MCQ/MSQ on Materials Characterization such as Scanning Electron / Ion / Probe Microscopy

QUESTION 1: 

In a scanning electron microscope, the light source is replaced by a beam of very fast-moving                              . 

a.  Proton

b.  Neutron

c.   Electron

d.  Photon

Correct Answer: c. Electron 

Detailed Solution: the electron is used as a source in an electron microscope as it can generate secondary electron as a signal after bombarding on the specimen. 

QUESTION 2: 

Which of the following electron gun can provide the best resolution to examine the materials of size less than 1 nm? 

a.  Thermionic gun

b.  LaB₆ gun

c.   Field emission gun

d.  Schottky gun

Correct Answer: c. Field emission gun 

Detailed Solution: The tip size/diameter of the field emission gun is the smallest, resulting in the finest electron beam. In a field emission gun, electrons are generated at room temperature from the tip of the gun by applying an electric field through the tunneling mechanism

QUESTION 3: 

Which of the following is preferred for a high-resolution 3D image of a sample? 

a.  Sscanning electron microscope

b.  Transmission electron microscope

c.   Compound microscope

d.  Helium ion microscope

Correct Answer: d. Helium ion microscope 

Detailed Solution: For a 3D image, the transmission mode will not work. A helium ion microscope offers higher resolution and depth of field using ion beams instead of light or electron.

QUESTION 4: 

Why a scanning ion microscope provides a higher resolution than a scanning electron microscope at the same acceleration voltage (beam energy)? 

a.  Shorter wavelength of ions as compared to electrons

b.  Longer wavelength of ions as compared to electrons

c.   Smaller angle of aperture or divergence angle of the beam

d.  Larger spot size of ion beam

Correct Answer: a. Shorter wavelength of ions as compared to electrons 

Detailed Solution: The resolution of a microscope is directly proportional to wavelength and inversely proportional to the angle of aperture. The heavier  mass of ions as compared to electrons leads to a shorter wavelength of ions.

QUESTION 5: 

Which of the following is/are true for electron microscopy? 

a.  Specimen should be dry

b.  Electron beam must pass through an evacuated chamber

c.   Image can be obtained on a phosphorescent screen or any display

d.  All of the above

Correct Answer: d. All of the above 

Detailed Solution: Specimens must be completely dehydrated prior to examination; otherwise, it is difficult to maintain a high vacuum. Since electrons can travel only in high vacuum, the entire electron path through the instrument must be evacuated. The magnified image may be viewed on a phosphorescent or fluorescent screen.

QUESTION 6: 

If the eyepiece of a microscope magnifies by 10, and the objective lens magnifies by 4, then what is the total magnification of the microscope?

a. 14

b. 2.5

c. 40

d. 0.4

 

Correct Answer: c. 40 

Detailed Solution: Total magnification is the product of magnification power of the eyepiece lens and objective lens.

QUESTION 7:

On what factors do the intensity of secondary electrons depend upon?

a.  Shape of the irradiated object

b.  Chemical composition of the irradiated object

c.   Number of electrons ejected

d.  All of the above

Correct Answer: d. All of the above

Detailed Solution: Upon electron beam is incident on the specimen in an SEM, secondary electrons (signal) are ejected from the specimen proportional to the number of electrons striking the detector. The intensity or the number of secondary electrons depends on the shape and the chemical composition of the irradiated object and also on the number of electrons ejected.

QUESTION 8:

What is the main bottleneck parameter of electron microscopes, due to which resolution can’t be further improved?

a.  Diameter of the source beam

b.  Beam current

c.   Working distance

d.  None of the above

Correct Answer: a. Diameter of the source beam

Detailed Solution: The diameter of the focused electron beam can be reduced in size no further. In practical terms, the smallest beam spot that can be anticipated is in the order of 0.5–1.0 nm in diameter. Hence, the electron microscope is now close to reaching its absolute limit of imaging performance.

QUESTION 9:

Which of the following is not a component of an STM (scanning tunneling microscope)?

a.  Cantilever

b.  Tip sensor

c.   Piezoelectric scanner

d.  Feedback control

Correct Answer: a. Cantilever 

Detailed Solution: Tip, piezoelectric scanner, and feedback controller are important STM components, but there is no cantilever. When the tip is replaced by a tip-cantilever system, it is an AFM.

QUESTION 10:

Which of the following microscope is best suited to measure the thickness of 2D materials with 1 or 2 layers?

a.  Scanning electron microscopy (SEM)

b.  Helium ion microscopy (HIM)

c.   Transmission electron microscopy (TEM)

d.  Atomic force microscopy (AFM)

Correct Answer: d. Atomic force microscopy (AFM) 

Detailed Solution: Atomic force microscope provides the best resolution along the z-axis, thus measuring the thickness of a layer in the angstrom range.

QUESTION 11:

Resolving power of an electron microscope is a function of                   .

a.  Wavelength of electron used

b.  Numerical aperture of the lens system

c.   Mass of the electron

d.  both (a) and (b)

Correct Answer: d. both (a) and (b) 

Detailed Solution: The ability of a microscope to distinguish two adjacent points as a distinct and separate entity is known as resolving power. Resolving power is a function of the wavelength of electron used and the numerical aperture (NA) of the lens system. NA refers to the refractive index of the medium multiplied with the sine value of the half aperture angle.

QUESTION 12:

Which of the following statement is true for an electron microscope?

a.  Higher the angle of aperture, smaller will be the achromatic aberration

b.  Higher the angle of aperture, smaller will be the chromatic aberration

c.   Smaller the angle of aperture, smaller will be the diffraction aberration

d.  Smaller the angle of aperture, smaller will be the spherical aberration

Correct Answer: d. Smaller the angle of aperture, smaller will be the spherical aberration 

Detailed Solution: The half-angle of aperture (a) is directly related to spherical aberration.

 QUESTION 13:

Which of the following properties of an electron makes it possible to scan the electron beam over the surface in an SEM?

a.  It has smaller mass

b.  It has charge

c.   It has smaller wavelength

d.  It has less scattering effect

Correct Answer: b. It has charge 

Detailed Solution: The charge of electrons makes it possible to scan using deflector coils.

 QUESTION 14:

If the magnification of a lens is dependent on the distance from the principal axis, the aberration that arises is called                        

a.  Coma

b.  Astigmatism

c.   Curvature

d.  Distortion

Correct Answer: d. Distortion 

Detailed Solution: Distortion is the defect that arises when the images of equal parts of an object will not be of the same length. In such a case, the lens's magnification depends on the distance from the principal axis.

 QUESTION 15:

Which of the following electron gun requires maximum vacuum for the operation?

a.  Thermionic gun

b.  LaB₆ gun

c.   Field emission gun

d.  Schottky emission gun

Correct Answer: c. Field emission gun 

Detailed Solution: The tip size of the field emission gun is the smallest and thus needs a high vacuum for its stability.

 QUESTION 16:

Which of the following is the correct pathway of electrons in the SEM?

a.  Anode → condenser lens → deflectors → objective lens → sample → detector

b.  Anode → deflectors → condenser lens → objective lens → sample → detector

c.   Cathode → condenser lens → deflectors → objective lens → sample → detector

d.  Cathode → deflectors → condenser lens → objective lens → sample → detector

Correct Answer: c. Cathode → condenser lens → deflectors → objective lens → sample → detector 

Detailed Solution: Electron gun is the cathode, placed at a negative potential. Then condenser lens is used to condense the electron beam, deflectors to scan the electron beam, the objective lens to focus the beam on the sample, and finally, signal from the sample goes to the detector.

 QUESTION 17:

The major advantages of the scanning electron microscope include all of the following except:

a.  Producing colored images

b.  Its great depth of field

c.   Its high-resolution

d.  Its high magnification

Correct Answer: a. Producing colored images 

Detailed Solution: SEM has a high resolution, magnification power, and depth of field but cannot produce color images because the signal's energy does not fall in the visible length of electromagnetic radiation.

QUESTION 18:

The cathode current density of a tungsten thermionic gun will be in the range of                  (A/cm²) at 2700 K. Consider work function of tungsten as 4.5 eV and the constant A_c = 120 A/cm² K².

a. 2 to 3

b. 3.0 to 3.3

        c. 3.3 to 3.6

d. 0.001 to 0.003

Correct Answer: c. 3.3 to 3.6

Detailed Solution: Use the formula J_c = A_c T² exp (-f / kT)

 QUESTION 19:

The brightness of an electron gun is

a.  Directly proportional to both probe current and probe diameter

b.  Inversely proportional to both probe current and probe diameter

c.   Directly proportional to probe current but inversely related to probe diameter

d.  Inversely proportional to probe current but directly proportional to probe diameter

Correct Answer: c. Directly proportional to probe current but inversely related to probe diameter

 

QUESTION 20:

Which of the following objective lens is best suited for magnetic samples to be examined by an SEM at high magnification with high resolution?

a.  Out-of-lens type

b.  In-lens type

c.   Pinhole lens

d.  Semi-in-lens type

Correct Answer: d. Semi-in-lens type 

Detailed Solution: Semi-in-lens type in which the sample is not kept inside the lens. Thus, the magnetic field of the sample cannot affect the electron beam. It also allows the magnetic field of the lens to reach out to the specimen below the lens, allowing high-resolution measurement.

 

QUESTION 21:

The probe current of an electron beam in an SEM depends on         . (Fill in the blanks)

a.  Spherical aberration coefficient

b.  Probe diameter

c.   Brightness

d.  All of the above

QUESTION 22:

When an electron beam hits the sample, the formed interaction volume increases with              (1)      beam energy and     (2)      atomic number. (Fill in the blanks)

a.  (1) increasing, (2) increasing

b.  (1) increasing, (2) decreasing

c.   (1) decreasing, (2) decreasing

d.  (1) decreasing, (2) increasing

Correct Answer: b. (1) increasing, (2) decreasing 

Detailed Solution: When an electron beam hits the sample, the formed interaction volume increases with increasing beam energy and decreasing atomic number.

 QUESTION 23:

The SE3 signal in an SEM analysis is generated from 

a.  Primary electron beam

 b.  BSE  

c.   SE1

d.  SE2

 Correct Answer: b. BSE

 QUESTION 24:

Which electron signal will be your choice if you want to generate an atomic number contrast in your SEM analysis?

a.  SE1

b.  SE2

c.   SE3

d.  BSE

Correct Answer: d. BSE

Detailed Solution: The monotonic increase in the BSE coefficient provides atomic number contrast or Z contrast in the image.

 QUESTION 25:

The bias voltage applied to the E-T detector in SEM is

a.  ~ 100 eV

b.  ~ 1 kV

c.   ~ 5 kV

d.  ~ 10 kV

Correct Answer: d. 10 kV 

Detailed Solution: The energy of secondary electrons (< 50 eV) is too low to excite the scintillator. Thus, they are first accelerated by applying a bias voltage of ~10-12 kV to an Al film coated on the scintillator.

QUESTION 26:

To increase the secondary electron yield from the backscattered electrons,       layer is coated on the target. (Fill in the blank)

a.  MnO₂

b.  MgO

c.   ZnO

d.  Pt

Correct Answer: b. MgO 

Detailed Solution: To improve the secondary electron yield, the converter target is covered with a thin layer of MgO, which has a high secondary electron yield.

QUESTION 27:

Which of the following should not be done to reduce the charge-up phenomenon in SEM?

a.  Reduce the accelerating voltage

b.  Low vacuum

c.   Reduce the sample irradiating current

d.  Low scan rate

Correct Answer: d. Low scan rate 

Detailed Solution: To avoid the charge-up phenomenon high scan rate should be used so that the beam does not make contact with the sample for a longer period of time.

QUESTION 28:

For a high-resolution surface image of your sample, what will be your choice of accelerating voltage from the following?

a.  5 kV

b.  10 kV

c.   15 kV

d.  20 kV

Correct Answer: a. 5 kV

 Detailed Solution: The 5-kV image will show greater surface detail due to low penetration power/depth. The high-kV image will have a loss of surface information due to large beam penetration.

 QUESTION 29:

Which types of samples cannot be directly examined in an SEM?

a.  Powder samples

b.  Insulating samples

c.   Wet samples

d.  Thin films

Correct Answer: b. Insulating samples c. Wet samples

Detailed Solution: Insulating samples cannot be examined directly because of surface charge-up, and thus they must be coated with a metal. As SEM is operated under a high vacuum, wet samples cannot be examined directly with an SEM.

QUESTION 30:

Which of the following electron gun is best suited to achieve the highest resolution?

a.  Thermionic gun

b.  LaB₆ gun

c.   Field emission gun

d.  Schottky emission gun

 Correct Answer: c. Field emission gun 

Detailed Solution: The field emission gun has the smallest apex diameter and can produce the smallest probe diameter, which is a primary criterion to obtain high-resolution images.

QUESTION 31:

      (1)      objective aperture and     (2)      working distance is preferred to obtain high-resolution images in SEM. (Fill in the blanks)

a.  (1) Large, (2) Large 

b.  (1) Large, (2) Small

c.   (1) Small, (2) Small

d.  (1) Small, (2) Large

 

Correct Answer: b. (1) Large, (2) Small

Detailed Solution: Large objective aperture and small working distance is preferred to obtain high-resolution images as it allows obtaining the smallest probe size.

 

QUESTION 32:

Contamination on the sample surface will increase if there is 

a.  Poor vacuum in the sample chamber 

b.  Good vacuum in the sample chamber 

c.   High acceleration voltage

d. Low acceleration voltage

 

Correct Answer: a: Poor vacuum in the sample chamber c: High acceleration voltage

Detailed Solution: In addition to poor vacuum, high acceleration voltage will increase the contamination on the sample surface due to energetic beam interacting with the gas particles around the sample surface.

QUESTION 33:

The transition of an electron from M shell to K shell will produce which of the following x-ray line?

a.  Ka

b.  Kb

c.   Kg

c. La

 

Correct Answer: b. Kb

Detailed Solution: Transition of an electron from L to K shell, M to K shell, and N to K shell produces Ka, Kb, and Kg lines, respectively. On the other hand, the transition of M to L shell produces La lines.

QUESTION 34:

What can be done to improve x-ray collection efficiency for the EDS?

a.  Place the detector close to sample 

b.  Detector with small surface area should be used

c.   Place detector away from sample

d.  Detector with large surface area should be used

 

Correct Answer: a. Place detector close to sample d. Detector with large surface area should be used

Detailed Solution: If we place detector close to the sample and the surface area of the detector is large, it will increase the X-ray collection efficiency as chances of loss of X-ray will be reduced.

 

QUESTION 35:

The energy of a particular x-ray line increases with increase in the

a.  Energy of incident electron beam

b.  Atomic number of the sample

c.   Performance of the x-ray detector

d.  None of the above 

 

Correct Answer: b. Atomic number of the sample 

Detailed Solution: The energy of the x-ray line (for example, Ka) follows the Moseley’s Law, i.e., E = A (Z - C)².

 

QUESTION 36:

The EDX detector is made from which of the following material

a.  p-n junction of Si

b.  p-i-n junction of Si

c.   p-i-n junction of Si with insulating part doped with Li

d.  Yttrium aluminum garnet (YAG) 

 

Correct Answer: c. p-i-n junction of Si with insulating part doped with Li 

Detailed Solution: The detector of the energy-dispersive x-ray spectrometer is a p-i-n detector of Si in which Li is doped in the insulating part.

QUESTION 37:

What is/are the bottleneck(s) of the SEM due to which resolution can’t be further enhanced?

a.  Probe diameter

b.  Wavelength of the incident radiation

c.   Electron diffraction

d.  All of these

 

Correct Answer: d. All of these 

Detailed Solution: The probe diameter and wavelength cannot be decreased further for the SEM operated in the range of accelerating voltage up to 30 kV. The electron diffraction is another reason that limits the resolution of SEM.

QUESTION 38:

Which of the following statement(s) is/are correct for a field ion microscope?

a.  The sample to be viewed is used as an emitter while biased positively

b.  The sample to be viewed is used as an emitter while biased negatively

c.   The source must be metal

d.  Both a and c

e.   Both b and c

 

Correct Answer: d. Both a and c 

Detailed Solution: Any metal can be used as an emitter to view its surface. The source/sample must be biased positively relative to the counter electrode.

 

QUESTION 39:

In a field ion microscope, the magnitude of the field at the tip depends on which of the following parameter(s).

a.  Work function of the tip material

b.  Potential difference between tip and counter electrode

c.   Diameter of tip

d.  All of the above

 

Correct Answer: b: Potential difference between tip and counter electrode c: Diameter of tip 

Detailed Solution: The electric field on the tip, E = V/R, where E is the magnitude of electric field, V is the potential difference between electrodes, and R is the radius of the tip.

 

QUESTION 40:

In the current generation helium ion microscope, the source/tip fabricated by ALIS Corporation is

a.  An atomically sharp tip (with one atom at tip)

b.  A trimer with three atoms at its apex

c.   A hexamer with six atoms at its apex

d.  A LaB₆ gun 

 

Correct Answer: b. A trimer with three atoms at its apex

Detailed Solution: The tungsten tip with a trimer (three atoms at the tip) demonstrated by ALIS Corporation is currently used in HIM for its greater stability and strong enough field for helium ionization to produce emission current of about 100 pA.

 

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