KR20170024450A - Crystalline bismuth nanoparticle arrays, and preparing method thereof using magnetically assisted growth of Bi nanoparticles - Google Patents

Abstract

The present invention relates to crystalline bismuth (Bi) nanoparticle arrays which are prepared by co-sputtering using bismuth (Bi) and cobalt (Co) as a target material, and to a preparing method thereof, comprising the following steps of: locating a silicon (Si) substrate in a vacuum chamber; and forming a deposited film by co-sputtering using the Bi and Co as the target material on the silicon substrate. According to the present invention, crystalline Bi nanoparticle arrays of which a particle size, density, and morphology can be adjusted by using a magnetically assisted growth of Bi nanoparticles (MAGBIN) are prepared. According to the present invention, a size and morphology of the Bi nanoparticles can be adjusted by co-sputtering using the Bi and Co as the target material, and by adjusting the relative power ratio of the two target materials, the substrate temperature, and a deposition time. The MAGBIN of the present invention enables to easily synthesize the crystalline Bi nanoparticle arrays. Also, since some chemical substances, complex processes, lithography, or the like are not required, the crystalline Bi nanoparticle arrays can be industrially used.

Description

[0001] Crystalline bismuth nanoparticle arrays and methods of preparing them using magnetically assisted growth of Bi nanoparticles [0002]

The present invention relates to a crystalline bismuth (Bi) nanoparticle array and a method of manufacturing the same. More particularly, the present invention relates to a crystalline bismuth (Bi) nanoparticle array capable of controlling particle size, density, and morphology using Bi- ) Nanoparticle arrays and a method of manufacturing the same.

Bismuth (Bi) is a semimetallic material in an anisotropic Fermisurface and a bulk state with a low overlap (38 meV) between the conduction band and the balance band. In addition, it is possible to achieve unique characteristics such as low carrier effective mass (0.001 m ₀ ), low carrier concentration (3 x 10 ¹⁷ cm ^-3 ), long carrier mean free movement distance (1.35 μm) Because of these, they have attracted much attention as physical materials.

Bi is also a material having thermoelectric properties, and such thermoelectric performance is known to be significantly improved as material size decreases.

So far, there have been a lot of studies on the one-dimensional nanostructures of Bi and 2-D thin films such as nanowires and nano-rods. However, in comparison to these one-dimensional or two-dimensional nanostructures, studies on Bi nanoparticles have not received much attention for two reasons: (i) the production of uniform, well-developed Bi nanoparticles Difficulty, and (ii) breakage (separation) between nanoparticles in the nanoparticle array.

Conventional methods for preparing Bi nanoparticles are mostly chemical methods in solution, in which nanoparticles are produced in the course of the reduction of metal salts or in the pyrolysis of organometallic precursors in the presence of suitable surfactants.

However, these methods require the use of toxic, difficult to handle components and require complicated processes.

Deposition of a Bi thin film on a suitable substrate using a post-heating process is another way to obtain Bi nanoparticles. Although this method is simple and the nanoparticle size is easy to control, there is a problem in that it requires a step of heating to a temperature higher than the melting point of Bi, and it is difficult to obtain a large particle size (> 100 nm).

Another method of producing Bi nanoparticles is electrochemical deposition. When a voltage pulse is applied between well-designed electrodes, the Bi nanoparticles are formed in a solution containing Bi nitrate, tartaric acid, potassium nitrate, glycerol, and nitric acid. However, there is a problem that the shape and size of the Bi nanoparticles obtained by this method are not uniform.

By heating Bi granules in oil under heating, or by adding Bi ₂ O ₃ Other methods have been proposed, such as production by oxidation synthesis of Bi particles in glass, but these methods also have limitations and problems in commercialization.

 E.A. Olson, M.Y. Efremov, M. Zhang, Z. Zhang, L.H. Allenb, J. Appl. Phys. 97 (2005) 034304.  C.N. Tharamani, H.C. Thejaswini, S. Sampath, Bull. Mater. Sci. 31 (2008) 207-212.

Therefore, in the present invention, various problems of the conventional methods (difficulty in using toxic chemicals, complexity of the process, difficulty in producing particles having a large particle size, difficulty in obtaining uniform particles, etc.) And to develop a method for the preparation of Bi nanoparticles capable of controlling particle size and shape by a relatively simple method.

Accordingly, an object of the present invention is to provide a method of manufacturing a Bi nanoparticle array using a self-assisted growth method (MAGBIN) of Bi nanoparticles by a simple method that does not require any chemical substance, complicated process or lithography.

Another object of the present invention is to provide a Bi nanoparticle array produced by the above simple method.

The crystalline bismuth (Bi) nanoparticle array according to the present invention is characterized in that it is manufactured by co-sputtering using bismuth (Bi) and cobalt (Co) as target materials.

According to the present invention, it is preferable that the crystalline bismuth nano-particle array uses a silicon (Si) substrate having an oxide layer formed on its surface.

The target material bismuth (Bi) / cobalt (Co) may be co-deposited using a power ratio range of 50/200 W to 10/400 W.

As the power ratio of Bi to Co increases, the size of the crystalline bismuth (Bi) nanoparticles increases.

The silicon substrate may be heated to a temperature in the range of 200 to 300 ° C.

As the temperature of the silicon substrate is increased, the size of the crystalline bismuth (Bi) nanoparticles may be increased.

The co-deposition may be performed in the range of 10 seconds to 400 seconds.

According to one embodiment of the present invention, when the power ratio applied to the target material and the substrate temperature are constant, the size of the crystalline bismuth (Bi) nanoparticles increases as the growth time increases, There is a feature that is possible.

In addition, when the power ratio and the substrate temperature applied to the target material are constant, the crystal structure may have a hexagonal crystal structure when the growth time is 3 minutes or less, and may have an elliptical structure when the growth time exceeds 3 minutes.

The crystalline bismuth (Bi) nanoparticles are characterized in that their particle size can be adjusted to have a range of 10 to 800 nm.

The method for producing a crystalline bismuth (Bi) nanoparticle array according to the present invention includes the steps of positioning a silicon (Si) substrate in a vacuum chamber, and simultaneously depositing Bi and Co on the silicon substrate as a target material, And a step of forming a MAGBIN method using the MAGBIN method.

According to one embodiment of the present invention, it is preferable that the substrate is heated and stabilized at about 200 to 300 ° C. so as to be relatively close to the melting point of Bi (271.5 ° C.).

The Bi target preferably uses radio frequency (RF) power in the range of 10 to 50 W.

It is preferable that the Co target uses direct current (DC) power in the range of 200 to 400W.

It is preferable that the target material bismuth (Bi) / cobalt (Co) is co-deposited using a power ratio range of 50/200 W to 10/400 W.

In the present invention, a crystalline Bi nanoparticle array capable of controlling particle size, density, and morphology using a self-assisted growth method (MAGBIN) of Bi nanoparticles was prepared.

In the present invention, the size and morphology of Bi nanoparticles can be controlled by co-sputtering Bi and Co as target materials, and adjusting the relative power ratio of the two target materials, the substrate temperature, and the deposition time .

The MAGBIN of the present invention can be used industrially because it can easily synthesize a crystalline Bi nanoparticle array and does not require any chemicals, complicated processes or lithography.

FIG. 1 is a graph showing the relationship between the nanoparticles (a, b) prepared by simultaneously applying a power combination of Bi / Co = 50 / 300W to a silicon substrate at 200 ° C and nanoparticles (c) and a Bi single target of 50 W, and the thin film (d) deposited on the substrate at 200 ° C,
Fig. 2 is a SEM photograph of Bi nanoparticles prepared by simultaneous vapor deposition of Bi / Co powders on a silicon substrate at 200 ° C. (A) Bi / Co = 50/200 W, 50/300 W, (c) Bi / Co = 50/400 W, (d) Bi / Co = 30/300 W, the scale bar is 300 nm,
3 shows the average diameter and the average density of Bi nanoparticles according to the relative power ratio applied to Bi and Co target materials. The diameter and the density are measured and calculated from the SEM photograph of FIG. 2,
FIG. 4 is a cross-sectional TEM photograph ((a) to (c)) of Bi nanoparticles prepared by simultaneous deposition of a silicon substrate with a Bi / Co = 50 / Represents the EDX component mapping result in the selected region,
Fig. 5 shows the XRD patterns of the three nanoparticle films formed on the silicon substrate and the Bi film. Nanoparticle samples were the same as those used in the SEM measurement of Fig. 2, The same sample was used, and the scan speed was 4 ° / min.
(B) 30 s, (c) 75 s. Co-deposition was performed at a temperature of 200 ° C on a substrate of Bi / Co = 50 / 300W power combination,
7 is a schematic diagram showing the growth mechanism of Bi nanoparticles by the MAGBIN method according to the present invention,
(A) Bi / Co = 10/400 W, T _sub = 200 ° C, and (b) Bi / Co = 10/400 W. FIG. 8 is a SEM photograph of Bi nanoparticles prepared by varying the power combination or substrate temperature. and _{30/300 W, T sub = 200 ℃} , (c) Bi / Co = 50/300 W, T sub = 200 ℃, (d) Bi / Co = 50/300 W, T sub = 250 ℃,
9 (a) and 9 (b) show SEM photographs and particle size distributions over time at the same power combination and substrate temperature (Bi / Co = 50/300 W, (A, c, and e are growth time of 3 minutes, b, d, and f are growth time of 6 minutes), and 9 (c) and
Fig. 10 shows the results obtained when (a) 75 seconds, (b) 3 minutes, and (c) 6 minutes respectively at the same power combination (Bi / Co = 50/300 W) and substrate temperature AFM image of Bi nanoparticles,
11 is a schematic diagram showing a growth mechanism of Bi nanoparticles in which a morphology is transferred from a well-developed facet structure to an elliptical structure,
Fig. 12 shows magnetic coupling characteristics of Bi nanoparticles synthesized at a substrate temperature of 200 deg. C and a power combination condition of Bi / Co = 30/300 W. (a) shows magnetic moments at 300 K and 4.2 K, and (b) shows the temperature dependence of magnetic moments under field cooling (FC) and zero-field cooling (ZFC).

Hereinafter, the present invention will be described in more detail.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a,""an," and "the" include singular forms unless the context clearly dictates otherwise. Also, " comprise "and / or" comprising "when used herein should be interpreted as specifying the presence of stated shapes, numbers, steps, operations, elements, elements, and / And does not preclude the presence or addition of one or more other features, integers, operations, elements, elements, and / or groups.

The present invention relates to a method for producing crystalline bismuth (Bi) nano-particles by using a crystalline bismuth (Bi) nanoparticle array and magnetically assisted growth of Bi nanoparticles (hereinafter referred to as "MAGBINs" ≪ / RTI > The present invention relates to a novel synthesis method for producing particle arrays.

In the present invention, a completely different method of synthesizing crystalline Bi nanoparticles, called self-assisted growth of Bi nanoparticles, abbreviated as "MAGBINs" The MAGBIN method according to the present invention uses a co-evaporation method using Bi and cobalt (Co) as a target material. This is because the magnetic Co is used for the synthesis of Bi nanoparticles to form a Bi nanoparticle array Can be obtained.

The crystalline bismuth (Bi) nanoparticle array according to the present invention is characterized in that it is manufactured by co-sputtering using bismuth (Bi) and cobalt (Co) as a target material.

In the present invention, bar hayeotneun using Co as the target substance for simultaneous deposition and Bi, which large magnetic moment (1.75Bohr magneton / atom), a high Curie temperature (1388 K), and giant magneto-crystalline anisotropy (7 x 10 ⁶ erg cm ^-3 ), it was selected as an auxiliary magnetic material.

In the present invention, when using MAGBIN, a monodispersed crystalline bismuth nanoparticle array capable of controlling the size to some extent could be produced.

According to the present invention, it is preferable that the crystalline bismuth nano-particle array uses a silicon (Si) substrate 100 having a thin oxide layer formed on its surface.

Since the target materials Bi and Co have different vapor deposition rates, the growth rate can be appropriately adjusted through the combination of the application power. In the present invention, the Bi / Co content is in the range of 50/200 W to 10/400 It is preferable to perform simultaneous vapor deposition using a power ratio range of W. And has a crystal structure according to the present invention and can be adjusted to an appropriate size at the power combination ratio.

Also, in the target material to be co-deposited, the size of the crystalline bismuth (Bi) nanoparticles increases as the power ratio of Bi to Co increases.

In the present invention, it is preferable that the silicon substrate is heated to a temperature in the range of 200 to 300 ° C. This is to ensure that the Bi nanoparticles according to the present invention have a unique crystal structure. When the substrate is not heated, a crystal such as the hexagonal structure according to the present invention is not formed.

Also, as the temperature of the silicon substrate is increased, the size of the crystalline bismuth (Bi) nanoparticles may be increased.

The co-deposition may be performed within a range of 10 seconds to 400 seconds, and may be appropriately adjusted depending on the size of the Bi nanoparticles to be finally produced.

According to an embodiment of the present invention, when the power combination ratio of the target material and the substrate temperature are constant, the size of the crystalline bismuth (Bi) nanoparticles increases as the growth time increases, There are features.

In addition, when the power combination ratio of the target material and the substrate temperature are constant, the crystal structure may have a hexagonal crystal structure when the growth time is 3 minutes or less, and may have an elliptical structure when the growth time exceeds 3 minutes.

The crystalline bismuth (Bi) nanoparticles are characterized in that their particle size can be adjusted to have a range of 10 to 800 nm.

The method for producing a crystalline bismuth (Bi) nanoparticle array according to the present invention includes the steps of positioning a silicon (Si) substrate in a vacuum chamber, and simultaneously depositing Bi and Co on the silicon substrate as a target material, The method comprising the steps of:

According to one embodiment of the present invention, it is preferable that the substrate is heated and stabilized at about 200 to 300 ° C. so as to be relatively close to the melting point of Bi (271.5 ° C.). The heating time of the substrate is preferably maintained at the above temperature for 1 hour or more for sufficient stabilization.

The thickness of the deposited film deposited on the silicon substrate is preferably controlled according to the target nanoparticle size.

Since the deposition rates of Bi and Co which are target materials used in the simultaneous deposition of the present invention are different, it is necessary to control the growth rate through the combination of the application power. In other words, the deposition rate of Bi in the normal condition is as large as ~ 50 nm / min at 50 W, while the deposition rate of Co is very small at ~ 1.2 nm / min at 300 W. Therefore, It is important.

In the present invention, the Bi target preferably uses radio frequency (RF) power in the range of 10 to 50 W.

Also, the Co target preferably uses direct current (DC) power in the range of 200 to 400W.

It is preferable that the target material bismuth (Bi) / cobalt (Co) is co-deposited using a power ratio range of 50/200 W to 10/400 W. The size, density and shape of the final Bi nanoparticles can be controlled by controlling the relative power of the target material, bismuth (Bi) / cobalt (Co).

Hereinafter, preferred embodiments of the present invention will be described in detail. The following examples are intended to illustrate the present invention, but the scope of the present invention should not be construed as being limited by these examples. In the following examples, specific compounds are exemplified. However, it is apparent to those skilled in the art that equivalents of these compounds can be used in similar amounts.

Example

In order to fabricate a crystalline Bi nanoparticle array based on the MAGBIN method, co-deposition was performed using Bi and a Co target, where Bi sputtering and Co sputtering were simultaneously carried out. A silicon (Si) (100) wafer having a thin oxide layer on its surface was used as a substrate. Radio frequency (RF) and direct current (DC) power were applied to the Bi and Co targets, respectively. The RF power was set to a range of 10 to 50 W, and the DC power was set to a range of 200 to 400 W. Prior to sputtering, the chamber was lowered to 10 ^-7 Torr pressure and the process pressure was adjusted using an argon flow. Under the commercial conditions, the deposition rate of Bi was as large as ~ 50 nm / min at 50W, while the deposition rate of Co was very small at ~ 1.2 nm / min at 300W. Due to the difficulty of plasma ignition from the Co target, the process pressure was set at a relatively high 20 mTorr while the argon flow was maintained at 12 SCCM.

The substrate was heated and stabilized at 200 ° C so that it was relatively close to the melting point of Bi (271.5 ° C). The co-deposition time was adjusted from 75 to 360 s depending on the relative power applied to the target. The thickness of the deposited film was adjusted to approximately 50 nm in almost the same conditions.

Coated films were simultaneously prepared for a reduced time (10 s, 30 s), and nanoparticle growth mode was experimented. After deposition, the film was cooled to room temperature in a vacuum chamber.

Comparative Example  One

Bi nanoparticles were prepared in the same manner as in Example 1 except that the substrate was heated.

Comparative Example  2

Bi nanoparticles were prepared in the same manner as in Example 1 except that the Bi nanoparticles were deposited on a substrate at 200 ° C using a Bi single target of 50W.

Experimental Example

1) The surface morphology of the film and the Bi nanoparticle array was analyzed by field emission scanning electron microscopy (FE-SEM, Hitachi S-4800).

2) Cross-sectional structure analysis and component mapping were performed using a transmission electron microscope (TEM, Tecnai20) equipped with an energy dispersive x-ray spectrometer (EDX).

3) The crystal structure of the film was x-ray diffraction (XRD, Rigaku Model D / MAX-2500V).

Next, Fig. 1 is a schematic view showing a case where nano particles (a, b) produced by co-deposition of a silicon substrate with a Bi / Co = 50 / Fig. 1 (a) shows an SEM photograph of a thin film (d) deposited on a substrate at 200 ° C using a particle (c) and a Bi single target of 50 W, wherein nanoparticles having small sizes are almost monodispersed .

Next, Fig. 1 (b) is an enlarged photograph of a central portion (rectangular portion) of Fig. 1 (a), in which nanoparticles exhibit a bimodal distribution in size and smaller nanoparticles It was observed to be located between the nanoparticles. The larger nanoparticles were measured to have a particle size distribution of 109-179 nm. Most of the nanoparticles were observed to have a hexagonal or truncated hexagonal form, except for some nanoparticles with a central peanut shape.

The films co-deposited at the same power conditions (Bi / Co = 50/300 W) without heating of the substrate (Comparative Example 1) exhibited different surface morphologies (Fig. 1 (c)). It can be seen that irregular protrusions are irregularly distributed over the substrate.

The surface morphology (Fig. 1 (d)) of the Bi film grown at 200 ° C using Bi single target (Comparative Example 2) is completely different from the monodispersed structure shown in Fig. 1 (a) Other results are shown.

These results suggest that well - developed hexagonal nanoparticles are formed only when Co and Bi are co - deposited under the condition of applying a temperature to the substrate.

SEM-EDX and TEM component mapping were used to analyze the constituents of the nanoparticles. Based on the fact that the sensitivity of EDX for detecting Co is ~ 1 wt% (~ 0.5 at%), it was confirmed that the nanoparticles consisted of Bi only in the tolerance range of ~ 0.5 at%. The well developed hexa of Bi nanoparticles The high-end morphology indicates that the nanoparticles have a rhombohedral structure of Bi crystals. The size and distribution of the Bi nanoparticles were found to vary according to the manufacturing conditions as shown in FIG.

Next, FIG. 2 is a SEM image of Bi nanoparticles prepared by co-evaporation of Bi / Co powders on a silicon substrate at 200 ° C. (A) Bi / Co = 50/200 W, = 50/300 W, (c) Bi / Co = 50/400 W, (d) Bi / Co = 30/300 W and the scale bar is 300 nm.

Here, the main process variables are the relative power applied to the Bi and Co targets and other process conditions such as the substrate temperature, and the process pressure was kept constant. From the results shown in FIG. 2, the size of the Bi nanoparticles was found to decrease as the power applied to Co was increased with respect to the power of Bi. Therefore, the density of nanoparticles, defined as the number of nanoparticles per unit area, increased as the relative power of Co to Bi increased.

This tendency in the size and density of the nanoparticles relative to the relative power applied to Bi and Co is more clearly shown in Fig. FIG. 3 shows average diameters and average densities of Bi nanoparticles according to the relative powers of the applied Bi and Co target materials, and the diameter and density are measured and calculated from the SEM photograph of FIG.

FIG. 3 shows the measurement and calculation of the size and density of Bi nanoparticles based on a larger group of two groups of different sizes. Referring to FIG. 3, when the output is Bi / Co = 30/300 W, Nanoparticles of diameter (92 nm) and largest density (70 μm ^-2 ) were obtained.

Cross-sectional TEM measurements were performed to confirm the vertical structure, composition, and crystal quality of the nanoparticles, and the results are shown in FIG. 4 is a cross-sectional TEM photograph ((a) to (c)) of a Bi nanoparticle produced by simultaneously depositing a Bi / Co = 50/300 W power combination on a silicon substrate at 200 ° C., g) shows the result of EDX component mapping in the selected region.

Samples were carefully prepared using a focused ion beam so that the vertical structure of nanoparticles containing a large number of weak Bi atoms would not break. 4 (a) and 4 (b) show cross-sectional TEM images of samples prepared at Bi / Co = 50/300 W in wide and narrow regions.

Small particles are located between the larger particles, and these results are in good agreement with the SEM observations of FIGS. 1 and 2 above. However, unlike SEM images, where two different sized nanoparticle groups seem to be isolated, these TEM images show that they are weakly connected. This weakly linked nanoparticle structure can provide a solution to the second issue related to nanoparticles that inhibit application to thermoelectric materials, such as disconnection of nanoparticles. The coupled structure of the nanoparticles is capable of conducting current through the nanoparticle array, thereby increasing the required electrical conductivity in the thermoelectric field. The aspect ratio of the height to the diameter of the nanoparticles is generally between 0.6 and 1.

4 (c) is an enlarged TEM image near the interface between the substrate and the nanoparticles. An oxide layer with a thickness of 4-5 nm was observed on the surface of the silicon substrate. More surprisingly, the particles have a high crystallinity without any defects.

The electron diffraction pattern in the selected region showed a well-developed rhombohedral structure of Bi crystals. (See Fig. 4 (c)). From the EDX component mapping results shown in Figs. 4 (d) to 4 (g), it was confirmed that the components of the nanoparticles were Bi and Co. In almost all combinations (Bi / Co = 50/200 ~ 30/300) tested in the present invention, only Bi nanoparticles were produced, and no significant Co content was observed. This seems to be immiscible because of the absence of Bi and Co at the substrate temperature of 200 ° C, and Co atoms are seen to interact magnetically to form agglomerates, which are back-sputtered by a strong Bi flux (back-sputtering).

The crystal structure of the nanoparticles was measured by XRD and the results are shown in Fig. Fig. 5 shows the XRD patterns of the three nanoparticle films formed on the silicon substrate and the Bi film. Nanoparticle samples were the same as those used in the SEM measurement of Fig. 2, The same sample was used and the scan speed was 4 [deg.] / Min.

In the Bi film, two peaks are observed at around 55 ° and 76 °, corresponding to the (024) and (125) planes of rhombohedral Bi crystals. As the relative power applied to the Co increases until the power applied to the Co becomes 10 times as much as that of the Bi, the intensity of the characteristic peak of Bi is decreased significantly.

From these results, it can be seen that the nanoparticles are Bi having a well-developed crystal structure of Bi crystals. The slight shift of the characteristic peaks toward the lower angle appears to be due to the increase in the surface-to-volume ratio in Bi nanoparticles.

As shown in FIG. 3, the average diameter of the Bi nanoparticles decreases as the relative power applied to the Co increases, and the decrease in the particle size leads to an increase in the atomic fraction near the surface. Since the interplanar spacing is larger near the surface, the atom fraction of the increased surface can be seen to increase the average surface spacing. Another possibility is that although Co is not measured in the EDX results, Co is an influential factor. If a very small amount of Co is introduced into Bi crystals, the Co atoms will separate the crystal faces of Bi, which will increase the spacing.

Significant reduction in the characteristic peak intensity at the top XRD pattern (Bi / Co = 30/300 W) can be attributed to the initial Co layer and very small Bi particles. When the relative power applied to Co is large, the atomic density of Co reaching the substrate is increased, and the absorbed Co atoms in the initial stage prevent the Bi atoms from moving to a stable position. The extremely small nanoparticles produced under these power conditions, as described above, increase the surface atomic fraction and degrade the overall crystal quality. Thus, the overall sharp XRD characteristic peaks reflect the high crystallinity of Bi nanoparticles, which is in good agreement with the SEM and TEM results.

To investigate the growth mechanism of Bi nanoparticles, we observed the initial stage of nanoparticle formation. Next, Fig. 6 shows a comparison of the growth times ((a) 10 s, (b) 30 s, (c) 75 s) under the same power combination (Bi / Co = 50/300 W) SEM photograph of the prepared sample is shown.

It can be seen that small nanoparticles of 20 to 30 nm in diameter were produced at a short co-deposition time (10 s) (Fig. 6 (a)). The size of the nanoparticles can be confirmed to be relatively uniform, but the morphology is somewhat irregular . Interestingly, SEM-EDX analysis confirmed that the major component of the nanoparticles is Co (FIG. 6 (a)).

As a result of EDX analysis in a larger region (1250 nm x 920 nm), the Bi content for Co was about 10 at% larger than the spot value smaller than Co in the gap between nanoparticles, This is supported by the inference that there are many distributions. The initial structure means that Co plays an important role in the formation of Bi nanoparticles based on MAGBIN.

In order to better understand the MAGBIN process, the growth mechanism of Bi nanoparticles is shown in FIG. The Co atoms are absorbed on the substrate to form a Co agglomerate to reduce the total magnetic energy, and the Co atoms are not mixed with the Co atom, and the strong atomic Bi atoms are located in the remaining region between the Co aggregates (see FIG. 7 Since the strength of the Co flux is much weaker than that of the Bi flux (Co deposition rate ratio to Bi ~ 0.024), the initially formed Co assemblages may collide with the in- There is a high possibility of back-sputtering. (The second picture in Fig. 7), the damaged portions (white portions) between the larger nanoparticles near the substrate surface are observed in Figs. 4 (a) and (b).

When the growth time is maintained at 30s, two groups of nanoparticles having different particle sizes are formed (see Fig. 6 (b)). One group consists of large nanoparticles with a diameter> 50 nm and the other is a group of small nanoparticles with a diameter of 15 nm or less.

The distance between the larger nanoparticles was wider than that of the nanoparticles grown for 10 s. This can be attributed to Ostwald ripening, which is activated at elevated temperatures and accelerated at reduced diameters of the nanoparticles. Through the Ostwald-Leifing process, Bi atoms diffuse from small nanoparticles toward large nanoparticles, reducing the total surface energy and creating two groups of nanoparticles with separate sizes. At the same time, the surface morphology of the larger nanoparticles represents a more advanced hexagonal shape through continued atomic rearrangement to further reduce surface energy. (Third figure in Fig. 7)

Finally, both groups of nanoparticles grow as the growth time increases (Fig. 6 (c)). This is accomplished by the Bi atoms introduced by sputtering and the Bi atoms surface-diffused by Ostwald leeping (the last stage of FIG. 7). When large nano particles were analyzed by SEM-EDX after completion of MAGBIN for 75 s, Co content was not observed as in Fig. 6 (c), and only Bi was measured. Also, the space between the large nanoparticles did not detect both of these components, which appears to be due to the fact that only a small amount remained in this region. From these results, it can be concluded that MAGBIN is a method for rapidly and simultaneously growing crystalline Bi nanoparticles, which is a process based on physical processes such as magnetic interaction, atomic separation, and Ostwald leaching .

Example  2

A silicon (Si) (100) substrate having an oxide thin film formed on its surface was mounted on a heating stage of a vacuum chamber. The temperature of the stage was adjusted to 200 and 250 DEG C, which were close to the melting point of Bi, and then the stage was maintained at the set temperature for 1 hour or more to stabilize the substrate temperature. The vacuum chamber was then lowered to a pressure of 9 x 10 ^-7 Torr or less.

Simultaneous deposition was performed by applying RF and DC power to Bi and Co targets, respectively. The power combination was set at 10, 30, and 50 W RF power, and 300 and 400 W DC power. During the deposition, the argon fluid velocity and process pressure were adjusted to 12 SCCM and 20 mTorr, respectively. The deposition time was adjusted to determine the size and morphology of the nanoparticles grown in a fixed power combining condition (RF 50 W to Bi and DC 300 W to Co). The total thickness of the deposited films was about 50 nm to 500 nm.

(A) Bi / Co = 10/400 W, T _sub = 200 ° C, and (b) Bi / Co = 10/400 W. FIG. 8 is a SEM photograph of Bi nanoparticles prepared by varying the power combination or substrate temperature. 30/300 is _{W, T sub = 200 ℃,} (c) Bi / Co = 50/300 W, T sub = 200 ℃, (d) Bi / Co = 50/300 W, T sub = 250 ℃.

8 (a) to 8 (c), it can be seen that as the RF power ratio of Bi to Co increases, larger nanoparticles are produced. That is, the average diameter of the nanoparticles of Fig. 8 (a) with Bi / Co = 10/400 W was 64 nm and the average diameter of the nanoparticles of Fig. 9 (c) with Bi / Co = 50/300 W was 146 nm.

The faceted structure of nanoparticles was also observed more clearly as the relative power of Bi increased.

8 (d)), the size ( d _avg ) of the Bi nanoparticles was increased to 297 nm, and the crystal facets thereof were the same power combination (Bi / Co = 50 / 300W) at 200 ° C. This is seen as an increase in the diffusion of Bi atoms and a promoting action of Ostwald ripening at higher temperatures.

Next, FIG. 9 confirms the structure of Bi nanoparticles grown while increasing the MAGBIN time. At the same power combination and substrate temperature, SEM images and particle size distributions over time were shown. 9 (a) and 9 (b) are plane SEM images, and 9 (c) and 9 (d) are 45 ° -tilted SEM images.

As compared with the Bi particles grown for 75 seconds in FIG. 8 (c), it was obvious that the nanoparticles grew larger as the growth time increased. The statistical distribution of the measured diameters is shown in Figures 8 (e) and 8 (f) below, wherein 40 to 100 or more nanoparticles were measured to create a distribution. At the growth times of 3 and 6 minutes, the particle size distribution showed a similar tendency showing Gaussian distributions centering around 300 nm and 550 nm, respectively. The average diameter and spatial density of the nanoparticles grown for 3 minutes were 324 nm and 5.81 μm ^-2 , while the Bi nanoparticles grown for 6 min were 542 nm and 2.34 μm ^-2 , respectively. As the time of MAGBIN increased, Bi It was confirmed that the nanoparticles grow larger.

In order to investigate the time dependence of the size and morphology of the nanoparticles, the AFM was measured with different growth times. The results are shown in FIG. Fig. 10 shows the results obtained when the growth times at the same power combination (Bi / Co = 50/300 W) and substrate temperature (200 占 폚) were changed to (a) 75 seconds, AFM image of Bi nanoparticles.

As the growth time increased, the size of the nanoparticles increased and the height and valleys of the nanoparticles became deeper. Particularly, the tip-to-valley height of the nanoparticles grown for 6 minutes reached up to about 800 nm, considering that the nanoparticles have an elliptical morphology considering that the average diameter of FIG. 9 (d) is 542 nm Can be explained.

11 is a schematic diagram showing a growth mechanism of Bi nanoparticles in which a morphology is transferred from a well-developed facet structure to an elliptical structure.

As a result, the Bi nanoparticles have a well-developed hexagonal form at a growth time of 1 to 2 minutes. Because Bi is one of the strongest semi-magnetic materials with a magnetic susceptibility (x) of -1.7 x 10 ^-4 , the Bi is left as a phase-separated domain by pushing off the Co atoms exhibiting strong ferromagnetism. Due to the overwhelming intensity of the Bi atom flux, Co clusters are back-sputtered and removed from the substrate. At the same time, Bi atoms continue to flow into the substrate and nanoparticles. These Bi-adsorbing atoms (adatoms) are rearranged in a uniform manner to reduce the total surface energy through solid-state diffusion due to the high substrate temperature, resulting in a hexagonal surface structure.

In addition, at high substrate temperatures, these hexagonal-faceted structures will have a growth time of more than 3 minutes, and surface atoms will lose their ability to determine total nanoparticle energy due to a reduction in the fraction of surface atoms to bulk atoms . Instead, thermal energy provided from the substrate for a long time disturbs the constant rearrangement of surface atoms. As a result, the morphology changes from the surface structure to the elliptical structure.

Also, deep valleys between large Bi nanoparticles can prevent the Co atoms that are repelled by back-sputtering from escaping. Rather, the Co atoms can be re-deposited on the surface of the Bi nanoparticles to cause surface contamination.

Next, Fig. 12 shows magnetic coupling characteristics of Bi nanoparticles synthesized at a substrate temperature of 200 DEG C under conditions of Bi / Co = 30/300 W power combination. (a) shows magnetic moments at 300 K and 4.2 K, and (b) shows the temperature dependence of magnetic moments under field cooling (FC) and zero-field cooling (ZFC). For FC, a magnetic field of 1 kOe was applied.

The sample has a high relative power to Co and nanoparticle arrays are well formed and selected. FIG. 12 (a) shows magnetic moments ( M ) and magnetic field ( H ) curves at 300 K and 4.2 K. Referring to FIG. 12, it can be seen that only the semi- Co is not present but can be expressed only by a semi-magnetic Bi. Co is a ferromagnetic substance with a bulk magnetization of 166 emu / g, which is known to be stronger in very small nanoparticles. Very weak magnetic moment ^{(~ 2 x 0 -4 emu /} g at -2 kOe) means that the nanoparticles consist simply only Bi, which is in good agreement with the result of EDX.

The absence of the Co component is well supported by the field-cooled (FC) and zero-field-cooled (ZFC) magnetic moment curves of FIG. 12 (b). Here, field cooling was performed under a magnetic field of 1 kOe. The two curves showed almost flat results at very low levels (-1.05 x 10 ^-4 emu / g), appearing superimposed over almost all temperature ranges, which do not contain Co in the nanoparticles .

Claims (15)

(Bi) nanoparticle array characterized in that it is produced by co-sputtering using bismuth (Bi) and cobalt (Co) as a target material.
The method according to claim 1,
Wherein the crystalline bismuth nanoparticle array uses a silicon (Si) substrate having an oxide layer formed on its surface.
The method according to claim 1,
(Bi) / cobalt (Co), which is the target material, is co-deposited using a power ratio range of 50/200 W to 10/400 W. The crystalline bismuth (Bi)
The method of claim 3,
Wherein the size of the crystalline bismuth (Bi) nanoparticles increases as the power ratio of Bi to Co increases.
3. The method of claim 2,
Wherein the silicon substrate is heated at a temperature in the range of 200 to 300 占 폚.
6. The method of claim 5,
Wherein the crystalline bismuth (Bi) nanoparticle size increases as the temperature of the silicon substrate increases.
The method according to claim 1,
Wherein the co-deposition is performed in the range of 10 seconds to 400 seconds.
The method according to claim 1,
When the power combination ratio of the target material and the substrate temperature are constant,
Wherein the crystalline bismuth (Bi) nanoparticle size increases as the growth time increases and the crystal structure thereof can be controlled.
9. The method of claim 8,
When the growth time is 3 minutes or less, it has a hexagonal crystal structure,
(Bi) nanoparticle array characterized in that it has an elliptical structure when the growth time exceeds 3 minutes.
The method according to claim 1,
Wherein the crystalline bismuth (Bi) nanoparticles have a particle size in the range of 10 to 1000 nm.
Placing a silicon (Si) substrate in a vacuum chamber, and
(Bi) and Co as a target material on the silicon substrate to form an evaporated film. The method of manufacturing a crystalline bismuth (Bi) nanoparticle array using the MAGBIN method.
12. The method of claim 11,
Wherein the silicon substrate is heated at 200 to 300 占 폚 before use.
12. The method of claim 11,
Wherein the Bi target uses radio frequency (RF) power in the range of 10 to 50W.
12. The method of claim 11,
Wherein the Co target uses direct current (DC) power in the range of 200 to 400 W.
12. The method of claim 11,
Wherein the target material bismuth (Bi) / cobalt (Co) is co-deposited using a power ratio range of 50/200 W to 10/400 W.

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