JP2000022129A - Multicolor assembly of patterned luminescent and optically polarized arrays of semiconductor nanoparticles manufactured by wetting film process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shift radiation of light to the longer wavelength side by forming a multicolor device of patterned spots of semiconductor nanoparticles on a solid substrate by liquid film process. SOLUTION: An assembly of circular nanoparticle spot array is formed of a plurality of cell blocks having a cell wall block sealed from below by a solid substrate 12. A nanoparticle array 10 begins growth in the center of cell through formation of a kind of nucleus at a thinnest part and crystal nucleus in an amorphous layer begins to grow in the radial direction through convection of nanoparticles 20 from a suspension film 21. The array substantially grows circularly and the thickness increases toward the circumference according to the shape of meniscus. Array grow process finishes within several minutes depending on the conditions. Radius R of the nanoparticle array increases linearly as the time elapses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor device comprising an array of semiconductor nanoparticles having patterned luminescent or optical polarization characteristics formed by a wet process, and a method of manufacturing the same.

2. Description of the Related Art

[0002] Nanoparticles, also known as semiconductor nanocrystals or quantum dots, are usually II-VI or III-VI.
-Consisting of a group V semiconductor. The nanoparticles have a shape close to a spherical surface, the size of which is about several nanometers, and are synthesized by a known colloid chemistry method.

[0003] The arrangement (spot) of such nanoparticles
Are produced by drying a thin suspended film on a solid substrate, so that these particle arrays are essentially two-dimensional arrays. By controlling the dimensions and other characteristics of the liquid film, macroscopic patterning is introduced throughout the array. This patterning process is considered to be a type of lithography based on self-assembly of particles by the force of a capillary or the like in a liquid film. By controlling the size and shape of the film, an array of arbitrary size, size and shape is formed.

[0004] The patterned particle arrays thus obtained exhibit remarkable luminescence properties and can be used in various optoelectronic devices and coatings. For example,
Light can be polarized by these patterned arrangements, and charges and light can be transported depending on the emission time.

A multicolor device made of such an array (spot) formed by a systematic method is constituted by a kind of super array having elements (spots), and emits light of various colors and intensities upon excitation. Unit (pixel)
Plays a role.

Examples of such arrays, circular rings, and these multicolor devices are provided below.

[0007] Thin layers of semiconductor nanoparticles can be used in light emitting devices (Alivisatos et al.), Photovoltaic elements (Green).
nham, N .; C. Et al., Phys. Rev .. B, 5
4, 17628 (1996)), a photoelectric detector (Bhar
gava), photoconductive components (Herron et al.), storage devices (Chen et al.), EL panels (Alivisa)
tos, etc.). All of these applications stem from the fact that the size of the nanoparticles is smaller and the emission wavelength is drastically shorter (energy is increased) compared to the respective bulk semiconductors. This increase in energy is due to the confinement of the excited charge size within the nanoparticles, the so-called quantum confinement effect.

In order to put this property to practical use, various production methods for producing a nanoparticle layer have been proposed. Most of these methods are considered to be "continuous" methods,
The common feature is that a uniform coating is made on a large scale, for example a few cm, and then cut into small pieces for a specific purpose (see Goldstein).

[0009] However, our new approach is a method that aims at the opposite. According to the present invention, a thin liquid film can be used to directly produce an array of nanoparticles having a size as small as a single pixel (chip, device). Moreover, such fragmentation can result in a patterned layer with new properties,
This cannot be done with other available methods. It also combines several single arrays (spots) to assemble large arrays with new functional properties (individual coatings)
Can be assembled.

Other available methods and the liquid film method we use will be briefly described with emphasis on the differences between the two. Often, the nanoparticle layer is grown, for example, by spin coating, in which case the substrate on which the suspension droplets are placed is rotated at a specific speed until a thin film is formed.

This method has the following two embodiments. A first aspect includes spin coating (Alivisatos et al.) With nanoparticles dissolved in a volatile solvent. In this case, a uniform dry layer is formed after the solvent has completely evaporated. The disadvantage of this method is that the form formed is limited to a circular layer that is predetermined by centrifugal force. Since the centrifugal force is so strong, the (weak) attractive force between the particles for forming the ordered structure is suppressed. The most significant drawback is the inability of spin coating to form regular nanoparticle arrays (spots) as reported by the present inventors.

A second embodiment is spin coating with nanoparticles dispersed in an organic matrix. The matrix is a photoconductive polymer (binder) that connects the nanoparticles in a conductive network (Greenha).
m, N. C. Et al., Phys. Rev .. B, 54, 176
28 (1996) / Buetje et al./Elshner
Other) or polystyrene latex particles (Chevr
eau, A et al. Mater. Chem. , 6,1
643 (1996)). The binder (organic molecule) acts as a spacer that keeps the nanoparticles apart. According to this aspect, the aggregation property of the nanoparticles due to the adhesion at the semiconductor interface is eliminated. Anchor agent,
For example, a self-assembled monolayer (Colvi)
The use of n) allows the nanoparticles to adhere to the solid interface. When a specific binder (organic molecule) is used, the substrate is limited to a metal interface. Again, the spacing between the particles in the monolayer is too large to cause photoelectric interaction between the particles.

The importance of such interactions has recently been discussed in M.
urray et al. (Kagan, CR et al., Phys.
Rev .. Lett. , 76, 1517 (1996)). In their experiments, single crystals of semiconductor nanoparticles are produced by a method that precipitates in solution. Single crystals have a three-dimensional structure consisting of CdSe quantum dots arranged in a hexagonal or tetragonal lattice. The spacing is about 1 nm, which corresponds to the length of the passivation agent (organic molecule). At this distance, the exciton exchange by the particles is immediately possible, resulting in a slight fraying of the quantum confinement effect, and the luminescence compared to the distance of the non-interacting particles from the suspension. Red shift.

A similar interaction effect was observed with our particle array. However, there are some substantial differences between the grain array of Murray et al. And our grain array, as follows. It is because (i) the single crystal is essentially a three-dimensional aggregate and the size is quite small (5-50 μm)
m), practical applications are limited. In contrast, our proposed nanoparticle array is a two-dimensional structure produced by a liquid film whose thickness is much smaller than its lateral dimensions. Therefore, the horizontal size of the nanoparticle array is several mm, several cm,
It is easy to increase significantly, and practical enough.
In addition, the number of particle layers and their dimensions (array pattern)
Can be easily controlled by the growth conditions. (Ii) Particle arrays produced according to the present invention exhibit a red shift in luminescence even in the amorphous state. (Iii) The present invention uses various capping (surface passivation) particles to eliminate particle-particle interactions, ie, red shifts in the luminescence of nanoparticle arrays.

To create a dense spot of nanoparticles, D
disclosed by uskin et al. and Nagayama et al.
Substantial changes were made to the single membrane method. The changes are shown below. (I) The simultaneous operation of several membranes and a multi-cell method that can produce a spot assembly are proposed here. (Ii) Extend the application of the production method to nanoparticles of different types and smaller sizes. (Iii) The application of this method is extended to an organic solvent. In this case, it is preferable that the semiconductor nanoparticles have dispersibility. (Iv) Extend the application of this method to spots of any shape and size. (V) Use an inert gas as a desiccant to protect the nanoparticles from oxidation and preserve the luminescence of the particles.

[0016]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a patterned luminescent array (spot) of semiconductor nanoparticles.
And a method of forming it on a solid substrate using a liquid film process. According to the method of the present invention,
Individual nanoparticles in a patterned array emit light of a specific wavelength upon excitation, depending on, for example, the type of semiconductor and the size of the particles, without compromising optical and electrical properties (Quantum confinement effect). At the same time, the tightest contact between the nanoparticles in the array shifts the light emission to longer wavelengths, depending on the degree of interaction between the particles. If one type of nanoparticle that is close to monodisperse is used, there is only one luminescence peak. In the case of a mixture of monodisperse particles having different (average) sizes, or a mixture of particles of different materials, luminescence peaks are obtained at two or more places depending on the number of components. When the number of components reaches the limit, the luminescence emitted from the mixed particle array overlaps, resulting in the emission of white light.

The method of array growth and the optical characteristics are determined by the type of solvent (water or organic substance) and the substrate (the first case is preferably hydrophilic, and the second case is preferably hydrophobic). By controlling the wetting of the substrate with the solvent, a variety of patterned particle arrays can be formed that exhibit significant luminescence and other special photoelectric properties that are important in practical applications. The substrate used directly affects the luminescence of the nanoparticle array in two ways: That is, (i) the luminescence of the nanoparticles overlaps with any luminescence coming from the solid substrate itself. Thus, there is another possibility to enhance or suppress nanoparticle emission by altering the substrate emission. (Ii) Substrate coating with a thin reflective film (mirror effect) can dramatically increase the luminescence intensity of the nanoparticles.

Various wet film processes have been used to pattern nanoparticle arrays. That is, (i) a method of drying a suspended film formed in a cell having an arbitrary shape and size. Thereby, a nanoparticle array (spot) having uniform luminescence from the entire array is formed. This method was modified and improved to produce a regular and uniform spot assembly (ordered lattice structure) that could serve as a multicolor light emitting panel. An example of a circular assembly is shown below.

(Ii) A method of drying suspension droplets spread on a solid substrate. In this case, the droplets naturally become circular, resulting in an array of circular ring-shaped nanoparticles,
Luminescence occurs from the ring. By pre-patterning the substrate, i.e., by changing its local wettability, the droplets can be determined to any shape and a final ring arrangement with individual shapes can be formed.
By changing the methods (i) and (ii) and expanding these techniques, it is possible to manufacture an assembly of regularly arranged uniform rings (ordered lattice structure). This assembly can also be used as a component of a light-emitting multicolor panel. An example of a circular ring assembly is shown below.

In forming arrays in these ways, which are essential for nanoparticles, a thin liquid film, or droplet, is maintained in which the meniscus makes a certain gradient (contact angle) to the array. Therefore, the present invention also provides a calculation method for numerically solving an equation relating to a meniscus profile at the shape and size of each film. In addition, a kinetic model for array growth is provided to explain important experimental parameters such as evaporation rate, array size, membrane meniscus shape, and nanoparticle volume fraction. For monolayers of particles formed in very thin membranes, the contribution of suction capillary forces acting along the meniscus surrounding individual nanoparticles trapped in the membrane can also be explained.

By maintaining the conditions of growth instability, spot micropatterning can be performed. This forms an array of wavy patterns with strong polarization composed of arrows of unidirectional nanoparticles.

According to the present invention, it has the highest luminescence and is arranged in a macro-patterned area,
And can fully meet the requirements of multicolor illuminants, patterned luminescent coatings and other photoelectric devices,
It is possible to provide a method for producing an amorphous nanoparticle array having regularity (crystal lattice) with good reproducibility.

[0023]

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a multicolored device of a patterned two-dimensional array (spot) of semiconductor nanoparticles, which emits light of various colors upon excitation and thus emits light. Serve as a panel, coating, or other multi-component optoelectronic device. Single element nanoparticle arrays (spots) are initially produced by a wetting process that dries a suspended thin film containing nanoparticles. By changing the composition and size of the nanoparticles, the wavelength of the emitted light (luminescence) can be changed. By changing the pattern of the nanoparticle array, the absolute value of the emission intensity in time and space can be changed.

As used herein, the term “semiconductor nanoparticles” or simply “nanoparticles” refers to quantum confinement effects,
That is, it indicates the dependence of the wavelength of the emitted light on the size of the particles, and means a semiconductor single crystal having an average diameter of about several nm. Semiconductor nanoparticles are generally semiconductors of the II-VI or III-V components. Under certain conditions, the nanoparticles can be any other nano species exhibiting semiconductor and luminescent properties, such as family semiconductors, titanium dioxide, fullerenes, and the like.
-Species).

As used herein, the term "solvent" refers to an organic or inorganic solvent in which nanoparticles are first dissolved to form a suspension, which is used to form a substrate. Spread as a film (droplets) on top. The solvent is preferably volatile to evaporate and be completely removed from the nanoparticle dry array.

As used herein, the term "substrate" refers to a solid material, the surface of which is at the molecular level to enhance the movement of the nanoparticles along the substrate and adherence on the substrate. However, it is preferable to be flat even at the atomic level. The substrate surface is not dissolved or contaminated by the solvent. To preserve the initial luminescence of the nanoparticles, the substrate material is selected so that it does not emit significant emission at or near the emission peak of the nanoparticles. A substrate that emits light by itself can also be used to modify the emitted light of the nanoparticles. The substrate can be a composite material, and its surface exposed to the nanoparticle array is coated with a reflective film made of another material that improves the nanoparticle properties such as luminescence, charge conduction, and the like.

As used herein, "nanoparticle array",
The term "array" or simply "spot" means a dry nanoparticle film, typically less than a few microns thick, grown on a solid substrate by a wetting process.
The spot is obtained by self-assembly of nanoparticles in a thin liquid film driven by various kinds of microscopic forces such as capillary force, fluid force, and electrostatic force. The spot is formed with a good size and shape by controlling the film shape. The number of nanoparticle layers determines the thickness of the spot. Although the spot structure has a large proportion of amorphous (a randomly packed nanoparticle), it can also form a crystal lattice, that is, a layer of nanoparticles having an array of arrows. The characteristic capillary length (approximately a few mm) is the typical size of a spot, which is of the same order of magnitude as the example described below. However, micron-sized spots can also be easily obtained.

In a wet process (film or droplet), two types of spots, namely, a frame (cell),
A distinction must be made between high-density spots produced by membranes and hollow spots (rings) produced by adherent droplets. The structural differences between these spots reflect the growth mechanism. This mechanism will be used later.

The nanoparticle array produced by a liquid film is independent of a polycrystalline film that grows directly from a mixed solution of semiconductor compounds by electrophoresis, chemical precipitation, or the like.

As used herein, the term “assembly of arrays”, “assembly of spots”, or simply “assembly” refers to a collection of single spots (super arrays) having a macroscopic array of nanoparticles as defined above. ). In this way, the array (spot) becomes an element of the assembly. The number of single spots, their size, and the distance between the spots determine the dimensionality of the assembly. The dimensions and structure of the assembly can be extensively and mechanically controlled.

The present invention, that is, a method, components, and emission characteristics of a multicolor device having a two-dimensional array of emission of semiconductor nanoparticles, mainly by a liquid film process, will be described below. Since the assembly itself is the sum of the individual spot characteristics, the following discussion will mainly describe the characteristics of a single array (spot).

A. Growth of high-density nanoparticle spots and assembly of the spots: An array assembly is formed as a block of cells supporting a liquid film. Each cell is individually manufactured by perforating the block in a manner appropriate to obtain the desired size and shape of the cell. Next, the blocks are attached to a solid substrate to isolate the individual cells from each other. In order to obtain a super array of uniform elements,
A uniform volume of suspension is loaded simultaneously on each cell. Select a block material that has a wetting angle with the solution of about 90 °. In such a case, a meniscus having a slightly concave cell center is formed. To form this meniscus,
The cell wall and the solvent are of different types such as a hydrophobic wall for a hydrophilic solvent and a hydrophilic wall for a hydrophobic solvent. In contrast, for a good liquid film, the substrate and solvent must be of the same type combination, such as hydrophilic substrate and solvent, hydrophobic substrate and solvent.

Under these conditions, the height of the suspension film gradually decreases due to evaporation of the solvent while maintaining the initial wetting angle toward the substrate. On the other hand, the volume fraction of the nanoparticles substantially increases from the initial value. The nanoparticle array begins to grow at the cell center due to a kind of nucleation in the thinnest part of the film. The crystal nuclei then begin to increase due to the convective flow of nanoparticles from the suspension film. The shape of the growing array follows the symmetry of the cell. The thickness of the array increases in the direction of the cell wall following the meniscus shape. The time to complete the array growth depends on the evaporation rate of the solvent, i.e., the vapor pressure (or humidity in the case of water). Working in an inert atmosphere (zero humidity) greatly accelerates this process.

B. Growing Hollow Nanoparticle Spots and Assembling the Spots: To grow uniformly shaped hollow spots (rings) of nanoparticles, a suspension of nanoparticles is spread as droplets on a solid substrate. With a substrate without pretreatment, the droplets assume a shape close to a circle, the diameter of which depends on the volume of the liquid and the diffusion pressure, ie the contact angle between the solvent and the substrate, described by the Young's equation of capillary action. For a substrate with a pre-patterned surface, the droplets occupy the following expected points. That is, the water droplet shrinks and occupies only the hydrophilic point (enclosed by the hydrophobic portion). Organic droplets shrink at hydrophobic points (surrounded by hydrophilic parts). Immediately after diffusion, the nanoparticle ring begins to grow at the edge of the droplet due to pinning of the contact line. Solvent evaporation from the ring makes the convective flow of particles from the suspension increasingly noticeable. The thickness of the array increases from the droplet rim toward the center. The volume of the droplet is reduced by solvent evaporation,
The final volume is the volume of the nanoparticles. The completion time of the ring growth depends on the suspension volume and the nanoparticle concentration.

The method of the present invention for producing uniform droplets in place can produce a ring array assembly. For example, by sputtering a droplet having a uniform volume, a ring assembly having a substantially uniform size can be obtained. This technique can also be applied when forming a circular ring. Pre-patterned substrates were used in the present invention to improve ring uniformity and to form rings other than circular. A method of patterning such a substrate will be described below by way of example.

Under special circumstances, unstable waves are formed on the outer ring side surface. The unstable wavelength has excellent uniformity and reproducibility reflecting the growth state. Due to this fact, a nanoparticle array having a finer pattern can be formed.

A similar instability is due to gravity flow (Hupp
ert, Nature, 300, 427 (198
2)); centrifugation (Melo et al., Phys. Rev.
Lett. , 63, 1958 (1989)); heating (Cazabat et al., Nature, 346, 824).
(1990)), the surface tension gradient (Mar
angoni-Gibbs effect).

The instability in the present invention cannot be explained for the above reasons. On the other hand, using the description of instability in the literature first written by the present inventor, it is considered that the reason is a solvent having a high diffusion pressure and a high volatility. Under these conditions, a spontaneous flow of solvent occurs inside the droplet. The streamlines of this flow keep the dry nanoparticles aligned along these lines,
Shows remarkable symmetry. Nanoparticle arrays prepared by this procedure exhibit strong polarization and can be used in new applications by combining with the luminescence of the nanoparticles.

C. Emission characteristics of nanoparticle array: When array growth is performed in a nitrogen atmosphere, emission of nanoparticles is not impaired.
To protect the final array from oxygen, the array on the substrate was sealed, which allowed the luminescence of the nanoparticles to be preserved for months. Luminescence stability also depends on the capping layer. This layer also affects the degree of photoelectric interaction between the nanoparticles in the array and reflects luminescence. When the core nanoparticles are capped with organic molecules, this interaction becomes even more pronounced, resulting in a red shift in the sequence luminescence compared to the emitted light from the nanoparticles suspended in the liquid. In core / shell particles, the shell effectively isolates the light emitting cores from each other, and the wavelength of the emitted light of the core / shell particles is kept the same as in the suspension. With this discovery,
By controlling the capping layer, fine tuning of the emitted light wavelength became possible.

The intensity of the luminescence depends on the thickness of the nanoparticle array, ie the number of emitters (particles) per unit area. The luminescence is microscopically position-dependent because both the high-density spot and the hollow spot are non-uniform in thickness. However, from a macro perspective, nanoparticle spots
The luminescence is uniform (monochromatic) across the nanoparticles, which has practical value. The key to altering the luminescence intensity is the average array thickness.

The luminescence intensity of the ring-shaped spot increases with the illumination time. This particular fact is found in both smooth and wavy rings. This is also observed for both core and core / shell particles, but the mechanism is different in each case. The increase in luminescence is observed continuously or intermittently during successive measurements in various illumination modes.

These facts suggest that the change in luminescence observed over time is an essential property of the ring structure, probably due to the movement of charge along the ring. The fact that only part of the ring emits light is important. Thus, it is believed that the charge generated locally at the illuminated spot is transferred to the non-illuminated portion of the ring by a particular mechanism. This transfer is performed, for example, by hopping between cores or between surface traps on core / shell particles. The extra charge stored there contributes to the luminescence between the next excitation and during the detection.

The increase in luminescence due to this mechanism can well exceed the initial value. This fact, coupled with the potential for circulation of charge and most likely light along the ring, will support another practical application of a single ring of semiconductor nanoparticles.

D. Multicolor light emitting array assembly: The assembly is composed of a large number of nanoparticle arrays manufactured as high density spots or hollow spots. The unit elements are, in principle, a grid array having a uniform size. fact,
By varying the size of individual cells or by varying the volume of the droplets, assemblies composed of elements of various sizes can be produced. The spacing between elements and the type of grating can also be varied.

However, the greatest advantage of this embodiment is that the components of the assembly element can be varied, so that monochromatic or polychromatic luminescence of different intensities is obtained. This can be done in two ways:

(I) Varying the number, size, and composition of nanoparticles containing single layer devices: To do this, different cells are loaded with different types of nanoparticle suspensions in different cells. . Alternatively, droplets of suspensions of equal volume but of different types are formed. First, the volume fraction of the nanoparticles is changed. This results in different amounts of dry growth, ie different levels of luminescence. Therefore, by controlling the arrangement thickness, the intensity of light emitted from each element can be changed. Second, the type and / or size of the nanoparticles in the suspension is changed. In this way, different colors of luminescence emerge from the device. Therefore, a color pattern is created by controlling the wavelength of light emitted from the device.

(Ii) The growth of a plurality of component elements can be performed by the following two methods. First, by growing a monolayer array consisting of a mixture of different nanoparticles. In this way, an emission of light at several different wavelengths is obtained by the radiation of the individual components. This procedure is suitable for nanoparticles that dissolve in the same solvent. Second, a multi-layer growth method, where each layer consists of one type of nanoparticles. After the previous layer has dried, another type of suspension is added dropwise to form the next nanoparticle layer thereon. The end result is a multilayer array of nanoparticles emitting various colors. This procedure is suitable for nanoparticles that dissolve in different solvents.

The multi-component assembly of the nanoparticle array produced by the above procedure is a prototype of a multicolor luminescent panel.

[0049]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

EXAMPLE 1 Assembly of Circular Nanoparticle Spots As shown in FIG. 1 (a), an array assembly is formed of a plurality of cell blocks with cell wall blocks sealed from below by a solid substrate 12. In order to obtain an excellent nanoparticle array, the diameter of the bottom cell is about 2 mm,
Close to capillary length. Each cell simultaneously receives a uniform volume of suspension of about 1 microliter. The wall material (unit cell) 24 and the solvent may be a hydrophobic wall (for example, paraffin, Teflon) for a hydrophilic solvent (water), or a hydrophilic wall (for example, glass) for a hydrophobic (organic) solvent. Different. The substrate and solvent are similar, such as both hydrophilic (eg, clean glass and cleaved mica for water, and both hydrophobic (eg, silanized or carbon-coated glass for organic solvents).

The initial nanoparticle volume fraction is about 0.001. As shown in FIG. 1B, the nanoparticle array 10
A kind of nucleation at the thinnest part of the film initiates growth at the cell center. The crystal nucleus is an amorphous multilayer, which in turn begins to grow radially by convective flow of nanoparticles 20 from suspended film 21. The shape of the growing array is
Almost circular. The thickness of the array increases toward the periphery following the meniscus shape shown in FIG. The array growth process is completed within minutes depending on the conditions.

It has been found that the radius of the nanoparticle array R increases linearly with time. The growth model provided by the present invention and the theoretical model of the meniscus profile to which the Laplace's equation of capillary action applies can optimize the growth conditions of individual arrays and assemblies.

The growth of the nanoparticle array described above was performed by Dushk
Not the same as the observations on submicron latex particles by In et al. and Nagayama et al. The diameter of the latex particles they used was 144 nm, comparable to the thickness of the liquid film. For this reason, the particles aggregate as a single layer of a hexagonal lattice due to capillary attraction. Further, a crystalline latex multilayer is formed.

Example 2: Assembly of circular ring nanoparticle spot As shown in FIG. 2 (a), in order to grow the nanoparticle ring to have a uniform shape, a suspension (filled as small as 1 microliter) was used. Is dispersed as a circular droplet 31 having a diameter of several millimeters or less. The contact angle between the solvent and the substrate 12 is usually several degrees. Immediately after diffusion, the nanoparticle ring 11 begins to grow at the periphery of the droplet due to convective flow of the particles 20 from the suspension. The thickness of the array is
As can be seen from FIG. 3, the density increases from the periphery toward the center. The relationship between ring width and time is non-linear. The growth of the ring has a final width δ, as shown in FIG.
Complete in about 1 minute. Almost all particles that were initially present in the suspension aggregate into the ring. A small amount (less than 10%) of them remains and disperses as islands in the area initially occupied as droplets.

FIG. 4 shows an embodiment of the dry nanoparticle ring. The ring width, ie the amount of material, is determined by the initial volume fraction of the particles ψ
It is increasing with. The theoretical model of the present invention allows predicting ring growth kinetics and final ring width as a function of experimental parameters.

To manufacture the ring spot assembly, a uniform drop of liquid is generated at a predetermined location.

Example 3 Ring Growth Instability A schematic diagram of an unstable wave of wavelength で outside a circular ring is shown in FIG. The alignment of the nanoparticles along the streamline of the naturally occurring flow of the solvent can be clearly seen by the polarization in FIG. The streamlines of this flow both exhibit significant radial symmetry in the droplet and in the ring. The intersection of all lines is the singular point of the flow.

Example 4: Nanoparticle Array Luminescence In the case of CdSe arrays (organic molecule-capped cores), the array luminescence is compared to the emitted light from the same nanoparticles suspended in a solvent. A red shift is seen (FIG. 7 (a)). Such a shift is represented by CdSe / C
dS (core / shell particles) is not found in the shell (C
It can be seen that the (dS layer) plays a role of effectively isolating the light emitting cores from each other.

FIG. 8 shows the relationship between the luminescence intensity and the emitter (particle) per unit area for CdSe rings of various thicknesses proportional to the particle volume fraction. It can also be seen that the luminescence of the nanoparticles has almost the same intensity immediately after exposing the array to the atmosphere. However, if the exposure is performed for a long time, the strength may decrease due to the strength of the passivation (capping) of the nanoparticle surface.

Example 5: Protection of Dry Nanoparticle Arrays A simple method for protecting single nanoparticle spots and spot assemblies was performed using double-sided scotch tape and a plastic sheet cover frame. The tape surrounding the spot acts as both a sealant and a spacer. In this way, the nanoparticle luminescence is preserved unchanged for months.

Example 6: Method for Pre-Patterning a Substrate That Enables Uniform Arrangement of Droplets In order to provide a place that matches the position of the droplet, the desired size, shape, position, Use a mask with the number of holes. For the growth of hydrophobic droplets, the initially hydrophilic substrate (eg, glass) is covered with a mask, and then the uncovered portions (holes) are exposed to hydrophobic (eg, silazane) vapor. Conversely, in the case of hydrophilic droplets,
The mask is initially attached to a hydrophobic substrate (eg, glass exposed to silazane vapor), and the holes are then exposed to an etchant (eg, chromic acid) to make them hydrophilic.

Example 7 Multicolor Light Emitting Array Assembly with Circular High-Density Spots and Hollow Spots The final appearance of the multiple array assembly is shown in FIG. As can be seen, the assembly is composed of a number of nanoparticle spots formed as a circle (FIG. 10 (a)) or a ring (FIG. 10 (b)). In these embodiments, uniformly sized unit elements (circles or rings) arranged in a square lattice are selected. In fact, by changing the size and shape of the individual cells in FIG. 1 (b) and by changing the volume of the droplet in FIG. 2 (a), an assembly composed of elements of various sizes and shapes is produced. can do. The spacing between the elements and the type of grating can also be varied.

The greatest advantage, however, is that component changes in the elements of the assembly can be made, which result in monochromatic or polychromatic luminescence of varying intensity as described above. The entire assembly is covered as described in Example 5 to prevent damage to the device (the protective coating is not shown in FIG. 10). The specified multi-component assembly of the nanoparticle array produced by the above procedure is a prototype of a multi-color luminescent panel.

[Brief description of the drawings]

FIG. 1 (a) is a cross-sectional view of a block of a unit cell 24 for producing a collection of circular nanoparticle spots 10; FIG. 1 (b) is attached to a solid substrate 12 and includes nanoparticles 20; Unit cell 24 occupied by suspended thin film 21
FIG. The particle array 10 begins to grow at the center of the cell and then by convective flow of particles from the liquid film,
Growth proceeds to the cell periphery. (C) is a circle 10 of nanoparticles formed by drying a single suspension film. The intensity of the gray area corresponds to an increase in the thickness of the array from the center of the circle to its periphery, and also corresponds to an increase in the intensity of the luminescence.

FIG. 2 (a) is a suspension droplet 31 initially containing semiconductor nanoparticles 20 having an initial volume fraction 乾燥, which is dried on the solid substrate 12. FIG. Circular ring-shaped nanoparticle array 11
Grow around the droplet by convective flow of particles from the suspension. (B) is the final (dry) with outer radius R and width δ
This is a nanoparticle ring spot 11.

FIG. 3 is an AFM image of the outer end of a CdSe / CdS nanoparticle ring grown on a glass substrate.

FIG. 4 is the ratio of the final width δ of the CdS nanoparticle ring to the volume fraction 粒子 of the particles in the suspension. The solid line is a line drawn theoretically.

FIG. 5 is a schematic diagram of a dry nanoparticle ring 41, which has a characteristic wavy pattern of length Λ due to growth instability.

FIG. 6 is a polarization photograph of a wavy ring of CdSe nanoparticles ordered in a radial direction.

FIG. 7 (a) shows a photoluminescence peak value (solid line) obtained from an array of CdSe nanoparticles, and a peak value (dot-dash line) obtained from a CdSe suspension in heptane.
Red shift compared to. In (b), CdS
The photoluminescence peak values (solid line) obtained from the arrangement of the e / CdS core-shell particles coincide with the respective peak values obtained from the suspension of the same particles.

FIG. 8 shows the increase in the luminescence peak intensity of the CdSe ring with increasing volume fraction 体 of the particles, filled symbols are luminescence from samples maintained in a nitrogen atmosphere, and open symbols are the same After exposing the sample to the atmosphere.

FIG. 9 shows the increase in the maximum of the photoluminescence of the nanoparticle ring with respect to the illumination time, where the filled symbols are Cd
Se / CdS, and the outlined symbol is CdSe.

10 (a) is an overall view of a circular, and FIG. 10 (b) is an overall view of a circular ring-shaped multicolor device having a luminescent nanoparticle array.

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[Procedure amendment]

[Submission date] August 18, 1998 (1998.8.1)
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Multicolor device consisting of an array of semiconductor nanoparticles with patterned luminescent or optical polarization properties fabricated by wet process

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Maenozono 1000-F, Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory F-term (reference) 5F052 DA04 DA06 DA10 DA10 DB10 EA11 FA13 GB02 JA10

Claims (17)

[Claims] 1. A multicolor or monochromatic device having patterned optical polarization properties of semiconductor nanoparticles, consisting of high-density nanoparticle spots of arbitrary arrangement, shape, and size grown on a solid substrate. 2. The method of manufacturing a multi-color or mono-color device according to claim 1, comprising using a plurality of cells comprising blocks of cell walls sealed from below by said solid substrate;
Suspension droplets containing one type of nanoparticles or a mixture of different types of nanoparticles are dropped into the cell and diffused into a thin film; from evaporating the solvent from the film in an inert atmosphere or atmosphere. Consisting of a multicolored nanoparticle array that begins to grow from the center of the cell and progresses toward the periphery of the cell, with the final dry array having the desired shape, average thickness, and luminescence. Or how to make a monochromatic device. 3. The production method according to claim 2, wherein layers of various nanoparticles dissolved in various solvents are sequentially laminated to form a dry multilayer arrangement emitting emitted light or white light of a plurality of wavelengths. 4. A multicolor or monochromatic device in a patterned luminescent array of semiconductor nanoparticles consisting of hollow nanoparticle spots (rings) of any arrangement, shape, and size grown on a solid substrate. 5. A method for producing a multi-color or mono-color device according to claim 4, wherein a suspension containing one type of nanoparticles or a mixture of nanoparticles is prepared; Forming a collection of droplets; evaporating the solvent of the suspension from the droplets in an inert atmosphere or atmosphere, wherein the nanoparticle rings begin to grow from the periphery of the droplets and toward the interior of the droplets To produce a multicolor or monochromatic device, characterized in that the final dry array is a ring with an average width that depends on the nanoparticle volume fraction and the luminescence wavelength depends on the type of particle Method. 6. The method according to claim 5, wherein layers of various nanoparticles dissolved in various solvents are sequentially laminated to form a dry multilayer arrangement emitting a plurality of wavelengths of emitted light or white emitted light. 7. The method according to claim 5, comprising pre-patterning a substrate having hydrophilic points separated from each other by hydrophobic spaces or hydrophobic points separated from each other by hydrophilic spaces. Method. 8. The device according to claim 1, wherein the semiconductor nanoparticles comprise a single crystal of a size of a few nanometers, the surface of which is finally capped for passivation. 9. The method according to claim 1, wherein the semiconductor nanoparticles are a compound semiconductor,
5. A method according to claim 1 or 4, comprising a II-VI or III-V compound or other semiconductor nanoparticles having semiconductor and luminescent properties such as semiconductors of the group, titanium dioxide, fullerenes. The described device. 10. The solid substrate comprises a substrate supporting an array of nanoparticles, the substrate being flat to be resistant to the solvent in which the nanoparticles are suspended and to allow movement of the nanoparticles. 5. The device according to claim 1 or 4, having suitable optical properties that complement the luminescence of the nanoparticles. 11. The manufacturing method according to claim 5, wherein a wave-like pattern is formed on the periphery of the ring by performing array growth in unstable flow characteristics. 12. The production method according to claim 11, wherein the formed nanoparticle array has a polarization characteristic in addition to a light emission characteristic. 13. The method according to claim 5, wherein the luminescence intensity from the nanoparticle ring increases with time. 14. A solid substrate coated with a metal film,
3. The method of claim 2, wherein the luminescence intensity is enhanced by a mirror effect.
12. The production method according to any one of 5 and 11. 15. The manufacturing method according to claim 2, wherein the nanoparticle spot of the device according to claim 1 or 4 is sealed to preserve the luminescence of the nanoparticle. 16. A method for predicting and controlling the influence of experimental parameters (meniscus shape, evaporation rate, particle volume fraction) on the growth dynamics of high-density nanoparticle spots produced by the method of claim 2. Calculation method. 17. A calculation for predicting and controlling the influence of experimental parameters (meniscus shape, evaporation rate, particle volume fraction) on the growth kinetics of a nanoparticle ring produced by the method of claim 5. Method.