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Prep, characterisation and structures of nano Flashcards

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1
Q

name 10 different types of synthesis

A 
hydrothermal
solvothermal
biomimetic
electrochemical
solvent-free
self-assembly
templating
dip-coating
exfoliation and cleavage
surface reaction controlled directional
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2
Q

what is hydrothermal synthesis

A

high temperature aqueous solutions at high vapour pressure to make a crystal

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3
Q

give examples of structures made by hydrothermal synthesis

A

H2Ti3O7 nanotubes

TiO2 + NaOH at 100C for 3 days - flat sheets rolled into layers using Na+ ions

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4
Q

what is solvothermal synthesis?

A

pressurised polar solvents at a temp above their bp

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5
Q

how does adding water affect a solvothermal synthesis

A

makes the single crystals hollow

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6
Q

how do you control size in solvothermal synthesis

A

via surface protection by organic molecules

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7
Q

give some examples of materials made by solvothermal synthesis

A

Nanotubes of perovskite
MOF-5
MnO3 crystallites on graphene

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8
Q

What is EEG? and give some properties

A

electrochemically exfoliated graphene
low level of defects, no O containing surface functional groups, mechanically strong, high conductivity, insoluble in water, soluble in DMF

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9
Q

What is GO? and give some properties

A

high level of defects, many OH groups, mechanically weak, low conductivity, soluble in water

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10
Q

what is biomimetic synthesis

A

application of biological principles for materials formation

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11
Q

give some examples of biomimetic synth

A

hydrothermal growth of ZnO twin-crystals with Gelatin or Gum Arabic
Calcite nanocrystals grown in alienate beads (controls size)

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12
Q

what compounds are made from electrochemical synthesis

A

anodic aluminium oxide (AAO)

anodic titanium oxide (ATO)

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13
Q

what is the ideal pore base shape according to the equifield strength model?

A

hemispherical

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14
Q

what is the main structural feature of compounds made by electrochemical synthesis

A

cylindrical pores

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15
Q

name a mechanism used in solvent-free synthesis

A

VLS - vapour-liquid-solid

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16
Q

what cal be made by VLS

A

Si nanowire

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17
Q

what controls the shape of a Si nanowire?

A

direction controlled by AAO holes, diameter controlled by size of gold

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18
Q

what compound is used for liquid coating to begin a Si nanowire?

A

SiH4

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19
Q

what is another example of a solvent -free synthesis?

A

catalytic growth by Co nanoparticles on Mg2SiO2 fibres

or Chemical Vapour Deposition eg carbon encapsulated Co nanoparticles

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20
Q

what is a benefit of chemical vapour deposition

A

low reaction temperature
low carbon concentration
short rxn time

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21
Q

what is the self-assembly phenomenon

A

then particles naturally form larger nanostructures

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22
Q

give 3 examples of self-assembly phenomenon

A

C60 nanowires
self assembly of surfactants used to template formation of mesoporous silicates
monolayer on a metal surface (alkanethiolate on Au(III) substrate)

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23
Q

give 3 examples of templating methods

A

porous single crystals - make porous structure (KIT-6) and fill with H2Cr2O7
AAO templated Si or Ni nanowire
electron beam induced metal nanowire growth - zeolite containing AgNO3 or CuCl irradiate with e beam giving ag or Cu nanowire.

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24
Q

what are the 5 stages of dip-coating?

A

1) immersion
2) start-up
3) deposition
4) drainage
5) evaporation of solvent

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25
how do you control thickness of a layer in dip-coating?
depends on how fast substrate pulled out of coating liquid.
26
what are 3 things that can be made from exfoliation and cleavage methods?
graphene (top-down synthesis) -intercalation of ions followed by exfoliation of layer (by EtOH) H2Ti3O7 nano sheet unrolled from a nanotube using ligands. nanotube made from crystal layers separated by Na+ ions disassembly of 3D UTL framework into a 2D lamellae
27
what is the general shape of a structure formed by a surface reaction controlled by highly selective growth direction?
snowflakes
28
how to make a snowflake shaped Fe2O3 (hematite)
K3Fe(CH)6 + H2O --> (180C 20h) --> a-Fe2O3 1) nucleation 2)very slow hydrolysis of Fe(CN)6 3- only grows along 110 directions
29
give some examples of how to control size and morphology.
nanoparticle by cleavage - thickness of layers and minimum lattice tension Si wires by AAO - using nanotube template Dip coating - thickness of liquid film catalytic growth of Si nanowire - size of catalyst Porous single crystals - Size of mesopores C60 nanowires - thickness of solution film surface protection - reaction rate.
30
what is braggs law?
n(lambda) = 2dsin(theta)
31
what determines peak position in XRD
function of d-spacings --> each peak accounts for a miller plane
32
what determines peak intensities in XRD?
intensity proportional to |F|^2
33
what determines peak width in XRD?
(width = FWHM - full width half height) | size of crystal - narrow peak = big crystal
34
what are the 2 types of electrons picked up on by SEM
backscattered and secondary
35
what does a secondary electron tell you in SEM?
morphology and type of material
36
what info do backscattered electrons give in SEM?
number of backscattered electrons reaching the detector is proportional to the atomic number of the sample.
37
what are ways of improving resolution of SEM + problems
a shorter wavelength of incoming energy gives higher res BUT a higher energy gives more damage to the sample beam size working distance
38
what does TEM show?
direct structural images
39
what are the 3 image formation mechanisms of TEM?
Mass-thickness contrast Diffraction contrast Phase contrast
40
what is SAED?
selective area electron diffraction
41
what do you need to do to reduce problems arising from spherical aberration
always want to under-focus the electron microscope to increase contrast
42
how to increase mass-thickness contrast?
1) choose smaller objective aperture | 2) use a lower accelerating voltage
43
Explain EDX spectroscopy
outer shell electron jumps into inner shell hole and releases x-rays
44
what is a big problem you have to take into consideration with EDX?
dead time - keep between 20-30% otherwise could give false elemental analysis
45
What is the procedure for EDX?
use a reference sample with a similar composition to sample. Calculate K for alpha peaks then calculate the ratio for the solid solution. Do this 20-30 times and find avg value.
46
what is a good sample material to use for EDX?
1) monobasic 2) similar composition 3) similar specimen thickness 4) >30 particles to find average for K
47
what counts as a good peak for EDX?
high intensity, high energy no overlapping
48
what is the main premise of STEM?
images formed by passing electrons through sufficiently thin specimen
49
what is STEM good at?
detect transmitted or diffracted beam pixel-by-pixel less beam damage due to small probe and short illumination time z-contrast low for smaller atoms - cleans up messier structures
50
What is the Cs correction?
dx = 0.66 Cs^1/4 (lambda)^3/4
51
what is electron energy loss spectroscopy?
detects elements by core loss | useful for detecting light elements
52
what is energy resolution of EELS cf EDX?
higher energy resolution (-1eV cf 10-90eV)
53
what does EELS allow you to do?
detect chemical states, oxidation states and bonding of selected elements
54
describe FIB
focussed ion beam - used to cut a sample mill trenches, U-cut, attach to easy-lift probe, final cut and lift out sample, attach to TEM grid, free sample from probe, thin the sample and then run spec.
55
what is AFM?
atomic force microscopy for imagine, measuring and manipulating matter at the nanoscale.
56
what is AFM based ?
Hooke's law - F=-kx | forces between tip and sample surface deflecting a cantilever in contact and non-contact modes
57
what is XPS?
x-ray photoelectron spectroscopy - eject photoelectrons from a sample and record spectrum.
58
name some 0D nanomaterials
clusters, nano crystallites, core-shell nanoparticles, bimetallic alloys, nanoparticles of carbon
59
name 2 methods of assembly of nanoparticles
1) reversed crystal growth | 2) dipole field assembly
60
what should a perfectly mixed alloy follow? + equation
Vegard's law - a(A1-xBx)=(1-x)a(A)+a(B)
61
what further effects can a point defect cause
local dislocation
62
what defect has a crystal within the crystal?
domain structure
63
what defect has 1 row shift in layers
anti-face defect
64
what defect has two row shift in layers
twin defect
65
what does the BFDH law say?
a crystal would rather grow faster up the way but slower to the sides
66
properties of nanoclusters
very small - n>3; often fixed number of atoms; often no defined crystal structure
67
examples of a nanocluster metal
Ru and Ag
68
different 1D nanomaterials
carbon nanotubes, oxide nanotubes, C60 nanowire, Si nanowire, ZnO nano belts, Core-shell nanowires
69
explain possible planar defects in Si nanowires
slower, thermodynamically controlled, growth goes in 111 direction with no defects faster, kinetically controlled, growth goes in 112 direction with lots of defects
70
give some examples of 2D nanomaterials
nano plates, graphene
71
give some properties of graphene
``` fast moving current perfect thermal conductor 1-atom thick planar sheet visible to eye harder than diamond and 300 times harder than steel more reactive than graphite edge more reactive than surface ```
72
what does adding Mn3O4 do to rGO
lowers conductivity large amount of defects uneven distribution of nanoparticles
73
give some examples of 3D nanomaterials
mesoporous materials ATO inorganic frameworks MOFs
74
explain how a MOF is synthesised
MOF-5 - Zn5(OH)8(NO3)2.2H2O microplanes grown to nanoplatelets, develop multiplayer particles to polycrystalline cubes inside the multilayer particles gives a polycryslltine cube.
75
what is special about MOF synthesis
Reversed crystal growth mechanism
76
what is important about O vacancies in Ce(1-x)Bi(x)O(2-d)
as number of oxygen vacancies increase, catalytic activity increases there is an easy come easy go oxygen mechanism here.

nano (2 decks)

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