In Situ Atom Probe Deintercalation of Lithium-Manganese-Oxide 317
impinging rate is expected to be influenced by the electric field in the vicinity of the sample (Van Eekelen, 1970), and the reaction and ionization probability of the residual gas molecules are unknown, a deterministic calculation of the contribution of residual gas molecules to theOcontent is not straight forward. However, subtracting a constant O supply rate from the residual gas, before calculation of the content of Li, Mn, and O, yields different temporal evolutions of the Li, Mn, and O content. Particularly, for a supply rate of 4,500 O atoms per hour from the residual gas, the content of Li, Mn, and O becomes constant from 20 h on, as shown by the solid lines in Figure 2b. Such a constant content for all three species would be expected for Li being practically immobile in the sample and evaporating only together with the Mn–O host structure. A further indication for no significant Li transport in the sample, but significant O supply from the residual gas, is given by the average number of Li, Mn, andO atoms present in the detected ions when omitting noise. Not considering O supply from the residual gas, the average composition of these ions is Li0.34Mn0.50O0.55–0.65 with an increasing O content with time. Subtracting a constant supply rate of 4,500 O atoms per hour from the residual gas, the composition becomes Li0.34Mn0.50O0.52, indepen- dent of time for times from 20 h on. In both cases, the Li content is observed to be constant, indicating no Li transport in the sample. Thus, it can be concluded that, under conventional atom
mobility at 30K under field free conditions and the electro- static field would cause a driving force for O transport into the sample. Besides the sample, another source of O can be the residual gas in the atom probe and a simple estimate yields that several thousand molecules from the residual gas are impinging on the specimen apex per hour.a As the
probe analysis conditions at 30K, no transport of Li, Mn, and O is observed. From the noise level of the atom probe analysis a possible Li flux can be estimated to be below jLi<1×109cm−2/s.
In Situ Atom Probe Deintercalation at 298K
The mass spectra for the in situ deintercalation experiments differ significantly from those for the conventional atom probe analysis displayed in Figure 1. Two characteristic types of mass spectra are observed, which usually appear subse- quently and are attributed to two consecutive characteristic stages of deintercalation, as discussed below. Figure 3 shows the normalized mass spectra. For stage 1 the mass spectrum is formed by the peaks for
the two Li isotopes at 6 and 7 amu. Besides an additional small peak at 19.3amu no further peaks are observed. Particularly, no peaks for Mn+,Mn2+,O+,O +
occur, revealing that the Mn–O host structure is not subject to field evaporation during in situ deintercalation at 298 K.
2 ,or MnxOz+ y
aFor a total background pressure of ≈1×10−8 at 30 K, a typical specimen apex area of around 5×103nm2 and the molecular mass of O2 or H2O the Hertz–Knudsen equation gives ~2×104 molecules/h impinging on the specimen apex.
For stage 2, the mass spectrum exhibits no peaks for Li
at 6 and 7 amu. Instead, the spectrum is dominated by a peak at 19.3 amu. In addition, small peaks at 17amu (OH+), 18amu (OH +
peaks at 29, 30, 43, 44 amu, and a broad peak around 36.5 amu. To assign the peak at 19.3amu, control experi- ments with a tungsten sample under similar field evapora- tion conditions were performed, yielding the reference mass spectrum in Figure 3, with peaks at 17, 18, 19, and 44 amu. Compared with the mass spectrumof stage 2, the peaks at 19 and 19.3amu differ in both, peak position and peak shape. Possible assignments for the peak at 19.3amu are OH + + (cf. Table 1). In the case ofOH +
2 ), and 32amu (O + 2 ) are observed, as well as MnH3+, and 7Li OH
observed peak shape could be explained by delayed emission due to inhomogenous optical absorption of the sample (Vella et al., 2011; Kelly et al., 2014). However, as the other peaks in the mass spectrum for stage 2 exhibit no peak broadening, this explanation seems unlikely. For an assignment of MnH3
3 ðÞ
3 3
assignment unlikely as well. Thus, the peak at 19.3amu is attributed to 7Li OH
3
high ionization state is unexpected under the electric field conditions present during stage 2. The assignment is supported by the spatial distribution of Li in the recon- structed volume as discussed below. As the field evaporation rate for stage 2 is comparable with the impinging rate of residual gas molecules onto the specimen (cf. Lithium Mobility Under Conventional Atom Probe Analysis at 30K section), the O and H necessary to form the Li(OH)3 molecule is expected to originate from the residual gas. Due to the peak broadening, the 6Li OH
ðÞ
3 3
19amu is not resolved. Considering this, there is deinterca- lation in stage 2, too, where the Li from the LMO reacts with residual gas and is detected as lithium hydroxide. As in
ðÞ
3 3
stage 1, the Mn–O host structure is not or only marginally field evaporated. The spatial distribution of the detected Li-ions for stage 1
is displayed in Figure 4. The Li signal is observed to be inhomogeneously distributed, with Li-ions appearing at about 10 spots. These spots have a characteristic lifetime from several seconds up to several minutes, then the individual
Table 1. Possible Peak Assignments for the Mass Spectrum Shown in Figure 3 for Stage 2 of the In Situ Deintercalation of Lithium-Manganese-Oxide.
Mass (amu) 17
18
≈19 29 30 32
≈36.5 43 44
Ions OH+
OH + 7Li OH 2
6Li7LiO+, 7Li OH + 7Li2O+ 2
ðÞ O +
7Li3OH+ 7Li OH2 CO +
ðÞ2 2
x ; MnOH2+; O2H + +
x 5
3 3
3
2 3
+;MnH3+;OH + ðÞ
3 + peak expected at 3 , the 3 ,
+ , a lack of field evaporated Li and O would make this +, although the presence of such a
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238 |
Page 239 |
Page 240 |
Page 241 |
Page 242 |
Page 243 |
Page 244 |
Page 245 |
Page 246 |
Page 247 |
Page 248 |
Page 249 |
Page 250 |
Page 251 |
Page 252 |
Page 253 |
Page 254 |
Page 255 |
Page 256 |
Page 257 |
Page 258 |
Page 259 |
Page 260 |
Page 261 |
Page 262 |
Page 263 |
Page 264 |
Page 265 |
Page 266 |
Page 267 |
Page 268 |
Page 269 |
Page 270 |
Page 271 |
Page 272 |
Page 273 |
Page 274 |
Page 275 |
Page 276 |
Page 277 |
Page 278 |
Page 279 |
Page 280 |
Page 281 |
Page 282 |
Page 283 |
Page 284
