Electrostatic doping of a layer of a conductive or non-conductive material

Abstract

The invention relates to a process for permanently electrostatically doping a layer of a conductive or non-conductive material that is deposited on a solid substrate, to the doped material obtained according to this process, and to the use of such a material.

Claims

1. Process for controllably and reversibly electrostatically doping a conductive or non-conductive material that is deposited in the form of a layer on a solid substrate, wherein: said conductive or non-conductive material is chosen from graphene, molybdenum disulfide and zinc oxide, and said process is carried out under vacuum, that said substrate is a glassy matrix, said process comprises at least the following steps: heating said glassy matrix including said layer of conductive or non-conductive material to a doping temperature (T.sub.D) ranging from 50 C. to 130 C.; applying an electric field between said glassy matrix and said conductive or non-conductive material having a voltage ranging from 300 V to +300 V, while maintaining the temperature at the doping temperature; cooling said glassy matrix including said layer of conductive or non-conductive material to an operating temperature (T.sub.U), said operating temperature being lower than 50 C.; said process being carried out on at least a portion of the surface of said conductive or non-conductive material.

2. Process according to claim 1, the thickness of the doped material at the material-glass interface varies between atomic thickness and a few nanometres.

3. Process according to claim 1, wherein said process is carried out at a pressure that is lower than 10.sup.3 mbar.

4. Process according to claim 1, wherein the doping temperature varies from 65 C. to 130 C.

5. Process according to claim 1, wherein the electric field is applied by connecting both said layer of conductive or non-conductive material and the glassy matrix to a voltage source by means of a first and of a second electrode, respectively.

6. Process according to claim 5, wherein the doping operation is an n-type doping operation and that the electrical potential applied to the second electrode is positive with respect to the potential of the first electrode.

7. Process according to claim 5, wherein the doping operation is a p-type doping operation and that the electrical potential applied to the second electrode is negative with respect to the potential of the first electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following figures and examples illustrate the invention in greater detail without however limiting the scope thereof.

(2) FIG. 1 shows the device for doping a conductive or non-conductive material (2) that is deposited on one face of an inorganic glass substrate (4), a voltage source (1) connected to the conductive or non-conductive material by an electrode (3) and to the other face of the glassy matrix by another electrode (5).

(3) FIG. 2 shows the doping of a layer of graphene with time in terms of the variation in its sheet resistance;

(4) FIG. 3 shows the doping of a layer of molybdenum disulfide with time in terms of the variation in its sheet resistance;

(5) FIG. 4 shows the doping of a layer of zinc oxide with time in terms of the variation in its sheet resistance;

(6) FIG. 5 shows an example of a doping operation carried out under vacuum compared with a doping operation carried out in air, in terms of the variation in its sheet resistance.

DETAILED DESCRIPTION

Examples

Example 1: Doping a Layer of Graphene on Borosilicate Glass According to the Process in Accordance with the Invention

(7) The doping process has been carried out using commercially available single-layer CVD (chemical vapour deposition) graphene on copper foil (Graphene Supermarket, graphene-supermarket.com) deposited on borosilicate glass to a thickness of 0.5 mm. The deposition operation has been carried out by means of the poly(methyl methacrylate) transfer method (as per the method explained by X. Li et al. Nano Lett., 2009, 9, 4359). The assembly has been linked to a voltage source by electrodes, one making contact with the graphene (chromium/gold; respective thicknesses 2 nm/70 nm, thermally evaporated through a mask) and the other making contact with the glassy matrix (silver lacquer). The assembly has then been placed under vacuum at a pressure of less than 10.sup.6 mbar and has been heated to a temperature of 142 C. A voltage of 285 V has been applied for 100 min. The van der Pauw method (van der Pauw, L. J. (1958) Philips Research Reports 13: 1-9) has been used to measure the resistivity of the material, the doping type (n or p) and the charge carrier density. Change in sheet resistance of the material, Rs=609 /sq (FIG. 2) Charge carrier density: N=4.410.sup.13 cm.sup.2 Transparency=97% at 550 nm

Example 2: Doping a Layer of Molybdenum Disulfide on Borosilicate Glass According to the Process in Accordance with the Invention

(8) The doping operation has been carried out according to the process of Example 1, on a 2 nm-thick MoS.sub.2 sample deposited by anodic bonding using a sample comprising a layer of molybdenum disulfide, having an area of 50 m.sup.2, deposited on a 0.5 mm-thick borosilicate glass matrix. The sample has been placed under vacuum at a pressure of 10.sup.6 mbar then heated to a temperature of 130 C. A voltage of +4 V has been applied for 30 minutes.

(9) Change in sheet resistance of the material, Rs=5 k/sq (FIG. 3)

(10) Charge carrier density: N=10.sup.13 cm.sup.2

Example 3: Doping a Layer of Zinc Oxide on Glass According to the Process in Accordance with the Invention

(11) The doping operation has been carried out using a sample comprising a 25 nm-thick layer of zinc oxide, having an area of 1 mm.sup.2, deposited by RF (radiofrequency) sputtering on a 0.5 mm-thick soda-lime glass matrix. The sample has been placed under vacuum at a pressure of 10.sup.6 mbar then heated to a temperature of 130 C. A voltage of +35 V has been applied for 70 minutes. Change in sheet resistance of the material, Rs, decreases by four orders of magnitude, from 10.sup.8 to 10.sup.4 k/sq (FIG. 4) Charge carrier density: N=10.sup.14 cm.sup.2 Transparency=92% at 550 nm

Example 4: Comparative Example Between a Process Carried Out in Air and a Doping Operation Carried Out Under Vacuum

(12) In this example, the process has been carried out using two identical samples 1 and 2 comprising a 0.4 nm-thick layer of graphene on a 0.5 mm-thick borosilicate glass matrix. The sample 1 has been placed under vacuum at a pressure of 10.sup.6 mbar then heated to a temperature of 71 C. A voltage of 190 V has been applied for 120 minutes. The sample 2 has been left in air then heated to a temperature of 145 C. A voltage of 200 V has been applied for 120 minutes. Change in sheet resistance of sample 1, Rs=0.65 k/sq (substantially horizontal curve, FIG. 5) Change in sheet resistance of sample 2, Rs=0.06 k/sq (curved curve, FIG. 5)

(13) The doping results obtained for each of the comparative samples 1 and 2 are given in the appended FIG. 5. These results show that when the process is carried out in air at atmospheric pressure (Sample 1: substantially horizontal curve) instead of under vacuum (Sample 2: curved curve), no doping is obtained.