Transmission of ∼10 keV electron beams through thin ceramic foils: Measurements and Monte Carlo simulations of electron energy distribution functions

Electron beams with particle energy of ~10 keV were sent through 300 nm thick ceramic (Si₃N₄ + SiO₂) foils and the resulting electron energy distribution functions were recorded using a retarding grid technique. The results are compared with Monte Carlo simulations performed with two publicly available packages, Geant4 and Casino v2.42. It is demonstrated that Geant4, unlike Casino, provides electron energy distribution functions very similar to the experimental distributions. Both simulation packages provide a quite precise average energy of transmitted electrons: we demonstrate that the maximum uncertainty of the calculated values of the average energy is 6% for Geant4 and 8% for Casino, taking into account all systematic uncertainties and the discrepancies in the experimental and simulated data.     

First μ+SR studies on thin films with a new beam of low energy positive muons at energies below 20 keV

At the Paul Scherrer Institute slow positive muons (μ⁺) with nearly 100% polarization and an energy of about 10 eV are generated by moderation of an intense secondary beam of surface muons in an appropriate condensed gas layer. These epithermal muons are used as a source of a tertiary beam of tunable energy between 10 eV and 20 keV. The range of these muons in solids is up to 100 nm which allows the extension of the μ⁺SR techniques (muon spin rotation, relaxation, resonance) to the study of thin films. A basic requirement for the proper interpretation of μ⁺SR results on thin films and multi-layers is the knowledge of the depth distribution of muons in matter. To date, no data are available concerning this topic. Therefore, we investigated the penetration depth of μ⁺ with energies between 8 keV and 16 keV in Cu/SiO₂ samples. The experimental data are in agreement with simulated predictions. Additionally, we present two examples of first applications of low energy μ⁺ in μ⁺SR investigations. We measured the magnetic field distribution inside a 500-nm thin High-T_C superconductor (YBa₂Cu₃O_7-δ), as well as the depth dependence of the field distribution near the surface. In another experiment a 500-nm thin sample of Fe-nanoclusters (diameter 2.4(4) nm), embedded in an Ag matrix with a volume concentration of 0.1%, was investigated with transverse field μ⁺SR. This revised version was published online in August 2006 with corrections to the Cover Date.     

Design of anisotropic reflector with birefringent thin films

A novel design for dielectric anisotropic mirrors with birefringent thin films for normal incidence is presented. This mirror consists of a stack of quarter-wave biaxial layers. The biaxial anisotropic layers can be fabricated by oblique deposition. The reflectance is different for two linear polarizations of light incidence on the mirrors. As a numerical example, the design is carried out on glass with TiO2 and ZrO2. These thin films could be applied to anisotropic reflective devices for lasers.     

Investigation of ultra—thin ferromagnetic films with a simple cubic lattice

Using Green‘s function method,we investigate ferromagnetic films with a simple cubic lattice containing up to ten monolayers.The Hamiltonian includes the Heisenberg exchange term,surface anisotropy (SA) and dipole interaction (DI).We calculate the magnetization as a function of temperature and film thickness,and we analyse the behaviour of spin canting.The result is in agreement with experiments.We calculate phase diagrams of SA versus DI to show the conditions under which spontaneous magnetization can occur.As a special case,we discuss the Heisenberg model without SA and DI.     

Thermal phase change and activation energy of crystallization of Ge-Sb-Te-Sn thin films

To improve the optical storage performance, Sn was doped into Ge2Sb2Te5 phase change thin films. The optical and thermal properties of Sn-doped Ge2Sb2Te5 film were investigated. The crystal structures of the as-sputtered and the annealed films were identified by the X-ray diffraction (XRD) method. The differential scanning calorimeter (DSC) method is used to get the crystallization temperature and crystallization energy (Ea). It was found that proper Sn-doping could highly improve storage performance of the Ge2Sb2Te5 media.     

Breakdown of thin films “cured” with tantalum oxide

Studies have been made of the temperature and time characteristics of breakdown in a thin Ta₂O₅ film produced by reactive evaporation with subsequent curing of the defect sites, with aluminum electrodes. The data obtained are explained from the viewpoint of classical thermal breakdown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 120–124, April, 1977.In conclusion, we express our indebtedness to N. S. Mukhachev and N. R. Spiridonov for their assistance in measuring the temperature dependence of E_br.     

A study of the influence of surface layers’ disordering on the spectrum of energy losses of electrons passed through copper thin single crystal films

Results of the experimental investigation of energy losses of electron passed through thin films Cu (100) with a thickness of d ≈ 420 ? at E _p = 3 keV are presented. It is revealed that the surface plasmon peak disappears at a primary electron energy of ≥6 keV. For the first time, the degree of surface amorphization and area of the disordered layer are estimated by the change of elastic peak intensity during the passage of electrons through thin films of Cu (100). There is an additional energy loss of electrons peak caused by bulk plasmon, its intensity depending on the irradiation dose under ionic bombardment.     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Conduction through 71° domain walls in BiFeO3 thin films

Local conduction at domains and domain walls is investigated in BiFeO(3) thin films containing mostly 71° domain walls. Measurements at room temperature reveal conduction through 71° domain walls. Conduction through domains could also be observed at high enough temperatures. It is found that, despite the lower conductivity of the domains, both are governed by the same mechanisms: in the low voltage regime, electrons trapped at defect states are temperature activated but the current is limited by the ferroelectric surface charges; in the large voltage regime, Schottky emission takes place and the role of oxygen vacancies is that of selectively increasing the Fermi energy at the walls and locally reducing the Schottky barrier. This understanding provides the key to engineering conduction paths in BiFeO(3).     

Transmission of electron through an Aharonov－Bohm interferometer with a quantum dot in Coulomb blockade regime

We calculate conductance of an Aharonov－Bohm (AB) interferometer for which a single-level quantum dot in the Coulomb blockade regime is embedded in one of its arms. Using the Schr?dinger equations and taking into account the Coulomb interaction on the dot, we calculate conductance G as a function of flux φ threaded through the ring and as a function of gate voltage V applied to the dot. It is found that the AB oscillations of G(φ) depend on the particle occupation on the dot, controlled by V. If the system is closed, there is no loss of particles, G(φ) is periodic and G(φ)=G(-φ), satisfying the Onsager relation. In this case G(φ) can reach its maximum value, 2e^2/h, at the resonance. When the system is open, one has G(φ)≠G(-φ), G(φ) yields a phase shift which depends on the loss rate of electrons in this open system.     

Growth of YBa2Cu3O7−x thin films on sapphire with a cerium-oxide sublayer

The possibility is demonstrated of preparing high-quality films of the high-temperature superconductor YBa₂Cu₃C_7-δ with thicknesses up to 2.6 μm by dc magnetron sputtering. It is found that inclusions consisting of CuO and YBa₂Cu₃O₈ coexist with the growing film and are “sinks” for defects, nonstoichiometric atoms, and mechanical stresses. Using x-ray diffraction and Rutherford backscattering, we find that the structural perfection of the films is improved by increasing the thickness when using the proposed fabrication technique. Zh. Tekh. Fiz. 69, 94–98 (January 1999)     

Characterization of Fe–Nb sputtered thin films

Structure, composition and chemical behavior of co-sputtered Fe–Nb thin films are analyzed by different techniques, as conversion electron Mössbauer spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. It is shown that oxygen is determinative in hindering the Fe–Nb alloy formation and, as a result, Fe_1−xO and Nb₂O₅ occur in significant amounts, even in vacuum. In spite of the oxygen role, a Fe–Nb alloy is formed in little amounts, which increase as the Nb content is increased. The increase of the Nb content is also related with the increase of Fe_1−xO and with a decreasing of the metallic Fe present. Mössbauer data indicate the Fe–Nb phase present is the Fe₂Nb Laves phase.     

Femtosecond laser interaction with pulsed-laser deposited carbon thin films of nanoscale thickness

The dependence of optical, electronic and thermal penetration zones on the thickness of nanoscale layers grown on silicon wafers is reported. Tetrahedral amorphous carbon (ta-C) and amorphous carbon nitride (a-C_xN_y) films were prepared by inverse pulsed laser deposition (IPLD). Single-pulse modification thresholds for femtosecond laser processing proved to be dependent on the actual film thickness below 60 nm for ta-C and 90 nm for a-C_xN_y. The modification behaviour was governed by multiphoton processes. An effective penetration depth of the laser radiation in a-C_xN_y was of ca. 110 nm in accordance with two-photon absorption. Both the emergence length of ballistic hot electrons and the heat diffusion length are negligible in these thin film materials. The lower bulk value of the threshold fluence of the a-C_xN_y films as compared to ta-C is mainly controlled by optical contributions due to nitrogen-related defects.     

Effect of α-irradiation of energy 0.5 MeV on the hydrogen bonding in a-Si:H thin films

Hydrogenated amorphous silicon thin films (a-Si:H) have been prepared by the rf glow discharge technique. The configuration of bonded hydrogen was investigated by infrared absorption measurements of Si:H vibrational modes before and after bombardment with an α-particle beam energy of 125 keV/n. The results showed an increase in the absorption mode near 2100, 890 and 850 cm^?1 and a decrease in the absorption mode near 2000 cm^?1 after bombardment. These observations are interpreted in terms of changes of the oscillator strengths of vibrational modes.     

A computer simulation of nucleation and growth of thin films

~~A computer simulation of nucleation and growth of thin films~~     

Write-once medium with BiO_x thin films for blue laser recording

BiO_x films are prepared by reactive direct current(DC)magnetron sputtering from a metallic bismuth target in Ar O_2 with different O_2/Ar ratios.It is found that the optical property of BiO_x films is sensitive to O_2/Ar ratios and the films deposited at O_2/Ar ratio of 0.5 have the best reflectivity contrast under the same conditions.The structure and optical characteristics of the films are studied by X-ray diffraction (XRD),X-ray photoelectron spectroscopy(XPS),and spectrophotometer.As revealed by investigations, the phase transition is mainly responsible for the change of optical properties.The static test results indicate that the BiO_x films have good writing sensitivity for blue laser beams.A high reflectivity contrast of about 52% at a writing power of 11 mW and writing pulse width of 800 ns is obtained.In addition,the films demonstrate good stability after being read for 10000 times.     

Influence of 120 MeV Si9+ ion irradiation on ZnTe semiconductor thin films

ABSTRACT

ZnTe (Zinc Telluride) is a potential semiconducting material for many optoelectronic devices like solar cells and back contact material for CdTe-based solar cells. In the present study, ZnTe thin films were prepared by thermal evaporation technique and then irradiated with 120?MeV Si⁹⁺ ions at different fluences. These films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Visible spectroscopy techniques. XRD study confirms increased crystallinity and grain growth for post-irradiated ZnTe thin films for fluences, up to 1?×?10¹¹ ions cm^?2. However, the grain size and crystallinity decreased for higher fluence-exposed samples. SEM images confirm the observed structural properties. Modification of the surface morphology of the film due to the ion irradiation with different fluences is studied. Optical band gap of film is decreased from 2.31?eV (pristine) to 2.17?eV after irradiation of Si⁹⁺ ions.