness, Λ, between 410 Å and 500 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 13.0 volume % and 30.5 volume % for the bilayer having the thickness, Λ, of 450 Å. In some embodiments, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be between 14.5 volume % and 34 volume % for the bilayer having the thickness, Λ, of 500 Å. In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be 15 volume % or 20 volume % for the bilayer having the thickness, Λ, of 500 Å.

[0045] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be up to 34 volume % for the bilayer having the thickness, Λ, up to 500 Å, and the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C may be:

[0046] (i) at least 2.5 volume % for the bilayer having the thickness, Λ, up to 100 Å, such as between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, Λ, up to 50 Å, and between 2.5 volume % and 10 volume % for the bilayer having the thickness, Λ, between 60 Å and 100 Å;

[0047] (ii) at least 3.0 volume % for the bilayer having the thickness, Λ, between 110 Å and 200 Å, such as between 3.0 volume % and 16 volume % for the bilayer having the thickness, Λ, between 110 Å and 200 Å;

[0048] (iii) at least 6.0 volume % for the bilayer having the thickness, Λ, between 210 Å and 300 Å, such as between 6.0 volume % and 22 volume % for the bilayer having the thickness, Λ, between 210 Å and 300 Å;

[0049] (iv) at least 8.5 volume % for the bilayer having the thickness, Λ, between 310 Å and 400 Å, such as between 8.5 volume % and 28 volume % for the bilayer having the thickness, Λ, between 310 Å and 400 Å; or (v) at least 11.5 volume % for the bilayer having the thickness, Λ, between 410 Å and 500 Å, such as between 11.5 volume % and 34 volume % for the bilayer having the thickness, Λ, between 410 Å and 500 Å.

[0050] In an embodiment, the concentration of the at least one of11B4C,10B4C, B4C,11B,10B, B and C is:

[0051] (i) at least 2.5 volume % for the bilayer having the thickness, Λ, up to 100 Å, such as between 2.5 volume % and 4.0 volume % for the bilayer having the thickness, Λ, of 10 Å; between 2.5 volume % and 4.5 volume % for the bilayer having the thickness, Λ, of 20 Å; between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, Λ, of 25 Å, preferably 2.5 volume % or 5.0 volume %; between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, Λ, of 30 Å, preferably 2.5 volume % or 5.0 volume %; between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, Λ, of 50 Å, preferably 2.5 volume % or 5.0 volume %; and between 2.5 volume % and 9.5 volume % for the bilayer having the thickness, Λ, of 100 Å, preferably 2.5 volume % or 5.0 volume %;

[0052] (ii) between 4.0 volume % and 12.5 volume % for the bilayer having the thickness, Λ, of 150 Å; and between 5.5 volume % and 15.5 volume % for the bilayer having the thickness, Λ, of 200 Å;

[0053] (iii) between 7.0 volume % and 18.5 volume % for the bilayer having the thickness, Λ, of 250 Å; and between 8.5 volume % and 21.5 volume % for the bilayer having the thickness, Λ, of 300 Å, preferably 10 volume %, 15 volume % or 20 volume %;

[0054] (iv) between 10.0 volume % and 24.5 volume % for the bilayer having the thickness, Λ, of 350 Å; and between 11.5 volume % and 27.5 volume % for the bilayer having the thickness, Λ, of 400 Å; or

[0055] (v) between 13.0 volume % and 30.5 volume % for the bilayer having the thickness, Λ, of 450 Å; and between 14.5 volume % and 34 volume % for the bilayer having the thickness, Λ, of 500 Å, preferably 15 volume % or 20 volume %.

[0056] In an embodiment, the at least one of the first layer and the second layer may comprise at least one of11B4C,10B4C and B4C. Although all of11B4C,10B4C, B4C,11B,10B, B and C are expected to provide the previously mentioned advantages in the bilayer,11B4C,10B4C and B4C sputter targets are more stable, cheaper and readily available. In a preferred embodiment, the at least one of the first layer and the second layer may comprise11B4C.

[0057] In an embodiment, X may be selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti. In a preferred embodiment, X may be Si. In a preferred embodiment, X may be Cr. In some embodiments, the stress of the low-stress thin film may be reduced by at least 50%. In a preferred embodiment, X may be Si or Cr and the stress of the low-stress thin film may be reduced by at least 50%. In certain embodiments, the stress of the low-stress thin film may be reduced by at least 90%, such as at least 95%, preferably at least 98%. In a preferred embodiment, X may be Cr and the stress of the low-stress thin film may be reduced by at least 90%, such as at least 95%, preferably at least 98%. The term "low-stress film" is thus used herein to refer to a film comprising a number of bilayers, wherein the stress of a bilayer is reduced by the addition of at least one of at least one of11B4C,10B4C, B4C,11B,10B, B and C. The stress of the bilayer is reduced by at least 50%, such as by at least 90%, such as by at least 95%, such as by at least 98 %, after the addition of at least one of at least one of11B4C,10B4C, B4C,11B,10B, B and C, as measured using a X-ray diffractometer of a bilayer without any of11B4C,10B4C, B4C,11B,10B, B and C and of a bilayer comprising at least one of11B4C,10B4C, B4C,11B,10B, B and C. The term "stress-reduced film" is used interchangeable for the term "low-stress film" in the present disclosure.

[0058] In an embodiment, the thickness of the first layer and the second layer may be equal. In an embodiment, the thickness of the first layer and the second layer may be different.

[0059] In an embodiment the number of the bilayers may be at least 20, such as at least 50, such as at least 100, such as at least 500, such as at least 1000, such as at least 10 000.

[0060] In an embodiment, the thickness of bilayers may be the multilayer is equal. In certain embodiment, the multilayer may be a multilayer mirror. In some embodiments, the thickness of bilayers in the multilayer may be equal and the multilayer may be a multilayer mirror.

[0061] In an embodiment, the thickness of bilayers in the multilayer may be different. In certain embodiments, the multilayer may be a supermirror. In some embodiments, the thickness of bilayers in the multilayer may be different and the multilayer may be a supermirror.

[0062] According to a second aspect, the present invention provides use of a low-stress thin film according to the first aspect for one or more of neutron optics, such as polarizing neutron optics, neutron detectors, magnetic sensors, data storage units, such as hard disc drives (HDDs), giant magnetoresistance (GMR) read heads, magnetoresistive random access memory (MRAMs), magnetic recording media, ferromagnetic resonance devices, ferromagnetic resonance (FMR) devices, spintronic devices. Said use also benefits from all previously-described advantages of the first aspect of the invention.

[0063] In an embodiment, the use may be for one or more of neutron optics, neutron detectors, magnetic sensors, and data storage units.

[0064] According to a third aspect, there is provided a method of producing a neutron-reflective and neutron-polarizing bilayer according the first aspect or a multilayer according to the second aspect, wherein the method comprises the steps of: mixing Fe with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a first mixture; mixing X with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a second mixture; the method further comprises the steps of: depositing the first mixture on a substrate such that a first layer is formed, followed by depositing the second mixture on the first layer such that a second layer is formed; or depositing the second mixture on a substrate such that a second layer is formed, followed by depositing the first mixture on the second layer such that a first layer is formed.

[0065] In an embodiment, the method may further comprise the steps of: depositing the first mixture on the second layer; depositing the second mixture on the first layer. The steps of depositing the first mixture on the second layer and depositing the second mixture on the first layer may be repeated until the multilayer with a number of bilayers is obtained. The number of bilayers may be at least 20, such as at least 50, such as at least 100, such as at least 500, such as at least 1000, such as at least 10 000.

[0066] In an embodiment, depositing may be performed using magnetron sputtering, ion beam sputtering, evaporation, radio frequency (RF) sputtering, or pulsed laser deposition (PLD). In some embodiments, depositing may be performed using magnetron sputtering or ion beam sputtering. In a preferred embodiment, depositing may be performed using magnetron sputtering.

[0067] In an embodiment, M may be a metal. In some embodiments, M may be a magnetic metal. In certain embodiments, M may be selected from one or more of Fe, Co and Ni. In a preferred embodiment, M may be Fe.

[0068] In an embodiment, X may be selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti. In a preferred embodiment, X may be Si. In a preferred embodiment, X may be Cr.

[0069] The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0070] In the present disclosure, the term "bilayer" refers to a material comprising one layer comprising M and another layer comprising X. This bilayer may be also referred to as a "M / X" bilayer. The thickness of the bilayer is, in the present disclosure, denoted as A, and it is typically nominal. On the other hand, a "multilayer" refers to a material comprising a number of bilayers, wherein the number could be even higher than 10000 bilayers, while the bilayers may have a thickness of between 1 A and 500 A. The multilayer may have a multilayer mirror geometry or a supermirror geometry depending on a specific application thereof. Fig. 1A illustrates the multilayer mirror geometry and the supermirror geometry, wherein the multilayer mirror geometry has all bilayers with equal thicknesses in the multilayer, i.e., has periodic repetition of the layer thicknesses, while the supermirror has bilayers with different thicknesses in the multilayer, i.e., has depth-graded layer thickness distribution.

[0071] The present invention utilizes at least one of11B4C,10B4C, B4C,11B,10B, B and C to achieve improved interfaces and stress-free films. For examples, Fig. 1B illustrates the tensile stress present in the Fe / Cr sample, which can cause substrate curvature, cracking, or delamination during or after deposition, together with the resulting wafer curvature and potential mechanical failure pathways in the unstabilized Fe / Cr film (Fig. 1b left). In stark contrast, Fig. IB also illustrates the stress-free condition in the Fe(B4C) / Cr(B4C) sample, resulting in a flat and stable film surface, exhibits virtually no curvature across the wafer (Fig. IB right). The extracted stress is -2 MPa (compressive), effectively a stress-free state. This dramatic stress relaxation is attributed to the presence of at least one of11B4C,10B4C, B4C,11B,10B, B and C in the samples according to the present invention. Moreover, the suppression of grain boundary formation and associated volume mismatch during growth likely reduces the buildup of internal stress. Furthermore, boron-containing alloys are known to exhibit lower atomic mobility and reduced columnar growth, both of which contribute to mechanical stabilization during deposition. These results demonstrate that incorporating e.g. B4C into Fe / Cr multilayers not only improves structural and interface quality, but also eliminates problematic residual stress. This represents a significant processing advantage, especially for high-repetition multilayers where mechanical reliability is critical.

[0072] As used herein, the term "B4C" refers to boron carbide, which is a ceramic material primarily composed of boron and carbon. However, due to inherent synthesis challenges, boron carbide frequently deviates from strict stoichiometry of B4C. The material typically exists in a solid solution as BXC with x that spans from 1 to 13, such as from 4 to 13, preferably from 4.3 to 10.5, depending on synthesis conditions and thermal history. The term "B4C" thus encompasses all materials exhibiting the characteristic properties of boron carbide represented by the formula "BXC", regardless of precise composition or structure. Examples of boron carbides include B4C, B5C, B12C3, B12CBC or B13C2, B4.3C, B6.7C, and B10.5C. Variations arising from synthesis methods and processing conditions are included within this definition. Moreover, the term "11B4C" represents any of said boron carbides enriched in the11B isotope, while "10B4C" represents any of said boron carbides enriched in the10B isotope.

[0073] Examples of systems which could be used for performing the method of producing the bilayer or the multilayer are illustrated on Fig. 2a-2b. Fig. 2a illustrates a system which can perform magnetron sputtering deposition, such as magnetron co-sputtering deposition. The system has two shutters which control if M (denoted as Fe on Fig. 2a) or X (denoted as Si on Fig. 2a) is intermixed with at least one of11B4C,10B4C, B4C,11B,10B, B and C (denoted as B4C on Fig. 2a) above a substrate, to form a first mixture comprising Fe and the at least one of11B4C,10B4C, B4C,11B,10B, B and C, or a second mixture comprising X and the at least one of11B4C,10B4C, B4C,11B,10B, B and C. The system may also have an additional shutter (not shown on Fig. 2a) below the at least one of11B4C,10B4C, B4C,11B,10B, B and C, such that the system may deposit pure M or X, i.e., to deposit M or X without the at least one of11B4C,10B4C, B4C,11B,10B, B and C.

[0074] The first mixture or the second mixture is then deposited on a substrate, on which a substate bias is applied to form a first layer comprising the first mixture or the second layer comprising the second mixture. The deposition is continued by depositing the second mixture or the first mixture, i.e., the mixture which is not part of the already-formed layer. The bilayer is thus obtained, but the system may continue depositions to obtain the multilayer. Specifically, the multilayer may be obtained by repeating the steps of: depositing the first mixture on the second layer; depositing the second mixture on the first layer.

[0075] Fig. 2b illustrates another system which can be used for producing the bilayer or the multilayer using ion beam sputtering. The system is arranged to change the position (indicated with a double-sided arrow) of the substrate and thereby control which material mixture is deposited thereon. The first mixture comprises a block of M (denoted as Fe on Fig. 2b) in which one or more pieces of the at least one of11B4C,10B4C, B4C,11B,10B, B and C (denoted as11B4C on Fig. 2b) are included. The second mixture comprises a block of X (denoted as Si on Fig. 2b) in which one or more pieces of the at least one of11B4C,10B4C, B4C,11B,10B, B and C are included. The system may also lack the at least one of11B4C,10B4C, B4C,11B,10B, B and C in Fe or X, such that the system may deposit Fe or X without the at least one of11B4C,10B4C, B4C,nB,10B, B and C. The method is performed as described in relation to Fig.

[0076] 2a.

[0077] As previously mentioned, the inventors have discovered that incorporation of at least one of11B4C,10B4C, B4C,11B,10B, B and C into the M / X multilayer thin films can decrease and, in some cases, eliminate the internal stress, leading to possibilities of growing thicker metal-based multilayer films, thus achieving higher efficiencies in their respective applications. Furthermore, the decreased stress leads to more stable films with less risk of breakage.

[0078] The incorporation of the at least one of11B4C,10B4C, B4C,11B,10B, B and C into the M / X multilayer thin films, for example into Fe / Cr multilayer thin films may at least partly amorphize the layers by B-Fe or B-Cr bonds that replace the Fe-Fe bonds or Cr-Cr bonds. The amorphization of the layers decreases the stress caused by grain boundary formations related to the crystallinity of the layers. The interfaces between layers become smoother, thus also decreasing the stress caused by interface imperfections, which is related dislocations, vacancies and grain boundaries which also is related to crystallinity. The decreased stress leads to higher stability and less risk of cracking, shattering, delamination, and tearing of the films.

[0079] The stress in B4C-incorporated Fe / Si and Fe / Cr multilayer thin films have been investigated using wafer curvature measurements and quantified using the Stoney's equation with linear fits.

[0080] Fig. 3a-3b shows wafer curvature measurements of Fe / Si and Fe / Si + B4C (Fig.

[0081] 3a) and Fe / Cr and Fe / Cr + B4C (Fig. 3b). The spread of the incidence angle when measuring at different positions on the sample shows the curvature caused by stress within the films. Fe / Si and Fe / Cr have higher incidence angle spread than their B4C counterparts, meaning that B4C incorporation decreased the stress. To quantify the stress, the Stoney's equation was used with linear fits to compare the stress for Fe / Si and Fe / Si + B4C (Fig. 3c) and Fe / Cr and Fe / Cr + B4C (Fig. 3d). The stress was reduced by half when incorporating B4C into Fe / Si while the stress was almost fully eliminated when incorporating B4C into Fe / Cr.

[0082] Given the results for the stress reduction, the implications prove that incorporation of B4C considerably outperforms state-of-the-art pure metal-based thin film multilayers, such as Fe / Si and Fe / Cr. It is expected that identical or similar results can be achieved even when changing Fe for any metal or magnetic metal, such as or one or more of Fe, Co and Ti, or when changing Cr or Si for similar elements, such as for one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti.

[0083] Moreover, it is also expected that identical or comparable results can be achieved with any one of11B4C,10B4C, B4C,11B,10B, B and C.

[0084] Examples

[0085] Example 1

[0086] Experimental Methods

[0087] Film Deposition:

[0088] Fe / Si and Fe / Si +11B4C multilayers were deposited using DC magnetron sputtering under ultra-high vacuum conditions (background pressure ~10-7Pa) on Si(100) substrates with native oxide. Substrates were rotated at 15 rpm and maintained at room temperature during deposition. The targets used were Fe,11B4C, and Si, with respective power settings of 33 W, 50 W, and 10-40 W. A substrate bias of -30 V was applied. Layer thicknesses were controlled using computer-operated shutters, and deposition rates were calibrated. Fe / Si +11B4C multilayers were created by co-sputtering11B4C with Fe and with Si, with fine adjustments to the Si vs11B4C ratio achieved by varying Si target power.

[0089] Wafer Curvature Measurement:

[0090] Residual stress in the Fe / Si, Fe / Cr, with and without11B4C, multilayers was evaluated using wafer curvature measurements. This method allowed for the assessment of the mechanical stress induced by film deposition. Measurements were conducted using a Panalytical Empyrean X-ray diffractometer by focusing on the Si substrate peak, and the resulting curvature data were analyzed to calculate film stress using Stoney's equation.

[0091] The X-ray diffraction (XRD) data were collected across multiple positions along the surface of the film, capturing the shift in the diffraction peak as a function of position. The analysis included both Fe / Si and Fe / Cr systems, with and without the addition of11B4C.

[0092] Results:

[0093] The results are shown on Fig. 3. As seen in Fig. 3a and 3b, the diffraction peaks shifted and broadened in the Fe / Si and Fe / Cr samples, indicating significant stress in the films. The inclusion of11B4C in both systems reduced the peak shifts, suggesting a reduction in stress. The wafer curvature results (Fig. 3c and 3d) showed that the Fe / Si multilayer exhibited a compressive stress of approximately -658 MPa, which was reduced to -348 MPa in the Fe / Si +11B4C sample. Similarly, the Fe / Cr system displayed a tensile stress of 881 MPa, which was nearly eliminated (-2 MPa) when11B4C was added to the multilayer.

[0094] These results demonstrate that the incorporation of11B4C significantly reduces stress in both Fe / Si and Fe / Cr multilayer systems, likely due to the amorphous nature of the layers, which disrupts crystallinity and relaxes stress within the multilayers, especially for metals.

[0095] Example 2

[0096] Experimental methods

[0097] Sample preparation

[0098] The 35 samples were deposited on a Si substrate using an ion-assisted magnetron sputtering technique (see Table 1). Across the sample series, the nominal period thicknesses were fixed for each sample but varied between samples, taking values of 500, 300, 100, 50, 30, and 25 A. The number of periods was adjusted accordingly (from 2 to 24) to maintain an overall multilayer thickness of approximately 600 A. Isotope enriched 11B was used, instead of natural B, to increase the sensitivity for neutron measurements. The samples #1 to #32 all have the same amount of Fe and the B4C addition is increasing the multilayer volume and not replacing any amount of Fe or Si.

[0099] Table 1. All deposited samples with their respective number of periods (N), period thickness (A) and concentration ofB4C throughout the multilayer in vol.%. The period thickness is solely nominal. The percentage B4C is an added value, thus the period is an actuality increasing with B4C content. The layer thickness ration Fe / (Fe+Si) was aimed to be 0.5, thus equally thick Fe as Si layers.

[0100]

[0101]

[0102] Magnetic measurements

[0103] All the samples were measured using vibrating sample magnetometry (VSM) to obtain the hysteresis curves as seen in Fig. 4(a-e), where Fig. 4(a-e) shows the hysteresis for each period thickness 300, 100, 50, 30 and 25 A respectively. All samples measured showed considerable magnetization, even when 80 % of the period of the Fe / Si multilayer consisted of B4C. It is apparent that pure Fe / Si multilayers always have a large magnetic coercivity, while the addition of B4C decreases this coercivity until the coercivity disappears. For the samples with A=300 A and 25 A, it is clear how the increasing B4C content decreases the saturated magnetization as well, besides when comparing the pure Fe / Si 25 A with 2.5-10 % B4C Fe / Si 25 A. For the samples with A=100 A and 50 A, the addition of B4C does not alter the saturated magnetization. Note that the saturated magnetization values seen in Fig. 4(f) is obtained from the magnetization at H = 100 Oe, where almost all the samples are arguably saturated. This subplot shows that M decreases as a function of x. Fig. 4(g) shows the coercivity as a function of x for each period thickness. This indicates a decrease in coercivity with increasing x, besides the samples with A=300 A and x = 2.5 vol%. Fig. 4(h) shows the saturated magnetization as a function of A in log scale. The magnetization always decreases with increasing A, regardless of x. Fig. 4(i) shows the coercivity as a function of A for x = 0, 2.5, 5, 10 and 15 vol%. The coercivity is always negligeable when x > 10 %, while the coercivity clearly decreases for thinner A with x = 2.5 and 5 %. However, for pure Fe / Si, the coercivity increases significantly for A=50 and 25 A. The Fe / Si multilayer seems to not be fully saturated even at 100 Oe as seen in Fig. 4(d), but as seen in Fig. 4(j) the Fe / Si sample is not saturated until 5000 Oe is reached.

[0104] Observations and Results

[0105] The results in Fig. 4 show the saturated magnetization amplitude for samples with varying amounts of B4C (samples #1 - #32 in Table 1). The magnetization amplitude in a material is governed by the ferromagnetic coupling between the neighboring atoms: specifically, the greater the number of neighboring magnetic atoms, the higher the magnetization. When the material is diluted with B4C, although the total number of Fe atoms remains constant, the reduced number of neighboring Fe atoms due to the presence of non-ferromagnetic atoms leads to a decrease in magnetization amplitude. Such a dilution effect vs magnetization process allows us to tune the magnetization in X / Y multilayers depending on the B4C concentration, where X is a ferromagnetic material such as Fe and Y is a nonmagnetic material such as Si. However, for the 100, 50 and 25 A periodicity, the decrease in magnetization is not observed in the field range within hundreds of Oe, due to a weak antiferromagnetic coupling for pure Fe / Si multilayers, which is common for Fe layers between 15 and 50 A. The antiferromagnetic coupling between Fe layers naturally requires higher external fields to align all Fe layers' magnetization parallel. Note that a tilt in a hysteresis curves is typical for the multilayers with an antiferromagnetic coupling [Fig. 4(b, c and e)]. The coercivity can also be controlled by incorporating specific amounts of B4C. The coercivity is related to the crystallinity of the ferromagnetic layers. The higher the crystallinity of the Fe layer the larger the coercivity. The incorporation of B4C leads to amorphization of the Fe layers. Thus, the required concentration of B4C for the desired outcome can be extracted. Therefore, the optimal concentration ranges between the fully amorphous concentration and 0 % so as to achieve the desired coercivity. Note however that the thinner the Fe layer are, the smaller amount of B4C is required to eliminate the coercivity.

[0106] Furthermore, these results enables to determine the optimal amount of B4C which leads to amorphization of the Fe layers and stress reduction therein, which has the maximum concentration determined by the formula 0.045 • A + 1.545 + (2.000 + 0.016 ■ A) volume %, and is optionally in a range from (0.045 ■ A + 1.545 -(2.000 + 0.016 ■ A)) volume % and up to (0.045 • A + 1.545 + (2.000 + 0.016 • A)) volume %, wherein A is the thickness of the bilayer in Angstrom, A. Fig. 5 shows schematics of the concentration of11B4C for the various period thicknesses. Fig. 5a shows the concentration of the additive up to the maximum concentration determined by the formula 0.045 • A + 1.545 + (2.000 + 0.016 • A) volume % and is represented by a grey area beneath the black line corresponding to the maximum concentration of the additive for the various period thicknesses. The presence of the additive, such as B4C, optionally at the concentration up to the maximum concentration mentioned herein, would provide desired properties, specifically reduced stress, of M / X multilayers, such as Fe / Si multilayers. Preferably, the concentration of the additive may be at least 1 volume %. Fig. 5b shows the concentration of the additive within said range from (0.045 ■ A + 1.545 - (2.000 + 0.016 ■ A)) volume % and up to (0.045 ■ A + 1.545 + (2.000 + 0.016 ■ A)) volume % and it is illustrated as a grey area between two black lines on the schematics. The black lines represent the maximum and the minimum concentrations of the additive for the various period thicknesses. The concentration of the additive in the mentioned range is sufficient to provide a satisfactory amorphization of the at least one of the first layer and the second layer and thereby provide a reduction of stress in the at least one of the first layer and the second layer. Moreover, the concentration of the additive in the mentioned range additionally enables suppression or elimination of antiferromagnetic coupling, magnetic domains and correlated properties in the bilayer, while preventing any negative effects, connected to a reappearance of antiferromagnetic coupling, which are associated with its excess in the bilayer. Although the maximal concentration and the range were developed for Fe / Si with B4C as the additive, it is expected to withstand for any M / X bilayer, such as for M selected from one or more of Fe, Co and Ni, and X selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, and for any additive selected from at least one of of11B4C,10B4C, B4C,11B,10B, B and C.

[0107] Several linear, tilted, M-H curves are seen in Fig. 4(d) for the samples with a periodicity of 30 A and B4C concentrations 10 % and above. This tilted behavior is common for the antiferromagnetic materials or antiferromagnetically coupled ferromagnetic layers. Another possibility could also be due to magnetic domains within the layers which gives rise to tilted M-H curves. The pure Fe / Si samples also exhibit a slight tilted increase in M with H even beyond its coercive fields. As seen in Fig- 4(j) the Fe / Si sample is not saturated until approximately 5000 Oe is reached. To investigate such tilted behaviors, the PNR results is coupled with the VSM results. Half-order Bragg peaks would only appear if there is a second periodicity, such as an antiferromagnetic coupling between Fe layers causing a magnetic variation with a period twice as large as a bilayer. The pure Fe / Si sample had a half-order Bragg peak for both 5 and 200 Oe meaning that the antiferromagnetic coupling is persistent enough to not let the Fe layers saturate at 200 Oe. The first-order Bragg peak is more polarized for 200 Oe than 5 Oe, which is expected due to the Fe / Si being the common polarizer material system for neutron optics, where the polarization is better the closer to saturation reached. The 5 % sample showed no tilt behavior in the hysteresis seen in Fig. 4, and also had no half-order Bragg peak at 5 or 200 Oe in PNR, as expected. The first-order Bragg peak and its polarization was well defined and prominent for 200 Oe, in agreement with literature. Hence the 5 % sample has no antiferromagnetic coupling. The 15 % sample has the linearly tilted behavior in the hysteresis in Fig. 4(d) and an antiferromagnetic half-order Bragg peak at 5 Oe. Further, as expected, the half-order Bragg peak is gone at 200 Oe in good agreement with the hysteresis curve in being fully saturated already at 70 Oe. In other words, the 15 % sample is antiferromagnetically ordered only within the external field range of -70 Oe to 70 Oe, since the external magnetic force overpowers the antiferromagnetic coupling outside this field range. The reason as to why only a certain period thickness indicate antiferromagnetic coupling is due to a critical spacer thickness that optimizes interlayer exchange interactions. It seems as if the addition of B4C further enhances AFM coupling at 30 A, potentially by promoting amorphization, reducing crystallinity, and improving spacer uniformity. This behavior contrasts with larger periods (50 A, 100 A, 300 A), where weaker coupling arises from reduced overlap of exchange fields. For smaller periods (25 A), the system remains ferromagnetic (FM) but may no longer exhibit effective coupling, as interlayer mixing and structural disruptions dominate, and the spacer layer approaches an insulating-like state, limiting its ability to mediate interactions. These results emphasize the pivotal role of spacer thickness and composition in modulating magnetic properties, underscoring how the interplay between structural and electronic factors shapes the observed behavior.

[0108] The temperature-dependent studies revealed a transition from antiferromagnetically coupled to ferromagnetically coupled phases below specific critical temperatures (TCR). Samples with 10 % and 12.5 % compositions exhibit weaker antiferromagnetic coupling compared to the 15 % sample, as they transition to ferromagnetic coupling below 150 K, whereas the 15 % sample maintains partial antiferromagnetic coupling until 20 K. The 15 % sample demonstrates the strongest antiferromagnetic coupling, indicated by its lowest TCR and the largest field dependence in its M(T) curve, while the 2.5 % sample is ferromagnetically coupled throughout.

[0109] Regarding the magnetic TEM, the complexity of Fe / Si multilayers amorphized by B4C highlights the role of disrupted crystallinity and weakened interlayer interactions in creating weakened magnetic domain behaviors within different layers. Collectively, these results demonstrate how amorphization impacts the coherence and distribution of magnetic domains, while still retaining in-plane closure domain structures across all samples. The lack of thin and well-defined domain walls renders it easy to manipulate the in-plane magnetization.

[0110] Conclusively, hysteresis loops can therefore be controlled in terms of saturated magnetization, coercivity and control between FM and AFM coupling, all depending on the concentrations of B4C, as seen in Fig. 6(a-c).

[0111] Conclusions

[0112] This study investigated the ability to control the magnetization amplitude, the magnetic coercivity, and the ferro- / antiferromagnetic coupling, in Fe / Si multilayers, by simply incorporating B4C throughout the layers in different amounts. The results should withstand regardless of ferromagnetic layer and / or non-magnetic spacer layer material since it is the amorphization of the ferromagnetic layers by using B4C that is crucial. The magnetic tuneability possibilities could give opportunities for applications within spintronics, magnetoresistance, data storage and sensors where many prevalent limitations are caused by the conditions of the magnetic hysteresis, by simply incorporating B4C in magnetic multilayers. The XRD analysis reveals that incorporating B4C into Fe layers causes lattice expansion until amorphization, evidenced by a shift in diffraction peaks to lower angles. Despite the disruption of medium-to long-range crystallinity, Fe-Fe bonds persist, as confirmed by XPS, NEXAFS and magnetic measurements such as magnetometry, polarized neutron reflectivity and microscopy. This unique behavior maintains strong ferromagnetic properties even in the amorphous state, highlighting B C'S potential as an effective amorphization agent while causing negligeable loss in magnetization.

[0113] In the drawings and specification, there have been disclosed example aspects of the disclosure. However, many variations and modifications can be made to these aspects without substantially departing from the principles of the present disclosure. Thus, the disclosure should be regarded as illustrative rather than restrictive, and not as being limited to the particular aspects discussed above. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0114] The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of processes, products, and systems. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other.

[0115] It should be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, and that the example embodiments may be realized in the broadest sense of the claims.

[0116] Itemized list of embodiments

[0117] 1. A low-stress thin film comprising a number of bilayers, wherein a bilayer comprises: a first layer comprising M, and

[0118] a second layer comprising X; and

[0119] wherein at least one of the first layer and the second layer comprises at least one ofnB4C,10B4C, B4C,nB,10B, B and C.

[0120] 2. The low-stress thin film of claim 1, wherein M is a metal.

[0121] 3. The low-stress thin film of claim 1 or 2, wherein M is a magnetic metal.

[0122] 4. The low-stress thin film of any one of the preceding claims, wherein M is selected from one or more of Fe, Co and Ni.

[0123] 5. The low-stress thin film of any one of the preceding claims, wherein M is Fe.

[0124] 6. The low-stress thin film of any one of the preceding claims, wherein the maximal concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is determined by the formula:

[0125] 0.045 ■ A + 1.545 + (2.000 + 0.016 ■ A) volume %,

[0126] wherein A is the thickness of the bilayer in Angstrom, A.

[0127] 7. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is determined by the formula:

[0128] 0.045 ■ A + 1.545 ± (2.000 + 0.016 ■ A) volume %,

[0129] such as wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is in a range from (0.045 ■ A + 1.545 - (2.000 + 0.016 ■ A)) volume % and up to (0.045 ■ A + 1.545 + (2.000 + 0.016 ■ A)) volume %,

[0130] wherein A is the thickness of the bilayer in Angstrom, A.

[0131] 8. The low-stress thin film of claims 6 or 7, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is at least 1 volume %.

[0132] 9. The low-stress thin film of any one of the preceding claims, wherein both of the first layer and the second layer comprise the at least one ofnB4C,10B4C, B4C,nB,10B, B and C. 10. The low-stress thin film of claim 9, wherein the first layer and the second layer comprise different concentrations of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C.

[0133] 11. The low-stress thin film of claim 9, wherein the first layer and the second layer comprise the same concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C.

[0134] 12. The low-stress thin film of any one of the preceding claims, wherein the thickness, A, of the bilayer is between 1 A and 500 A, such as between 20 A and 500 A.

[0135] 13. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is up to 34 volume % for the bilayer having the thickness, A, up to 500 A, such as up to 22 volume % for the bilayer having the thickness, A, up to 300 A.

[0136] 14. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is at least 2.5 volume % for the bilayer having the thickness, A, up to 100 A.

[0137] 15. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, A, up to 50 A, such as the thickness, A, between 15 A and 50 A, such as between 2.5 volume % and 4.0 volume % for the bilayer having the thickness, A, of 10 A; such as between 2.5 volume % and 4.5 volume % for the bilayer having the thickness, A, of 20 A; such as between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, A, of 25 A; such as between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, A, of 30 A; and such as between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, A, up to 50 A, such as the thickness, A, of 50 A.

[0138] 16. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 2.5 volume % and 10 volume % for the bilayer having the thickness, A, between 60 A and 100 A, such as between 2.5 volume % and 9.5 volume %, for the bilayer having the thickness, A, of 100 A.

[0139] 17. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is at least 3.0 volume % for the bilayer having the thickness, A, between 110 A and 200 A.

[0140] 18. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 3.0 volume % and 16 volume % for the bilayer having the thickness, A, between 110 A and 200 A, such as between 4.0 volume % and 12.5 volume % for the bilayer having the thickness, A, of 150 A; and such as between 5.5 volume % and 15.5 volume %, for the bilayer having the thickness, A, of 200 A.

[0141] 19. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is at least 6.0 volume % for the bilayer having the thickness, A, between 210 A and 300 A.

[0142] 20. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 6.0 volume % and 22 volume % for the bilayer having the thickness, A, between 210 A and 300 A, such as between 7.0 volume % and 18.5 volume % for the bilayer having the thickness, A, of 250 A; and such as between 8.5 volume % and 21.5 volume %, for the bilayer having the thickness, A, of 300 A.

[0143] 21. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is at least 8.5 volume % for the bilayer having the thickness, A, between 310 A and 400 A.

[0144] 22. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 8.5 volume % and 28 volume % for the bilayer having the thickness, A, between 310 A and 400 A, such as between 10.0 volume % and 24.5 volume % for the bilayer having the thickness, A, of 350 A; and such as between 11.5 volume % and 27.5 volume % for the bilayer having the thickness, A, of 400 A. 23. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is at least 11.5 volume % for the bilayer having the thickness, A, between 410 A and 500 A.

[0145] 24. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is between 11.5 volume % and 34 volume % for the bilayer having the thickness, A, between 410 A and 500 A, such as between 13.0 volume % and 30.5 volume % for the bilayer having the thickness, A, of 450 A; and such as between 14.5 volume % and 34 volume % for the bilayer having the thickness, A, of 500 A.

[0146] 25. The low-stress thin film of any one of the preceding claims, wherein the at least one of the first layer and the second layer comprises at least one ofnB4C,10B4C and B4C.

[0147] 26. The low-stress thin film of any one of the preceding claims, wherein the at least one of the first layer and the second layer comprisesnB4C.

[0148] 27. The low-stress thin film of any one of the preceding claims, wherein X is selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti.

[0149] 28. The low-stress thin film of any one of the preceding claims, wherein X is Si.

[0150] 29. The low-stress thin film of any one of claims 1-27, wherein X is Cr.

[0151] 30. The low-stress thin film of claim 28 or 29, wherein the stress of the low-stress thin film is reduced by at least 50%.

[0152] 31. The low-stress thin film of claim 29, wherein the stress of the low-stress thin film is reduced by at least 90%, such as at least 95%, preferably at least 98%.

[0153] 32. The low-stress thin film of any one of the preceding claims, wherein the thickness of the first layer and the second layer is equal. 33. The low-stress thin film of any one of the preceding claims, wherein the thickness of the first layer and the second layer is different.

[0154] 34. The low-stress thin film of any one of the preceding claims, wherein the number of the bilayers is at least 20, such as at least 50, such as at least 100, such as at least 500, such as at least 1000, such as at least 10 000.

[0155] 35. Use of a low-stress thin film according to any one of claims 1-34 for one or more of neutron optics, such as polarizing neutron optics, neutron detectors, magnetic sensors, data storage units, such as hard disc drives (HDDs), giant magnetoresistance (GMR) read heads, magnetoresistive random access memory (MRAMs), magnetic recording media, ferromagnetic resonance devices, ferromagnetic resonance (FMR) devices, spintronic devices.

[0156] 36. The use of claim 35, wherein the use is for one or more of neutron optics, neutron detectors, magnetic sensors, and data storage units.

[0157] 37. A method of producing a low-stress thin film according to any one of claims 1-34, wherein the method comprises the steps of:

[0158] mixing M with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a first mixture;

[0159] mixing X with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a second mixture;

[0160] the method further comprises the steps of:

[0161] depositing the first mixture on a substrate such that a first layer is formed, followed by depositing the second mixture on the first layer such that a second layer is formed;

[0162] or

[0163] depositing the second mixture on a substrate such that a second layer is formed, followed by depositing the first mixture on the second layer such that a first layer is formed.

[0164] 38. The method of claim 37, wherein depositing is performed using magnetron sputtering, ion beam sputtering, evaporation, radio frequency (RF) sputtering, or pulsed laser deposition (PLD). 39. The method of claim 37 or 38, wherein depositing is performed using magnetron sputtering or ion beam sputtering.

[0165] 40. The method of any one of claims 37-39, wherein depositing is performed using magnetron sputtering.

[0166] 41. The method of any one of claims 37-40, wherein M is selected from a metal, such as a magnetic metal.

[0167] 42. The method of any one of claims 37-41, wherein M is selected from one or more of Fe, Co and Ni.

[0168] 43. The method of any one of claims 37-42, wherein M is Fe.

[0169] 44. The method of any one of claims 37-43, wherein X is selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti.

[0170] 45. The method of any one of claims 37-44, wherein X is Si.

[0171] 46. The method of any one of claims 37-44, wherein X is Cr.

Claims

CLAIMS1. A low-stress thin film comprising a number of bilayers, wherein a bilayer comprises:a first layer comprising M, anda second layer comprising X; andwherein at least one of the first layer and the second layer comprises at least one ofnB4C,10B4C, B4C,nB,10B, B and C.

2. The low-stress thin film of claim 1, wherein M is a metal, such as a magnetic metal, and preferably wherein M is selected from one or more of Fe, Co and Ni.

3. The low-stress thin film of any one of the preceding claims, wherein the maximal concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is determined by the formula:0.045 ■ A + 1.545 + (2.000 + 0.016 ■ A) volume %,wherein A is the thickness of the bilayer in Angstrom, A.

4. The low-stress thin film of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is in a range from (0.045 • A + 1.545 -(2.000 + 0.016 ■ A)) volume % and up to (0.045 ■ A + 1.545 + (2.000 + 0.016 • A)) volume %,wherein A is the thickness of the bilayer in Angstrom, A.

5. The low-stress thin film of claims 3 or 4, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C in the at least one of the first layer and the second layer is at least 1 volume %.

6. The low-stress thin film of any one of the preceding claims, wherein the thickness, A, of the bilayer is between 1 A and 500 A, such as between 20 A and 500 A.

7. The neutron-reflective and neutron-polarizing bilayer of any one of the preceding claims, wherein the concentration of the at least one ofnB4C,10B4C, B4C,nB,10B, B and C is:(i) at least 2.5 volume % for the bilayer having the thickness, A, up to 100 A, such as between 2.5 volume % and 4.0 volume % for the bilayer having the thickness, A, of 10 A; between 2.5 volume % and 4.5 volume % for the bilayer having the thickness,A, of 20 A; between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, A, of 25 A, preferably 2.5 volume % or 5.0 volume %; between 2.5 volume % and 5.0 volume % for the bilayer having the thickness, A, of 30 A, preferably 2.5 volume % or 5.0 volume %; between 2.5 volume % and 6.5 volume % for the bilayer having the thickness, A, of 50 A, preferably 2.5 volume % or 5 volume %; and between 2.5 volume % and 9.5 volume % for the bilayer having the thickness, A, of 100 A, preferably 2.5 volume % or 5.0 volume %;(ii) between 4.0 volume % and 12.5 volume % for the bilayer having the thickness, A, of 150 A; and between 5.5 volume % and 15.5 volume % for the bilayer having the thickness, A, of 200 A;(iii) between 7.0 volume % and 18.5 volume % for the bilayer having the thickness, A, of 250 A; and between 8.5 volume % and 21.5 volume % for the bilayer having the thickness, A, of 300 A, preferably 10 volume %, 15 volume % or 20 volume %;(iv) between 10.0 volume % and 24.5 volume % for the bilayer having the thickness, A, of 350 A; and between 11.5 volume % and 27.5 volume % for the bilayer having the thickness, A, of 400 A; or(v) between 13.0 volume % and 30.5 volume % for the bilayer having the thickness, A, of 450 A; and between 14.5 volume % and 34 volume % for the bilayer having the thickness, A, of 500 A, preferably 15 volume % or 20 volume %.

8. The low-stress thin film of any one of the preceding claims, wherein X is selected from one or more of Si, Ge, Cr, Zr, Cu, Ti, Mo, W, Al, V, Mn, Zn, Nb, Ag, Au, Hf, Ta and Pd, such as one or more of Si, Ge, Cr, Zr, Cu, Ti, Al, V, Mn, Zn, Nb, Mo, Ag, Au, Hf, Ta, W and Pd, such as one or more of Si, Ge, Cr, Zr, Cu and Ti.

9. Use of a low-stress thin film according to any one of claims 1-8 for one or more of neutron optics, such as polarizing neutron optics, neutron detectors, magnetic sensors, data storage units, such as hard disc drives (HDDs), giant magnetoresistance (GMR) read heads, magnetoresistive random access memory (MRAMs), magnetic recording media, ferromagnetic resonance devices, ferromagnetic resonance (FMR) devices, spintronic devices.

10. A method of producing a low-stress thin film according to any one of claims 1-8, wherein the method comprises the steps of:mixing M with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a first mixture;mixing X with at least one of11B4C,10B4C, B4C,11B,10B, B and C to produce a second mixture;the method further comprises the steps of:depositing the first mixture on a substrate such that a first layer is formed, followed by depositing the second mixture on the first layer such that a second layer is formed;ordepositing the second mixture on a substrate such that a second layer is formed, followed by depositing the first mixture on the second layer such that a first layer is formed.

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