PROCESS FOR DEPOSITING METAL OR METALLOID CHALCOGENIDES

Abstract

The instant invention provides a process for making metal or metalloid dichalcogenides from a metal or metalloid and elemental chalcogen using magnetron sputtering. The process may comprise the steps of directing sputtering gas ions at a metal or metalloid target, reacting the ejected metal or metalloid atoms from the target surface with an elemental chalcogen vapor and assembling the metal or metalloid dichalcogenides on a substrate. It can be used to make thin films of the dichalcogenides which have a use in layered semiconductor devices. The process of the invention is suitable for upscaling to potentially make the films on a wafer level. Films on large areas with high uniformity have for instance been obtained utilizing the reaction of the metal or metalloid in an ambient of vaporized chalcogen under controlled conditions and with low growth rates. The process of the invention can be used to deposit two dimensional channels as part of field effect transistors. The materials made with the process in general can have a use in nanoelectronics as a catalyst, as a photo-detector, photovoltaic or photocatalyst.

Claims

1. A process for making metal or metalloid chalcogenides from a metal or metalloid and an elemental chalcogen using magnetron sputtering, wherein the process involves a chemical reaction between the ejected metal or metalloid atoms and the elemental chalcogen.

2. The process of claim 1 wherein the process is a one-step process.

3. The process of claim 1 comprising: a) directing sputtering gas ions at a target comprising a metal or metalloid b) reacting the ejected metal or metalloid atoms from the target surface with an elemental chalcogen vapor and c) assembling the metal or metalloid chalcogenides on a substrate. cm 4. The process of claim 1, wherein sputtering is performed in an apparatus comprising: (i) a vacuum deposition chamber ii) a sputtering target comprising the metal or metalloid iii) a reservoir of elemental chalcogen optionally linked to a vaporizer iv) a power source to effect ejection of the metal or metalloid atoms, v) a substrate on which the deposition of the metal or metalloid chalcogenide occurs.

5. The process of claim 1, wherein the process is performed using a substrate for assembling the chalcogenide which heated to temperature of between about 300° C. and 1000° C.

6. The process of claim 1, wherein the chalcogen is vaporized by heating.

7. The process of claim 6, wherein the heating of the chalcogen is performed by using wrapped heating tape.

8. The process of any of claim 6, wherein the vaporized chalcogen produces a partial pressure of about 1.0 to 9.0×10−7 mbar.

9. The process of any of claim 1, wherein a sputtering gas is used.

10. The process of claim 9, wherein the sputtering gas is provided with a fixed pressure of about 1.0×10.sup.−4 to 3.0×10.sup.−3 mbar.

11. The process of claim 9, wherein the sputtering gas comprises an inert gas.

12. The process of claim 11, wherein the inert gas comprises argon.

13. The process of claim 1, wherein the power source to effect ejection of the metal or metalloid atoms comprises a DC power and a RF power source.

14. The process of claim 13, wherein the power source to effect ejection of the metal or metalloid atoms comprises a DC power.

15. The process of claim 14, wherein the DC power source with a power of less than 10 W is used for the sputtering.

16. The process of claim 1, wherein a substrate is used which is cleaned prior to the sputtering process.

17. The process of claim 16, wherein the cleaning involves using acetone in an ultrasonic bath.

18. The process of claim 1, wherein a substrate is used which comprises materials from the group consisting of glass, silicon, silicon oxides, metal, metal alloy, metal oxides and any mixture thereof.

19. The process of claim 1, wherein the substrate comprises silicon or silicon oxide, optionally in amorphous phase and optionally hafnia-stabilized.

20. The process of claim 18, wherein the substrate comprises aluminum oxide.

21. The process of claim 18, wherein the substrate comprises zirconia.

22. The process of claim 1, wherein the metal or metalloid chalcogenide is deposited as a film on a substrate.

23. The process of claim 22, wherein the film comprises one or multiple monolayers of the metal or metalloid chalcogenides.

24. The process of claim 23, wherein the film has a thickness of about 0.5 to 10 nm.

25. The process of claim 1, wherein the metal or metalloid has an oxidation state of +4 and the atomic ratio between the metal or metalloid and the chalcogen is between about 1:1.75 to 2.05.

26. The process of claim 25, wherein in the metal or metalloid chalcogenide, the metal or metalloid is prismatically coordinated by six surrounding chalcogen atoms and the c-axis is perpendicular to the substrate used in the process.

27. The process of claim 22, wherein the metal or metalloid chalcogenide has semi-conducting properties.

28. The process of claim 1, wherein the metal or metalloid comprises a transition metal.

29. The process of claim 28, wherein the transition metal comprises aluminium, chromium, copper, tungsten and molybdenum.

30. The process of claim 28, wherein the transition metal comprises a metal that is selected from tungsten, molybdenum or a mixture thereof.

31. The process of claim 30, wherein the transition metal comprises molybdenum.

32. The process of claim 1, wherein a sputtering target is used that comprises elemental molybdenum.

33. The process of claim 1, wherein the metal or metalloid chalcogenide comprises a transition metal dichalcogenide.

34. The process of claim 1, wherein the chalcogen comprises sulphur, selenium, tellurium or a mixture thereof.

35. The process of claim 34, wherein the chalcogen comprises sulphur.

36. The process of claim 1, wherein the chalcogen is provided in the form of a powder for vaporization.

37. Creating one or multiple 2D monolayers of the transitional chalcogenide on a substrate by using a process for making metal or metalloid chalcogenides from a metal or metalloid and an elemental chalcogen using magnetron sputtering, wherein the process involves a chemical reaction between the ejected metal or metalloid atoms and the elemental chalcogen.

38. A metal or metalloid chalcogenide obtainable by a process for making metal or metalloid chalcogenides from a metal or metalloid and an elemental chalcogen using magnetron sputtering, wherein the process involves a chemical reaction between the ejected metal or metalloid atoms and the elemental chalcogen.

39. A metal or metalloid chalcogenide in a layered semiconductor device, wherein the metal or metalloid chalcogenide is obtainable by a process for making metal or metalloid chalcogenides from a metal or metalloid and an elemental chalcogen using magnetron sputtering, wherein the process involves a chemical reaction between the ejected metal or metalloid atoms and the elemental chalcogen.

40. A metal or metalloid chalcogenide in nanoelectronics, wherein the metal or metalloid chalcogenide is obtainable by a process for making metal or metalloid chalcogenides from a metal or metalloid and an elemental chalcogen using magnetron sputtering, wherein the process involves a chemical reaction between the elected metal or metalloid atoms and the elemental chalcogen, wherein the metal or metalloid chalcogenide acts as a catalyst, a photo-detector, a photovoltaic or photocatalyst.

41. The metal or metalloid chalcogenide in nanoelectronics of claim 40, wherein the photovoltaic or photocatalyst can be used under visible light conditions.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0078] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0079] FIG. 1 is a schematic drawing of an example of the apparatus suitable for the disclosed process.

[0080] FIG. 2 shows the core level spectra of X-ray photoelectron spectroscopy (XPS).

[0081] FIG. 3 shows a high-resolution X-ray diffraction result for MoS2 film grown as compared to the bulk materials.

[0082] FIG. 4 shows a Raman spectrum of a few-layer large scale MoS2.

EXAMPLES

[0083] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

Example

[0084] The magnetron sputtering of molybdenum is carried out in a vaporized sulphur ambient. The sputtering gun is a Torus magnetron sputtering (TM3u) from K. J Lesker. The target is molybdenum (99.9% from Able Target). The chalcogenide is sulphur (99.5% sulphur powder, purchased from Sigma Aldrich). The power source is DC power. The substrates were pre-cleaned using acetone in an ultrasonic bath before introducing to the deposition chamber. The deposition was performed with a substrate temperature of 700° C. Sulphur powder was heated up above 250° C. by wrapped heating tape to obtain the desired sulphur partial pressure, 4.0×10.sup.−7 mbar in the present system. The argon pressure is fixed at 6.0×10.sup.−4 mbar. Both partial pressures were measured and monitored by RGA CIS 200 from SRS. The DC power is kept as low as 6 W for low growth rate. Using this process, few layers of MoS.sub.2 can be grown on variable substrates, such as sapphire, yttria-stabilized zirconia (YSZ), amorphous SiO.sub.2 and Si etc. To demonstrate the process, few layers of MoS.sub.2 were first grown on c-plane sapphire [Al.sub.2O.sub.3(0001)] and YSZ(111). The out-of-plane orientation of MoS.sub.2 film was determined to be (0001) by high-resolution x-ray diffraction (HR-XRD), recorded on a PANalytical X′pert pro with step size 0.1 degree, dwell time 0.2 second, and a range of 10-80 degree. FIG. 2 shows the core-level XPS spectra of Mo 3d and S 2p on MoS.sub.2/Sapphire, and MoS.sub.2/YSZ systems, recorded on a VG ESCALAB 220i-XL with monochromated X-Ray and 10 eV pass energy to achieve high resolution. As shown in FIG. 2 (a) and (c), the Mo 3d spectra on both substrates are almost identical, which can be fitted using two components at 229.81 and 232.94 eV, respectively, in agreement with reported values. As shown in FIG. 2 (b) and (d), the spin-orbital splitting for S 2p is well resolved which suggest the good film quality. On YSZ, the lower binding energy peaks at 161.31 eV and 159.21 eV come from the Y 3d.sub.3/2 and 3d.sub.5/2 orbitals. The atomic ratio between Mo and S is determined to be 1:2 from quantitatively analysis of XPS peaks. In addition, HR-XRD was used and the crystal structure is of the film confirmed to be 2H—MoS.sub.2 phase on both substrates. In this phase, each Mo atom is prismatically coordinated by six surrounding S atoms and it exhibits semiconducting behaviour. As shown below by HR-XRD, (FIG. 3) and Raman spectrum (FIG. 4), the films can be grown on variable substrates with the c-axis of MoS.sub.2 perpendicular to the substrate surface. All these results demonstrate that the films exhibit correct phase and they are in good quality Raman spectra were obtained on a single-gating micro-Raman spectrometer (Horiba-JY T64000) excited with 532 nm laser. The signal was collected through a 100× objective, dispersed with a 1800 g/mm grating, and detected by a liquid nitrogen cooled charge-coupled device. Photoluminescence (PL) was obtained from the same micro-Raman spectrometer. The Si peak at 520 cm .sup.−1 was used for calibration in the experiments.

[0085] This process can be easily applied to other metal or metalloid dichalcogenide film growth by switching the target between, for example, molybdenum and tungsten, and switching the vapor source between, for example, sulphur and selenium.

INDUSTRIAL APPLICABILITY

[0086] The process for the production of metal or metalloid chalcogenides described in this disclosure may be useful as a facile and low-cost procedure for a high-yield preparation of the materials. Such metal or metalloid chalcogenides have a direct band gap, and can be used in electronics as transistors and in optics as emitters and detectors. The metal or metalloid chalcogenide monolayer crystal structure has no inversion center, which allows to access a new degree of freedom of charge carriers, namely the k-valley index, and to open up a new field of physics: valleytronics.

[0087] The strong spin-orbit coupling in metal or metalloid chalcogenide monolayers lead to a spin-orbit splitting of hundreds meV in the valence band and a few meV in the conduction band, which allows control of the electron spin by tuning the excitation laser photon energy.

[0088] The work on metal or metalloid chalcogenide monolayers is an emerging research and development field since the discovery of the direct bandgap and the potential applications of the very peculiar electron valley physics. The process according to the invention provides a new method for producing such monolayers on larger areas and is therefore suited for mass fabrication of the materials.

[0089] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.