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    • 专利摘要:
    Manufacture of multiple optical resonators in the visible range based on metal oxides. Due to its wide variety of applications, recent advances have been made in the design of resonators using different methods that are difficult to scale for industrial exploitation due to the manufacturing techniques used. The present invention presents a method that is based on obtaining a highly textured ceramic pellet using a semiconductor oxide as the base material, which gives rise to multiple optical resonances in the visible and near infrared range when excited with ultraviolet laser light., individually or together. The manufacturing process used in this invention is inexpensive compared to other methods used to date. Furthermore, it is easily scalable to simultaneously produce a large number of platforms at the same time and does not require a vacuum technique. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2788823A1
    申请号:ES202030900
    申请日:2020-09-03
    公开日:2020-10-22
    发明作者:González María Taeño；Varea David Maestre；Rodríguez Ana Isabel Cremades
    申请人:Universidad Complutense de Madrid；
    IPC主号:
    专利说明:

    [0002] Manufacture of multiple optical resonators in the visible range based on metal oxides
    [0004] TECHNICAL SECTOR
    [0006] The present invention falls within the field of optical devices. More specifically, it refers to a method of manufacturing multiple self-organizing resonators using a single highly textured metal oxide platform exhibiting a controlled grain size. Resonators have potential application as sensors of various types (chemical, biological, mechanical, thermal, etc.) and other optical elements such as tunable filters, for example.
    [0008] BACKGROUND OF THE INVENTION
    [0010] Optical resonators are relevant in the field of photonics for their use in various applications that require optical resonances to achieve gain in optical systems such as lasers, in optical sensors for chemical or biological analytes, or others such as mechanical and thermal ones. Optical resonators can also be designed to function as tunable filters and multiplex splitters, for example.
    [0012] Due to this wide variety of applications, recent advances have been made in resonator design using different methods. Thus, resonators have been made through cavities made by lithography (DB Burckel et al., Advanced Materials 22 , 3171-3175, (2010) ), using photonic crystals (N. Hidalgo et al., Advanced Functional Materials 21 , 2534-2540 (2011) ) or by using dielectric materials of reduced dimensions that confine the light inside, functioning as a cavity (J. Flannery et al., ACS Photonics 5 , 337-341 (2018) ).
    [0014] Some of the previous designs, especially those that achieve higher quality factors Q, are difficult to scale for industrial exploitation due to the manufacturing techniques used. To overcome this drawback, recent developments in technology have been used to design methods of synthesis of micro and nanocrystalline structures that can work well as they result in well faceted nanocrystalline materials. Thus, optical resonators based on micro and nanostructures of metallic oxides such as zinc, indium, gallium, tin or titanium, among others, have been described (DJ Gargas et al., ACS Nano 4, 3270-3276 (2010); J. Bartolomé and col., Journal of Materials Chemistry C 1, 6790-6799 (2013); I. López et al., Applied Physics Letters 100, 261910 (2012)). However, they have the disadvantage of being difficult to handle and integration with other elements can be complicated, since they are individual structures of small size.
    [0016] For all the above, it is still necessary to develop new resonator manufacturing processes, which provide ease in procedures and lower costs.
    [0018] EXPLANATION OF THE INVENTION
    [0020] In the present invention, a method of manufacturing optical resonators is proposed in such a way that multiple active resonators are obtained on the same platform by using inexpensive and scalable materials and techniques, avoiding both the use of expensive manufacturing techniques (such as those that operate vacuum) such as the use of expensive post-manufacturing techniques (such as lithography) or manipulation of individual low-dimensional structures.
    [0022] The method is based on obtaining a highly textured ceramic tablet using a semiconductor oxide as the base material, so that the presence of a polycrystalline structure with crystals of certain sizes and textured surfaces gives rise to multiple optical resonances in the visible and range range. near infrared when they are excited with ultraviolet laser light, individually or together.
    [0024] The fabrication is carried out using the procedure previously described by the inventors (Taeño, M. et al. Self-Organized NiO Microcavity Arrays Fabricated by Thermal Treatments. Cryst. Growth Des. 2020, 20, 4082-4091) where a variant is introduced in heat treatment. As a precursor material metal powder and performing different heat treatments varying the temperature and duration of these, maintaining a constant dynamic inert atmosphere. In more detail, the method comprises the following steps:
    [0026] a) Compacting the metal powder to obtain a disk-shaped tablet that acts as a platform.
    [0027] b) Heat treatment of the metal pellet in three stages in an inert gas atmosphere with controlled flow;
    [0028] Stage 1. Temperature ramp. There is a linear increase in temperature until the desired temperature is reached.
    [0029] Stage 2. Plateau. The temperature is kept constant for a period of time.
    [0030] Stage 3. Cooling down. There is a decrease in temperature freely until reaching room temperature.
    [0032] The oxidation of the metal carried out in this way gives rise to the corresponding oxide whose grain size and crystalline orientation (and, therefore, the optical resonance characteristics) depend on the treatment time, the temperature, the flow and composition of the gaseous atmosphere. .
    [0034] The temperature and duration of each stage of the heat treatment are key to obtain homogeneous crystals with high crystalline quality and with a certain size that can act as resonant cavities. The treatments carried out favor the crystallization phenomena of the corresponding oxide and have been designed after multiple tests. In the first stage, the temperature is raised following a ramp that lasts 180 minutes until reaching the plateau temperature. In this first stage, the oxidation of the metallic precursor begins in a controlled way, forming small nucleation points of the oxide on the surface of the tablet due to the interaction with the remaining oxygen in the growth chamber, since in this type of method we avoid the growth under vacuum conditions. During the treatment plateau, which is the part with the highest temperature and duration of the heat treatment, the material is textured and self-organizes with crystallites of similar sizes and high crystalline quality. Depending on the chosen temperatures, the sizes and internal stresses that arise from the oxidation of the metallic precursor can be modulated. Finally, materials that can undergo phase transformations when cooling slowly are usually quenched, but that, in the case, for example, of nickel oxide, there is no possible phase transformation when cooling slowly and therefore a cooling for hours with the inertia of the furnace gives rise to a more resistant sample avoiding the appearance of cracks due to shock thermal. In addition, it helps to accommodate the stresses that occur in the oxidation of the precursor material in a more consistent way with the system.
    [0036] This synthesis of samples composed of metal oxides by means of a ceramic method with a dynamic atmosphere using metal powder as a precursor can be applied to different metals, provided that crystals of the required size are formed on their surface and that they present an adequate refractive index (in general, next to 2). These metals can be Ti, In, Sn, Zn, Ga or Ni.
    [0038] In a preferred embodiment, NiO samples are synthesized by a ceramic method with a dynamic atmosphere using Ni metallic powder as a precursor (Ni, Aldrich 99.9%) and carrying out different thermal treatments varying their temperature and duration, maintaining a constant Ar dynamic atmosphere. .
    [0040] In detail, the precursor material is made of nickel metal powder compacted by means of a Mega KP-30A hydraulic press applying a pressure of 2t. In this way, tablets (102) are obtained in the form of a disc of 5 mm in diameter and a thickness close to 1 mm, which gives the system robustness and, in turn, once the tablets have been made, they are introduced on a tray of alumina (101) in a Carbolite RHF 1500 muffle furnace (100) and are subjected to heat treatments assisted by a controlled flow of Argon gas of 1.5 - 2.0 l / min (104 and 105). The temperature ramp lasts 180 minutes until reaching 1000 - 1400 ° C, the plateau stage is maintained between 5 and 15 hours and, finally, the cooling takes place from when the heating resistances (103) are turned off until the oven reaches temperature environment.
    [0042] The adequate growth window to obtain the dielectric cavities or optical resonators is reduced, so it is necessary to control both the flow and the composition of the atmosphere, as well as the chosen precursor, the temperatures and the duration of the heat treatment steps to obtain the texture and crystal sizes required for application as optical resonators. Out of this Growth range, surfaces with various micro and nanostructures with different morphologies and crystalline orientations are obtained, as seen by way of example in Fig. 1, where the loss of texture of a sample grown outside the appropriate growth window is shown. These samples can be used in other applications, but they do not function as optical resonators.
    [0044] The manufacturing process used in this invention is inexpensive compared to other methods used to date. It does not need vacuum technique or presence of catalyst. In addition, it is easily scalable to simultaneously produce a large number of platforms at the same time and is reproducible.
    [0046] BRIEF DESCRIPTION OF THE DRAWINGS
    [0048] To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which, with an illustrative and non-limiting nature, the following has been represented next:
    [0050] Figure 1. X-ray diffractograms in which the influence of the experimental parameters (in this case the presence of Ar) is observed on the texturing and preferential orientation of the studied samples.
    [0052] Figure 2. Scheme of the furnace in which the different heat treatments have been carried out to obtain pure nickel oxide microcrystals.
    [0054] Figure 3.a) Optical image acquired from a confocal microscope of one of the analyzed cavities corresponding to the sample grown at 1200 ° C for 10 hours in which experimental optical paths of 7 and 5.4 pm respectively can be measured. b) PL spectrum acquired on the cavity shown in a) in which periodic modulations are observed in the visible region.
    [0056] Figure 4. a) Linear fit of AA versus A2 to obtain the theoretical optical path and b) Linear fit of A versus 1 / N to obtain the experimental refractive index.
    [0057] Figure 5. a) Optical image acquired from a confocal microscope of one of the analyzed cavities corresponding to the sample grown at 1100 ° C for 15 hours in which experimental optical paths of 7 and 5.4 pm respectively can be measured. b) PL spectrum acquired on the cavity shown in a) in which periodic modulations are observed in the visible region.
    [0059] Figure 6. a) Linear fit of AA versus A2 to obtain the theoretical optical path and b) Linear fit of A versus 1 / N to obtain the experimental refractive index.
    [0061] Next, a list of the different elements represented in the figures that are integrated in the invention is provided:
    [0063] 100 = Oven
    [0064] 101 = Alumina platform
    [0065] 102 = Metal powder tablet
    [0066] 103 = Resistors
    [0067] 104 = Ar gas inlet
    [0068] 105 = Ar gas outlet
    [0070] PREFERRED EMBODIMENT OF THE INVENTION
    [0072] The present invention is illustrated by the following examples, which are not intended to be limiting of its scope.
    [0074] Example 1.
    [0075] This example describes the fabrication of a NiO sample.
    [0077] The first stage of temperature rise is carried out at about 6.5 ° per minute. The plateau or central stage is carried out at 1200 ° C for 12 h. The third stage of free cooling lasts 4 hours.
    [0079] The thermal treatments have been carried out using a controlled argon atmosphere with a flow of 1.6 l / min. The presence of a controlled atmosphere of Ar implies a lower partial pressure of oxygen and therefore greater conditions of supersaturation of the atmosphere in Ni species, playing a role fundamental in oxidation kinetics. At 1200 ° C, the most likely oxidation mechanism for Ni is predominantly supported by ionic diffusion of Nickel through the NiO lattice.
    [0081] This treatment gives rise to highly textured surfaces formed mainly by microcrystals with dimensions between 10 and 20 pm, being able to find microcrystals with dimensions less than 10 pm as seen in Fig. 3a. These last microcrystals present the phenomenon of optical resonance.
    [0083] The study of optical resonances is carried out using a confocal microscope with the photoluminescence (PL) technique. One of the advantages of the PL technique in the confocal microscope is that it allows to analyze the luminescent signal of the material with micrometric resolution, being able to carry out spectra in specific areas of the sample. In this specific case, one of the cavities analyzed for said sample is shown as an example, which has the dimensions indicated in Fig. 3a. The PL spectra acquired on this cavity show a periodic modulation in the emissions between 450 and 650 nm, which indicates the existence of a resonant phenomenon as shown in Fig.3b.
    [0085] The resonance phenomena observed in this case are of the Fabry-Pérot (FP) type. As can be seen in Fig. 3a, FP-type resonances occur between two opposite faces and for them to occur, the condition of resonance that occurs when the product between the optical path (L fp ) and the refractive index (n) is an integer (N) times of the wavelength (A) of the light confined in the resonant cavity following the equation :
    [0087] n * Lfp = NA
    [0089] In this way, the separation between the modes (AA) in the PL spectrum is given by the equation:
    [0091] A A A l = - Lp- ^
    [0092] p ---- ng
    [0093] where ng is the group refractive index of the medium, having taken a value of 2.18 for the case of NiO for the initial settings. Once the corresponding adjustments have been made (which are shown in Figure 4), it can be seen that the resonant modes are adjusted to a FP type optical resonance. From the adjustment made in Fig. 4a a theoretical optical path of 14.2 ± 2.7 ^ m is obtained. Said value is very close to the expected experimental geometric value for a longitudinal resonance along the longest side of the microcavity as shown in Fig. 3a. After making the adjustment shown in Fig. 4b, a value of the experimental refractive index of 2.3 ± 0.2 is obtained, in accordance with the values observed for this oxide.
    [0095] There are other fundamental parameters in the study of optical resonators such as the fineness factor (F) and the quality factor (Q), which provide information on the magnitude of energy losses through the edges of the cavity and the the relationship between stored energy and dissipated energy, respectively. In this case, the values of F and Q for the resonant cavity studied are 1.8 and 207.3 respectively.
    [0097] Example 2 .
    [0098] This example shows the influence of temperature and heat treatment time on crystal size modulation and optical resonances.
    [0100] The same study detailed in Example 1 is carried out, this time with a NiO sample grown in the plateau stage at 1100 ° C for 15 hours. The temperature rise ramp is carried out at a rate of 6 ° C per minute and the sample is removed from the oven after 4 hours of cooling.
    [0102] This treatment gives rise to highly textured surfaces formed mainly by microcrystals with dimensions slightly lower than those observed in example 1, being able to find microcrystals with dimensions close to 5 ^ m and with a square section as can be seen in Fig. 5th. The procedure carried out to study the resonances observed in the PL spectrum shown in Fig. 4b is identical to that described in example 1. In this case, and as observed in Fig.
    [0103] 4a the experimental optical path of a FP type resonance between the faces of a microcavity is 11.6 ^ m.
    [0105] Once the corresponding adjustments have been made, which are shown in Fig. 6, it can be observed that the resonant modes are adjusted to an optical resonance of the FP type. From the adjustment made in Fig. 6a, a theoretical optical path of 13 ± 1.9 ^ m is obtained. Said value is very close to the expected experimental geometric value for a longitudinal resonance as shown in Fig. 4a. After making the adjustment shown in Fig. 6b, a value of the experimental refractive index of 2.4 ± 0.2 is obtained, in accordance with the values observed for this oxide.
    [0107] In this case, the fineness (F) and quality (Q) values for the resonant cavity studied of the sample grown at 1100 ° C for 15 hours are 1.2 and 142 respectively.
    权利要求:
    Claims (9)
    [1]
    1. Manufacturing method of multiple optical resonators in the visible range based on metal oxides characterized in that it uses metal powder as a precursor with a refractive index close to 2 that comprises the following stages:
    a) Compacting the metallic powder to obtain disc-shaped tablets that act as a platform.
    b) Heat treatment of the metal pellets in three stages in an inert gas atmosphere with controlled flow;
    Stage 1. Temperature ramp. There is a linear increase in temperature until the desired temperature is reached.
    Stage 2. Plateau. The temperature is kept constant for a period of time.
    Stage 3. Cooling down. There is a decrease in temperature freely until reaching room temperature
    where particles of the oxide of the precursor metal are obtained with a highly textured surface formed by microcrystals of different dimensions that present different optical resonances on the same platform depending on the temperature, time and flow and composition of the inert atmosphere during the heat treatment.
    [2]
    2. Method of manufacturing multiple optical resonators in the visible range based on metallic oxides, according to claim 1, where the precursor metal is Ni metallic.
    [3]
    3. Manufacturing method of multiple optical resonators in the visible range based on metallic oxides, according to claim 2, where the compaction is carried out by means of a hydraulic press applying a pressure of 2t, obtaining disc-shaped pads of 5mm in diameter and 1mm in diameter. thickness.
    [4]
    4. Manufacturing method of multiple optical resonators in the visible range based on metallic oxides, according to claims 2 and 3, where the tablets are introduced into a muffle-type furnace where they are subjected to heat treatment assisted by a controlled flow of Argon gas of 1.5 - 2.0 l / min.
    [5]
    5. Manufacturing method of multiple optical resonators in the visible range based on metallic oxides, according to claim 4, where the temperature ramp is carried out for approximately 180 minutes, until reaching 1000-1400 ° C, it is kept between 5 and 15 hours and then allowed to cool to room temperature.
    [6]
    6. Method of manufacturing multiple optical resonators in the visible range based on metallic oxides, according to claim 5, where the temperature ramp is carried out until it reaches 1200 ° C and is maintained for 12 h, obtaining NiO with a highly textured surface formed mainly by microcrystals with dimensions between 10 and 20 ^ m and microcrystals with dimensions less than 10 ^ m which present optical resonance.
    [7]
    7. Manufacturing method of multiple optical resonators in the visible range based on metallic oxides, according to claim 5, where the temperature ramp is carried out until reaching 1100 ° C and is maintained for 15 h, obtaining NiO with a highly surface where microcrystals with dimensions less than 5 ^ m which present optical resonance.
    [8]
    8. Multiple optical resonator comprising an oxide of a metal with a refractive index close to 2, textured polycrystalline semiconductor in the form of a compacted tablet subjected to the heat treatment formed by microcrystals.
    [9]
    9. Multiple optical resonator, according to claim 8, wherein the oxide is NiO with a textured surface formed that contains microcrystals with dimensions less than 10 µm.
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