CN115652258A - Amorphous film with good electric transport performance and preparation method thereof - Google Patents
Amorphous film with good electric transport performance and preparation method thereof Download PDFInfo
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- CN115652258A CN115652258A CN202211438775.8A CN202211438775A CN115652258A CN 115652258 A CN115652258 A CN 115652258A CN 202211438775 A CN202211438775 A CN 202211438775A CN 115652258 A CN115652258 A CN 115652258A
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Abstract
The invention discloses a preparation method of an amorphous film with good electric transport performance, which comprises the following steps: (1) Uniformly mixing lanthanum oxide and titanium oxide precursor powder, grinding, pressing a target by using a tablet press, and sintering at a high temperature in a muffle furnace to obtain LaTiO 3 A target material; (2) Cleaning and etching SrTiO 3 A substrate; (3) LaTiO is added 3 Target and treated SrTiO 3 Putting the substrates into a pulsed laser deposition system together, and growing LaTiO under appropriate conditions 3 An amorphous film; (4) Amorphous LaTiO with different thickness is grown in room temperature and vacuum environment 3 A film. The invention can show that the film shows metallicity through curves, and has good electric transportation property.
Description
Technical Field
The invention belongs to the field of Pulse Laser Deposition (PLD) technology and preparation of perovskite oxide film, and particularly relates to LaTiO with good electric transport performance 3 Amorphous film and method of making the same.
Background
The application of amorphous films has been widely studied in the last decades, and they have a wider application prospect due to their more convenient preparation and simpler environmental requirements than single crystals. However, an amorphous thin film is generally poor in conductivity, and it is difficult to achieve excellent electric transport properties as a single crystal thin film. This is mainly due to the poor crystallinity of amorphous films and the relatively few electrons that can move freely within the interface. How to prepare the amorphous film with better electric transport property is an important field of research of amorphous substances. Epitaxial film LaTiO on single crystal 3 /SrTiO 3 The presence of a two-dimensional electron gas has been demonstrated in this system, which is essentially the LaTiO of the Mott insulator 3 And SrTiO with energy band insulator 3 The amorphous film formed instead exhibits metallic properties and may even serve as a superconducting material. And LaTiO 3 /SrTiO 3 The amorphous film also exhibits metallic properties and has good electrical transport properties, which may be caused by the presence of a two-dimensional electron gas in the amorphous film.
For amorphous LaTiO 3 The interfacial transport property of the film is researched, and no relevant research is available at present. Thus, amorphous LaTiO was studied 3 The interfacial transport properties of the thin film and the preparation of an amorphous thin film having good electrical transport properties are very significant.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides LaTiO with good electric transport performance 3 Amorphous film and a method for preparing the same.
In order to achieve the above object, the technical scheme adopted by the invention is as follows:
LaTiO with good electric transport performance 3 The amorphous film and the preparation method thereof comprise the following steps:
(1) Uniformly mixing lanthanum oxide and titanium oxide precursor powder in proportion, grinding, pressing a target by using a tablet press, and sintering at high temperature in a muffle furnace to obtain LaTiO 3 A target material;
(2) Cleaning and etching SrTiO 3 A substrate;
(3) Mixing LaTiO with water 3 Target material and treated materialSrTiO of (2) 3 Putting the substrates into a pulsed laser deposition system together, and growing LaTiO under appropriate conditions 3 An amorphous film;
(4) Under the environment of vacuum and room temperature, laTiO with different thicknesses is obtained 3 A film. LaTiO 2 3 The electric transport property of the thin film increases with the increase of the thickness, and the trend of the change is gradually gentle after the thickness reaches 24 nm.
Further, in step (1): due to Ti 3+ Is oxidizable, and LaTiO is fired at a high temperature in an atmosphere exposed to air 3 The ceramic target material can only obtain Ti 4+ Of LaTiO 3.5 Phase targets, however the presence of excess oxygen in the target material is not conducive to growing LaTiO for PLD systems 3 The film has influence because the invention only needs to grow LaTiO 3 The environment of the film is high vacuum, the molar ratio of lanthanum oxide to titanium oxide in the target material is 1 3.5 Use of phase ceramic target material for growth of LaTiO 3 And (6) epitaxial thin film. Firstly, grinding lanthanum oxide and titanium oxide precursor powder according to a certain proportion for 30min for half an hour, then adding 10ml of absolute ethyl alcohol into the mixed powder, grinding while stirring in the process, and then placing the mixed powder into a drying oven at 60 ℃ for ventilation drying for 30min to obtain fully mixed powder. Grinding the dried mixed powder for 2min, adding 10ml anhydrous ethanol, stirring, grinding for 15min, and ventilating to volatilize ethanol completely. And then putting the obtained mixed powder into a crucible, placing the crucible into a muffle furnace, and heating to 1200-1250 ℃ to obtain lanthanum titanium oxide powder. Cooling, placing the powder into a clean mold, maintaining at 12Mpa for 10min to obtain LaTiO powder with diameter of 1 inch and thickness of 4mm 3 And (4) pre-sintering the target material. Finally, placing the pre-sintered target material into a muffle furnace to be sintered for 11-13h at 1300-1350 ℃ to obtain compact LaTiO 3.5 A ceramic target material.
Further, in the step (2), acetone is firstly used for ultrasonic cleaning for 5-10min, then absolute ethyl alcohol is used for ultrasonic cleaning for 5-10min, finally deionized water is used for cleaning for 5-10min, and nitrogen is used for drying to obtain the STO substrate with a clean surface. Firstly, adding a proper amount of BOE solution into a polytetrafluoroethylene beaker, and etching the STO substrate solution for 10-15 s; then putting the substrate into deionized water for ultrasonic cleaning for 5-10min, and removing the residual BOE solution on the surface of the substrate; and drying by using nitrogen to obtain the etched STO substrate. Then annealing at 1000 deg.C for 60min and cooling to room temperature at the same rate to obtain the etched STO substrate.
Further, depositing LaTiO in the step (3) 3 When the deposition temperature is 25-30 ℃ and the gas pressure is 10 -6 -10 -7 Torr, energy density of 1.5J. Cm in the growth process -2 。
Further, in the step (4), samples with different thicknesses of 4nm to 32nm are grown in a high vacuum environment, and LaTiO with the thicknesses of 4nm, 6nm, 8nm, 10nm, 12nm, 16nm, 24nm and 32nm are respectively grown 3 Film, higher thickness (. Gtoreq.24 nm) of LaTiO is determined 3 The better the film transport.
Compared with the prior art, the invention has the following beneficial effects:
the invention aims to solve the technical problem of providing LaTiO with good electric transport performance 3 Compared with other film preparing technology, the pulse laser deposition technology can prepare high quality film to prepare LaTiO film 3 The epitaxial thin film material is an amorphous thin film and has excellent electric transport property, and is used for researching LaTiO 3 Provide high quality film samples.
Drawings
FIG. 1 shows LaTiO obtained in example 1 3.5 XRD spectrogram of the ceramic target material;
FIG. 2 shows amorphous LaTiO films of different thicknesses in example 1 3 Film XRR results plot;
FIG. 3 shows amorphous LaTiO films of different thicknesses in example 1 3 XAS spectrum of film Ti L-edge;
FIG. 4 shows amorphous LaTiO films of different thicknesses in example 1 3 Film R-T plot;
FIG. 5 is a graph of sheet resistance versus thickness for the film at 300K in example 1.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
In the embodiment, the LaTiO with good electric transport performance 3 The preparation method of the amorphous film comprises the following steps:
(1) Target burning: firstly, mixing lanthanum oxide and titanium oxide mixed precursor powder according to the molar ratio of 1 3 Pre-sintering the target material; finally, placing the pre-sintered target material into a muffle furnace to be sintered for 11-13h at 1300-1350 ℃ to obtain compact LaTiO 3 Ceramic target material, and finally polishing the fired target material by using sand paper to obtain LaTiO for pulse laser deposition 3 A ceramic;
(2) SrTiO 2 3 Sequentially placing the substrate into acetone, alcohol and deionized water, performing ultrasonic treatment for 5min, 5min and 10min, and cleaning; then, etching the substrate for 10-15s by using hydrofluoric acid diluted by the 10;
(3) LaTiO is added 3 Target and treated SrTiO 3 The substrates are placed together in a pulsed laser deposition system under appropriate conditions at SrTiO 3 Epitaxially growing LaTiO on the substrate 3 An amorphous film;
(4) Under high vacuum (10) -7 Torr), and LaTiO grown at room temperature at 30 deg.C to have different thicknesses of 4nm, 6nm, 8nm, 10nm, 12nm, 16nm, 24nm, and 32nm 3 Amorphous film, and preparing LaTiO with different thicknesses 3 An amorphous film.
The following is a more specific example.
Example 1
A preparation method of an amorphous film with good electric transport performance comprises the following steps:
(1) Firstly, lanthanum oxide and titanium oxide are mixed according to the proportion of 1LaTiO with thickness of 4mm 3 Pre-sintering the target material; finally, placing the pre-sintered target material into a muffle furnace to be fired for 12 hours at 1300-1350 ℃ to obtain compact LaTiO 3 Ceramic target material, and finally polishing the fired target material by using sand paper to obtain LaTiO for pulse laser deposition 3 A ceramic;
(2) Mixing SrTiO 3 Sequentially putting the substrate into acetone, alcohol and deionized water for cleaning for 5min, 5min and 10min respectively; then etching the substrate for 12s by using hydrofluoric acid diluted by 10;
(3) Mixing LaTiO with water 3 Target and treated SrTiO 3 The substrates are put into a pulsed laser deposition system together, and SrTiO 3 LaTiO grown on the substrate 3 An amorphous film; deposition of LaTiO 3 The temperature is 30 ℃ and the air pressure is 10 -7 torr, energy density 1.5 J.cm -2 。
(4) Under high vacuum (10) -7 Torr), energy density of 1.5J. Cm -2 Then, laTiO with different thicknesses of 4nm, 6nm, 8nm, 10nm, 12nm, 16nm, 24nm and 32nm are respectively grown 3 A film.
For LaTiO with different thicknesses 3 The amorphous film is subjected to electric transportation performance test by adopting a 4200-SCS system and adopting an ultrasonic spot welding machine to connect a lead wire, and LaTiO is tested 3 The resistance curve of the film explores the influence of two-dimensional electron gas between the film and the substrate.
The resistance measurement mainly uses a four-probe method to test the resistivity of the film, the wire binder equipment film is used for connecting pins, and in the connection process, the overlong lead needs to be prevented from contacting other pins or other parts of the inner container of the low-temperature cavity, so that the wiring is prevented from being broken; after the low-temperature cavity sample rack shell is installed, whether air leakage exists needs to be checked, the vacuum degree in the low-temperature cavity is guaranteed, and test data are reliable and accurate.
Test examples
Powder crystal XRD was used to align LaTiO prepared in example 1 3.5 Target material, laTiO through figure 1 3.5 XRD result and LaTiO of ceramic target material 3.5 Comparison of standard card PDF #42-0517 can determine the fired LaTiO 3.5 No diffraction peak of other phases appears in the ceramic target material, and in an XRD spectrogram, the intensity of the diffraction peak is high, the diffraction peak is sharp, and the half-height width is small, which indicates that the prepared LaTiO 3.5 The target material has very good crystallinity and can be used for carrying out LaTiO on a PLD system 3 And (4) epitaxial growth of the thin film.
FIG. 2 is a graph for accurately measuring LaTiO with different thicknesses 3 Thickness of amorphous film, the invention for the above LaTiO 3 Amorphous XRR characterization was performed on 8 different thickness (LTO-4 nm, 6nm, 8nm, 10nm, 12nm, 16nm, 24nm, 32 nm) films of the amorphous film, with the results shown in figure 2 below. The amorphous LaTiO with different thicknesses can be seen through XRR results 3 The period of oscillation and the thickness of the film.
FIG. 3 shows amorphous LaTiO with different thicknesses 3 The XAS spectrum of the thin film Ti L-edge is researched, and the amorphous LaTiO with three different thicknesses can be found 3 L of thin film (LTO-4 nm, 8nm, 32 nm) 3 e g The peak-to-peak binding energy was 459.6eV 2 e g The peak corresponding binding energy is 465eV, which shows that the amorphous LaTiO 3 All Ti in the film is +3 valent LaTi which is completely not crystallized 3+ O 3 A film.
FIG. 4 shows LaTiO compounds with different thicknesses (LTO-4 nm, 6nm, 8nm, 10nm, 12nm, 16nm, 24nm, 32 nm) 3 The R-T plot of the film, it can be seen that as the test temperature is lowered, the conductivity at the interface of the film and the substrate increases, exhibiting metallic behavior, and thicker films are more conductive.
Fig. 5 is a graph showing the square resistance of the film as a function of thickness at 300K, and it can be seen from the results that the square resistance of the film becomes gradually smaller as the thickness of the film increases. The curve shows that the decrease of the resistance value of the square resistor gradually becomes stable after reaching 24 nm.
In conclusion, the LaTiO compound is considered to be under the conditions of high vacuum and room temperature 3 The electric transport property of the thin film increases with the increase of the thickness, and the decreasing tendency gradually flattens after the thickness reaches 24 nm.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concept. Therefore, the technical solutions that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the prior art according to the concepts of the present invention should be within the scope of protection determined by the claims.
Claims (9)
1. A preparation method of an amorphous film with good electric transport performance is characterized by comprising the following steps:
(1) Uniformly mixing lanthanum oxide and titanium oxide precursor powder in proportion, grinding, pressing a target by using a tablet press, and sintering at high temperature in a muffle furnace to obtain LaTiO 3 A target material;
(2) Cleaning and etching SrTiO 3 A substrate;
(3) LaTiO is added 3 Target and treated SrTiO 3 Putting the substrates into a pulsed laser deposition system together, and growing LaTiO under appropriate conditions 3 An amorphous film;
(4) Under the environment of vacuum and room temperature, laTiO with different thicknesses is obtained 3 A film.
2. The method for preparing an amorphous film with good electrical transport properties as claimed in claim 1, wherein in step (1), after mixing the precursor powders of lanthanum oxide and titanium oxide in a molar ratio of 1.
3. The method for preparing an amorphous film having good electric transportation properties as claimed in claim 1, wherein the target pressing pressure of the sheet press in step (1) is 20-25MPa, the target pressing time is 10-20min, and the size of the die for pressing the target is 0.5-1 inch.
4. The method for preparing an amorphous thin film having good electric transport properties as claimed in claim 1, wherein the sintering temperature in the step (1) is 1300-1350 ℃ and the sintering time is 11-13h.
5. The method of claim 1, wherein the step (2) comprises washing SrTiO with acetone, alcohol, and deionized water sequentially 3 And cleaning the substrate for 5min, 5min and 10min respectively.
6. The method for preparing an amorphous film having good electrical transport properties according to claim 1, wherein hydrofluoric acid diluted with 10.
7. The method for preparing an amorphous thin film having good electric transport properties as claimed in claim 1, wherein LaTiO is deposited in the step (3) 3 The temperature is 25-35 deg.C, and the air pressure is 10 -6 -10 -7 torr, energy density 1.5 J.cm -2 。
8. The method of claim 1, wherein the step (4) of growing the LaTiO thin film with the thickness of 4nm to 32nm at an interval of 4nm is performed to obtain LaTiO thin film with different thickness 3 A film.
9. An amorphous thin film having good electrical transport properties prepared according to the method of any one of claims 1 to 8.
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