Shulou(Shulou.com)11/24 Report--

As the saying goes, food is the most important thing for the people.

I don't realize that the Spring Festival of the year of the Rabbit is over.

Presumably these days

Friends have enjoyed all kinds of delicacies!

For the editor, the New year's Eve dinner

Enjoying good food is the happiest thing!

And as we all know,

The methods of cooking food are ever-changing:

Fried, fried, cooked, fried, steamed

Boil, stew, boil, burn, stew

Stewed, roasted, boiled, baked, baked.

Steamed sausage also uses a variety of ingredients, generally speaking, the ingredients can be cooked completely, or cut into pieces, sliced, shredded, or chopped, or ground into powder, mud and then processed.

In the cooking process or separate cooking, or mix ingredients, of course, do not forget to add a variety of seasonings.

Finally, a delicious dish of delicious food is out of the pot!

Iron plate shrimp slippery for physicists, many important physics are hidden in a variety of materials. Such as metals, semiconductors, superconductors, or bulk single crystals, polycrystalline alloys, thin film materials, nanowires.

For example, high temperature superconductivity is found in iridium barium copper oxide (YBCO) alloys, and the process of making these materials is like "cooking": various compounds are processed like ingredients.

Chemical raw materials are decomposed and synthesized by a series of methods to produce chemical reactions, thus combining different elements together. Finally, the final desired material or sample is obtained by various methods.

A plate of scrambled eggs with tomatoes and a doped semiconductor discover new physics from the material and use the material to develop new technologies. Aren't all kinds of materials "delicious food" in the eyes of physicists?

Today, the editor will take you to take an inventory of some common material preparation methods.

Lump Crystal × delicious stir-fry √ before cooking, we need to determine the ingredients to use, and the same is true for making materials. The first step is to choose the appropriate reaction materials.

A common method for preparing polycrystalline materials is solid phase synthesis.

Solid phase synthesis means that the raw materials and products of the whole reaction process are in solid state. (just like chopping and mixing different ingredients to make a stir-fried dish)

First of all, the reaction raw materials are mixed together according to a certain stoichiometric proportion, and the general raw materials are powdered chemicals.

Ingredient room-neatly placed bottles and cans it is worth noting that if the reaction material is easily oxidized and wet, the drug weighing and mixing process needs to be carried out in a glove box filled with inert gas.

Glove box photo source: only the molecules on the contact surface between different raw material particles in the SC9 group of the Institute of Physics of the Chinese Academy of Sciences have a chance to react with another molecule. Therefore, it is necessary to fully mix the powder particles between the raw materials.

The raw materials are generally mixed with anhydrous ethanol or deionized water and mixed by mechanical ball milling.

In the process of mechanical ball milling, the raw materials are pressed into sheets after mixing evenly, which increases the compactness between the particles.

Then it is heated to a certain temperature to enhance the thermal movement of the molecules and promote the ion diffusion between the molecules on the surface of the particles, resulting in chemical reactions.

The source of powder pressing machine and tablet pressing die: after the reaction for a period of time, the network generally mixes it evenly after grinding, and then heats the tablet again, so as to reconstruct the reaction interface and shorten the time of ion diffusion.

The heating or final crystallization sintering process usually involves putting the pressed sheet into a crucible or quartz tube and then heating it in a muffle furnace.

The molecules on the interface continue to react to form the product, the accumulation of the product will form a crystal nucleus, in the process of continuous reaction, the crystal nucleus will grow and eventually form a crystal.

For single crystals, solution method is also the main technology of crystal growth for polycrystalline ferroelectric ceramics prepared by solid phase synthesis.

For example, crystals can be dissolved in specific high-temperature molten salts to form a high-temperature "solution", which will precipitate crystals by cooling or solvent volatilization to make the "solution" supersaturated.

Source of crystallization process: [2] this reminds the editor of a traditional delicacy-pig skin jelly: make soup first and then solidify.

In addition, with the realization of the top seed technology, the seed can be widely used to grow optical crystals [1].

Seed crystal is a kind of small single crystal or polycrystal material. Seed crystal is used to promote crystal growth and avoid the slow randomness of natural crystal growth.

This is because after the introduction of a pre-formed target crystal, the interaction between molecules is easier to form than dependent on random motion [2].

Source of the schematic diagram of the internal structure of the top seed crystal growth furnace: [1] the optical floating zone method can also be used to grow single crystals, that is, the light source can be reflected through the ellipsoid to form in the narrow area of the center where the temperature is high and the edge temperature is low.

The polycrystal rod is placed in the central high temperature zone, which is heated and melted into a liquid, and the compound melted by the moving rod is recrystallized on the seed crystal to complete the single crystal growth [3].

Optical floating zone furnace sample heating zone source: [3] Nano-film × thousand-layer cake √ film refers to the material with single or multi-layer atomic and molecular layers.

Compared with three-dimensional bulk crystals, the arrangement of atoms in the thickness direction of thin film materials disappears periodically, which leads to the characteristics that the corresponding bulk materials do not have, which makes thin film materials an indispensable part of condensed matter physics research.

Monolayer, bilayer symmetrical and antisymmetric graphene have special sources of energy band structure respectively: [4] the basic principle of growing thin films is to separate atoms or molecules from the target by heating or using ions or laser bombardment, and finally deposited on some kind of substrate.

The thin film heterojunction, that is, the interface composed of two kinds of substances, can also be constructed by depositing atoms and molecules of different substances sequentially. In this way, some interface effects can be explored.

The common preparation methods of multilayer thin films and durian thousand-layer cake in laboratory are vacuum evaporation, ion beam growth, chemical vapor deposition, magnetron sputtering, molecular beam epitaxy and laser molecular beam epitaxy [4].

Because the growth process of thin films requires atoms and molecules to be deposited on the substrate in the environment, it needs to be carried out in a high vacuum environment.

The method of vacuum classification vacuum evaporation is to deposit the atoms on the top substrate freely and without collision by heating evaporation in the vacuum environment, which is often used to evaporate metal electrodes.

Just like steaming a pot of delicious Xiaolongbao ion cluster growth, it means that the steam formed by high-temperature heating materials is ejected into the high vacuum to form a cluster of thousands of atoms, and then ionized to form ion bunches. Finally, it is accelerated by an electric field and deposited to the surface of the substrate at a high speed.

Chemical vapor deposition (CVD) refers to the chemical decomposition of gaseous compounds on the surface of the substrate.

Magnetron sputtering means that in a magnetic field, Ar ions ionized by electron collision bombard the target at high speed, thus sputtering a large number of target atoms deposited on the surface of the substrate.

Source of magnetron sputtering equipment: [6] Molecular beam epitaxy excitates the target material by heating, evaporation, pyrolysis or electron beam bombardment to turn the solid material into gaseous atoms or molecules and deposit on the substrate.

The method of laser molecular beam epitaxy is to use pulsed laser to hit the target material in vacuum, and the target material will be ionized after absorbing laser energy, resulting in plasma plume containing ions, molecules, electrons, atoms and clusters.

The plasma plume glow precipitates on the surface of the substrate to complete the growth of the film.

In the process of thin film growth, the substrate used to grow the film is first heated to a certain temperature, and then flowing oxygen is introduced into the cavity to ensure a certain oxygen pressure. The target is placed directly below the substrate, and then the target is irradiated by a pulsed laser.

Source of laser molecular beam epitaxy system: [7] because the plasma plume has a highly directional and dense shape, it expands rapidly in a vacuum chamber and precipitates on the substrate surface in an almost vertical direction. As a result, extremely high quality single crystal films are grown.

Laser molecular beam epitaxy system source: [7] the process in which atoms are deposited into thin films on the substrate is divided into four types. The reasons for different growth processes are substrate temperature, deposition rate, growth pressure, substrate surface smoothness and so on.

Source of four modes of thin film epitaxial growth: [6] therefore, in the process of thin film growth, reflective high energy electron diffraction system (RHEED) is generally used to monitor the growth process in real time. Generally speaking, the more flat the film surface, the easier it is to see oscillating RHEED images.

The source of RHEED diagram during the growth of La1-xSrxMnO3 (LSMO) system: [8] the method of obtaining nano-sized two-dimensional materials is also peeling method. That is, layer by layer of atoms are stripped off the bulk crystal.

Like cutting off a piece of ham, the most famous stripping method is the monolayer graphene obtained by the British Geim team for the first time in 2004 using transparent tape to paste and fold repeatedly. Nowadays, the use of transparent tape to prepare thin films is also a common method in the laboratory.

In addition to rough scotch tape, there are some auxiliary means to help peel off.

For example, the material powder suspension is dispersed in organic solvents, and the nanowires are peeled off by eddy current shear stress in the process of ball milling.

Eddy current stripping boron nitride nanowires source: [9] or with the aid of ultrasound, substances that are not easy to hydrolyze can be dissolved in water, thus achieving more effective stripping [9].

The schematic source of ultrasound-assisted hydrolysis stripping boron nitride nanowires: [9] the nanowires obtained by stripping method can have several or even single atomic layers.

Material treatment × preparation of √ some materials may have some defects after preparation.

For example, for some iron-containing crystals, iron ions may exist in the gap between the crystal layers to change the magnetism of the crystals or affect their properties; or some crystals have many internal defects during sintering due to lack of oxygen in the environment, which is not good for their properties.

At this time, the method of annealing can be used, that is, the material can be re-placed in a certain gas atmosphere and kept at a lower temperature for a period of time, which can reduce the internal defects of the crystal and improve the material properties.

The meat back to the pot is delicious, of course, because it is "back to the pot" ~ for some materials, such as semiconductors, we have to adulterate them after making the intrinsic materials. For example, only when doped into p-type or n-type semiconductors can the device be further made.

At this time, ion implantation can be used for doping. For semiconductors, ion implantation is the main means of doping and regulation.

In the process of ion implantation, the ion beam is first purified. After the ion source produces some specific positive and negative ions, such as nitrogen, boron, arsenic, phosphorus and germanium, an ion beam with a certain kinetic energy is formed under the acceleration of an adjustable strong electric field [11].

Because different ions have different charge-mass ratios, impurity ions can be screened out.

Subsequently, the incident direction of the accelerated ion beam will show a certain deflection angle with the surface of the target crystal and irradiate uniformly on the surface of the crystal.

(a) Diamond structure diagram overlooking along a particular crystal axis (b) different paths of ions passing through the cubic lattice show that after penetrating the crystal, ions will have a series of complex collisions and scattering with atoms in the crystal, so they will eventually stay in a certain position inside the crystal, thus realizing ion doping in the crystal [11].

Sample characterization × American Food Review √ Q: what is the most important step in making delicious food?

A: yes, of course!

Source: the movie "God of Food" similarly, after preparing the materials we need, we need to use some methods to characterize these materials to test the quality of our samples.

First of all, the shape and appearance of the sample can be observed directly by optical microscope.

Because of the diffraction limit of visible light wavelength, its spatial resolution is limited. So if you want to see a more microscopic and clearer morphology of the sample, you can use a shorter wavelength electron beam to make a microscope, that is, a scanning electron microscope.

Scanning electron microscope photos of boron nitride nanoflakes source: [9] because the wavelength of the X-ray is in the same order of magnitude as the distance between the atoms in the crystal, the X-ray is very prone to diffraction in the crystal. According to this, the lattice structure of the sample can be determined by X-ray diffraction pattern.

Source of X-ray diffraction schematic diagram: [8] in addition, the microscopic surface morphology of the sample can be observed by atomic force microscope.

The probe of an atomic force microscope is a sharp cone composed of several atoms. When the probe moves on the sample surface, the interaction forces between the probe atoms and the atoms on the sample surface will be different when the ups and downs of the sample surface are encountered. Then the magnitude of the force is converted into an electrical signal, and the surface morphology of the sample can be obtained by simulation software.

Source of atomic force microscope structure diagram: [7] Raman spectroscopy is also a commonly used method in various material characterization methods.

When the light is incident into the crystal, the laser may interact with the molecular bond and lattice phonon in the solid. As a result, the wavelength of the outgoing light is changed, which is the occurrence of Raman scattering.

Because the vibrational energies or phonon energies of molecular bonds of different substances are different, different phases can be identified by analyzing the change of laser frequency and peak intensity in Raman spectra.

Source of Raman spectrum of carbon nanotubes: [13] with so many ways to make and taste physical "food", will New Year's Eve set up another physical "gourmet meal" next year?

References:

[1] Crystal growth and characterization of a new optical crystal material BaTeW2O9, Zhang Zhonghan, Master thesis of Shandong University, 2016

[2] Wikipedia https://en.wikipedia.org/ wiki / Seed_crystal

[3] preparation and physical properties of Ba-based perovskite oxide single crystals under high pressure, Qin Qingjun, Ph. D. thesis, University of Chinese Academy of Sciences, 2022

[4] Ohta T, et al. Controlling the electronic structure of bilayer graphene, Science 313, 5789 (2006)

[5] Martin, et al. Room temperature exchange bias and spin valves based on BiFeO3/SrRuO3/SrTiO3/Si (001) heterostructures, Appl. Phys. Lett. 91, 172513 (2007)

[6] preparation and performance study of new solid lithium secondary battery and related materials, Tan Guoqiang, doctoral thesis of Beijing Institute of Technology, 2014

[7] Laser preparation and interface effect of BiFeO3-based multilayers, Yao Xiaokang, Ph. D. thesis, University of Chinese Academy of Sciences, 2022

[8] Regulation of magnetic and electrical properties of LaMnO3 and Sr-doped (Pr, Nd) NiO3 films prepared by laser method, Yang Mingwei, Ph. D. thesis, University of Chinese Academy of Sciences, 2022

[9] preparation and properties of boron nitride nanoparticles, du Miao, doctoral thesis of Shandong University, 2013

[10] preparation and performance Optimization of FeSe-based Superconducting Materials, Shao Baitao, Master thesis of Xi'an University of Technology, 2019

[11] Regulation and characterization of physical properties of silicon carbide epitaxial graphene by boron ion implantation, Guo Yunlong, Ph. D. thesis, University of Chinese Academy of Sciences, 2021

[12] Chen, et al. A 1.7 nm resolution chemical analysis of carbon nanotubes by tip-enhanced Raman imaging in the ambient, Nat. Commu. 5:3312 2014

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop). Author: want to eat delicious Xiao Ming

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