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The surface and bulk plasmon energies in EELS can be theoretically modeled or measured experimentally. In general, Table 4623a lists the trend of inelastic mean free paths (λ) under different experimental conditions.

Table 4623a. Trend of inelastic mean free paths (λ) under different experimental conditions.

	Accelerating voltage of the electron beam (V)		Collection semi-angle (β)
	High	Low	Large	Small
Mean free path	Large	Small	Small	Large

Table 4623b lists bulk plasmon energies, full-width-at-half-maximum of bulk plasmon energies, bulk plasmon mean free path, and inelastic mean free path of some common elements and compounds, as well as their crystal structure (Notation: a for amorphous, b for body-centered cubic, c for cubic, f for face-centered cubic, h for hexagonal, l for liquid, o for orthorhombic, r for rhombohedral, t for tetragonal) [1 -  6].The bulk plasmon mean free path λ_p represents the collective valence electron component of inelastic scattering. The differences between λp and λi reflect single-electron excitation, for example, an inner-shell ionization edge occurring below 150 eV. In addition, Table 4623b also lists surface plasmon energies (E_s) of some elements and components. Note that the accuracies are ~5%–10% for λ and ~10%–30% for λ_p. [16]

For specific experimental conditions or structures of materials, the plasmon energies are slightly affected by many factors:
         i) Plasmon energies slightly depend on the incident beam energy. In EELS measurement, the decrease of electron-beam energy gives rise to a low energy shift and a widened plasmon peak.
         ii) The energies of plasmon peaks can be lowered by defect excitations or interband transitions.

Table 4623b. Surface plasmon energies (Es), bulk plasmon energies (Ep in eV), full width at half-maximum Ep (ΔEp), bulk plasmon mean free path (λp in nm), elastic mean free path (λe in nm), approximate bulk plasmon mean free path obtained by theoretical calculation (λapp in nm), and inelastic mean free path (λi in nm) at different incident kinetic energies (λi3, λi30, λi100, λi200, and λi300 at incident kinetic energies of 3 keV, 30 keV, 100 keV, 200 keV, and 300 keV, respectively). Note: for some elements, the table lists multiple values gathered from different references.

Materials	Es , eV	ΔEp, eV	Ep, eV	Origin of Ep	λe, nm	λ for <100 keV, nm *	λi100, nm	λi200, nm	λi300, nm	λapp, nm	λp, nm**
Ag (f)	3.7		25					100			125
Ag (poly-c)							71 (β = 10-100 mrad) [20]
Ag2O								112
Al	10.3[7,8]		15.3[7,8]			λi30=55.5	107.5	134		155	160
Al (c)			~15				100 (β = 10-100 mrad) [17]
Al (poly-c)							101 (β = 10-100 mrad) [18]
AlAs			16.1							146
Al2O3 (α)		10 - 20	22.2-26[9-12]					130-140		109
Al2O3 (poly-c)							106 (β = 10-100 mrad) [19]
As (r)			18.7							129
As (a)			16.7							142
Au						λi30=38	67
Au (poly-c)							56 (β = 10-100 mrad) [20]
Au (f)	~1		24.8					84			120
B(a)		18	22.7					123		110	126
Ba (b)		7.5	27.8							94
BaO			27.6					125
Be (c)	12–14		19.2				129 (β = 10-100 mrad) [17]
Be(h)		4.8	18.7					160		129	169
Be3N2			23
Bi (r)		6.5	14.2					105		162	147
Bi2O3								125
BN (h)			9 & 26
BN (a)			24								106
BN (c)							99 (β = 10-100 mrad) [21]
B2O3								120
C						λi30=67	133
C (diamond)		13	33.2				88 (β = 10-100 mrad) [19]	112		81	116
DLC			27
C (graphite)			23~25
C (a)		20	24			λi40=34	74	116-160	24.5 eV		106
C (C60)							115 (β = 10-100 mrad) [19]
Ca (f)		2.1	8.8							241
CaO								130
Cd (h)								107			130
Ce2O3								125
Co (h)			20.9					98		118	108
CoO			24.6					115
Cr (b)			24.9					104		102	149
Cr (poly-c)							74 (β = 10-100 mrad) [19]
Cr2O3								118
Cs (b)			2.9							175
Cu						λi30=46.4	87
Cu (f)			19.3					100		126	100
Cu (poly-c)							63 (β = 10-100 mrad) [18]
Dy (h)								118			310
Dy2O3								126
Er (h)			14
Er2O3								115
Eu2O3								118
Fe (b)			23					102		109	121
Fe (poly-c)							74 (β = 10 mrad); 57 (β = 100 mrad) [18, 20]
Fe (306 stainless steel)							78 (β = 10 mrad); 61 (β = 100 mrad) [17]
Fe2O3			21.8					116
Ga		0.6	13.8							166
GaAs (c)			15.8				95 (β = 10 mrad); 74 (β = 100 mrad) [19]			148
GaN			19.4
GaP			16.5							143
GaSb			13.3							171
Ge			16.0			λi30=~ 20
Ge (c)			15.8					120-140		148	126
GeO2								130
Gd (h)								110			275
Gd2O3			14.6					125		158
Hf (h)								95			237
Hf (c)							57 (β = 10 mrad); 41 (β = 100 mrad) [17]
HfOx					87 at 300 keV			~112	95 [20 mrad]
Hg (l)		1	6.4
HgO								116
H2O (c)							220 (β = 10 mrad); 200 (β = 100 mrad) [19, 22]
Ho2O3								120
I (o)								140			233
In (t)		12	11.4					110			129
InSb			12.9
Ir (b)								78			121
IrO2			29					110
La2O3								130
Li (b)		2.2	7.1-7.4							289
LiH			20.9							118
LiF			24.6							103
Li12Si7			14.1
Li7Si3			13.6
Li13Si4			13.1
Li22Si5			12.9
Mg (h)		0.7	10.3					150		211	214
MgB2			18.9
MgF2			24.6							103
MgO			22.3				93	133	152	112
Mn (c)			21.6					106		115	146
Mo (b)			25.2					98			163
MoO3			24.4					111
Na (b)		0.4	5.7							348
NaCl			15.5							151
Nb (b)								105			194
NbC			24.0
Nd2O3			14.2					120		162
Ni (f)			20.7					98		119	103
NiO			22.6					115		111
NiO (c)							89 (β = 10 mrad); 71 (β = 100 mrad) [17]
NiSi2			19.75 - 20.0
NiSi			20.25 - 20.7
Ni2Si			21.9
NiTi alloy										100
P (o)								160			160
Pb (f)			13					99			141
PbO								122
Pd (b)	6.5[13]		25.1&31.9[13]					94			118
PdO			3.7&7.6[13]					110
Pr2O3								122
Pt (b)			22.6					82		111	120
Rb (b)		0.6	3.41							539
Re (h)			28					78			141
Ru (b)								90			134
S (o)								200			200
Sb (r)		3.3	15.2					120		145	234
Sc (h)			14							604
Sc2O3								125
Se (h)		6.2	17.1					130			205
Se (a)		6.2	16.3							145
SeO2			3.95					130
Si						λi3< 5; λi30=~ 20; λi1.5=2.11; λi0.15=0.4	97	147	180
Si (c)	8.2	3.2	16.7	Si 2p			111 (β = 10 mrad); 91 (β = 100 mrad) [20]	145		142	168
Si (a)		3.9	16.3							145
SiC (α)		3.9	21.5
Si3N4 (α)		10.1	23.7	N 1s
SixNy (with excess Si)			17 - 24 [25,26]
Si3N4/wet SiO2 interface			21-22 [23]
Si3N4/native oxide interface			19.6-20 [24]
SiO2 (α)		16.6	22.4	O 1s		λi1.5=2.96; λi0.15=0.7	119 (β = 10 mrad); 99 (β = 100 mrad) [19]	155		112
SiO2					660 at 300 keV		102	178	247 [10 mrad], 140 [20 mrad]
Sm (r)								112			280
Sm2O3			13.5					120
Sn (t)	10	1.3	13.7			λi0.1= 0.7, λi2= 1.0, λi4 = 1.4, λi6= 1.6 [14]		115		167	273
SnO						λi0.1 = 1.0, λi2 = 1.4, λi4 = 1.9, λi6 = 2.3 [14]
SnO2						λi1 = 1.0, λi2 = 1.4, λi4 = 1.9, λi6 = 2.3 [14]		115
Sr (b)		2.3	8							261
SrO			32					126
SrTiO3								115[15]
Ta (b)								88			183
TaC			22.4
Tb (h)			13.3
Tb2O3								125
Te (h)		6.2	17.1					130			216
Ti (h)			17.9					120		134	202
TiN								~140
TiO								120
Tl (h)								95			135
V (b)			21.8					109		114	158
Vacuum***								50 meters
VC			22.2
V2O5								116
W (b)								82			151
WO3								110
Y (h)		7	12.5					124			354
Yb (f)								110			275
Yb2O3								115
YH2			15.3
Y2O3			5.01					122
Zn (h)			17.2					106		138	106
ZnO	16
Zr (h)								113			268
Zr (c)							75 (β = 10 mrad); 57 (β = 100 mrad) [17]
ZrO2								115
Epon									21.5 eV

In the applications of material science and engineering, the incident electron beam in TEMs used for EELS analysis is normally accelerated to 200 keV. Therefore, the bulk plasmon mean free path (λ_i200) at such incident kinetic energies is generally in the range of ~80 and 200 nm. Figure 4623 shows a clear periodic dependence of λ_i200 such that within one row of the Periodic Table, the minimum (maximum) of λ_i200 is observed for the elements with completed (empty) outer d shell. The oxides present a smaller variation. For oxides, the atomic number Z corresponds to the main element, e.g., Z=14 for SiO₂.

Figure 4623. Periodic dependence of λ_i200 on atomic number Z. [16]

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