Ultrahigh Vacuum Ion Beam Sputter Research Articles

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.

Growth of exchange-biased MnPd/Fe bilayers

The growth of exchange-biased MnPd/Fe bilayers has been investigated using x-ray diffraction. The bilayers were deposited on MgO(001) substrates in an ultrahigh-vacuum ion-beam sputter system. It was found that the orientation of the MnPd unit cell and the crystalline quality could be controlled as a function of the deposition temperature. Twinned a-axis oriented MnPd films are obtained below 100 °C while single-crystalline c-axis films are obtained above 450 °C. Intermediate temperatures yield a mixture of both orientations with a poor crystalline quality. Moreover, the interface quality depends strongly on the deposition temperature and also the order in which MnPd and Fe are deposited. The results clearly show that interdiffusion is initiated at the Fe/MnPd interface at a lower temperature as compared to the MnPd/Fe interface. The close relationship between the structural and magnetic properties is also discussed.

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.

Evolution of surface roughness in epitaxial Si0.7Ge0.3(001) as a function of growth temperature (200–600 °C) and Si(001) substrate miscut

The evolution of surface roughness in epitaxial Si0.7Ge0.3 alloys grown on Si(001) as a function of temperature (200–600 °C), thickness (t=7.5–100 nm), and substrate miscut were investigated by atomic force microscopy and quantified in terms of the height-difference correlation function G(ρ), in which ρ is lateral distance and [G(ρ→∞)]1/2 is proportional to the surface width. The films were deposited by ultrahigh vacuum ion-beam sputter deposition at 0.1 nm s−1. Strain-induced surface roughening was found to dominate in alloys grown on singular Si(001) substrates at Ts≳450 °C where [G(ρ→∞)]1/2 initially increases with increasing t through the formation of coherent islanding. The islands are preferentially bounded along 〈100〉 directions and exhibit 105 faceting. This tendency is enhanced, with much better developed 〈100〉 islands separated by deep trenches—of interest for growth of self-assembled nanostructures—in films grown on Si(001)-4°[100]. Increasing the film thickness above critical values for strain relaxation leads to island coalescence and surface smoothening. At very low growth temperatures (Ts≤250 °C), film surfaces roughen kinetically, due to limited adatom diffusivity, but at far lower rates than in the higher-temperature strain-induced regime. Si0.7Ge0.3 alloy surfaces are smoother, while the films exhibit larger critical epitaxial thicknesses, than those of pure Si films grown in this temperature regime. There is an intermediate growth temperature range, however, over which the alloy film surfaces remain extremely smooth even at thicknesses near critical values for strain relaxation. This latter result is of potential importance for device fabrication.

Surface roughening during low-temperature Si epitaxial growth on singular vs vicinal Si(001) substrates.

The evolution of surface roughness on epitaxial Si films grown at 300 \ifmmode^\circ\else\textdegree\fi{}C by ultrahigh vacuum ion-beam sputter deposition onto nominally singular, [100]-, and [110]-miscut Si(001) is inconsistent with conventional scaling and hyperscaling laws for kinetic roughening. Unstable growth leading to the formation of mounds separated by a well-defined length scale is observed on all substrates. Contrary to previous high-temperature growth results, the presence of steps during deposition at 300 \ifmmode^\circ\else\textdegree\fi{}C increases the tendency toward unstable growth resulting in a much earlier development of mound structures and larger surface roughness on vicinal substrates. \textcopyright{} 1996 The American Physical Society.

Effects of Sb doping on Si(001) surface roughening and epitaxial thickness at low growth temperatures (100–300 °C)

The Sb incorporation probability in homoepitaxial Si(001) films grown by ultrahigh vacuum ion-beam sputter deposition at temperatures Ts between 100 and 300 °C was found, using quantitative secondary ion mass spectrometry, to be unity with no evidence of surface segregation. Surface roughnesses and epitaxial thicknesses te were measured by atomic force microscopy and cross-sectional transmission electron microscopy, respectively, for both undoped and Sb-doped Si layers. Sb doping was found to dramatically increase the rate of surface roughening and to decrease te by a factor of ≳2 at growth temperatures between 250 and 300 °C while having no measurable effect at lower temperatures.

Crystal growth and electronic properties of ultrahigh vacuum ion-beam sputter deposited Sb-doped Si(001)2×1

High-quality homoepitaxial Sb-doped Si(001)2×1 films have been grown on p-type Si(001) substrates by ultrahigh vacuum ion-beam sputter deposition (IBSD) at temperatures Ts between 450 and 750 °C. The load-locked multichamber system is equipped with in situ reflection high-energy electron diffraction. Sputter deposition was carried out using a 1 keV Kr+ ion beam generated by a modified Kaufman-type ion source with post-extraction electrostatic ion optics. All films were 1 μm thick and deposited at a rate of 0.35 μm h−1. Results of plan-view, cross-sectional, and convergent-beam transmission electron microscopy analyses showed that as-deposited films are highly perfect with no visible defects. Sb incorporation probabilities σSb ranged from ≂0.1 at Ts=750 °C to ≂1 for Ts≤550 °C with no indication by secondary-ion mass spectrometry (SIMS) of Sb surface segregation. These σSb values are one to three orders of magnitude larger than for coevaporative Sb doping during molecular beam epitaxy where extensive Sb surface segregation is observed. A comparison of calibrated SIMS and Hall-effect measurements established that the incorporated Sb exhibited complete electrical activity. SIMS analyses also showed no detectable Kr (detection limit ≂5×1017 cm−3). Temperature-dependent (15–300 K) electron mobilities were equal to the best reported bulk Si values.

Epitaxial growth of Cu (001) on Si (001): Mechanisms of orientation development and defect morphology

We describe the evolution of microstructure during ultrahigh vacuum ion beam sputter deposition of Cu (001) at room temperature on hydrogen-terminated Si (001). In situ reflection high energy electron diffraction indicates growth of an epitaxial Cu (001) film on Si (001) with the intensity of the Bragg rods sharpening during 5–20 nm of Cu film growth. Post-growth x-ray diffraction indicates the Cu film has a mosaic spread of (001) textures of about ±2° and that a small fraction (0.001–0.01) is of (111) textures. High-resolution transmission electron microscopy shows an abrupt Cu/Si interface with no interfacial silicide, and reveals an evolution in texture with Cu thickness so as to reduce the mosaic spread about (001). Moiré contrast suggests a nearly periodic elastic strain field extending into the Cu and Si at the interface. Other aspects of film growth which are critical to epitaxy are also discussed.

Growth of homoepitaxial Ge(001)2 × 1 by ultrahigh vacuum ion beam sputter deposition

High quality epitaxial Ge(001)2 × 1 films have been grown on Ge(001) substrates by ultrahigh vacuum (UHV) ion beam sputter deposition. The load-locked multichamber growth system is equipped with in situ reflection high-energy electron diffraction. Sputter deposition was carried out using a 1 keV Kr + ion beam generated by a modified UHV Kaufman-type ion source with post-extraction electrostatic ion optics. All films were 1 microm thick and deposited at a rate of 0.5 microm h −1. Results of plan-view, cross-sectional, and convergent-beam transmission electron microscopy analyses showed that films deposited at temperatures T s between 300 and 650°C had a high degree of perfection with no observable defects. Temperature-dependent carrier mobilities were found to be equal to or to exceed the best reported values for bulk Ge. A1-doped p-type films grown at T s = 400–600° C exhibited 77 K hole mobilities ranging from 3890 to 1200 cm 2 V −1 s −1 for corresponding hole concentrations between 2.8 × 10 16 and 1.5 × 10 17 cm −3.

Bilayer Permalloy films grown in orthogonal applied fields

Permalloy bilayers grown in orthogonal applied fields demonstrated unusual coupling phenomena in Kerr-effect observations. The films were grown by ultrahigh-vacuum ion-beam sputtering in an applied field of 28 Oe that established a well-defined anisotropy direction. Midway through the deposition, the substrates were rapidly turned 90 degrees in the applied field, including an orthogonal anisotropy direction in the second layer of the film. With layers of equal thickness, a simple model predicts the bilayer to be isotropic in the plane of the film, regardless of the strength or mechanism of any interlayer coupling. Instead, the initial layer acquired the anisotropy orientation of the second layer grown. This unusual coupling was investigated for a number of bilayer structures of different thicknesses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Epitaxial growth of yttria-stabilized zirconia films on silicon by ultrahigh vacuum ion beam sputter deposition

Yttria-stabilized zirconia (YSZ) films have been grown on Si (100) substrates by ion sputter deposition using ultrahigh vacuum system with in situ diagnostic equipment. Epitaxial conditions of YSZ (100) films were achieved between 700 and 800 °C by using an oxygen partial pressure around 3×10−4 Pa during the deposition. The film stoichiometry was measured by Rutherford backscattering spectrometry and nuclear reaction analysis. Crystalline quality of the YSZ layers was determined by x-ray diffraction, channeling of 4He+ ion beam, and in situ reflection high-energy electron diffraction pattern.