Microstructural and surface morphological studies on Co doped ZnS diluted magnetic semiconductor thin films

Microstructural and surface morphological studies of Co (2.5%) doped ZnS thin films deposited at different substrate temperatures (T_S) of 200, 400 and 600 °C by means of pulsed laser deposition are presented. The deposited films are in wurtzite-hexagonal crystal structure as confirmed by X-ray diffraction and Raman spectroscopy techniques. The films deposited at higher T_S show columnar morphology, as evidence by transmission electron microscopy measurements. Images of the surface topography have been taken by atomic force microscopy (AFM) for the film deposited at different T_S. The film deposited at T_S of 200 °C shows cone-like structures while deposited at T_S of 400 and 600 °C show columnar structures. A fractal analysis has been performed on AFM images to understand the microstructure and surface morphology of thin film at different T_S. Fractal analysis also reveals the morphological changes in the film with increasing T_S. The observed ferromagnetism is correlated with columnar growth of the film which can be used as diluted magnetic semiconductor for spintronic applications.     

Magnetization in Nanocrystalline PLD Zinc Ferrite Thin Films Deposited on Fused Quartz Substrate

The nanocrystalline zinc ferrite (ZnFe₂ O ₄) thin films were grown on the fused quartz substrate using pulsed laser deposition. The effects of atmospheric conditions on structural, magnetic, and morphological properties have been systematically studied using X-ray diffraction, vibrating sample magnetometry, and atomic force microscopy. The films showed textured growth of zinc ferrite for the substrate temperatures at ≥ 600 °C irrespective of the ambient environment. Interestingly, thin films of zinc ferrite showed a magnetic hysteresis loop in contrast to the paramagnetic nature of their bulk counterpart. The value of saturation magnetization (4π M _s) increased from 130 to 360 G when the substrate temperature was increased from room temperature (RT) to 800 °C in the oxygen atmosphere. In the absence of oxygen pressure, the value of 4π M _s is observed to be 330 G for the film deposited at RT and found to increase to a value of 670 G when the film is deposited at 400 °C and the maximum value of 2580 G is observed for the film deposited at 700 °C. However, the value of 4π M _s of 800 °C dropped down to 2000 G.     

Superconducting Ti/TiN Thin Films for mm-Wave Absorption

Polarization-sensitive detectors at 120–500 GHz are required for the observation of the cosmic microwave background radiation. In this paper, superconducting thin films based on Ti/TiN bilayers are developed to be integrated as electromagnetic wave absorbers in suspended cooled silicon bolometers. The critical temperature (T_c) is tuned in the range of 600–800 mK through the superconductivity proximity effect between Ti and TiN to optimize the absorption of the incident power while minimizing the heat capacity of the system at low temperature. Ti/TiN bilayer samples are fabricated on silicon with two different thicknesses (100/5 and 300/5 nm). Electrical characterizations at low temperature have been performed and revealed the effect of thermal annealing (20–250 °C) on residual stress, T_c, critical magnetic field (H_c) and resistance above T_c. A physical characterization by X-ray photoelectron spectroscopy provides evidences of oxidized states which may explain these effects.     

The microstructural evolution in high sodium epitaxial sodium potassium niobate films deposited by low-temperature hydro-thermal method

Sodium potassium niobate [(K _x Na_1?x )NbO₃] films with high sodium composition (x = 0.06 and 0.24) were fabricated using a low-temperature (240 °C) hydro-thermal method on (001) niobium-doped strontium titanate (Nb-STO) substrate. The films were annealed subsequently at 600 °C. Thicknesses of the films were maintained in the range of ~800–1000 nm. Transmission electron microscopy-selected area electron diffraction studies revealed the appearance of super-spots, thereby confirming the tilting of the oxygen sub-lattice at both high Na compositions. The bright-field imaging and scanning transmission electron microscopy-energy dispersive spectroscopy elemental mapping revealed KNN film with K-rich interfacial regions and Na-rich top region of the film at both the high Na composition, whereas the potassium niobate (KNbO₃, x = 1) film showed no such oxygen sub-lattice tilting, and a sharp substrate-film interface was observed. The observed tilting of oxygen sub-lattice is a direct consequence of the reduced structural stability in high Na compositions in the KNN solid solutions.     

Nanodomain and interface structure in epitaxial BaTiO<Subscript>3</Subscript> thin films on MgO deposited by magnetron sputtering

High epitaxial quality BaTiO₃ films were deposited on the MgO (001) substrate using RF magnetron sputtering at 800 °C by manipulating processing parameters. The BaTiO₃ films have a ~200 nm thickness with a very low surface roughness but a rough interface structure with respect to the substrate. The epitaxial BaTiO₃ films have a tetragonal crystal structure (a = 4.02 Å and c = 4.11 Å) with a tetragonality (c/a) of 1.02. The c-axis of the film is parallel to the growth direction as characterized by X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. The orientation relationship between the film and the MgO is (001)_BTO//(001)_MgO and 〈100〉_BTO//〈100〉_MgO. Epitaxial nanodomains were formed in the film with a size ranging from 3 to 20 nm. The formation of the nanodomains is associated with the rough film/substrate interface due to the modification of the substrate surface characteristics (steps, terraces, and kinks) during the process. The two-dimensional interface structure between the film and the substrate was studied and its influence on the film microstructure is discussed.     

Structure,thermal stability,and microhardness of ZrO<Subscript>2</Subscript> coatings produced by different techniques

Using ion-beam and rf magnetron sputtering of oxide targets, we have grown thin ZrO₂ coatings on 12Kh18N10T high-temperature steel substrates. Depending on the deposition technique, amorphous or crystalline (t + c) coatings have been obtained. The amorphous zirconia retains a disordered structure and high microhardness values up to 600°C. Its crystallization leads to a sharp drop in its microhardness and peeling from the substrate. The initially crystalline coating retains continuity and high microhardness values despite the t → с phase transition at 600 and 700°C. Only annealing at 800°C or higher temperatures reduces its microhardness. This is tentatively attributed to the influence of the substrate.     

Optical and electrical properties of E-Beam deposited TiO<Subscript>2</Subscript>/Si thin films

In this paper, optical and electrical properties of E-Beam deposited TiO₂/Si thin films have been studied and investigated extensively. The films were deposited on p-type (100) silicon wafer by using electron beam evaporation technique. The thickness of the thin films was measured by a spectroscopic reflectometer, which is about 216 nm. The fabricated titanium oxide (TiO₂) thin films were annealed at 800 °C for 1 h under N₂ ambient. X-ray diffraction measurements were performed to study the structure and phase identification of the fabricated TiO₂ thin films. For the optical properties, reflection, transmittance, refractive index and absorption coefficient were obtained and analyzed. The photocurrent and dark current of the fabricated films were measured by I–V measurements. The measurement of the current–voltage (I–V) characteristics possesses good ohmic contact. The electrical characterizations of the films were performed in the range of the low frequencies (50 and 100 kHz) and high frequencies (750 kHz and 1 MHz) by the capacitance–voltage and conductance–voltage measurements at room temperature. The capacitance of the fabricated TiO₂ MOS capacitor at both high and low frequencies increases with the decrease in frequencies. The obtained conductance curves (peaks) increase with the decreasing in the frequencies. This can be due to the interface state density, series resistance and interfacial dielectric of the fabricated MOS capacitors. The variation in the characteristics of the fabricated film shows that TiO₂ is a promising candidate to be used in the optoelectronic and future UV detector applications as a switch, such as an optical amplifier, emitter, and UV light detectors.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Characterization of CuInGeSe<Subscript>4</Subscript> thin films and Al/n–Si/p–CuInGeSe<Subscript>4</Subscript>/Au heterojunction device

CuInGeSe₄ thin films of various thicknesses were prepared on a glass substrate by thermal evaporation followed by selenization at 700 K. Energy dispersive X-ray analysis shows that the CuInGeSe₄ thin films are near stoichiometric. The X-ray diffraction patterns indicate that the as-deposited CuInGeSe₄ thin films are amorphous, while the CuInGeSe₄ thin films annealed at 700 K are polycrystalline with the chalcopyrite phase. The structure of the films was further investigated by transmission electron microscopy and diffraction, with the results verifying the X-ray diffraction data. High-resolution scanning electron microscopy images show well-defined grains that are nearly similar in size. The surface roughness increases with film thickness, as confirmed by atomic force microscopy. The optical transmission and reflection spectra of the CuInGeSe₄ thin films were recorded over the wavelength range of 400–2500 nm. The variation of the optical parameters of the CuInGeSe₄ thin films, such as the refractive index n and the optical band gap E_g, as a function of the film thickness was determined. The value of E_g decreases with increasing film thickness. For the studied films, n were estimated from the Swanoepl’s method and were found to increase with increasing film thickness as well as follow the two-term Cauchy dispersion relation. A heterojunction with the configuration Al/n–Si/p–CuInGeSe₄/Au was fabricated. The built-in voltage and the carrier concentration of the heterojunction was determined from the capacitance–voltage measurements at 1 MHz and were found to be 0.61 V and 3.72?×?10¹⁷ cm^?3, respectively. Under 1000 W/m² solar simulator illumination, the heterojunction achieved a conversion efficiency of 2.83%.     

Growth and magnetic properties of spin coated Co<Subscript>0.6</Subscript>Zn<Subscript>0.4</Subscript>Mn<Subscript>0.3</Subscript>Fe<Subscript>1.7</Subscript>O<Subscript>4</Subscript> ultrathin films on silicon (100), (110) and (111) substrates

This paper reports growth of Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄ (CZFMO) ultrathin films (thickness: 23–30 nm) by spin coating technique on silicon (100), (110) and (111) substrates. The deposited films were annealed at 700 °C for 1 h in the oxygen environment. All the films were found to be polycrystalline in nature. The CZFMO films were found to have minimal residual stress (13–50 MPa), which could be an encouraging feature for novel microwave miniaturized device applications. Room temperature magnetic measurements demonstrated completely saturated hysteresis loop with the highest squareness ratio (M _R /M _S )?~?60% for the film grown on Si (110) substrate. On the other hand CZFMO films on Si (100) and Si (111) substrates showed unsaturated hysteresis loops with M _R /M _S ~ 10 and 5%, respectively. The reason for the better magnetic properties of the ultrathin CZFMO film on Si (110) substrate seems to be its better crystalline quality and larger grain size compared to those of other films.     

Deposition of luminescent a-SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H Films with SiH<Subscript>4</Subscript>–N<Subscript>2</Subscript> gas mixture by VHF–PECVD using novel impedance matching method

Hydrogenated amorphous silicon nitride (a-SiN _x :H) films are produced from a SiH₄–N₂ gas mixture by plasma enhanced chemical vapor deposition (PECVD) system with a newly developed impedance matching method at frequencies 13.6–150 MHz. An increase in the rf power from 35 to 350 mW/cm² at the highest frequency of 150 MHz increases the optical bandgap (E _opt) from 2.0 to 4.5 eV. Optical emission spectroscopy (OES) of the SiH₄–N₂ plasma shows that the emission intensity of SiH* (414 nm) is almost proportional to deposition rate. Films of a-SiN _x :H deposited at 150 MHz and 210 mW/cm² has an optical bandgap of E _opt ≈ 4.1 eV and emits visible photoluminescence (PL) at room temperature (RT).     

Optical properties of silver containing As–S–Se thin films

The As₃₃S_{67- y} Se _y , where y = 0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by vacuum thermal evaporation technique. Range of the silver content dissoluted in films was x = 0 – 25 at. %. The refractive index increase with increasing silver and selenium content. The difference of the refractive index (Δn) between undoped and silver doped films was ～ 0.4 and between As₃₃S₆₇ and As₃₃Se₆₇ was films ～ 0.42. The values of non-linear refractive index grow with increasing silver and selenium content. The difference of optical bandgap, ΔE _g ^opt , between undoped As₃₃S₆₇ and fully dopped films with Ag and Se was ～ 1 eV.     

Improved short-circuit current density of a-Si:H thin film solar cells with n-type silicon carbide layer

In this work, the performance of p–i–n hydrogenated amorphous silicon thin film solar cells by adopting n-type silicon carbide (n-SiC_x:H) layer was investigated. By varying CH₄/SiH₄ gas flow ratio, refractive index and electrical conductivity of n-SiC_x:H thin films were changed in the range of 3.4 to 3.8 and 1.48E?5 to 1.24 S/cm, respectively. Compared with solar cells with n-Si:H/Ag configuration, short-circuit current density (J _sc ) of solar cells with n-SiC_x:H/Ag configuration was improved up to 8.4%, which was comparable with that of solar cells with n-Si:H/ZnO/Ag configuration. Improved J _sc was related with enhanced spectral response at long wavelength of 500–800 nm. It was supposed that the decreased refractive index of n-SiC_x:H layer resulted in the increased back reflectance, which contributed to the improved J _sc. Our experiments demonstrated that n-SiC_x:H thin films were attractive choice because they functioned both as n-layer and interlayer in back reflector, and their deposition method was compatible with preparation process of solar cells.     

Investigation of earth-alkaline (EA = Mg,Ca, Sr) containing methylammonium tin iodide perovskite systems

Methylammonium tin iodide systems containing earth-alkaline ions (CH₃NH₃Sn_1?x (EA) _x I₃, EA = Ca²⁺, Sr²⁺, Mg²⁺, 0 ≤ x ≤ 0.30) were investigated. The X-ray diffraction patterns detected the formation of tetragonal nearly cubic CH₃NH₃SnI₃ (space group P4mm), SnI₂, and not identified phases. The morphological analysis confirmed the presence of secondary phases with formation of irregularly shaped crystallites. The Sn3d and I3d photoemission spectra revealed the typical position and separation of spin–orbit components for Sn²⁺ in halides. Static thermogravimetric measurements (T = 85 °C) showed a barely measurable weight loss for EA = Mg, a dramatic decrease of the weight loss rate for EA = Ca, and recorded weight losses till t ≈ 1.5 h only for EA = Sr, respectively. The optical spectra displayed absorption edges which increased at increasing the (EA)-content with maximum values for x = 0.050 (λ _on-set = 1754 nm, EA = Mg; λ _on-set = 1692 nm, EA = Ca; and λ _on-set = 1338 nm, EA = Sr, respectively). The Tauc plots revealed a direct semiconducting behavior with band energy gaps depending on the nature and amount of the (EA)-ions. The photoluminescence (PL) spectra showed, for EA = Mg, an increase of the PL-band intensity at increasing the Mg content with a maximum at x = 1.0 and, for EA = Ca, an increase of band intensity at increasing the Ca-content and for EA = Sr, a band intensity maximum at x = 0.025. This was explained by the similar ionic radius between Sn²⁺ and Sr²⁺ ions which can be easily exchanged in the SnI₆ ^2? octahedra.     

A new niobate-based CaO–2CuO–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> microwave dielectric ceramic composite for LTCC applications

A novel CaO–2CuO–Nb₂O₅ (CCN) ceramic composite was prepared by the solid-state reaction method in the temperature range of 810–890 °C. Typically, the CCN sintered at 870 °C exhibited the excellent microwave properties of ε _r ?=?15.7, Q?×?f?=?28,700 GHz, τ _f = ? 38.4 ppm/°C. The τ _f of CCN was turned to be near zero by adding TiO₂, while the ε _r increased slightly and the Q?×?f decreased. The 0.91CCN–0.09TiO₂ ceramic sintered at 920 °C showed modified properties of ε _r ?=?16.9, Q?×?f?=?21,500 GHz, τ _f = ? 1.6 ppm/°C, which shows potential in LTCC applications.     

Understanding of post deposition annealing and substrate temperature effects on structural and electrical properties of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> MOS capacitor

The purpose of this study is to understand the effects of substrate temperature (ST) and post deposition annealing (PDA) on the structural-electrical properties of Gd₂O₃ film and to evaluate the electrical performances of the MOS based devices formed with this dielectric. The Gd₂O₃/Si structures were annealed at 500, 600, 700, and 800 °C under N₂ ambient after the films were grown on heated p-Si substrate at various temperatures ranged from 20 to 300 °C by RF magnetron sputtering. For any given ST, the crystallization/grain size increased with increasing PDA temperature. The bump in the accumulation region or continuous decrease in the capacitance values of the inversion region of the C–V curves for 800 °C PDA was not observed. The lowest effective oxide charge density (Q _eff ) value was obtained to be ??1.13?×?10¹¹ cm^?2 from the MOS capacitor with Gd₂O₃, which is grown on heated Si at 300 °C and annealed at 800 °C. The density of the interface states (D _it ) was found to be in the range of 0.84?×?10¹¹ to 1.50?×?10¹¹ eV^?1 cm^?2. The highest dielectric constant (ε) and barrier height \(({\Phi _B})\) values were found to be 14.46 and 3.68, which are obtained for 20 °C ST and 800 °C PDA. The results show that the negative charge trapping in the oxide layer is generally more than that of the positive, but, it is reverse of this situation at the interface. The leakage current density decreased after 20 °C ST, but no significant change was observed for other ST values.     

Epitaxial growth and magnetic properties of <Emphasis Type="Italic">h</Emphasis>-LuFeO<Subscript>3</Subscript> thin films

In this paper, the epitaxial hexagonal LuFeO₃ (h-LuFeO₃) thin films with c-axis-oriented single phase, smooth surface were grown on YSZ (111) substrates by pulsed laser deposition method. Furthermore, a structural distortion of increased lattice constant of c is found in the epitaxial h-LuFeO₃ thin films. Moreover, the epitaxial h-LuFeO₃ thin films show room-temperature ferromagnetism. The coercive field and remnant magnetization of the epitaxial h-LuFeO₃ thin film decrease with the increase in the test temperature from 50 to 300 K. The study would be of benefit to the room-temperature single-phase multiferroic materials.     

Mechanical properties of amorphous silicon carbonitride thin films at elevated temperatures

The mechanical properties of amorphous silicon carbonitride (a-SiC _x N _y ) films with various nitrogen content (y = 0–40 at.%) were investigated in situ at elevated temperatures up to 650 °C in inert atmosphere. A SiC film was measured also at 700 °C in air. The hardness and elastic modulus were evaluated using instrumented nanoindentation with thermally stable cubic boron nitride Berkovich indenter. Both the sample and the indenter were separately heated during the experiments to temperatures of 300, 500, and 650 °C. Short duration high temperature creep tests (1200 s) of the films were also carried out. The results revealed that the room temperature hardness and elastic modulus deteriorate with the increase of the nitrogen content. Furthermore, the hardness of both the a-SiC and the a-SiCN films with lower nitrogen content at 300 °C drops to approx. 77 % of the corresponding room temperature values, while it reduces to 69 % for the a-SiCN film with 40 at.% of nitrogen. Further increase of temperature is accompanied with minor reduction in hardness except for the a-SiCN film with highest nitrogen content, where the hardness decreases at a much faster rate. Upon heating up to 500 °C, the elastic modulus of the a-SiCN film decreases, while it increases at 650 °C due to the pronounced effect of short-range ordering. The steady-state creep rate increases at elevated temperatures and the a-SiC exhibits slower creep rates compared to the a-SiCN films. The value of the universal constant x = 7 relating the W _p/W _t and H/E ^* was established and its applicability was demonstrated. Analysis of the experimental indentation data suggests a theoretical limit of hardness to elastic modulus ratio of 0.143.     

Effect of annealing on exchange bias in Mg<Subscript>0.2</Subscript>Fe<Subscript>x</Subscript>Cr<Subscript>1.8−x</Subscript>O<Subscript>3</Subscript> nano oxides

Magnesium-iron chromium oxides (Mg_0.2Cr_1.8?x Fe _x O₃ with x varying from 0.3 to 0.9) produced by hydrothermal process in a stirred pressure reactor from pure metal chlorides have been annealed at 700 °C. Single phase corundum structure and nanophase structure of the as-synthesized samples were confirmed by X-ray diffraction (XRD). Instead of the correlation between H _EB and D _XRD observed at T _A = 600 °C, we find significant changes. The H _EB increases with decreasing particle size reaches a maximum at ~43 nm (x = 0.5) then decreases.     

Role of lanthanum in thermoluminescence properties of La<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>Lu<Subscript>2(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>SiO<Subscript>5</Subscript>:Ce crystals

The influence of lanthanum content on thermally stimulated luminescence properties of La_2xLu_2(1?x)SiO₅:Ce (x = 0, 0.08, 0.18 and 1.50 at.%) crystals was investigated. Trapping parameters such as electron trap depth E_t and electron traps content n ₀ were fitted with general order kinetic function. According to the results of the VUV transmittance spectra and band gap calculation which based on the density functional theory with the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA–PBE), band structure of the crystals and recombination mechanisms of released electrons were further studied. Results showed that there were mainly two kinds of electron traps, namely shallow (E_t ≈ 0.2 eV) and deep (E_t ≈ 1.0 eV) traps. With the increasing of La content, the concentration of deep traps was obviously depressed, and the depth of deep traps decreased at the same time, which was explained by suggesting the downward shift of the bottom of conduction band.