Electrochemically deposited thermoelectric n-type Bi2Te3 thin films

Electrochemically deposited n-type BiTe alloy thin films were grown from nitric acid baths on sputtered Bi_xTe_y/SiO/Si substrates. The film compositions, which varied from 57 to 63 at.% Te were strongly dependent on the deposition conditions. Surface morphologies varied from needle-like to granular structures depending on deposited Te content. Electrical and thermoelectric properties of these electrodeposited Bi_xTe_y thin films were measured before and after annealing and compared to those of bulk Bi₂Te₃. Annealing at 250 °C in reducing H₂ atmosphere enhanced thermoelectric properties by reducing film defects. In-plane electrical resistivity was highly dependent on composition and microstructure. In-plane Hall mobility decreased with increasing carrier concentration, while the magnitude of the Seebeck coefficient increased with increasing electrical conductivity to a maximum of −188.5 μV/K. Overall, the thermoelectric properties of electrodeposited n-type BiTe thin films after annealing were comparable to those of bulk BiTe films.     

Electrodeposition of P-type BixSb2−xTey thermoelectric film from dimethyl sulfoxide solution

The electrochemical behaviors of Bi(III), Te(IV), Sb(III) and their mixtures in DMSO solutions were investigated using cyclic voltammetry and linear sweep voltammetry measurements. On this basis, Bi_xSb_2−xTe_y film thermoelectric materials were prepared by potentiodynamic electrodeposition technique from mixed DMSO solution, and the compositions, structures, morphologies as well as the thermoelectric properties of the deposited films were also analyzed. The results show that Bi_xSb_2−xTe_y compound can be prepared in a very wide potential range by potentiodynamic electrodeposition technique in the mixed DMSO solutions. After anneal treatment, the deposited film prepared in the potential range of −200 to −400 mV shows the highest Seebeck coefficient (185 μV/K), the lowest resistivity (3.34 × 10⁻⁵ Ω m), the smoothest surface, the most compact structure and processes the stoichiometry (Bi_0.49Sb_1.53Te_2.98) approaching to the Bi_0.5Sb_1.5Te₃ ideal material most. This Bi_0.49Sb_1.53Te_2.98 film is a kind of nanocrystalline material and (0 1 5) crystal plane is its preferred orientation.     

One-step electrochemical preparation of the ternary (BixSb1−x)2Te3 thin films on Au(1 1 1): Composition-dependent growth and characterization studies

This study reports on the synthesis of ternary semiconductor (Bi_xSb_1−x)₂Te₃ thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi³⁺, SbO⁺, and HTeO₂⁺ at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (Bi_xSb_1−x)₂Te₃ with various compositions (0.0 ≤ x ≤ 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (Bi_xSb_1−x)₂Te₃ thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition.     

Bi and Te thin films synthesized by galvanic displacement from acidic nitric baths

Bismuth (Bi) and tellurium (Te) thin films were formed by galvanic displacement of different sacrificial iron group thin films [i.e. nickel (Ni), cobalt (Co) and iron (Fe)] where the formation was systematically investigated by monitoring the change of open circuit potential (OCP), surface morphology and microstructure. The surface morphologies and crystal structures of galvanically displaced Bi or Te thin films strongly depended on the type and thickness of the sacrificial materials. Continuous Bi thin films were successfully deposited with the sacrificial Co. However, dendrites and nanoplatelets were formed from the Ni and Fe thin films. Te thin films were synthesized with all the three sacrificial thin films. Chemical dissolution rate of the sacrificial thin films and mixed potential strongly influenced formation of Bi or Te thin films.     

The underpotential deposition of Bi2Te3−ySey thin films by an electrochemical co-deposition method

Bi₂Te_3−ySe_y thin films were grown on Au(1 1 1) substrates using an electrochemical co-deposition method at 25 °C. The appropriate co-deposition potentials based on the underpotential deposition (upd) potentials of Bi, Te and Se have been determined by the cyclic voltammetric studies. The films were grown from an electrolyte of 2.5 mM Bi(NO₃)₃, 2 mM TeO₂, and 0.3 mM SeO₂ in 0.1 M HNO₃ at a potential of −0.02 V vs. Ag|AgCl (3 M NaCl). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. XRD and EDS results revealed that the films are single phase with approximate composition of Bi₂Te_2.7Se_0.3. SEM studies showed that the films are homogeneous and have micronsized granular crystallites.     

Oxygen reduction reaction on electrodeposited Pt100−x−yNixPdy thin films

The kinetics of the oxygen reduction reaction (ORR) were examined on a series of Pt_100−x−yNi_xPd_y ternary alloys. Films were produced by electrodeposition that involved a combination of underpotential and overpotential reactions. For Pt-rich Pt_100−x−yNi_xPd_y alloy films (x < 0.65) Ni co-deposition occurred at underpotentials while for Ni-rich films (x > 0.65) deposition proceeded at overpotentials. Rotating disk electrode (RDE) measurements of the ORR kinetics on Ni-rich Pt_100−x−yNi_xPd_y thin films revealed up to ∼6.5-fold enhancement of the catalytic activity relative to Pt films with the same Pt mass loading. More than half of the electrocatalytic gain may be attributed to surface area expansion due to Ni dealloying. Surface area normalization based on the H_upd charge reduced the enhancement factor to a value less than 2. The most active ternary alloy film for ORR was Pt₂₅Ni₇₃Pd₂. Comparison of the ORR on Pt, Pt₂₀Ni₈₀, Pt₂₅Ni₇₃Pd₂ thin films indicate that the binary alloy is the most active with a H_upd normalized ORR enhancement factor of up to 3.0 compared to 1.6 for the ternary alloy.     

Fabrication and electrical properties of Bi2-xSbxTe3 ternary nanopillars array films

Highly oriented Bi_2-xSb_xTe₃ (x?=?0, 0.7, 1.1, 1.5, 2) ternary nanocrystalline films were fabricated using vacuum thermal evaporation method. Microstructures and morphologies indicate that Bi_2-xSb_xTe₃ films have pure rhombohedral phase with well-ordered nanopillars array. Bi, Sb and Te atoms uniformly distributed throughtout films with no precipitation. Electrical conductivity of Bi_2-xSb_xTe₃ films transforms from n-type to p-type when x?>?1.1. Metal-insulator transition was observed due to the incorporation of Sb in Bi₂Te₃. Bi_2-xSb_xTe₃ film with x?=?1.5 exhibits optimized electrical properties with maximum electrical conductivity σ of 2.95?×?10⁵ S?m^?1 at T?=?300?K, which is approximately ten times higher than that of the undoped Bi₂Te₃ film, and three times higher than previous report for Bi_0.5Sb_1.5Te₃ films and bulk materials. The maximum power factor PF of Bi_0.5Sb_1.5Te₃ nanopillars array film is about 3.83?μW?cm^?1 K^?2 at T?=?475?K. Highly oriented (Bi,Sb)₂Te₃ nanocrystalline films with tuned electronic transport properties have potentials in thermoelectric devices.     

Structural and electrochemical characterization of SnOx thin films for Li-ion microbattery

SnO_x thin films were prepared by reactive radio frequency magnetron sputtering with different sputtering powers. X-ray photoelectron spectroscopy suggested that all the films have similar chemical stoichiometry as SnO_1.5. X-ray diffraction and transmission electro microscopy results showed that crystal size of the SnO_x thin films gradually increases with increase of sputtering power from 50 to 150 W. Cyclic voltammetry and galvanostatic charge/discharge cycling measurements indicated that the electrochemical properties of SnO_x films strongly rely on their crystal sizes as well as surface morphologies. The SnO_x film deposited at sputtering power of 120 W exhibits the best electrochemical performances. It could deliver a reversible capacity of 670 μAh cm⁻² μm⁻¹ at 50 μA cm⁻² in the voltage range of 0.1-1.2 V up to 50 cycles.     

Laser ablation of Ga-Sb-Te thin films monitored with quadrupole ion trap time-of-flight mass spectrometry

Laser ablation of Ga-Sb-Te chalcogenide thin films prepared by radiofrequency magnetron co-sputtering was monitored with quadrupole ion trap time-of-flight mass spectrometry (QIT-TOF-MS). The mass spectra of 11 thin films of various compositions (Ga: 0–53.1, Sb: 0–52.0, and Te: 0–100.0 at. %) were recorded. Several series of unary (Ga_x, Sb_y, and Te_z) binary (Ga_xSb_y, Ga_xTe_z, and Sb_yTe_z), and ternary Ga_xSb_yTe_z clusters were identified in both positive and negative ion modes. Stoichiometry of observed clusters was determined. Up to 18 binary clusters (positively and negatively charged) were detected for thin film with low Sb content of 6.5 at. %. The highest number (4) of ternary clusters was observed for thin film with high Te content of 66.7 at. %. The number of generated clusters and their peaks intensity varied according to the chemical composition of thin films. Altogether, 41 clusters were detected. The laser ablation monitoring shows laser-induced fragmentation of thin film structure. The relation of clusters stoichiometries to the chemical composition of thin films is discussed. The fragmentation can be diminished by covering a surface of thin films with paraffin's, glycerol, or trehalose sugar thin layers. The stoichiometry of generated clusters shows partial structural characterization of thin films.     

Amorphous LiCoO2 thin films on Li1+x+yAlxTi2−xSiyP3−yO12 prepared by radio frequency magnetron sputtering for all-solid-state Li-ion batteries

Amorphous LiCoO₂ thin films were deposited on the NASICON-type glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 180 °C. The as-deposited LiCoO₂ thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscope. All-solid-state Li/PEO₁₈-Li (CF₃SO₂)₂N/LATSP/LiCoO₂/Au cells were fabricated using the amorphous film. The electrochemical performance of the cells was investigated by galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. It was found that the amorphous LiCoO₂ thin film shows a promising electrochemical performance, making it a potential application in microbatteries for microelectronic devices.     

Pulsed electrodeposition of (Bi1-xSbx)2Te3 thermoelectric thin films

(Bi_1-xSb_x)₂Te₃ thermoelectric thin films were deposited on stainless steel discs in 1 M perchloric acid and 0.1 M tartaric acid by pulse electrodeposition in order to optimize the grain growth. The influence of the electrolyte composition, the cathodic current density and the cathodic pulse time on film stoichiometry were studied. The results show that it is necessary to increase the Sb content in the electrolyte to obtain the (Bi_0.25Sb_0.75)₂Te₃ film stoichiometry. Pulse plating reduced the grain size and the roughness, compared with continuous plating. Thermoelectric and electrical properties were also studied and it was found that the Seebeck coefficient and electrical resistivity were related to two parameters: the cathodic pulse current density and the films thickness.     

Novel synthesis method for quaternary Cd(Cu,Zn)Se thin films and its characterizations

Nowadays, the search for novel compounds by chemical synthesis is in trend. Herein, we report the deposition of Cd_1-x-yZn_xCu_ySe (0.025 ≤ x = y ≤ 0.15) films by facile, industry-oriented chemical synthesis. The Cd_1-x-yZn_xCu_ySe thin films were deposited at the optimized growth conditions (temperature = 70 ± 0.1 °C, pH = 10.3 ± 0.1, substrate rotation speed = 70 ± 2 rpm and time = 100 min). As-synthesized thin films were characterized for physical, chemical, topographical and electrical attributes. The study of vibrational modes in Cd_1-x-yZn_xCu_ySe thin films was done with the help of Raman spectroscopy. Improvement in surface topography with the integration of Cu²⁺ and Zn²⁺ into the CdSe lattice has been noticed by the atomic force microscopy (AFM). The electrochemical impedance spectroscopy revealed lower values of R_s and R_ct for x = y = 0.05 composition. Chemical deposition of Cd_1-x-yZn_xCu_ySe thin films may offer an excellent way to fabricate quaternary chalcogenide-based absorber materials for solar cells.     

Recent progress in electrodeposition of thermoelectric thin films and nanostructures

Thermoelectric power generators and coolers have many advantages over conventional refrigerators and power generators such as solid-state operation, compact design, vast scalability, zero-emissions and long operating lifetime with no maintenance. However, the applications of thermoelectric devices are limited to where their unique advantages outweigh their low efficiency. Despite this practical confine, there has been a reinvigorated interest in the field of thermoelectrics through identification of classical and quantum mechanical size effects, which provide additional ways to enhance energy conversion efficiencies in nanostructured materials. Although, there are a few reports which demonstrated the improvement of efficiency through nanoengineering, the successful application of these nanostructures will be determined by a cost-effective and high through-put fabrication method. Electrodeposition is the method of choice to synthesize nanoengineered thermoelectric materials because of low operating and capital cost, high deposition rates, near room temperature operation, and the ability to tailor the properties of materials by adjusting deposition conditions. In this paper, we reviewed the recent progress of the electrodeposition of thermoelectric thin films and nanostructures including Bi, Bi_1−xSb_x, Bi₂Te₃, Sb₂Te₃, (Bi_1−xSb_x)₂Te₃, Bi₂Se₃, Bi₂Te_3−ySe_y, PbTe, PbSe, PbSe_1−xTe_x and CoSb₃.     

Multi-doped bismuth ferrite thin films with enhanced multiferroic properties

Thin films of multi-doped bismuth ferrite, Bi_0.97−xLa_xSr_0.03Fe_0·94Mn_0·04Co_0·02O₃ (BL_xSFMC, x = 0.00–0.18), are synthesized on a fluorine-doped tin oxide (FTO)/glass substrate. The structure and multiferroic properties of the film samples are characterized and tested. The results indicate that on doping, the structure of the BL_xSFMC film changes has been changed. The concentrations of both oxygen vacancies and Fe²⁺ are decreased. The BL_0.18SFMC thin film exhibits Ohmic conduction, which reduces the influence of the built-in electric field E_bi of the space-charge region at the interface between an Au electrode and the BL_xSFMC during polarization. The BL_0.18SFMC thin film also exhibits enhanced ferroelectric properties than the undoped film, with a higher residual polarization of 188 μC/cm² and a higher squareness ratio of 1.21. Meanwhile, the reduced number of oxygen vacancies also reduces the Fe²⁺/Fe³⁺ ratio, thereby enhancing the Dzyaloshinskii–Moriya interaction of Fe–O–Fe bonds, and so the BL_0.18SFMC thin film exhibits enhanced ferromagnetism, with a saturation magnetization of M_s ≈ 3.94 emu/cm³. Thus, multi-ion doping can improve both the ferroelectric and ferromagnetic properties of BL_xSFMC thin films.     

High thermoelectric performance achieved in Bi0.4Sb1.6Te3 films with high (00l) orientation via magnetron sputtering

To obtain p-type Bi–Sb–Te-based thin films with excellent thermoelectric performance, the Bi_0.4Sb_1.6Te₃ target is prepared by combining mechanical alloying with the spark plasma sintering technique. Afterward, Bi_0.4Sb_1.6Te₃ thin films are deposited via magnetron sputtering at variable working pressures. With an increasing working pressure, the frequency of collisions between the argon ions and sputtered atoms gradually increases, the preferred orientation of (00l) increases, and the sputtering rate decreases. The Seebeck coefficient increases from ∼140 μV/K to ∼220 μV/K as the carrier concentration decreases along with an increasing working pressure. Furthermore, the decrease in carrier concentration and acceleration of carrier mobility also affect the change in electrical conductivity. The maximum power factor of the p-type Bi_0.4Sb_1.6Te₃ thin film deposited at 4.0 Pa and at room temperature exceeds 20.0 μW/cm K² and is higher than that of most p-type Bi–Sb–Te-based films.     

Electrodeposition of antimony telluride thin films from acidic nitrate-tartrate baths

Electrochemical quartz crystal microbalance (EQCM) and rotating disk electrode (RDE) techniques were utilized to systematically investigate the electrodeposition of Sb_xTe_1−x (0.1 < x < 0.8). In addition, the effect of applied potential and agitation were correlated to the film composition, crystal structure, and morphology. Although the film composition was independent of the agitation rate, the deposition rate, current efficiency, crystallinity and phase of Sb_xTe_1−x were all strongly influenced by it. The deposition rate monotonically increased with increases in the rotation rate because of the faster diffusion rate of HTeO₂⁺ ions to the cathode. Amorphous thin films were electrodeposited in the absence of agitation, whereas polycrystalline Sb₂Te₃ with elemental Sb and Te were co-deposited at a higher agitation independent of the applied deposition potential.     

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi₄Ti_3-xCo_xO₁₂/La_0.67Sr_0.33MnO₃ (BITC_x/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co²⁺ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITC_x/LSMO composite thin films was investigated. Co²⁺ doping induces improved ferroelectricity and weak ferromagnetism for the BITC_x phase. Especially, the single-phase BITC_0.05 film exhibits a maximum ME voltage coefficient (α_E) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC_0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ?_r, minimum tanδ, highest remnant polarization of 24.2 μC/cm², lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum a_E value of 27.3 V/cm·Oe. Based on these findings, Co²⁺-doped Bi₄Ti₃O₁₂ has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi₄Ti₃O₁₂ with ferromagnetic oxides benefits the improvement of ME composite thin films.     

High-quality c-axis oriented non-vacuum Er doped ZnO thin films

Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn_1−xEr_xO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol–gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn_1−xEr_xO thin films with different Er doping concentration were grown on glass substrate using sol–gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV–vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn_1−xEr_xO films depend on substrate nature and sol–gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400–700 nm).     

Enhanced bolometric properties of nickel oxide thin films for infrared image sensor applications by substitutional incorporation of Li

This study aims to investigate the influence of substitutionally incorporated Li on sensing performance of nickel oxide films for bolometer applications by comparing Ni_1-xO and (Li_yNi_1-y)_1-xO films. From the results of structural analysis, it was confirmed that the film deposited from Li_0.2Ni_0.8O target contained Li which substitutionally occupies the Ni cation site while maintaining a cubic NiO structure. The substitutionally incorporated Li in nickel oxide can serve as an acceptor providing a hole carrier, like as a structural defect. However, in contrast to the structural defect, the substitutional incorporation of Li made it possible to increase the number of hole carriers in nickel oxide film while maintaining excellent film quality. In addition, the contact resistance with electrode was greatly reduced as a result of the substitutionally incorporated Li. These changes in structural and electrical properties lead to a significant reduction of 1/f noise arisen from the (Li_yNi_1-y)_1-xO film. As a result, the sensing performance of the (Li_yNi_1-y)_1-xO film as evaluated using the (α_H/n)^1/2/|β| value was nearly 10 times better than that of the Ni_1-xO film. Consequently, it can be concluded that the substitutional incorporation of Li can significantly improve the sensing performance of nickel oxide films for bolometer applications.     

Novel mixed method for the electrochemical deposition of thick layers of Bi2+xTe3−x with controlled stoichiometry

A new method for the electrochemical deposition of Bi_2+xTe_3−x is presented, which combines voltage-controlled deposition pulses with current-controlled resting pulses. This method is based on results of a comprehensive electrochemical investigation including cyclic voltammetry, chronoamperometry and chronopotentiometry, which has been performed on the system Bi and Te on Pt in 2 M HNO₃. The influence of electrolyte composition, deposition potential and deposition pulse duration on morphology and stoichiometry of the deposited material as well as the variation of the composition over the thickness of the layer has been investigated by means of SEM and EDX. The crystal structure was examined with XRD. Layers deposited with the new method show a constant and reproducible stoichiometry over their entire thickness. Layers of up to 800 μm thickness deposited with deposition rates of up to 50 μm/h have been achieved. The composition and hence the thermoelectric behavior may be adjusted via electrolyte composition or the deposition potential. Fabrication of n-type and, for the first time, p-type Bi_2+xTe_3−x is demonstrated and verified by measurements of the Seebeck coefficients. The suitability of the proposed method for low-cost fabrication of micro-thermoelectric devices is shown. The advantages of this method may also apply for electrochemical deposition of other binary or ternary compounds.