Scanning Sensor Having a Spin Defect

Abstract

A sensor device includes a carrier, a force feedback sensor, and a probe containing a spin defect, the probe being connected to the force feedback sensor either directly or indirectly via a handle structure. In order to couple the spin defect to a microwave field in an efficient and robust manner, the sensor device includes an integrated microwave antenna arranged at a distance of less than 500 micrometers from the spin defect. The sensor device can be configured as a self-contained exchangeable cartridge that can easily be mounted in a sensor mount of a scanning probe microscope.

Claims

1. A sensor device, comprising: a carrier; a force feedback sensor connected to the carrier; a probe containing a spin defect, the probe being connected to the force feedback sensor either directly or indirectly via a handle structure; and an integrated microwave antenna arranged at a distance of less than 500 micrometers from the spin defect.

2. The sensor device of claim 1, wherein the probe is made of a diamond material, and wherein the spin defect is an NV center.

3. The sensor device of claim 1, wherein the probe comprises a tip having a free end defining a sensing surface, the spin defect being embedded in the tip within 100 nanometers from the sensing surface.

4. The sensor device of claim 1, comprising a handle structure connected to the force feedback sensor, wherein the probe comprises a flat slab defining a bottom surface and a top surface, the tip protruding from the bottom surface of the flat slab, wherein the handle structure has a distal end defining a flat mounting surface for the probe; and wherein the top surface of the flat slab is bonded to the flat mounting surface of the handle structure.

5. The sensor device of claim 4, wherein the mounting surface is producible by lithographic patterning of a wafer material.

6. The sensor device of claim 1, wherein the force feedback sensor is a piezoelectric force feedback sensor.

7. The sensor device of claim 1, wherein the microwave antenna comprises a wire, the wire being attached to the carrier, the force feedback sensor, the handle structure or the probe.

8. The sensor device of claim 1, wherein the microwave antenna comprises a conductor that has been lithographically patterned onto at least one of the following structures: the carrier; the force feedback sensor; the handle structure; the probe; a separate dielectric substrate connected to the carrier, to the force feedback sensor, to the handle structure, or to the probe.

9. The sensor device of claim 1, comprising a feed line structure for feeding an AC electric current to the microwave antenna, the microwave antenna being coupled to the feed line structure via ohmic coupling, via capacitive coupling or via inductive coupling.

10. The sensor device of claim 9, wherein the feed line structure comprises at least one conductor that has been lithographically patterned onto at least one of the following structures: the carrier; the force feedback sensor; the handle structure; the probe.

11. The sensor device of claim 1, wherein the sensor device is configured as a self-contained exchangeable cartridge.

12. The sensor device of claim 11, wherein the carrier is configured as a flat chip, one end of the carrier being configured for connection to a sensor mount of a scanning probe microscope.

13. A scanning probe microscope comprising: a sensor device; and a microscope head comprising a sensor mount for mounting the sensor device to the microscope head, the microscope head comprising a positioning device that permits relative motion between the probe and a surface of a sample, the sensor device being removably held in the sensor mount, the sensor device comprising: a carrier; a force feedback sensor connected to the carrier; a probe containing a spin defect, the probe being connected to the force feedback sensor either directly or indirectly via a handle structure; and an integrated microwave antenna arranged at a distance of less than 500 micrometers from the spin defect.

14. The scanning probe microscope of claim 13, further comprising: a distance controller for controlling a distance between the probe and the surface of the sample, the distance controller having an input for receiving signals from the force feedback sensor, and an output connected to the positioning device; a microwave transmitter for supplying microwaves to the microwave antenna; an optical excitation source configured to generate excitation light for optically exciting the spin defect; and a photodetector configured to detect fluorescent light emitted from the spin defect.

15. A method of optically detecting magnetic resonance using a scanning probe microscope, the scanning probe microscope comprising a sensor device, a microscope head, a distance controller, a microwave transmitter, an optical excitation source, and a photodetector, the sensor device comprising a carrier, a force feedback sensor connected to the carrier, a probe containing a spin defect, the probe being connected to the force feedback sensor either directly or indirectly via a handle structure, and an integrated microwave antenna arranged at a distance of less that 500 micrometers from the spin defect, the microscope head comprising a sensor mount for mounting the sensor device to the microscope head and a positioning device that permits relative motion between the probe and a surface of a sample, the sensor device being removably held in the sensor mount, the distance controller being configured to control a distance between the probe and the surface of the sample, the distance controller having an input for receiving signals from the force feedback sensor and an output connected to the positioning device, the microwave transmitter being configured to supply microwaves to the microwave antenna, the optical excitation source being configured to generate excitation light for optically exciting the spin defect, and the photodetector being configured to detect fluorescent light emitted from the spin defect, the method comprising: operating the optical excitation source to expose the spin defect to excitation light so as to spin-polarize the spin defect; operating the pulsed microwave transmitter to expose the spin defect to microwave radiation so as to manipulate a spin state of the spin defect; operating the optical excitation source to expose the spin defect to excitation light so as to optically excite the spin defect; and operating the photodetector to detect fluorescent light from the spin defect.

16. The sensor device of claim 1, wherein the carrier forms two parallel distal arms protruding in a distal direction, defining a slot between them.

17. The sensor device of claim 16, wherein the microwave antenna is attached to the distal arms, traversing the slot between the distal arms.

18. The sensor device of claim 17, wherein the microwave antenna comprises a wire having two ends, each of the ends of the wire being attached to one of the distal arms.

19. The sensor device of claim 6, wherein the force feedback sensor is a tuning-fork sensor arranged to operate in tapping mode or in shear mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

[0038] FIG. 1 shows a sensor device according to a first embodiment; (a) top view; (b) side view;

[0039] FIG. 2 shows a schematic illustration of the relative arrangement of the scanning probe and the antenna in a sensor device according to the first embodiment;

[0040] FIG. 3 shows a magnified schematic illustration of the handle structure and the scanning probe of the sensor device; inset A: magnification of tip portion;

[0041] FIG. 4 shows a scanning electron micrograph of the distal end of the sensor device of the first embodiment, without the scanning probe attached;

[0042] FIG. 5 shows a magnified view of the handle structure, the scanning probe and the antenna;

[0043] FIG. 6 shows a scanning electron micrograph of the handle structure and the scanning probe;

[0044] FIG. 7 shows a highly schematic view of a scanning probe microscope employing the sensor device of the first embodiment;

[0045] FIG. 8 shows a sketch that illustrates the physical principle of the sensor device (adapted from R. Schirhagl, K. Chang, M. Loretz, and C. L. Degen, Nitrogen-vacancy centers in diamond: Nanoscale sensors for physics and biology, Annu. Rev. Phys. Chem. 65, 83 (2014);

[0046] FIG. 9 shows an energy level diagram for a nitrogen-vacancy center;

[0047] FIG. 10 shows optically detected magnetic resonance spectra of a nitrogen-vacancy center at different magnetic fields;

[0048] FIG. 11 shows a functional sketch of the sensor device according to the first embodiment; (a) top view; (b) side view;

[0049] FIG. 12 shows a functional sketch of a sensor device according to a second embodiment; (a) top view; (b) side view;

[0050] FIG. 13 shows a functional sketch of a sensor device according to a third embodiment; (a) top view; (b) side view;

[0051] FIG. 14 shows a functional sketch of a sensor device according to a fourth embodiment; (a) top view; (b) side view;

[0052] FIG. 15 shows a functional sketch of a sensor device according to a fifth embodiment; (a) top view; (b) side view;

[0053] FIG. 16 shows a functional sketch of a sensor device according to a sixth embodiment; (a) top view; (b) side view; and

[0054] FIG. 17 shows a functional sketch of a sensor device according to a seventh embodiment; (a) top view; (b) side view.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0055] A first embodiment of a sensor device according to the present invention is illustrated in FIGS. 1-6. The sensor device is configured as an exchangeable cartridge that forms a self-contained unit for use in a scanning probe microscope.

[0056] As apparent from FIG. 1, the sensor device comprises a carrier 10 in the form of a flat chip made of a dielectric material, e.g., of alumina. The carrier 10 has a proximal end 11 configured for connection to a correspondingly designed sensor mount of a scanning probe microscope. To this end, the carrier 10 forms two parallel proximal arms 13 protruding in the proximal direction, defining a slot of width G between them. The carrier 10 further has a distal end 12. In the region of its distal end 12, the carrier 10 forms two parallel distal arms 14 protruding in the distal direction, defining a slot of width g between them. The outer contour of the carrier 10 tapers towards the distal end over approximately half of its length. Thereby the width w of the carrier 10 at its distal end 12 is smaller than its width W at the proximal end 11. As apparent from FIG. 2, the carrier has constant thickness D. The carrier defines a horizontal plane.

[0057] The sensor device further comprises a force feedback sensor 20 in the form of a piezoelectric tuning fork sensor. In the present embodiment, the tuning fork sensor is arranged to be operated in tapping mode, i.e., the vertical plane defined by the two prongs of the tuning fork is perpendicular to the horizontal plane defined by the carrier 10. The tuning fork sensor is electrically connected to electrically conducting readout lines 15 that have been patterned onto the surface of the carrier 10 by known patterning techniques.

[0058] A thin handle structure 30 made of silicon is attached to the free end of one of the two prongs of the tuning fork sensor. The handle structure is illustrated in greater detail in FIGS. 2 and 3. The handle structure 30 has the shape of a thin, flat arm extending in a vertical plane that is generally perpendicular to the horizontal plane of the carrier and, in the present embodiment, parallel to the vertical plane defined by the two prongs of the tuning fork sensor. In the present embodiment, the proximal end of the handle structure 30 is bonded to a side face of the lower prong of the tuning fork sensor. At the distal end of the handle structure 30, a horizontal mounting surface 31 is formed. By manufacturing the handle structure 30 from a wafer material like silicon in a photolithographic process, it is possible to provide an extremely well-defined, flat mounting surface 31 with minimal roughness.

[0059] A probe 40 made of diamond is attached to the distal free end of the handle structure 30. The probe is illustrated in greater detail in FIG. 3. It comprises a flat slab 41 of diamond material with a flat bottom surface 42 and a flat top surface 43. The top surface 43 is bonded to the mounting surface 31 of the handle structure. Due to the excellent planarity of the mounting surface 31 and of the top surface 43, the probe 40 will always be attached to the handle structure 30 in a readily reproducible, well-defined orientation. A small tip 44 of diamond material, having the form of a frustoconical pillar, protrudes from the bottom surface 42. At its free end, the tip 44 defines a sensing surface 45, which in the present example is flat and has circular shape. The tip 44 comprises a spin defect 46 in the form of an NV center, which is situated in the tip material within 100 nm or less from the sensing surface, e.g., about 10 nm from the sensing surface.

[0060] An antenna 50 in the form of a thin wire is attached to the distal arms 14 of the carrier 10, traversing the distal slot between the arms. The antenna passes the sensing surface 45 of the tip 44 (and therefore the spin defect 46) within less than 500 micrometers, e.g., within 50-150 micrometers in the present example where the antenna is formed by a wire. The antenna is electrically connected to feed lines 16 on the top of carrier 10 for feeding microwave radiation to the antenna. The feed lines 16 have been patterned onto the carrier by known patterning techniques, e.g. lithographic techniques or other pattern transfer techniques. At its proximal end, each feed line 16 defines a contact pad 17 for connection to a microwave transmitter. Likewise, each readout line 15 defines a contact pad at its proximal end. In the present embodiment, the antenna 50 is coupled to the feed lines 15 via an ohmic connection, i.e., the antenna directly electrically contacts the feed lines to feed the current to the antenna.

[0061] The diameter of the wire that forms the antenna can vary in a wide range. For instance, the wire may have a diameter between less than 1 micrometer and more than 100 micrometers. The antenna does not necessarily have to be a wire. More generally the antenna may, e.g., consist of a wire, strip or pattern of a conductive material like Al, Au or Cu in a wide range of sizes, e.g. having a width between 50 nm and 300 micrometers.

[0062] A sensor device according to the first embodiment was manufactured as follows. [0063] a) The carrier chip was cut to size. Size was 14—5.1×0.4 mm.sup.3, and the material was alumina. [0064] b) Electrical readout lines for the piezoelectric force feedback sensor and feed lines for microwave transmission were patterned onto the chip surface. [0065] c) The microwave antenna was bonded to the feed lines. In the present example, the antenna was a wire of 25 micrometers diameter. The antenna was attached in such a manner that it passed within about 130 micrometers from the spin defect. [0066] d) The piezoelectric force feedback sensor was affixed to the chip. In the present example, the force feedback sensor was a quartz tuning fork. [0067] e) The handle structure was affixed to the force feedback sensor. The handle was lithographically fabricated from silicon. It had sub-millimeter size. The shape and size of the handle were tailored to precisely adjust the tilt of the probe, to ensure unblocked optical access to the probe, and to interface with the electromagnetic antenna. [0068] f) A probe in the form of a diamond slab with a diamond tip was affixed to the handle. The diamond tip contained one or several NV centers near the free end of the tip.

[0069] Optionally, further electrically conducting elements can be patterned on either the handle, the diamond slab, or both. These elements may serve to enhance the electromagnetic field at the locus of the NV center.

[0070] Electron micrographs of the actual sensor device are shown in FIGS. 4-6. These images illustrate the large dimensional difference between the dimensions of the carrier and the force feedback sensor (in the millimeter range) and the tip (in the micrometer range). The handle structure aids in bridging this large dimensional gap.

[0071] In the exemplary embodiment, dimensions of the carrier were as follows: overall length of carrier, L=14 mm; width of carrier at proximal end, W=5.1 mm; width of proximal slot, G=1.5 mm; width of carrier at distal end, w=3 mm; width of distal slot, g=1.5 mm; length of proximal portion having constant width, P=7 mm; thickness of carrier, D=0.4 mm. Dimensions of the probe were as follows: length of slab, 5 to 20 micrometers; thickness of slab, 2.5 micrometers; length of tip (measured between bottom surface of slab and free end of tip), 2 micrometers; diameter of tip at base of tip, 0.9 micrometers; diameter of sensing surface at free end of tip, 0.2 micrometers.

[0072] While in the above-described embodiment the carrier has the shape of a flat chip, it is to be understood that shape, layout and dimensions of the carrier can vary in wide ranges. The length of the carrier is preferably less than 100 mm, more preferably less than 50 mm. The maximum width of the carrier is preferably less than 20 mm, more preferably less than 10 nun. The thickness of the carrier is preferably less than 2 mm, more preferably less than 1 mm.

[0073] The shape and dimensions of the probe can also vary. In particular, the tip does not need to be formed on a slab and does not need to have the shape of a truncated cone. For instance, in other embodiments, the tip can have a rounded free end or can be sharply pointed.

[0074] FIG. 7 illustrates, in a highly schematic manner, a complete scanning probe microscope (SPM) setup including the sensor device. The setup comprises a microscope head 110, a microwave transmitter 120, an optics setup 130, an SPM controller 140 and an ODMR controller 150.

[0075] The microscope head 110 comprises a base 111 and a sensor mount 112 configured to receive the proximal end 11 of the carrier 10. The sensor mount 112 comprises contacts 113 for establishing electrical connections to the contact pads 17 on the carrier 10. The microscope head further comprises a first positioning device 114 in the form of a scanning stage, on which a sample 115 is held, and a second positioning device 116, on which a permanent magnet 117 is held. In addition, the microscope head 110 comprises an objective 118 focused onto the free end 45 of the probe tip 44 through the (optically transparent) slab 41 and through the probe tip itself. In other embodiments, the microscope head can be configured to image the probe tip from below. In this case the slab would not have to be transparent.

[0076] The microwave transmitter 120 comprises a continuous (cw) microwave source 121 for generating an AC voltage in the range of typically 0-20 GHz, and a pulse shaper 121 for creating microwave pulses 123.

[0077] The optics setup 130 comprises a laser 131, an acousto-optic modulator (AOM) 132, a semitransparent mirror 133, and a photodetector 134.

[0078] The SPM controller 140 interfaces with the force feedback sensor 20 and the first positioning device 114 to control the distance between the probe tip 44 and the surface of the sample 115 in a manner known per se, and to scan the probe tip 44 over the surface of the sample. The SPM controller further interfaces with the second positioning device 116 to adjust the position of the permanent magnet 117, so as to vary the external static magnetic field to which the sample is exposed.

[0079] The ODMR controller 150 interfaces with the microwave transmitter 120 and with the optical setup 130 to excite and optically polarize the spin defect, to manipulate the spin state of the spin defect, and to record fluorescent light emitted by the spin defect.

[0080] The scanning sensor is operated using the following procedure: [0081] a) The sensor chip is mounted in the scanning probe microscope. [0082] b) The readout lines of the piezoelectric force feedback sensor are connected to the SPM controller 140. [0083] c) The microwave transmission lines are connected to the microwave transmitter 120. [0084] d) The fluorescence of the diamond probe is measured while the probe is scanned over a sample surface of interest. Continuous (cw) or pulse microwave fields are applied to manipulate the spin defect, so as to perform a desired measurement. In addition, DC or low frequency electric or magnetic fields may be applied.

[0085] FIG. 8 illustrates the operational principle of the sensor device. The spin state of the spin defect 46 is influenced by a magnetic field, which in turn is influenced by magnetic structures 116 at or near the surface of the sample 115

[0086] FIG. 9 is an energy level diagram of an NV center. An NV center is a point defect in the diamond lattice. It consists of a nearest-neighbor pair of a nitrogen atom, which substitutes for a carbon atom, and a lattice vacancy. NV centers can be produced by ion implantation with nitrogen ions. NV centers can also be produced from single substitutional nitrogen centers (P1 centers) by irradiation with high-energy radiation such as electron, proton, neutron, ion or gamma irradiation. The P1 centers can be either native or within a purposely grown doped layer at the diamond surface. In both method, NV centers are formed from P1 defects and vacancies by an annealing process. An NV center in the negative charge state comprises an unpaired nitrogen electron and an extra electron, which together form a spin S=1 pair. In the present disclosure, all references to NV centers are to be understood as meaning NV centers in the negative charge state (sometimes also called [NV-] centers in the literature). One important property of NV centers is that close to 100% electron spin polarization can be created by optically pumping the NV centers with green laser light, causing the NV centers to be driven into the m.sub.s=0 substate of the ground state.

[0087] The ground state is a spin one (S=1) triplet. In the absence of a magnetic field, the triplet is split into an m.sub.s=0 and two degenerate m.sub.s=±1 sublevels. The m.sub.s=0 and m.sub.s=±1 are separated by a Δ=2.87 GHz zero field splitting. By irradiating green laser light, the excited state is populated. The system returns to the ground state by fluorescence. The electronic transition is spin-preserving. The m.sub.s=±1 substate of the excited can in addition return to the m.sub.s=0 substate of the ground state via a dark intermediate state. In this manner, the m.sub.s=0 substate becomes preferentially populated. A further consequence is that fluorescence of the m.sub.s=0 transition is brighter than for the m.sub.s=±1 transition. Microwave excitation at the resonance frequency manipulates the spin states and thereby causes a fluorescence drop. A static magnetic field causes a Zeeman splitting between m.sub.s=±1 substates. The degeneracy of the m.sub.s=±1 states is thus lifted, and the electron spin resonance spectrum contains two resonance lines, one shifted to the higher and the other shifted to the lower frequency (see FIG. 10). By measuring the frequency difference 2γB between the resonances, the magnitude of the external field can be calculated. The NV center has a preferred axis, given by the principal axis of the zero field splitting tensor and corresponding to the (111) crystallographic axis. B is the component of the vector magnetic field that is parallel to the NV principal axis.

[0088] It has also been shown that NV centers can be used to measure temperature (V. M. Acosta, E. Bauch, M. P. Ledbetter, A. Waxman, L. S. Bouchard, and D. Budker, Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond, Phys. Rev. Lett. 104, 070801 (2010)) and electric fields (Nature Physics Volume 7, Pages 459-463 (2011)).

[0089] In more detail, measurements are carried out as follows: [0090] a) The spin defect 46 (a nitrogen-vacancy center) is exposed to green laser light. This polarizes the spin defect within 1 microsecond. [0091] b) The spin defect 46 is exposed to cw or pulsed microwaves 123 of a defined frequency ω. If this frequency matches a resonance frequency ω.sub.0 of the spin defect, the spin state of the spin defect is manipulated. [0092] c) The resulting spin state is measured using a second laser pulse and fluorescence detection. Fluorescent light from the spin defect is read out through the diamond material of the probe. The diamond material thus acts as an optical outcoupling structure for the fluorescent light, which guides the fluorescent light towards an output end of the outcoupling structure. In the present case, the top surface of the probe forms the output end. The recorded signal is the fluorescence intensity, which depends on the spin state. [0093] d) The resonance frequency coo is very specific. It shifts with field as ω.sub.0=2870 MHz±(B/1 mT)*28.0 MHz. By measuring coo, the local magnetic field is measured. The local magnetic field can, e.g., be influenced by a magnetic moment on the sample surface. The spin state can also be influenced by other parameters such as an electric field, causing a Stark shift, or temperature, causing variations of axial zero-field splitting. [0094] e) 2D or 3D scanning is used to measure the magnetic field or other parameters as a function of position. [0095] f) The spatial resolution is roughly given by the sensor-to-surface distance, which can be <20 nm. [0096] g) By using sophisticated microwave pulse sequences, different details of the magnetic sample surface can be probed (like, a frequency spectrum).

[0097] In summary, the above disclosure can be characterized as relating to a novel scanning probe that uses quantum metrology for enhanced sensitivity and spatial resolution. The system consists of a diamond tip with one or several defect spins (such as nitrogen-vacancy centers, or NV centers) at its free end, a distance sensor, and a microwave antenna. These elements are integrated on a single carrier, which preferably has the form of a chip. The carrier moreover contains suitable electrical connections to efficiently and conveniently operate the distance sensor and microwave antenna. For performing a measurement, the sensing surface of the tip is positioned within 500 nm, better within 200 nm, more preferably within 100 nm from the investigated sample surface while the spin resonance of the defect spin is analyzed using optical and microwave pulses. Advantageously the distance between the sensing surface and the sample surface is as small as possible, ideally less than 10 nm. In practice, distances between 25 and 100 nm have already been achieved. In this way, magnetic, electrical, thermal or other properties of the surface can be detected and imaged with <100 nm, and possibly <10 nm spatial resolution. In addition, the frequency characteristics of signals can be analyzed. Measurements can be carried out at any temperature from 0-400 K, and in particular at room temperature. Since the sensor consists of a single, atom-like magnetic impurity, magnetic back-action on the sample is negligible (in contrast to other probes, such as magnetic force microscopy tips). The combination of the above features greatly enlarges the range of samples and phenomena that can be studied at the nanoscale.

[0098] FIG. 11 is a functional sketch of the sensor device according to the first embodiment, wherein the relative dimensions of the different components of the sensor device are deliberately drawn not to scale. In particular, the size of the probe is greatly exaggerated in relation to the size of the carrier, the force feedback sensor, and the handle structure. This sketch is provided in order to enable a more direct comparison of the design of the first embodiment to the designs of the further embodiments that will be discussed in the following. For simplicity the readout lines are not shown in the sketch.

[0099] As illustrated in FIG. 11, the bottom side of the carrier 10 can be provided with an electrically conducting layer 18 forming a ground plane for the microwave feed lines 16 and for the readout lines. As discussed above, the antenna 50 is a piece of wire passing in close proximity to the NV centers. Contact between the antenna and the microwave feed line are ohmic. The feed lines can form a microstrip waveguide, a coplanar waveguide or another arrangement for efficient microwave transport.

[0100] FIGS. 12 to 17 are functional sketches of sensor devices according to a second to seventh embodiment. In all these sketches, relative dimensions between the various components are not to scale.

[0101] FIG. 12 is a functional sketch of a sensor device according to a second embodiment. The general setup largely corresponds to the setup of the first embodiment; however, the piezoelectric force feedback sensor 20 is mounted for operation in shear mode. To this end, the two prongs of the tuning fork are arranged in a horizontal plane rather than in a vertical plane as in the first embodiment.

[0102] FIG. 13 is a functional sketch of a sensor device according to a third embodiment. In this embodiment, the microwave feed lines 16 and the antenna 50 are formed on a separate dielectric substrate 60 connected to the carrier 10. The dielectric substrate 60 has the shape of a flat slice extending parallel to the horizontal plane defined by the carrier 10. It has a through opening 71 allowing free access to the probe 40 from above, so as to be able to shine light on to the probe 40 from above. The feed line 16 and the antenna 50 are lithographically patterned on the dielectric substrate. As in the previous embodiment, contacts between the antenna and the microwave feed lines are ohmic. By patterning the antenna on a dielectric substrate, the impedance characteristics of the antenna and its coupling to the spin defect can be controlled in a highly reproducible manner.

[0103] FIG. 14 is a functional sketch of a sensor device according to a fourth embodiment. In this embodiment, the antenna 50 is a planar loop passing in close proximity to the probe tip 44. The antenna 50 is attached to the handle structure 30. It can be formed by a piece of wire or can be lithographically patterned on an annular dielectric substrate. The antenna 50 can be brought closer to the spin defect than in the previous embodiments; the minimal distance between the antenna and the spin defect will typically be in the range between 10 and 100 micrometers. A microwave field is inductively coupled to the antenna 50 by means of a transmit antenna (not shown). The antenna can be part of a resonant circuit, or it can form a resonant circuit by itself. The transmit antenna can be integrated with the sensor device itself, e.g., can be arranged on the carrier 10 or on any other component of the sensor device. In other embodiments, the transmit antenna can be provided separately from the sensor device itself and can be arranged on any other structure of the scanning probe microscope setup in which the sensor device is used.

[0104] FIG. 15 is a functional sketch of a sensor device according to a fifth embodiment. In this embodiment, the antenna 50 is a planar loop formed directly on the probe 40 itself, in close proximity to the probe tip 44. By arranging the antenna directly on the probe, the distance between the antenna and the spin defect can be further minimized. For instance, in the present embodiment, the minimal distance can be chosen to be 1-50 nm. To achieve efficient coupling, the antenna may be made of or be surrounded by a high-ϵ or high-μ material. As in the previous embodiment, a microwave field is inductively coupled to the antenna 50 by means of a transmit antenna (not shown), which can be part of the sensor device itself or can be provided separately.

[0105] FIG. 16 is a functional sketch of a sensor device according to a sixth embodiment. As in the previous embodiment, the antenna 50 is a planar loop formed directly on the probe 40 itself, in close proximity to the probe tip 44. In contrast to the previous embodiment, however, the antenna 50 is capacitively coupled to the feed lines 16 across an air gap between the feed lines 16 and the antenna 50. In the present embodiment, the feed lines 16 are provided on the sensor device itself, in particular, on the carrier 10. In other embodiments, a feed line structure for capacitive coupling to the antenna 50 can be arranged separately from the sensor device itself.

[0106] FIG. 17 is a functional sketch of a sensor device according to a seventh embodiment. As in the previous embodiment, the antenna is a planar loop formed directly on the probe 40 itself. The microwave feed lines extend from the carrier 10 via the handle structure 30 directly to the antenna 50. The antenna 50 is directly electrically connected to the microwave feed lines via an ohmic connection.

[0107] From the above examples it is apparent that many further modifications are possible without leaving the scope of the present invention.

LIST OF REFERENCE SIGNS

[0108] 1 sensor device 61 through opening
10 carrier 110 microscope head
11 proximal end 111 base
12 distal end 112 sensor mount
13 proximal arm 113 contact
14 distal arm 114 first positioning device
15 readout line 115 sample
16 feed line 116 second positioning device
17 contact pad 117 permanent magnet
18 ground plane 118 objective
20 force feedback sensor 120 microwave transmitter
30 handle structure 121 microwave source
31 mounting surface 122 pulse shaper
40 probe 123 microwave pulses
41 slab 130 optics setup
42 bottom surface 131 laser
43 top surface 132 acousto-optic modulator
44 probe tip 133 semitransparent mirror
45 sensing surface 134 photodetector
46 spin defect 140 SPM controller
50 antenna 150 ODMR controller
60 dielectric substrate