Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1262—Process of deposition of the inorganic material involving particles, e.g. carbon nanotubes [CNT], flakes
  • C23C18/127—Preformed particles
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/1208—Oxides, e.g. ceramics
  • C23C18/1216—Metal oxides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1254—Sol or sol-gel processing
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1295—Process of deposition of the inorganic material with after-treatment of the deposited inorganic material

Definitions

• the invention relates to a method for producing a coating with nanodiamonds doped with foreign atoms embedded in the coating. Furthermore, the invention relates to such a coating and a substrate coated with such a coating. Furthermore, the invention relates to the use of such a coating.
• Doping diamonds with specific foreign atoms leads to the formation of color centers, which exhibit characteristic fluorescence behavior. Interactions of the electrons involved in the color centers with the nuclear and electron spins of atoms in their immediate vicinity, as well as with external magnetic fields, lead to defined changes in this fluorescence behavior and can thus be used to measure various quantities. Since the interactions of individual electrons or their spin states with their environment are used for metrological purposes, these sensors are also referred to as quantum sensors. Doping atoms that can be used for such quantum sensing applications include nitrogen, silicon, or germanium.
• the excitation of the color centers is typically achieved with laser light with a wavelength matched to the absorption behavior of the respective color center.
• the information sought is obtained from the intensity spectrum of the emitted fluorescent light measured in different measurement configurations, e.g., the position, width, and, if applicable, splitting of the fluorescence lines or their temporal change after short excitation pulses (pulse-probe measurement, e.g., for determining spin relaxation times).
• Quantum sensors can also be used as detectors (signal pickups) for magnetic resonance spectroscopy (NMR, ESR) (see e.g. Bucher et al., Quantum diamond spectrometer for nanoscale NMR and ESR spectroscopy. Nat Protoc 14, 2707-2747 (2019 In this case, polarization of the spins to be detected in the sample by an external magnetic field and excitation by electromagnetic waves in the radio to microwave range coupled into the sample are also required.
• NMR magnetic resonance spectroscopy
• ESR magnetic resonance spectroscopy
• This high chemical stability must also be maintained over a wider temperature range, which ideally is only limited by the chemical-thermal stability of the quantum sensors themselves, i.e. the doped diamond(s) or the color centers they contain, or that of the substrate (wall material of the device) to which they are applied.
• the stable application range of the fixation should extend over a temperature window up to approximately 350 °C, which covers the majority of applications for reactions in liquid media.
• the stability requirements relate in particular to the application of the quantum sensors to surfaces and materials, as they are used in chemical or are common in micro-process engineering equipment construction, such as glass, sapphire, silicon carbide or other oxide, carbide or nitride ceramic materials, as well as stainless steels, nickel-based materials (including nickel), titanium, tantalum, zirconium or other refractory metals and their alloys.
• the quantum sensors must be fixed in such a way that at least a significant proportion of the color centers used for the measurement are in sufficiently close contact with the process medium, i.e. are not covered by passive material or are covered only to a very small thickness (max. a few nanometers).
• CVD chemical vapor deposition
• additional species e.g., hydrogen
• the dopant atoms can be introduced, for example, by using suitable precursors during diamond growth or by ion implantation into the finished diamond layer.
• the GB 258 67 05 A a fluorescence sensor for determining various quantities, in particular concentrations of certain analytes, based on fluorescent nanoparticles, which can be nanodiamonds, among others, and which are embedded in a "matrix material".
• the matrix materials can be hydrogels, e.g. on a Cellulose-based materials, which preferably exhibit a certain degree of permeability to the respective analyte to promote its contact with the fluorescent nanoparticles, are suitable.
• the disclosed matrix materials do not exhibit sufficient chemical, thermal, and mechanical stability to allow for long-term use in a wider range of chemical processes.
• the CN 101 585 534 B describes a process for producing thin layers containing nanodiamonds, which is incorrectly referred to here as a "sol-gel process" because the starting materials for the matrix material are only ethyl cellulose, graphite, and terpineol, which are dried at temperatures of up to 620 K and apparently carbonize at least partially in the process. Due to its opacity, the disclosed layer is not suitable, or at best only very limitedly suitable, for sensor applications using light.
• the EP 230 34 71 B1 relates to a process for applying a thin layer of nanodiamonds to gemstones to improve their optical appearance and surface hardness.
• the nanodiamonds are first deposited onto the substrate surface from a dispersion, possibly containing a sol, but are not fixed to a satisfactory chemical stability.
• EP 230 34 71 B1 Therefore, the application of a cover layer made of a particularly hard material is proposed as an optional follow-up step, but this, in turn, requires significantly increased equipment complexity.
• sensor applications are not possible or only possible to a limited extent due to the cover layer completely covering the near-surface nanodiamonds.
• a sol-gel process using a sol based on tetraethylorthosilicate is described in the CN 112 146 782 B for the fixation of nitrogen-doped nanodiamonds for use as quantum sensors.
• the described method also fails to achieve satisfactory chemical resistance.
• the JP 2009 102 188 A discloses a silicate-based glass material containing nanodiamonds, which can also be used for coating purposes, as well as the production of the glass material using sol-gel methods.
• the nanodiamonds essentially serve to improve the mechanical properties of the resulting composite. Due to their limited chemical The durability of the layer containing the nanodiamonds is also not suitable or only partially suitable for use as quantum sensors in chemical applications.
• the present invention is therefore based on the object of designing and developing the method, the coating, the coated substrate and the use of the type mentioned at the outset and explained in more detail above in such a way that a fixation of doped nanodiamonds on solid surfaces can be provided which has a high mechanical stability and a high resistance to a wide selection of chemicals over a wide temperature range, can be applied using simple and cost-effective methods and enables the nanodiamonds to have as little restricted contact as possible with fluid media in the environment.
• the stated object is further achieved according to claim 6 by a coating comprising zirconium(IV) oxide crystallized in the tetragonal phase with doped nanodiamonds embedded therein, preferably produced by a method according to one of claims 1 to 5.
• the above-mentioned object is also achieved according to claim 9 by a coated substrate with a coating according to one of claims 6 to 8, characterized in that the coating is applied to a substrate made of glass, sapphire, an oxide, carbide or nitride ceramic material, stainless steel, nickel, a refractory metal or a base alloy of nickel or a refractory metal and/or that the substrate is part of an apparatus for carrying out physical, chemical or biological processes, in particular a chemical or biological reactor.
• the above-mentioned object according to claim 10 is achieved by using a coating according to one of claims 6 to 8 or a coated substrate according to claim 9 for measuring physical or chemical quantities such as temperature, pressure, fluid velocity, magnetic flux density, pH value or concentration of one or more substances.
• the coating is deposited onto the substrate using a sol-gel process from a liquid phase containing doped nanodiamonds suspended or dispersed therein and dried.
• the coating is then converted into a crystalline state at elevated temperature, in which the zirconium is present as zirconium(IV) oxide, at least partially in its tetragonal phase.
• the zirconium-based sol required for the coating can be prepared according to recipes known to those skilled in the art.
• a zirconium alkoxide such as zirconium(IV) butoxide or zirconium(IV) propoxide
• an alcohol e.g., ethanol or 2-methoxyethanol
• a complexing agent such as acetylacetone or 1-benzoylacetone
• Nitric acid for example, can be used to acidify the water.
• the mixture is stirred at room temperature for an extended period—e.g., several hours to days—where the sol forms by hydrolysis.
• Other known processes include the addition of aqueous ammonia solution to an aqueous or aqueous-alcoholic solution of zirconyl chloride, optionally mixed with complexing agents such as citric acid.
• a soluble yttrium salt for example, yttrium(III) nitrate hexahydrate, yttrium(III) chloride, yttrium(III) bromide, or yttrium(III) iodide
• the amount of this yttrium salt in the sol can preferably be such that between 0.01 mol and 0.1 mol, preferably between 0.03 mol and 0.06 mol, of yttrium is used per mole of zirconium.
• Nanodiamonds are diamonds whose dimensions as individual particles are less than one micrometer in at least one spatial direction. Nanodiamonds doped with foreign atoms are preferably used as Quantum sensors are used, which have a dimension between 10 nm and 100 nm in at least one spatial direction. Doping in this context means the introduction of foreign atoms into the diamond lattice with the aim of generating color centers, i.e., local irregularities in the diamond lattice that can absorb light. Color centers that also exhibit fluorescence in the wavelength range of visible light or in the infrared range are preferred. This is achieved, for example, by doping with nitrogen, silicon, or germanium.
• the doping strength i.e., the concentration of dopant atoms in the nanodiamond lattice, depends on the application and, where applicable, on the spatial distribution of the dopant atoms within the diamond particles. Typical values range from approximately 1 ppm to 10 ppm, but significantly lower or significantly higher values are also possible. Sometimes it is desirable to have only one active color center in each nanoparticle, e.g., to avoid statistical superposition of fluorescence signals caused by different influences on different color centers by targeted observation of individual color centers. In other cases, it may be useful to achieve the highest possible density of color centers, e.g., to achieve a high signal strength by simultaneously recording the fluorescence signals of several color centers or to average over a spectrum of local environmental influences.
• the nanodiamonds can be provided with chemical surface functionalization, e.g. to change their wetting properties towards the sol, their dispersion behavior or their adhesion properties to the substrate or to the coating in which they are embedded, and to adapt them to the conditions of the coating process or the subsequent applications.
• the doped nanodiamonds can be added directly to the sol in powder form, or they can first be pre-dispersed in a suitable solvent, e.g., an alcohol. Pre-dispersion can facilitate the handling of the small amounts of doped nanodiamonds required for the process, particularly in laboratory or small-scale production.
• Their concentration in the sol is typically in the range of 0.01 ⁇ g/mL to 100 ⁇ g/mL, depending on the size of the doped nanodiamonds, layer thickness, and desired areal density of diamond particles in the coating.
• the dispersion can be advantageous to subject the dispersion to ultrasound for a certain period of time, e.g., one hour or longer, in order to break up any aggregates that may be present.
• the sol can be applied to the substrate using methods known to those skilled in the art, which allow liquid media to be applied to solid substrates with the most uniform thickness possible. These include, for example, dip coating, spin coating, doctor blade coating, spraying, roller coating, or screen printing. Dip and spin coating have proven particularly effective, particularly for planar or slightly curved substrates with an otherwise smooth surface, in producing coatings with a uniform thickness within the desired range.
• the thickness of the coating in its final crystalline state should be of a similar order of magnitude to the average minimum dimension of the nanodiamonds embedded therein. In particular, the layer thickness should not be greater than five times, preferably less than three times, the average dimension of the nanodiamonds embedded therein.
• d 0 denotes the thickness of the still-moist sol layer immediately after its application
• ⁇ the dynamic viscosity of the sol
• ⁇ its density the speed at which the substrate is pulled out of the sol.
• U 0 the speed at which the substrate is pulled out of the sol.
• g 9.81 m/s 2 is the acceleration due to gravity.
• the sol layer After the sol layer has been applied, it must first be dried. This can take place at room temperature or - or followed by - a further drying step at elevated temperature. The choice of drying time and temperature depends on the composition of the sol, in particular the volatile components it contains. Gel formation also occurs during the drying process.
• the coating After drying, the coating must be calcined, i.e. subjected to a thermal treatment at temperatures above approximately 400°C. Preferred temperatures are in the range of 500°C to 800°C, particularly preferably in the range of 550°C to 650°C. The duration of the heat treatment is between 30 minutes and several hours, preferably 1 hour to 3 hours. Calcination is preferably carried out under a protective gas, e.g., nitrogen or argon.
• a protective gas e.g., nitrogen or argon.
• zirconium(IV) oxide determines the essential mechanical and chemical properties of the coating and in particular contributes significantly to the chemical resistance of the coating, it is preferred if at least 70 mass percent, preferably at least 80 mass percent, in particular at least 90 mass percent of the coating is formed by zirconium(IV) oxide.
• the substrate can preferably be a workpiece made of glass, sapphire, an oxide, carbide, or nitride ceramic material, stainless steel, nickel, a refractory metal, or a base alloy of nickel or a refractory metal.
• the coating can form a permanent bond with these substrates.
• Such substrates are also suitable for forming at least part of an apparatus for conducting physical, chemical, or biological processes in a fluid medium, in particular a chemical reactor. The advantages of the coating are particularly evident in connection with such components.
• At least 30%, preferably at least 50%, in particular at least 70%, of the zirconium(IV) oxide of the coating is crystallized in the tetragonal phase.
• zirconium(IV) oxide in the tetragonal phase can be promoted if up to 10 mol percent of the zirconium contained in the coating is replaced by yttrium.
• a sol containing a soluble yttrium compound preferably yttrium(III) nitrate hexahydrate, yttrium(III) chloride, Yttrium(III) bromide and/or yttrium(III) iodide is used for deposition on the substrate.
• a sol containing a soluble yttrium compound preferably yttrium(III) nitrate hexahydrate, yttrium(III) chloride, Yttrium(III) bromide and/or yttrium(III) iodide is used for deposition on the substrate.
• sufficient replacement of zirconium(IV) oxide with yttrium(III) can occur during crystallization.
• sols are generally suitable for deposition on
• Effective coatings with efficient use of nanodiamonds can be achieved if the coating thickness is no more than five times, preferably no more than three times, the average minimum dimension of the embedded nanodiamonds. If the nanodiamonds are approximately spherical in shape, their minimum dimension can be considered their respective diameter. If the nanodiamonds are elongated or flattened rather than spherical, i.e., have different dimensions in different directions, the smallest dimension of the individual nanodiamonds is used to determine the average minimum dimension. This is then preferably greater than one-fifth, particularly preferably greater than one-third, of the average coating thickness.
• the coating to form a sensor, depending on the sensory application, it is advisable if at least some of the doped nanodiamonds are partially uncovered by the surrounding matrix material of the coating. In principle, it is preferable if as large a proportion of the doped nanodiamonds as possible are partially uncovered by the surrounding matrix material, without losing contact with the matrix material and thus its fixing effect.
• the nanodiamonds can then form part of the surface of the coating and thus come into direct contact with the adjacent medium.
• the nanoparticles can partially protrude from the surrounding coating, but this is not absolutely necessary.
• the matrix material of the surrounding coating should therefore not completely cover or enclose all or almost all of the nanodiamonds, since such covered nanodiamonds provide no or at best reduced sensory properties, depending on the application.
• a preferred use of a coating of the aforementioned type is to measure physical or chemical quantities such as temperature, pressure, fluid velocity, magnetic flux density, pH value or concentration of one or more substances. These quantities can be determined with the coating, especially with very high spatial resolution.
• Sample substrates used included microscope slides and cover glasses made of soda-lime glass for microscopy, or round, polished sapphire discs with a diameter of 25.4 mm and a thickness of 0.5 mm.
• the substrate is first cleaned in water with a little household detergent for 10 minutes in an ultrasonic bath, then rinsed successively with deionized water and acetone, and finally treated in ethanol for a further 15 minutes in an ultrasonic bath.
• adhering ethanol residues are blown off using oil-free compressed air, thus drying the substrate.
• the substrate thus prepared is hung vertically on the The substrate is then attached to the dip coater's lifting unit and immersed in the sol. After approximately one minute in the lower immersion position, the substrate is completely pulled vertically upwards out of the sol at a uniform speed of approximately 0.1 to 0.3 mm/s.
• the coating is first dried for approximately 1.5 hours at room temperature and then for 30 minutes in a drying cabinet at 70 °C. Further heat treatment takes place in a tube furnace under a gentle nitrogen stream. The temperature is initially raised at 300 K/h to 250 °C, where a dwell time of 15 minutes occurs. The temperature is then further increased at 300 K/h to the calcination temperature of 600 °C, which is held for 2 hours. This is followed by uncontrolled cooling to room temperature at the natural cooling rate of the furnace.
• the resulting layers of yttrium-stabilized zirconium oxide mixed with nitrogen-doped nanodiamonds are characterized by a homogeneous thickness of approximately 70 nm to 150 nm, high hardness, and good substrate adhesion, thus offering scratch resistance, high chemical resistance, optical transparency, and a virtually crack-free surface.
• Their ceramic matrix is essentially in the tetragonal crystal phase of zirconium oxide, as demonstrated by X-ray diffraction measurements (see figures). A coating produced in this way showed no visible changes after two days of aging in 80% sulfuric acid at room temperature.
• the doped nanodiamonds embedded in the layer still exhibited the typical fluorescence behavior of the nitrogen vacancy centers they contained, even after undergoing the thermal treatment during the calcination process.
• An aqueous solution of gadolinium(III) chloride applied to the layer surface led to measurable changes in the spin relaxation behavior of the nitrogen vacancy centers, which demonstrates a high sensitivity of the embedded quantum sensors and thus their close proximity to the applied sample liquid.
• Figure 1 shows a schematic cross-section through the substrate (1) and a coating (2) according to the invention applied thereon, made of crystalline zirconium(IV) oxide in the tetragonal crystal phase with doped nanodiamonds (3) embedded therein.
• some of the doped nanodiamonds (3a) are not completely covered by the coating material and thus have direct contact with the medium adjacent to the coating.
• FIGS. 3 and 4 Scanning electron micrographs of a zirconium(IV) oxide layer according to the invention, produced using a sol-gel process and dip coating and calcined at 600 °C, with embedded (doped) nanodiamonds.
• White arrows mark positions where carbon-containing particles were detected by EDX analysis (energy-dispersive X-ray spectroscopy). These particles can largely be assumed to be the doped nanodiamonds introduced during layer production, several of which protrude from the layer surface.
• Comparative EDX scans for carbon (K ⁇ 1.2) and zirconium (L ⁇ 1.2) at various locations on such samples also show that at least some of the diamond particles in this sample are not covered by zirconium oxide.
• FIG. 5 A 100 ⁇ 100 ⁇ m2 section of the surface of a zirconium(IV) oxide layer according to the invention, produced using a sol-gel process and dip coating and calcined at 600 °C, with doped nanodiamonds embedded therein, is shown, as viewed under a confocal laser fluorescence microscope.
• the fluorescence centers are thus displayed as bright spots in the raster image.
• the diagram in the lower right quadrant of the image shows the photoluminescence spectrum of one of the luminous points in the image field, which identifies it as a nitrogen vacancy center and thus provides evidence that the doped nanodiamonds at least partially retain their quantum optical properties during the layer production according to the invention.
• Figure 6 shows the intensity curve of the fluorescence signal of an ensemble of nitrogen vacancy centers in a zirconium(IV) oxide layer according to the invention, produced by means of a sol-gel process and dip coating and calcined at 600 °C, with doped nanodiamonds embedded therein, as a function of the time interval between a preceding laser pulse for spin polarization and the actual readout pulse for excitation of the nitrogen vacancy centers ("pump-probe measurement"). From this signal curve, the spin relaxation time of the fluorescence centers can be determined, which in the case shown here consists of two components ( ⁇ 1,long and ⁇ 1,short ).
• the measurement was first carried out with the bare sample and then repeated, whereby in the case of the second series of measurements, the sample was wetted with an aqueous solution of gadolinium(III) chloride.
• Gd(III) ions are strongly paramagnetic due to their seven unpaired electrons in the f-shell and, with sufficiently close contact (over a few nanometers) to the nitrogen vacancy centers, cause an accelerated spin-lattice relaxation and consequently a shortening of the relaxation time ⁇ 1 , which in the Figure 6 This is clearly evident from the measurement results presented here. These therefore confirm that the doped nanodiamonds embedded in the coating according to the invention investigated here have, at least in part, very close or even direct contact with the surface of the coating or adjacent media and can thus interact with them as quantum sensors.

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• 2024
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