Weak Chemical Bonds Research Articles

Electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds: the case of Pd2MnTi

Abstract In this study, taking Pd2MnTi as a representative example, the electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds was systematically studied and revealed theoretically. The calculation and theoretical analysis suggest that Pd2MnTi is not stable in cubic structure and prones to transform to low-symmetric tetragonal structure. By tetragonal deformation, the shrinkage of lattice parameters and the decrease of symmetry promote the electron accumulation between Pd and its first nearest neighboring Ti atom, resulting in the increased covalent hybridization. The occurrence of pesudogap in density of states (DOSs) of tetragonal Pd2MnTi near the Fermi level also verifies the enhancement of covalent bond. Comparatively, the stronger interatomic bond in tetragonal Pd2MnTi, i.e., covalent bond here, would strengthen interatomic coupling and consequently lower the energy of the material. By the martensitic phase transition, more stable state in energy was achieved. Thus, based on the analysis of electronic structure evolution, the nature of martensitic phase transition is a process wherein symmetry breaking weakens the original weak chemical bonds in high-symmetric parent phase and induces the strong chemical bond to lower the energy of the materials and achieve a more stable state. This study could help to deepen the understanding of martensitic phase transition and the exploration of novel materials for potential technical applications.

New hybrid adsorbent based on APTES functionalized zeolite W for lead and cadmium ions removal: Experimental and theoretical studies

Water pollution remains a primary worldwide concern, requiring various treatment technologies for efficient and effective remediation. In recent years, zeolites have gained extensive attention as promising materials and approaches for removing heavy metals from wastewater. This study presents a new hybrid adsorbent based on zeolite W (ZW) chemically modified with aminopropyltriethoxysilane (APTES), demonstrating excellent Pb(II) and Cd(II) removal efficiency, was developed. The prepared zeolites were characterized using several advanced techniques. XPS, NMR, FTIR spectroscopy, elemental analysis and TGA confirmed the successful functionalization via covalent bonds between the zeolite W inorganic surface and the available APTES silanol groups. The adsorption behavior of both metal ions onto the prepared zeolites was well-fitted by the Redlich-Peterson and Langmuir isotherms, and the Pseudo-second order model. Results showed that ZW@APTES provides a larger adsorption capacity than ZW under all studied experimental conditions. The maximum adsorption capacity of ZW@APTES for Pb(II) and Cd(II) reached 421.7 and 253.5 mg/g, respectively. Moreover, batch experiments indicated that ion exchange and surface complexation with weak chemical bonds were the main adsorption mechanisms for Pb(II) and Cd(II). This study demonstrates that APTES-modified zeolite W could be a valuable and promising material for removing heavy metal ions from contaminated water in real-world applications.

Multiscale study on the solid-liquid synergistic lubrication mechanism of graphite and liquid lubricant in polymer composites

Solid-liquid synergistic lubrication, in combination with the advantages of solid and liquid lubrication, has gained the great popularity in recent years. However, the mechanism of solid-liquid synergetic lubrication is still unclear. In this paper, graphite and poly α-olefin base oil (PAO) were used as self-lubricating additives to evaluate their synergistic effect. The results show that the composites possess good mechanical and excellent tribological properties with a nanoindentation modulus of 3.8 GPa, a coefficient of friction of 0.0998, as well as a wear rate of 1.3 × 10−14 m3/N·m. Both transfer film and lubricating oil film exist on the friction interface, and the lubricating oil film protects the counter ball from excessive oxidation. At the same time, with combination of molecular dynamics (MD) simulation and first-principles calculations, the synergistic lubrication mechanism of graphite and PAO was manifested. PAO destroyed the interlayer structure of graphite, making it easier to form a transfer film on the counter ball surface. The weak chemical bond between graphite and PAO facilitates more PAO molecules to gather at the interface while forming the transfer film, which benefits the formation of lubricating oil film. The synergistic effect of graphite and PAO molecules is critical in promoting the further reduction of COF.

Advanced GeSe-based thermoelectric materials: Progress and future challenge

GeSe, composed of ecofriendly and earth-abundant elements, presents a promising alternative to conventional toxic lead-chalcogenides and earth-scarce tellurides as mid-temperature thermoelectric applications. This review comprehensively examines recent advancements in GeSe-based thermoelectric materials, focusing on their crystal structure, chemical bond, phase transition, and the correlations between chemical bonding mechanism and crystal structure. Additionally, the band structure and phonon dispersion of these materials are also explored. These unique features of GeSe provide diverse avenues for tuning the transport properties of both electrons and phonons. To optimize electrical transport properties, the strategies of carrier concentration engineering, multi-valence band convergence, and band degeneracy established on the phase modulation are underscored. To reduce the lattice thermal conductivity, emphasis is placed on intrinsic weak chemical bonds and anharmonicity related to chemical bonding mechanisms. Furthermore, extra-phonon scattering mechanisms, such as the point defects, ferroelectric domains, boundaries, nano-precipitates, and the phonon mismatch originating from the composite engineering, are highlighted. Additionally, an analysis of mechanical properties is performed to assess the long-term service of thermoelectric devices based on GeSe-based compounds, and correspondingly, the theoretical energy-conversion efficiency is discussed based on the present zT values of GeSe. This review provides an in-depth insight into GeSe by retrospectively examining the development process and proposing future research directions, which could accelerate the exploitation of GeSe and elucidate the development of broader thermoelectric materials.

Thermodynamic and elastic properties of laves phase AB2-based alloys and their hydrides: A density functional theory (DFT) study

A first-principles method based on the density functional theory (DFT) was employed in conjunction with quasi-harmonic Debye model to investigate the structural, elastic, and thermodynamic properties of a series of AB2-based Laves phases alloys and their hydrides. Simulation results revealed that the studied materials possess the Laves phase structure with lattice parameters comparable to experimental findings. For the first time, to the best of our knowledge, mixing entropy determined using Debye model was used to classify alloys into (Low- Medium-High Entropy Alloys) LEA, MEA and HEA categories rather than the commonly used ideal solution model, which is often inaccurate and ignores the impact of temperature. Lattice analyses of the alloy materials indicated that cell volume increases with the addition of elements, while the enthalpy of hydride formation indicates that hydrogen absorption in these alloys is exothermic and that the 3.00 H/F.U configuration is energetically stable. The alloys and their hydrides are metallic with no band gap at the Fermi level. The thermodynamic properties were studied using the quasi-harmonic Debye model and it was found that Bulk modulus decreases with increasing volume, and the hydrides possess lower bulk modulus compared to their metallic counterparts. Moreover, Debye temperature decreases with the gradual addition of elements, indicating weaker chemical bonds in ternary and other alloys. All hydrides have lower Debye temperature than their parent alloy materials. Finally, The alloys are classified into low-, medium-, and high-entropy alloys based on mixing entropy calculated using the Debye model. TiMn2 is classified as a low-entropy alloy, ZrMn2, Ti0.5Zr0.5Mn2, and Ti0.5Zr0.5MnFe as medium-entropy alloys, and Ti0.5Zr0.5(MnCr)2, Ti0.5Zr0.5Mn2/3Fe2/3Cr2/3, and Ti0.5Zr0.5Mn0.5Fe0.5Cr0.5Ni0.5 as high-entropy alloys.

Effect of Rare Earth Ion Substitution on Phase Decomposition of Apatite Structure.

The paper describes an investigation of phase decomposition of apatite lattice doped with rare earth ions (cerium, samarium, and holmium) at temperatures ranging from 25-1200 °C. The rare-earth ion-doped apatite minerals were synthesized using the sol-gel method. In situ high-temperature powder X-ray diffraction (XRD) was used to observe the phase changes and the lattice parameters were analyzed to ascertain the crystallographic transformations. The expansion coefficient of the compounds was determined, and it was found that the c-axis was the most expandable due to relatively weak chemical bonds along the c-crystallographic axis. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the decomposition properties of the materials. Due to rare earth ion doping, the produced materials had slightly variable decomposition behaviour. The cerium and samarium ions were present in multiple oxidation states (Ce3+, Ce4+, Sm3+, Sm2+), whereas only Ho3+ ions were observed. Rare earth ion substitution affects tri-calcium phosphate proportion during decomposition by regulating concentrations of vacancies. X-ray photoelectron spectroscopy (XPS) analysis indicated that cerium and samarium ion-doped apatite yielded only 25 % tricalcium phosphate during decomposition. This finding advances our understanding of apatite structures, with implications for various high-temperature processes like calcination, sintering, hydrothermal processing, and plasma spraying.

Unusually high thermal conductivity in suspended monolayer MoSi2N4

Two-dimensional semiconductors with high thermal conductivity and charge carrier mobility are of great importance for next-generation electronic and optoelectronic devices. However, constrained by the long-held Slack’s criteria, the reported two-dimensional semiconductors such as monolayers of MoS2, WS2, MoSe2, WSe2 and black phosphorus suffer from much lower thermal conductivity than silicon (~142 W·m–1·K–1) because of the complex crystal structure, large average atomic mass and relatively weak chemical bonds. Despite the more complex crystal structure, the recently emerging monolayer MoSi2N4 semiconductor has been predicted to have high thermal conductivity and charge carrier mobility simultaneously. In this work, using a noncontact optothermal Raman technique, we experimentally measure a high thermal conductivity of ~173 W·m–1·K–1 at room temperature for suspended monolayer MoSi2N4 grown by chemical vapor deposition. First-principles calculations reveal that such unusually high thermal conductivity benefits from the high Debye temperature and small Grüneisen parameter of MoSi2N4, both of which are strongly dependent on the high Young’s modulus induced by the outmost Si-N bilayers. Our study not only establishes monolayer MoSi2N4 as a benchmark 2D semiconductor for next-generation electronic and optoelectronic devices, but also provides an insight into the design of 2D materials for efficient heat conduction.

Halogenated Hole Selective Contact Enhances Interfacial Weak Bonding of Perovskite Solar Cells

AbstractWeak bonding between the perovskite and charge transport layers can lead to interfacial defects, hindering charge transfer and limiting the efficiency and stability of perovskite solar cells (PSCs). To address this issue, two halogenated spiro[fluorene‐9,9′‐xanthene]‐based molecules (SFX‐DM‐F and SFX‐DM‐Cl) are designed as an interfacial layer between perovskite and hole transport materials (HTMs). Both first‐principles simulations and experimental results are used to demonstrate that these halogenated interfacial layers improve the contact stability between perovskite's Pb(II) and HTMs, increasing the efficiency of charge transfer. The similar structure of interlayer to HTM also enhances the interfacial hole transfer integral, favoring effective hole transport. The PSCs based on SFX‐DM‐Cl achieve power conversion efficiencies of 24.8% (0.0625 cm2) and 23.1% (1 cm2). Even after 2000 h at a relative humidity of 15–20%, the unencapsulated PSC retains 94% of its initial efficiency. This work proposes the halogenated homologous HTMs as interfacial molecular bridges to optimize weak chemical bonds and hole transfer, thereby enabling efficient and stable PSCs.

The interplay of surface stability and oxygen vacancy dynamics in RE2Si2O7‐based environmental barrier coatings

AbstractSurface structure and relevant oxygen vacancy play an important role in the application of RE2Si2O7 for environmental barrier coatings, in which the oxygen vacancies in RE2Si2O7 may influence their thermal and optical properties. In this work, the structure and thermodynamics of (0 0 1) and (1 1 0) surfaces of RE2Si2O7 (RE = Yb, Lu) are studied via first‐principles calculations to reveal the underlying mechanism of the surface formation and the associated oxygen vacancy behavior. The (1 1 0) surface is preferred energetically, being in good agreement with the experiential results. It is uncovered that the weak chemical bond broken dominates the decrease of the surface energy, together with the contribution from the polyhedral distortion. Furthermore, the [O3Si–O–SiO3] site is found to be the preferred site for oxygen vacancies on (1 1 0) surface. The formation energies of oxygen vacancies on the (1 1 0) surfaces are lower than those in the bulk, suggesting their segregation on the surfaces. These findings provide essential insights into the surface excitation and oxygen vacancy behaviors of RE2Si2O7, which could shield light on the experimental improvement of the thermal, mechanical, and corrosion properties for RE2Si2O7‐based environmental barrier coating materials.

Deep eutectic solvent assisted swell and highly efficient catalytic pyrolysis of raw coal

The development of catalytic pyrolysis strategy is the key to the efficient utilization of raw coal. Herein, a novel microwave-assisted deep eutectic solvent (DES) swelling strategy was used to catalyze the pyrolysis of Naomaohu coal. The multifunctional FeCl3-Levulinic acid DES was synthesized, it could not only act as the solvent to swell coal, but to highly efficient catalyzed the pyrolysis of the swelled coal. During the process of microwave swelling, DES enhanced the induced polarization of unsaturated bonds, destroyed the weak intermolecular chemical bonds, increased the spacing of aromatic layers and reduced the particle size of raw coal, thus exhibiting a superior swelling effect. Notably, with the catalytic action of DES, it effectively promoted the conversion of coal as well as the escape of light components in the pyrolysis process. Based on the advantages of DES, the pyrolysis tar yield increased significantly (from 11.85% to 17.63%) and the yield of Benzene-Toluene-Xylene was as high as 11.31% in the tar and its content was 14.48 mg g−1. The light component (BP ≤ 360 °C, 67.50%) and light oil (BP ≤ 170 °C, 42.00%) of the tar reached high levels. What’s more, the pyrolysis behavior and kinetics results indicated that the pre-exponential factor was 2.61 × 1016 min−1 and the average apparent activation energy was 267.39 kJ mol−1. The proposed efficient method is expected to provide novel strategy for the swell and catalytic pyrolysis of raw coal using diverse multifunctional DES.

The influence of crystal chemistry on lithium isotopic fractionation in pegmatite minerals

The understanding of lithium (Li) isotopic fractionation controlled by mineral species, especially those containing trace or minor amounts of Li (e.g., a few to tens of ppm), is hindered by lack of knowledge about the crystal chemistry of Li-bearing minerals. In this study, we performed solid-state Nuclear Magnetic Resonance (NMR) experiments, employing the Li7 Magic Angle Spinning (MAS) to investigate the local coordination environments of Li in minerals and their impact on Li isotopic fractionation. Our investigation focused on four coexisting minerals sourced from the Koktokay No. 3 pegmatite dike in the Xinjiang, China, namely quartz, K-feldspar, muscovite, and tourmaline, which has Li content and δLi7 value of 14.6 ppm and 3.90‰, 19.3 ppm and 7.09‰, 430 ppm and − 14.2‰, and 108 ppm and 13.42‰, respectively. Muscovite displayed the lowest δLi7 value, whereas tourmaline exhibited the highest value, and a considerable variation of 27.62‰ in δLi7 value was observed between muscovite and tourmaline. The analysis of Li7 MAS-NMR spectra further revealed distinct Li coordination environments among these minerals. A notable counterintuitive negative correlation exists between the δLi7 value and the chemical shift for the four Li-bearing minerals. This negative correlation contrasts to the expected Li isotopic fractionation under equilibrium conditions, in which enrichment of heavy Li isotopes is accompanied with large chemical shifts in Li-bearing minerals. This unexpected observation can be potentially attributed to nonequilibrium conditions of crystallization of the investigated minerals, coupled with fast diffusion of Li6 in minerals, boasting abnormally high coordination numbers due to weak LiO chemical bonds. Essentially, our study suggests that Li isotopic fractionation among Li-bearing minerals in pegmatite can be significant and is intricately influenced by both crystal chemistry and chemical diffusion.

Deformation Characteristics of Combined Heavy Metals-Contaminated Soil Treated with nZVI through the Modified Slurry Consolidation Method

Nanoscale zero-valent iron (nZVI) has been widely applied to remediate heavy metal-contaminated soils and water. Its in situ treatment of combined heavy metal contaminated soil, followed by backfilling or other sustainable reutilizations, attracted attention to the treated soil’s deformation characteristics. In this study, soil samples were prepared using the modified slurry consolidation method to simulate the natural settling of backfilled soil and optimize the reactivity between nZVI and contaminants in soil. The deformation characteristics of natural soil, contaminated soil, and soil treated with varying dosages of nZVI (0.2%, 0.5%, 1%, 2%, and 5%) were investigated. Moreover, the plasticity indexes and particle-size distribution of the samples were examined through Atterberg limits and laser-diffraction particle-size analysis. After a 4 d slurry consolidation process, a typical result indicated the immobilization efficiency of all three heavy metal ions achieved over 90% with 2% nZVI. The presence of three heavy metal ions decreased the Atterberg limits and increased the compression index, permeability, and consolidation coefficient of the soil. Conversely, the introduction of nZVI increased plasticity and resulted in higher permeability, stable secondary consolidation, and less swell. Microscopically, with an increase in the dosage of nZVI, the soil aggregates transformed from a weak chemical bond with insoluble precipitates/iron oxides to larger aggregates consisting of nZVI/-soil aggregates, thereby enhancing the soil skeleton. This study shows improved permeability and deformation characteristics in nZVI-treated combined heavy metal-contaminated soil, offering valuable insights for practical nanomaterials’ in-situ treatment in engineering applications.

Bonding mechanism of laser joining of Poly-Ether-Ether-Ketone film which used for 5G antenna substrate to copper foil

The bonding of copper foil to Poly Ether Ether Ketone (PEEK) film has become a hotspot in research of the 5G RF (Radio Frequency) antenna substrate. In order to make the flexible copper clad laminates(FCCL) in the RF substrate thinner and more resistant to bending, there is an urgent need to replace the use of adhesive to join the copper foil to the PEEK film with a direct joining method. In this paper, a nanosecond laser was used to join the copper foil to the PEEK film effectively and the comprehensive property of joint was enhanced by the laser-textured grid on the surface of copper foil. The influence of textured grid on the adhesion work between copper foil and PEEK film was investigated. The interfacial morphology was observed and the result showed that molten PEEK completely filled the textured grid and formed a mechanical interlocking with copper. The complex reaction between Cu and PEEK was indicated by detecting the red-shift for the wave number of functional groups and the weak chemical bond between Cu and PEEK. Besides, the bonding mechanism was proved by density functional theory (DFT) calculation. The tensile shear strength of Cu/PEEK joint was significantly enhanced by laser texturing treatment, and the maximum force of joint with 0.4 mm-textured grid was increased by approximately 1.29 times compared to the untreated condition. This study proposes the use of nanosecond laser joining to replace the traditional use of adhesives to join copper foils to PEEK films.

Exploring the ultra-low lattice thermal conductivity of a two-dimensional compound Tl2Se3

Two-dimensional (2D) materials have attracted extensive attention in the field of thermoelectric (TE) materials, where heat transport properties play an important role in determining the performance of TE devices. In this paper, we investigate the thermal transport properties of novel 2D Tl2Se3 by means of first-principles approach combined with the Boltzmann transport equation (BTE). The small phonon sound group speed and strong anharmonicity are responsible for an ultra-low kl of 0.28 W/mK of 2D Tl2Se3 at room temperature. Meanwhile, the lattice thermal conductivity gradually decreases with the increase of temperature, indicating its potential value at high-temperature. The anti-bonding orbital filling between the Se-4p and Tl-6p states leads to the weak chemical bonds using the crystal orbital Hamiltonian population (COHP) analysis, which results in low phonon group velocities. Also, due to the strong acoustic-optical coupling in 2D Tl2Se3, the scattering processes of different acoustic modes is further studied to analyze how kl is suppressed. These findings demonstrate that 2D Tl2Se3 has potential applications in TE devices, which will motivate Tl2Se3 based experimental investigations.

Two-step phase manipulation by tailoring chemical bonds results in high-performance GeSe thermoelectrics

In thermoelectrics, phase engineering serves a crucial function in determining the power factor by affecting the band degeneracy. However, for low-symmetry compounds, the mainstream one-step phase manipulation strategy, depending solely on the valley or orbital degeneracy, is inadequate to attain a high density-of-states effective mass and exceptional zT. Here, we employ a distinctive two-step phase manipulation strategy through stepwise tailoring chemical bonds in GeSe. Initially, we amplify the valley degeneracy via CdTe alloying, which elevates the crystal symmetry from a covalently bonded orthorhombic to a metavalently bonded rhombohedral phase by significantly suppressing the Peierls distortion. Subsequently, we incorporate Pb to trigger the convergence of multivalence bands and further enhance the density-of-states effective mass by moderately restraining the Peierls distortion. Additionally, the atypical metavalent bonding in rhombohedral GeSe enables a high Ge vacancy concentration and a small band effective mass, leading to increased carrier concentration and mobility. This weak chemical bond along with strong lattice anharmonicity also reduces lattice thermal conductivity. Consequently, this unique property ensemble contributes to an outstanding zT of 0.9 at 773 K for Ge0.80Pb0.20Se(CdTe)0.25. This work underscores the pivotal role of the two-step phase manipulation by stepwise tailoring of chemical bonds in improving the thermoelectric performance of p-bonded chalcogenides.

Ultralow lattice thermal conductivity in bulk and monolayer TlCuSe: a comparative study from first-principles

Layered TlCuSe was experimentally found to possess ultralow lattice thermal conductivity due to the weak chemical bond and the strong anharmonicity, however, there is an imaginary frequency in the calculated phonon spectrum based on density functional theory (DFT) (Lin et al 2021 Adv. Mater. 33 2104908). Herein, using DFT + U (Coulomb interaction) and phonon Boltzmann transport theory, we demonstrate that the Coulomb interaction can effectively eliminate the imaginary frequency of the phonon spectrum for both bulk and monolayer TlCuSe. The lattice thermal conductivity can be further decreased from bulk (0.43 W m−1K−1 in-plane at 300 K) to monolayer (0.35 W m−1K−1 at 300 K), which comes from the competition between the increased phonon group velocity and the decreased phonon relaxation time. The larger Grüneisen parameters and phase space volume of the monolayer compared to the bulk indicate an enhanced anharmonicity, leading to a low phonon relaxation time and dominating the decreasing lattice thermal conductivity. The present work highlights the indispensability of Coulomb interaction when exploring the phonon transport. The ultralow lattice thermal conductivity of TlCuSe, especially in the form of monolayers, suggests promising thermoelectric applications.

Two-channel thermal transport and scattering channel of high-temperature phase SnSe using temperature-dependent effective potential

To resolve the imaginary phonon frequency of high-temperature phase SnSe (853 K) caused by ground-state theory, the temperature-dependent effective potential (TDEP) method is used to evaluate the temperature-dependent interatomic force constants (IFCs). Based on the Boltzmann transport equation, both two-channel transport and scattering channel are studied using the temperature-dependent IFCs. Considering three-phonon and four-phonon scattering, the particle-like thermal conductivity along the xx axis, yy axis, and zz axis is 0.66, 0.34, and 0.61 W/mK, respectively. For glass-like thermal conductivity, the value along the xx axis, yy axis, zz axis are 0.0777, 0.0316, and 0.0791 W/mK, respectively. For the three-phonon scattering channel, the scattering channels of X + O/A→O and X→O+O/A play a major role. For four-phonon scattering channel, the major scattering channels are X + O+A→O, X + A+A→O, X + O-O/A→A, X + A-O→A, X-O/A-O/A→O, X-O-A→A. By utilizing the crystal orbital Hamilton population (COHP) analysis, the low lattice thermal conductivity is attributed to the weak chemical bonds from anti-bonding orbitals between Se4p and Sn5s states. This work provides new insight into the physical mechanisms for thermal transport of high-temperature phase SnSe with strong anharmonic effects.

In-doping induced resonant level and thermoelectric performance enhancement in n-type GeBi2Te4 single crystals with intrinsically low lattice thermal conductivity

Resonant level, the impurity level located inside the valence/conduction band, is an effective strategy for decoupling the electrical conductivity and Seebeck coefficient and enhancing the thermoelectric power factor. In this work, we show that In doping induces resonant level and enhances the thermoelectric performance of GeBi2Te4, a promising n-type thermoelectric material with layered structure. Single crystals grown by Bridgman method were used in this study to take the advantage of its anisotropic transport properties. An ultralow lattice thermal conductivity of ∼0.51 W m−1 K−1 at 323 K was found along the c-axis of GeBi2Te4, driven by intrinsic cation disorder and the low phonon group velocity from the relatively weak chemical bonds as well as the strong lattice anharmonicity caused by hierarchical bond orders. Both enhanced electrical conductivity and Seebeck coefficient were observed in the In-doped samples, indicating that In-doping not only increases the carrier concentration, but also introduces the resonant level that was further confirmed by the first-principles calculation. A maximum zT of ∼0.42 at 523 K and an average zT of 0.36 over 323 to 573 K were achieved in Ge0.97In0.03Bi2Te4 crystal sample, ∼100% and ∼89% enhancement compared to those of pristine single crystal sample, respectively. This study demonstrates another example of resonant level for thermoelectric performance enhancement, which may be applied to other related materials.

Colossal enhancement of electrical and mechanical properties of graphene nanoscrolls

One of the most important characteristics of two-dimensional (2D) electrolytes [1] is their ability to reversibly transform into one-dimensional (1D) structures, such as nanoscrolls. However, when formed, these 1D structures are soft and unstable (because of the weak internal chemical bonds) and poorly electrically conducting (since chemical functionalization introduces a large degree of disorder in the 2D material basal plane). Using PeakForce™ quantitative nano-mechanics (PF-QNM™) mode in atomic force microscopy (AFM) and electrical transport measurements, we demonstrate that a one-step, catalyst-free, graphitization of 1D graphene nanoscrolls leads to an enhanced structural stability (an increase of 6 times in the Young's modulus) and a dramatic reduction of structural disorder (observed by a resulting 5 orders of magnitude reduction of the electrical resistance) These large changes in physical properties open up the doors for the use of 1D graphene nanoscrolls in the study of exotic materials in 1D as well as a plethora of possible industrial applications, such as hydrogen and energy storage, akin to carbon nanotubes but with a much bigger flexibility in terms of morphologies and functionalities.

Impact of Variant Gate Insulator Fabrication Process on Reliability of Dual-Gate InGaZnO Thin-Film Transistors

The effect of hydrogen diffusion in the bilayer bottom gate insulator (BGI) in dual-gate InGaZnO (IGZO) thin-film transistors (TFT) is investigated. It is discovered that hydrogen diffuses from the first deposited GI, migrates toward the second one, and forms a weak chemical bond with a dangling bond at the interface between the GI and the active layer. The stress condition with a positive gate bias at various temperatures makes the weakly bonded hydrogen break, thereby forming defects that can induce electron trapping in the interface and bulk, causing the threshold voltage to increase. With the rising temperature of positive bias temperature stress (PBTS), more broken bonds appear at the interface, which results in more trapped electrons. Through a charge trapping model and data fitting, the parameter that indicates the quality of the film can be extracted and compared. The trend of degradation between threshold voltage, bond breaking, and defect generation is examined.