Nitrogen Beam Research Articles

Deposition of amorphous CNx by d.c. and rf plasma sputtering using a rf radical nitrogen beam source

Amorphous CNx thin films were deposited by d.c. and rf Ar plasma sputtering combined with a nitrogen rf radical beam source which supplies active nitrogen species to the growing film surface. The dependence modifications of the optical and the structural properties on nitrogen incorporation were investigated using ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, a four-point-probe method and electron energy-loss spectroscopy. For the rf-sputtered films, the optical band gap was found to increase with the increase in the nitrogen content. For the d.c.-sputtered films, the optical gap first decreased to zero at low nitrogen content, and then increased with a further increase in the nitrogen content. CK energy-loss near-edge structure (ELNES) showed a slight broadening on the lower energy side. The local environment of C and N atoms are almost similar as observed by comparing the CK and NK ELNESs.

Study of Lateral Spread of Ions Emitted from 2.3 kJ Plasma Focus with Hydrogen and Nitrogen Gases

The characteristics of ion beams of hydrogen and nitrogen with different filling pressures emitted from the plasma focus device of 2.3 kJ energy are investigated. CR-39 SSNTDs are employed for the registration of tracks of ions. The exposed detectors are etched in 6N NaOH solution at 70°C and then examined with an optical microscope. The ion flux is estimated to be of the order of 105–6 tracks/cm2. The flux with the radial position does not exhibit any regular pattern of variation.

Pulsed laser deposition of ZnSe:N epilayers assisted by active atomic nitrogen beams

Abstract Epilayers of ZnSe doped with nitrogen have been grown on polished GaAs(1 0 0) and Si(1 0 0) substrates by pulsed laser deposition (PLD) assisted by atomic nitrogen beams. An arc-heated beam source was used to dissociate N 2 and produced neutral nitrogen atom beams with concentration of 10 17 –10 19 at. sr −1 s −1 , which intersected with laser ablated plumes and substrate surfaces in the process of deposition. X-ray diffraction (XRD) results indicate that the ZnSe film grown on GaAs(1 0 0) at 2×10 −3 Torr is a single crystalline epitaxial layer. XRD analysis gives that the crystallographic quality of PLAD-grown ZnSe thin films largely depends on ambient pressure and lattice match. X-ray photoelectron spectroscopy (XPS) demonstrates that Zn and Se atoms in the PLD-grown ZnSe epilayers on GaAs(1 0 0) at 2×10 −3 Torr bonded each other, and besides 11% [N] and 5% [O] no other impurity exist. The concentration of doped nitrogen for the best ZnSe thin film grown on GaAs(1 0 0) was estimated to be over 10 21 cm −3 .

Preparation of short-period Fe-N magnetic multilayers using an atomic nitrogen beam

Magnetic multilayers containing Fe-N layers with bilayer periods of between /spl sim/15-84 /spl Aring/ and sharp interfaces, are successfully grown using an atomic (free radical) nitrogen beam. The phase composition and microstructure is found to be a function of the initial Fe layer thickness prior to nitrogenation. Generally, higher N content phases are found as the initial Fe layer is reduced. Small grains (/spl sim/10 nm) are observed in multilayers containing /spl alpha/-Fe and /spl gamma/-Fe/sub 4/N phases. In these films, a perpendicular anisotropy is found for a certain thickness of the Fe layers. A stripe domain structure associated with this anisotropy is observed. The origin of this anisotropy may be induced stress caused by lattice mismatch between layers and/or lattice dilation due to N incorporation.

Experimental investigation of inclusion of hexagonal GaN phase-domain by varying nitrogen-beam direction to a 〈1 1 1〉 axis in MBE growth of cubic GaN

Crystalline quality of cubic phase (c-) GaN epilayers on (0 0 1) GaAs has been systematically investigated by varying nitrogen (N-) beam direction in molecular beam epitaxy. In this study, the N-beam was obliquely incident to the surface normal. The N-beam direction during both buffer layer and epilayer depositions could approximate either c-GaN[1 1 1]A or c-GaN [ 1 ̄ 1 1] B. In the c-GaN epilayers grown with different N-beam directions, the c-GaN domain or hexagonal (h-) GaN domain showed the tilt and the mosaicity. From the X-ray rocking curves, the extraordinary c-GaN domains and the h-GaN domains were tilted by influence of oblique incidence of the N-beam. The phase purity of c-GaN domain became high when the N-beam direction was along a c-GaN[1 1 1]A direction during both the buffer layer and the epilayer depositions. In order to understand the difference in crystalline quality with change in the N-beam direction, we took account of stack of the Ga and N precursors on (1 1 1)A (or ( 1 ̄ 1 1) B) c-GaN facet. It is considered that the difference of the crystalline quality result from the polarity of the facets.

Electrical transients in the ion-beam-induced nitridation of silicon

We have studied the dynamics of the initial stages of silicon nitride formation on silicon surfaces under nitrogen beam bombardment in the secondary ion mass spectrometry apparatus. We have shown that the secondary ion signal exhibits damped oscillations below the critical impact angle for nitride formation. We have described this oscillatory response by a second-order differential equation and argued that it is initiated by some fluctuations in film thickness followed by the fluctuations in surface charging.

Fe–N alloy films prepared using a nitrogen atom source

We have studied the magnetic and structural properties of Fe–N alloy films prepared by magnetron sputtering in the presence of a highly reactive beam of atomic nitrogen. The nitrogen content was varied by altering the exposure time of the growing film to the beam. The lowest N content film comprises a pseudo-amorphous phase. As N content is increased this gives way to predominantly single-phase structures of ε-Fe 2–3N and ζ-Fe 2N, respectively. Differences in the hysteretic behaviour of the samples are attributed to anisotropy properties.

Measurements of source divergence angle of pulsed nitrogen ion beams

Singly or doubly ionized nitrogen beams, including a small part of oxygen ion beams, were extracted from a cryogenic diode with N 2O ice on the anode surface. The nominal diode voltage was 100–360 kV, and the peak ion current was 300 A. With a one-dimensional arrayed pinhole camera with 5 pinholes, very small divergence angle at the beam source was measured. Although, we used a very rough apparatus (not being as sophisticated as the modern version), the absolute value (measured) of the divergence angle was 5–6 mrad. This value was small enough for us to recommend this beam as one of the candidates for the future ICF or IFE driver. With the same apparatus, we observed a rather large angle of 25–60 mrad for the proton beam in our former experiment. These results indicated that this kind of medium-mass ion beam must be investigated in more detail to make clear the potential of the beam. We also developed a Thomson ion spectometer with a CCD detector, which could be applicable to the above ion beams. The energy spectrum of a proton beam was measured as the early stage preparation of the spectometer development.

Single-walled BN nanostructures.

We describe in situ synthesis and characterization of single-walled BN nanotubes terminated by fullerenelike structures using electron-cyclotron resonance nitrogen and electron beam boron sources onto polycrystalline tungsten substrates. Detailed comparisons of experimental high-resolution electron microscopy images and simulations based upon molecular models show a dominance of kinks and bends involving fourfold and eightfold ring structures as against fivefold or sevenfold which have been found with carbon. Analysis of the structures as a function of film thickness indicates that they are growing by addition of atoms to the exposed ends of single sheets, not at the substrate-nanostructure interface.

Microstructure of Fe–N thin films prepared using an atomic nitrogen beam

The formation of Fe–N thin films by exposure to an atomic (free radical) nitrogen beam is reported. This new method of preparing Fe–N films uses fluxes of highly reactive, thermal energy N atoms that do not disturb the film microstructure. It is shown that by careful control of the exposure conditions, a range of predominantly single phase films can be obtained. At low nitrogen concentrations an amorphous-like phase is observed, whereas crystalline phases of ε-Fe2-3N and ζ-Fe2N are formed at higher concentrations. Dramatic differences in the microstructure and crystallographic texture of these films reveal the inherent microstructure of the different phases rather than the influence of the growth technique.

Non-self-sustained discharge in nitrogen with a condensed dispersed phase

A non-self-sustained discharge in nitrogen with a condensed dispersed phase is studied experimentally for the first time under atmospheric pressure at room temperature. It is shown that macroparticles strongly affect the current-voltage characteristics as well as the stability of the discharge process. A numerical simulation of dust particle charging in nitrogen is carried out at room temperature and cryogenic temperatures under continuous medium conditions. It is shown that a considerable charge is accumulated at macroparticles in the nitrogen beam plasma. As the gas temperature decreases, the charge of macroparticles in nitrogen increases, while in argon their charge decreases. For this reason, the Coulomb interaction parameter for dust particles in nitrogen increases strongly upon a transition from room to cryogenic temperature, while in argon this parameter decreases. It is also shown that the characteristic time of dust particle charging is shorter than 1 μs for a beam current density of 90 μA/cm2, while the neutralization of the charge takes milliseconds. Possible mechanisms of the influence of the dust component on the characteristics of non-self-sustained discharge are considered.

GaNxAs1-xGrowth by Molecular Beam Epitaxy with Dispersive Nitrogen

AbstractThe effect of energetic nitrogen ion bombardment during growth may have a deleterious effect on the material quality. To avoid the bombardment effect of energetic nitrogen ions, a modified mode for GaAsN growth using dispersive nitrogen is reported. High quality GaAsN epilayers and good GaAsN/GaAs interface were achieved using this growth mode. The results suggest that the surface of samples grown using dispersive nitrogen has fewer defects than those grown using direct nitrogen beam. The optical property of GaAsN samples grown using the dispersive nitrogen technique was found to improve, due to the lower ion bombardment effect. This growth technique is expected to be advantageous for growing high quality GaAsN materials for optoelectronic applications.

XPS study of ion beam modified polyimide films

Irradiation of argon, oxygen and nitrogen ion beams onto polyimide films was performed and the surface chemical structure was analyzed in detail by X-ray photoelectron spectroscopy (XPS). The acceleration voltages were 0.5, 1.5 and 3.0 kV for argon and nitrogen beams, and 0.1, 0.5, 1.5 and 3.0 kV for oxygen beam. The elemental ratios of oxygen, nitrogen and carbon were calculated from 1s peaks of the corresponding elements. The results show that the content of oxygen and nitrogen in near-surface layer decreased after argon beam irradiation, while the ratios of oxygen and nitrogen increased after irradiation of oxygen and nitrogen ion beams, respectively, especially in the case of samples treated at low acceleration energies. These findings indicate that the oxygen and nitrogen atoms contained in polyimide films were selectively sputtered by the incident particles, and oxygen and nitrogen ions from the beams were incorporated into the film. The spectra were deconvoluted into the component peaks and the ratios of these peaks were calculated. The XPS results show that the bonds originally contained in the polyimide structure were destroyed as a result of random collisions of the incident ions and the energy transfer to the atoms of polyimide. The XPS spectra after ion beam irradiation are related to the rearrangement of those recoil atoms and the ions incorporated into the film, and formation of new types of bond such as CCC, COC and CNC.

Nitride thin films grown by pulsed laser deposition assisted by atomic nitrogen beam

Pulsed laser deposition of nitride semiconductors offers an alternative to typically employed growth techniques, such as metalorganic chemical vapor deposition and molecular beam epitaxy. PLD can produce good quality thin films at reduced growth temperatures. Growth of these materials requires provision of excess nitrogen in a reactive form during deposition. In our approach, we provide the reactive nitrogen by a low-energy atomic beam. This has the advantage of reducing dependence on substrate temperature to surmount the kinetic barrier for compound formation while avoiding a source of hydrogen during growth. Plume wandering occurring in some cases was effectively deterred by a dual-beam technique. Good quality films were successfully produced for InN, from metallic indium targets, for GaN, from both metallic gallium and ceramic GaN targets, for AlN, from ceramic AlN targets, and for In x Ga 1− x N, from an In/Ga slurry. Growth rates are low except for InN, but there is scope for increasing rates without affecting quality. Films were grown on sapphire, silicon, and glass substrates, at a range of temperatures from ambient to 700°C for AlN and GaN, from ambient to 400°C for InN, and from ambient to 600°C for In x Ga 1− x N. Films are textured in all cases, very strongly so for the higher temperatures. Composition of the binary materials, as determined from RBS analysis, was nominally stoichiometric. Luminescence results were obtained for all types of film, except, for lack of suitable excitation source, AlN. Direct interband luminescence was observed from thin GaN films grown directly on sapphire. Nearly all films showed broad luminescence response attributed to defects, which are not yet understood. In x Ga 1− x N films produced had compositions from nearly pure GaN to x>0.3, depending on growth temperature. Absorption coefficients as functions of photon energy were measured for all films on transparent substrates. Interband edge absorption values for the binary films correspond well with known values. For the In x Ga 1− x N films the absorption edge values were correlated to composition as determined from X-ray diffraction results.

Collision-induced dissociation and density functional study of the structures and energies of cyclic C2nN5− clusters

In this paper, we report mass spectrometry studies on C2nN5− cluster ions by collision-induced dissociation (CID). The mass-selected cluster ions were dissociated by collision with a crossed nitrogen beam and the fragment ions were mass analyzed in a secondary mass spectrometer. Characterization of the species as cyano-substituted, planar five-membered rings is supported by density functional theory (DFT) calculations. Based on the analysis of the experimental and computational results, cluster structures, energies, and stabilities are discussed.

High-current ECR ion source

The ECR ion source is designed for the production of high-current ion beams of various gaseous elements. The ion source consists of a cylindrical discharge chamber, solenoidal coils for generation of the magnetic field along the chamber axis, three electrode accel–decel ion extraction system and a microwave power supply system. Beams of oxygen, nitrogen and hydrogen ions with a current up to 75 mA have been produced. The atomic ion content of the beam exceeds 70%.

Near-edge X-ray absorption fine structure study of carbon nitride films

Near-edge X-ray absorption fine structure (NEXAFS) measurements have been made on carbon nitride films containing as much as 44at.% of nitrogen. The films have been synthesized by dual ion beam deposition (IBD) bombarding a carbon target with low-energy nitrogen ions at varying nitrogen beam energies and substrate temperatures ranging from the liquid nitrogen temperature up to 400°C. The structural changes induced by the reduction of the temperature have been previously investigated [Hammer et al., J. Vac. Sci. Technol. A 15 (1) (1997) 107; Baker et al., Surf. Coat. Technol. 97 (1997) 544]. The transition from a predominantly sp2/sp3 CN amorphous arrangement to a more polymer-like structure has been confirmed and more deeply examined by X-ray absorption spectroscopy. In particular, for samples deposited at liquid nitrogen temperature, a relevant reduction of sp2 CC fraction has been detected. Moreover, the condensation on the growing film surface of hydrogen containing species (i.e. HCN) has been well identified by the appearance of the CH∗ peak.

High-current ion source development for the Korea Multipurpose Accelerator Complex

The Korea Multipurpose Accelerator Complex (KOMAC) project has been initiated to develop and build a high current proton/H− linear accelerator capable of delivering an 1 GeV cw proton beam with an intensity of 20 mA in the final stage. The major proton beam will be used for nuclear-waste transmutation, energy production, and nuclear physics experiments while utilizing the minor negative hydrogen beam for basic science research and medical therapy. A Duoplasmatron proton source for the KOMAC linear accelerator has been built at Korea Atomic Energy Research Institute. The hydrogen beam currents of up to 50 mA at the extraction voltage of 50 kV are routinely obtained. A low normalized rms emittance of 0.2 π mm mrad and a proton fraction of over 80% are obtained in this source. With the 100% duty factor of ion source operation, the arc filaments of the source have survived over 40 h. Except for the filament lifetime, the achieved parameters of the proton beam source are satisfying most requirements of the KOMAC ion source. The ion sources can extract the 10 mA nitrogen beam and 3 mA argon beam for the industrial surface modification processes.

Growth of ZnSe:N epilayers by pulsed laser ablation deposition

Epilayers of nitrogen doped ZnSe have been grown on GaAs(100) substrates by pulsed laser ablation deposition assisted by a nitrogen beam produced by a supersonic nozzle beam source. X-ray photoelectron spectroscopy (XPS) shows that the epilayers are composed of 83.8% Zn and Se, 10.4% N and 5.8% O, and other kinds of impurity are rare. XPS spectra of Zn(2p3/2) and N(1s) core levels indicate that doped nitrogen with an estimated concentration of over 1021 cm-3 exists in the as-grown epilayer. Atomic force microscopy indicates that the surface of an as-grown ZnSe epilayer on GaAs(100) is flat with roughness of about 1.2 nm, which is less than that of some good-quality metalorganic vapour phase epitaxy grown layers. X-ray diffraction results show that these ZnSe epilayers are a characteristic of single crystallinity.

Modification of steel and aluminium by pulsed energetic ion beams

The treatment of surfaces and thin layers of material with pulsed high-energy ions is a novel technique developed in Russia, Poland and USA. The advantages of this method, which is comparable with pulsed laser treatment, is the well-defined modification depth because of partial melting with subsequent quenching, the possibility of simultaneous doping and the low treatment costs in comparison with conventional ion-beam treatment. Important results of other groups and our own results are described and discussed. Stainless steel as well as aluminium and aluminium alloys were bombarded with pulses of different ions ranging from 10 ms down to 50 ns width. The energy density was in the region of 0.01–2 J cm−2. Thus the region where the microstructure of the materials was modified in the solid state was covered up to the melting point. The longer pulses (≥1 ms) were generated with the Heidelberg ion source MUCIS, the short ones (≤1 μs) in collaboration with the Institute of Nuclear Physics in Tomsk, Russia. The resulting microstructure was studied by X-ray diffraction, conversion electrons Mössbauer spectroscopy and atomic force microscopy; the macroscopic properties by hardness measurements and corrosion tests. The most important result was the proof that aluminium and stainless steel can be nitrided at low temperatures by pulsed nitrogen beams with ms pulse width. In addition, it was shown that various phase transitions occurred in stainless steel after ms- and ns-pulsed ion bombardment. This has consequences for the hardness of the material. For aluminium-based materials the hardness and pitting resistance could be improved.