Electric conduction through supramolecular assemblies of triarylamines

Abstract

A method is provided for modifying a surface of a solid conducting material, which includes applying a potential difference between this surface and a surface of another conducting solid material positioned facing it, and wherein, simultaneously, the surface (S) is put into contact with a liquid medium comprising in solution triarylamines (I): ##STR00001##
while subjecting these triarylamines (I) to electromagnetic radiation, at least partly converting them at into triarylammonium radicals. Also provided is a conducting device which includes two conducting metal materials, the surfaces of which, (S) and (S′) respectively, are electrically interconnected through an organic material comprising conducting fibrillar organic supramolecular species comprising an association of triarylamines of formula (I).

Claims

1. A method for preparing fibrillar supramolecular species comprising triarylamines of formula (I) below: ##STR00010## wherein: each of the groups -A.sup.1- and -A.sup.2-, either identical or different designates a covalent bond or a group —O—, —S—, —NH—, —NH(C═O)—, or —NR.sup.3—; each of the groups R.sup.1, R.sup.2 and R.sup.3, either identical or different, represents: an aromatic group; or a hydrocarbon chain comprising from 4 to 30 carbon atoms, optionally halogenated and optionally interrupted with one or more heteroatoms selected from N, O or S; or a polyethylene glycol chain; and R is a terminating group; said method comprising: (i) preparing a liquid medium containing said triarylamines of formula (I); (ii) subjecting said liquid medium containing said triarylamines of formula (I) to an electric field and irradiating said liquid medium containing said triarylamines of formula (I) with an electromagnetic radiation; and (iii) obtaining said fibrillar supramolecular species comprising triarylamines of formula (I).

2. The method of claim 1, wherein said liquid medium comprises a chlorinated solvent.

3. The method of claim 1, wherein said fibrillar supramolecular species comprising triarylamines of formula (I) are formed and immobilized on a surface (S) of a solid conducting material.

4. The method of claim 1, wherein said fibrillar supramolecular species comprising triarylamines of formula (I) are electrically connecting two conducting solid elements.

5. The method of claim 1, wherein said method comprises: grafting on a surface (S) of a solid conducting material said fibrillar supramolecular species comprising triarylamines of formula (I); and connecting surface (S) and a surface (S′) of another conducting solid placed facing the surface (S) with said fibrillar supramolecular species comprising triarylamines of formula (I).

6. The method according to claim 1, wherein the liquid medium comprises a solvent of said triarylamines of formula (I) and wherein said solvent is removed.

7. The method according to claim 1, wherein the wavelength of said radiation corresponds to the absorption peak λ.sub.max of the triarylamines of formula (I) on a UV-visible light absorption spectrum.

8. The method of claim 1, wherein each of the groups -A.sup.1- and -A.sup.2- represent —NH(C═O)—.

9. The method of claim 1, wherein each of the groups -A.sup.1- and -A.sup.2- represent a group —O—.

10. The method of claim 1, wherein each of the groups R.sup.1 and R.sup.2, represents, independently: a benzyl group; or an alkyl group comprising from 6 to 18 carbon atoms.

11. The method of claim 1, wherein the triarylamines fit the formula (Ia) below: ##STR00011## wherein: each of the groups R.sup.1 and R.sup.2, either identical or different, designates a benzyl group or a linear alkyl group, comprising from 6 to 18 carbon atoms; and A is a hydrogen group: a halogen group, or an alkyl group.

12. The method of claim 11, wherein R.sup.1, R.sup.2, and A have one of the following meanings: R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=Cl; or R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=H; or R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=C.sub.6H.sub.13; or R.sup.1═R.sup.2=benzyl and A=H; or R.sup.1═R.sup.2=benzyl and A=Cl.

13. The method of claim 11, wherein each of the groups R.sup.1 and R.sup.2 independently represents a linear alkyl group comprising from 4-7 to 10 carbon atoms.

14. The method of claim 1, wherein each of the groups R.sup.1 and R.sup.2, either identical or different, designates a linear alkyl group comprising from 7 to 10 carbon atoms or a benzyl group.

15. The method of claim 1, wherein R is CH.sub.2-A and A is a hydrogen group; a halogen group; or an alkyl group comprising from 4 to 30 carbon atoms.

16. The method of claim 1, wherein each of the groups R.sup.1 and R.sup.2 independently represents a linear alkyl group comprising from 4 to 30 carbon atoms.

17. The method of claim 1, wherein each of the groups -A.sup.1- and -A.sup.2-designates a group —NH(C═O)—; and wherein each of the groups R.sup.1, and R.sup.2, either identical or different, represents a hydrocarbon chain comprising from 4 to 30 carbon atoms, optionally halogenated and optionally interrupted with one or more heteroatoms selected from N, O or S.

18. The method of claim 1, wherein said fibrillar supramolecular species comprising triarylamines of formula (I) form nano-wires or nano-filaments.

19. A method for modifying a surface (S) of a solid conducting material, wherein said method comprises: positioning a surface (S) of a solid conducting material and a surface (S′) of another conducting solid material so that surface (S′) is facing said surface (S); putting said surface (S) in contact with a liquid medium comprising in solution at least triarylamines of formula (I); applying a potential difference between said surface (S) and said surface (S′), and subjecting said liquid medium comprising in solution at least triarylamines of formula (I) to an electromagnetic radiation or to chemical or electrochemical oxidation to produce triarylammonium radicals from said triarylamines; wherein said triarylamines of formula (I) are as follows: ##STR00012## wherein: each of the groups -A.sup.1- and -A.sup.2-, either identical or different designates a covalent bond or a group —O—, —S—, —NH—, —NH(C═O)—, or —NR.sup.3—; each of the groups R.sup.1, R.sup.2 and R.sup.3, either identical or different, represents: an aromatic group; or a hydrocarbon chain comprising from 4 to 30 carbon atoms, optionally halogenated and optionally interrupted with one or more heteroatoms selected from N, O or S; or a polyethylene glycol chain; and R is a terminating group; and forming fibrillar supramolecular species comprising triarylamines of formula (I) immobilized on said surface (S) of said solid conducting material.

20. The method according to claim 19, wherein said method comprises electrically connecting surfaces (S) and (S′) where the surfaces (S) and (S′) facing each other are distant from each other by 1 micron or less.

21. A method for a preparing or repairing an electronic or optoelectronic device, said method comprising: (i) preparing a liquid medium containing said triarylamines of formula (I) below: ##STR00013## wherein: each of the groups -A.sup.1- and -A.sup.2-, either identical or different designates a covalent bond or else a group —O—, —S—, —NH—, —NH(C═O)—, or —NR.sup.3—; each of the groups R.sup.1, R.sup.2 and R.sup.3, either identical or different, represents: an aromatic group; or a hydrocarbon chain comprising from 4 to 30 carbon atoms, optionally halogenated and optionally interrupted with one or more heteroatoms selected from N, O or S; or a polyethylene glycol chain; and R is a terminating group; (ii) providing a solid device comprising two conducting metal materials having surfaces (S) and (S′) facing each other and made of at least one metal material; (iii) putting said solid conducting device into contact with said liquid medium containing said triarylamines of formula (I); (iv) subjecting said liquid medium containing said triarylamines of formula (I) to an electric field; (v) subjecting said liquid medium containing said triarylamines of formula (I) to an electromagnetic radiation while subjecting said liquid medium containing said triarylamindes of formula (I) to an electric field according to step (iv); and (vi) obtaining an electronic or optoelectronic device comprising two conducting metal materials, the surfaces of which, (S) and (S′) respectively, are electrically interconnected by an organic material comprising electronic conducting fibrillar organic supramolecular species comprising an association of triarylamines of formula (I).

22. The method of claim 21, wherein said step (iv) begins before step (v) of subjecting said liquid medium containing said triarylamines of formula (I) to an electromagnetic radiation.

23. The method of claim 21, wherein said metal materials are selected from the group consisting of gold (Au), nickel (Ni), titanium (Ti), silver (Ag), iron (Fe), platinum (Pt), copper (Cu), cobalt (Co), zinc (Zn), chromium (Cr), manganese (Mn), or alloys comprising one or more of these metals.

24. The method of claim 21, wherein said metal materials are metal materials of conducting electrodes and wherein at least one electrode is covered with a gold (Au) deposit.

Description

(1) In the figures:

(2) FIG. 1 illustrates a schematic view of the geometry of a nano-gap associated with a typical conductance measurement and with atomic force microscopy (AFM) images. (A) in particular represents a solution of compounds of the invention drop-casted in the dark, on nano-patterned Au/Ni electrodes. The applied potential difference between both electrodes is comprised between 0.3 and 0.8V. The measured conductance for the interconnection without the structures of the invention is of the order of one picosiemens. The sample is then subjected to light, which produces radicals inducing the supramolecular structures of the invention by live radical polymerization resulting in aligned self-assembling along the electric field and strong connection of both electrodes. (B): topography of the open gap (on the left) as seen with AFM before irradiation and after irradiation, filled with the supramolecular structures of the invention (on the right). (C): an AFM image before radiation showing a nano-gap (surface scale 1500×1500 nm.sup.2). (D) an AFM image after irradiation (surface scale 1500×1500 nm.sup.2): the nano-gap filled with nano-wires or nano-filaments is seen. (E) Zoom on the nano-gap filled with nano-wires (surface scale 250×250 nm.sup.2).

(3) FIG. 2 represents the ohmic behavior and conductivity characteristics of the supramolecular structures versus temperature: (A) current versus voltage curve, measured at a low temperature (1.5K). (B) normalized R(T) measurement of three devices functionalized by supramolecular structures of the invention, between room temperature and 1.5K. The initial resistances for each sample at 300K are the following: 22, 45 and 360Ω. Each sample is correlated by using the equation

(4) $\frac{1}{R}\left(T\right)=\frac{1}{R_0}.Math.\exp \left(\frac{{\mathrm{\hslash \omega }}_0}{k_{B}T}\right)$
wherein k.sub.B is Boltzmann's constant and wherein hω.sub.0 is the energy of the photons.

(5) FIG. 3 illustrates a design of electrodes: (A) a nano-gap of electrodes observed under a scanning electron microscope (SEM). (B) A zoom illustrating four pseudo-connection points, limiting the series resistance of the interconnections to below 2Ω. (C) A zoom on the nano-gap illustrating a typical distance of less than 100 nm.

(6) FIG. 4 illustrates the current versus voltage I(V) measurements: (A) (IV) of an empty nano-gap (width 100 μm, length 0.08 μm). (B) I(V) of a reference nano-gap immersed in a solution of the compounds of the invention, before light irradiation. The residual current is ascribed to ion impurities in the solution. (C) I(V) of a nano-gap after self-assembly of the compounds of the invention under light irradiation. (D) I(V) of a nano-gap showing the effect of the applied voltage during the initial light irradiation (diamonds: 0.01 V, circles 0.1 V, squares: 0.3 V).

(7) FIG. 5 represents the differential conductance measured at 200K in vacuo by using the AC bridge technique. (A) reduction of the conductance with the potential difference indicating possible heating of the samples in solution. (B) an integrated curve illustrating current values of a few tens of mA at higher potential differences.

EXAMPLE 1

(8) A connection of two electrodes was achieved according to the method of the invention, by using a device of the type of the one described in Nanotechnology, 21, 335303 (2010), which has two electrodes facing each other.

(9) To do this, a compound fitting the aforementioned formula (Ia), wherein R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=Cl, was used, dissolved in an amount of 10 mmol/L in chloroform.

(10) The solution of the compound was placed in the gap between two electrodes and then the device was irradiated with white light with a power of 100 W, while imposing a potential difference of 300 mV between the electrodes.

(11) The very rapid formation of an electric connection between both electrodes was then observed, which is expressed by a measurement of the conductivity between both electrodes: before the treatment, a current is measured of the order of a few picoamperes between both electrodes, versus a current of 0.5 A (i.e. 10.sup.8 fold increase) after the treatment.

(12) Micrographs reveal the presence of fibrillar supramolecular species which ensure the electric connection between the electrodes, organized in parallel and extending perpendicularly to the surface of the electrodes.

EXAMPLE 2

(13) By an optical lithography technique on a silicon substrate, Au and Ni electrodes were made, the surfaces of the electrodes being separated by a distance of about 80±20 nm, over a width of 100 μm. The residual current is less than 1 pA between both surfaces. This circuit is immersed in a solution of molecules of formula (Ia) and in particular of molecules of formula (Ia), wherein R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=Cl, in 1,1,2,2-tetrachloroethane (C.sub.2H.sub.2Cl.sub.4) (FIG. 1A), in the absence of light. An increase in the current between the electrodes by a few hundred pA was observed under a differential voltage of a few hundred mV (see FIG. 4). Following irradiation, using white light, a six fold increase in the current is observed, thereby attaining values in the mA range. The corresponding conductance is of a few tens of mS. These devices with 2 terminals with channels and interfaces of series contacts have an ohmic resistive behavior related to high conductivity values as shown by the measurement of the intensity versus the voltage I(V) (according to FIGS. 2A and 4). The conductivity of the channel is estimated as ranging beyond 10.sup.4 S.Math.m.sup.−1. Alternatively, it is estimated that the interface resistance per unit length is equal to or greater than 10.sup.−4 Ω.Math.m. This value is of the order of six times less than that of the best contacts of simple organic crystals and less than what is obtained with graphene flakes.

(14) After intense washing of the samples with the solvent, Atomic Force Microscopy (AFM) imaging reveals a length of <<nano-wires>> of conducting organic supramolecular structures exactly in line with the distance between the electrode surfaces (FIGS. 1B-E), with orientations along the electric field applied to the assembly and with a homogeneous diameter of 12±2 nm. It was discovered that it is important to apply an initial threshold voltage (of at least 0.1V and preferably at least 0.3V?) between the electrodes, before light irradiation, in order to effectively obtain in a stable way the fibrillar supramolecular structures.

(15) It was also observed that the method for preparing these structures may be reversible when the sample is heated for example to 60° C. overnight, since the formed supramolecular structures dissolve. After repeated assemblings and disassemblings (six times), the metal interconnections were not significantly effected by the heating cycles.

(16) After evaporation of the solvent, the obtained structures become stable and provide reproducible results after one night of heating at 100° C. The performances of the samples are not notably sensitive to humidity nor to oxygen which is highly positive for organic electronic devices. It was not necessary to operate under inert atmosphere conditions during the preparation of the supramolecular structures. After one month of storage, the samples exhibited comparable conducting properties.

(17) Studies versus temperature confirmed that the samples had high conductivity since they systematically and reliably reveal resistivity decreasing with temperature, down to 1.5K (FIG. 2B). The ohmic profile of the structures was also noted up to high currents at low temperature (FIG. 2A). For the samples exhibiting the smallest resistance, currents up to 25 mA were observed when they are subject to a potential difference of 1V in vacuo (FIG. 4B). The current density is estimated to be of the order of 10.sup.7 A.Math.cm.sup.−2, which is remarkably high for organic compounds and corresponds to electromigration density currents in the metal circuits.

EXAMPLE 3

(18) Samples were also made with analogs of compounds of Example 1. In a blind test configuration, it was noticed that the inter-electrode gap was only filled with supramolecular structures when they are capable of self-assembling. This confirms that the conducting properties result from the supramolecular structures of the invention. The following compounds were tested.

(19) TABLE-US-00001 TABLE 1 Behavior in solution Molecule Determined by .sup.1H NMR (1) State of the gap   1 Self-assembled Closed   2 Self-assembled Closed   3 Self-assembled Closed   4 Non self-assembled Open   5 Non self-assembled Open   6 Non self-assembled Closed (a)

(20) a: The gap was however opened after rinsing with solvent under conditions where STANWs derivatives 1-3 remain stable; this shows the weakened mechanical properties of STAWNs starting from compound 6.

(21) With .sup.1H NMR, it was determined that the compounds 1-3 self-assemble in solutions of CDCl.sub.3 after light stimulation, which is not the case of the compounds 4-6. This property related to the structure shows that only the compounds of the invention have the capability of self-assembling.

(22) The experimentation was carried out by blind tests. The person having prepared the solutions did not carry out the conductivity measurements. The samples were coded. Each sample was measured under the same conditions: the 1V potential difference was applied on the solution of triarylamines 1-6 (1 mg.Math.mL.sup.−1), simultaneously with an irradiation of 100 W at a constant distance for a period of 10 seconds (≈10 W.Math.cm.sup.−2); and then the I/V dependency was measured for each distance. The results are summarized in Table 1. The correlations clearly show that the conductivity is dependent on self-assembly.

(23) Images of the Nano-Gaps.

(24) The morphology and the difference between the electrodes before and after self-assembly were observed, for this, a scanning electron microscope (SEM) was used and an atomic force microscope (AFM) was used for obtaining qualitative and quantitative information on the nano-gaps.

(25) The images taken with AFM (FIGS. 1C, D and E) give a specific indication of the fibrillar structure of the filled nano-gaps.

EXAMPLE 4

(26) Electrodes were made with edge mediated shadow mask lithography according to the technology described in J-F Dayen et al; Nanotrench for nano and microparticle electrical interconnects; Nanotechnology 21 335303 (2010)—a triple layer Ti(5 nm)/Ni(35 nm)/Au(20 nm) was first deposited by electron beam evaporation, followed by a standard lift-off method. The second step comprises the deposition under an angle of 60°, by creating a triple layer Ti(5 nm)/Ni(25 nm)/Au(10 nm) followed by a lift-off. The first electrode has a composition related to the superposition of two steps, and the second thinner electrode, has a composition only corresponding to the second layer of the deposited triple layer (this explains the height difference observed with AFM). The <<nano-gaps>> were made with a fixed inter-electrode distance of 80 nm and a length of 100 μm (FIG. 3). After checking the absence of any residual current, a solution of the compound formula (Ia), wherein R.sup.1═R.sup.2═C.sub.8H.sub.17 (linear) and A=Cl (at 1 mg/mL in C.sup.2H.sup.2Cl.sup.4), were deposited by drop casting on the electrodes. A potential difference of more than 0.3V and up to 0.8V with a DC current, was immediately applied between the electrodes, the time-dependent change in the current was recorded by using a measurement instrument with high resistances (electrometers) of the Keithley 6517B Electrometer/High Resistance Meter type. The sample was irradiated for a few seconds under illumination through a microscope condenser (numerical aperture of 0.55) with a 100 W halogen light source. An infrared filter was used for limiting the heating of the sample to a few degrees, which results in irradiation with a wide band power density of 10 W.Math.cm.sup.−2. The typical irradiation time of 10 s corresponds to the total number of photons used in about 30 minutes for achieving self-assembly in solution by using a power density of about 0.07 W.Math.cm.sup.−2, which is more than required for generating self-assembly. It was also discovered that a transition metal in the electrode was necessary for ensuring more satisfactory interconnection of the self-assembly. It is not possible to obtain stable and reliable self-assembly only between Au and Pt electrodes (with a Ti adhesion layer). The self-assembly has a success rate of more than 90% between two Ni and Fe electrodes. It was discovered that use of a gold deposit (Au) on the electrodes provides better long term stability of the samples, and with this it is possible to overcome the problem of surface oxidation of the transition metals.

(27) On the other hand, an effect initiating the growth of the self-assembly was observed with a substrate of the transition metal type.

(28) After the formation of the supramolecular structures, the samples were rinsed with chloroform, followed by intensive washing with acetone and ethanol, and then finally dried with a stream of nitrogen.

(29) Low temperature electric measurements were conducted with a cryostat having a vacuum pump (P<10.sup.−6 mbar) or in a helium (He) flow system lowering the temperature to 1.5K. The measurements of the electric properties were conducted with an Agilent E5270B semiconductor parameter analyzer (DC properties), and with an SRS 830 lock-in amplifier (AC properties).

(30) Differential conductance measurements were also conducted at 200K in vacuo. A current with an intensity of a few tens of mA was observed in a reproducible way with a 1V potential difference applied on different samples (FIG. 5).