NANOSCALE THERMOMETRY

Abstract

A nanoscale temperature detector including a diamond sensing probe with a transverse dimension of at least 200 nanometres and a sensing tip-having a curvature radius of less than 100 nanometres, less than 10 nanometres or less than 1 nanometre, and a plurality of colour centres, whose emission count rate show temperature-sensitive features. The diamond sensing probe has a transverse dimension of at least 200 nanometres and is connected to a to a detector system by means of a mounting structure. A thermal isolation barrier thermally decouples the sensing probe from the detector system.

Claims

1-15. (canceled)

16. A nanoscale temperature detector comprising - a diamond sensing probe with a sensing tip having a curvature radius (R) of less than 100 nanometres, or less than 10 nanometres, or less than 1 nanometre, and a plurality of colour centres, whose emission count rate show temperature-sensitive features, o wherein the diamond sensing probe is configured to optically guide a light emitted by the colour centres, o wherein the diamond sensing probe has a transverse dimension of at least 200 nanometres, the nanoscale temperature detector further comprising - a mounting structure connectable to a detector system, and - a thermal isolation barrier thermally decoupling the sensing probe from said detector system.

17. The nanoscale temperature detector of claim 16, whereby the plurality of colour centres are NV (nitrogen-vacancy) defects whose electron spin resonance spectra show temperature-sensitive features.

18. The nanoscale temperature detector of claim 16, wherein the colour centres are distributed across the sensing probe.

19. The nanoscale temperature detector of claim 16, wherein the colour centres are localised in a region with a separation distance from the tip no more than 1 micrometre.

20. The nanoscale temperature detector of claim 16, wherein the sensing probe comprises up to 100 ppm colour centres.

21. The nanoscale temperature detector of claim 16, wherein the sensing probe is connected to a diamond holding structure.

22. The nanoscale temperature detector of claim 16, wherein the sensing probe is formed of a single crystal diamond material.

23. The nanoscale temperature detector of claim 21, wherein the sensing probe and said diamond holding structure are formed of a single crystal diamond material.

24. The nanoscale temperature detector of claim 16, wherein the shape of the sensing probe features a conical or pyramidal shape with a sharp apex, and a sidewall inclination angle between 0° and 45°.

25. The nanoscale temperature detector of claim 23, wherein the shape of the sensing probe features a conical or pyramidal shape with a sharp apex and a sidewall inclination angle between 0° and 45°.

26. The nanoscale temperature detector of claim 21, wherein the thermal isolation barrier consists of the same single crystal diamond material as the diamond holding structure featuring structural impediments to thermal conduction, such as a decreased thickness or decreased width, or a phononic structure, or an isotopically modulated diamond structure, or a porous structure, or a grid structure, or other suitable changes in structure.

27. The nanoscale temperature detector of claim 16, wherein the thermal isolation barrier consists of a material with low thermal conductivity, such as quartz or a low-density material.

28. A method of manufacturing the nanoscale temperature detector according to claim 16, comprising a series of lithography and dry etching, commonly known as “plasma etching”, steps to shape the diamond crystal in the desired shape, produce the sensor probe containing NV centres and release the shape from the diamond host.

29. A detector system comprising a nanoscale temperature detector of claim 16, further comprising - an optical excitation source configured to excite the colour centres - a microwave source configured to direct microwaves towards the colour centres - the mounting structure to positioning the sensing probe in relation to a heat source sample - an optical detector capable of measuring the light emitted by the colour centres.

30. A detector system according to claim 29, wherein the optical excitation source is a laser or an LED tuneable to a wavelength less than 575 nm, typically a wavelength of 515 nm or 532 nm.

31. A detector system according to claim 29, wherein the optical detector is a confocal microscope 9 integrated in a scanning atomic force microscope (AFM).

32. A method employing the detector system according to claim 29 comprising: - movably positioning the sensor tip in proximity of or in contact with the surface of a heat source, - applying one or more optical pulse generated by the optical excitation source to the colour centres to polarize the ground electronic spin state, - applying continuously or a plurality of microwave pulses to the colour centres of the sensing probe to alter the spin population, - measuring the spin-state-dependent fluorescence rate of the colour centres, - determining the temperature of the heat-source based on the measured spin-state-dependent emission photon count rate.

33. The nanoscale temperature detector of claim 16, whereby the plurality of colour centres are NV (nitrogen-vacancy) defects whose electron spin resonance spectra show a temperature-dependent zero-field splitting of its ground electronic spin state.

34. The nanoscale temperature detector of claim 16, wherein the shape of the sensing probe features a conical or pyramidal shape with a maximum transversal dimension between 200 nanometres and 500 nanometres, and a sidewall inclination angle between 5° and 30°.

35. The nanoscale temperature detector of claim 23, wherein the shape of the sensing probe features a conical or pyramidal shape with a maximum transversal dimension between 200 nanometres and 500 nanometres, and a sidewall inclination angle between 5° and 30°.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0035] Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

[0036] FIG. 1 illustrates schematically view the scanning sensor probe 1, in which [0037] (A) illustrates the scanning sensor probe 1 connected to a mounting structure 6 [0038] (B) is a detailed view of the scanning sensor tip 2.

[0039] FIG. 2 illustrates schematically possible locations of sensor colour centres 5 in the scanning sensor probe 1, in which [0040] (A) an ensemble of colour centres 5 is located at a distance from the sensor tip 2, [0041] (B) colour centres 5 are distributed over the entire volume of the sensor probe 1, [0042] (C) one or more colour centres 5 are located in the sensor tip 1.

[0043] FIG. 3 is a schematic presentation of the overall thermometry system.

[0044] FIG. 4 is a performance overview of available nanoscale thermal imaging devices at room temperature. Figure adapted from Halbertal et al., Nanoscale thermal imaging of dissipation in quantum systems, Nature 539, 407.

EXAMPLES OF EMBODIMENTS OF THE PRESENT INVENTION

[0045] With reference to FIG. 1, the schematic illustration of this preferred embodiment depicts the nanoscale temperature detector’s essential elements, including a scanning sensing probe 1, which is preferably a monocrystalline diamond probe with microscale volume, featuring a sharp apex, which serves as the scanning sensor tip 2, a plurality of sensor colour centres 5 located in the scanning probe 1, a mounting system 6 and a thermal isolation barrier 3 decoupling said sensing probe 1 from a detector system. In a preferred embodiment, the temperature detector furthermore comprises a diamond holding structure 4, which is preferably part of the of the same diamond monocrystal forming the scanning sensor probe 1. The diamond holding structure 4 essentially serves as a connection to the mounting structure 6.

[0046] With respect to the sample heat source, the scanning sensor can be positioned in contact, non-contact or in tapping mode. The sample heat source is presented on a sample stage 12. Positioning of the scanning sensor is preferably, by employing a quartz tuning fork method according to known methods, wherein diamond to-to-sample distance is based on the piezoelectric effect and achieved with sub-nanometre precision.

[0047] Alternatively, the diamond holding structure may be employed to control positioning in analogy to known positioning methods relying on cantilevers.

[0048] In order to achieve the desired spatial resolution of below 100 nm, below 10 nm, or below 1 nm the curvature radius R of the scanning sensor tip 2 is less than 100 nm, or less than 10 nm, or less than 1 nm.

[0049] The surface temperature of a sample heat source 8 is sensed by means of optically excited colour centres 5 which are located within the sensing probe 1. An ensemble of said colour centres 5 can be distributed over the entire volume of the sensing probe, located in close proximity to the apex of the sensing probe, as shown in FIGS. 2 B and 2 C respectively, or, in a preferred embodiment, located at a separation distance from the sensor tip 2 of the scanning probe 1, as shown in FIG. 2 A. Such separation distance ranges from 0 nm to 1 .Math.m.

[0050] In a preferred embodiment said sensor colour centres 5 are nitrogen vacancy (NV) point defects in the diamond lattice. One property of said NV centres is photoluminescence. NV centres can be optically excited by visible light, in particular a yellow-green laser light or an LED light with wavelength below 575 nm, typically with wavelength of 515 nm or 532 nm. Such light is emitted by an optical excitation source 9a, which forms part of the detector system. Upon relaxation, said excited NV centres 5 emit red fluorescence light which can be detected by an optical detector 9b comprised in the detector system 13. Furthermore, the NV centres spin sub-levels can be manipulated using microwave fields emitted from a nearby antenna that impacts the number of photons emitted by said NV centres when in resonance with said spin sub-levels, constituting an optically detected magnetic resonance (ODMR) spectrum. Importantly, the ODMR spectra of these NV centres show temperature-sensitive features, in particular a temperature-dependent zero-field splitting enabling fluorescence-based thermometry.

[0051] The temperature-sensitive NV centres 5 are directly linked to the sensor tip 2 through the single-crystal diamond material of the sensor probe 1. Said diamond link ensures a rapid thermal conduction from the tip 2 to the sensor NV centres 5. The sensor probe comprises up to 100 ppm colour centres, wherein ppm, or “parts per million”, refers to the ratio between the NV centers and the number of carbon atoms in the diamond lattice. Typically, a sensor probe 1 of an approximate volume of 10.sup.-3 .Math.m.sup.3 to 1 .Math.m.sup.3 comprises up to 3000 sensor NV centres 5.

[0052] The sensor probe is capable of self-calibrated temperature measurements. This is due to the fact, that the zero field splitting D0 of the NV centre electron spin resonance line has a well-known temperature dependence, which is identical for all NV centres and does not require calibration. In particular, D0 2.87 GHz at room temperature, where dD0/dT~-78 kHz/K. Further disturbances such as electric and/or magnetic fields, strain, etc. can affect D0. However, since these effects are well understood, their impact can be separated from the measured temperature changes.

[0053] The microscale diamond sensor probe 1 has a geometrical shape which is suited to guide the light emitted by the colours centres 5, preferably towards the optical window 7. Said geometrical shape comprises at a minimum a transverse dimension of at least 200 nm and a sharp apex, which constitutes the sensor tip 2.

[0054] In one embodiment, said geometrical shape is a cone, a pyramid, or a suitable diverging shape. Said conical, pyramidal or similar shape may have a minimal transversal dimension of between 200 nm and 500 nm, and a sidewall inclination angle between 1° and 45°, preferably between 5° and 30°. Optionally, the shapes may be truncated. Said preferred shapes widen from the sensor tip 2 to the optical window 7, and this widening is suited to reinforce thermal conduction.

[0055] In an alternative embodiment the sensor tip 2 has a parabolic shape. The shape may also be locally parabolic, for example near the tip.

[0056] In terms of its thermal sensitivity, the microscale volume sensor probe 1 is superior to the diamond-based thermal sensors known in the state of the art. At room temperature the sensor described in this invention is capable of attaining thermal sensitivity values in the low K/(Hz) .sup.½ to mK/(Hz) .sup.½ range. At present, the most sensitive single NV centre-based diamond thermal probes can reach sensitivities of approximately 65 mK/Hz.sup.½ under the same temperature conditions.

[0057] As seen from the graphical presentation of FIG. 4 which plots spatial resolution over thermal sensitivity, the microscale sensor probe 1 compares extremely favourably with currently available thermal and spatial high-resolution technology, as it combines a DC thermal sensitivity at room temperature in the low mK/Hz.sup.½ range with values of less than 70 mK/Hz.sup.½, ideally less than 10 mK/Hz.sup.½,with a spatial resolution of 100 nm and below.

[0058] The thermal isolation barrier 3 serves to thermally decouple the scanning probe 2 from the detector system. The thermal isolation barrier 3 may form part of the scanning probe 1 monocrystal, whereby it constitutes a defined section of structural features impeding thermal conductivity of the diamond.

[0059] Alternatively, the thermal barrier 3 may form part of the diamond coupling structure 4.

[0060] In an alternative embodiment the thermal barrier 3 may form part of the mounting structure 6.

[0061] The thermal barrier 3 may be provided by structural features, it may be a porous structure, for example resulting from etched holes, a grid structure, a phononic structure, an isotopically modulated diamond structure, or other structural amendments, which reduce thermal conduction through the thermal isolation barrier 3 section.

[0062] Alternatively, the thermal isolation barrier 3 may consist of a different material, which connects the scanning probe with the mounting structure but prevents conduction of heat. Such material may be a low-density material such as a porous polymer, ceramics other porous material. It may also be any other material which blocks conduction and is sufficiently strong to serve as connector section between scanning sensor probe 1 and the mounting structure 6.

[0063] The thermal isolation barrier 3 may furthermore consist of diamond material with varying isotopic concentrations, quartz, a polymer, a curable resin, or an adhesive.

[0064] Due to its larger micrometre size and its preferred simple shape, production of the diamond sensor probe 1 is readily scalable. The sensing probes can be produced by a series of lithography and dry etching (commonly known as “plasma etching”) steps to shape the diamond crystal in the desired shape, produce the sensor probe containing NV centres and release the shape from the diamond host.

[0065] In a preferred embodiment the thermal sensing probe 1 is connected to the detector system 13, as is shown in FIG. 3. Said detector system comprises the optical excitation source 9a, a microwave source 10, the mounting structure 6, which optionally comprises the microwave source 10, and the optical detector 9b. Both optical excitation 9a and detector 9b are part of a confocal microscope 9 with an objective lens 9c. The microwave source comprises a microwave delivery system 10a and a microwave antenna 10b. Preferably, the system furthermore comprises a sample stage 12 and a sample course positioning structure 11.

[0066] The optical excitations source 9a is configured to excite the colour centres 5. In a preferred embodiment the optical excitation source 9a is a blue or green laser light or an LED light below 575 nm, typically green laser light at 532 nm, suited to excite the electron spins of the sensor NV colour centres 5 from their ground state to their excited state.

[0067] The microwave 10 is configured to direct continuous or pulsed wave microwave radiation to the colour centres, which changes the spin population of the sublevels within the ground and excited state. The microwave frequency is swept to detect spin resonance frequencies, generating an ODMR spectrum.

[0068] A course positioning structure 11 to change the relative position between tip and sample can be used to localize the region of interest of the sample heat source 8. The sample or tip stage 12 is then used to scan the scanning sensor probe 1 with respect to the sample heat source 8. The mode of movement of the sample course positioning 11 and sample stage 12 can be manual but is preferably automated when the system is in measuring mode. During measurements the sensor tip remains static with respect to the optical detection path to ensure the alignment between the optical excitation source 9a, the optical detection source 9b, the objective lens 9c and the scanning sensor probe 1.

[0069] In one embodiment the mounting structure 6 is fixed and the objective lens 9c is movable.

[0070] In an alternative embodiment the mounting structure 6 is movable and the objective lens 9c is fixed.

[0071] In one embodiment the microwave source 10 applies a plurality of microwave pulses to the colour centres.

[0072] In an alternative embodiment the microwave source 10 applies a continuous microwave to the colour centres.

[0073] The optical detector 9b is capable of detecting and quantifying the light emitted by the sensor colour centres 5. For a NV centre-based probe 1, the optical detector 9b must optimally be capable of measuring emission wavelengths ranging from 600 nm to 800 nm. In a preferred embodiment said optical excitation source 9a, the optical detector 9b and the objective lens 9c constitutes a confocal microscope 9 integrated in a scanning atomic force microscope (AFM).

[0074] The nanoscale temperature detector and detector system claimed in this invention can be employed in a method to determine and/or map the surface temperature of a sample heat source 8. Said method comprises several steps, including [0075] movably positioning the sensor tip 2 in proximity of or in contact with the surface of a heat source 8a, [0076] applying one or more optical pulse generated by the optical excitation source 9 to the colour centres 5 to polarize the ground electronic spin state, [0077] applying either a plurality of microwave pulses or a continuous microwave to the colour centres 5 of the sensing probe 1 to alter the spin population, [0078] measuring the spin-state-dependent fluorescence rate of the colour centres 5, [0079] determining the temperature of the heat-source based on the measured spin-state-dependent emission count rate.