No abstract

By methods of field ion microscopy and mass spectrometry, the presence of linear carbon chains at the surface of carbon fibers after high-voltage treatment using a pulse generator with pulse duration of 10 ns was revealed. The carbon chains attached to the specimen tips can be produced in situ in a field ion microscope using low-temperature pulsed evaporation by electric fields of the order of 80 V nm −1 . These nanowires are perfectly resolved in the field ion microscope. An analysis of the cluster images and determination of the fieldenhancement factors strongly indicate that the field produced clusters are linear chains of one carbon atom in diameter. The process of field evaporation at the pulse voltage loading is sporadic with an anomalously large instant rate of evaporation corresponding to explosive removal of about 10 11 atomic layers s −1 . Atomic C chains are produced during the high-field unraveling of nanofibers at 4.2 and 77 K.

No abstract

The constant tendency toward miniaturization in modern technology implies high requirements on the accuracy in the experimental determination of the entire complex of mechanical characteristics of mate rials in samples with dimensions in the micron and submicron range; it poses the task of developing notions about the nature of strength on the atomic level. The tensile testing of superstrong single crystal line whiskers dates back to the pioneering works of Brenner in the late 1950s, where the experimental val ues of strength close to the theoretical limit were obtained for the first time [1]. The appearance of field ion microscopy (FIM) techniques allowed the tensile testing of needle and filament shaped samples with diameters in the nanometer range [2, 3]. These exper iments employ the method of mechanical loading of nanocrystals in ultrastrong electric fields and admit in situ monitoring of the crystallographic orientation, atomic structure, and microtopography of samples before and after fracture. As a result, it was established that, in contrast to experiments with micron sized metal whiskers [1], nanodimensional single crystals are characterized by the almost complete absence of the scaling dependence of strength and the dispersion of strength characteristics. Based on these results, it was concluded that ultimate breaking stresses had been achieved corresponding to the theoretical strength of metals [2-4] and carbon nanofibers. This conclusion was also confirmed by recent theoretical investigations using many body potentials and ab ini tio calculations [6][7][8].In this study, the method of high field mechanical loading in a field ion microscope has been used to determine the ultimate tensile strength of monatomic carbon chains, which are promising materials for car bon nanoelectronics. The results of mathematical simulations and theoretical calculations of the mechanical response of monatomic carbon chains [9,10] showed that the ultimate tensile strength of these one dimensional objects can exceeds the ideal strength of metal monatomic filaments and that of graphene-one of the strongest known materials.We have studied various commercial fibers such as Rovilon, high modulus poly(acrylonitrile) (PAN) fibers with various graphitization temperatures (900, 1500, 2000, and 2600°C), and pyrolytic carbon fibers. The PAN fibers consisted of nanofibrils with an aver age transverse size of 20-50 nm. The experiments were performed at 77 K in a high vacuum chamber of a field ion microscope. Details of the experimental procedure, including in situ preparation of mona tomic carbon chains on top of a parabolic carbon point with a vertex curvature radius below 1 μm, are described elsewhere [11]. The controlled formation of monatomic carbon chains on top of mesoscopic points took pace as a result of high field unraveling [11,12]. The atomic chains were obtained at low tem peratures under high vacuum conditions at a positive applied voltage within 0.5-25 kV. All experiments were performed at a residual pressure of 1 × 10 -5...