Negative Carbon Cluster Ions Research Articles

Preparation of graphene on Cu foils by ion implantation with negative carbon clusters**Project supported by the National Natural Science Foundation of China (Grant Nos. 11105100, 11205116, and 11375135) and the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, China (Grant No. AWJ-M13-03).

We report on few-layer graphene synthesized on Cu foils by ion implantation using negative carbon cluster ions, followed by annealing at 950 °C in vacuum. Raman spectroscopy reveals IG/I2D values varying from 1.55 to 2.38 depending on energy and dose of the cluster ions, indicating formation of multilayer graphene. The measurements show that the samples with more graphene layers have fewer defects. This is interpreted by graphene growth seeded by the first layers formed via outward diffusion of C from the Cu foil, though nonlinear damage and smoothing effects also play a role. Cluster ion implantation overcomes the solubility limit of carbon in Cu, providing a technique for multilayer graphene synthesis.

Cooling dynamics of photo-excited negative carbon cluster ions stored in an ion storage ring

A newly found fast radiative cooling process of C6- is studied by simulation based on statistical sharing of the internal energy by the vibrational modes both in the electronic ground and excited states. For comparison, a contrasting slow cooling of C6H− is simulated by the same procedure. The simulation demonstrates a distinct difference in the time evolution of energy distributions between C6- and C6H−, and well reproduces the observed fast cooling of C6- by recurrent electronic transitions and the slow cooling of C6H− by vibrational de-excitation.

Application of Time-of-Flight Secondary Ion Mass Spectrometry to study diamond-like carbon films

Chemical composition and some differences between surface and bulk structure of diamond-like carbon (DLC) thin films studied with Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) are the subject of this paper. The DLC films were deposited using radio-frequency plasma-chemical vapor deposition (RF PCVD) method by the decomposition of CH 4 gas in high-frequency plasma. The negative self-bias voltage defining the power used for deposition was in the range of − 100 V to − 400 V. The results obtained show that the DLC films primarily contain carbon and hydrogen. The collected depth profiles also show that all samples contain considerable amount of Fe, Ni, Cr and some other elements introduced during the deposition process. These elements are mainly placed at the interface region of the substrate and deposited in the DLC film. The mass spectra obtained show that the amount of hydrogen in the surface layer is much greater than in the sample bulk which is consistent with widely accepted models of deposition of hydrogenated DLC films. The structure of the studied DLC samples was characterized by the analysis of negative carbon cluster ions in the mass spectra obtained. Some significant differences in the surface and bulk energy of fragmentation of carbon clusters are registered. The results suggest that the fragmentation pattern is independent of the self-bias voltage used during film deposition.

Intensity variation dependence of secondary ion emission of carbon clusters from graphite, diamond-like carbon and diamond surfaces on number of carbon atoms

Secondary ions of carbon clusters from graphite, diamond-like carbon (DLC) and diamond have been investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). A series of negative carbon cluster ions C n - ( n = 1 – 15 ) were observed. Considering the electron affinities ( E A) of the clusters, the dependence of the intensities on the value of n was analyzed using multiple regression analyses. After subtracting the influence of E A, the slopes of the lines in the range of C 1 - – C 9 - were obtained. The slope was shown to be higher for graphite than for diamond. DLC shows almost similar behavior as diamond. These results indicate that negative carbon cluster ions in TOF-SIMS can be strongly correlated with the matrix.

Formation of Positive and Negative Carbon Cluster Ions in the Initial Phase of Laser Ablation in Vacuum

In this paper, the formation of Cn+ and Cn- cluster ions has been investigated. The carbon cluster ions were produced by the laser ablation of a rotating graphite target in vacuum. The study has been carried out using time-of-flight mass spectrometry. Mass spectra of positive and negative cluster ions were observed as a function of delay time between the irradiation of the laser pulse and the acceleration of ions. The mass distribution of clusters changed significantly in the initial phase (≤10 µs) after the irradiation of the laser pulse. The sizes of both positive and negative cluster ions grow with the increase in the delay time. These results indicate that clustering reactions progress even in vacuum without ambient gas. The mechanism of clustering is considered to be reactions among various carbon ions and neutral species in the laser ablation plume.

Reactions of carbon cluster ions stored in an RF trap

Reactions of carbon clusterions with O2 were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions Cn− (n=4−8) were much less reactive than positive cluster ions. The CnO− products were seen only in n=4 and 6.

Low-energy collision of negative carbon cluster ions with surfaces: collision-induced electron detachment

The authors report the results of low energy (0-1 keV) collisions of negatively charged carbon clusters C{sub n} (n=2-18) with MoS{sub 2} solid surfaces, where what was observed was the electron emission. These carbon clusters represent several isometric structures. They observe two types of emission. One is related simply to the incident kinetic energy of the cluster ions. The second evidences narrow peaks, present for collisions of less than 100eV, and for only certain types of cluster.

Simultaneous storage of hetero-charged carbon cluster ions in an RF trap

Positive and negative carbon cluster ions produced by laser ablation have been simultaneously stored in an RF ion trap. The size distributions of the stored cluster ions, which were measured by means of ion dumping followed by time-of-flight mass analysis, are consistent with that reported previously.

Production, dissociation and reactivity of carbon cluster anions

Negative carbon cluster ions, C − n ( n ⩽ 13), produced by the direct laser vaporization of graphite have been studied by using Fourier transform mass spectrometry. Low-energy collision-induced dissociation (CID) of C − n ( n = 5–13) results in loss of neutral C 3 which also competes with electron detachment. The ion/molecule reactions of C − n ( n = 4–13) with F 2 and C 2N 3indicate that only linear C − n are formed by direct laser vaporization. No evidence for structural isomers of C − n is observed, although product ion isomers are formed in the reaction of C − n with C 2N 2. The C 5C 2N − 2 isomers are differentiated by differences in their reactivity and CID spectra. The differences observed in the reactivity and CID of reaction products for odd and even n are consistent with polyacetylene (even n) and cumulene (odd n) structures for the carbon clusters. These results are compared with previous C − n studies, including a discussion of structural implications and formation mechanisms of C − n produced by various techniques.

Production of small doubly charged negative carbon cluster ions by sputtering.

Carbon cluster ions with a double negative charge, and lifetimes of at least 10 \ensuremath{\mu}s, have been produced by sputtering graphite, and observed in a double-focusing mass spectrometer. Ions as small as ${\mathrm{C}}_{7}^{2\mathrm{\ensuremath{-}}}$ have been detected. The intensities of the doubly charged clusters (${\mathrm{C}}_{\mathit{n}}^{2\mathrm{\ensuremath{-}}}$ where n=7--28) follow an alternating pattern, with even-n clusters being more intense than neighboring odd-n clusters. In contrast, even-n singly charged clusters are more intense than odd n for n\ensuremath{\le}9, and less intense for n\ensuremath{\ge}13, where the clusters are believed to be cyclic.

Photofragmentation of C n−, 4⩽ n⩽20: Loss of neutral C 3

Size-selected photofragmentation of the negative carbon cluster ions C itn −, 4⪕ n⪕20, has been surveyed when excited both above and below their electron binding energies (at 3.49, and 2.33 eV, respectively). For most clusters smaller than n=14, fragmentation occurs via loss of C 3 neutrals, analogous to the behavior found in the carbon cations.

Fourier transform ion cyclotron resonance mass spectrometry of trapped carbon cluster ions

Positive and negative carbon cluster ions containing up to 27 carbon atoms have been produced by laser vaporization and detected via FT/ICR mass spectrometry. A periodic pattern of “magic numbers” is found in the positive clusters. The application of this technique to the study of ion-molecule reactions of clusters is demonstrated.