The role of the dopant in the magnetism of Fe-doped SnO2 films

Transparent pure and Fe-doped SnO₂ thin films were grown by pulsed laser deposition technique on LaAlO₃ substrates. X-ray diffraction shows that the films are polycrystalline and have the rutile structure. Surprisingly, the pure film presents magnetic-like behavior at room temperature with a saturated magnetization of almost one-third of the doped film (∼3.6 and 11.3 emu/g, respectively) and its magnetization could not be attributed to any impurity phase. Taking into account the magnetic moment measured in the pure film, the effective contribution of the impurity in the doped one can be inferred to be ∼2 μ_B per Fe atom. A large magnetic moment was also predicted by an ab initio calculation in the doped system, which increases if an oxygen vacancy is present near the Fe impurity.     

Microstructure, magnetic and optical properties of sputtered polycrystalline ZnO films with Fe addition

Microstructure, magnetic and optical properties of polycrystalline Fe-doped ZnO films fabricated by cosputtering with different Fe atomic fractions (x_Fe) have been examined systematically. Fe addition could affect the growth of ZnO grains and surface morphology of the films. As x_Fe is larger than 7.0%, ZnFe₂O₄ grains appear in the films. All the films are ferromagnetic. The ferromagnetism comes from the ferromagnetic interaction activated by defects between the Fe ions that replace Zn ions. The average moment per Fe ion reaches a maximum value of 1.61 μ_B at x_Fe = 4.8%. With further increase in x_Fe, the average moment per Fe ion decreases because the antiferromagnetic energy is lower than the ferromagnetic one due to the reduced distance between the adjacent Fe ions. The optical band gap value decreases from 3.245 to 3.010 eV as x_Fe increases from 0% to 10%. Photoluminescence spectra analyses indicate that many defects that affect the optical and magnetic properties exist in the films.     

Application of spectroscopic ellipsometry to the investigation of the optical properties of cobalt-nanostructured silica thin layers

Spectroscopic ellipsometry is used to investigate optical properties of cobalt-implanted silica thin films. The films under investigation are 250 nm thick thermal SiO₂ layers on Si substrates implanted with Co⁺ ions at energy of 160 keV and at fluences of 10¹⁷ ions/cm² for different temperatures of substrate during implantation (77 and 295 K). Changes due to Co⁺ implantation are clearly observed in the optical response of the films. Optical behaviours are furthermore different for the three implantation temperatures. To understand the optical responses of these layers, the ellipsometric experimental data are compared to different models including interference effects and metal inclusions effects into the dielectric layer. The simulated ellipsometric data are obtained by calculating the interferences of an inhomogeneous layer on a Si substrate. The material within this layer is considered as an effective medium which dielectric function is calculated using the Maxwell-Garnett effective medium approximation. We show that although the structures of these layers are very complicated because of ion-implantation mechanisms, quite simple models can provide relatively good agreement. The possibilities of ellipsometry for the study of the optical properties of such clusters-embedded films are discussed. We especially provide the evidence that ellipsometry can give interesting information about the optical properties of nanostructured layers. This is of special interest in the field of nanostructured layered systems where ellipsometry appears to be a suitable optical characterization technique.     

A study of structural, compositional and optical properties of spray-deposited non-stoichiometric (Zn,Fe)S thin films

Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl₂, FeCl₂ and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N₂ as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase.     

Infrared optical properties of Ba(Zr0.20Ti0.80)O3 and Ba(Zr0.30Ti0.70)O3 thin films prepared by sol-gel method

Ba(Zr_xTi_1−x)O₃ (BZT) (x = 0.20 and 0.30) thin films are deposited on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrate by sol-gel method. X-ray diffraction patterns show that the thin films have a good crystallinity. Optical properties of the films in the wavelength range of 2.5-12 μm are studied by infrared spectroscopic ellipsometry (IRSE). The optical constants of the BZT thin films are determined by fitting the IRSE data using a classical dispersion formula. As the wavelength increases, the refractive index decreases, while the extinction coefficients increase. The effective static ionic charges are derived, which are smaller than that in a purely ionic material for the BZT thin films.     

Structural and optical properties of Fe-doped hydrogenated amorphous carbon films prepared from trans-2-butene by plasma enhanced metal organic chemical vapor deposition

Fe-doped hydrogenated amorphous carbon (a-C:H:Fe) films were deposited from a gas mixture of trans-2-butene/ferrocene/H₂ by plasma enhanced metal organic chemical vapor deposition. X-ray photoelectron spectroscopy, Fourier transform infrared spectra and Raman spectra were used to characterize the composition and the bonding structure of the a-C:H:Fe and a-C:H films. Optical properties were investigated by the UV–visible spectroscopy and the photoluminescence (PL) spectra. The Fe-doped films contain more aromatic structures and C=C bonds than the undoped films. The sp ² carbon content and sp ² clustering of the films increase, and aromatic-like rings’ structures become richer after Fe-doping. The Tauc optical gap of the a-C:H:Fe films become narrower by 0.3 eV relative to the value of the a-C:H films. The PL peak shifts from 2.35 eV of the a-C:H films to 1.95 eV of the a-C:H:Fe films, and the PL intensity of the a-C:H:Fe films is greatly enhanced. A deep level emission peak around 2.04 eV of the a-C:H:Fe films is observed.     

Structural-electronic aspects related to the near-infrared light emission of Fe-doped silicon films

The need of efficient (fast and low consumption) optoelectronic devices has always been the driving force behind the investigation of materials with new or improved properties. To be commercially attractive, however, these materials should be compatible with our current micro-electronics industry and/or telecommunications system. Silicon-based compounds, with their matured processing technology and natural abundance, partially comply with such requirements—as long as they emit light. Motivated by these issues, this work reports on the optical properties of amorphous Si films doped with Fe. The films were prepared by sputtering a Si +Fe target and were investigated by different spectroscopic techniques. According to the experimental results, both the Fe concentration and the thermal annealing of the samples induce changes in their atomic structure and optical-electronic properties. In fact, after thermal annealing at ∼750 °C, the samples partially crystallize with the development of Si and/or β- FeSi₂ crystallites. In such a case, certain samples present light emission at ∼1500 nm that depends on the presence of β- FeSi₂ crystallites and is very sensitive to the annealing conditions. The most likely reasons for the light emission (or absence of it) in the considered Fe-doped Si samples are presented and discussed in view of their main structural-electronic characteristics.     

Polarized neutron reflectometry of the influence of Fe/Si,Fe/FeSi2 and Au/Fe interfaces on the magnetic properties of epitaxial Fe films

The magnetic and structural properties of epitaxial Fe films grown on Si(1 1 1) are investigated by polarized neutron reflectometry (PNR) at room temperature. The influence of different types of interfaces, Fe/Si, Fe/FeSi₂ and Au/Fe on the magnetic properties of Fe films deposited by molecular beam epitaxy onto Si(1 1 1) are characterized. We observe a drastic reduction of the magnetic moment in the entire Fe film deposited directly on the silicon substrate essentially due to strong Si interdiffusion throughout the whole Fe layer thickness. The use of a silicide FeSi₂ template layer stops the interdiffusion and the value of the magnetic moment of the deposited Fe layer is close to its bulk value. We also evidence the asymmetric nature of the interfaces, Si/Fe and Fe/Si interfaces are magnetically very different. Finally, we show that the use of Au leads to an enhancement of the magnetization at the interface.     

Structural and magnetic properties of evaporated Fe thin films on Si(1 1 1), Si(1 0 0) and glass substrates

We present experimental results on the structural and magnetic properties of series of Fe thin films evaporated onto Si(1 1 1), Si(1 0 0) and glass substrates. The Fe thickness, t, ranges from 6 to110 nm. X-ray diffraction (XRD) and atomic force microscopy (AFM) have been used to study the structure and surface morphology of these films. The magnetic properties were investigated by means of the Brillouin light scattering (BLS) and magnetic force microscopy (MFM) techniques. The Fe films grow with (1 1 0) texture; as t increases, this (1 1 0) texture becomes weaker for Fe/Si, while for Fe/glass, the texture changes from (1 1 0) to (2 1 1). Grains are larger in Fe/Si than in Fe/glass. The effective magnetization, 4πM_eff, inferred from BLS was found to be lower than the 4πM_S bulk value. Stress induced anisotropy might be in part responsible for this difference. MFM images reveal stripe domain structure for the 110 nm thick Fe/Si(1 0 0) only.     

Electrosynthesis and characterization of CdSe thin films: Optimization of preparative parameters by photoelectrochemical technique

CdSe thin films have been electrodeposited potentiostatically onto stainless-steel and fluorine-doped tin oxide-coated glass substrates from an aqueous acidic bath using cadmium acetate ((CH₃COO)₂Cd·2H₂O) as a Cd ion source. Preparative parameters such as deposition potential, solution concentration, bath temperature, pH of the electrolytic bath and deposition time have been optimized by using photoelectrochemical (PEC) technique to obtain well adherent and uniform thin films. The electrodeposits were dark brown in colour. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption techniques. XRD studies reveal that films are polycrystalline, with hexagonal crystal structure. SEM shows that the films are compact, with spherical grains. Optical absorption studies reveal that the material exhibits a direct optical transition having band gap energy ∼1.72 eV. PEC study shows that the films are photoactive.     

Characterization of nanocrystalline gold/DLC composite films synthesized by plasma CVD technique

Composite films containing gold nanoparticles embedded in diamond-like carbon (Au-DLC) matrix were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition technique (CVD). Particle size and metal volume fraction were tailored by varying the relative amount of argon in the methane + argon gas mixture in the plasma. Optical constants of the films were evaluated. Bonding environment in these films were obtained from Raman and Fourier transformed infrared spectra (FTIR) studies. Blue-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was observed with the increase in volume fraction of metal particles in the DLC films. Absorption spectra recorded in the reflection mode indicated dichromatism in these films.     

Epitaxial growth and optical characterization of compound semiconductor β-FeSi2 prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on FZ n-Si (1 1 1) substrates by pulsed laser deposition (PLD). The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) analysis. This indicates that β-FeSi₂/Si (2 0 2/2 2 0) and the single-crystalline β-FeSi₂ can be prepared using PLD. In photoluminescence (PL) measurements at 8 K detected by Ge detector, the PL spectra of the samples annealed at 900 °C for 1, 5, 8 and 20 h showed that the PL intensity of the A-band peak increased depending on annealing time in comparison with those of as-deposited samples. The intrinsic PL intensity of the A-band peak at 0.808 eV of the β-FeSi₂ from the 20-h-annealed sample was investigated for the first time by the PLD method detected by an InGaAs detector. This result has been confirmed by temperature dependence and excitation power density of the 20-h-annealed sample with the comparison of other defect-related band peaks of the sample. Cross-sectional scanning electron microscopy (SEM) observation was also performed and the thickness of the thin films was found to be at 75 nm for 20-h-annealed. The thermal diffusion for the epitaxial growth of β−FeSi₂/Si was observed when the compositional ratio of Fe to Si was around Fe:Si=1:2 for 20-h-annealed carried out by energy dispersive X-ray spectroscopy (EDX). We discussed high crystal quality of the epitaxial growth and optical characterization of β-FeSi₂ achieved after annealing at 900 °C for 20 h.     

Mössbauer spectroscopy and magnetic properties in thin films of FexNi100−x electroplated on silicon (1 0 0)

Fe_xNi_100−x thin films were produced by galvanostatic electrodeposition on Si (1 0 0), nominal thickness 2800 nm, and x ranging 7-20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature ⁵⁷Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization.     

Porosity depth profiling of spin-coated silica thin films produced by different precursors sols

The structural evolution of nanoporous silica thin films was studied by Doppler broadening spectroscopy (DBS), 2-3 gamma ratio of positronium (3γ-PAS) and Fourier transform infrared spectroscopy (FT-IR). Four series of silica films with thickness in the 300-600 nm range were deposited by spin coating on Si substrate changing the content of sacrificial porogen in the sol precursors. The effect on the porosity of different amount of porogen and of the thermal treatments in the 400-900 °C temperature range have been highlighted. The evolution of the porosity is discussed considering the removal of porogen and of the silanol Si-OH groups by thermal treatments as pointed out by FT-IR. Pores with size from less than 1 nm up to sizes larger than 2.0 nm have been detected. In samples with maximum porogen load oPs escaping was observed indicating onset of connected porosity. At temperatures higher than 700 °C a decrease of the porosity due to a progressive pore collapsing was evidenced. A strong correlation was found between the shift of the Si-O-Si transversal optical (TO₃) mode in the FT-IR spectra and the pore size in the porous silica films as revealed by DBS and 3γ-PAS.     

Effects of Fe doping on crystalline and optical properties of yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) samples with different Fe concentrations were prepared to study the effects of Fe doping on crystalline and optical properties of YSZ. The former properties were determined by X-ray diffraction, while the latter properties were determined by diffuse reflectance (DR) and photoluminescence (PL) spectroscopies. Lattice contraction of YSZ caused by the Fe doping was observed. We revealed that the DR spectra of the 3 and 6 mol% Fe-doped YSZ samples originate from the Fe ions dissolved and undissolved in the YSZ, respectively. Moreover, two PL bands centered around 440 and 530 nm were observed for the YSZ sample, whereas one PL band centered around 440 nm was observed for the Fe-doped YSZ samples. The Fe doping reduced the PL intensity of YSZ and quenched the PL band around 530 nm. This could be explained by considering that the concentration of Fe ions near the surface of YSZ is much larger than that in the bulk of YSZ or by considering that the Fe doping enhances surface band bending of YSZ.     

Leakage current, ferroelectric and structural properties in Pb1−xBaxTiO3 thin films prepared by chemical route

Single-phase perovskite structure Pb_1−xBa_xTiO₃ thin films (x=0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO₂/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively.     

Enhancement in hydrophobicity of silica films using metal acetylacetonate and heat treatment

Water is one of the most affecting chemicals that can cause damage to the solid surface. To protect the surface due to the action of water, the surface should be made hydrophobic. In the present study, the improvement in hydrophobicity of silica films using metal acetylacetonate (M-acac) by employing heat treatment to methyltrimethoxy silane (MTMS) based silica coatings is reported as a novel attempt. Instead of following the established trends of the surface derivatization or co-precursor method, iron acetylacetonate Fe(acac)₃, copper acetylacetonate Cu(acac)₂ and heat treatment were used to incorporate hydrophobicity with silica coatings. As M-acac is readily soluble in organic solvents, Fe(acac)₃ and Cu(acac)₂ were dissolved in methanol (MeOH) and their concentration was varied from 0 to 0.025 M. The coating solution was prepared by optimizing molar ratio of MTMS:MeOH:basic H₂O to 1:7.15:6.34, respectively. Gelation time (t_g) for Cu(acac)₂ containing silica sol and that containing Fe(acac)₃ were noted to be 30 and 55 min, respectively. The substrates were taken out after gelation and heat treated at 150 °C for 2 h. The heat treated films showed a dramatic increase in the static water contact angle from 82° to as high as 142°.     

Investigation of thin TiO2 films cosputtered with Si species

Titanium dioxide (TiO₂) films were fabricated by cosputtering titanium (Ti) target and SiO₂ or Si slice with ion-beam-sputtering deposition (IBSD) technique and were postannealed at 450 °C for 6 h. The variations of oxygen bonding, which included high-binding-energy oxygen (HBO), bridging oxygen (BO), low-binding-energy oxygen (LBO), and three chemical states of titanium (Ti⁴⁺, Ti³⁺ and Ti²⁺) were analyzed by X-ray photoelectron spectroscopy (XPS). The enhancement of HBO and reduction of BO in O 1s spectra as functions of SiO₂ or Si amount in cosputtered film imply the formation of Si-O-Ti linkage. Corresponding increase of Ti³⁺ in Ti 2p spectra further confirmed the property modification of the cosputtered film resulting from the variation of the chemical bonding. An observed correlation between the chemical structure and optical properties, refractive index and extinction coefficient, of the SiO₂ or Si cosputtered films demonstrated that the change of chemical bonding in the film results in the modification of optical properties. Furthermore, it was found that the optical properties of the cosputtered films were strongly depended on the cosputtering targets. In case of the Si cosputtered films both the refractive indices and extinction coefficients were reduced after postannealing, however, the opposite trend was observed in SiO₂ cosputtered films.     

Surface morphology and luminescence characterization of β-FeSi2 thin films prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on Si (1 1 1) substrates by pulsed laser deposition (PLD) with a sintering FeSi₂ target and an electrolytic Fe target. The thin films without micron-size droplets were prepared using the electrolytic Fe target; however, the surface without droplets was remarkably rougher using the Fe target than using the FeSi₂ target. After deposition at 600 °C and then annealing at 900 °C for 20 h, XRD indicated that the thin film prepared using the Fe target had a poly-axis-orientation, but that prepared using the FeSi₂ target had a one-axis-orientation. The PL spectra of the thin films prepared using the FeSi₂ and Fe targets at a growth temperature of 600 °C and subsequently annealed at 900 °C for 20 h had A-, B- and C-bands. Moreover, it was found that the main peak at 0.808 eV (A-band) in the PL spectrum of the thin films prepared using the FeSi₂ target was the intrinsic luminescence of β-FeSi₂ from the dependence of PL peak energy on temperature and excitation power density.     

Electrosynthesis and characterization of Fe doped CdSe thin films from ethylene glycol bath

The CdSe and Fe doped CdSe (Fe:CdSe) thin films have been electrodeposited potentiostatically onto the stainless steel and fluorine doped tin oxide (FTO) glass substrates, from ethylene glycol bath containing (CH₃COO)₂·Cd·2H₂O, SeO₂, and FeCl₃ at room temperature. The doping concentration of Fe is optimized by using (photo) electrochemical (PEC) characterization technique. The deposition mechanism and Fe incorporation are studied by cyclic voltammetry. The structural, surface morphological and optical properties of the deposited CdSe and Fe:CdSe thin films have been studied by X-ray diffraction, scanning electron microscopy (SEM) and optical absorption techniques respectively. The PEC study shows that Fe:CdSe thin films are more photosensitive than that of undoped CdSe thin films. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. SEM studies reveal that the films with uniformly distributed grains over the entire surface of the substrate. The complete surface morphology has been changed after doping. Optical absorption study shows the presence of direct transition and a considerable decrease in bandgap, E_g from 1.95 to 1.65 eV.