Thermoelectric Properties of Ag-doped Mg<Subscript>2</Subscript>Ge Thin Films Prepared by Magnetron Sputtering

Silver doped p-type Mg₂Ge thin films were grown in situ at 773 K using magnetron co-sputtering from individual high-purity Mg and Ge targets. A sacrificial base layer of silver of various thicknesses from 4 nm to 20 nm was initially deposited onto the substrate to supply Ag atoms, which entered the growing Mg₂Ge films by thermal diffusion. The addition of silver during film growth led to increased grain size and surface microroughness. The carrier concentration increased from 1.9 × 10¹⁸ cm⁻³ for undoped films to 8.8 × 10¹⁸ cm⁻³ for the most heavily doped films, but it did not reach saturation. Measurements in the temperature range of T = 200–650 K showed a positive Seebeck coefficient for all the films, with maximum values at temperatures between 400 K and 500 K. The highest Seebeck coefficient of the undoped film was 400 μV K⁻¹, while it was 280 μV K⁻¹ for the most heavily doped film at ∼400 K. The electrical conductivity increased with silver doping by a factor of approximately 10. The temperature effects on power factors for the undoped and lightly doped films were very limited, while the effects for the heavily doped films were substantial. The power factor of the heavily doped films reached a non-optimum value of ∼10⁻⁵ W cm⁻¹ K⁻² at 700 K.     

Effect of pH on Structural and Electrical Properties of Electrodeposited Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Thin Films

Bi₂Te₃ thin films were electrodeposited at various pH values of a bismuth nitrate and tellurium oxide plating solution. Enhancement in pH results in a decrease in grain size. Transmission electron microscopy reveals the transformation of the film morphology from dispersed nanoparticles to connected chain-like nanostructures of Bi₂Te₃ as pH is increased. Electrical characterization for samples deposited in the temperature range of 300 K to 425 K shows a fourfold increase in Seebeck coefficient, S, between its maximum and minimum value as the solution pH changes from 1 to 3.5. Such enhancement of S is attributed to the increased connectivity of the nanostructures at higher pH.     

Transport Properties and Cationic Substitutions in Sr<Subscript>2</Subscript>IrO<Subscript>4</Subscript>

We realized cationic substitutions in Sr₂IrO₄ and measured resistivity, thermoelectric power, and the Hall coefficient. A two-carrier model, reflecting the presence of thermally activated carriers at high temperature, qualitatively explains the behavior of the Hall coefficient of Sr_1.95La_0.05IrO₄ in comparison with Sr₂IrO₄. Concerning the substitution of Ir by different transition metals, Pt with 5d orbitals does not affect the transport properties, contrary to Ti and Rh with 3d and 4d orbitals, respectively. This may be explained by strong spin–orbit coupling involved in Ir and Pt, in comparison with 3d or 4d transition metals.     

Formation and optical properties of CuInTe<Subscript>2</Subscript> nanoparticles in silicate matrices

The conditions for the formation of CuInTe₂ nanoparticles in silicate matrices are studied by means of optical spectroscopy and electron microscopy. The formation of the particles of the semiconductor phase in size from 15 to 30 nm occurs at the stage of cooling of the melt and depends essentially on the composition of the vitreous matrix. The optical absorption in the infrared and visible regions of the spectrum and the effect of additional heat treatment on the formation and optical properties of the nanoparticles are studied. The changes in the optical spectra are attributed to possible changes in the type of the crystal lattice of the nanoparticles formed in the matrix.     

How r-Plane Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Surface Modifications Impact the Growth of Epitaxial (001) CeO<Subscript>2</Subscript> Thin Films

We present evidence that it is the presence or absence of atomic terraces with a specific crystallographic orientation on the (102) Al₂O₃ surface that promotes growth of single-crystal (001) CeO₂ films over polycrystalline (111) CeO₂ films. The CeO₂ film nucleates so that the [010] and [100] directions of the film align parallel and perpendicular to the terrace edges. In the absence of terraces, multidomain (111) CeO₂ films result in which the in-plane orientation of the two domains are rotated by 85.71°, so that a [110] CeO₂ direction aligns parallel to either the or Al₂O₃ direction.     

Electrical and Structural Real-Time Changes in Thin Thermoelectric (Bi<Subscript>0.15</Subscript>Sb<Subscript>0.85</Subscript>)<Subscript>2</Subscript>Te<Subscript>3</Subscript> Films by Dynamic Thermal Treatment

A recent trend in thermoelectrics is miniaturization of generators or Peltier coolers using the broad spectrum of thin-film and nanotechnologies. Power supplies for energy self-sufficient micro and sensor systems are a wide application field for such generators. It is well known that thermal treatment of as-deposited p-type (Bi_0.15Sb_0.85)₂Te₃ films leads to enhancement of their power factors. Whereas up to now only the start (as-deposited) and the end (after annealing) film stages were investigated, herein for the first time, the dynamical changes of sputter-deposited film properties have been observed by real-time measurements. The electrical conductivity shows a distinct, irreversible increase during a thermal cycle of heating to about 320°C followed by cooling to room temperature. The interpretation of the Seebeck and Hall coefficients points to an enhancement in Hall mobility after annealing. In situ x-ray diffractometry shows the generation of an additional Te phase depending on temperature. This is also confirmed by energy-dispersive x-ray microanalysis and the corresponding mapping by scanning electron microscopy. It is presumed that the Te enrichment in a separate, locally well-defined phase is the reason for the improvement in the integral film transport properties.     

Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films

Nd/Nb-co-substituted Bi_3.15Nd_0.85Ti_3?x Nb _x O₁₂ (BNTN _x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO₂/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN _x thin films were investigated. A low-concentration substitution with Nb ions in BNTN _x can greatly enhance its remanent polarization (2P _r) and reduce the coercive field (2E _c) compared with those of Bi₄Ti₃O₁₂ (BIT) thin film. The highest 2P _r (71.4 μC/cm²) was observed in the BNTN_0.03 thin film when the 2E _c was 202 kV/cm. Leakage currents of all the films were on the order of 10^?6 to 10^?5 A/cm², and the BNTN_0.03 thin film has a minimum leakage current (2.1 × 10^?6 A/cm²) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN_0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN_0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.     

Synthesis and Characterization of In<Subscript>2</Subscript>S<Subscript>3</Subscript> Thin Films Deposited by Chemical Bath Deposition on Polyethylene Naphthalate Substrates

Indium sulfide (In₂S₃) thin films were deposited on polyethylene naphthalate (PEN) by chemical bath deposition (CBD). The materials were characterized by ultraviolet (UV)–visible spectroscopy, x-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), and x-ray diffraction (XRD) to investigate the influence of the polymeric substrate on the resulting thin In₂S₃. The films showed polycrystalline (cubic and tetragonal) structure. A reduction of the ordering of the polymeric chains at the surface of the PEN was also observed, demonstrated by the appearance of two infrared bands at 1094 cm⁻¹ and 1266 cm⁻¹. Presence of oxygen during the early stages of In₂S₃ growth was also identified. We propose a reaction mechanism for both the equilibrium and nucleation stages. These results demonstrate that In₂S₃ can be deposited at room temperature on a flexible substrate.     

Microstructure and Raman Scattering of Cu<Subscript>2</Subscript>ZnSnSe<Subscript>4</Subscript> Thin Films Deposited onto Flexible Metal Substrates

Cu₂ZnSnSe₄ thin films are produced by selenizing electrochemically layer-by-layer deposited and preliminarily annealed Cu–Zn–Sn precursors. For flexible metal substrates, Mo and Ta foils are used. The morphology, elemental and phase compositions, and crystal structure of Cu₂ZnSnSe₄ films are studied by scanning electron microscopy, X-ray spectral microanalysis, X-ray phase analysis, and Raman spectroscopy.     

Microstructure and Electrochemical Properties of ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanopowder Synthesized Using Different Surfactants

ZnMn₂O₄ (ZMO) nanopowders have been synthesized by a hydrothermal method using different surfactants [cetyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG)-400, and Polysorbate-80]. The as-prepared ZnMn₂O₄ samples exhibited single phase with tetragonal structure, showing honeycomb, spinel microsphere, and flower-cluster morphology, respectively. Cyclic voltammetry curves for all samples presented rectangular shape with symmetric nature and good cycling properties, with no obvious redox peak. Galvanostatic charge–discharge curves were triangular and symmetric. The specific capacitance of the ZnMn₂O₄ nanopowders gradually decreased with increase of the scanning rate. ZMO-PEG exhibited higher specific capacitance of 191 F g^?1 at scan rate of 5 mV s^?1 and retained superior large-current cycling stability of 98.4% after 1000 cycles compared with ZMO-CTAB (93.8%) or ZMO-Polysorbate-80 (97.7%). Electrochemical impedance spectroscopy revealed that the ZnMn₂O₄ nanopowders had low resistance. These results suggest that ZnMn₂O₄ nanopowders have good capacitance characteristics.     

Effect of Rapid Thermal Annealing on Sputtered CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> Thin Films

Calcium copper titanium oxide (CaCu₃Ti₄O₁₂, abbreviated to CCTO) films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature was 700°C in air, and the grain size increased signifi- cantly with annealing in O₂. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O₂ exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10⁻⁵ A/cm² (at 25 kV/cm).     

Effects of Annealing on Structural and Electrical Properties of CuInSe<Subscript>2</Subscript> Thin Films Prepared by Hybrid Sputtering/Evaporation Processes

CuInSe₂ (CIS)-based absorber layers have been fabricated on soda-lime glass substrates by co-sputtering Cu/In and evaporating Se. The effects of annealing in the Se environment on the structural and electrical properties of the CIS layers were studied. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to investigate the surface morphology and crystal structures of the CIS films, respectively. XRD patterns showed that the CIS films had a single chalcopyrite structure with preferential (112) orientation. The asymmetry of the Se 3d x-ray photoelectron spectroscopy (XPS) peak for the as-grown films and a separated peak for the annealed films are indications of the existence of two different valence states in the two kinds of CIS films. The electrical properties of the CIS films were studied by the four-probe method and Hall measurements. The results showed that the as-grown films had lower carrier mobility than the annealed films. However, the as-grown films had higher carrier concentration.     

Vapor Annealing as a Post-Processing Technique to Control Carrier Concentrations of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Thin Films

This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 × 10¹⁹ carriers/cm³ with Seebeck coefficients of −170 μV K⁻¹. For temperatures below 300°C and for film thicknesses of 0.4 μm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach.     

Effects of Pulsed Laser Deposition Conditions on the Microstructure of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> Thin Films

The influence of deposition conditions on the microstructure of Ca₃Co₄O₉ (CCO) thin films fabricated by the pulsed laser deposition technique was investigated. X-ray diffraction revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca _x CoO₂ secondary phase. The Ca _x CoO₂ structure was further confirmed by high-resolution transmission electron microscopy. The CCO thin-film growth was deduced to be a kinetically controlled process, and the quality of the thin films strongly depended on the coalescence process. The formation of Ca _x CoO₂ was inevitable during the thin-film growth. However, given enough time and supply of oxygen at a lower deposition rate, it was possible to transform the Ca _x CoO₂ phase into the desired CCO phase during the coalescence process, while with faster deposition, more Ca _x CoO₂ structure was formed, and the secondary phase could hardly transform into the CCO phase.     

Superconducting and Transport Properties of (Bi-Pb)-Sr-Ca-Cu-O with Nano-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Additions

The effect of nano Cr₂O₃ additions in (Bi, Pb)-Sr-Ca-Cu-O superconductors using the coprecipitation method is reported. Nano Cr₂O₃ with 0.1, 0.3, 0.5, 0.7, and 1.0 wt.% were added to the (Bi, Pb)-Sr-Ca-Cu-O system. The critical temperature (T _c) and transport critical current density (J _c) were determined by the four-point probe technique. The phases in the samples were determined using the powder X-ray diffraction method. The microstructure was observed by a scanning electron microscope and the distribution of nano Cr₂O₃ was determined by energy-dispersive X-ray analysis (EDX). The maximum T _c and J _c were observed for the sample with 0.1 wt.% nano Cr₂O₃. The variation in the J _c of all the samples was explained by the effective flux pinning by nano Cr₂O₃ in the samples. Using the self-field approximation together with the dependence of J _c on temperature, the characteristic length (L _c) associated with the pinning force was estimated to be approximately the same as the average grain size in all the samples.     

Effect of Annealing Temperature on Flowerlike Cu<Subscript>3</Subscript>BiS<Subscript>3</Subscript> Thin Films Grown by Chemical Bath Deposition

For widespread application of thin-film photovoltaic solar cells, synthesis of inexpensive absorber material is essential. In this work, deposition of ternary Cu₃BiS₃ absorber material, which contains abundant and environmentally benign elements, was carried out on glass substrate. Flowerlike Cu₃BiS₃ thin films with nanoflakes as building block were formed on glass substrate by chemical bath deposition. These films were annealed at 573 K and 673 K in sulfur ambient for structural improvement. Their structure was characterized using Raman spectroscopy, as well as their surface morphological and optical properties. The x-ray diffraction profile of as-deposited Cu₃BiS₃ thin film revealed amorphous structure, which transformed to orthorhombic phase after annealing. The Raman spectrum exhibited a characteristic peak at 290 cm^?1. Scanning electron microscopy of as-deposited Cu₃BiS₃ film confirmed formation of nanoflowers with diameter of around 1052 nm. Wettability testing of as-deposited Cu₃BiS₃ thin film demonstrated hydrophobic nature, which became hydrophilic after annealing. The measured ultraviolet–visible (UV–Vis) absorption spectra of the Cu₃BiS₃ thin films gave an absorption coefficient of 10⁵ cm^?1 and direct optical bandgap of about 1.42 eV after annealing treatment. Based on all these results, such Cu₃BiS₃ material may have potential applications in the photovoltaic field as an absorber layer.     

Study of the Transport Properties and Domain Structure of Thin CoPt Films Obtained by Electron Evaporation

Journal of Communications Technology and Electronics - Abstract—CoPt films obtained by electron beam evaporation with deposition of ten Co and Pt bilayers with a total thickness of 8 nm are...     

Influence of the Thermal Conditions of Fabrication and Treatment on the Optical Properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript> Films

In₂O₃ films on Al₂O₃ (012) substrates are fabricated by dc magnetron sputtering at various temperatures (20–600°C). The effect of annealing and the substrate temperature on the film properties are studied by the ellipsometric method and the optical transmission method. Refractive-index profiles are constructed and band gaps for direct and indirect transitions are found. It is established that annealing leads to densification of the film material and unifies the refractive index. Annealing also decreases and unifies the energies of band-to-band transitions, which can be explained by lowering the influence of barriers in annealed films. However, the band gap for direct transitions varies greater than for indirect transitions. This fact can be associated with the mechanism of indirect transitions, notably, the participation of phonons facilitates interband transitions even if they are hindered by extra barriers caused by grain boundaries. The latter can be indirect evidence of the actuality of indirect transitions in indium oxide.     

Fabrication and Characterization of Pb(Zr<Subscript>0.53</Subscript>,Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>-Pb(Nb<Subscript>1/3</Subscript>,Zn<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> Thin Films on Cantilever Stacks

0.9Pb(Zr_0.53,Ti_0.47)O₃-0.1Pb(Zn_1/3,Nb_2/3)O₃ (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO₂/Si or SiO₂/Si₃N₄/SiO₂/poly-Si/Si membranes capped with a sol–gel-derived ZrO₂ buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO₃ (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO₂ surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.     

Low-Temperature Transport Properties of Sn<Subscript>24</Subscript>P<Subscript>19.3</Subscript>Br<Subscript>8</Subscript> and Sn<Subscript>17</Subscript>Zn<Subscript>7</Subscript>P<Subscript>22</Subscript>Br<Subscript>8</Subscript>

We report on temperature-dependent thermal conductivity, resistivity, and Seebeck coefficient of two polycrystalline Br-containing Sn-clathrate compounds with the type I crystal structure. Interstitial Br atoms reside inside the polyhedral cavities formed by the framework, resulting in hole conduction. The framework bonding directly influences the transport properties of these two compositions. The transport properties of these two clathrates are compared with those of other Sn-clathrates. We also discuss our results in terms of the potential for thermoelectric applications.