search.noResults

search.searching

note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
Meteoritic Nanodiamonds


in this research would be the discovery of a method to distinguish carbon isotopes of diamond from those of amorphous carbon in order to determine if diamonds, disordered carbon, or both contain a presolar fraction. T e development of such a method is the topic of this article.


Materials and Methods


To prepare nanotips for APT we embedded a layer of acid residue between two layers of ion-beam sputter-deposited platinum and used focused ion beam (FIB) milling to create small radius (<100 nm) nanotips of the multilayer, with the plane of the acid residue running along the long axis through the nanotip ( Figure 1 ). T e nanotip shape is required so that high voltage in the atom probe will generate a high enough electric fi eld to evaporate ions from the apex of the nanotip. We used a LEAP 4000x straight-fl ight-path atom probe to collect time-of-fl ight spectra from the samples. Including data sets reported earlier [ 7 , 9 ], we analyzed a total of 36 data sets from samples of acid residue from the Allende chondrite meteorite and 26 standard data sets from detonation nanodiamonds [ 10 ]. We detected in the acid residue clusters high in carbon—namely C 1 , C 2 , C 3 , and PtOC—as well as O and N, in charge states 1 + and 2 + , and used the recorded concentrations of carbon in various molecules to distinguish between diamond-dominated and disordered-carbon-dominated regions of acid residue. We hypothesized that a higher fraction of the disordered carbon would fi eld evaporate as PtOC molecules rather than pure C molecules, compared to the nanodiamonds because the disordered carbon is more porous than nanodiamond with more exposed surface area where the Pt could bond. T us, we investigated variations in the concentration of carbon in PtOC versus carbon in C 1 , C 2 , and C 3 (using the sum C 1 +2×C 2 +3×C 3 ) as a potentially useful discriminator between the two carbona- ceous fractions. T e species Na and NaO, presumably from the acid dissolution process, are co-located with the carbon clusters,


so we included the concentrations of these molecules in our study. We also investigated O and N concentrations. Scanning transmission electron microscopy with energy-dispersive X-ray spectrometry (STEM/EDXS) showed that in the acid residue O is located primarily in the disordered C, and the N is primarily in the diamond [ 3 ]. Trace amounts of O and N were detected by APT, although some of this signal is from the Pt matrix in which the acid residue is embedded for APT analysis. To calculate concentrations, we divided counts of the atoms and molecules of interest by the sum of the counts of all the ions detected in the acid residue regions of interest in the APT reconstructions, including C, Na, Cl, F, N, and O. We tested the resulting data to ascertain whether the concentrations of these atoms and molecules could be used to distinguish disordered carbon from diamond. Finally, we conducted two analyses to see if there was any correlation between these concentrations and the 12 C/ 13 C ratios of the samples.


Results


Isolated regions of carbonaceous material a few nm in size are typically dominated by C, whereas lower density, larger, and less-ordered regions of acid residue material are dominated by PtOC and laboratory contaminants, such as Na and NaO, along with acid dissolution products Cl and F. In many cases, high concentrations of C ions are surrounded by PtOC, Na, and NaO ( Figure 2 ). Atom-probe reconstructions of the acid residues with higher N concentration tend to have higher concentrations of C 1 +C 2 +C 3. However, these are not consistent or strong trends. T e highest concentrations of C 1 +2×C 2 +3×C 3 correspond to the highest N/O ratios ( Figure 3 ). For C 1 +2×C 2 +3×C 3 concentra- tions over 0.6, the minimum N/O ratio increases steadily from < 0.01 to 0.05. One out of seven nanotips, or ~14% of data sets with C 1 +2×C 2 +3×C 3 concentration < 0.4, had a N/O ratio > 0.05, but ~31% (9/29) with C 1 +2×C 2 +3×C 3 concentration > 0.4 had a N/O ratio > 0.05. T ere was also a loose trend of lower N/O for higher


Figure 2 : Longitudinal sections of reconstructed APT data set ADM R06 18430. The Pt reconstruction (orange ions) is 5 nm thick to reveal holes. Only a small percentage of the Pt ions are shown to improve visibility. The remaining maps are of a 20 nm thick section. C atoms are in black, PtOC in brown, Na/NaO in red, and N in pink. All the ions except Pt and N represent material from the meteoritic acid residue embedded in the sample. The PtOC and NaO concentration is higher on the edges of C clusters, suggesting that they are from disordered C surrounding or adjacent to nanodiamonds. Concentrations of these ions align with holes in the thin cross section of Pt. The concentration of N in the Pt is too high to distinguish it from N in the acid residue. Scale bars are in nm.


20 www.microscopy-today.com • 2018 March


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