ES2558625B1 - PLASMONIC BLACK METAL COATINGS MANUFACTURED BY DEPOSITION BY CATHODIC SPRAYING AT RASING INCIDENCE - Google Patents

Abstract

Plasmonic black metal coatings manufactured by sputtering sputtering deposition. # The present invention relates to coated materials where the coating comprises nanostructures of a metal selected from gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium, copper, chromium and any combination thereof, characterized in that more than 45% of the nanostructures have a diameter of less than 10 to 50 nm, and the distribution of the diameters of the nanostructures has a standard deviation of more than 5 nm in the range of 0 to 50 nm

Description

5

10

fifteen

twenty

25

30

35

Plasma black metal coatings manufactured by cathode spray deposition at ground level

DESCRIPTION

The present invention relates to plasmonic black metal coatings that have application in the manufacture of surfaces for various devices that involve the absorption of visible light.

STATE OF THE TECHNIQUE

The method of physical extraction of atoms of a massive metal blank by plasmas is called cathode spray or sputtering in English. It is a technique well known for decades to grow very compact thin sheets with low roughness. In this technique, a solid block, also called white, of a given metal is placed inside a reactor or vacuum chamber with an inert gas inside, such as argon. By injecting an electromagnetic power through the target, a gaseous plasma is generated, rich in energy ions, which pulverize the surface of the block, emitting metal atoms in a direction preferably perpendicular to the target, with kinetic energies of the order of 10 eV. These atoms, upon reaching a surface inside the reactor parallel to the target, called the substrate, accumulate and agglomerate, generating a thin film. Depending on the pressure of argon in the reactor, the energy with which these atoms reach the surface can be controlled. At high pressures (above 1 Pa under standard conditions), the collisions inside the plasma are numerous, so the atoms reach the substrate with low energy (tenths or hundredths of eV). At low pressures, however, the arrival energy is very similar to that of the target (ballistic regimen), generating highly compact thin films.

In recent years, the sputtering technique is also being used in flush-angle angles, the so-called sputtering at glancing angle (also GLAD), the substrate where the atoms accumulate is no longer placed parallel to the white, but forming with it an angle greater than 60 °, which causes the atoms to reach the substrate preferably with oblique incidence. This configuration induces shadow processes on the surface of

5

10

fifteen

twenty

25

30

35

the thin layer in growth that generate structures, in principle, inclined. However, if the substrate is also rotating around an axis perpendicular to its surface, the structures produced are not inclined, but grow vertical, that is, perpendicular to the substrate.

Black metal is understood as metal that has a high absorption of light in a region of the electromagnetic spectrum. Being strict, the black color only occurs when that great absorption of light takes place in the visible range (wavelength between 400 and 750 nm), but by analogy it also speaks of black metals that they absorb in other spectral ranges ( ultraviolet, infrared, etc.).

The physical basis of light absorption in submicrometer and nanometric scale metal structures is the so-called localized resonance resonance: collective excitations of the conduction band electrons that appear for a given wavelength or incident light color (AR) It depends on the material as well as the dimensions and shape of the structure. Thus, when we illuminate with white light and collect the signal reflected in the sample in a spectral analyzer, we see that the component with AR has decreased significantly. This means that a large part of the component with AR has been absorbed: it has been used to excite conduction electrons, that is, to produce localized plasmon resonance. When preparing surfaces with metal structures that have a certain distribution of sizes, there is a whole set of wavelengths that can be absorbed, since the smaller structures will present their resonance from plasmon to AR1, the following in order of size will present it to AR2 (with AR2> AR1), etc., and so on until the older ones resonate with RNA. Although this phenomenology can be presented by any metal, noble metals are the most commonly used as black metals, since their plasmon resonances are more intense and have less losses than in other metals. In addition, since silver oxidizes under ambient conditions, the most studied black metal is black gold.

To date, black metal coatings have been manufactured using various techniques:

- evaporation in the presence of an inert atmosphere (He or N2), which is the oldest method, the generated coatings have a percolative structure

5

10

fifteen

twenty

25

30

35

(nanostructures that percolate forming aggregates or clusters) over which there is little control, and the great absorption occurs in the infrared;

- electrochemical deposition, which requires that the starting substrate be conductive, otherwise the electrodeposition cannot be carried out. In addition, chemical residues are generated;

- anodization of a previously deposited layer, which, like the previous method, needs a conductive substrate and generates chemical residues;

- ultra-fast laser attack of a previously deposited layer, which is a very expensive process because it requires the use of very specific femtosecond lasers, in addition to having previously deposited the layer to be nanostructured;

- manufacturing matrices of plasmatic nanostructures, such as nanosurks in a metal layer, is an inherently expensive process because it requires nanolithography techniques (FIB, e-beam);

- Manufacturing of thin films with nanoparticles by means of the so-called jetprinting method, which is a resistive evaporation of the material in a crucible, surrounded by a winding that is heated when a current passes, which then travels through a column and leaves through a small collimating hole. It is a slow technique to achieve large areas.

Likewise, and although they are not conductive coatings, it is worth mentioning that metamaterials have been used to obtain light absorbers in the visible. These materials always combine metal nanostructures with dielectric layers, e.g. eg, manufacturing gold discs by lithographic techniques on multilayers, metal / dielectric or embedding metal nanoparticles in dielectric matrix.

Recently, US20130183540A1 describes a method of manufacturing in metal nanopillar vacuum with SERS application (in English, Surface Enhanced Raman Scattering), in which the samples have absorption greater than 80% in the range between 400 and 800 nm, prepared through an evaporation system assisted by electron fees and using oblique incidence and rotation of the substrate. However, this technique cannot be industrially scaled, because so that the heating is uniform, the crucibles that contain the starting material have a small diameter (of the order of 1 cm), so it is not possible to manufacture a coating in a large area.

5

10

fifteen

twenty

25

30

35

The cathode spray of Au a flush incidence in ballistic regime has been described in Nanotechnology 24 (2013) 045604 and in Applied Physics Letters 97, 173103 (2010), although without rotation of the substrate around the perpendicular to its surface. However, the coatings obtained did not exhibit black metal behavior.

Zig-zag or helical nanostructure have also been obtained by means of cathode spraying at ground level in ballistic regime with rotation of the Ti substrate (J. Mater. Res., Vol. 14, No. 4, Apr 1999) and Co or Ni (J. Vac. Sci. Technol. A, Vol. 18, No. 4, 2000).

DESCRIPTION OF THE INVENTION

The present invention is directed to plasmonic black metal coatings that have application in the manufacture of surfaces for various devices that involve the absorption of visible light, such as radiative heat exchangers, solar energy absorbing materials, photovoltaic cell electrodes, separators to avoid cross effects between optical devices, thermal light emitters, electrodes in biosensors, etc.

Given the techniques mentioned above, the cathode spray technique with flush incidence and with rotating substrate, has numerous advantages:

- uses vacuum techniques, so that no aggressive waste is generated with the environment;

- it is efficient from an energetic point of view since cathode spraying allows manufacturing at room temperature and in a single step, that is, it does not require any previous deposition;

- It is based on the technique of sputtering, which is widely used in industry and allows the growth of nanostructured material on large surfaces and with enough control of the final morphology;

- It can be done on any type of substrate (conductor, insulator, semiconductor, temperature sensitive, etc.), which makes the cathode spray technique at ground level and with rotating substrate much more versatile;

- the rate of growth of the coating can be controlled by injecting more or less electromagnetic power into the plasma, so it can be used industrially on large surfaces and also control the time required

5

10

fifteen

twenty

25

30

35

of processing. This particularity gives the proposed technique a high degree of scalability with controlled efficiency and low cost;

- greater control of the size of the structures that are formed and reproducibility than in other techniques, such as with laser.

Therefore, a first aspect of the present invention relates to a material

coated where the coating comprises nanostructures of a metal

Selected from gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium, copper, chrome and

any of its combinations, characterized in that:

more than 45% of the nanostructures have a diameter of less than 50 nm;

the distribution of the nanostructure diameters has a standard deviation

greater than 5 nm in the range of 0 to 50 nm.

That there is this percentage of nanostructures with diameters below 50 nm and that the distribution of the nanostructure diameters has the indicated standard deviation causes the coating to have a plasmonic black metal behavior in the visible spectrum. It is necessary that there be a distribution of diameters with remarkable width so that there is resonance over the entire range of visible wavelengths.

In an embodiment of the first aspect of the present invention, the coated material is referred to as characterized in that:

more than 45% of the nanostructures have a diameter of less than 50 nm; the distribution of the nanostructure diameters has a standard deviation greater than 5 nm in the range of 0 to 50 nm; Y

The average height of the nanostructures is between 50 and 250 nm.

As can be seen in the micrograph of Figure 3, which is a top view of a coating of the invention, the nanostructures of the coating have a quasi-circular geometry. The diameter of the nanostructures is therefore understood as the diameter of said calculation.

In another embodiment of the first aspect of the present invention, the distribution of the nanostructure diameters has a standard deviation between 10 nm and 25 nm in the range of 0 to 50 nm.

5

10

fifteen

twenty

25

30

35

In another embodiment of the first aspect of the present invention, the distribution of the nanostructure diameters has a standard deviation between 10 nm and 25 nm in the range of 0 to 50 nm and the distribution of the nanostructure diameters is an asymmetric distribution to the right in the range of 0 to 50 nm. This means that the diameters have a quasi-normal distribution of diameters, with a maximum slightly below 25 nm.

In another embodiment of the first aspect of the present invention, the coating has an absorption greater than 60% in the range of 400 nm to 700 nm of the electromagnetic spectrum, preferably the coating has an absorption greater than 75% in the range of 400 to 500 nm of the electromagnetic spectrum.

In another embodiment of the first aspect of the present invention, the nanostructures form an angle with the substrate between 45 ° and 90 °, preferably form an angle with the substrate between 60 ° and 90 ° and even more preferably form an angle with the substrate between 75 ° and 90 °. That is, the nanostructures are substantially perpendicular to the substrate.

In another embodiment of the first aspect of the present invention, less than 15% of the nanostructures have a diameter greater than 100 nm.

In another embodiment of the first aspect of the present invention, where the density of nanostructures is between 80 and 300 nanostructures / pm2, preferably between 160 and 250 nanostructures / pm2 and even more preferably the density is between 170 and 230 nanostructures / pm2.

In another embodiment of the first aspect of the present invention, the average height of the nanostructures is 50 nm to 250, preferably 80 nm to 140 nm.

In another embodiment of the first aspect of the present invention, the metal is selected from gold, silver, palladium and platinum, ruthenium, rhodium, osmium, iridium and any combination thereof, preferably the metal is selected from gold, silver, palladium, platinum and any of its combinations, more preferably the metal is gold. The noble metals have more intense plasmon resonances. In addition, gold coatings have good resistance to oxidation.

5

10

fifteen

twenty

25

30

35

In another embodiment of the first aspect of the present invention, the coating exhibits electrical conductivity. Without being limited by the theory, this property of the coating seems to indicate that below the nanostructures there is a continuous layer of the metal.

A second aspect of the present invention relates to a method of obtaining a coated material as described above by cathode spray at flush angle on rotating surfaces of a metal selected from gold, silver, palladium, platinum, ruthenium, rhodium , osmium, iridium, copper, chromium and any combination thereof;

where the angle of inclination of the substrate is between 85 ° and 90 °; where the inert gas pressure is less than 0.5 Pa, preferably the gas pressure is less than 0.4 Pa, more preferably the gas pressure is less than 0.2 Pa; and where the deposition of the metal takes place in a ballastic regime.

By cathode spraying at a flush angle on rotating surfaces, the physical vapor deposition process is understood in which atoms of a target are removed by a gaseous plasma and deposited on a substrate; flush angle means that the angle of inclination is greater than 75 °; by rotating surfaces it is understood that the substrate rotates around an axis perpendicular to its surface.

By substrate means the material to be coated.

Ballistic regime means that atoms travel from the target to the material to be coated with a preferred directionality. It is necessary that the atoms arrive at the material to be coated with a well-defined preferential directionality so that the atomic shading phenomenon is necessary, so that the coating has nanostructures and not a continuous coating. If the ballistic regime condition is not met, the atoms suffer collisions and reach the material to be coated in all directions, disappearing the phenomenon of atomic shading. It is routine for a person skilled in the art to adjust the parameters to achieve the deposition of the metal in a ballistic regime.

An angle of inclination of the substrate means the angle defined between the straight line that goes from the center of the substrate to the surface of the target and perpendicular to the surface of the substrate.

5

10

fifteen

twenty

25

30

35

In an embodiment of the second aspect of the present invention, the rotation speed of the material to be coated is less than 20 rpm, preferably the rotation speed is between 0.5 rpm and 15 rpm, more preferably the rotation speed is between 1 rpm and 10 rpm (revolutions per minute).

In an embodiment of the second aspect of the present invention, the ratio L / d is greater than 2.5, preferably greater than 3.5, where L is the distance between the target and the material to be coated and d is the target diameter.

The distance between white and the material to be coated, L, is defined by the straight line that goes from the center of the substrate to the surface of the target (Fig. 1, 5). The lower limit of L is given by the condition L / d> 2.5 that ensures collimation of atom flow. The upper limit is given by the distance from which the shot atoms lose their initial direction. L is less than 45 cm, preferably L is less than 30 cm.

By white it is understood the metallic block of gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium, copper, chromium and any of its combinations from which atoms are torn.

Normally, white has circular geometry. In cases where, for example, when the target has square geometry or cylindrical geometry, by diameter of the target, d, the diameter of the circle is understood to have the same area as the area of the target (regardless of its shape) .

As previously mentioned, cathodic pulverization takes place in ballistic regimes. For example, the formalism detailed in Nanotechnology 24 (2013) 045604 and in Plasma Process can be used. Polym 11 (2014) 571, with which a condition is reached in which the value (pg.L) must be less than a value (1.5 / x) determiner for the ballistic regime condition to be met, where pg is the Argon pressure in Pa, and L is the distance between white and the material to be coated in cm. The specific value depends on the metal to be deposited, the composition of the gas and its temperature.

5

10

fifteen

twenty

25

As an example, assuming that the inert gas is argon and that the temperature is 300K, the ballistic regime condition will be given for these values:

 Mass (uma) Radius (pm) ^ g (m2) V x (Pa _1m_1) (300 ^) Ballistic criteria Pg L <(Pa.cm)

 Cr

 52.00 128 1.8874e-19 3 15.15 10

 Cu

 63.55 128 2.0025e-19 3.8 12.75 11.8

 P.S

 106.42 137 2.6016e-19 6.8 9.3 16.1

 Ag

 107.87 144 2.7934e-19 6.8 9.9 15.1

 Pt

 195.08 139 3,3604e-19 12.8 6.3 23.8

 Au

 197 144 3,5367e-19 12.8 6.75 22.2

where the geometric effective section is ag, v the average number of collisions necessary to thermalize the atomized atom, and% = ag / kBTgv where kB is the Boltzmann constant.

Therefore, in an embodiment of the second aspect of the present invention, the metal is gold, the inert gas is argon, and Pg.L <22.2 Pa.cm;

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

In another embodiment of the second aspect of the present invention, the metal is platinum, the inert gas is argon, and Pg.L <23.8 Pa.cm;

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

In another embodiment of the second aspect of the present invention, the metal is silver, the inert gas is argon, and Pg.L <15.1 Pa.cm;

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

In another embodiment of the second aspect of the present invention, the metal is copper, the inert gas is argon, and Pg.L <11.8 Pa.cm;

5

10

fifteen

twenty

25

30

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

In another embodiment of the second aspect of the present invention, the metal is chromium, the inert gas is argon, and Pg.L <10 Pa.cm;

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

In another embodiment of the second aspect of the present invention, the metal is platinum, the inert gas is argon, and Pg.L <23.8 Pa.cm;

where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm.

A third aspect of the present invention relates to the use of the coated material as defined above as an element for the manufacture of visible light absorbing devices.

In an embodiment of the third aspect of the present invention, visible light absorbing devices are selected from radiative heat exchangers, solar energy absorbing devices, photovoltaic cell electrodes, optical device separators, thermal light emitters, biosensor electrodes , photocatatic devices and detectors in the near infrared.

A fourth aspect of the present invention relates to a visible light absorbing device comprising the coated material as defined above.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and characteristics of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

5

10

fifteen

twenty

25

30

35

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Assembly diagram for cathode spraying at flush angle and rotating substrate. 1: Noble metal block; 2: plasma; 3: Angle of inclination; 4: Rotation of the substrate; 5: Block-substrate distance.

FIG. 2. Photograph of two Au coatings deposited on Si substrates obtained with a rotation speed of 3.6 RPM and a ratio L / d = 5. A: Coating obtained with an inclination angle of 87 °; B: Coating obtained with an inclination angle of 75 °.

FIG. 3. Micrographs of the nanostructures of the coating A of Fig. 2 with an approximate density of 220 nanostructures / pm2.

FIG. 4. Distribution of the size of the gold nanostructures, where pg <0.5 Pa, specifically pg = 0.15 Pa. D: diameter of the upper base of the nanostructures; Y axis:% abundance; 75 °, 80 °, 85 °, 87 °: distribution of the nanostructures formed in the coating at 75 °, 80 °, 85 ° and 87 ° of inclination of the material to be coated, respectively.

FIG. 5. Distribution of the size of the nanostructures when pg> 0.5 Pa, specifically pg = 0.6 Pa. D: diameter of the upper base of the nanostructures; Y axis:% abundance; 75 °, 80 °, 85 °, 87 °: distribution of the nanostructures formed in the coating at 75 °, 80 °, 85 ° and 87 ° of inclination angle during the manufacturing process respectively.

FIG. 6. Reflectance of coated materials at different degrees of incidence and at pg <0.5 Pa, specifically pg = 0.15 Pa. R: reflectance in%; A: wavelength in nm; 75 °, 80 °, 85 ° and 87 °: coated materials at 75 °, 80 °, 85 ° and 87 °, respectively.

FIG. 7. Reflectance of coated materials at different degrees of incidence and at pg> 0.5 Pa, specifically pg = 0.6 Pa. R: reflectance in%; A: wavelength in nm; 80 ° and 87 °: coated materials at 80 ° and 87 °, respectively.

5

10

fifteen

twenty

25

FIG. 8. Spectral behavior of samples 7 and 8 of Example 1 (on a transparent substrate). Am, Tm and Rm: Absorbance, transmittance and reflectance of sample 8 (thin continuous metal layer, prepared at angle of incidence 0); A85, T85, R85: Absorbance, transmittance and reflectance of sample 7 (nanostructured coating, prepared at angle of incidence 85); A (nm): wavelength in nm.

EXAMPLES

The invention will be illustrated below by tests carried out by the inventors, which shows the effectiveness of the product of the invention.

Example 1. Procedure for obtaining a coated material

Square sheets of silicon (opaque) or magnesium oxide (transparent) of 1 cm side were coated with Au by cathode spraying at ground level and with rotating substrate (3.6 rpm), with collimation (L = 19 cm and d = 3 , 8 cm, so L / d = 5) and in the ballistic regime, with the following variables:

 Sample

 Noble metal material angle inclination Pg [Pa]

 one

 Au Si 75 ° 0.15

 2

 Au Si 80 ° 0.15

 3

 Au Si 85 ° 0.15

 4

 Au Si 87 ° 0.15

 5

 Au Si 80 ° 0.6

 6

 Au Si 87 ° 0.6

 7

 Au MgO 85 ° 0.15

 8

 Au MgO 0 ° 0.15

 Table 1. Variab

 It is from the procedure for obtaining each

e each of the examples.

Sample 8 was made without flush incidence to have a continuous sheet with which to compare.

The assembly to carry out the coating of the material is shown in Figure 1.

5

10

fifteen

twenty

25

30

35

Example 2. Effect of the angle of inclination

Figure 6 shows the effect of the angle of inclination of the substrate on the reflectance of the resulting coating. It can be seen that samples 3 and 4, prepared at inclination angles of 85 ° and 87 °, have a reflectance of less than 15% in the wavelength range of 400 nm to 700 nm, that is, they have a higher absorbance to 85% in said interval. These two samples are close to meeting the specifications of absorbent material ideal for use in solar cells (Kravets etal., Phys. Rev. B 78, 205405 (2008).

This difference in absorbance can be observed with the naked eye. A picture of the sheets of examples 1 (B) and 4 (A) is shown in Figure 2. Figure 3 shows a micrograph of the nanostructures obtained in sample 4.

Figure 4 shows the effect of the angle of inclination of the substrate on the diameter of the nanostructures that are created on the substrate. As can be seen, coatings made at inclination angles greater than 80 ° have a large percentage of nanostructures with diameters below 50 nm.

Figure 8 shows the absorbance, reflectance and transmittance of samples 7 and 8, in MgO (transparent).

Sample 8 was prepared by normal incidence during the cathode spraying process, that is, 0 ° of inclination of the substrate, and a much shorter deposit time, specifically cosine (85 °) times less (less time because to deposit the same amount of gold requires less time) That is, sample 8 is a sample coated with the same amount of gold as 7 but deposited in the form of a continuous film.

It can be seen that the spectral dependence of sample 7 (with nanostructured coating) is very different from that of a continuous thin sheet: while sample 8 has low absorption (20%) and high reflectivity (above 70%) a from 600 nm, sample 7 (nanostructured) has high absorption (above 60%) and low reflectivity (below 30%) throughout the visible spectrum.

Example 3. Effect of inert gas pressure (pg)

In Figure 7 it can be seen that when pg> 0.5 Pa, the resulting coatings have a reflectivity greater than 20%, even at angles of inclination greater than 80 °.

Figure 5 shows the distribution of the nanostructures obtained at different angles when pg> 0.5 Pa (samples 5 and 6). It can be seen that the distribution obtained has a proportion of nanostructures with diameters less than 50 nm lower than that obtained when pg <0.4 Pa (Fig. 4).

10

Claims (18)

5 10 fifteen twenty 25 30 35 1. Coated material where the coating comprises nanostructures of a metal selected from gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium, copper, chromium and any combination thereof, characterized in that more than 45% of the nanostructures have a diameter of less than 50 nm; The distribution of the nanostructure diameters has a standard deviation greater than 5 nm in the range of 0 to 50 nm. 2. The material according to the preceding claim wherein the distribution of the nanostructure diameters has a standard deviation between 10 nm and 25 nm in the range of 0 to 50 nm. 3. Material according to any of the preceding claims, wherein the coating has an absorption greater than 60% in the range of 400 nm to 700 nm of the electromagnetic spectrum. 4. Material according to any of the preceding claims, wherein the coating has an absorption greater than 75% in the range of 400 to 500 nm of the electromagnetic spectrum. 5. The material according to any of the preceding claims, wherein the nanostructures form an angle with the substrate between 45 ° and 90 °. 6. Material according to any of the preceding claims where less than 15% of the nanostructures have a diameter greater than 100 nm. 7. Material according to any of the preceding claims, wherein the density of nanostructures is between 80 and 300 nanostructures / pm2. 8. Material according to any of the preceding claims, wherein the average height of the nanostructures is 50 nm to 250 nm. 9. Material according to any of the preceding claims, the metal is selected from gold, silver, palladium, platinum, ruthenium, rhodium, osmium, iridium and any combination thereof. 5 10 fifteen twenty 25 30 35 10. Material according to any of the preceding claims, wherein the metal is gold. 11. Material according to any of the preceding claims, wherein the coating has electrical conductivity. 12. Method for obtaining a coated material according to any of claims 1 to 11 by cathode spray in the presence of an inert gas at flush angle on rotating surfaces of a metal selected from gold, silver, palladium, platinum, ruthenium, rhodium, osmium , iridium, copper, chromium and any combination thereof; where the angle of inclination of the substrate is between 85 ° and 90 °; where the inert gas pressure is less than 0.5 Pa; and where the deposition of the metal takes place in a ballastic regime. 13. Method of obtaining according to the previous claim, where the rotation speed of the material to be coated is less than 20 rpm. 14. Method of obtaining according to any of claims 12 or 13, wherein the ratio L / d is greater than 2.5, where L is the distance between the target and the material to be coated and d is the diameter of the target. 15. Method according to any of claims 12 to 14, wherein the metal is gold, the inert gas is argon, and Pg.L <22.2 Pa.cm; where pg is the pressure of argon in Pa; and L is the distance between white and the material to be coated in cm. 16. Use of the coated material according to any of claims 1 to 11 as an element for the manufacture of visible light absorbing devices. 17. Use according to the preceding claim where the visible light absorption devices are selected from radiative heat exchangers, solar energy absorbing devices, electrodes in photovoltaic cells, optical device separators, thermal light emitters, electrodes in biosensors, photocatatic devices and near infrared detectors. 18.- Visible light absorption device comprising the coated material according to any one of claims 1 to 11.