Energy-Dispersive X-ray Spectroscopy: Basic Function

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来自 Duke University 的课程

Nanotechnology: A Maker’s Course

260 个评分

Duke University

Nanotechnology: A Maker’s Course

260 个评分

How can we create nano-structures that are 10,000 times smaller than the diameter of a human hair? How can we “see” at the nano-scale? Through instruction and lab demonstrations, in this course you will obtain a rich understanding of the capabilities of nanotechnology tools, and how to use this equipment for nano-scale fabrication and characterization. The nanoscale is the next frontier of the Maker culture, where designs become reality. To become a Nanotechnology Maker pioneer, we will introduce you to the practical knowledge, skills, and tools that can turn your nanotechnology ideas into physical form and that enable you to image objects at the nano-scale. This course has been developed by faculty and staff experts in nano-fabrication, electron beam microscopy, and nano-characterization through the Research Triangle Nanotechnology Network (RTNN). The RTNN offers training and use of the tools demonstrated in this course to schools and industry through the United States National Nanotechnology Coordinated Infrastructure program. The tools demonstrated in this course are available to the public through the RTNN.

从本节课中

Nano Measurement and Characterization Tools: Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy

After this module, you will be able to explain sample preparation and imaging techniques used in scanning electron microscopy. You will also be able to explain the benefits of environmental scanning electron microscopy. Furthermore, you will discover how energy-dispersive x-ray spectroscopy can be paired with scanning electron microscopy to gain elemental information about samples.

Energy-Dispersive X-ray Spectroscopy: Basic Function4:43

Energy-dispersive X-ray Spectroscopy: Sample Preparation Demonstration2:17

Energy-Dispersive X-ray Spectroscopy: Measurement Demonstration4:16

与讲师见面

Nan M. Jokerst
J. A. Jones Professor of Electrical and Computer Engineering
Electrical and Computer Engineering, Duke University
Carrie Donley
Director of CHANL (Chapel Hill Analytical and Nanofabrication Laboratory)
Applied Physical Sciences, UNC Chapel Hill
James Cahoon
Assistant Professor
Chemistry, UNC Chapel Hill
Jacob Jones
Professor
Materials Science and Engineering, North Carolina State University

Hello. I'm Roberto Garcia.

I'm a lab manager at the Analytical Instrumentation Facility at NC State University,

part of the Research Triangle Nanotechnology Network.

In this video, you will learn the basics of energy-dispersive X-ray spectroscopy or EDS.

EDS is a non-destructive analytical technique.

It provides information on the elemental and chemical composition of a sample.

EDS essentially allows us to determine what something is made out of.

To perform an EDS experiment,

we need an electron microscope,

a special detector known as an EDS detector,

and software to analyze the data.

You may be wondering how a microscope,

a tool that are used primarily for imaging can provide elemental or chemical information.

In electron microscope, a high-energy electron beam is accelerated towards the specimen.

When the electron beam hits the atoms that make up the sample,

electron signals are generated such as secondary and backscattered electrons.

These electrons signals are used to produce an image of the sample.

However, electrons are not the only signals

generated as a result of the beam interacting with the sample.

The beam also causes X-rays to be emitted from the sample.

To understand how this happens,

let's consider a single atom in the sample.

When an electron from the incident beam imparts enough energy to the sample,

an electron can be ejected from one of the atom's electron shells.

This leaves a vacancy like a hole in

the electron shell where the electron originally was.

For the atom to return to a stable state,

an electron must replace the one that was emitted.

An electron from a higher energy shell will drop down into this lower energy shell.

When an electron from a higher energy outer shell

dropped into a lower energy shell vacancy,

it must lose some of its original energy.

The electrons excess energy is emitted in the form of an X-ray.

This X-ray can be detected by the EDS detector and

analyzed by software to identify the element that it came from.

How can an X-ray identify a specific element?

Well, not all X-rays are alike.

X-rays can have varying energies measured in kiloelectron volts or keV for short.

They can also have different wavelengths.

In energy-dispersive spectroscopy, we are

analyzing the energy of the X-rays generated from the sample.

When X-rays are emitted from a sample in an SEM,

the energy of each generated X-ray will be dictated by

the elements present and the electron shells that make up the atoms.

Basically, this means each element will have its own unique identifying X-ray signal,

just like how humans each have their own unique fingerprint.

Analyzing this signal for an EDS experiment involves measuring the energy of each

characteristic X-ray signal and counting how often that particular energy signal appears.

The special detector must be installed on

the electron microscope to detect and measure these signals,

simply called an EDS detector.

The beam hits the sample,

characteristic energy signals are generated from the sample,

and the EDS detector amplifies and measures the energy of the X-ray.

Then analysis software counts the amount of X-rays at

each energy and plots them on a graph called a spectrum.

On this spectrum, the software plots the number of X-rays as count or intensity on

the y-axis versus the energy of the photons counted

in thousands of electron volts or kiloelectron volts,

keV, on the x-axis.

Remember, each element has its own characteristic X-rays,

each with a unique energy measured in keV.

EDS software helps to match

the measured piece along the x-axis with their respective elements.

EDS software makes it easy to match

these piece with the corresponding elements that they originated from.

Here are important things to note about EDS.

Some elements have overlapping energy peaks with other elements.

Careful analysis and experience will help avoid a misidentification.

EDS requires a lot of energy to generate enough signal to get a conclusive result.

Generally speaking, you want to make sure you are

exciting enough X-rays by using a high voltage in the range of

15 to 30 kV to produce plenty of

signal that can be used to identify elements present in the sample.

Some elements are not detectable and others pose difficulties for EDS analysis.

For instance, hydrogen and helium do not have characteristic X-rays.

Similarly, lithium and beryllium produce X-rays that are too low-energy to be detected.

Despite these challenges, EDS is nonetheless

a very useful and simple narrow measurement technique to provide

very fast elemental information in many different types of samples.

Thank you for watching this video.

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