Properties of boron and phosphorous incorporated tetrahedral amorphous carbon films grown using filtered cathodic vacuum arc process

This paper reports the electrical, mechanical, structural and field emission properties of as grown and also boron and phosphorous incorporated tetrahedral amorphous carbon (ta-C) films, deposited using a filtered cathodic vacuum arc process. The effect of varying boron and phosphorous content (up to 2.0 at.% in to ta-C) on the conductivity (σ_D), activation energy (ΔE₁), hardness, microstructure, emission threshold (E_turn-ON) and emission current density (J) at 12.5 V/μm of ta-C: B and ta-C: P films deposited at a high negative substrate bias of −300 V are reported. It is observed that both boron and phosphorous incorporation leads to a nearly an order increase in σ_D and corresponding decrease in ΔE₁ and a slight increase in hardness as compared to as grown ta-C films. In the case of field assisted electron emission, it is observed that E_turn-ON increases and J decreases. The changes are attributed to the changes in the sp³/sp² ratio of the films due to boron and phosphorous incorporation. The effect of boron on ta-C is to give a p-type effect whereas the effect of phosphorous gives n-type doping effect.     

Switching phenomenon and optical properties of Se85Te10Bi5 films

Se₈₅Te₁₀Bi₅ films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se₈₅Te₁₀Bi₅ films were amorphous. Electrical conduction activation energy (ΔE_σ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se₈₅Te₁₀Bi₅ films reveals that it is typical for a memory switch. The switching voltage V_th increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of V_th is found to be 0.325 eV. The switching phenomenon in amorphous Se₈₅Te₁₀Bi₅ films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se₈₅Te₁₀Bi₅ films. Allowed non-direct transitions with an optical energy gap (E_g^opt) of 1.33 eV have been obtained. ΔE_σ is almost half the obtained value of E_g^opt, which suggested band to band conduction as indicated by Davis and Mott.     

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

The structural and magnetic properties of as-grown 5–50 nm thin ion-beam sputter deposited transition metal–metalloid Co₂₀Fe₆₀B₂₀ (CFB) films are reported in this communication. A broad peak observed at 2θ∼45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300 K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (K_u). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of K_u on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Magnetic properties of strontium hexaferrite films prepared by pulsed laser deposition

The magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films fabricated by pulsed laser deposition on the Si(100) substrate with Pt(111) underlayer have been studied as a function of film thickness (50–700 nm). X-ray diffraction patterns confirm that the films have c-axis perpendicular orientation. The coercivities in perpendicular direction are higher than those for in-plane direction which indicates the films have perpendicular magnetic anisotropy. The coercivity was found to decrease with increasing of thickness, due to the increasing of the grain size and relaxation in lattice strain. The 200 nm thick film exhibits hexagonal shape grains of 150 nm and optimum magnetic properties of M_s=298 emu/cm³ and H_c=2540 Oe.     

Preparation of strontium hexaferrite film by pulsed laser deposition with in situ heating and post annealing

Strontium hexaferrite (SrFe₁₂O₁₉) films have been fabricated by pulsed laser deposition on Si(1 0 0) substrate with Pt(1 1 1) underlayer through in situ and post annealing heat treatments. C-axis perpendicular oriented SrFe₁₂O₁₉ films have been confirmed by X-ray diffraction patterns for both of the in situ heated and post annealed films. The cluster-like single domain structures are recognized by magnetic force microscopy. Higher coercivity in perpendicular direction than that for the in-plane direction shows that the films have perpendicular magnetic anisotropy. High perpendicular coercivity, around 3.8 kOe, has been achieved after post annealing at 500 °C. Higher coercivity of the post annealed SrFe₁₂O₁₉ films was found to be related to nanosized grain of about 50–80 nm.     

Effect of thermal process on magnetic anisotropy in FeCoB soft underlayer

Relationship between magnetic anisotropy field H_k and thermal processes during the preparation has been studied for FeCoB thin films. The FeCoB films deposited on the glass substrates by facing targets sputtering successfully showed strong magnetic anisotropy when the substrate was heated at the substrate temperature T_s above 100 °C. Additionally, the lattice spacing of FeCo(1 1 0) in the perpendicular direction was found to decrease depending on the substrate temperature T_s. Among various temperature histories, the heating processes with a phase of increasing T_s revealed the further improvement of H_k. Meanwhile, high H_k in the films disappears after the post-deposition annealing at the temperature above 400 °C.     

Influence of the nitrogen contents on the permeability characteristics and soft magnetic properties of FeHfN films

High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, the uniaxial anisotropy and coercivity should be as low as possible. This study employed dc reactive magnetron sputtering to fabricate nanocrystalline FeHfN thin films. The influence of the nitrogen flow on the composition, microstructure, and permeability characteristics, as well as magnetic properties was investigated. Increasing the nitrogen content can alter FeHfN films from amorphous-like to crystalline phases. The magnetic properties and permeability depend on variations in the microstructure. With the optimum N₂/Ar flow ratio of 4.8% (N₂ flow: 1.2 sccm), low anisotropy (H_K = 18 Oe), low coercivity (H_C = 1.1 Oe) and high permeability (μ′ > 600 at 50 MHz) were obtained for fabrication of a nanocrystalline FeHfN film with a thickness of around 700 nm. Such as-fabricated FeHfN films with a permeability of over 600 should be a promising candidate for high-permeability ferromagnetic material applications.     

Memory switching of germanium tellurium amorphous semiconductor

The dc conductivity and switching properties of amorphous GeTe thin film of thickness 262 nm are investigated in the temperature range 303-373 K. The activation energy ΔE_σ, the room temperature electrical conductivity σ_RT and the pre-exponential factor σ₀ were measured and validated for the tested sample. The conduction activation energy ΔE_σ is calculated. The I-V characteristic curves of the thin film samples showing a memory switching at the turnover point (TOP) from high resistance state (OFF state) to the negative differential resistance state (NDRS) (ON state). It is found that the mean values of the threshold electrical field E_th decreased exponentially with increasing temperatures in the investigated range. The switching activation energy ΔE_th is calculated. Measurements of the dissipated threshold power P_th and the threshold resistance R_th were carried out at TOP point at different temperatures of the samples. The activation energies ΔE_R and ΔE_P caused by resistance and power respectively are deduced. The results obtained support thermal model for initiating switching process in this system.     

Influence of assisted ion energy on surface roughness and mechanical properties of boron carbon nitride films synthesized by DIBSD

The BCN thin films were produced by dual ion beam sputtering deposition (DIBSD). The influence of assisted ion energy on surface roughness and mechanical properties of BCN films were investigated. The surface roughness was determined by atomic force microscopy (AFM) and the mechanical properties of BCN firms were evaluated by nano-indentation in N₂ gas. The composition, structure and chemical bonding of the BCN thin films were analyzed by using energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), laser Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). These films appeared as amorphous structure. As a result, the BCN films with the smoothest surface (R_a = 0.35 nm and R_p-v = 4.4 nm) and the highest nano-hardness of 30.1 GPa and elastic modulus of 232.6 GPa were obtained at 200 eV and 12 mA with N₂:Ar = 1:1, and the chemical composition of this BCN film was 81 at.% B, 14 at.% C and 5 at.% N. Moreover, several bonding states such as B-N, B-C and C-N were observed in BCN thin films.     

Structure, magnetic and magnetostrictive properties of as-deposited Fe-Ga thin films

Polycrystalline Fe_100−xGa_x (19?x?23) films were grown on Si(1 0 0) substrates at different partial pressures of sputtering gas ranging from 3 to 7 μbar. Microstructural, magnetic and magnetostrictive properties were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and magneto-optic Kerr effect (MOKE) magnetometry respectively. X-ray diffraction showed that all films have the body-centered cubic (bcc) Fe-Ga phase with the 〈1 1 0〉 direction out of the film plane. Magnetic characterization of the films showed that the films prepared at 3 μbar had weak uniaxial anisotropy whereas films grown at Ar pressures in the range 4-7 μbar were magnetically isotropic. The effective saturation magnetostriction constants (λ_eff) of the films were measured using the Villari effect. It was found that effective saturation magnetostriction constants were almost constant over the Ga composition range achieved by varying the sputtering pressure. The measured effective magnetostriction constants fit closely to the calculated saturation magnetostriction constants of 〈1 1 0〉 textured polycrystalline films with the 〈1 1 0〉 directions slightly canted with respect to the normal to the sample surface. It was found that a high pressure of the sputtering gas effected the magnetic softness of the films. The saturation field increased and remanence ratio decreased with increase in pressure.     

Dependence of magnetic characteristics on sputtering-power and substrate-temperature in amorphous Tb40(FeCoV)60 films

The amorphous Tb₄₀(Fe₄₉Co₄₉V₂)₆₀ films were deposited at different sputtering powers and substrate temperatures. The microstructural and magnetic characteristics were investigated by means of field emission scan electron microscope, magnetic force microscope and vibrating sample magnetometer. Our results show that with increasing sputtering power, out-of-plane coercivity decreases monotonically while saturation magnetization has a maximum value of 231 kA/m for the sample prepared at 50 W. The as-deposited alloy films are amorphous, whereas the coercivity and saturation magnetization are strongly dependent on the substrate temperature. An out-of-plane hysteresis loop with coercivity below 22 mT and saturation magnetization over 290 kA/m is obtained combining dc power and substrate temperature. The dominant mechanism of room temperature coercivity appears to be domain wall pinning, rather than nucleation under all conditions measured. The variation of saturation magnetization is similar to that of perpendicular magnetic anisotropy with either sputtering power or substrate temperature according to the difference of magnetic domain structure.     

Influence of porous morphology on optical dispersion properties of template free mesoporous titanium dioxide (TiO2) films

This paper focuses the influence of porous morphology on the microstructure and optical properties of TiO₂ films prepared by different sol concentration and calcination temperatures. Mesoporous TiO₂ thin films were prepared on the glass substrates by sol-gel dip coating technique using titanium (IV) isopropoxide. Porous morphology of the films can be regulated by chemical kinetics and is studied by scanning electron microscopy. The optical dispersion parameters such as refractive index (n), oscillator energy (E_d), and particle co-ordination number (N_c) of the mesoporous TiO₂ films were studied using Swanepoel and Wemple-DiDomenico single oscillator models. The higher precursor concentration (0.06 M), films exhibit high porosity and refractive index, which are modified under calcination treatment. Calcinated films of low metal precursor concentration (0.03 M) possess higher particle co-ordination number (N_c = 5.05) than that of 0.06 M films (N_c = 4.90) due to calcination at 400 °C. The lattice dielectric constant (E_∞) of mesoporous TiO₂ films was determined by using Spintzer model. Urbach energy of the mesoporous films has been estimated for both concentration and the analysis revealed the strong dependence of Urbach energy on porous morphology. The influence of porous morphology on the optical dispersion properties also has been explained briefly in this paper.     

Self-assembled strontium ferrite dot array on Au underlayer

Strontium ferrite (SrM) thin films were deposited on thermally oxidized silicon wafer with Au underlayer. Gold underlayers were prepared at various substrate temperatures by using a magnetron sputtering system. C-axis oriented SrM perpendicular films and preferred (1 1 1) orientation of underlayer have confirmed by X-ray diffraction patterns. The intensity of (1 1 1) diffraction line for Au and that of (0 0 l) diffraction line for strontium ferrite decrease with increase in substrate temperature (T_u) The maximum coercivity and remanent squareness ratio in perpendicular direction, at T_u of 500 °C, are 5.4 kOe and 0.68, respectively. The strength of the intergranular interaction of SrM magnetic particles is described by the parameter Δm. The SrM/Au films prepared at T_u above 100 °C have smaller Δm peak values than that for SrM/Au films prepared at T_u of room temperature. This behavior is related to low magnetostatic coupling between the magnetic particles separated by the non-magnetic amorphous phase.     

Effect of magnetic field annealing on microstructure and magnetic properties of FePt films

FePt (20 nm) films were annealed in a magnetic field (along the normal direction of the films) at a temperature around the Curie temperature of L1₀ FePt. The influence of magnetic filed annealing on texture and magnetic properties of FePt films were investigated. The results indicate that preferential (0 0 1) orientation and perpendicular anisotropy can be obtained in L1₀ FePt films by using magnetic field annealing around the Curie temperature of L1₀ FePt. This is one of the potential methods to obtain (0 0 1) orientation and thus to improve the perpendicular anisotropy in FePt films.     

Effects of substrate bias and nitrogen flow ratio on the surface morphology and binding state of reactively sputtered ZrNx films before and after annealing

ZrN_x films were sputtered in an Ar + N₂ atmosphere, with different substrate biases (0 to −200 V) at various nitrogen flow ratios (%N₂ = 0.5-24%). The surface morphology, resistivity, crystllinity, and bonding configuration of ZrN_x films, before and after vacuum annealing, were investigated. As compared with ZrN_x films grown without substrate bias, before and after annealing, the resistivity of 1% and 2% N₂ films decreases with increasing substrate biases. Simultaneously, if the applied bias is too high, the crystallinity of ZrN_x film will decrease. The surfaces of 1% and 2% N₂ flow films deposited without bias have small nodules, whereas the surface morphology of films deposited at −100 V of substrate bias exhibits large nodules and rugged surface. Once a −200 V of substrate bias is applied to the substrate, the surface morphology of ZrN_x films, grown at 1% and 2% nitrogen flow ratios, is smooth. Furthermore, there are two deconvoluted peaks in XPS spectra (i.e., Zr-O and Zr-N) of ZrN_x films deposited at −200 V of substrate bias before and after annealing. On the other hand, the surface morphology changes dramatically from rugged surfaces for film deposited at lower nitrogen flow ratio (%N₂ < 1%) to smoother and denser surfaces for film grown at higher nitrogen flow ratio (%N₂ ≥ 1%). The Zr-N bonding in 2% N₂ films still exist after annealing at 700 °C, while the Zr-N bonding in 0.5% and 16% N₂ flow film vanish at the same temperature. The connection between the resistivity, crystallinity, surface morphology, and bonding configuration of ZrN_x films and how they are influenced by the substrate bias and nitrogen flow ratio are discussed in this paper.     

Titanium oxynitride thin films sputter deposited by the reactive gas pulsing process

DC reactive sputtering was used to successfully make thin films of titanium oxynitride using titanium metallic target, argon as plasma gas and nitrogen and oxygen as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas oxygen flow rate was pulsed using a square pattern. The study consisted in analysing the influence of the shape of the pulsed rate on physical properties of these films. In order to adjust the metalloid concentration to get films with a wide range of oxygen-to-nitrogen ratios, the reactive gas pulsing process (RGPP) was used. In this process, the oxygen flow switches “on” and “off” periodically according to a duty cycle α = t_ON/T. Electrical conductivity of films measured against temperature was gradually modified from metallic (σ_300K = 4.42 × 10⁴ S m⁻¹) to semi-conducting behaviour (σ_300K = 7.14 S m⁻¹) with an increasing duty cycle. Mechanical properties like nanohardness (H_n) and reduced Young's modulus (E_r) of the films were investigated. Experimental values of H_n and E_r obtained by nanoindentation at 10% depth ranged from 15.8 to 5.2 GPa and from 273 to 142 GPa, respectively. Evolutions of H_n and E against duty cycle were similar. A regular decrease was observed for duty cycle α ≤ 25% corresponding to the occurrence of TiO_xN_y phase. Higher duty cycles led to the smallest values of H_n and E and correlated with TiO₂ compound composition. At last, the colour variation of these titanium oxynitrides was investigated as a function of α in the L^*a^*b^* colour space. It was related to the chemical composition of the films.     

Pattern guided structure formation in polymer films of asymmetric blends

Two off-critical blends of poly(2-vinylpyridine) and polystyrene, 2:3 and 3:2 (w:w) PVP:PS, were spin-cast (with varied domain scale R) onto periodically (λ = 4 μm) patterned substrate. The pattern consisted of two alternating symmetric stripes: Au attracting PVP and neutral self-assembled monolayer. The resulting droplet-type morphologies were recorded with Scanning Force Microscopy and examined with integral geometry approach. PVP-rich islands of the 2:3 PVP:PS films form, for a wide R/λ range, strongly anisotropic morphologies. They show up, for R/λ ∼ 0.5, a weak λ/2-substructure of smaller PVP droplets in addition to the domains periodic with λ. The 3:2 blend exhibits morphologies with dominant λ-structure of PVP ribbons, which encircle PS droplets. For R/λ ∼ 0.5, smaller PS domains are also present but no λ/2-substructure is formed. The |χ_E|-values of droplet surface density are reduced, as compared to homogeneous substrate, for the 3:2 blend (with |χ_E| → 0 for R ∼ λ). This effect is absent for the 2:3 mixture.     

Structural characterization and optical properties of ZnSe thin films

Zinc selenide (ZnSe) thin films (d = 0.11-0.93 μm) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. Their structural characteristics were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The experiments showed that the films are polycrystalline and have a zinc blende (cubic) structure. The film crystallites are preferentially oriented with the (1 1 1) planes parallel to the substrate surface. AFM images showed that the films have a grain like surface morphology. The average roughness, R_a = 3.3-6.4 nm, and the root mean square roughness, R_rms = 5.4-11.9 nm, were calculated and found to depend on the film thickness and post-deposition heat treatment.The spectral dependence of the absorption coefficient was determined from transmission spectra, in the range 300-1400 nm.The values of optical bandgap were calculated from the absorption spectra, E_g = 2.6-2.7 eV.The effect of the deposition conditions and post-deposition heat treatment on the structural and optical characteristics was investigated.     

Microstructure and magnetic properties of nanocomposite FePt/MgO and FePt/Ag films

An in-plane magnetic anisotropy of FePt film is obtained in the MgO 5 nm/FePt t nm/MgO 5 nm films (where t=5, 10 and 20 nm). Both the in-plane coercivity (H_c∥) and the perpendicular magnetic anisotropy of FePt films are increased when introducing an Ag-capped layer instead of MgO-capped layer. An in-plane coercivity is 3154 Oe for the MgO 5 nm/FePt 10 nm/MgO 5 nm film, and it can be increased to 4846 Oe as a 5 nm Ag-capped layer instead of MgO-capped layer. The transmission electron microscopy (TEM)-energy disperse spectrum (EDS) analysis shows that the Ag mainly distributed at the grain boundary of FePt, that leads the increase of the grain boundary energy, which will enhance coercivity and perpendicular magnetic anisotropy of FePt film.