METHOD FOR GENERATING NANOPARTICLES ON THE SURFACE OF A SUBSTRATE AND PART COMPRISING SUCH A SUBSTRATE

Abstract

A process for generating nanoparticles on the surface of a substrate includes a step of providing the substrate made of a material including at least one element from columns 4, 5, 13 and 14 of the periodic classification, and at least one noble or transition metal; a step of irradiating the substrate by laser, with a pulse duration between 1 fs and 100 ps, a pulse between 0.01 J/cm.sup.2 and 100 J/cm.sup.2, a wavelength between 100 nm and 5000 nm, and a number of pulses per point between 1 and 1000; and a step of generating at least one nanoparticle on the surface of the substrate, the at least one nanoparticle including at least the noble or transition metal, and having a different chemical composition from that of the substrate. Also disclosed is a part including such nanoparticles.

Claims

1. A process for generating nanoparticles on the surface of a substrate, the process including: a step of providing the substrate having a free surface, the substrate being made of a material having a chemical composition including: at least one element from columns 4, 5, 13 and 14 of the periodic classification of elements; at least one noble metal or one transition metal; a step of irradiating at least a part of the free surface of the substrate by a laser radiation source producing a pulsed radiation, with a pulse time between 1 fs and 100 ps, a pulse fluence between 0.01 J/cm.sup.2 and 100 J/cm.sup.2, a wavelength between 100 nm and 5000 nm, and a number of pulses per point treated between 1 and 1000; and a step of generating at least one nanoparticle on the free surface of the substrate from the material of the substrate, the at least one nanoparticle including at least the noble metal or the transition metal, and having a different chemical composition from that of the substrate.

2. The process according to claim 1, wherein the laser emits pulses of duration between 1 fs and 100 ps.

3. The process according to claim 1, wherein the surface is irradiated by laser pulses repeated at a repetition frequency between 1 kHz and 25GHz.

4. The process according to claim 1, including a step of scanning the laser over the free surface of the substrate using a scanner, and/or a step of moving the free surface of the substrate in relation to the laser, using a turntable.

5. A part including at least one substrate made of a material having a chemical composition including at least: one element from columns 4, 5, 13 or 14 of the periodic classification of elements, and one noble metal or one transition metal, and the substrate having a surface of which at least a part has a nanostructure including at least one nanoparticle, the at least one nanoparticle including at least the noble metal or the transition metal, and having a different chemical composition from that of the substrate.

6. The part according to claim 5, wherein the at least one element from columns 4, 5, 13 or 14 of the periodic classification of elements is selected from among Ti (titanium), Zr (zirconium), Hf (hafnium), Nb (niobium), Ta (tantalum), V (vanadium), Al (aluminum), or Si (silicon).

7. The part according to claim 5, wherein the at least one noble metal or transition metal from columns 8 to 11 of the periodic classification of elements is selected from among Au (gold), Ag (silver), Pt (platinum), Pd (palladium), Cu (copper), Fe (iron), Co (cobalt), Ni (nickel).

8. The part according to claim 5, wherein the at least one nanoparticle has a characteristic size between 1 nm and 200 nm.

9. The part according to claim 5, wherein the at least one nanoparticle including the at least one noble metal or transition metal includes one from among Au, Ag, Pt, Pd, Cu, Fe, Co, or Ni.

10. The part according to claim 5, wherein the at least one nanoparticle is crystallized.

11. The part according to claim 5, wherein the nanostructure furthermore includes periodic undulations.

12. The part according to claim 5, wherein the periodic undulations are repeated periodically on the surface according to a spatial periodicity between 200 nm and 1000 nm.

13. The part according to claim 11, wherein the at least one nanoparticle is formed on a ridge of one of the undulations.

14. The part according to claim 5, wherein only a part of the surface of the substrate has the nanostructure.

15. The part according to claim 5, wherein the at least one element from columns 4, 5, 13 and 14 forms a layer of oxide on the surface of the treated material.

16. The process according to claim 2, wherein the surface is irradiated by laser pulses repeated at a repetition frequency between 1 kHz and 25 GHz.

17. The process according to claim 16, including a step of scanning the laser over the free surface of the substrate using a scanner, and/or a step of moving the free surface of the substrate in relation to the laser, using a motorized turntable.

Description

DETAILED DESCRIPTION

[0087] The invention, according to an embodiment example, will be understood clearly and its advantages will become more apparent on reading the following detailed description, given as an indication and in no way limitation, with reference to the appended drawings wherein:

[0088] FIG. 1 schematically illustrates a difference in anchorage of a nanoparticle on a substrate, according to whether it is obtained with a deposition process (FIG. 1A) or with a generation process from the support material (FIG. 1B);

[0089] FIG. 2 schematically illustrates a part obtained with the process according to an implementation of the invention, the part including any support (metallic, ceramic, composite or plastic) coated with a substrate on the surface from which nanoparticles are generated;

[0090] FIG. 3 shows an SEM (scanning electron microscope) photo of the nanostructured surface obtained with a process according to a first example of implementation of the invention;

[0091] FIG. 4 illustrates the chemical segregation effect obtained with the process according to the first example of implementation of the invention as illustrated in FIG. 3;

[0092] FIG. 5 shows in more detail the top of a ridge showing the Cu nanoparticles on the thin layer of ZrO.sub.2;

[0093] FIG. 6 illustrates a surface obtained by the implementation of the process according to a third example of implementation of the invention; and

[0094] FIG. 7 illustrates a surface obtained by the implementation of the process according to a fourth example of implementation of the invention.

[0095] The process according to an implementation of the invention makes it possible to functionalize a material by generating nanostructures on its surface, and in particular nanoparticles.

[0096] FIG. 1 illustrates the difference in principle between nanoparticles 2 added on the surface of a substrate 1, as with a process of the prior art (illustrated in FIG. 1A), and nanoparticles 12 generated from a substrate 11, as with a process according to an implementation of the invention (illustrated in FIG. 1B).

[0097] It is clear from the scenario of FIG. 1B that the nanoparticles 12 are then better anchored to the surface of the substrate 11.

[0098] To implement the process according to an implementation of the invention a part 10 to be treated is provided including at least one substrate 11 on the surface of which the process is applied.

[0099] FIG. 2 schematically illustrates such a part 10 including the substrate 11 on the surface. This figure shows that such a part 10 to be treated may also include any support 13 (for example metallic, ceramic, composite or plastic) which is then coated with the substrate 11.

[0100] A part to be treated may thus be a massive solid having the same composition in its entire volume, or be composed of a first support material 13 covered on the surface with a coating having the features described here (i.e., the substrate 11).

[0101] Plastic, metallic, ceramic or composite support materials may thus be functionalized.

[0102] In this example, the substrate 11 includes a metal alloy AB, formed from the elements A and B.

[0103] Under the effect of a localized heating induced by a laser treatment according to an example of implementation of the process, the element A of the material of the substrate 11 diffuses on the surface of the substrate 11 and nanoparticles 12 are formed, mainly based on the element A.

[0104] In particular, the elements forming the nanoparticles 12 are elements known for their tendency to form nanoparticles: if a surface of the substrate including such an element is irradiated by femtosecond (or picosecond) laser for example, it is common that the nanoparticles of the same element be observed on the surface (e.g.: Ag nanoparticles on an irradiated Ag surface).

[0105] Thus, these nanoparticles 12 are composed of some of the chemical elements of the treated material of the substrate, but has a different chemical composition from it (chemical segregation effect).

[0106] Such nanoparticles 12 are then well anchored in the substrate 11, as represented in FIG. 1A.

[0107] The process used to generate these nanoparticles 12, according to an implementation considered here, is irradiation by an ultrashort (femtosecond or picosecond) laser beam of the surface of the material of the substrate 11.

[0108] An ultrashort laser emits very short light pulses, for example of durations between 1 fs (=10.sup.15 s) and 100 ps.

[0109] The wavelength of the laser is for example here between 100 nm and 5000 nm, or for example between 400 nm and 1030 nm.

[0110] The surface is irradiated by laser pulses repeated at a frequency here between 1 KHz and 25 GHz.

[0111] The number of pulses used to treat a point of the surface (corresponding to a laser beam size of approximately 50 m) is here between 1 and 1000.

[0112] The pulse fluence (energy received per unit of surface area) to generate nanostructures and in particular nanoparticles is preferably less than the threshold fluence for the material in question (fluence from which the material is ablated), for example of the order of a fraction of J/cm.sup.2. This fluence is dependent on the material to be treated and the other femtosecond laser irradiation parameters (likewise with a picosecond laser).

[0113] The laser treatment may be carried out in air or in an inert atmosphere.

[0114] These ultrashort laser irradiations induce a localized heating of the treated surface: the laser-material interaction takes place over a typical depth of around fifteen nanometers, and the energy supplied is propagated in the form of heat and pressure waves over a typical depth of around one hundred nanometers in the treated material.

[0115] Under the effect of this treatment, the material from the surface (on a scale of around one hundred nanometers) is decomposed, and one or more elements forming the initial material diffuse toward the surface to form nanoparticles.

[0116] In order to treat large surfaces, of considerably greater size than that of the laser beam, it is possible, for example, to scan the beam over the part using a scanner, or move the part facing the beam using a turntable.

[0117] The material of the substrate to be treated is preferably in the solid state, and at least formed of metallic elements.

[0118] In particular, this material includes for example at least one noble metal or one transition metal from columns 8 to 11 of the periodic classification (for example: Au, Ag, Pt, Pd, Cu, Fe, Co, Ni), preferably Cu, Ag and/or Au. These elements then rise on the surface to form nanoparticles. These elements have advantageous catalytic and/or antimicrobial and/or plasmonic properties.

[0119] It possibly also includes at least one element (for example metallic or non-metallic) from columns 4, 5, 13 and 14 of the periodic classification (selected in particular from among Ti, Zr, Hf, Nb, Ta, V, Al, Si), preferably Ti and/or Zr. These elements are thermodynamically less noble than the elements cited above, and are found more rarely in the nanoparticles formed after irradiation. On the other hand, they may optionally form a layer of oxide on the surface of the treated material, possibly of a thickness up to around one hundred nanometers.

[0120] The treated material is optionally crystalline.

[0121] The surface of the material to be treated preferably has a sufficiently low roughness on the scale of the laser beam (of characteristic size of around ten m).

Example 1: treatment of a Part Including Amorphous Zr.SUB.0.5.Cu.SUB.0.5 .Coating Deposition

[0122] According to a first example of implementation, the process is applied to a part including a Zr.sub.0.5Cu.sub.0.5 coating.

[0123] In this example, a stainless steel metallic part is provided, which then forms a support here.

[0124] To functionalize a surface of the part, the process includes here a preliminary step of depositing a coating including the elements described hereinafter.

[0125] A layer of 50/50 atomic percentage ZrCu alloy is applied on the support by vacuum deposition.

[0126] To do this, the support is for example cleaned (degreased, rinsed and blown), then fastened to a substrate holder and placed in a vacuum deposition machine.

[0127] A degassing and a heating of the machine with the support in place makes it possible to attain pressures of the order of 10.sup.7 to 10.sup.5 mbar in the deposition machine. The support is stripped in order to remove any oxide layer on the surface. Then, a solid target of the sought composition (here 50/50 ZrCu) is sputtered by magnetron cathode sputtering, opposite the part to be treated (here the support). A coating of approximately 2 m of amorphous 50/50 ZrCu alloy is thus obtained on the surface of the stainless steel support. The same alloy may also be obtained by sputtering two metallic targets (co-sputtering process).

[0128] The coating then forms the substrate which will undergo steps of the process according to an implementation of the invention to generate nanoparticles.

[0129] A femtosecond laser treatment (with a wavelength of approximately 800 nm) is then applied on at least one targeted zone of the surface of the substrate; such a zone is for example of centimetric size.

[0130] One hundred pulses of duration 50 fs, and of fluence 0.1 J/cm.sup.2 are applied per irradiated point, at a frequency of 1 kHz. The zone to be treated is for example scanned by the beam using a motorized turntable.

[0131] FIG. 3 shows an SEM view of a surface of a substrate 11 of which one part 11a has been treated with the process according to the first example of implementation of the invention described above.

[0132] In FIG. 3A, the irradiated part 11a has a width of approximately 30 m; at either end (at the top and bottom in FIG. 3A), the surface has not undergone the process according to the invention.

[0133] FIG. 3B shows a detail in FIG. 3A.

[0134] This figure shows that the irradiation of the surface of the substrate has generated a nanostructure including periodic undulations 22 (LIPPS-Laser-Induced periodic surface structures) and nanoparticles 12.

[0135] The spatial periodicity of the undulations 22 is generally between 200 nm and 1000 nm according to the material treated and the irradiation parameters of the laser used.

[0136] Here, the undulations 22 have a mean height of approximately 300 nm (measured between a bottom of a valley and an adjacent ridge) and a lateral characteristic size (thickness) of approximately 500 nm.

[0137] The nanoparticles 12 are here more particularly present on the undulations 22, in particular on a ridge of the undulations 22.

[0138] The nanoparticles have for example a characteristic size (mean diameter for example) between 10 nm and 200 nm and are for example crystallized. Here, they have a characteristic size of approximately 50 nm.

[0139] FIGS. 4 and 5 show cross-sections of the substrate of FIG. 3.

[0140] In FIG. 4, FIG. 4A shows a TEM (transmission electron microscopy) image, FIG. 4B shows EDS (energy dispersion spectroscopy) mapping, and Images 4C, 4D and 4E respectively illustrate the presence of Cu, Zr and O.

[0141] FIG. 5 shows in more detail the top of an undulation 22. FIG. 5A shows a TEM image of the top of an undulation 22, FIG. 5B shows EDS mapping of FIG. 5A, and Images 5C, 5D and 5E give chemical mapping of Cu, Zr and O, respectively.

[0142] According to these FIGS. 4 and 5, it is apparent that the undulations are formed essentially of the base material (ZrCu layer), whereas the upper part of the undulations includes a layer of around one hundred nanometers of ZrO.sub.2. Finally, partially anchored in this layer of ZrO.sub.2, nanoparticles of pure, crystallized Cu are present on the undulations.

[0143] FIG. 5 shows in more detail the top of an undulation, showing more clearly the Cu nanoparticles (for example, FIG. 5C) on the thin layer of ZrO.sub.2 (the presence of O being more visible in FIG. 5E). Furthermore, FIG. 5b indicates that the thin layer of ZrO.sub.2 measures approximately 130 nm in thickness, whereas the Cu nanoparticles form a layer of approximately 60 nm in thickness.

[0144] The process described above thus makes it possible to generate Cu nanoparticles on the surface of a metallic part, moreover protected by a thin layer of ZrO.sub.2. Catalytic, antimicrobial, plasmonic, hydrophobic functions (by the nanostructure) may thus be added to the treated part, with potential applications linked with these functions.

Examples 2: Atomic Ratio Effect and Numbers of Elements Present in the Material

[0145] The effects of the process according to an implementation of the invention may be obtained for other amorphous substrates based on Zr and Cu: for example, a binary alloy Zr.sub.xCu.sub.1-x where x is between 0.35 and 0.65, a ternary alloy Zr.sub.xCu.sub.1-x-yTa.sub.y, for the same range of values of x, and for y<0.15, or for a more complex alloy, such as Zr.sub.52.5Al.sub.10Cu.sub.27Ni.sub.8Ti.sub.2.5.

[0146] To form the substrate, these materials may be made in the form of thin layers, for example by magnetron cathode sputtering, either of a solid target of the sought composition, or of several solid targets. In the second scenario (co-sputtering of several targets), the powers applied on the different targets are adjusted so as to obtain the sought composition for the layer thus produced. Thus, to produce an alloy Zr.sub.xCu.sub.1-x-yTa.sub.y, three sputtering targets, respectively of Zr, Cu and Ta may be used, and the power ratios between these targets are adjusted according to the sought x and y ratios.

[0147] The laser irradiation parameters are adjusted according to the composition of the alloy to obtain the nanostructuring (nanoparticles, and optionally undulations) and chemical segregation effect.

[0148] In these different scenarios, after laser irradiation treatment, the formation of Cu nanoparticles on the surface of the alloy is observed, the size and number of which are dependent on the proportion of Cu in the alloy of the substrate.

[0149] Alloys having a strong tendency to remain amorphous, for example complex alloys, for example of composition Zr.sub.52.5Al.sub.10Cu.sub.27Ni.sub.8Ti.sub.2.5 or Zr.sub.41.2Ti.sub.13.8Cu.sub.12.5Ni.sub.10Be.sub.22.5, may be obtained in massive solid form (of limited dimensions), in the amorphous state.

[0150] The laser irradiation may be performed directly on the massive solid according to the same protocol as that described above, and a similar result to that for a layer of the same, or identical, material is obtained.

[0151] Ultrashort laser irradiation inducing a localized heating effect on the surface of the treated material, the chemical nature of that located below (support of different chemical nature, or homogeneous material) has no influence on the treatment and its effect.

Example 3: Effect of Chemical Nature of the Elements of the Alloy of the Substrate and of Irradiation Environment

[0152] Substrates of other binary alloys, of compositions as described above, may be functionalized.

[0153] The irradiation of a substrate of Ti.sub.0.5Cu.sub.0.5 thus results in the generation of Cu nanoparticles, that of Zr.sub.0.66Ag.sub.0.33 in Ag nanoparticles, and that of Zr.sub.0.5Au.sub.0.5, in Au nanoparticles.

[0154] According to the material of the substrate and the laser treatment environment, the nanoparticles generated may be located either above for one the oxide formed by the passivatable element of the alloy, and be anchored in the oxide, or be located below (or in) a thin layer of this oxide.

[0155] Thus, the first scenario is for example obtained with a laser treatment in air of a Zr.sub.0.5Cu.sub.0.5 alloy: the Cu nanoparticles generated are on the surface and anchored in a layer of ZrO.sub.2. The oxygen then stems from the passivation of the material after reventing. This is also the case for a laser treatment in an inert environment of a Ti.sub.0.5Cu.sub.0.5 alloy: the Cu nanoparticles are anchored in a layer of TiO.sub.2.

[0156] The second scenario is for example obtained for a laser treatment in air of a Ti.sub.0.5Cu.sub.0.5 alloy: the Cu nanoparticles are located under a very thin layer of TiO.sub.2.

[0157] This is for example illustrated by FIG. 6.

[0158] In this figure, FIG. 6A shows a TEM image of a cross-section of a Ti.sub.0.5Cu.sub.0.5 substrate on an Si support, FIG. 6B shows EDS mapping of a detail of FIG. 6A, and Images 6C, 6D, 6E and 6F illustrate the presence of Cu, Ti, TiCu and O, respectively.

[0159] The EDS mapping of FIG. 6B shows a series of Cu nanoparticles, under a thin layer of TiO.sub.2.

[0160] These figures show that after laser treatment in air of a Ti.sub.0.5Cu.sub.0.5 alloy, the Cu nanoparticles are located in, or below, a thin layer of TiO.sub.2 formed on the surface of the substrate.

Examples 4: Effect of Crystalline Nature of the Treated Material

[0161] The treated substrates may not be amorphous, unlike the amorphous alloys of Zr.sub.xCu.sub.1-x, Zr.sub.xCu.sub.1-x-yTa.sub.y, Zr.sub.52.5Al.sub.10Cu.sub.27Ni.sub.8Ti.sub.2.5, Ti.sub.0.5Cu.sub.0.5 described above.

[0162] Substrates of Zr.sub.0.66Ag.sub.0.33 and Zr.sub.0.5Au.sub.0.5, having X-ray diffraction crystalline phase signatures before laser treatment, may have the same surface nanoparticle generation and chemical segregation effect after laser irradiation.

[0163] This is for example illustrated by FIG. 7.

[0164] In this figure, FIG. 7A shows a TEM image of a cross-section of a Zr.sub.0.66Ag.sub.0.33 substrate on an Si support, FIG. 7B shows EDS mapping of a detail of FIG. 7A, and Images 7C, 7D, 7E and 7F illustrate the presence of Ag, Zr, ZrAg and O, respectively.

[0165] The EDS mapping of FIG. 7B shows that after laser treatment in air of an alloy Zr.sub.0.66Ag.sub.0.33, Ag nanoparticles are formed on a layer of ZrO.sub.2 formed on the surface of the nanocrystalline alloy Zr.sub.0.66Ag.sub.0.33.