Shadowing Practice: Intro to Scanning Electron Microscopy (SEM) - Learn English Speaking with Video
Creando lección...
1
Welcome to the Technological Institute at Northwestern University.
2
Today we are going to tour the Northwestern Atomic and Nanoscale Characterization Experimental Center,
3
or the Nuance Center.
4
We're going to start in the EPIC lab,
5
which stands for Electron Probe Instrumentation Center.
6
Here at EPIC, scientists from all over the world use high-powered electron microscopes to characterize a large range of different materials.
7
Scientists such as geologists who study rocks,
8
biologists who study cells, and even scientists who look at individual atoms and teeth use these electron microscopes.
9
But what is an electron microscope?
10
How is it different from a traditional light microscope you see in labs all over the country?
11
What even is a microscope?
12
Let's take a tour of the EPIC facility to learn more about the vast and growing field of microscopy.
13
So what is a microscope?
14
Let's dissect the word.
15
The root scope means to watch or to see,
16
and the prefix micro means extremely small.
17
Together we can see that a microscope is an instrument
18
that allows someone to see a very small object and comes in many shapes and sizes.
19
The microscope you're probably most familiar with is an optical or light microscope.
20
It was developed in the 1600s by scientists who made glasses.
21
are made out of glass lenses that bend light.
22
This makes objects seen through a lens look much bigger or smaller than they actually are.
23
Telescopes, binoculars, microscopes, and cameras are all examples of objects that use glass lenses.
24
In this microscope, a light source travels through a series of glass lenses.
25
The first lens is the eyepiece lens.
26
This makes the image bigger that's produced by what's called the objective lens.
27
The objective lens is the highest power lens that's closest to the sample.
28
Some microscopes have a condenser lens which concentrates the light beam before it travels through your sample.
29
The sample is placed on the stage above the condenser lens and below the objective lens.
30
Light then travels up through the lenses reaching your eye.
31
What we're looking at now is a fly's wing in the light microscope.
32
You can start to see the texture
33
and even the hairs on the fly's wing that you couldn't see before with the naked eye.
34
With the objective lenses on an optical microscope you can magnify the object up to 2,000 times.
35
The way this microscope works is very similar to the microscope you have in your pocket.
36
Light is energy that travels in waves of different wavelengths ranging from about 400 to 700 nanometers.
37
This is visible by the human eye.
38
Using light, we can make objects appear thousands of times larger than they actually are.
39
But what if we want to see something millions of times larger?
40
Something like a cell or a virus?
41
Another form of energy comes as an electron beam.
42
An electron is a very small negative charged particle that is part of an atom.
43
A beam of electrons has a wavelength several orders of magnitude smaller than visible light.
44
In order to use an electron beam to create an image,
45
we have to use a special microscope called an SEM,
46
or a scanning electron microscope.
47
Here is one of our SEMs.
48
It has an electron source at the top of the column
49
that travels through the microscope column itself and into the specimen chamber where the image is created by a series of detectors.
50
You cannot bend an electron beam with glass so you have to use special electromagnetic lenses.
51
The lens set up in electron microscope is very similar to a light microscope.
52
It has a light source or an energy source at the top,
53
a condenser lens, an objective lens,
54
and the sample is kept in a slightly different spot inside the specimen chamber.
55
The image you see from light microscope is projected directly onto your eye.
56
The electron microscope image is processed and displayed on a computer screen.
57
An electron microscope sample is prepared on an aluminum pin stub using special carbon glue or carbon tape.
58
We then coat the sample with metal,
59
something that the electrons can pass through like a filament in your light bulb.
60
If the electrons cannot pass through your sample,
61
charging artifacts can make your image look really messy.
62
Adding a layer of metal can help dissipate the charge buildup on the surface of the sample,
63
making your image look much better.
64
Once the samples are ready,
65
they are inserted into the stage inside the SEM.
66
Inside the SEM you can see the special detectors we use to create the image,
67
as well as the objective lens pull piece that houses the objective lens and where the beam comes out.
68
Now we can close the door and pump down the chamber.
69
We have to remove all the air molecules inside the specimen chamber.
70
If the electron beam interacts with air,
71
it will scatter and not make it to the sample.
72
By removing the air molecules,
73
we create an unobstructed path directly to the sample surface.
74
Now we are ready to go.
75
Let's turn on the beam and see how this works.
76
We move the stage under the pole piece to move around the sample.
77
But how is the image being created?
78
As the beam hits the sample,
79
it interacts and creates secondary electrons that get sucked up by the secondary electron detector inside the chamber.
80
As it scans across the sample,
81
the signal is collected for each point or pixel and creates your image.
82
This is the same fly we were looking at before.
83
Unlike light microscopy,
84
the signal you see in this image is from the surface of the specimen it does not travel through the specimen.
85
Now we can see details on the wing that we couldn't see with the light microscope.
86
Look at the hairs on the surface of the fly's legs.
87
With an electron microscope like this SEM,
88
you can magnify the image up to one million times.
89
This is much greater than the 2,000 times of an optical microscope.
90
This is the fly's leg.
91
We also saw this with the light microscope,
92
but what we didn't see are these hairs on the surface.
93
The electron microscope allows you to achieve resolutions that you are unable to see with a light microscope.
94
Sometimes the charge buildup on the surface of a sensitive sample can make the sample move.
95
Here's the fly's compound eye.
96
Have you ever seen this before by looking at a fly with the naked eye?
97
Can you guess what this is?
98
These tiny squares are about 1 micron wide.
99
That's 1,000th of a millimeter.
100
And makes up the pixels in your cell phone camera.
101
Finally, this is the back end of a spider.
102
It almost looks like the texture in your fingerprint.
103
Another type of signal ejected from the specimen during the electron beam interaction are x-rays.
104
With x-rays, we can determine the chemical composition of a material, like this penny.
105
You can see that this penny is composed of copper and zinc.
106
Since 1982, pennies were no longer made of pure copper and were made of copper-coated zinc.
107
Have you ever noticed that Abraham Lincoln is sitting inside the Lincoln Memorial on a penny?
108
Some other electron microscopes have an ion beam that can mill away your sample or deposit metal on the surface.
109
So what is the difference between a light microscope and an electron microscope?
110
The major difference is that light microscopy uses light as an energy source,
111
whereas electron microscopy uses a beam of electrons.
112
Light microscopy is easy to use,
113
easy to prepare samples, and you can view live specimens.
114
You can also see them in color,
115
but you get much lower resolution and magnification.
116
With an electron microscope you get high resolution,
117
up to 1 million times magnification,
118
with a larger depth of field,
119
but you only get black and white images.
120
You also have to do more involved sample preparation,
121
and you cannot view live specimens.
122
You also need an electrically conductive sample.
123
The invention of the electron microscope changed the world of science forever.
124
It is used in many fields such as biology,
125
medicine, chemistry, geology, material science, and even forensics.
126
Thank you for visiting the EPIC lab at the Nuas Center.
127
We hope that you'll come back sometime and explore inner space with us.
Context & Background
In the video "Intro to Scanning Electron Microscopy (SEM)," experts from the Northwestern Atomic and Nanoscale Characterization Experimental Center offer an insightful tour of their Advanced Electron Probe Instrumentation Center (EPIC). They delve into the world of microscopy, differentiating between traditional light microscopes and advanced scanning electron microscopes (SEM). This educational dialogue aims to familiarize viewers with the inner workings and applications of electron microscopy, demonstrating its crucial role across various scientific fields such as biology, geology, and material science.
Top 5 Phrases for Daily Communication
- What is a microscope? - An inquiry regarding the basic definition of an instrument used for magnifying small objects.
- Let's take a tour. - A phrase expressing the intention to guide someone through a particular space or topic.
- What even is? - A colloquial way to emphasize confusion or curiosity about a concept.
- We can see that. - A phrase used to conclude or clarify information that has been presented.
- This makes objects look bigger. - A statement explaining the primary function of microscopes in enhancing visibility.
Step-by-step Shadowing Guide
Improving your English pronunciation and fluency is essential for effective communication. One effective method to enhance your skills is through shadow speech, a technique where you mimic a speaker to improve your speaking abilities. Here is a step-by-step guide tailored to the content of this video:
- Choose a Shadowing App: Start by selecting a shadowing app or site that allows you to play back the video or audio at varying speeds. This will allow you to understand the nuances of pronunciation and intonation.
- Watch and Listen: Before attempting to shadow, watch the video while actively listening to how the speakers articulate their words. Pay attention to the phrases highlighted above.
- Mimic the Dialogue: Start shadowing by pausing the video after short segments. Repeat what the speaker says, focusing on matching their pronunciation, rhythm, and tone. This practice will help you improve English pronunciation.
- Record Yourself: Use your shadowing app to record your voice as you mimic the speaker. Listening to these recordings can help you identify areas for improvement.
- Practice Regularly: Consistent practice is key. Integrate this shadowing practice into your daily routine to reinforce your learning and build confidence in speaking.
Engaging with this content through shadowing techniques fosters a deeper understanding of English vocabulary and scientific terminology, making it easier for you to communicate effectively in professional and academic settings.
¿Qué es la Técnica de Shadowing?
Shadowing es una técnica de aprendizaje de idiomas respaldada por la ciencia, desarrollada originalmente para la formación de intérpretes profesionales y popularizada por el políglota Dr. Alexander Arguelles. El método es simple pero poderoso: escuchas audio en inglés nativo y lo repites en voz alta de inmediato, como una sombra que sigue al hablante con solo 1-2 segundos de retraso. A diferencia de la escucha pasiva o los ejercicios de gramática, el shadowing obliga a tu cerebro y músculos de la boca a procesar y reproducir simultáneamente patrones de habla reales. Las investigaciones muestran que mejora significativamente la precisión de la pronunciación, la entonación, el ritmo, el habla conectada, la comprensión auditiva y la fluidez al hablar, convirtiéndola en una de las metodologías más efectivas para la preparación del IELTS Speaking y la comunicación en inglés en el mundo real.