A method for preparing a composite thin film of an oxide single crystal and metal nanoparticles

Abstract

This invention discloses a method for preparing a composite thin film of oxide single crystal and metal nanoparticles, comprising: alternately preparing oxide buffer layers on an oxide substrate using laser ablation; preparing an oxide epitaxial thin film on the oxide buffer layers; embedding metal nanoparticles on the oxide epitaxial thin film using a metal target; designating the oxide epitaxial film without embedded metal nanoparticles as film layer A, and the oxide epitaxial thin film with embedded metal nanoparticles as film layer B; alternately preparing film layers A and B using oxide targets and metal targets respectively, thereby obtaining a multilayer composite thin film of oxide single crystal and metal nanoparticles (A / B / A / B…A) on the oxide substrate. The dielectric and metal nanoparticle composite thin film prepared by this invention has a stable structure, is easy to control, has good experimental repeatability, is non-toxic, and has high operational safety.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and more specifically, this invention relates to a method for preparing a composite thin film of oxide single crystal and metal nanoparticles. Background Technology

[0002] Giant dielectric materials have a large dielectric constant (ε≥10). 3 ), such as Fe:BaTiO3, CaCu3Ti4O 12 (CCTO), (Nb+In):TiO2, etc., have been successfully applied to various capacitor structures, including multilayer ceramic capacitors (MLCC), internal barrier layer capacitors (IBLCs), and ferroelectric ceramic oxide-metal composites (CMCs). Among them, MLCC is composed of thin dielectric layers and internal electrode layers, and is widely used in various electronic products. However, MLCC has two disadvantages: (1) there are differences in physical properties such as sintering temperature, thermal diffusivity, and lattice constant between the dielectric layer and the metal layer, which can easily lead to interface cracking; (2) residual stress at the interface causes the performance of MLCC to degrade. As for IBLCs capacitors, such as CCTO, due to the presence of n-type grains and insulating grain boundaries inside the polycrystalline material, [2] This resulted in an anomalous giant dielectric constant. However, the microstructure (including grain size, grain distribution, degree of grain boundary oxidation, etc.) and the number of defects (such as oxygen vacancies) inside IBLC ceramics are difficult to control, leading to large variations in their dielectric constant and relatively high dielectric loss.

[0003] Another type of capacitor material structure, CMCs, fills a ferroelectric oxide matrix with metal particles, where the oxide acts as the insulating phase and the metal particles act as the conductive filler, resulting in a significant enhancement of the dielectric constant. Compared to MLCCs and IBLCs, CMCs have the following advantages: (1) The enhancement of the dielectric constant mainly depends on the metal particles rather than the oxide matrix, thus avoiding the temperature dependence of the dielectric constant of materials such as BaTiO3 (i.e., the ferroelectric to paraelectric transition at the Curie temperature); (2) IBLCs have relatively high dielectric loss, while CMCs can achieve lower dielectric loss by optimizing the material structure.

[0004] To obtain even smaller nanocapacitors, researchers embedded transition metal nanoparticles (NPs) into a ferroelectric oxide film matrix. Although the size of the transition metal particles reached the nanoscale, their distribution, size, and spacing were difficult to control, and the oxide film matrix still exhibited a polycrystalline state, resulting in a low dielectric constant (~10).2 Therefore, CMC capacitor materials (bulk and thin films) face the following challenges: (1) uneven distribution of metal particles, making it difficult to control their size and shape; (2) the presence of grains and grain boundaries in polycrystalline ferroelectric oxide matrices. The interaction between metal particles, grains, and grain boundaries is detrimental to the regulation of dielectric properties.

[0005] An ideal CMC structure consists of nanoscale transition metal particles uniformly distributed within a single-crystal ferroelectric oxide matrix, where the grain and grain boundary effects of the single-crystal ferroelectric oxide matrix are almost negligible, and the number, size, and distribution of the transition metal nanoparticles can be controlled. This makes it easier to control the giant dielectric properties of the oxide matrix by the metal nanoparticles, without being affected by the matrix itself. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] To achieve these objectives and other advantages according to the present invention, a method for preparing a composite thin film of oxide single crystal and metal nanoparticles is provided, comprising:

[0008] Oxide buffer layers were alternately prepared on an oxide substrate using laser ablation. Oxide epitaxial films were then prepared on the oxide buffer layers. Metal nanoparticles were embedded in the oxide epitaxial films using a metal target. The oxide epitaxial film without embedded metal nanoparticles was designated as film layer A, and the oxide epitaxial film with embedded metal nanoparticles was designated as film layer B. Film layers A and B were prepared alternately using oxide targets and metal targets, respectively, to obtain a multilayer composite film of oxide single crystal and metal nanoparticles (A / B / A / B…A) on the oxide substrate.

[0009] Preferably, the process specifically includes the following steps:

[0010] Step 1: Anneal the oxide substrate;

[0011] Step 2: Clean the oxide target and the metal target;

[0012] Step 3: First, use a KrF excimer laser to ablate the oxide target, and then epitaxially grow an oxide buffer layer on the oxide substrate;

[0013] Step 4: Use a laser beam to bombard the oxide target to achieve epitaxial growth of an oxide epitaxial film on the oxide buffer layer;

[0014] Step 5: Use a laser beam to ablate the metal target material to achieve controllable embedding of metal nanoparticles on the oxide epitaxial film. The oxide epitaxial film without embedded metal nanoparticles is denoted as film layer A, and the oxide epitaxial film with embedded metal nanoparticles is denoted as film layer B.

[0015] Step 6: Repeat steps 4-5, alternating between the growth of oxide epitaxial films and the embedding of metal nanoparticles, to obtain a multilayer oxide single crystal and metal nanoparticle composite film of A / B / A / B…A on an oxide substrate.

[0016] Preferably, in step one, the specific method for annealing the oxide substrate includes:

[0017] First, the oxide substrate is placed on the sample stage in the main cavity of the pulsed laser deposition system. The background vacuum of the vacuum cavity is less than 1 × 10⁻⁶. -7 Pa, thus beginning the high-temperature annealing of the substrate; the annealing process is as follows: the temperature is increased from room temperature to 600-900℃ at a rate of 2-10℃ / min, then oxygen is introduced into the vacuum chamber, and the pressure of the vacuum chamber is adjusted to 5-20Pa by the gas flow controller. The entire annealing process lasts for 20-40 minutes, and then the annealing is ended.

[0018] Preferably, in step two, the method for cleaning the oxide target and the metal target is to pre-ablate the oxide target and the metal target using a laser.

[0019] Preferably, in step three, the background vacuum degree before coating is 1×10⁻⁶. -7 Pa, the working vacuum degree during the coating process is 1×10⁻⁶. -6 Pa, the temperature of the oxide substrate is 500–700℃, the laser pulse frequency of KrF excimer laser bombardment and ablation of the oxide target is 1–10 Hz, and the laser energy density is 1–10 J / cm². 3 .

[0020] Preferably, in step four, the laser pulse frequency for bombarding and ablation of the oxide target with KrF excimer laser is 1–10 Hz, and the laser energy density is 1–10 J / cm². 3 .

[0021] Preferably, in step four, the heat annealing parameters are 5-20 Pa oxygen pressure for 5-20 min.

[0022] Preferably, in step four, the laser frequency of the KrF excimer laser ablation of the metal target is 1–10 Hz, and the laser energy density is 1–10 J / cm². 2The number of laser pulses ranges from 0 to 1000, meaning the number of metal quantum dots embedded is 0 to 1000.

[0023] Preferably, the oxide substrate is a single-crystal SrTiO3 conductive substrate, the oxide target is a single-crystal SrTiO3 ceramic target with a purity greater than 99.99 wt%, and the metal target is a Fe metal target with a purity greater than 99.99 wt%.

[0024] This invention offers at least the following advantages: It utilizes laser molecular beam epitaxy to obtain a composite thin film where transition metal nanoparticles and epitaxially grown single-crystal ferroelectric materials coexist. Since the single-crystal thin film itself possesses a large dielectric constant, and the single-crystal ferroelectric matrix almost entirely lacks grains and grain boundaries, the modulation of the ferroelectric dielectric properties by the transition metal nanoparticles is not affected by factors inherent to the matrix itself. Furthermore, by optimizing the growth process parameters, specifically the laser frequency (1–10 Hz) and laser energy density (1–10 J / cm²), the advantages are further enhanced. 2 The number, size, distribution, and spacing of transition metal nanoparticles can be effectively controlled by adjusting the laser pulse count (0-1000 pulses). After each oxide epitaxial film has grown, oxygen is introduced into the vacuum chamber to anneal it under oxygen partial pressure, thus reducing the generation of oxygen vacancies and improving surface quality. The dielectric-metal nanoparticle composite film prepared by this invention has a stable structure, is easy to control, exhibits good experimental repeatability, is non-toxic, and has high operational safety.

[0025] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the composite thin film structure of oxide single crystal and metal nanoparticles provided by the present invention;

[0027] Figure 2 This is a transmission electron microscope (TEM) image of the composite thin film formed by 6 layers of SrTiO3 single crystal layers and 5 layers of metallic Fe nanoparticles in Example 6.

[0028] Figure 3 This is a transmission electron microscope (TEM) image of the composite thin film formed by 16 SrTiO3 single crystal layers and 15 layers of metallic Fe nanoparticles in Example 7.

[0029] Figure 4 This is a high-resolution transmission electron microscope image of the composite thin film formed by Fe nanoparticles and SrTiO3 single crystal layer in Example 6.

[0030] Figure 5The image shows a comparison of the light absorption intensity of the 6-layer SrTiO3 single crystal layer and the 5-layer metal Fe nanoparticle composite film prepared in Examples 1-6. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0032] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0033] Example 1

[0034] like Figure 1 As shown, this embodiment provides a method for preparing a composite thin film of 6 layers of SrTiO3 single crystal layer and 5 layers of metal Fe nanoparticles, including the following steps:

[0035] Step 1: Anneal the single-crystal SrTiO3(100) substrate 1. The specific method includes: first, placing the single-crystal SrTiO3(100) substrate on the sample stage in the main cavity of the pulsed laser deposition system. The background vacuum of the vacuum cavity is less than 1×10⁻⁶. -7 Pa, thus initiating high-temperature annealing of the substrate. The annealing process is as follows: the temperature is increased from room temperature to 700°C at a rate of 5°C / min, then oxygen (O2) is introduced into the vacuum chamber, and the vacuum chamber pressure is adjusted to 10 Pa using a gas flow controller. The entire annealing process lasts for 30 minutes, after which the annealing is terminated.

[0036] Step 2: Clean the SrTiO3 target with a purity greater than 99.99% and the Fe metal target with a purity greater than 99.99%. This involves pre-ablating the SrTiO3 target and the Fe metal target with laser to remove contaminants from their surfaces and avoid the influence of impurities in the early stages of growth.

[0037] Step 3: First, use a KrF excimer laser to ablate the SrTiO3 target material, and then epitaxially grow a SrTiO3 buffer layer 2 on the (100) phase single crystal SrTiO3 (100) substrate; the background vacuum degree before coating is 1×10 -7 Pa, the working vacuum degree during the coating process is 1×10⁻⁶. -6 The temperature of the SrTiO3 substrate was 650℃, and the laser pulse frequency of the KrF excimer laser ablation of the SrTiO3 target was 1Hz, with a laser energy density of 1J / cm². 3 ;

[0038] Step 4: Using a laser beam to bombard the SrTiO3 target, an epitaxial SrTiO3 film is grown on the SrTiO3 buffer layer 2. Thermal annealing is then performed. After each SrTiO3 epitaxial film has grown, oxygen is introduced into the vacuum chamber to anneal it under oxygen partial pressure, thus reducing the generation of oxygen vacancies and improving surface quality. The KrF excimer laser bombarding the SrTiO3 target has a laser pulse frequency of 1 Hz and a laser energy density of 1 J / cm². 3 The process parameters for hot annealing are: hot annealing at 10 Pa oxygen pressure for 10 min;

[0039] Step 5: Ablate the Fe target material using a laser beam to achieve controllable embedding of Fe nanoparticles on the SrTiO3 epitaxial film. The SrTiO3 epitaxial film without embedded Fe nanoparticles is designated as layer A3, and the SrTiO3 epitaxial film with embedded Fe nanoparticles is designated as layer B4. The KrF excimer laser ablation of the Fe target material uses a laser frequency of 2 Hz and a laser energy density of 1 J / cm². 2 The number of laser pulses is 100, which means that the number of Fe quantum dots embedded is 100.

[0040] Step 6: Repeat steps 4 and 5, alternating between growing the SrTiO3 epitaxial film and embedding the Fe nanoparticles, to obtain an 11-layer composite film of SrTiO3 single crystal and Fe nanoparticles (A / B / A / B / A / B / A / B / A / B / A) on the SrTiO3 substrate, which is equivalent to obtaining a 6-layer composite film of SrTiO3 single crystal and 5-layer composite film of Fe nanoparticles.

[0041] Example 2

[0042] This embodiment provides a method for preparing a composite thin film of 6-layer SrTiO3 single crystal layer and 5-layer metal Fe nanoparticles. The difference between this method and Example 1 is that the number of laser pulses in step five is 200 pulses, that is, the number of embedded metal Fe quantum dots is 200. The rest of the process is the same as in Example 1.

[0043] Example 3

[0044] This embodiment provides a method for preparing a composite thin film of 6-layer SrTiO3 single crystal layer and 5-layer metal Fe nanoparticles. The difference between this method and Example 1 is that the number of laser pulses in step five is 300 pulses, that is, the number of embedded metal Fe quantum dots is 300. The rest of the process is the same as in Example 1.

[0045] Example 4

[0046] This embodiment provides a method for preparing a composite thin film of 6-layer SrTiO3 single crystal layer and 5-layer metal Fe nanoparticles. The difference between this method and Example 1 is that the number of laser pulses in step five is 400 pulses, that is, the number of embedded metal Fe quantum dots is 400. The rest of the process is the same as in Example 1.

[0047] Example 5

[0048] This embodiment provides a method for preparing a composite thin film of 6-layer SrTiO3 single crystal layer and 5-layer metal Fe nanoparticles. The difference between this method and Example 1 is that the number of laser pulses in step five is 500 pulses, that is, the number of embedded metal Fe quantum dots is 500. The rest of the process is the same as in Example 1.

[0049] Example 6

[0050] This embodiment provides a method for preparing a composite thin film of 6-layer SrTiO3 single crystal layer and 5-layer metal Fe nanoparticles. The difference between this method and Example 1 is that the number of laser pulses in step five is 600 pulses, that is, the number of embedded metal Fe quantum dots is 600. The rest of the process is the same as in Example 1.

[0051] The transmission electron microscope (TEM) image of the 6-layer SrTiO3 single-crystal layer and 5-layer Fe nanoparticle composite film prepared in this embodiment is shown below. Figure 2 As shown, a high-resolution transmission electron microscope (TEM) image of the composite thin film formed by metallic Fe nanoparticles and a SrTiO3 single crystal layer is shown below. Figure 4 As shown in the figure, it is clear that there is a clear separation between the film layers. The Fe nanoparticles were successfully embedded in the SrTiO3 epitaxial film. The dots in the figure are film layer B with embedded Fe nanoparticles. The composite film of 6 SrTiO3 single crystal layers and 5 Fe nanoparticle layers was successfully prepared.

[0052] The light absorption intensity of the composite thin films consisting of 6 SrTiO3 single crystal layers and 5 Fe nanoparticle layers prepared in Examples 1-6 was measured to obtain... Figure 5 ,from Figure 5 It can be seen that the composite films of 6-layer SrTiO3 single crystal layer and 5-layer Fe nanoparticles prepared in Examples 1-6 all exhibit enhanced absorption of light in the ultraviolet band. Among them, the composite film of 6-layer SrTiO3 single crystal layer and 5-layer Fe nanoparticles prepared in Example 6 shows the most significant enhancement of light absorption in the ultraviolet band.

[0053] Example 7

[0054] This embodiment provides a method for preparing a composite film of 16-layer SrTiO3 single crystal layer and 15-layer Fe nanoparticle layer. The method described in Example 1 prepares a 31-layer SrTiO3 single crystal and Fe nanoparticle composite film.

[0055] The transmission electron microscope (TEM) image of the 16-layer SrTiO3 single-crystal layer and 15-layer Fe nanoparticle composite film prepared in this embodiment is shown below. Figure 3 As shown in the figure, it is clear that there is a clear separation between the film layers. The Fe nanoparticles were successfully embedded in the SrTiO3 epitaxial film. The dots in the figure are film layer B with embedded Fe nanoparticles. The composite film of 16 SrTiO3 single crystal layers and 15 Fe nanoparticle layers was successfully prepared.

[0056] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0057] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a composite thin film of oxide single crystal and metal nanoparticles, characterized in that, include: Oxide buffer layers were alternately prepared on an oxide substrate using laser ablation. Oxide epitaxial films were then prepared on the oxide buffer layers. Metal nanoparticles were embedded in the oxide epitaxial films using a metal target. The oxide epitaxial film without embedded metal nanoparticles was designated as film layer A, and the oxide epitaxial film with embedded metal nanoparticles was designated as film layer B. Film layers A and B were prepared alternately using oxide targets and metal targets, respectively, to obtain a multilayer composite film of oxide single crystal and metal nanoparticles (A / B / A / B…A) on the oxide substrate. Specifically, the following steps are included: Step 1: Anneal the oxide substrate; Step 2: Clean the oxide target and the metal target; Step 3: First, use a KrF excimer laser to ablate the oxide target, and then epitaxially grow an oxide buffer layer on the oxide substrate; Step 4: Use a laser beam to bombard the oxide target to achieve epitaxial growth of an oxide epitaxial film on the oxide buffer layer; Step 5: Use a laser beam to ablate the metal target material to achieve controllable embedding of metal nanoparticles on the oxide epitaxial film. The oxide epitaxial film without embedded metal nanoparticles is denoted as film layer A, and the oxide epitaxial film with embedded metal nanoparticles is denoted as film layer B. Step 6: Repeat steps 4-5, alternating between the growth of oxide epitaxial films and the embedding of metal nanoparticles, to obtain a multilayer oxide single crystal and metal nanoparticle composite film of A / B / A / B…A on an oxide substrate. In step one, the specific method for annealing the oxide substrate includes: First, the oxide substrate is placed on the sample stage in the main cavity of the pulsed laser deposition system. The background vacuum of the vacuum cavity is less than 1 × 10⁻⁶. -7 Pa, thus beginning the high-temperature annealing of the substrate; the annealing process is as follows: the temperature is raised from room temperature to 600~900 ℃ at a rate of 2~10℃ / min, then oxygen is introduced into the vacuum chamber, and the pressure of the vacuum chamber is adjusted to 5~20 Pa by the gas flow controller. The entire annealing process lasts for 20~40 min, and then the annealing is ended. In step three, the background vacuum level before coating is 1×10⁻⁶. -7 Pa, the working vacuum degree during the coating process is 1×10⁻⁶. -6 Pa, the temperature of the oxide substrate is 500~700 ℃, the laser pulse frequency of KrF excimer laser ablation of the oxide target is 1~10 Hz, and the laser energy density is 1~10 J / cm². 3 ; In step four, the laser pulse frequency of the KrF excimer laser bombarding the oxide target is 1~10 Hz, and the laser energy density is 1~10 J / cm². 3 ; In step four, the heat annealing parameters are 5~20 Pa oxygen pressure for 5~20 min; In step four, the KrF excimer laser ablation of the metal target uses a laser frequency of 1~10 Hz and a laser energy density of 1~10 J / cm². 2 The number of laser pulses is 100 to 1000, which means that the number of metal quantum dots embedded is 100 to 1000. The oxide substrate is a single-crystal SrTiO3 conductive substrate, the oxide target is a single-crystal SrTiO3 ceramic target with a purity greater than 99.99 wt%, and the metal target is a Fe metal target with a purity greater than 99.99 wt%.

2. The method for preparing the composite thin film of oxide single crystal and metal nanoparticles as described in claim 1, characterized in that, In step two, the method for cleaning the oxide target and the metal target is to pre-ablate the oxide target and the metal target using a laser.

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