跟讀練習: Intro to Scanning Electron Microscopy (SEM) - 通過影片學習英語口語

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Welcome to the Technological Institute at Northwestern University.

Today we are going to tour the Northwestern Atomic and Nanoscale Characterization Experimental Center,

or the Nuance Center.

We're going to start in the EPIC lab,

which stands for Electron Probe Instrumentation Center.

Here at EPIC, scientists from all over the world use high-powered electron microscopes to characterize a large range of different materials.

Scientists such as geologists who study rocks,

biologists who study cells, and even scientists who look at individual atoms and teeth use these electron microscopes.

But what is an electron microscope?

How is it different from a traditional light microscope you see in labs all over the country?

What even is a microscope?

Let's take a tour of the EPIC facility to learn more about the vast and growing field of microscopy.

So what is a microscope?

Let's dissect the word.

The root scope means to watch or to see,

and the prefix micro means extremely small.

Together we can see that a microscope is an instrument

that allows someone to see a very small object and comes in many shapes and sizes.

The microscope you're probably most familiar with is an optical or light microscope.

It was developed in the 1600s by scientists who made glasses.

are made out of glass lenses that bend light.

This makes objects seen through a lens look much bigger or smaller than they actually are.

Telescopes, binoculars, microscopes, and cameras are all examples of objects that use glass lenses.

In this microscope, a light source travels through a series of glass lenses.

The first lens is the eyepiece lens.

This makes the image bigger that's produced by what's called the objective lens.

The objective lens is the highest power lens that's closest to the sample.

Some microscopes have a condenser lens which concentrates the light beam before it travels through your sample.

The sample is placed on the stage above the condenser lens and below the objective lens.

Light then travels up through the lenses reaching your eye.

What we're looking at now is a fly's wing in the light microscope.

You can start to see the texture

and even the hairs on the fly's wing that you couldn't see before with the naked eye.

With the objective lenses on an optical microscope you can magnify the object up to 2,000 times.

The way this microscope works is very similar to the microscope you have in your pocket.

Light is energy that travels in waves of different wavelengths ranging from about 400 to 700 nanometers.

This is visible by the human eye.

Using light, we can make objects appear thousands of times larger than they actually are.

But what if we want to see something millions of times larger?

Something like a cell or a virus?

Another form of energy comes as an electron beam.

An electron is a very small negative charged particle that is part of an atom.

A beam of electrons has a wavelength several orders of magnitude smaller than visible light.

In order to use an electron beam to create an image,

we have to use a special microscope called an SEM,

or a scanning electron microscope.

Here is one of our SEMs.

It has an electron source at the top of the column

that travels through the microscope column itself and into the specimen chamber where the image is created by a series of detectors.

You cannot bend an electron beam with glass so you have to use special electromagnetic lenses.

The lens set up in electron microscope is very similar to a light microscope.

It has a light source or an energy source at the top,

a condenser lens, an objective lens,

and the sample is kept in a slightly different spot inside the specimen chamber.

The image you see from light microscope is projected directly onto your eye.

The electron microscope image is processed and displayed on a computer screen.

An electron microscope sample is prepared on an aluminum pin stub using special carbon glue or carbon tape.

We then coat the sample with metal,

something that the electrons can pass through like a filament in your light bulb.

If the electrons cannot pass through your sample,

charging artifacts can make your image look really messy.

Adding a layer of metal can help dissipate the charge buildup on the surface of the sample,

making your image look much better.

Once the samples are ready,

they are inserted into the stage inside the SEM.

Inside the SEM you can see the special detectors we use to create the image,

as well as the objective lens pull piece that houses the objective lens and where the beam comes out.

Now we can close the door and pump down the chamber.

We have to remove all the air molecules inside the specimen chamber.

If the electron beam interacts with air,

it will scatter and not make it to the sample.

By removing the air molecules,

we create an unobstructed path directly to the sample surface.

Now we are ready to go.

Let's turn on the beam and see how this works.

We move the stage under the pole piece to move around the sample.

But how is the image being created?

As the beam hits the sample,

it interacts and creates secondary electrons that get sucked up by the secondary electron detector inside the chamber.

As it scans across the sample,

the signal is collected for each point or pixel and creates your image.

This is the same fly we were looking at before.

Unlike light microscopy,

the signal you see in this image is from the surface of the specimen it does not travel through the specimen.

Now we can see details on the wing that we couldn't see with the light microscope.

Look at the hairs on the surface of the fly's legs.

With an electron microscope like this SEM,

you can magnify the image up to one million times.

This is much greater than the 2,000 times of an optical microscope.

This is the fly's leg.

We also saw this with the light microscope,

but what we didn't see are these hairs on the surface.

The electron microscope allows you to achieve resolutions that you are unable to see with a light microscope.

Sometimes the charge buildup on the surface of a sensitive sample can make the sample move.

Here's the fly's compound eye.

Have you ever seen this before by looking at a fly with the naked eye?

Can you guess what this is?

These tiny squares are about 1 micron wide.

That's 1,000th of a millimeter.

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And makes up the pixels in your cell phone camera.

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Finally, this is the back end of a spider.

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It almost looks like the texture in your fingerprint.

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Another type of signal ejected from the specimen during the electron beam interaction are x-rays.

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With x-rays, we can determine the chemical composition of a material, like this penny.

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You can see that this penny is composed of copper and zinc.

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Since 1982, pennies were no longer made of pure copper and were made of copper-coated zinc.

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Have you ever noticed that Abraham Lincoln is sitting inside the Lincoln Memorial on a penny?

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Some other electron microscopes have an ion beam that can mill away your sample or deposit metal on the surface.

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So what is the difference between a light microscope and an electron microscope?

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The major difference is that light microscopy uses light as an energy source,

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whereas electron microscopy uses a beam of electrons.

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Light microscopy is easy to use,

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easy to prepare samples, and you can view live specimens.

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You can also see them in color,

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but you get much lower resolution and magnification.

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With an electron microscope you get high resolution,

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up to 1 million times magnification,

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with a larger depth of field,

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but you only get black and white images.

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You also have to do more involved sample preparation,

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and you cannot view live specimens.

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You also need an electrically conductive sample.

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The invention of the electron microscope changed the world of science forever.

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It is used in many fields such as biology,

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medicine, chemistry, geology, material science, and even forensics.

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Thank you for visiting the EPIC lab at the Nuas Center.

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We hope that you'll come back sometime and explore inner space with us.

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背景與上下文

在這段影片中，主持人帶領觀眾參觀西北大學的技術學院，特別介紹了原子和奈米尺度表徵實驗中心。影片深入探討了電子顯微鏡的工作原理，以及它與傳統光學顯微鏡的區別。主持人通過生動的例子，幫助觀眾理解顯微鏡的基本概念及其在科學研究中的重要性。這段對話富有資訊量，適合想要提升英語聽說能力的學習者。

日常交流的五個關鍵短語

What is a microscope?（顯微鏡是什麼？）
It allows someone to see a very small object.（它讓人們能夠看到非常小的物體。）
How is it different from a traditional light microscope?（它與傳統光學顯微鏡有什麼不同？）
Light travels through a series of glass lenses.（光通過一系列玻璃鏡頭傳播。）
We need a special microscope called an SEM.（我們需要一個叫做掃描電子顯微鏡的特殊顯微鏡。）

逐步跟讀指南

要有效地掌握這段影片中的內容，以下是推薦的逐步跟讀方法：

觀看影片: 首先觀看整個影片，瞭解主要內容和主題。注意觀看時的聽力和理解。
選取短句: 從上述五個關鍵短語中，選擇你最感興趣的句子進行重點練習。
逐句跟讀: 一邊播放影片，一邊暫停，模仿主持人的發音和語調，儘量做到準確、流利。
重複練習: 多次重複跟讀，直到你能流利地說出這些句子，幫助你提高英語發音。
使用Shadowing Site: 利用線上資源進行更多的雅思口語練習，鞏固所學內容，提升你的口語能力。

通過這種有系統的練習方法，你可以在看YouTube學英語的同時，不斷提高自己的口語表達和聽力理解能力。記得堅持shadow speak，將每次的練習變成進步的階梯！

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	was developed · are made · is placed
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	Have you ever seen · Have you ever noticed

什麼是跟讀法？

跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

影子跟讀法: 閱讀完整分步指南 →

跟讀練習: Intro to Scanning Electron Microscopy (SEM) - 通過影片學習英語口語

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背景與上下文

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逐步跟讀指南

影片中的語法

什麼是跟讀法？