Temperature Resistivity Measurements Research Articles

Design of a multi-physics coupling MEMS pressure sensor

The pressure measurement of explosion shock wave puts forward high requirements on the temperature resistance and response speed of the sensor. In this paper, a multi-physics coupling pressure sensor is designed to meet requirements. The sensor mainly consists of a Fabry-Perot cavity optical fiber sensing unit, a piezoelectric pressure sensing unit and a thermometric resistance temperature measurement module. Firstly, the structure of the sensor is designed. The top and bottom surfaces of the Fabry-Perot cavity are composed of a silicon diaphragm and a quartz glass. The piezoelectric pressure sensing unit is an AlN film including its electrodes. Pt thermometric resistance is developed to realize real-time temperature monitoring. Secondly, the fabrication process of the sensor is discussed, especially three key technologies. An Al film is sputtered to increase the reflectivity of the quartz glass. The SU-8 photoresist is applied to accurately control the thickness of Fabry-Perot cavity. Etching is adopted to work out the graphics of the AlN piezoelectric film. At last, a complete fabrication process of the sensor is described. The fabrication of multilayer films begins with a double-sided polishing silicon wafer, while Fabry-Perot cavity was from a double-sided polishing quartz glass. Then two parts of the sensor are combined to ensure the multi-physics coupling sensor to achieve complete function.

Investigation of pyrochlore-type A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics as negative temperature coefficient thermistors for high-temperature application

This study puts forward a series of thermosensitive materials based on A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics for high-temperature applications. The A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics were synthesized following the solid-state route and characterized using techniques involving X-Ray diffraction, scanning electron microscopy, and Raman spectroscopy. It could be verified that the A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics had pyrochlore structures with relative densities ranging from 95.8 to 97.6%. The resistance-temperature measurements confirm that these ceramics have unique oxygen-insensitive negative temperature coefficient properties. The logarithm of resistivity depends on the reciprocal of temperature with excellent linearity over a wide temperature range of 400–1300 °C. A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics also exhibited well-ageing characteristics at their maximum upper applicable temperature of 1300 °C, in addition to the high resistivity and thermal constant B value that assured high accuracy. These properties outperformed those of the majority of high-temperature negative temperature coefficient ceramics based on scheelite or perovskite structures. The results suggested that the A2Sn2O7 (A = La, Nd, Sm, or Gd) ceramics could be potentially used for fabricating high-temperature NTC thermistors.

Uncovering the physical properties, structural characteristics, and electronic application of superlattice-like Ti/Sb phase-change thin films

Superlattice-like (SLL) Ti/Sb thin films were proposed and investigated from the viewpoint of physical properties, structural characteristics, and electronic application. Magnetron sputtering was employed to deposit the SLL Ti/Sb thin films with different thickness ratios. In-situ resistance–temperature measurement indicates that the crystallization temperature, crystallization-activation energy, and data-retention capacity increase significantly and the resistance drift index reduces with an increment in thickness ratio of the Ti to Sb layer, meaning higher amorphous thermal stability and reliability of SLL Ti/Sb thin films. X-ray diffraction and Raman spectra reveal that the inserted Ti layer can inhibit grain growth and refine the grain size, causing remarkable improvement of thermal stability and crystalline resistance. Analyses of x-ray reflectivity and atomic force microscopy demonstrate that the thickness fluctuation of SLL Ti/Sb thin films becomes smaller and the surface topography becomes smoother, respectively. The Avrami exponent of the SLL (Ti3Sb7)5 thin film reflects the growth-dominated crystallization mechanism, implying a rapid phase transition speed. Phase-change memory cells based on the SLL (Ti3Sb7)5 thin film can realize a reversible SET/RESET operation under an electrical pulse with a width of 100 ns. The RESET power consumption was estimated to be much lower than that of traditional Ge2Sb2Te5 material. The above results strongly prove that the suitable SLL structure of Ti/Sb thin films have tremendous potential in the area of high-temperature and low-power electronic storage.

New Metastable Baro- and Deformation-Induced Phases in Ferromagnetic Shape Memory Ni2MnGa-Based Alloys.

Structural and phase transformations in the microstructure and new metastable baro- and deformation-induced phases of the Ni50Mn28.5Ga21.5 alloy, typical of the unique class of ferromagnetic shape memory Heusler alloys, have been systematically studied for the first time. Phase X-ray diffraction analysis, transmission and scanning electron microscopy, and temperature measurements of electrical resistivity and magnetic characteristics in strong magnetic fields were used. It was found that in the course of increasing the pressure from 3 to 12 GPa, the metastable long-period structure of martensite modulated according to the 10M-type experienced transformation into a final non-modulated 2M structure. It is proved that severe shear deformation by high pressure torsion (HPT) entails grainsize refinement to a nanocrystalline and partially amorphized state in the polycrystalline structure of the martensitic alloy. In this case, an HPT shear of five revolutions under pressure of 3 GPa provided total atomic disordering and a stepwise structural-phase transformation (SPT) according to the scheme 10M → 2M → B2 + A2, whereas under pressure of 5 GPa the SPT took place according to the scheme 10M → 2M → B2 → A1. It is shown that low-temperature annealing at a temperature of 573 K caused the amorphous phase to undergo devitrification, and annealing at 623–773 K entailed recrystallization with the restoration of the L21 superstructure in the final ultrafine-grained state. The size effect of suppression of the martensitic transformation in an austenitic alloy with a critical grain size of less than 100 nm at cooling to 120 K was determined. It was established that after annealing at 773 K, a narrow-hysteresis thermoelastic martensitic transformation was restored in a plastic ultrafine-grained alloy with the formation of 10M and 14M martensite at temperatures close to those characteristic of the cast prototype of the alloy.

ZrO2 Reduction at Low Temperature in Co-Sputtered ZrxHf1−xO2 Thin-Films

A temperature dependent x-ray photoelectron spectroscopy (XPS) study reveals that ZrO2 reduces to metallic Zr and O at ∼ 140°C at Zr ratios of 8.38, 9.11, and 11.79 at.% in co-sputtered ZrxHf1−xO2 thin-films deposited on the silicon substrate. ZrO2 is reduced in the form of Zr metal. The oxygen evolved in this process reacts with carbon present in the film forming CO2 gas. Further, the presence of Zr in temperature treated samples at room temperature (RT) indicates the reduction as an irreversible one. Capacitance-voltage (C-V) curves depict increasing capacitance at high temperature (HT), confirms an increase in dielectric constant for all the films. The resistance obtained from Resistivity-temperature measurement offers a lower value at HT indicates partial metallization of films. Despite similar atomic radii of Zr and Hf, the stability of metastable tetragonal ZrO2 (t-ZrO2) decreases probably due to the influence of Hf present in ZrxHf1−xO2. This stabilization was ascribed to a decrease in the Zr coordination number upon the introduction of oxygen vacancies. A Less dense d band causes the formation of metallic Zr at such a low temperature. A reduction scheme for ZrO2 at low temperature is also proposed. Since the generation of metallic Zr sites at a lower temperature is a challenge to develop Zr-based catalyst, this combination may be used to design ZrHfO-based catalysts for low temperature catalytic applications.

Laser-induced transverse voltage effect in c-axis inclined CuCr0.98Mg0.02O2 thin films with dominant phonon thermal conductivity

CuCr1−xMgxO2 (x = 0 and 0.02) epitaxial thin films were prepared on 5°/10° vicinal cut α-Al2O3 (000l) substrates using pulsed laser deposition. The laser-induced thermoelectric voltage (LITV) effect in these inclined delafossite thin films was observed for the first time. The thin films were characterized by resistivity temperature measurement and atomic force microscopy. Because of the enhanced resistivity anisotropy and high carrier concentration in the ab-plane owing to Mg doping, the 10°-tilted CuCr0.98Mg0.02O2 film exhibits an evident LITV signal with a maximum transverse thermoelectric voltage of 156 mV. Thermal conductivity results indicate that CuCr1−xMgxO2 (x = 0 and 0.02) films have a dominant phonon thermal conductivity, which may contribute to a long decay time for the LITV signal. These results indicate potential for future transverse thermoelectric applications based on transparent conductive oxides.

Performance Improvement of Sb Phase Change Thin Film by Y Doping

Yttrium-doped Sb phase change thin films were prepared by magnetron sputtering and the in-situ resistance temperature measurement system was used to study the process of phase change thin films. With the addition of yttrium atoms, the crystallization temperature of Sb thin film increases, indicating improvement of their thermal stability and data retention ability. Furthermore, yttrium-doped Sb thin films have higher crystalline and amorphous resistance, which is conducive to the phase transition by Joule heating under electric pulse current. The optical band gap energy increases after yttrium doping, which means lower conductivity and higher conduction activation energy. X-ray diffraction shows that the doping of yttrium atoms can inhibit the grain growth and refine the grain size. X-ray photoelectron spectroscopy was used to examine the chemical state of the element, indicating the formation of a new Y-Sb bond, which verifies the improvement of stability. According to atomic force microscopy images, the yttrium-doped Sb material exhibits a surface morphology with less roughness, implying better interfacial properties and reliability. In general, yttrium-doped Sb thin films have better development in the application of phase change memory.

Thickness effect of Sn<sub>15</sub>Sb<sub>85</sub> phase change film

Sn<sub>15</sub>Sb<sub>85</sub> thin films with different thickness are prepared by magnetron sputtering. The evolution of Sn<sub>15</sub>Sb<sub>85</sub> thin film from the amorphous state to the crystalline state is studied by an <i>in-situ</i> resistance temperature measurement system. The crystallization temperature, electrical resistance, crystallization activation energy, and data retention capacity of Sn<sub>15</sub>Sb<sub>85</sub> thin film increase significantly with film thickness decreasing. The near infrared spectrophotometer is used to record the diffuse reflectance spectra of amorphous Sn<sub>15</sub>Sb<sub>85</sub> film. The results show that the band gap energy increases with film thickness decreasing. The surface morphology of Sn<sub>15</sub>Sb<sub>85</sub> film after being crystalized is observed by atomic force microscope, which shows that the thinner film has lower roughness. The analysis of X-ray diffraction indicates that the grain size becomes smaller and the crystallization may be inhibited by reducing the film thickness. T-type phase change memory cells based on Sn<sub>15</sub>Sb<sub>85</sub> thin films with different thickness are fabricated by the CMOS technology. The electrical performances of phase change memory show that the thinner Sn<sub>15</sub>Sb<sub>85</sub> film has a larger threshold switching voltage and smaller RESET operation voltage, which means the better thermal stability and lower power consumption. The outcomes of this work provide the guidance for designing the high-density phase change memory by reducing the size of Sn<sub>15</sub>Sb<sub>85</sub> thin film.

Changes in Resistance and Bandgap of V2O5 and Ge2Sb2Te5 during Phase Transition

V2O5 and Ge2Sb2Te5 (GST) films have been prepared by magnetron sputtering, and their transformation from amorphous to crystalline state studied by in situ resistance temperature measurements. During the heating process, a two-step transition was observed for both films, revealing three resistances corresponding to amorphous, intermediate, and crystalline states. The two phase-transition temperatures were 371.1°C and 394.0°C for V2O5, much higher than the values of ∼ 172.4°C and 240.4°C for GST. Compared with GST, the resistance of V2O5 was two orders of magnitude higher. The changes in the resistance and bandgap of V2O5 and GST during phase transition were investigated in detail. A phase-change memory device based on V2O5 was fabricated. Compared with GST, V2O5 exhibited a lower operating power and shorter phase-transition time. The application potential of V2O5 and GST for multilevel storage was compared.

A2Zr2O7 (A = Nd, Sm, Gd, Yb) zirconate ceramics with pyrochlore-type structure for high-temperature negative temperature coefficient thermistor

The aim of this paper is to present a novel negative temperature coefficient (NTC) thermistor based on A2Zr2O7 (A = Nd, Sm, Gd, Yb) zirconate ceramics with pyrochlore-type structure for high-temperature application. The zirconate ceramics were synthesized via a solid-state reaction method where rare-earth oxides and ZrO2 were used as starting materials. The physical structures were characterized by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. It was confirmed that Nd2Zr2O7 and Sm2Zr2O7 are pyrochlore phases, while Yb2Zr2O7 and Gd2Zr2O7 are defect fluorite phases. The electrical property investigated by using resistance–temperature measurements demonstrated that the prepared A2Zr2O7 zirconate ceramics exhibit a typical characteristic of NTC over a wide temperature range between 673 and 1273 K. Particularly, A2Zr2O7, in addition to having high activation energy to ensure better sensitivity, can still maintain higher resistivity under high-temperature environments. Furthermore, the resistivity of A2Zr2O7 is almost independent of the change in oxygen partial pressure. These properties are superior to the classical spinel-type or perovskite-type NTC thermistor, providing valuable information to explore new NTC thermistor for high-temperature applications.

Effect of phase structures and substrate temperatures on NTC characteristics of Cu-modified Ba–Bi–O-based perovskite-type thermistor thin films

Based on the formula of BaBi0·92Cu0·08O3, Cu-modified Ba–Bi–O-based perovskite-like negative temperature coefficient (NTC) thermistor thin films were successfully prepared by radio frequency (RF) magnetron sputtering method with the various deposition temperatures (25 °C, 100 °C, 200 °C and 250 °C). The effects of the substrate temperatures on the phase structures and electrical properties were respectively characterized and investigated by X-ray diffraction (XRD), resistance-temperature measurement, and complex impedance analysis for the Ba–Bi–O-based thin films. Additionally, the cross-sectional microstructures and grain morphologies of the BaBi0·92Cu0·08O3 thin films were analyzed by scanning electron microscope (SEM) and atomic force microscope (AFM). The XRD patterns results showed that the perovskite monoclinic structure with a small amount of BaBiO2.5 s phase could be obtained for the BaBiO3 thin film deposited at 200 °C, and also, the main crystalline phase was transferred from BaBiO2.82 to BaBiO2.5 when the BaBi0·92Cu0·08O3 thin films were deposited at 200 °C and 250 °C, respectively. Temperature dependent complex impedance spectroscopy was carried out to make clear the resistance contribution of grain (Rg), grain boundary (Rgb) and contact (Rs) response for the conduction mechanisms in the Ba–Bi–O-based thin film deposited at a given substrate temperature. Compared with the electrical properties of the BaBiO3 thin film deposited at 200 °C [such as the room-temperature resistivity (ρ25 ~ 1548 Ω cm) and the thermistor constant (B25/85–3245 K)], the better NTC characteristics of a lower ρ25 value of about 956 Ω cm and a higher B value of approximately 3480 K were found in the BaBi0·92Cu0·08O3 thin film deposited at a same temperature (200 °C). It is believed that the phase structures and electrical properties of the BaBiO3 perovskite-type NTC thermistor thin films could be adjusted and optimized by a trace amounts of Cu-ions substitutions and depositing at an appropriate substrate temperature, which also showed that such as these novel BaBiO3-based thin films are feasible with the extensive of actual applications for the NTC thermistors.

Study on the crystallization of Mg35Sb65/Sn15Sb85 superlattice-like films for phase change memory application

In this paper, the Mg35Sb65/Sn15Sb85 superlattice-like films were prepared by magnetron sputtering and the comprehensive properties of were systematically studied. The amorphous-to-crystalline transformation was researched with a situ resistance–temperature measurement system to evaluate the thermal stability. X-ray diffraction, Raman and transmission electron microscopy were employed to explore the change of phase structure at different annealing temperatures. The reversible resistance switching was achieved for [MgSb(7 nm)/SnSb(3 nm)]5-based devices. The results showed that Mg35Sb65/Sn15Sb85 superlattice-like film was a promising phase change material with good thermal stability, fast phase transition and low power consumption.

Stable and Tunable Current-Induced Phase Transition in Epitaxial Thin Films of Ca2RuO4.

Owing to the recent discovery of the current-induced metal-insulator transition and unprecedented electronic properties of the concomitant phases of calcium ruthenate Ca2RuO4, it is emerging as an important material. To further explore the properties, the growth of epitaxial thin films of Ca2RuO4 is receiving more attention, as high current densities can be applied to thin-film samples and the amount can be precisely controlled in an experimental environment. However, it is difficult to grow high-quality thin films of Ca2RuO4 due to the easy formation of the crystal defects originating from the sublimation of RuO4; therefore, the metal-insulator transition of Ca2RuO4 is typically not observed in the thin films. Herein, a stable current-induced metal-insulator transition is achieved in the high-quality thin films of Ca2RuO4 grown by solid-phase epitaxy under high growth temperatures and pressures. In the Ca2RuO4 thin films grown by ex situ annealing at >1200 °C and 1.0 atm, continuous changes in the resistance of over 2 orders of magnitude are induced by currents with a precise dependence of the resistance on the current amplitude. A hysteretic, abrupt resistive transition is also observed in the thin films from the resistance-temperature measurements conducted under constant-voltage (variable-current) conditions with controllability of the transition temperature. A clear resistive switching by the current-induced transition is demonstrated in the current-electric-field characteristics, and the switching currents and fields are shown to be very stable. These results represent a significant step toward understanding the high-current-density properties of Ca2RuO4 and the future development of Mott-electronic devices based on electricity-driven transitions.

Cationic Vacancy Mediated Conductivity and Charge Transport in Non‐Stoichiometric Epitaxial BaTi0.75Nb0.25O3 Films

High‐quality epitaxial BaTi0.75Nb0.25O3 (BNTO) films with controllable Ba/(Nb + Ti) ratio are fabricated by pulsed laser deposition, and a systematic investigation on their conductivity and charge transport behaviors is carried out. The Ba/(Nb + Ti) ratio can be significantly regulated from 0.96 to 0.53 when the laser fluence varies from 0.5 to 2.0 J cm−2. Resistivity–temperature measurements indicate that all the BNTO films exhibit semiconductor transport behaviors at temperatures from 50 to 400 K. Their conductivity increases monotonically with the decrease in the Ba/(Nb + Ti) ratio. For films with a high Ba/(Nb + Ti) ratio of 0.96, the small polaron (SP) hopping dominates in the temperature range from 200 to 400 K. Nevertheless, the SP hopping can only be observed at temperatures ranging from 285 to 400 K for the films with a Ba/(Nb + Ti) ratio of 0.53, implying that the reduction of Ba vacancy is favorable for SP hopping transport in BNTO films, especially at low temperature. Hall effect measurements indicate a higher carrier mobility observed in the films with lower Ba/(Nb + Ti) ratio, revealing the promotion of carrier mobility by Ba vacancy. The work reveals that cationic vacancy plays an important role in the conductivity and charge transport mechanisms in perovskite oxide materials, such as BNTO films.

Synthesis and Characterization of Magnesium Diboride Additions of Bi-2223 on the Microstructure and Superconducting Transition

In this paper, solid state method was using to synthesize the of magnesium diboride (MgB2) added in Bi 1.6Pb 0.4Sr2Ca2Cu3Oδ(Bi-2223) superconductor from 0.00 to 0.10 wt.%. The effect on additions were investigated through X-ray Diffraction (XRD), resistance-temperature (R-T) measurement and Scanning Electron Microscope (SEM). From the XRD result, volume fraction of Bi-2223 showed the highest volume percentage was 76 % correspond to addition with MgB2=0.02 wt.% and slightly decreased the percentage while increased the additions. From the R-T measurement, all samples showed the metallic behavior in the normal state. Morphology images showed that the grains were flaky plates and the size slightly increased. These results revealed that, additions of magnesium diboride change the microstructure and decrease the superconducting transition.

Study on positive temperature coefficient of resistivity of co-doped BaTiO3 with Curie temperature in room temperature region

As a temperature self-regulating heater material, the doped BaTiO3 exhibits an attractive application perspective in the thermal management of electrical devices. However, the high Curie temperature does not meet the requirement in the thermal control application. In this work, (Ba0.997−xCe0.003Srx)(TiNb0.002)O3 (x=0.2, 0.3, 0.35, abbreviated as BCSTNs) ceramics were prepared by the solid-state reaction method. The purpose of doping different content of strontium is to shift the Curie temperature of BaTiO3-based ceramic to the ambient temperature region, maintaining excellent PTC effect and low room-temperature resistivity by codoped cation ions in Ba- and Ti-site. The influences of sintering temperature and soak time on the microstructure as well as electrical properties of BCSTNs ceramics have been studied. The X-ray diffraction reveals that the composition with x=0.35 exhibits the coexistence of tetragonal and cubic lattice symmetries, confirmed by the Rietveld structure refinement. The dense microstructure with average grain sizes 0.84–7.87 μm was observed for BCSTN ceramics. Temperature-resistivity measurements demonstrate that TC of the ceramics with x=0.35 shifted to the room temperature region. Additionally, the BCSTN ceramic with heavy doping Sr exhibits relative low room-temperature resistivity and the resistance jump greater than 2.0 orders of magnitude.

Influence of Ag doping on electrical and magnetic properties of La0.67Ca0.33MnO3 polycrystalline ceramics

Structural, electrical, and magnetic properties of La0.67Ca0.33MnO3 with Ag doped (LCMO:Agx, 0 ≤ x ≤ 0.5) polycrystalline ceramics were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), four-probe resistance-temperature measurements (RT), X-ray photoemission spectroscopy (XPS), and vibrating sample magnetometry (VSM). Significant improvements in temperature coefficient of resistance (TCR) and magnetoresistance (MR) were observed in LCMO:Agx (x = 0.2) samples on addition of Ag. TCR and MR reached maximum values of 26.0% K−1 (269.5 K) and 47.4% (271.8 K) respectively, for x = 0.2. Interestingly, XPS along with XRD and SEM results indicated that silver existed in LCMO:Agx composites in two forms, at A sites (La3+/Ca2+) as Ag+ ion and segregated at grain boundaries (GBs) as metallic silver. All evidences supported the fact that Ag doping was beneficial in improving the electrical and magnetic transport properties of LCMO:Agx ceramics. Hence, they can be used in infrared detectors or magnetic sensor devices. Double-exchange (DE) mechanism and Jahn-Teller (JT) distortion were used to explain the optimal physical performance of LCMO ceramics with Ag doping.

Microstructures and electrical properties of Mn/Co/Ni-doped BaBiO3 perovskite-type NTC ceramic systems

Mn/Co/Ni-modified BaBiO3-based negative temperature coefficient (NTC) ceramics with the formula, x[(3-y-z)Mn/yCo/zNi-ions]+(1−x)BaBiO3 (x = 0.0–0.4, y = 0.96 and z = 0.48), were synthesized using a conventional solid state reaction. The effects of Mn/Co/Ni-substitute content on the phase structures and composition, microstructures and electrical properties were characterized by X-ray diffraction (XRD), scanning electron microscope and resistance–temperature measurements, respectively. XRD pattern analysis results revealed that the compound phases consisted of a main monoclinal BaBiO3 phase and a secondary phase of Ba(Mn, Co, Ni)O3 solid-solution with a hexagonal structure, which were detected at x = 0.05–0.2. In addition, according to the XRD patterns, the main phase changed from BaBiO3 to a rhombohedral Bi8.11Ba0.89O13.05 phase at x = 0.3, and this phase content increased dramatically as the x value increased to 0.4. For the related electrical properties, all of the samples demonstrated the typical characteristics of NTC thermistors across a relatively wide range of temperatures. The values obtained for B constant (B25/85) and the room-temperature resistivity (ρ25) were in the range of 2297–5235 K and 760 Ω cm−1, 620 kΩ cm, respectively, which implied that the electrical properties of the present ceramic systems could be optimized via various substitutions in the Mn/Co/Ni-ions content. The variable values of ρ25 were affected strongly by the changes in crystal structure and the decrease in charge carrier concentration. These composite ceramic materials are suitable candidates for a variety of NTC thermistor applications due to their widely adjustable electrical properties.

Structural Evolution and Phase Change Properties of C-Doped Ge2Sb2Te5 Films During Heating in Air☆☆Supported by the National Natural Science Foundation of China under Grant No 11704161, the Natural Science Foundation of Jiangsu Province under Grant Nos BK20170309 and BK20151172, and the Changzhou Science and Technology Bureau under Grant Nos CJ20159049 and CJ20160028.

We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbon-doped Ge2Sb2Te5 (C-GST) films during heating in air. Both the C-GST films without and with a thin SiO2 capping layer (C-GST and C-GST/SiO2) are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO2 films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistance-temperature measurement reveals an unusual smooth decrease in resistance above 110 °C during heating. X-ray diffraction result has excluded the possibility of phase change in the C-GST film below 170 °C. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe4−nGen (n = 0, 1) units above 110 °C in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.

Anomalous Cooling-Rate-Dependent Charge Transport in Electrolyte-Gated Rubrene Crystals.

Although electrolyte gating has been demonstrated to enable control of electronic phase transitions in many materials, long sought-after gate-induced insulator-metal transitions in organic semiconductors remain elusive. To better understand limiting factors in this regard, here we report detailed wide-range resistance-temperature ( R- T) measurements at multiple gate voltages on ionic-liquid-gated rubrene single crystals. Focusing on the previously observed high-bias regime where conductance anomalously decreases with increasing bias magnitude, we uncover two surprising (and related) features. First, distinctly cooling-rate-dependent transport is detected for the first time. Second, power law R- T is observed over a significant T window, which is highly unusual in an insulator. These features are discussed in terms of electronic disorder at the rubrene/ionic liquid interface influenced by (i) cooling-rate-dependent structural order in the ionic liquid and (ii) the intriguing possibility of a gate-induced glassy short-range charge-ordered state in rubrene. These results expose new physics at the gated rubrene surface, pointing to exciting new directions in the field.