Minimum Resistivity Research Articles

Effect of anionic fluorine incorporation on structural, optical and electrical properties of ZnO nanocrystalline films

ZnO and ZnO:F (fluorine doped Zinc oxide) films have been deposited on glass substrates at 325 ± 5 °C through ultrasonic spray pyrolysis method (USP). X-ray diffractometer (XRD) has been utilized to determine the crystal structural and some structural parameters such as lattice constants, texture coefficients TC (hkl), crystallite size and dislocation densities of all the ZnO films. The XRD results have revealed that all the ZnO films have the hexagonal wurtzite structure and F incorporation shows no significant effect on the crystal structure. X-ray photoelectron spectroscopy (XPS) measurements have confirmed the presence of fluorine atoms in the ZnO lattice and also the existence of Zn–F bonding states. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements have been carried out to investigate the effect of F doping on the surface morphology of the ZnO films. The optical properties of the films have been analyzed by utilizing transmittance, absorbance and reflectance measurements. Some optical parameters such as extinction coefficient (k), refractive index (n) and optical conductivity have been determined depending on the change in F incorporation. Increasing the F doping initially led to a decrease in the optical band gap, but later increased. Electrical resistivity and carrier concentration values of the deposited films have been determined with Hall effect measurement system and it has been detected that 6% F-doped ZnO film has the minimum resistivity and maximum carrier concentration.

Synthesis and Characterizations of Nanocrystalline Na and Al Codoped Nio Thin Films

In the present work, Na and Al codoped NiO thin films were successfully deposited on a glass substrate by spray pneumatic method. The effect of Al concentration on optical, structural and electrical properties was studied. The transmission spectra show that the Na and Al codoped NiO thin films have good optical transparency in the visible region. The optical band gap energy increased after co-doping by Al to maximum value was 3.926 eV for 2 % Al. The minimum value of Urbach energy was obtained at high Al concentration it is 0.319 eV for 3 % Al. The Na and Al codoped NiO films have a minimum electrical resistance obtained for 1 % Al. XRD patterns of the Na and Al codoped NiO thin films indicating that the Na and Al codoped NiO thin films have a cubic structure of NiO phase.

Coexistence of the Kondo effect and spin glass physics in Fe-doped NbS2

We report the coexistence of the Kondo effect and spin glass behavior in Fe-doped NbS2 single crystals. The FexNbS2 shows the resistance minimum and negative magnetoresistance due to the Kondo effect, and exhibits no superconducting behavior at low temperatures. The resistance curve follows a numerical renormalization-group theory using the Kondo temperature K for x = 0.01 as evidence of Kondo effect. Scanning tunneling microscope/spectroscopy (STM/STS) revealed the presence of Fe atoms near sulfur atoms and asymmetric spectra. The magnetic susceptibility exhibits a feature of spin glass. The static critical exponents determined by the universal scaling of the nonlinear part of the susceptibility suggest a three-dimensional Heisenberg spin glass. The doped-Fe atoms in the intra- and inter-layers revealed by the x-ray result can realize the coexistence of the Kondo effect and spin glass.

Oxygen Concentration Dependence of the Optical and Electrical Properties of Mn-Doped Tin Oxide Thin Films Deposited on a Polyethylene Terephthalate Substrate.

Mn (2.59 wt.%)-doped tin oxide (MTO) was deposited on a polyethylene terephthalate (PET) substrate using RF magnetron sputtering at room temperature. Oxygen was introduced during the sputtering process to prevent the reduction of transmittance and the formation of nonstoichiometric compositions. The dependence of the optical and electrical properties of MTO thin films on the O₂/(Ar+O₂) ratio was systematically investigated. The transmittance of the MTO single layer (24 nm) at 550 nm gradually increased from 85.9% to 88.2% with an increase of the O₂/(Ar+O₂) ratio from 0% to 7.9%. The optical band gap was also affected by the O₂/(Ar+O₂) ratio, varying from 3.30 to 3.64 eV. The MTO film deposited at an O₂/(Ar+O₂) ratio of 2.7% showed the minimum resistivity (0.03 Ω·cm). The XPS spectra indicated that the SnO₂ thin films become almost stoichiometric as the O₂/(Ar+O₂) ratio increased. Thus, this sputtering process can be used to prepare flexible MTO films with a wider optical band gap, improved transmittance, and decreased resistivity.

Behavior of conical peaks under the action of the electrical discharges

During the electrical discharge machining process, the electrical discharges are developing between the close asperities that exist on the tool electrode and workpiece surfaces, along a trajectory of minimum electrical resistance. As a consequence of the electrical discharges, small quantities of the electrode’s materials are melted or even vaporized and afterward removed from the machining gap. Various factors exert influence on the material removal from the peaks of asperities placed on the electrode’s surfaces. An experimental method of the simulation of the material removing process was designed and applied. Single electrical discharges characterized by distinct energies were generated between the conical peaks of the previously prepared test pieces made of some electroconductive materials and the flat surface of the copper electrodes. The quantities of the material removed from the conical peaks of the test piece materials under the action of electrical discharges were measured and used to determine empirical mathematical models. These models highlight the influence exerted by some factors specific to the electrical discharges (cone angle, the voltage between electrodes, the capacitance of the capacitors included in the discharge electric circuit) on the material removal from the conical peaks of the test pieces.

Magnetotransport in under and optimally hole-doped bulk nanocrystalline [formula omitted] manganites

Electrical-transport and magneto-transport in bulk nanocrystalline (BNC) La1-xCaxMnO3+δ (x = 1/8 with either δ = 0.00 or δ = 0.06, x = 3/8 with δ = 0.00) (LCMO) manganite system have been studied treating the bulk crystalline (BC) counterparts as the reference systems. Irrespective of the value of δ in under hole-doped (x = 1/8) LCMO, the metal-insulator (M-I) transition (not observed in the BC counterpart) appears at a temperature TMI≪TC, where TC is the temperature at which the ferromagnetic (FM)–paramagnetic (PM) second-order phase transition occurs. Oxygen off-stoichiometry makes the M-I transition more pronounced and reduces the overall magnitude of resistivity. Reducing the average crystallite size d below 150 nm, lowers both TMI and TC in the BNC samples with x = 1/8 and δ = 0.00 or 0.06 but decreases TMI while increasing TC in the optimally hole-doped x = 3/8 LCMO. The single-orbital double-exchange model, which predicts the coincidence, or otherwise, of the M-I and FM-PM transitions with some success in the BC LCMO, fails to correctly describe the above-mentioned results in BNC LCMO. The resistivity minima at low temperatures (Tmin), completely absent in BC, occur in BNC LCMO, regardless of the value of x,δ,d and the strength of the magnetic field (H). The mechanism for resistivity, ρ(T), changes from the adiabatic small polaron nearest-neighbor hopping (for x = 3/8) or from the Shklovskii-Efros variable range hopping, SE-VRH, (for x = 1/8), prevalent in BC, to the Mott-VRH in the PM insulating state in the BNC counterparts when d falls below 150 nm. At T < Tmin, the contributions due to the Mott-VRH (present only in the samples with x = 1/8 and δ = 0.00 or δ = 0.06) and the enhanced electron-electron Coulomb interaction (in all the BNC LCMO samples) are responsible for the negative temperature coefficient of resistivity (TCR). By contrast, the coherent electron-magnon scattering accounts for the positive TCR observed at T > Tmin. H suppresses the mean hopping energy difference between the hopping sites but increases the electron localization length. The field-induced enhancement in the localization length far outweighs the field-induced drop in the mean hopping energy difference to produce an increase in the mean hopping distance with H.

Structure, optical and electrical properties of Nb-doped ZnO transparent conductive thin films prepared by co-sputtering method

Nb-doped ZnO thin films were fabricated on glass substrates by using co-sputtering with direct-current and radio frequency magnetron sputtering. The structures, optical and electrical performances of Nb-doped ZnO thin films were investigated. The results showed that all thin films have (0 0 2) [Formula: see text]-axis preferential orientation. The minimum resistivity of [Formula: see text][Formula: see text]cm and the maximum carrier concentration of [Formula: see text][Formula: see text][Formula: see text] were obtained at the direct-current sputtering power of 10[Formula: see text]W, respectively. Nb-doped ZnO thin films have also shown high average transmittance of 89.6%, and lower surface roughness of 2.74[Formula: see text]nm. Meanwhile, a distinct absorption edge in the ultraviolet range of 300–400[Formula: see text]nm was observed in absorbance, the optical band gap of Nb-doped ZnO thin films illustrates an increased tendency with increasing Nb concentration.

Work function of doped zinc oxide films deposited by ALD

Abstract

Observation of the Kondo Effect in Multilayer Single-Crystalline VTe2 Nanoplates.

We report the chemical vapor deposition (CVD) growth, characterization, and low-temperature magnetotransport of 1T phase multilayer single-crystalline VTe2 nanoplates. The transport studies reveal that no sign of intrinsic long-range ferromagnetism but localized magnetic moments exist in the individual multilayer metallic VTe2 nanoplates. The localized moments give rise to the Kondo effect, evidenced by logarithmical increment of resistivity with decreasing temperature and negative magnetoresistance (NMR) regardless of the direction of magnetic field at temperatures below the resistivity minimum. The low-temperature resistivity upturn is well described by the Hamann equation, and the NMR at different temperatures, a manifestation of the magnetization of the localized spins, is well fitted to a Brillouin function for S = 1/2. Density functional theory calculations reveal that the localized magnetic moments mainly come from the interstitial vanadium ions in the VTe2 nanoplates. Our results will shed light on the study of magnetic properties, strong correlation, and many-body physics in two-dimensional metallic transition metal dichalcogenides.

Improved TCO characteristics of ZnO:Si films via utilization of Si4+ ionized donor states and its application in n-SZO/p-Si heterojunction solar cells

Utilizing Si4+ ionized states providing two free electrons per atom, ZnO:Si (SZO) thin films have been grown as a superior transparent conducting oxide (TCO) material ideal for Si-based electronic devices. Energetically favoured substitutional doping of Zn2+ by Si3+ and Si4+ states facilitates increase in concentration (ne) and mobility (μ) of the charge carriers. At increased dopant incorporation at the interstitial sites Si2+ and Si1+ states are proportionally contributed which are not electronically active and act as scattering centres for the existing free electrons. Further, the formation of non-conducting SiOx bonds and their segregation at grain boundaries restrict increase in charge carrier concentration and reduce their mobility. The ideal dopant incorporation in ZnO:Si network accommodates ~1.6 ± 0.07 at.% Si. A minimal resistivity, (ρ)min ~7.16 × 10−5 Ωcm corresponding to the highest mobility, (μ)max ~85 V−1cm2s−1 and superior carrier density, (ne)max ~1.0 × 1021 cm−3 signify a highly degenerate semiconductor characteristic of the SZO films with reduced effective mass of electron, m* ~0.15 m0. Significantly high magnitude of Figure-of-Merit (FoM: Φ) ~9.7 × 10−2 Ω−1, even at moderately low growth temperature ~150 °C demonstrates excellent TCO characteristics of SZO films. The n-SZO/p-Si solar cells reveal increased VOC ~312 mV and JSC ~27.9 mA/cm2 via moderate widening in optical band gap and a significant increase in carrier concentration in the SZO component, respectively. The n-SZO/p-Si heterojunction solar cells with a FF ~0.499 and photovoltaic conversion efficiency η ~4.34% has been obtained with improved SZO layer grown by optimized doping via consumption of Si4+ donor states.

Ohmic contact to AlN:Si using graded AlGaN contact layer

We formed a graded-AlGaN contact layer to improve the Ohmic characteristics of Si-doped AlN. Linear I-V characteristics were obtained for AlN with the graded-AlGaN layer, and the current was three orders of magnitude larger than that for AlN without the one. The specific contact resistivity decreased with the increasing thickness of the graded-AlGaN layer. This was probably due to a reduction in the three-dimensional negative charge density induced by the polarization charge in the graded AlGaN layer. A minimum contact resistivity of 1.4 ×10−2 Ω cm2 was obtained for a 330-nm-thick graded-AlGaN layer. To obtain the Ohmic contact, the Si-dopant concentration (NSi) should be larger than the negative fixed charge density (ρπ) induced by the polarization charge. However, the heavily doped graded-AlGaN layer (NSi=2.4×1019 cm−3) became semi-insulating due to self-compensation. The results indicated that reducing ρπ by relaxing the compositional slope in the graded layer can improve the Ohmic characteristics.

Evidence of weak antilocalization in epitaxial TiN thin films

Defect engineering provides a tremendous opportunity to impart novel functionalities to nanomaterials. This report is focused on TiN metallic system, where the unpaired spin structure and electron-transport are controlled by injecting nitrogen vacancies (VN). The TiN films are epitaxial, with the TiN/Al2O3 epitaxial relationship given by: (1 1 1) TiN//(0 0 0 1) Al2O3 as out-of-plane, and 〈11-0〉 TiN//〈1 0 1- 0〉 Al2O3 and 〈1 1 2-〉 TiN//〈1 1 2-0〉 Al2O3 as in-plane, after 30° rotation. Epitaxy in such a large misfit system (~9.24%) is rationalized to arise via domain matching epitaxy (DME) paradigm. Following the report of room-temperature ferromagnetism [1] in TiN1−x films formed by injecting nitrogen vacancies, we provide direct experimental evidence of weak antilocalization (WAL) effects by plugging VN using nitrogen annealing of TiN films. This evidence with simultaneous loss of magnetization in nitrogen annealed TiN films is the tell-tale sign of VN acting as magnetically active defects in TiN, as their removal facilitates Berry’s phase formation and generation of time-reversal symmetry. Through detailed EELS and Raman analysis, we have explicitly shown the absence of Ti+2 polarons in TiN films on N2 annealing. The resistivity minima in TiN films are attributed to the WAL effect with persistent log T behavior under 0–7 Tesla magnetic fields. The temperature-dependent coherence length analysis also highlights the emergence of WAL under the two-dimensional localization theory. The WAL effect in TiN is similar to topological insulators, quenching on the introduction of magnetically active defects, while stable against non-magnetic defects. Our findings demonstrate the prime importance of nitrogen vacancies in tuning the magentotransport characteristics in epitaxial nitride films for optoelectronic device applications.

Local magnetic study for cluster-layered Fe/Cr nanostructures

Local magnetic structures of cluster-layered Fe/Cr thin films are studied by X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure (EXAFS). The magnetic moment of Fe atoms evaluated from XMCD for Al2O3/Cr(70Å)/[Fe(1.2Å )/Cr(10.5Å)]30/Cr(12Å), which shows the minimum point in the resistivity, decreases as the temperature increases and disappears around the temperature of the minimum resistivity. EXAFS shows the local structure of this film around Fe atoms is rather disordered and it can be related the fluctuation of magnetic structure estimated from the theoretical analysis of the temperature dependence of magnetic moments.

Investigation of thermal stability, optical properties, phase and chemical composition of transparent conductive tin oxide films deposited by pyrolytic method on silica float glass

The object of research is transparent conductive coating based on fluorine doped tin oxide deposited on silica float glass by the pyrolytic method. However, both in the manufacturing process of such a coating and in the process of its operation, degradation of its electrically conductive properties is observed. This may be due to changes in the structure of the coating under the influence of certain technological and operational factors, namely: process temperature, holding time, gas environment during the application and operation of a transparent electrically conductive coating. Studies have confirmed a significant increase in electrical conductivity. They also found a slight decrease in the transmittance of transparent oxide-tin films obtained with the introduction of ammonium fluoride as a dopant during the pyrolysis of 1M alcohol solutions of Sn2+ and Sn4+chlorides and are widely used as precursors for the content of such coatings. So, with a ratio of Sn4+/F=10 in working solutions, a minimum of specific surface resistance was fixed at 32 Ohm/m2. At the same time, a decrease in the value of the averaged transmittance in the optical wavelength range of 0.2-6.0 μm by 51 %, and in its visible part (0.4-0.8 μm) by 11 %. It is shown that thermal degradation of the coating is a significant factor in increasing the resistance values both in the technological process and during operational impacts. The results obtained indicate that reheating to temperatures above 450 °C leads to the appearance of the phenomenon of thermal degradation of the electrically conductive properties of the coating. So, during a 1-hour exposure at a temperature of 550 °C, the increase in specific surface resistance increases by 2 times and is fixed at 68 Ohm/m2 after complete cooling. Repeated heating cycles with the indicated parameters lead to a significantly lesser effect, which may indicate stabilization of the processes that occur during thermal destruction of the electrically conductive coating.

Changes in peak expiratory flow rates using two head-tilt/chin-lift maneuver angles in young healthy conscious volunteers.

BackgroundThe head-tilt/chin-lift (HT/CL) maneuver is simple and routinely used to open a closed upper airway.ObjectivesIt has yet to be determined whether increasing the HT/CL angle further would be beneficial.MethodsWe enrolled 60 (30 males) 20-year-old conscious participants. Pre-HT/CL, post-HT/CL #1, and post-HT/CL #2 positions were defined as positions in which the angle between the ear–eye line and the horizontal line was 80°, 65°, and 50°, respectively. Peak exploratory flow rates (PEFRs) pre-HT/CL, post-HT/CL #1, and post-HT/CL #2 positions were recorded continuously at 1-minute intervals (one set). Five sets of measurements were performed (total, 15 measurements for each participant).ResultsWe analysed 900 measurements (180 sets). The mean PEFRs pre-HT/CL, post-HT/CL #1, and post-HT/CL #2 positions were 348.4 ± 96.9, 366.4 ± 104.9, and 378.8 ± 111.2 L/min (percentage change compared to pre-HT/CL, 5.2% and 8.7%), respectively. Significant differences were observed among pre-HT/CL, post-HT/CL #1, and post-HT/CL #2 positions in all participants, as well as in subgroup classified according to sex, and medians of height, body weight, and body mass index.ConclusionOur findings suggest that a greater HT/CL angle would be beneficial, as the PEFR increased gradually. The decreasing manner in the PEFR increase with the HT/CL angle implies the existence of an angle threshold beyond which there were no further benefits in airflow, indicating a minimum in airway resistance. A HT/CL maneuver may be appropriate until locking the atlanto-occipital and cervical spine joints in extension occurs and the chest (sternal notch) begins to rise.

Optical and electronic properties of high quality Sb-doped SnO2 thin films grown by mist chemical vapor deposition

Transparent Sb-doped epitaxial SnO2 (101) thin films were grown via mist chemical vapor deposition, a nonvacuum solution-based technique that involves the gas-assisted transport of ultrasonically-generated aerosols from simple aqueous Sn and Sb precursors. The electrical properties (at 300 K) of the resulting films could be varied from insulating to semimetallic via Sb doping, with a minimum resistivity of 8×10−4Ωcm, carrier concentrations up to 3.93×1020cm−3, and a maximum mobility of 48.1±0.1cm2V−1s−1, results similar to those achieved using molecular beam epitaxy and other more-sophisticated high vacuum techniques. Secondary ion mass spectrometry and Hall effect measurements revealed that 14% of Sb in the precursor solution incorporates into the Sb:SnO2 films, with almost all the Sb atoms forming shallow substitutional donors on the Sn-site. The increase in the carrier concentration with Sb doping produced a Burstein-Moss shift of the optical gap of 0.49 eV, without significantly reducing the more than 90% transparency of the films in the visible region. X-ray photoemission spectroscopy (hν=1486.6eV) showed an asymmetric Sn3d5/2 core-level emission characterized by a carrier concentration-dependent peak splitting. This effect was modeled in terms of the creation of an intrinsic plasmon loss satellite from which a conductivity effective electron mass of (0.49±0.11)me was determined.

Preparation and Characterization of 3D Printed PLA-Based Conductive Composites Using Carbonaceous Fillers by Masterbatch Melting Method

This study was aimed at improving the conductivity of polylactic acid (PLA)-based composites by incorporating carbonaceous fillers. The composites with the addition of graphene nanoplatelets (rGO) or multi-walled carbon nanotubes (MWCNTs) were fabricated by the masterbatch melting method in order to improve the dispersion of the two kinds of nano-fillers. The results showed that, with the addition of 9 wt % rGO, the volume electrical resistivity of the composite reached the minimum electrical resistance of 103 Ω·m, at which point the conductive network in the composites was completely formed. The interfacial compatibility, apparent viscosity, and the thermal stability of the composite were also good. The rGO functionalized by sodium dodecylbenzene sulfonate (SDBS) was an efficient method to further improve the electrical conductivity of the composite, compared with tannic acid and MWCNTs. The resistivity was reduced by an order in magnitude. Patterns printed onto different baseplates by fused deposition modeling illustrated that the functionalized composite had certain flexibility and it is suitable for printing complex shapes.

Physical properties of Ruddlesden-Popper (n = 3) nickelate: La4Ni3O10

Nickelates, just like their isoelectronic cousins (the cuprate superconductors), are candidates for high temperature superconductivity. As charge density waves (CDW) and superconductivity might share a similar microscopic origin and that CDW behaviour is earlier suggested for La4Ni3O10, we here provide a detailed physical characterization of the magnetic, electronic and thermodynamic properties of stoichiometric polycrystalline La4Ni3O10 at and below 300 K. By variable temperature, synchrotron powder X-ray diffraction, we observe noticeable expansion in the b-axis and a contraction in c-axis coinciding with the electronic transition. Magnetic measurements indicate Pauli paramagnetic behaviour for the entire temperature range of 4–300 K. Transport data suggest electron–phonon interaction based conduction from 150 to 300 K, at 138 K the we observe an anomaly of second order nature, previously reported as a CDW anomaly. Below this anomaly, we observe no indications of electron–phonon interaction, but rather, Fermi liquid (FL) based T2 dependence with resistivity minima at 20 K, below which T1/2 dependence occurs for the resistivity indicating pure electron–electron interactions (EEI) based transport. Specific heat data indicates that mass enhancement of La4Ni3O10 similar to that of the normal state of the cuprates and the entropy change at anomaly suggests close similarities to other quasi-two dimensional systems, such as molybdenum bronzes and manganites.

Effect of nitrogen flow rate on the properties of nitrogen-doped Cu&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O

Cuprous oxide (Cu₂O) has the potential applications in photovoltaic and photocatalytic fields. Nitrogen-doping in Cu₂O can improve the conductivity by increasing hole concentration. However, the chemical states of nitrogen in nitrogen-doped Cu₂O have not been studied thoroughly.A series of nitrogen-doped Cu₂O samples are prepared by increasing nitrogen flow rates and simultaneously keeping the sputtering pressure and other parameters unchanged. The samples are characterized by X-ray diffraction (XRD), step instrument, scanning electron microscope (SEM), energy dispersive spectrometer, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), spectrophotometer and Hall effect et al. The results of Hall effect measurement show that nitrogen-doping can increase the hole concentration by one order of magnitude. The band gap width decreases with the increase of nitrogen flow rate. The nitrogen in Cu₂O is in three forms: β-N (nitrogen atom), α-N₂(molecular nitrogen, —N=N—)and γ-N₂(molecular nitrogen, N≡N). With the increase of nitrogen gas flow rate, the peak of binding energy of β-N increases while that of α-N₂ decreases. The sample prepared at the nitrogen flow rate of 2.0 sccm has the minimum resistivity among all samples.

Investigation of Structural, Dielectric and Electrical Properties of Barium Titanate Ceramics Co-Doped with Bismuth and Yttrium

Bismuth and Yttrium co-doped Barium Titanate (BaTiO3) ceramics with the general formula (Ba[Formula: see text]BiX) (YxTi[Formula: see text]) O3(where [Formula: see text], 0.01, 0.03, 0.05) have been synthesized at 1300∘C for 3[Formula: see text]h by the standard solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Impedance Analyzer. Temperature-dependent dielectric properties of the samples were also measured. The XRD result revealed perovskite structure for un-doped and co-doped BaTiO3with tetragonal phase. However, with increasing doping concentration, a Pseudo cubic phase occurs also confirmed by the twin peaks (002) and (200) of XRD pattern. From SEM micrograph, submicron size particles were observed for all synthesized BaTiO3samples and exhibit a narrow size distribution with quiet uniform morphology. The crystalline size for un-doped BaTiO3found was 24.26[Formula: see text]nm, the size decreases (minimum 19.59[Formula: see text]nm for [Formula: see text]) for all compositions of co-doped BaTiO3. Dielectric constant values were apparently high and direct current (DC) resistivity follows a decreasing trend at higher doping concentration. The sample doped with [Formula: see text] shows minimum DC resistivity and maximum dielectric constant among the samples investigated.