1,721,260 research outputs found
Ion-beam synthesis and growth mechanism of diamond-like materials
No full textOpposite to most other deposition methods, the dominating nucleation and growth mechanism during ion-beam deposition of energetic ions in the range between 10 eV and 10 keV occurs in a region of a few nanometers below the surface of the growing film. This process is called 'subplantation' - emphasizing the implantation of ions into a subsurface region. Ordering and phase formation is a result of the interaction of the deposited ions with the solid state that takes place within the short time scale of femto- and picoseconds. This extreme non-equilibrium process can result in metastable amorphous or crystalline structures. This review will present several examples of the influence of the deposition parameters on the properties of diamond-like materials synthesized using mass-selected ion-beam deposition. Furthermore, several existing models of the deposition process will be presented and critically discussed
Field emission studies on swift heavy ion irradiated tetrahedral amorphous carbon
No full textWe investigate the feasibility of electrically structuring flat films by swift heavy ion irradiation to create durable field emitters. Using mass separated ion beam deposition amorphous carbon films, doped with H and F to influence sp(3)-fraction and dielectric properties, were grown on highly conducting Si substrates. After deposition, the films were irradiated with 350 MeV Au-197 ions creating embedded graphitic channels along their trajectories with diameters only a few nanometers. Those channels were examined using an atomic force microscope (AFM) with a conducting cantilever by applying a bias voltage to the substrate. The channels exhibit conductivities several orders of magnitude higher than the host matrix. Field emission was observed for the F doped samples, and field emission current characteristic and turn-on fields of 30 V/mum were measured. Using field emission energy distribution (FEED) analysis defect states at or near the Fermi level of the track could be identified as the emission source. Computer calculations were performed to approximate the geometric field enhancement of the ion tracks, which was found to be largely reduced by dielectric screening of the amorphous carbon host matrix. (C) 2003 Elsevier B.V. All rights reserved
Phase formation of boron nitride thin films under the influence of impurity atoms
No full textBoron nitride thin films have been prepared via mass selected ion beam deposition (MSIBD) by alternating deposition of B-11(+), N-14(+) and P-31(+) ions with ion energies between 200 and 500 eV and substrate temperatures ranging from 200 to 280 degreesC. The phase formation as a function of the P+ ion fraction was studied using infrared absorption spectroscopy (FTIR). The thresholds of substrate temperature and ion energy, which are required to nucleate cubic boron nitride using MSIBD are shifted to higher values with increasing P content. Electrical measurements showed Frenkel-Poole emission as conduction mechanism but without any apparent dependence of the phosphorous content on the conductivity. X-ray photoelectron spectroscopy was applied to probe the B, N and P core-level states, indicating a substitution of nitrogen atoms by phosphorous and formation of B-P bonds. (C) 2002 Elsevier Science B.V. All rights reserved
Cubic boron nitride thin film growth by boron and nitrogen ion implantation
No full textCubic boron nitride (c-BN) thin films were deposited on silicon substrates using mass separated ion beam deposition (MSIBD). In order to investigate the influence of the ion energy on the growth of c-BN films, B-11(+) and N-14(+) ions were implanted into c-BN with ion energies ranging from 5 keV to 43 keV and substrate temperatures (T-S) from room temperature (RT) to 250 degrees C. A systematic study on the interplay of E-ion and T-S has revealed a characteristic energy-dependent temperature threshold for c-BN growth. This behavior is explained by dynamic annealing of defects caused by a penetrating ion in a collison cascade. In this picture, the suppression of defect accumulation that is crucial for maintaining cubic phase formation is attributed to temperature-driven back diffusion and subsequent annihilation of B and N interstitial recoils. The model is confirmed by analyzing the depth profile of implanted, isotopically pure B-10, and its application for both c-BN nucleation and growth is discussed
Electric field gradients at Eu-151 sites in GaN
No full textThe electric field gradients at Eu sites in GaN have been investigated in conversion electron Mossbauer spectroscopy (CEMS) in which Eu-151 probe ions were implanted into an undoped GaN layer grown on a sapphire substrate. The sample was implanted with 120 keV Eu-151 ions to a fluence of 1 x 10(15), and annealed at 1,200 K. CEMS spectra of the Eu-151 21.6 keV transition were collected, of the GaN sample as well as of a Si sample implanted with overlapping profiles of Eu-151 and O. The GaN spectra were fitted with two symmetric doublets, D1 and D2, with isomer shifts and quadrupole splittings of delta = -0.27 mm/s (relative to Eu2O3), Delta E-Q = 0.85 (3) mm/s; and delta = - 0.22 mm/s, Delta E-Q = 2.90 (5) mm/s, respectively. D1 is attributed to Eu at substitutional Ga lattice sites; D2 to Eu at or near substitutional sites but with extensive lattice damage. The splittings of D1 and D2 correspond to quadrupole coupling frequency of 15 (2) and 50 (4) MHz, consistent with measurements of Ga-69, Ga-71 and In-111 in GaN
The role of ion energy on the growth mechanism of cubic boron nitride films
No full textBoron nitride (BN) film growth from mass selected B and N ion deposition has been investigated for ion energies beyond 10 keV Cubic boron nitride (c-BN) growth was achieved even for 20 keV boron and 27 keV nitrogen ions that cannot be explained by the existing models for the growth and nucleation of c-BN. A volume c-BN growth process using high-energy ions (> 3 keV) might be due to agglomeration of implanted ions at the c-BN grain boundaries. Additionally, the stability and compressive stress of c-BN thin films under nitrogen ion irradiation was studied. It is shown that cubic boron nitride is extremely stable under ion irradiation and that the compressive stress of the films can be reduced by ion irradiation. A decrease of the infrared (IR) absorption intensity at 1080 cm(-1) of c-BN was also observed after ion irradiation, which is due to smaller c-BN grain sizes. Point defects accumulate during successive irradiation into extended defects, stacking faults, and new c-BN/c-BN grain boundaries. This process can be avoided by annealing the sample prior to irradiation, where the compressive stress is reduced, that hampers dynamic annealing upon ion irradiation of BN at room temperature. (C) 2003 Elsevier B.V. All rights reserved
On the mechanisms of cubic boron nitride film growth
No full textCubic boron nitride (c-BN) is the most attractive BN allotrope due to its outstanding physical and chemical properties. Deposition of c-BN films is typically accomplished using ion-assisted physical vapor deposition methods. Recently, low-stress and thick c-BN films were successfully grown by chemical vapor deposition approaches. It was also shown that c-BN growth is possible by ion implantation with ion energies above 10 keV. Independent of the deposition method, there exist pronounced similarities regarding the nucleation and growth conditions as well as the film structure. Despite these similarities, the different c-BN growth methods are most probably based on different underlying physical processes. This is reflected in characteristic differences in the c-BN growth conditions, such as different ion energy and growth temperature regimes, and different chemical precursors. In this contribution the growth conditions for several c-BN growth methods are compared and an attempt will be made to extract the relevant physical processes for c-BN growth. We propose three different major processes leading to c-BN growth: (i) the subplantation process taking place in ion-assisted PVD and ion beam deposition; (ii) a process involving gas phase and surface chemistry taking place in fluorine-assisted plasma-CVD at high temperatures; and (iii) internal growth during B and N ion implantation into c-BN bulk material. (C) 2004 Elsevier B.V. All rights reserved
Wurtzite ZnS nanosaws produced by polar surfaces
No full textWurtzite structured ZnS nanoribbons have been synthesized by a catalyst-free solid-vapor deposition technique. The nanoribbon has a saw-teeth shape, and the nanosaw is formed by a two-step process: a fast growth along a-axis forms the body of the saw; a subsequent growth along c-axis creates the teeth. The one-sided teeth structure is suggested to be the self-catalyzed growth of the Zn-terminated (0 0 0 1) surface, while the oxygen-terminated (0 0 0 1) surface is relatively chemically inactive. The growth of 'feather'-like structure of ZnS is also reported. (C) 2003 Elsevier B.V. All rights reserved
Phase diagram of Si nanowire growth by disproportionation of SiO
No full textSilicon nanowires have been grown in a horizontal tube furnace by disproportionation of silicon monoxide in combination with the vapor-liquid-solid mechanism. We present a phase diagram of the nanowire growth, indicating different morphologies for varying growth pressure and temperature. The morphology was characterized by scanning electron microscopy and detailed structural analysis was performed by transmission electron microscopy. A variety of morphologies is found and the optimum parameter range for the growth of straight and uniform nanowires consisting of crystalline silicon cores and amorphous SiO(2) shells is identified and discussed. (C) 2010 Elsevier B.V. All rights reserved.German Research Foundation (DFG) [Ro1198/7
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