Ultrahigh Vacuum Ion Beam Research Articles

Квантово-каскадный лазер с выводом излучения через текстурированный слой

The results of studies of ring quantum-cascade laser with a surface emission with radiation output through a textured layer formed in the layers of the top cladding of the waveguide by ultrahigh vacuum ion beam milling are presented. The far-field profile shows that the radiation is output through the windows with a textured layer in the range of angles of ~ 63–75 degrees to the normal.

Investigation of the optical and the electrical characteristics of thin titanium dioxide films

This study dealt with the deposition of nanotitanium films with different thicknesses by using the ultrahigh vacuum ion beam sputtering system. It is found that the thickness of the titanium films was in the nanoscale thus the electric resistivity of the titanium films decreased. Moreover, the deposited titanium was transformed into titanium oxide in an oxygen atmosphere and by using a rapid annealing process. The photoelectronic properties of the nanotitanium thin film was enhanced, when the nanotitanium film was transformed to titanium dioxide.

Ultra-thin titanium nanolayers for plasmon-assisted enhancement of bioluminescence of chloroplast in biological light emitting devices

Ultra-thin titanium films were deposited via ultra-high vacuum ion beam sputter deposition. Since the asymmetric electric field of the metal foil plane matches the B-band absorption of chlorophyll a, the ultra-thin titanium nanolayers were able to generate surface plasmon resonance, thus enhancing the photoluminescence of chlorophyll a. Because the density of the states of plasmon resonance increases, the enhancement of photoluminescence also rises. Due to the biocompatibility and inexpensiveness of titanium, it can be utilized to enhance the bioluminescence of chloroplast in biological light emitting devices, bio-laser, and biophotonics.

Size evolution of nanomagnetic particles and magnetotransport properties of (Co90Fe10)20Ag80 nanogranular films: influence of Cu80Ag15Au5 underlayer

The influence of (Co90Fe10)20Ag80 film thickness and of Cu80Ag15Au5 underlayer on nanomagnetic, magnetotransport and structural properties of (Co90Fe10)20Ag80 nanogranular films prepared by ultra-high vacuum ion beam sputtering technique have been investigated using X-ray diffraction, X-ray reflectivity and vibrating sample magnetometer. Films indicate a superparamagnetic behavior. The evolution of the magnetic particle size in (Co90Fe10)20Ag80 film with different thicknesses was calculated by fit of magnetization curves using Langevin equation. A parallel resistance model has been used to determine particle size distribution. The average (mean) particle sizes range from 1.6 to 2.1 nm. A linear dependence of giant magnetoresistance (GMR) on the particle size has been found. This result is also supported by the observed linear correlation between the square root of the effective magnetization and the particle size. Furthermore, a linear correlation between the square of GMR and the distance between particles has been found. This remains unchanged also in (Co90Fe10)20Ag80 films with Cu80Ag15Au5 underlayer. Using of the underlayer leads to an enhancement of the mean particle size (1.8–2.5 nm) and GMR; however, to a reduction of distances between particles accompanied by the destruction of the 〈111〉 texture in the Ag matrix structure. The reason of the GMR effect in the nanogranular films is discussed by means of the obtained results.

Formation of microcrystalline silicon films using rapid crystal aluminum induced crystallization under low-temperature rapid thermal annealing

The process of obtaining thin film solar cells using the method of aluminum-induced crystallization under rapid thermal annealing (RTA) was investigated. 200-nm-thick amorphous Si (a-Si) film was deposited on a glass substrate using an ultra-high vacuum ion beam sputtering system. A 50-nm-thick crystal aluminum layer was then evaporated and deposited onto the a-Si film. In contrast to conventional furnace annealing, RTA can supply rapid thermal energy so that a-Si can be induced into microcrystalline-Si (μc-Si) in a short time at low temperatures. The crystal Al may promote the crystallization reaction because its surface energy is higher than 0.89 N/m, which is the minimum energy required to produce the (111) orientation. Free Si atoms are induced at the interface of the Al and Si sub-layers by the diffusion of Al along the grain boundaries. The Raman spectrum shows that the sample could be induced to crystallize at 350 °C. After the aluminum was etched, the maximum grain size was 4 μm. The carrier mobility was between 6.2 cm 2/Vs and 18.8 cm 2/Vs. The proposed method can be used to obtain μc-Si with reduced energy and time during the thermal annealing.

Effect of residual stress on nanoindented property of <inline-formula><math display="inline" overflow="scroll"><mrow><mi mathvariant="normal">Si</mi><mo>∕</mo><mi mathvariant="normal">C</mi><mo>∕</mo><mi mathvariant="normal">Si</mi></mrow></math></inline-formula> multilayers

The effect of residual stress on the nanoindentation property of Si/C/Si multilayers has been investigated. Sandwiched Si/C/Si multilayers were deposited on Si(100) substrates by means of ultrahigh-vacuum ion-beam sputtering at room temperature (RT). Four structures with different Si top-layer thickness of 5, 10, 25, and 50 nm and the constant thickness of C/Si underlayer at 100/50 nm were investigated in this study. The residual stress of the Si/C/Si (5/100/50 nm/nm/nm thick) film was about −17.76 GPa under compression, and its hardness was 20.39 GPa at RT. The compressive residual stress was decreased to −5.54 GPa with the increased thickness of Si toplayer up to 50 nm, and its hardness was reduced to ~16.22 GPa at RT. The effect of Si top-layer thickness (5-50 nm) on Si/C/Si residual stress on the nanoindentation property were also discussed. The results showed that the thicker was the Si toplayer, the lower was the residual stress and hardness, which was good for the suppression of the buckling or wrinkling in the C/Si-nanocomposite film.

High trap density and long retention time from self-assembled amorphous Si nanocluster floating gate nonvolatile memory

The memory performance of floating gate nonvolatile memory based on amorphous Si (a-Si) nanoclusters self-assembled during low-temperature oxidation is investigated. A 2nm thick a-Si layer was grown on a top of a 5.6nm thick thermal oxide tunneling layer by ultrahigh vacuum ion beam sputter deposition and subsequently oxidized by annealing in flowing N2∕O2 (9:1) environment for 0–540s at 900°C. After oxidation, a 14nm thick Al2O3 control oxide layer was grown by atomic layer deposition. The authors find that the a-Si layer breaks up upon oxidation, self-assembling into a dense array of 1000s at at 150°C.

Electron transport through individual Ge self-assembled quantum dots on Si

Electrical properties of self-assembled quantum dots have been the subject of intensive research due to quantum confinement. Here the authors report on the fabrication of Ge quantum dots (QDs) onto Si (100) by ultrahigh-vacuum ion beam sputtering and the electrical properties of individual QDs. Transmission electron microscopy images show that samples with completely incoherent or coherent semispherical islands can be produced under different ion energies. The current-voltage (I-V) characteristics with conductive atomic force microscopy at room temperature. exhibit linear behavior at low bias and nonlinear behavior at large bias from coherent islands, whereas the staircase structures are clearly observed in the I-V curve from incoherent islands, which are attributed to electron tunneling through the quantized energy levels of a single Ge QD.

Characterizations of Co/Al 2O 3/Co/NiFe multilayers elaborated by ultra-high vacuum ion beam sputtering

Ion beam sputtering is used for elaborating ferromagnetic Co/Al 2O 3/Co/NiFe multilayers. The interface state and the roughness of the multilayer are examined by TEM and AFM. The insulating layer is found to be homogenous with a low RMS roughness. Magnetic properties of each electrode and of the full stack are studied by P-MOKE and AGFM. The magnetic behaviour of the full stack is characteristic of two switching fields with a Néel coupling.

Investigation of the deformation behavior in nanoindented metal/nitride multilayers by coupling FIB-TEM and AFM observations

AbstractEpitaxial TiN/Cu bilayers and multilayers with periods L between 5 and 50 nm have been grown by ultrahigh vacuum ion beam sputtering on Si and MgO(001) substrates at room temperature. The deformation modes induced by a Berkovich nanoindent have been imaged using Focused Ion Beam – Transmission Electron Microscopy (FIB-TEM) and Atomic Force Microscopy (AFM). The observations suggest that the mechanical response of the multilayers is essentially governed by an extensive plastic flow inside the Cu layers, which is confined by a bending of the more rigid TiN layers. This specific deformation behavior, with no contribution of the interfaces as a barrier for dislocation motion could explain the absence of significant hardness enhancement in this system.

Effect of nitride passivation on the visible photoluminescence from Si-nanocrystals

The effect of nitride passivation on the visible photoluminescence from nanocrystal Si (nc-Si) is investigated. Silicon-rich silicon nitride (SRSN) and silicon-rich silicon oxide (SRSO), which consist of nc-Si embedded in silicon nitride and silicon oxide, respectively, were prepared by reactive ultrahigh vacuum ion beam sputter deposition followed by a high temperature anneal. Both SRSN and SRSO display photoluminescence peaks after high temperature annealing, coincident with the formation of Si nanocrystals, and similar changes in the peak luminescence position with the excess Si content. However, the luminescence peak positions from SRSN are blueshifted by about 0.6eV over that of comparable SRSO such that its luminescence peaks in the visible range. The results demonstrate that control of the surface passivation is critical in controlling the nc-Si luminescence, and indicate the possibility of using nitride-passivated nc-Si for visible luminescence applications including white luminescence.

Magnetic properties of Co/Al2O3/Co junctions deposited by ultra high vacuum ion beam sputtering

Cobalt and alumina layers are deposited by UHV ion beam sputtering to elaborate Co/Al2O3/Co junctions. To form the Al2O3 insulator barrier, oxygen is introduced into the chamber during the aluminum target sputtering. The experimental conditions to obtain stoichiometric Al2O3 are determined using auger electron spectrometer (AES) and Rutherford backscattering spectroscopy (RBS). Stoichiometric Al2O3 is obtained with an oxygen pressure of 6×10−7 mbar, i.e. a deposition rate of 0.5Å/mn, and a beam intensity of 55μA. Magnetic properties of the Co bottom electrode and the mutilayers are studied by magneto-optical Kerr effect (MOKE) and by alternating gradient field magnetometry (AGFM). The easy axis of magnetization is in-plane and the Co layers present an in-plane anisotropy. Moreover, the Co bottom electrode is paramagnetic for a thickness below 40Å, at room temperature.

Mn diffusion effect in the exchange biased NiFe/FeMn/NiFe trilayers

We have fabricated NiFe/Mn/FeMn/Mn/NiFe multilayers using ultrahigh vacuum ion-beam deposition system to study the diffusion effect of the inserted Mn on exchange biasing. As the thickness of the Mn layer was changed from 0 to 1.5 nm, the exchange biasing field Hex(top) at the top interface of FeMn/Mn/NiFe was decreased from 258 Oe to 24 Oe. On the other hand, the Hex(bottom) was slightly decreased 103 Oe to 78 Oe without a change in the coercive field Hc. Above 1.2 nm, a reverse phenomena of Hex was observed. After annealing at 200 °C, the Hex(top) was increased by almost a factor of 2; however, the Hex(bottom) did not change. The analyses of x-ray patterns and Auger spectroscopy showed that the abnormal tendency of Hex(bottom) originated from the diffusion of Mn atoms at bottom interface into the FeMn layer during film growth, and that the Mn was concentrated at the interface by annealing.

Change of preferred orientation in TiN thin films grown by ultrahigh vacuum reactive ion beam assisted deposition

Changes of the preferred orientation in TiN thin films grown on Si(0 0 1) by ultrahigh vacuum ion beam assisted deposition has been studied by using XRD, RBS and AFM. The preferred orientation of the TiN thin films changed systematically from (1 1 1) to (2 0 0) as the assist energy of reactive N 2 + ion increased. In the case without reactive ion irradiation, the TiN thin film grew with the (1 1 1) orientation having the lowest strain energy. For an assist ion energy over about 100 eV, the TiN thin film grew with the (2 0 0) orientation having the lowest surface energy. The average grain size of TiN thin films increased from 10 to 100 nm in diameter as the reactive ion assist energy increased.

Large-area surface treatment by ion beam technique

A large-area ion beam deposition system has been used extensively for depositing diamond-like carbon films by a direct ion-beam process. An ultra high vacuum ion beam system, consisting of a 20-cm diameter RF excited (13.56 MHz) ion gun and a four-axis substrate scanner, has been used to modify large surfaces (up to 1000 cm 2) of various materials, including 304 and 316 stainless steel, 440C and M50 steels, aluminum, aluminum alloys, Ti-6Al-4V, silicon carbide, silicon nitride, polycarbonates, infrared windows and polycrystalline diamond, by depositing varying chemical compositions of diamond-like carbon films. The influence of ion energy, RF power, and gas composition (H 2/CH 4, Ar/CH 4, O 2/H 2/CH 4 and N 2/H 2/CH 4), on the diamond-like carbon characteristics has been investigated. Particular attention was focused on the adhesion, environmental effects, coefficient of friction and wear factors of the diamond-like carbon films on the various substrates under space-like environments. A quadrupole mass spectrometer and a total ion-current measuring device have been utilized to monitor the ion compositions of the gas mixtures of CH 4/H 2, CH 4/Ar, CH 4/H 2/O 2 and CH 4/H 2/N 2 during the deposition process for quality control and process optimization.

Ion beam deposition of 107Ag(111) films on Ni(100)

Monolayer thick silver films were grown on an Ni(100) surface using direct ion beam deposition of 107Ag + ions with 20 eV kinetic energy and the substrate at 25°C. Deposition was performed by means of a mass-selected, low-energy, ultra-high vacuum ion beam system with a well-defined ion energy. The films were analyzed in situ by time-of-flight scattering and recoiling spectrometry (TOF-SARS) and by low energy electron diffraction (LEED). Classical ion trajectory simulations were used to model the TOF-SARS spectra. Results of the TOF-SARS spectra and azimuthal scans are consistent with the growth of a monolayer Ag film with a fcc (111) structure on the Ni(100) surface. The deposited films exhibited a faint hexagonal c(2×8) LEED pattern. Molecular dynamic simulations of the deposition process are in agreement with the experimental observations. The growth of such isotopically pure metal monolayers at room temperature with controlled orientations provides the opportunity for exploring a variety of unique physical properties.

Quantitative compositional depth profiling of Si 1− x− yGe xC y thin films by simultaneous elastic recoil detection and Rutherford backscattering spectrometry

Elastic recoil detection in conjunction with time-of-flight spectroscopy (ERD-TOF) has been used to simultaneously depth profile all elements in thin SiGeC films on Si (0 0 1). Ge-rich Si 1− x− y Ge x C y (0.025 < (1 − x − y) < 0.08 and 0.026 < y < 0.216) films were grown by ultra-high vacuum ion beam sputter deposition. X-ray diffraction and transmission electron microscopy (TEM) showed that samples with low carbon concentration (typically, y ≤ 0.07) were single crystals with stacking faults and twins while films with 0.07 < y < 0.15 were polycrystalline. Samples with y > 0.15 were amorphous. There was no evidence of SiC precipitates. Ge depth profiles were obtained from the recoil spectra as well as from the Rutherford scattered Cl spectra in the same ERD-geometry. The H concentration was determined simultaneously by selective-absorber ERD. Films with C concentrations approaching a fraction of an at.%, and Si concentrations as low as ∼ 1 at.%, could be routinely depth profiled in a single experiment even in the presence of relatively strong surface contamination.

Composition and morphology of InP{100} surfaces as a function of low energy Ar + bombardment and annealing

The surface composition and morphology of the InP{001} surface have been studied by in situ Auger electron spectroscopy (AES) and ex situ atomic force microscopy (AFM) as a function of Ar + ion bombardment energy over the range 5 eV to 500 eV and annealing temperatures up to 600°C. Ion bombardment has been performed by means of a low energy, mass-selected, ultrahigh vacuum ion beam system. The surface contamination can be removed by Ar + ion bombardment with ≥ 30 eV ion energies for carbon and ≥ 60 eV ion energies for oxygen species. However, Indium-rich clusters and islanding are observed for Ar + ion energies above ∼ 40 eV. The results show that a combination of 30 eV Ar + ion bombardment and annealing to ∼ 300°C can produce an InP{100} surface which is devoid of observable impurities in AES and devoid of defect features in AFM.

Large Area Surface Treatment by Ion Beam Technology

AbstractAn ultra high vacuum ion beam system, consisting of a 20 cm diameter Rf excilted (13.56 MHz) ion gun and a four-axis substrate scanner, has been used to modify large surfaces (up to 1000 cm2) of various materials, including; infrared windows, silicon nitride, polycrystalline diamond, 304 and 316 stainless steels, 440C and M50 steels, aluminum alloys, and polycarbonates; by depositing different chemical compositions of diamond-like carbon films. The influences of ion energy, Rf power, gas composition (H2/CH4 , Ar/CH4 and O2/CH4/H2), on the diamond-like carbon characteristics has been studied. Particular attention was focused on adhesion, environmental effects, IR(3–12 μm) transmission, coefficient of friction, and wear factors under spacelike environments of diamond-like carbon films on various substrates. A quadrupole mass spectrometer was utilized to monitor the ion beam composition for quality control and process optimization.

(100) Epitaxial and (111) Polycrystalline Spin Valve Heterostructures on si (100): Magnetotransport and the Importance of Interface Mixing in Ion Beam Sputtering

ABSTRACTWe have investigated magnetoresistance properties of (100) epitaxial, (11) textured and polycrystalline spin valve heterostructures of the form Ni80Fe20/Cu/NiNi80Fe20/Fe50Mn50 on (100) Si substrates by ultra high vacuum (UHV) ion beam sputtering at room temperature. Magnetoresistance was measured as a function of Cu interlayer thickness (ti) with 10 Å ≤ti ≤ 100 Å and the maximum was found at 20 Å in the case of (100) epitaxial spin valves. Highly (11) textured spin valves with heterostructure configurations similar to the (100) spin valves were found to have a slightly lower magnetoresistance than the (100) heterostructures, but the functional dependence of the magnetoresistance on ti was very similar.Interface mixing during the sputtering process by energetic neutral bombardment was found to significantly affect the magnetoresistance. Samples were made under various sputtering conditions (gas pressure, ion beam energy, target and substrate configuration) that could enhance or suppress high energy neutral bombardment of the growing film surface. Samples made under the conditions that suppressed neutral bombardment showed higher magnetoresistance and more abrupt interfaces as confirmed by small angle X-ray diffraction analysis of interface mixing by energetic neutral bombardment during sputter deposition.