EP1814818A2

EP1814818A2 - Particle network and method for realizing such a network

Info

Publication number: EP1814818A2
Application number: EP05814928A
Authority: EP
Inventors: Yves Samson; Franck Fournel; Joël EYMERY
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2004-11-09
Filing date: 2005-11-03
Publication date: 2007-08-08
Also published as: WO2006051186A3; FR2877662A1; WO2006051186A2; US7985469B2; FR2877662B1; JP2008520444A; US20080160316A1

Abstract

The invention relates to a method for realizing a particle network comprising a particle depositing step, capable of self-organizing with a determined increment along a first direction, onto a substrate exhibiting a property that permits an interaction between the substrate and the particles and modulated along the first direction with a period adapted to said increment. A substantial interaction thus subsists between each of the particles and its neighboring particles along the first direction.

Description

Particle network and method for producing such a network

The invention relates to a network of particles, for example nanoparticles, and a method for producing such a network.

The study of matter with smaller and smaller dimensions in different fields of science nowadays leads to orders of magnitude to which we can no longer consider it as a continuous structure, but as a discrete set of particles, called generally nanoparticles.

In this context, the organization of particles on a periodic network is sought in many applications, such as for example ultra-high density magnetic information carriers (ferromagnetic nanoparticles), memories based on semiconductor nanoparticles, networks of luminescent nanoparticles or the formation of catalytic or reaction sites of very small dimensions.

In these applications as naturally in others, the organization of particles in a network as perfect as possible is desirable, but very difficult to obtain in practice, especially over sufficiently large distances.

To try to answer this wish, it was for example proposed to form networks thanks to the self-organization of the particles, that is to say thanks to the interactions that the particles between them, as described by for example in the article "Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices" by S. Sun ef a /, in the Science magazine of March 17, 2000 (volume 287, pages 1989-1992).

However, one can not usually avoid the presence of defects

(eg lattice deficiencies - point defects - or translation or orientation deviations between network regions - extended defects), which makes it impossible in practice to form networks over long distances simply by means of self-organization ^. pârtîcûTêsT

In order to try to control the organization of particles over greater distances, it has been proposed to have assemblies of particles constituting a part of a network in lithographic structures formed at the surface of a substrate. The article "Templated Self-Assembly of Block Copolymers: Effect of Substrate Topogaphf by JY Chen et al., In Advance Materials 2003, 15, No. 19, October 2, Wiley-VCH Verlag, relates to such solutions.

By choosing dimensions of the lithographed structures smaller than the distance separating conventionally two defects of the network of particles, one obtains within each lithographed structure an assembly of particles in the form of a network which presents no defect if the average distance between defects, which is a statistical data, is respected in this assembly.

Although this technique reduces the number of defects, it can not prevent their occurrence in some cases. In addition, the actual extension of the network is limited to the dimensions of the lithographed structure, the presence of which further prevents the use of the entire available surface.

It has also been proposed to use a substrate whose lithographic patterns exhibit a strong interaction with the particles, to the extent that this substrate-particle interaction predominantly governs the location of the particles. In this solution, it is therefore the defects of the substrate, which it is naturally impossible to achieve in a perfect manner, which will cause the network organization defects (which could already be the case in the solution mentioned above) . The invention therefore aims in particular at a solution for the organization of a particle network that ensures the best regularity of the network, and also over great distances.

The invention thus proposes an array of particles arranged on a substrate having a property allowing interaction of the substrate and particles, characterized in that said property is periodically modulated in a first direction by allowing a substantial interaction between each of the particles and its particles. neighbors in the first direction.

The tendency of particles to self-organization (thanks to their interactions) is thus combined with the organizational effect provided by the substrate, and not dominated by it, which makes it possible to ensure a greater regularity in The organization of the network

Thus, in the absence of modulation of said property, the interaction between each of the particles and its neighboring particles would have allowed the local self-organization of the particles in this first direction. To obtain these effects in a particularly efficient manner, it can be predicted that the intensity of the particle - substrate interaction is not locally predominant in the particle - particle interactions.

A second property allowing an interaction of the substrate and particles, possibly identical to said property, can also be modulated in a second direction by allowing a substantial interaction between each of the particles and its neighboring particles in the second direction.

The great regularity of the aforementioned network is thus ensured in both directions of the face of the substrate. The network can in this case be square or hexagonal. Alternatively, it can be hexagonal.

When the particles are able to self-organize locally in the absence of modulation of the property with a determined pitch in the first direction, said property can be modulated according to the first direction with a period adapted to said step, that is, that is, for example, said period is substantially equal to said step or a multiple of said step.

Thus the particle network can be organized in correspondence with the modulation of the property presented by the substrate.

According to one possibility of implementation, at least some particles are formed by a central core covered by a shell. In this case, the shell participates in the substrate - particle interaction and / or the particle - particle interaction. The shell then makes it possible to facilitate the networking of the central cores. The shell can be deformed to allow the adaptation of the period of organization of the network. Said property is for example linked to the topography of the substrate.

The interaction of the substrate and the particles may also be a remote interaction, for example of the magnetic or electrical type.

The particle array may not be limited to two dimensions, but may also extend in a direction substantially perpendicular to the surface of the substrate.

L ^L ^~ égalernént invention provides a ^"ι method for producing an array of particles, characterized in that it comprises a step of deposition of particles, capable of self-organization with a given pitch along a first direction, on a substrate having a property allowing interaction of the substrate and particles and modulated according to the first direction with a period adapted to said step.

The particles may be formed prior to their deposition on the substrate. Thanks to this method, a substantial interaction remains between each of the particles and its neighboring particles and thus the effect mentioned above is obtained.

When the particles are able to self-organize in a network with a second pitch in a second direction, the substrate may also have a second property allowing an interaction of the substrate and the particles (possibly identical to said property) modulated according to the second direction with a period adapted to the second step.

This gives a network of particles of great regularity in two directions, that is to say in two dimensions.

According to one conceivable embodiment, the method may comprise a patterning step on the substrate. Substrate - particle interactions are thus performed, related to the topography of the substrate.

In practice, the patterning step may comprise a step of revealing a dislocation network.

Alternatively, the patterning step may be performed by lithography or nanoimprint technique.

The method may also include a material deposition step for developing said modulated property or determining the amplitude of the modulations of said modulated property.

The substrate - particle interactions are thus generated, or refined, by the deposited material.

The characteristics of the particle network mentioned above, and the advantages that derive therefrom, can also be applied to the method of producing the network that has just been mentioned.

Other characteristics and advantages of the invention will emerge in the light of the description which follows, made with reference to the appended drawings, in which -: -

- Figure 1 shows a top view of a substrate in a first embodiment of the invention;

- Figure 2 shows a section along the line AA of Figure 1; FIG. 3 represents a network of particles arranged on the substrate of FIG. 1 according to the first embodiment of the invention;

- Figure 4 shows a section according to section B-B of Figure 3;

- Figure 5 shows the particle array of Figure 3 at a defect in the substrate;

Fig. 6 shows the particle array of Fig. 3 at a defect therein;

FIG. 7 represents a sectional view of a substrate according to a second embodiment of the invention; FIG. 8 represents an array of particles arranged on the substrate of FIG. 7;

FIG. 9 represents a network composed of particles of two different types on the substrate of FIG. 7;

FIG. 10 represents a section of a substrate in a third embodiment of the invention;

FIG. 11 represents an array of particles arranged on the substrate of FIG. 10;

FIG. 12 represents an alternative embodiment of the substrate of FIG. 3; FIG. 13 represents an array of particles deposited on the substrate of FIG. 12;

FIG. 14 represents an alternative embodiment of the network represented in FIG. 9;

FIG. 15 represents a view from above of the network of particles represented in FIG. 14.

In a first embodiment given by way of non-limiting example with reference to FIGS. 1 to 4, monodisperse FePt alloy nanoparticles which each have a diameter of 6.3 nm and form a network of contiguous particles are used as particles. as detailed in the following. Alternatively, it could be a network of non-iointive particles

Figure la-i ^~ represents ^{"sdiêmatiquërnent} a substrate for receiving the particles. The surface of the substrate 2 has a network of grooves (or grooves) formed by a first set of parallel grooves 4 between them according to a first direction and a second set of grooves 6 parallel to each other in a second direction and perpendicular to the grooves 4 of the first set.

In each of the first and second sets of grooves, the grooves

4, 6 are separated by a distance at least substantially equal to the pitch of the particle array in the respective direction, or to an integer multiple thereof.

Furthermore, according to a possibility of embodiment used in the example described here, the distance between the grooves 4 of the first set is identical to the distance between the grooves 6 of the second set and the grooves 4, 6 thus form a square network. As a variant, especially when the pitch of the particle network is not the same in the first and second directions, the grooves may form a rectangular network. According to another variant, it is possible to use a hexagonal network.

In the example shown in FIGS. 1 to 4, the distance separating two adjacent parallel grooves 4, 6 is set at 18.9 nm (according to a technique described below), which corresponds to three times the pitch of the joined network formed. by FePt particles with a diameter of 6.3 nm.

As a variant, other distances between adjacent parallel grooves could be used, for example a distance of 6.3 nm equal to the pitch of the particle network in the case studied here, or a distance of 31.5 nm corresponding to five times the pitch of the network of these same particles.

A substrate 2 having grooves in the form of a square lattice of this type can be obtained for example by bonding a silicon-on-insulator (or SOI) substrate exhibiting a silicon-on-insulat ion substrate. silicon layer about 10 nm thick on a solid silicon substrate having a thickness of the order of 500 microns, with relative rotation of the crystalline axes of the two silicon surfaces (1, 0,0) to be assembled, then for example by revealing the dislocation network thus formed at the interface of the substrates by means of chemical etching. According to the aforementioned embodiment can be obtained a hexagonal network-Gθllage-by-same ^{^"method"} of ^'surfàcesUe silicon (1, 1, 1).

Such techniques are for example described in the articles "Ultra thin silicon films directly bonded to silicon wafers", F. Fournel et al., In Materials Science and Engineering B73 (2000) 42-46, Elsevier Science SA, and "ControUed surface nanopatieming with buried dislocation arrays", F. Leroy et al. in Surface Science 545 (2003) 221-219, Elsevier BV

According to this technique, the pitch λ of the groove network (that is to say the distance between adjacent parallel grooves) is connected to the angular rotation Ψ between

the two substrates (or disorientation) according to the formula λ = - η = -, where asi is

2V2.sin (y> 72) the pitch of the substrate network and is 0.5431 nm for silicon.

One can thus choose the angle Ψ of the disorientation so as to obtain the distance λ between adjacent parallel grooves desired, that is to say equal to the pitch of the particle network or an integer multiple of it. For example, in order to obtain a distance separating two adjacent parallel grooves (or not of the groove array) of 18.9 nm as in the example shown in FIGS. 1 to 4, disorientation is used between the SOI and solid silicon of 1, 164 °.

In the variants indicated above, an angle of 3.493 ° is used to obtain a pitch or groove grating period of 6.3 nm, and an angle of 0.698 ° to obtain a period of 31.5 nm.

It may be noted that since the angular resolution in the devices currently used is of the order of 5 thousandths of a degree for the disorientation between substrates, the distance between parallel parallel grooves obtained is valid to within 0.25 nm in the last case evoked and with a precision less than 0.1 nm in the first two cases.

Once the two substrates assembled by molecular bonding with a relative rotation defined as a function of the pitch of the network of grooves to be obtained, the SOI substrate is removed for example by chemical-mechanical polishing using the silicon oxide layer as a coating layer. 'stop. The silicon oxide layer is then removed, for example, with a solution of hydrofluoric acid (HF). The thin silicon layer of about 10 nm is then thinned by means of a chemical attack sensitive to the stresses induced by the dislocations, such as, for example, a modified version of the Yang type attack (HF / Crθ ₃ / H ₂ θ). ) or a modified version of the Dash-type attack (HF / HNO ₃ / H ₂ O) as indicated in the second-mentioned article above. By stopping the chemical attack at the bonding interface (or just past this interface) thanks to the knowledge of the attack speed of the solution used, we reveal the network of dislocations created at the interface of the substrates, this makes it possible to obtain the square network of grooves 4, 6 (or furrows) as represented in FIG. 1, which can also be seen as a network of protuberances 5.

Alternatively, one may be in a case where it is desired to use a structure complementary to that just described, that is to say with protuberances 34 in the grooves previously obtained, as shown in Figure 12 .

To obtain this type of structure, one can proceed as follows.

According to a first solution, a metal (for example gold) is diffused at the level of the dislocations before the chemical revelation step. Thus, a buried network of metal-rich regions is formed. The network of protuberances 34 is then revealed, for example by ionic abrasion.

According to a second solution, a network of grooves is produced as described previously with reference to FIGS. 1 and 2, and then deposited in these grooves a material whose abrasion speed under ion beam is smaller than that of the substrate (using example a metal like gold on a silicon substrate). The protuberances are then formed by ionic abrasion.

Once the substrate has been prepared, the FePt nanoparticles 8 are deposited on the substrate where they form a square lattice whose structure is determined by the combination of the self-organization of the particles (due to the interactions between particles, here in joined contact between these) and the location of at least a portion of the particles 8 at a preferred site of the substrate 2 (substrate-particle interaction) formed here by the grooves 4, 6 (or furrows) of the substrate 2 as illustrated in the figures 3 and 4 (or by the protuberances 34 in the variant envisaged in FIGS. 12 and 13, where the substrate-particle interaction under consideration generates a preferential localization of part of the particles 38 on the protuberances 34). Such a structure is for example obtained by pre-dispersion of nanoparticles-8 ^{^""} FePt ^{^"in"} ϋne hexane solution, deposit on the substrate 2 of this solution and then slow evaporation of hexane.

By construction, as indicated above, the pitch of the square network of grooves 4, 6 present on the surface of the substrate 2 is substantially equal to the pitch of the self-organized network of nanoparticles 8, or to an integer multiple thereof, such that the combined action of self-organization between particles 8 and the tendency to locate a portion of the particles 8 on the grooves 4, 6 leads to the organization of a network of particles with a structure substantially identical to the structure of the network that these particles would have adopted naturally locally on a substrate without modulation. The grooves 4, 6 of the substrate 2 (or the protuberances 34 if any) thus make it possible to ensure the regularity of the self-organized structure on a large scale.

FIG. 5 shows a network of nanoparticles 8 having the structure just described and represented in FIG. 4, in which the substrate 2 has a defect 3, in this case the absence of a groove 4 .

Since the location of the particles 8 of the network is not determined solely by the presence of the grooves 4, but also by the interaction with the other particles (interaction related to the self-organization of the particles), the particle 7 located the right of the fault 3 of the substrate 2 is correctly located in the network despite the groove fault.

Similarly, FIG. 6 shows a network of nanoparticles of the type shown in FIG. 4, in which certain particles 9 have a position slightly offset with respect to their theoretical position in the network (which is shown schematically in Figure 6 by a slightly smaller size for these particles 9), which would have led in the absence of the substrate 2 to a phase shift in the particle network.

However, thanks to the presence of the groove 4, the neighboring particle of the particles 9 introducing the offset is located precisely at the location determined by this groove 4, without phase shift relative to the particle located in line with the neighboring groove.

Thus, if the interaction between particles remains important for all the particles in the array, the presence of the grooves (and in general the substrate-particle interaction) makes it possible to correct a slight phase shift that could be introduced by a defect. in the particle network taken alone.

In -outrerdu -made dei'adaptation ^"of ^the" array of grooves 4, 6 to pitch of the array of particles self-organized in the first and second directions, the effect just described exists in both directions parallel to the surface of the substrate 2 and it thus makes it possible to ensure on a large scale the organization of the particle network in these two directions. The self-organization tendency of the square (or rectangular variant) network of particles is thus reinforced by the presence of the grooves 4, 6 simultaneously in the two directions of the surface of the substrate 2. FIGS. 7 to 9 represent a second embodiment of embodiment of the invention which will now be described.

According to this second embodiment, the raw substrate 12 comprises a square network of grooves obtained in a similar manner to the substrate described in the first embodiment. This substrate 12 is deposited in the grooves or between them of a material 4 having a particular affinity with first particles 18 to be organized (as described in detail below).

The surface of the substrate intended to receive the particles thus has a square network of regions formed of this material, for example strips 14; it may be noted that the surface of the substrate thus obtained may possibly in this case be generally flat, as shown in FIG. 7.

A set of particles 18 of a first type which have a particular affinity with the material 14 deposited in the grooves of the raw substrate 12 is deposited on the substrate which has just been described. The pitch of the self-organized network of particles is such that that the pitch of the square network of strips of material 14 is adapted to it, that is to say that the pitch of the square network of strips of material 14 is approximately equal to the pitch of the particle network of the first type 18 auto¬ organized, or an integer multiple of it.

Thanks to the affinity of the material 14 and the particles of the first type 18, some of these particles (one in two on the example shown) are placed at the preferential location determined by the strips of material 14. The substrate interaction - particle (here matter 14 - particle 18) is however of an amplitude such that it does not call into question the location of the rest of the particles at the locations determined by the self-organization of the particle network, that is to say say by the interactions between particles. The structure shown in FIG. 8 is thus obtained.

The material t4 ^" may for example be platinum having an affinity for particles having an amine function at the surface.

According to one possible embodiment, when it is desired to obtain a three-dimensional network structure, it is possible to use the particle network of the first type 18 as a substrate for the deposition and networking of particles of a second type optionally in accordance with the invention, as is schematically shown in FIG. 9.

As a variant, the particle network of the first type 18 may be used as an etching mask (or deposition mask according to another variant), in order to obtain a second modulation of the substrate for the deposition of another network of particles.

According to another variant illustrated in FIGS. 14 and 15, the network of particles of the first type 18 makes it possible to locate particles of a second type 17 in a network whose pitch is fixed by the size of the particles of the first type 18.

A third embodiment is shown in Figures 10 and 11.

According to this third embodiment, a material deposit 23 is produced on a substrate 22 having a pattern of grooves having a crenellated shape in section. The deposition of material 23 is here carried out in order to reduce the amplitude of the periodic variations of the topography of the substrate.

According to other embodiments in which the substrate-particle interaction is carried out by other properties of the latter than its topography, it would be possible analogously to reduce the amplitude of the periodic variations of this property; for example, when the property used is an interaction whose amplitude decreases with the distance (of the electric or magnetic interaction type), it would be possible to proceed to the deposition of a uniform layer to slightly move each of the particles of the substrate.

It is thus possible to adapt the amplitude of the modulation of the property of the substrate used to interact with the particles so that this interaction allows a preferential localization of the particles without, however, neglecting the effect of the interactions between particles.

As in the preceding examples, the period of the patterns (that is to say of the topography of the raw substrate), which is not modified by the deposition of material 23, is adapted to the pitch of the particle network which it must to receive.

In the example given here, the particles consist of a core 28 coated with a shell 29. The core 28 is for example the active element whose network structure is desired, whereas the shell 29 is intended to facilitate the formation of the network, for example by generating a particle interaction - specific particle and / or a specific substrate-particle interaction (Le., according to the schematic representation of FIG. 11, an adaptation of the size of the particle network to the grounds of the substrate 22, 23), or the generation of a certain elasticity in the particle network allowing a slight disagreement between the period of the pattern presented by the substrate and the period of self-organization of the particle network.

According to another possible embodiment (not shown), the substrate-particle interaction may be a remote interaction. In this context, it is possible to provide a buried network of a conductive material, for example according to the solution already mentioned for this purpose, it is possible to electrically charge in order to obtain a certain polarization. It is thus possible to obtain at the surface a modulated electric field acting on the particles to be organized. The polarization of the network may possibly be canceled once the organization is done. The embodiments which have just been described are only possible examples of embodiment of the invention. The various characteristics of these embodiments as well as those given as an alternative may in particular be combined differently from the examples given above.

Claims

A network of particles (8,18,19,28,29) disposed on a substrate (2; 12,14; 22,23) having a property for interaction of the substrate (2; 12,14; 22,23). and particles (8; 18,19; 28,29), characterized in that said property is periodically modulated in a first direction by allowing substantial interaction between each of the particles (8; 18,19; 28,29) and its neighboring particles in the first direction.

Particle grating according to claim 1, characterized in that a second property allowing an interaction of the substrate (2) and particles (8) is modulated in a second direction by allowing a substantial interaction between each of the particles (8) and its neighboring particles in the second direction.

3. Particle network according to claim 1 or 2, characterized in that the particles (8; 18, 19; 28, 29) are able to self-organize locally in the absence of modulation of said property with a step determined according to the first direction and in that said property is modulated according to the first direction with a period adapted to said pitch.

4. Particle network according to claim 3, characterized in that said period is substantially equal to said step or to a multiple of said step.

5. Particle network according to one of claims 1 to 4, characterized in that at least some particles (28, 29) are formed by a central core (28) covered by a shell (29).

6. Particle network according to claim 5, characterized in that the shell (29) is adapted to deform to allow the adaptation of the period of organization of the dream.

7. A particle network according to claim 5 or 6, characterized in that the shell (29) participates in the substrate-particle interaction and / or the particle-particle interaction.

8. Particle network according to one of claims 1 to 7, characterized in that said property is related to the topography of the substrate (2; 22, 23).

9. Particle network according to one of claims 1 to 7, characterized in that the interaction of the substrate (12, 14) and particles (18, 19) is a remote interaction.

10. Particle network according to claim 9, characterized in that the remote interaction is magnetic or electrical type.

11. Particle network according to one of claims 1 to 10, characterized in that it extends in a direction substantially perpendicular to the surface of the substrate (12, 14).

12. A method for producing a network of particles, characterized in that it comprises a step of:

- Deposition of particles (8; 18, 19; 28, 29), able to self-organize with a determined pitch in a first direction, on a substrate (2; 12, 14; 22, 23) having a property allowing an interaction of the substrate (2; 12,14; 22,23) and particles (8; 18,19; 28,29) and modulated in the first direction with a period matched to said pitch.

13. A method of producing a network of particles according to claim 12, characterized in that the particles (8) are able to self-organize in a network with a second pitch in a second direction and in that the substrate ( 2) has a second property allowing an interaction of the substrate (2) - and ^~ particles ^" (8) modulated ^" in the second direction with a period adapted to the second step.

14. A method of producing a particle network according to claim 12 or 13, characterized in that it comprises a step of forming patterns (4, 6; 22, 23) on the substrate.

15. A method of producing a particle network according to claim 14, characterized in that the patterning step comprises a step of revealing a dislocation network.

16. A method of producing a particle network according to claim 14, characterized in that the patterning step is carried out by lithography.

17. A method of producing a particle network according to claim 14, characterized in that the patterning step is carried out by nanoimprint.

18. A method of producing a particle network according to one of claims 12 to 17, characterized in that it comprises a material deposition step (14) for the development of said modulated property.

19. A method of producing a network of particles according to one of claims 12 to 18, characterized in that it comprises a material deposition step (23) determining the amplitude of the modulations of said modulated property.

20. A method of producing a particle network according to one of claims 12 to 19, characterized in that said period is substantially equal to said step or a multiple of said step.

21. A method of producing a network of particles according to one of claims 12 to 20, characterized in that at least some particles are formed by a central core (20) covered by a shell (29).

22. A method of producing a particle network according to claim 21, characterized in that the shell (29) is adapted to deform to allow the adaptation of the network organization period.

23. A method of producing a particle network according to claim 21 or 22, characterized in that the shell (29) participates in the substrate-particle interaction and / or the particle-particle interaction.

24. A method of producing a network of particles according to one of claims 12 to 23, characterized in that said property is related to the topography of the substrate (2; 22, 23).

25. A method of producing a particle network according to one of claims 12 to 23, characterized in that the interaction of the substrate (12, 14) and particles is a remote interaction.

26. A method of producing a particle network according to claim 25, characterized in that the remote interaction is magnetic or electrical type.