Journal articles: 'Electron doping induced metal-insulator transition'

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FARKAŠOVSKÝ, PAVOL, and HANA ČENČARIKOVÁ. "VALENCE AND METAL-INSULATOR TRANSITIONS IN THE SPINLESS FALICOV–KIMBALL MODEL INDUCED BY DOPING." International Journal of Modern Physics B 19, no. 23 (September 20, 2005): 3603–12. http://dx.doi.org/10.1142/s0217979205032395.

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The influence of doping on valence and metal-insulator transitions in the spinless Falicov–Kimball model is studied by the well-controlled numerical method. Two types of doping are examined, and namely, the substitution of rare-earth ions by non-magnetic ions that introduce (i) one or (ii) no additional electron (per non-magnetic ion) into the conduction band. It is found that the first type of substitution increases the average f-state occupancy of rare-earth ions, whereas the second type of substitution has the opposite effect. In both cases valence changes are accompanied by a doping induced insulator-metal transition. The results obtained are used to describe valence and metal-insulator transitions in the samarium hexaboride solid solutions.

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Bustarret, E., P. Achatz, B. Sacépé, C. Chapelier, C. Marcenat, L. Ortéga, and T. Klein. "Metal-to-insulator transition and superconductivity in boron-doped diamond." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366, no. 1863 (November 19, 2007): 267–79. http://dx.doi.org/10.1098/rsta.2007.2151.

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The experimental discovery of superconductivity in boron-doped diamond came as a major surprise to both the diamond and the superconducting materials communities. The main experimental results obtained since then on single-crystal diamond epilayers are reviewed and applied to calculations, and some open questions are identified. The critical doping of the metal-to-insulator transition (MIT) was found to coincide with that necessary for superconductivity to occur. Some of the critical exponents of the MIT were determined and superconducting diamond was found to follow a conventional type II behaviour in the dirty limit, with relatively high critical temperature values quite close to the doping-induced insulator-to-metal transition. This could indicate that on the metallic side both the electron–phonon coupling and the screening parameter depend on the boron concentration. In our view, doped diamond is a potential model system for the study of electronic phase transitions and a stimulating example for other semiconductors such as germanium and silicon.

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Piatti, Erik, Jessica Montagna Bozzone, and Dario Daghero. "Anomalous Metallic Phase in Molybdenum Disulphide Induced via Gate-Driven Organic Ion Intercalation." Nanomaterials 12, no. 11 (May 27, 2022): 1842. http://dx.doi.org/10.3390/nano12111842.

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Transition metal dichalcogenides exhibit rich phase diagrams dominated by the interplay of superconductivity and charge density waves, which often result in anomalies in the electric transport properties. Here, we employ the ionic gating technique to realize a tunable, non-volatile organic ion intercalation in bulk single crystals of molybdenum disulphide (MoS2). We demonstrate that this gate-driven organic ion intercalation induces a strong electron doping in the system without changing the pristine 2H crystal symmetry and triggers the emergence of a re-entrant insulator-to-metal transition. We show that the gate-induced metallic state exhibits clear anomalies in the temperature dependence of the resistivity with a natural explanation as signatures of the development of a charge-density wave phase which was previously observed in alkali-intercalated MoS2. The relatively large temperature at which the anomalies are observed (∼150 K), combined with the absence of any sign of doping-induced superconductivity down to ∼3 K, suggests that the two phases might be competing with each other to determine the electronic ground state of electron-doped MoS2.

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Huang, X. Z., A. Saxena, and A. R. Bishop. "Doping induced insulator-metal transition in the platinum based MX complexes." Synthetic Metals 56, no. 2-3 (April 1993): 3438–42. http://dx.doi.org/10.1016/0379-6779(93)90141-i.

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Raveau, B., A. Maignan, and C. Martin. "Insulator–Metal Transition Induced by Cr and Co Doping in Pr0.5Ca0.5MnO3." Journal of Solid State Chemistry 130, no. 1 (April 1997): 162–66. http://dx.doi.org/10.1006/jssc.1997.7373.

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Wen, Zhiyuan, Jiaheng Li, Ziqiang Wang, Yong Xu, and Jing Zhu. "Soft-mode-phonon-mediated insulator–superconductor transition in doped two-dimensional topological insulator RuC." Applied Physics Letters 121, no. 1 (July 4, 2022): 013102. http://dx.doi.org/10.1063/5.0095044.

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Recently, the search of superconducting materials with topological states has attracted extensive interest due to their exotic properties. By using first-principles calculations, we predict that RuC monolayer is a two-dimensional topological insulator (TI) and shows a TI–superconductor transition under electron doping, leading to a superconducting transition temperature Tc of 1.4 K. Further analysis reveals that the emergence of superconductivity in RuC depends critically on the existence of flatband optical phonons as well as the appearance of multiple electron-pockets and phonon mode softening induced by doping. Moreover, we find that Li-intercalated RuC (LiRuC) is a thermal dynamically stable, superconducting material with a high Tc of 9.8 K, benefitting from the strong electron–phonon coupling. Many other superconductors with flat phonon bands are also predicted via elemental substitution in LiRuC. Our results will broaden the research interest in exploring more superconductors and modulating their physical properties through flat phonon bands.

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OVCHINNIKOV, S. G. "THE NATURE OF THE IN-GAP STATES IN WEAKLY DOPED La2−x Srx CuO4." Modern Physics Letters B 06, no. 30 (December 30, 1992): 1927–33. http://dx.doi.org/10.1142/s0217984992001630.

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A single-particle density of states is calculated in the strong electron correlation limit of the generalized multiband Hubbard model by exact diagonalization for CuO4 cluster. Several in-gap states are induced by hole doping that are mixtures of Cu d(x2−y2) and b1 O states and Cu d(z2), O a1 states and nonbonding O states. The Fermi level depends on the hole concentration nonmonotonically. The critical concentration of the insulator-metal transition of the Anderson type is estimated.

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Wang, Helin, William M. Postiglione, Vipul Chaturvedi, Evan L. Runnerstrom, Angela Cleri, Josh Nordlander, Jon-Paul Maria, and Chris Leighton. "Electrolyte-gate-driven carrier density modulation and metal–insulator transition in semiconducting epitaxial CdO films." APL Materials 10, no. 12 (December 1, 2022): 121106. http://dx.doi.org/10.1063/5.0116294.

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CdO has drawn much recent interest as a high-room-temperature-mobility oxide semiconductor with exciting potential for mid-infrared photonics and plasmonics. Wide-range modulation of carrier density in CdO is of interest both for fundamental reasons (to explore transport mechanisms in single samples) and for applications (in tunable photonic devices). Here, we thus apply ion-gel-based electrolyte gating to ultrathin epitaxial CdO(001) films, using transport, x-ray diffraction, and atomic force microscopy to deduce a reversible electrostatic gate response from −4 to +2 V, followed by rapid film degradation at higher gate voltage. Further advancing the mechanistic understanding of electrolyte gating, these observations are explained in terms of low oxygen vacancy diffusivity and high acid etchability in CdO. Most importantly, the 6-V-wide reversible electrostatic gating window is shown to enable ten-fold modulation of the Hall electron density, a striking voltage-induced metal–insulator transition, and 15-fold variation of the electron mobility. Such modulations, which are limited only by unintentional doping levels in ultrathin films, are of exceptional interest for voltage-tunable devices.

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Anggarini, Ufafa, Liang Yu, Hiroki Nagasawa, Masakoto Kanezashi, and Toshinori Tsuru. "Metal-induced microporous aminosilica creates a highly permeable gas-separation membrane." Materials Chemistry Frontiers 5, no. 7 (2021): 3029–42. http://dx.doi.org/10.1039/d1qm00009h.

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Hybrid microporous aminosilica membranes have been successfully synthesized via doping with Ag-, Cu- and Ni-into dense bis[3-(trimethoxysilyl)propyl] amine (BTPA) membranes, which creates micropores via the crosslinking between donor pairs of electrons in the amine moiety and electron acceptors in the empty “d” orbital of a transition metal.

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Li, Bowen, Liyan Xie, Zhaowu Wang, Shi Chen, Hui Ren, Yuliang Chen, Chengming Wang, Guobin Zhang, Jun Jiang, and Chongwen Zou. "Electron–Proton Co‐doping‐Induced Metal–Insulator Transition in VO 2 Film via Surface Self‐Assembled l ‐Ascorbic Acid Molecules." Angewandte Chemie International Edition 58, no. 39 (September 23, 2019): 13711–16. http://dx.doi.org/10.1002/anie.201904148.

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Li, Bowen, Liyan Xie, Zhaowu Wang, Shi Chen, Hui Ren, Yuliang Chen, Chengming Wang, Guobin Zhang, Jun Jiang, and Chongwen Zou. "Electron–Proton Co‐doping‐Induced Metal–Insulator Transition in VO 2 Film via Surface Self‐Assembled l ‐Ascorbic Acid Molecules." Angewandte Chemie 131, no. 39 (August 23, 2019): 13849–54. http://dx.doi.org/10.1002/ange.201904148.

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Hanzawa, Kota, Hikaru Sato, Hidenori Hiramatsu, Toshio Kamiya, and Hideo Hosono. "Electric field-induced superconducting transition of insulating FeSe thin film at 35 K." Proceedings of the National Academy of Sciences 113, no. 15 (March 28, 2016): 3986–90. http://dx.doi.org/10.1073/pnas.1520810113.

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It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 1015 cm–2 (the average volume density of 1.7 × 1021 cm–3), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials.

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Kawasugi, Yoshitaka, and Hiroshi M. Yamamoto. "Simultaneous Control of Bandfilling and Bandwidth in Electric Double-Layer Transistor Based on Organic Mott Insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl." Crystals 12, no. 1 (December 28, 2021): 42. http://dx.doi.org/10.3390/cryst12010042.

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The physics of quantum many-body systems have been studied using bulk correlated materials, and recently, moiré superlattices formed by atomic bilayers have appeared as a novel platform in which the carrier concentration and the band structures are highly tunable. In this brief review, we introduce an intermediate platform between those systems, namely, a band-filling- and bandwidth-tunable electric double-layer transistor based on a real organic Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl. In the proximity of the bandwidth-control Mott transition at half filling, both electron and hole doping induced superconductivity (with almost identical transition temperatures) in the same sample. The normal state under electric double-layer doping exhibited non-Fermi liquid behaviors as in many correlated materials. The doping levels for the superconductivity and the non-Fermi liquid behaviors were highly doping-asymmetric. Model calculations based on the anisotropic triangular lattice explained many phenomena and the doping asymmetry, implying the importance of the noninteracting band structure (particularly the flat part of the band).

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Guerfi, T. "Out-of-plane ionicity versus in-plane covalency interplay in high-T c cuprates." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 73, no. 6 (November 28, 2017): 1164–71. http://dx.doi.org/10.1107/s205252061701575x.

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It may be argued that the remarkable properties of the high-temperature superconducting cuprates such as the insulator–metal transition (IMT) and the metal–superconductor transition (MST) originate from competition and interplay between the interlayer ionic interaction and the intralayer covalent bonds in these materials. It is proposed here that the microscopic order parameter is the local field estimated from the ionic polarization at the sub-unit cell level, and it is demonstrated that it shows a strong temperature as well as chemical doping dependence. The out-of-plane ionicity induces an interlayer electron transfer that reduces the ionicity of the layers and leads to IMT, while the in-plane covalency induces in-plane intersite hole transfer that increases the out-of-plane ionicity. It is suggested that this competition leads to a local field catastrophe at a critical temperature T c that drives the compound to MST. The asymmetry of the free charge carrier density breaks locally the mirror reflection symmetry of the order parameter, leading to a pairing between the real current and the polarization current.

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Rata, A. D., J. Herrero-Martin, I. V. Maznichenko, F. M. Chiabrera, R. T. Dahm, S. Ostanin, D. Lee, et al. "Defect-induced magnetism in homoepitaxial SrTiO₃." APL Materials 10, no. 9 (September 1, 2022): 091108. http://dx.doi.org/10.1063/5.0101411.

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Along with recent advancements in thin-film technologies, the engineering of complex transition metal oxide heterostructures offers the possibility of creating novel and tunable multifunctionalities. A representative complex oxide is the perovskite strontium titanate (STO), whose bulk form is nominally a centrosymmetric paraelectric band insulator. By tuning the electron doping, chemical stoichiometry, strain, and charge defects of STO, it is possible to control the electrical, magnetic, and thermal properties of such structures. Here, we demonstrate tunable magnetism in atomically engineered STO thin films grown on STO (001) substrates by controlling the atomic charge defects of titanium (VTi) and oxygen (VO) vacancies. Our results show that the magnetism can be tuned by altering the growth conditions. We provide deep insights into its association to the following defect types: (i) VTi, resulting in a charge rearrangement and local spin polarization, (ii) VO, leading to weak magnetization, and (iii) VTi–VO pairs, which lead to the appearance of a sizable magnetic signal. Our results suggest that controlling charged defects is critical for inducing a net magnetization in STO films. This work provides a crucial step for designing magnetic STO films via defect engineering for magnetic and spin-based electronic applications.

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Liu, Yiyuan, Yu-Fei Liu, Xin Gui, Cheng Xiang, Hui-Bin Zhou, Chuang-Han Hsu, Hsin Lin, Tay-Rong Chang, Weiwei Xie, and Shuang Jia. "Bond-breaking induced Lifshitz transition in robust Dirac semimetal VAI3." Proceedings of the National Academy of Sciences 117, no. 27 (June 18, 2020): 15517–23. http://dx.doi.org/10.1073/pnas.1917697117.

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Topological electrons in semimetals are usually vulnerable to chemical doping and environment change, which restricts their potential application in future electronic devices. In this paper, we report that the type-II Dirac semimetalVAl3hosts exceptional, robust topological electrons which can tolerate extreme change of chemical composition. The Dirac electrons remain intact, even after a substantial part of V atoms have been replaced in theV1−xTixAl3solid solutions. This Dirac semimetal state ends atx=0.35, where a Lifshitz transition to p-type trivial metal occurs. The V–Al bond is completely broken in this transition as long as the bonding orbitals are fully depopulated by the holes donated from Ti substitution. In other words, the Dirac electrons inVAl3are protected by the V–Al bond, whose molecular orbital is their bonding gravity center. Our understanding on the interrelations among electron count, chemical bond, and electronic properties in topological semimetals suggests a rational approach to search robust, chemical-bond-protected topological materials.

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Sun, Ruihao, Shiyu Sun, Xiu Liang, Hongyu Gong, Xingshuang Zhang, Yong Li, Meng Gao, Dongwei Li, and Guanchen Xu. "Surface Charge Transfer Doping of MoS2 Monolayer by Molecules with Aggregation-Induced Emission Effect." Nanomaterials 12, no. 1 (January 4, 2022): 164. http://dx.doi.org/10.3390/nano12010164.

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Surface charge transfer doping has attracted much attention in modulating the optical and electrical behavior of 2D transition metal dichalcogenides (TMDCs), where finding controllable and efficient dopants is crucial. Here, 1,1,2,2-tetraphenylethylene (TPE) derivative molecules with aggregation-induced emission (AIE) effect were selected as adjustable dopants. By designing nitro and methoxyl functional groups and surface coating, controlled p/n-type doping can be achieved on a chemical vapor deposition (CVD) grown monolayer, MoS2. We investigated the electron transfer behavior between these two dopants and MoS2 with fluorescence, Raman, X-ray photoelectron spectra and transient absorption spectra. 1,1,2,2-Tetrakis(4-nitrophenyl)ethane (TPE-4NO2) with a negative charge aggregation can be a donor to transfer electrons to MoS2, while 1,1,2,2-Tetrakis(4-methoxyphenyl)ethane (TPE-4OCH3) is the opposite and electron-accepting. Density functional theory calculations further explain and confirm these experimental results. This work shows a new way to select suitable dopants for TMDCs, which is beneficial for a wide range of applications in optoelectronic devices.

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Hitoshi, NITTA, SUZUKI Masato, and IIDA Takeshi. "MULTISTABLE NATURES AND PHOTO-INDUCED CHARGE-SEPARATION IN HOLE-DOPED STATES OF STRONGLY COUPLED ELECTRON-PHONON SYSTEMS." International Journal of Modern Physics B 15, no. 28n30 (December 10, 2001): 3904–7. http://dx.doi.org/10.1142/s0217979201008962.

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We investigate the effects of hole doping in the charge-density wave (CDW) state that has the strong electron-phonon (e-p) coupling, using the two-dimensional molecular crystal model. In calculations, we use the mean-filed theory for the interelectronic interactions and the adiabatic approximation for phonons. On the basis of this theory, we calculate e-p states of doped ground states for various values of the doping concentration of holes. From the calculated results, it is found that a multistable nature appears in the doped e-p states just before the CDW-metal phase transition. In order to see the effects of the photoexcitation in the hole-doped states, we also investigate the exciton states taking into account the electron-hole correlation. Results calculated here indicate that the separation of electron and hole occurs in the photoexcited states as a consequence of the energy relaxation of excitons.

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Yin, Zongyou, Moshe Tordjman, Youngtack Lee, Alon Vardi, Rafi Kalish, and Jesús A. del Alamo. "Enhanced transport in transistor by tuning transition-metal oxide electronic states interfaced with diamond." Science Advances 4, no. 9 (September 2018): eaau0480. http://dx.doi.org/10.1126/sciadv.aau0480.

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High electron affinity transition-metal oxides (TMOs) have gained a central role in two-dimensional (2D) electronics by enabling unprecedented surface charge doping efficiency in numerous exotic 2D solid-state semiconductors. Among them, diamond-based 2D electronics are entering a new era by using TMOs as surface acceptors instead of previous molecular-like unstable acceptors. Similarly, surface-doped diamond with TMOs has recently yielded record sheet hole concentrations (2 × 1014 cm−2) and launched the quest for its implementation in microelectronic devices. Regrettably, field-effect transistor operation based on this surface doping has been so far disappointing due to fundamental material obstacles such as (i) carrier scattering induced by nonhomogeneous morphology of TMO surface acceptor layer, (ii) stoichiometry changes caused by typical transistor fabrication process, and (iii) carrier transport loss due to electronic band energy misalignment. This work proposes and demonstrates a general strategy that synergistically surmounts these three barriers by developing an atomic layer deposition of a hydrogenated MoO3 layer as a novel efficient surface charge acceptor for transistors. It shows high surface uniformity, enhanced immunity to harsh fabrication conditions, and benefits from tunable electronic gap states for improving carrier transfer at interfaces. These breakthroughs permit crucial integration of TMO surface doping into transistor fabrication flows and allow outperforming electronic devices to be reached.

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Cao, Zhiqiang, Longqing Chen, Zhenxiang Cheng, and Wenbin Qiu. "Induced Superconducting Transition in Ultra-Thin Iron-Selenide Films by a Mg-Coating Process." Materials 14, no. 21 (October 25, 2021): 6383. http://dx.doi.org/10.3390/ma14216383.

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Binary Iron selenide (FeSe) thin films have been widely studied for years to unveil the high temperature superconductivity in iron-based superconductors. However, the origin of superconducting transition in this unconventional system is still under debate and worth deep investigations. In the present work, the transition from insulator to superconductor was achieved in non-superconducting FeSe ultrathin films (~8 nm) grown on calcium fluoride substrates via a simple in-situ Mg-coating by a pulsed laser deposition technique. The Mg-coated FeSe film with an optimized amount of Mg exhibited a superconducting critical temperature as 9.7 K and an upper critical field as 30.9 T. Through systematic characterizations on phase identification, carrier transport behavior and high-resolution microstructural features, the revival of superconductivity in FeSe ultrathin films is mostly attributed to the highly crystallized FeSe and extra electron doping received from external Mg-coating process. Although the top few FeSe layers are incorporated with Mg, most FeSe layers are intact and protected by a stable magnesium oxide layer. This work provides a new strategy to induce superconductivity in FeSe films with non-superconducting behavior, which might contribute to a more comprehensive understanding of iron-based superconductivity and the benefit to downstream applications such as magnetic resonance imaging, high-field magnets and electrical cables.

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Lv, Tianping, Jianhong Zhao, Mingpeng Chen, Kaiyuan Shen, Dongming Zhang, Jin Zhang, Genlin Zhang, and Qingju Liu. "Boosted Visible-Light Photodegradation of Methylene Blue by V and Co Co-Doped TiO2." Materials 11, no. 10 (October 11, 2018): 1946. http://dx.doi.org/10.3390/ma11101946.

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In this work, TiO2 photocatalysts, co-doped with transition metal ions vanadium (V) and cobalt (Co) ((V,Co)–TiO2), were synthesized by the sol–gel method. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption and desorption measurement, UV-Vis absorption and photoluminescence spectrum (PL) spectra. The results show that V and Co co-doping has significant effects on sample average crystalline grain size, absorption spectrum, recombination efficiency of photo-induced electron-hole pairs (EHPs), and photocatalytic degradation efficiency of methylene blue (MB). (V,Co)–TiO2 photocatalyst exhibits an obvious red shift of the absorption edge to 475 nm. Photocatalytic degradation rate of (V,Co)–TiO2 sample for MB in 60 min is 92.12% under a Xe lamp with a cut-off filter (λ > 400 nm), which is significantly higher than 56.55% of P25 under the same conditions. The first principles calculation results show that V and Co ions doping introduces several impurity energy levels, which can modulate the location of the valence band and conduction band. An obvious lattice distortion is produced in the meantime, resulting in the decrease in photo-generated EHP recombination. Thus, (V,Co)–TiO2 photocatalyst performance is significantly improved.

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Ping, Yuan. "(Invited) Effect of Polaron Formation on Optical and Carrier Transport Properties of Transition Metal Oxides As Photoelectrodes from First-Principles Calculations." ECS Meeting Abstracts MA2022-02, no. 48 (October 9, 2022): 1843. http://dx.doi.org/10.1149/ma2022-02481843mtgabs.

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Transition metal oxides are promising photoelectrode materials for solar-to-fuel conversion applications. However, their performance is limited by the low carrier mobility (especially electron mobility) due to the formation of small polarons. Recent experimental studies have shown improved carrier mobility and conductivity by atomic doping; however the underlying mechanism is not understood. A fundamental atomistic-level understanding of the effects on small polaron transport is critical to future material design with high conductivity. In this talk, we will discuss the effect of small polaron formation on optical and carrier transport properties of transition metal oxides from first-principles calculations. First, we resolve the conflicting findings that have been reported on the optical gap of a well-known catalysis Co3O4 as an example[1]. We confirm that the formation of small hole polarons significantly influences the optical absorption spectra and introduces extra spectroscopic signature below the intrinsic band gap, leading to a 0.8 eV transition that is often misinterpreted as the band edge that defines the fundamental gap. Then we discuss the formation of small polarons' effect on carrier concentration, by resolving the controversy of nature of "shallow" or "deep" impurities of intrinsic oxygen vacancies in BiVO4 as an example[2], i.e. how to unify different experiments with the correct definition of ionization energy in polaronic oxides. We further discuss why certain dopants can have very low optimal concentrations (or very early doping bottleneck) in polaronic oxides such as Fe2O3, through a novel "electric-multipole" clustering between dopants and polarons[3]. These multipoles can be very stable at room temperature and are difficult to fully ionize compared to separate dopants, and thus they are detrimental to carrier concentration improvement. This allows us to uncover mysteries of the doping bottleneck in hematite and provide guidance for optimizing doping and carrier conductivity in polaronic oxides toward highly efficient energy conversion applications. In addition, we show the importance of synthesis condition such as synthesis temperature and oxygen partial pressure on dopant and polaron concentrations, and how to optimize the synthesis condition based on theoretical predictions[4]. At the end, we show different theoretical models for polaron mobility calculations from a macroscopic dielectric continuum picture with an example of spin polarons in CuO[5] and a microscopic polaron hopping picture by combining generalized Landau-Zener theory and kinetic Monte-Carlo samplings for doped oxides[6]. Our first-principles calculations provide important insights and suggest design principles for optimal optical and transport properties of polaronic oxides. References: [1] “Optical Absorption Induced by Small Polaron Formation in Transition Metal Oxides – The Case of Co3O4”, T. Smart, T. Pham, Y. Ping*, and T. Ogitsu*, Physical Review Materials (Rapid Communications), 3, 102401(R), (2019). [2] “The Role of Point Defects in Enhancing the Conductivity of BiVO4”, H. Seo, Y. Ping and G. Galli*, Chemistry of Materials, 30, 7793, (2018). [3] “Doping Bottleneck in Hematite: Multipole Clustering by Small Polarons”, T. Smart, V. Baltazar, M. Chen, B. Yao, K. Mayford, F. Bridges, Y. Li, and Y. Ping*, Chemistry of Materials, 33, 4390, (2021). [4] “The Critical Role of Synthesis Conditions on Small Polaron Carrier Concentrations in Hematite- A First-Principles Study”, Tyler Smart, Mingpeng Chen, Valentin Urena Baltazar, Frank Bridges, Yat Li, Yuan Ping*, under review, (2021). [5]“Mechanistic Insights of Enhanced Spin Polaron Conduction in CuO through Atomic Doping”, T. Smart, A. Cardiel, F. Wu, K. Choi and Y. Ping*, npj Computational Materials, 4, 61, (2018). [6] “Combining Landau-Zener Theory and Kinetic Monte Carlo Sampling for Small Polaron Mobility of Doped BiVO4 from First-principles”, F. Wu and Y. Ping*, Journal of Materials Chemistry A, 6, 20025, (2018).

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Fu, Yu, Sichen Wei, Yingjie Chen, Huamin Li, Yuguang Chris Li, and Fei Yao. "Novel Hollow Spherical Carbon Nitride Synthesis and Its Application in Zinc-Air Batteries." ECS Meeting Abstracts MA2022-02, no. 8 (October 9, 2022): 654. http://dx.doi.org/10.1149/ma2022-028654mtgabs.

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The pressing need for carbon emission reduction calls for a rapid move toward electrified mobility and expanded deployment of solar and wind on the electric grid. As a result, high-performance electrical energy storage systems are highly demanded. Rechargeable lithium-ion batteries (LIBs) are the most widely used battery system in portable electronics and electric vehicles nowadays because of their high energy per unit mass, power-to-weight ratio, and high-temperature performance. However, concerns about their high cost (250 US$ kW h−1), inherent safety hazards, and limited cathode capacity have motivated the investigation beyond Li-ion technology. In particular, Zn-air batteries (ZABs) have emerged as a much more sustainable option than LIBs with high energy densities of 1218 Wh kg-1 (gravimetric) and 6136 Wh L-1 (volumetric) benefiting from the earth-abundant, low-cost, and environmentally friendly nature of Zn metal and the ample oxygen supply in ambient air. One of the major challenges in ZABs research is the inefficient oxygen reaction kinetics at the air cathode. Among various proposed bifunctional oxygen catalysts, metal-free carbon-based catalysts have drawn tremendous attention due to their potential in reducing the costs and environmental impacts of noble and transition metal-based catalysts. In particular, nitrogen-doped carbonaceous materials have been recognized as one of the most promising catalysts because of their increased electrical conductivity via stimulating the delocalization of electrons and induced electron depletion on carbon atoms which optimize valence orbital energy for active sites. Nevertheless, conventional post-synthesis doping methods not only involve complicated experimental setups but also offer limited nitrogen doping (1 - 20%) levels along with poor control over C-N configurations. Accordingly, a facile synthesis method enabling high nitrogen doping content with the C-N configuration controllability is highly demanded for high-performance ZABs. In this report, we successfully synthesized high nitrogen-content hollow carbon spheres (H-CxNy) via a novel metal-assisted denitrification (MAD) process. Specifically, we employed Zn metal and low-cost graphitic carbon nitride (g-C3N4) as catalyst and precursor, respectively, to construct the H-CxNy microstructures. During the annealing process, the Zn metal reacts with nitrogen during pyrolysis of the g-C3N4 and converts it into heat-stable Zn3N2 intermediates, which not only avoids the direct volatilization of nitrogen content but also displaces carbon atoms and subsequently rearranges carbon and nitrogen atoms into H-CxNy spherical structures. The content and the configuration of the nitrogen species on the hollow spherical skeleton were successfully modulated by controlling the synthesis conditions. To investigate the structure-property-activity relationship, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Raman spectroscopy, and various electrochemical characterizations were conducted. The optimized H-CxNy sample demonstrated excellent bifunctional catalysis performance with a stable cyclic performance when employed as an air electrode in ZABs.

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Singh, N. L., Chaitali Gavade, and P. K. Khanna. "Swift Heavy Ion Induced Modification in Physical Properties of Poly Methylmethacrylate (PMMA)/Nickel (Ni) Nanocomposites." Defect and Diffusion Forum 341 (July 2013): 51–68. http://dx.doi.org/10.4028/www.scientific.net/ddf.341.51.

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We have These films were irradiated with 85 MeV C-ions at the fluences of 1 x 1011 and 1 x 1012 ions/cm2. Changes in the optical, structural, dielectric, magnetic and thermal properties of (PMMA)/Ni nanocomposites of different concentrations of nickel nanoparticles (5%, 10%, 15%) due to swift heavy ion irradiation were studied by means of UVvisible spectroscopy, X-ray diffraction, impedance gain phase analyzer, SQUID and differential scanning calorimetry. Optical properties like band gap were estimated for pure polymer and nanocomposite films from their optical absorption spectra in the wavelength range 200-800 nm. It was found that the band gap value shifted to lower energy on doping with metal nanoparticles. Differential scanning calorimetry analysis revealed a decrease in the glass transition temperature upon irradiation, which may be attributed to the scissioning of polymer chain due to ion beam irradiation which is also corroborated with XRD analysis. Surface morphology of the pristine and irradiated films was studied by scanning electron microscopy (SEM). The breakage of chemical bonds resulted in an increase of free radicals, unsaturation etc. as revealed from FTIR analysis. The dielectric properties were observed to enhance with an increase in metal compound concentration as well as with irradiation dose. This may be due to metal/polymer bonding and conversion of polymeric structure into hydrogen-depleted carbon network. Zero-Field-Cooled (ZFC)/Field-Cooled (FC) magnetization and magnetic hysteresis measurements were performed using a superconducting quantum interference device (SQUID) magnetometer from temperatures ranging from 5 K to 300 K, to investigate the magnetic properties of nanocomposites. The changes in topography of surfaces were also observed upon irradiation.

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Quemerais, P., J. L. Raimbault, and S. Fratini. "Polarization catastrophe in doped cuprates and metal-ammonia solutions. Metal-to-superconductor transition versus phase separation." Journal de Physique IV 12, no. 9 (November 2002): 227–30. http://dx.doi.org/10.1051/jp4:20020400.

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On doping polar dielectrics, such as cuprates (solid) or amonia (liquid), the polarization induces the formation of polarons or solvated electrons. However, the exact role of such entities in the metal-to-insulator transition (MIT) which occurs at some critical densities still remains unclear. We think that their formation together with their long-range Coulomb interactions are responsable for a polarization catastrophe leading to the MIT. Moreover, the accompanishing phenomena is the occurence of a negative sign of the static dielectric constant, which could yield either an insulator-to-superconductor transition in cuprates, either a phase separation in metal-ammonia solutions. The difference of hehavior possibly could come from the nature of the counter ions of the doping charges, which are essentially frozen in oxides, while they remain in a liquid state in metal-ammonia system.

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Gu, Yanni, Sheng Xu, and Xiaoshan Wu. "Gd-doping-induced insulator-metal transition in SrTiO3." Solid State Communications 250 (January 2017): 1–4. http://dx.doi.org/10.1016/j.ssc.2016.11.013.

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Dobrovits, Sabine, Bongjae Kim, Michele Reticcioli, Alessandro Toschi, Sergii Khmelevskyi, and Cesare Franchini. "Doping-induced insulator-metal transition in the Lifshitz magnetic insulator NaOsO3." Journal of Physics: Condensed Matter 31, no. 24 (April 3, 2019): 244002. http://dx.doi.org/10.1088/1361-648x/ab0dc4.

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Melo Jorge, M. E., M. R. Nunes, R. Silva Maria, and D. Sousa. "Metal−Insulator Transition Induced by Ce Doping in CaMnO3." Chemistry of Materials 17, no. 8 (April 2005): 2069–75. http://dx.doi.org/10.1021/cm040188b.

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Cheong, S.-W., H. Y. Hwang, B. Batlogg, A. S. Cooper, and P. C. Canfield. "Electron-hole doping of the metal-insulator transition compound RENiO3." Physica B: Condensed Matter 194-196 (February 1994): 1087–88. http://dx.doi.org/10.1016/0921-4526(94)90873-7.

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30

Deniszczyk, Józef, and Andrzej Ślebarski. "Band Structure Studies of the R5Rh6Sn18 (R = Sc, Y, Lu) Quasiskutteridite Superconductors." Materials 15, no. 7 (March 26, 2022): 2451. http://dx.doi.org/10.3390/ma15072451.

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We report on X-ray photoelectron spectroscopy and ab initio electronic structure investigations of the skutterudite-related R5Rh6Sn18 superconductors, where R = Sc, Y, and Lu. These compounds crystallise with a tetragonal structure (space group I41/acd) and are characterised by a deficiency of R atoms in their formula unit (R5−δRh6Sn18, δ≪1). Recently, we documented that the vacancies δ and atomic local defects (often induced by doping) are a reason for the enhancement in the superconducting transition temperature Tc of these materials, as well as metallic (δ=0) or semimetallic (δ≠0) behaviours in their normal state. Our band structure calculations show the pseudogap at a binding energy of −0.3 eV for the stoichiometric compounds, which can be easily moved towards the Fermi level by vacancies δ. As a result, dychotomic nature in electric transport of R5Rh6Sn18 (metallic or semimetallic resistivity) depends on δ, which has not been interpreted before. We have shown that the densities of states are very similar for various R5Rh6Sn18 compounds, and they practically do not depend on the metal R, while they are determined by the Rh d-and Sn s- and p-electron states. The band structure calculations for Sc5Rh6Sn18 have not been reported yet. We also found that the electronic specific heat coefficients γ0 for the stoichiometric samples were always larger with respect to the γ0 of the respective samples with vacancies at the R sites, which correlates with the results of ab initio calculations.

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31

Damay, F., A. Maignan, C. Martin, and B. Raveau. "Mn site doping induced insulator to metal transition in Pr0.6Ca0.4MnO3." Journal of Applied Physics 82, no. 3 (August 1997): 1485–87. http://dx.doi.org/10.1063/1.365929.

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Wang, J., N. N. Zu, Y. Wang, and Z. J. Wu. "Half metal to insulator transition driven by electron doping in Ba2FeReO6." Journal of Magnetism and Magnetic Materials 339 (August 2013): 163–67. http://dx.doi.org/10.1016/j.jmmm.2013.03.016.

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FAN, J. D., and Y. M. MALOZOVSKY. "PHONON INDUCED METAL-INSULATOR PHASE TRANSITION IN A METAL." International Journal of Modern Physics B 13, no. 29n31 (December 20, 1999): 3505–9. http://dx.doi.org/10.1142/s0217979299003301.

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It is attempted to clarify a historically existing misunderstanding that Cooper's pairing leads to superconductivity. It was found that the well-known Cooper instability in the presence of a quiescent Fermi sea for a given attractive interelectronic interaction mediated by any boson field, such as phonon, plasmon, paramagnon, etc. causes a metal-insulator other than superconducting transition. This is because the phase transition in this scenario leads to a vanishing density response and hence vanishing conductivity of the Fermi system when temperature approaches the transition temperature T c at which Cooper's instability occurs. In contrast, it is argued that the origin of a metal-superconductor transition is due to the repulsive Coulomb field. Nevertheless, the results from BCS theory regarding a gap in the electron spectrum for conventional superconductors remain valid only if the interaction in the BCS Hamiltonian is re-interpreted as an attractive interaction between an electron and a hole.

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Guo, Wei, and Rushan Han. "From Charge Transfer Type Insulator to Superconductor." International Journal of Modern Physics B 17, no. 18n20 (August 10, 2003): 3347–53. http://dx.doi.org/10.1142/s021797920302096x.

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We propose a microscopic model Hamiltonian to account for impurity doping induced insulator-superconductor transition and the coexistence of antiferromagnetism and superconductivity in the high-Tc cuprates. The crossover from non Fermi liquid to Fermi liquid regime characterized by delocalization of d electrons on Cu sites is discussed.

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Achatz, P., J. Pernot, C. Marcenat, J. Kacmarcik, G. Ferro, and E. Bustarret. "Doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide." Applied Physics Letters 92, no. 7 (February 18, 2008): 072103. http://dx.doi.org/10.1063/1.2885081.

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Ivanenko, Olga, and Kirill Mitsen. "Insulator-Conductor Transition in Doped HTS as a Consequence of -U-Centers Generation." International Journal of Modern Physics B 12, no. 29n31 (December 20, 1998): 3095–98. http://dx.doi.org/10.1142/s021797929800212x.

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It is supposed that the transition from insulator to metal state under doping in high-T c superconductors (HTS) passes through the stage of -U-centers formation, which arise on the neighbor Cu ions when the definite spatial arrangement of the doping atoms is realized. In this doping region the free hole carriers (just as in hole-, so in electron-doped HTS) are generated when electron pairs transfer from the oxygen band into -U-centers.

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37

Gilman, John J. "Insulator-metal transitions at microindentations." Journal of Materials Research 7, no. 3 (March 1992): 535–38. http://dx.doi.org/10.1557/jmr.1992.0535.

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For all tetrahedrally bonded semiconductors (five group IV plus nine III-V compounds and nine II-VI compounds), it is shown that the critical pressure needed to transform the semiconductor into the metallic state correlates with the microindentation hardness number. The same is done for five alkaline earth oxides. The critical transition pressures have been estimated from Herzfeld's theory—that is, from the compression at which the dielectric constant diverges to infinity. Experimental transition pressures also correlate with hardness numbers, and they correlate with the activation energies for dislocation motion. Since these transitions are electronic they can be influenced by photons, doping (donors enhance while acceptors inhibit them), currents, surface states, etc. Microindentation also provides a simple experimental tool for observing pressure and/or shear induced transformations.

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Yoo, Pilsun, and Peilin Liao. "Metal-to-insulator transition in SmNiO3 induced by chemical doping: a first principles study." Molecular Systems Design & Engineering 3, no. 1 (2018): 264–74. http://dx.doi.org/10.1039/c8me00002f.

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39

Kallio, A., and X. Xiong. "Electron-hole liquid model for high-Tcsuperconductors: Metal-insulator transition and doping behavior." Physical Review B 43, no. 7 (March 1, 1991): 5564–75. http://dx.doi.org/10.1103/physrevb.43.5564.

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40

Jung, Hyeonjung, Kyung-Jong Noh, Jihyeon Song, Hyeonae Im, Yoojin Lee, Han Sol Jung, Sangmin Park, and Jeong Woo Han. "Computational Screening of New Dopants for Nife-Based Layered Double Hydroxide Catalysts for Seawater Splitting." ECS Meeting Abstracts MA2022-02, no. 50 (October 9, 2022): 2516. http://dx.doi.org/10.1149/ma2022-02502516mtgabs.

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Water electrolysis is a key technology to convert and store sustainable energy into high-energy-dense hydrogen. However, slow kinetics of oxygen evolution reaction (OER) at the anode hinders overall reaction rate of water splitting and delays realization of hydrogen energy society. OER consists of four electron steps and an ideal catalyst has 1.23 V potential barrier for each step, but a real catalyst has a step which requires higher potential than 1.23 V, i.e., overpotential. Therefore, exploring OER catalyst with minimized OER overpotential is an important challenge in increasing water electrolysis efficiency. On the other side, the direct use of abundant seawater as a splitting reactant has advantage in terms of resources and cost. It can also help commercialization of water electrolysis. Since seawater contains chloride which causes undesirable side reactions and accelerated corrosion of the anode material, appropriate OER catalyst is necessary to avoid these problems. Conventional trial-and-error method in catalyst design usually requires many years of R&D and high cost. Computational screening can preemptively narrow down the candidate group of high-efficient catalyst to reduce time and economic cost. NiFe-based layered double hydroxide (NiFe-LDH) is a promising OER catalyst due to the comparable activity to commercial IrO2catalyst and can provide easily tunable metal composition during synthesis process. Its unique layered structure and reversible oxidation state change in redox condition also have arisen interest of many researchers. In this study, starting from the mechanism study of OER, chloride evolution reaction (ClER), and chloride-induced corrosion on this material, we performed DFT calculations to predict which transition metal dopants can enhance the OER activity of NiFe-LDH without accelerating selectivity and corrosion problems in seawater. NiFe-LDH is known to experience its transition to NiFeOOH phase under OER condition. [001] and [110] facets were set as edge and terrace sides of NiFeOOH, respectively, after their surface energies were investigated. Surface Pourbaix diagram showed that the [001] facet has clean termination without any adsorbate while [110] facet has dissociated-H2O covered termination under alkaline OER condition. OER energetic profile showed that the Fe site on the [110] surface is an OER active site with a theoretical overpotential of 280 mV, and seawater conditions do not significantly affect the OER activity itself. ClER mechanism study revealed that it occurs via *ClOH intermediates on [110] metal sites or *Cl intermediates on deprotonated [001] oxygen sites. Energy calculation of surface chlorination and metal dissolution steps showed that gradual chlorination accelerates metal dissolution and [110] facet is more vulnerable to chloride-induced corrosion than [001] facet. As the third metal candidate of NiFe-LDH, 3d to 5d transition metals excluding heavy metals were screened. Gibbs free energy correction terms such as vibrational entropy, zero-point energy and solvation parameter were calculated only for NiFeOOH case, and applied them to other candidates to simplify the screening process. NiFeOOH [001] surface could not be better than NiFeOOH [110] surface due to the inherent low activity of the [001] facet, but interestingly seven dopants could reduce the overpotential of NiFeOOH [110] surface by affecting the Fe active site or being active sites themselves. Since these dopants increased the oxidation ability of the active site, all of them also lowered chloride oxidation potential. However, fortunately, none of their ClER operating potential was lower than their OER operating condition, which means that there still exist potential windows where 100% OER selectivity can be achieved. In the last screening step, dissolution energies of fully chlorinated metal sites were calculated for the seven candidates, and two cases of them showed negative dissolution energy, which indicates very unstable doping state. As a result, five candidates passed through all three screening criteria: OER activity, OER vs. ClER selectivity, and durability against corrosion. Further, the experimental validation has performed on three promising candidates considering the raw material price, and it revealed that their activity is higher activity than NiFe-LDH. In addition, for the two abandoned cases in the third screening step (about metal dissolution), the experimental data showed that they were not seem to be actually doped into NiFe-LDH, indicating that the computational screening of seawater compatibility really worked. This study supports the utility of theoretical screening in electrochemical catalyst design and presents computational approach method to consider seawater compatibility.

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YU, GANG, and ALAN J. HEEGER. "PHOTOINDUCED CHARGE CARRIERS IN INSULATING CUPRATES: FERMI GLASS INSULATOR, METAL-INSULATOR TRANSITION AND SUPERCONDUCTIVITY." International Journal of Modern Physics B 07, no. 22 (October 10, 1993): 3751–815. http://dx.doi.org/10.1142/s0217979293003498.

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The results of photoexcitation experiments in partially doped, insulating cuprates are reviewed, and the physical implications of these “photodoping” experiments are discussed. The existence of a Fermi-glass insulating state at intermediate doping levels is thoroughly explored. The localized electronic states near the Fermi energy (EF) are characterized through transport, steady-state photoconductivity (including spectral response) and time resolved transient photodoping experiments (sub-nanosecond through microsecond). The experimental results indicate an Anderson-type metal-insulator transition in the doped cuprates; i.e., the transition from metal to insulator is dominated by disorder-induced localization. The Fermi energy can be shifted across the mobility edge either by increasing the doping level or by transient photoexcitation at high pump intensities, thereby causing the metal-insulator transition. The high-Tc superconductors, therefore, can be characterized as disordered metals with the Fermi energy relatively close to the mobility edge (Ec). Although the photo-generated carriers are generated homogeneously, the data indicate electronic phase separation into metallic “droplets”. The temperature dependence of the photoinduced conductivity implies that these droplets become superconducting below the intrinsic transition temperature observed in the heavily doped metallic regime.

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42

Kawasugi, Yoshitaka, Kazuhiro Seki, Satoshi Tajima, Jiang Pu, Taishi Takenobu, Seiji Yunoki, Hiroshi M. Yamamoto, and Reizo Kato. "Two-dimensional ground-state mapping of a Mott-Hubbard system in a flexible field-effect device." Science Advances 5, no. 5 (May 2019): eaav7282. http://dx.doi.org/10.1126/sciadv.aav7282.

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A Mott insulator sometimes induces unconventional superconductivity in its neighbors when doped and/or pressurized. Because the phase diagram should be strongly related to the microscopic mechanism of the superconductivity, it is important to obtain the global phase diagram surrounding the Mott insulating state. However, the parameter available for controlling the ground state of most Mott insulating materials is one-dimensional owing to technical limitations. Here, we present a two-dimensional ground-state mapping for a Mott insulator using an organic field-effect device by simultaneously tuning the bandwidth and bandfilling. The observed phase diagram showed many unexpected features such as an abrupt first-order superconducting transition under electron doping, a recurrent insulating phase in the heavily electron-doped region, and a nearly constant superconducting transition temperature in a wide parameter range. These results are expected to contribute toward elucidating one of the standard solutions for the Mott-Hubbard model.

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43

Yang, Bo, Hongcai Zhou, Xiaoming Zhang, and Mingwen Zhao. "Electron spin-polarization and band gap engineering in carbon-modified graphitic carbon nitrides." Journal of Materials Chemistry C 3, no. 41 (2015): 10886–91. http://dx.doi.org/10.1039/c5tc02423d.

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Koshibae, W., N. Furukawa, and N. Nagaosa. "Photo-induced insulator-metal transition of a spin-electron coupled system." EPL (Europhysics Letters) 94, no. 2 (April 1, 2011): 27003. http://dx.doi.org/10.1209/0295-5075/94/27003.

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Inaba, F., T. Arima, T. Ishikawa, T. Katsufuji, and Y. Tokura. "Change of electronic properties on the doping-induced insulator-metal transition inLa1−xSrxVO3." Physical Review B 52, no. 4 (July 15, 1995): R2221—R2224. http://dx.doi.org/10.1103/physrevb.52.r2221.

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Wang, Yang, Yu Sui, Jinguang Cheng, Xianjie Wang, Zhe Lu, and Wenhui Su. "High Temperature Metal−Insulator Transition Induced by Rare-Earth Doping in Perovskite CaMnO3." Journal of Physical Chemistry C 113, no. 28 (June 12, 2009): 12509–16. http://dx.doi.org/10.1021/jp809049s.

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Wang, Yang, Yu Sui, Jinguang Cheng, Xianjie Wang, Wenhui Su, Xiaoyang Liu, and Hong Jin Fan. "Doping-Induced Metal−Insulator Transition and the Thermal Transport Properties in Ca3−xYxCo4O9." Journal of Physical Chemistry C 114, no. 11 (March 2010): 5174–81. http://dx.doi.org/10.1021/jp911078h.

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Yoo, Pilsun, and Peilin Liao. "First principles study on hydrogen doping induced metal-to-insulator transition in rare earth nickelates RNiO3 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Yb)." Physical Chemistry Chemical Physics 22, no. 13 (2020): 6888–95. http://dx.doi.org/10.1039/c9cp06522a.

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Modak, P., and Ashok K. Verma. "Pressure induced multi-centre bonding and metal–insulator transition in PtAl2." Physical Chemistry Chemical Physics 21, no. 24 (2019): 13337–46. http://dx.doi.org/10.1039/c9cp02034a.

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Zhang, Siyuan, Hsun Jen Chuang, Son T. Le, Curt A. Richter, Kathleen M. McCreary, Berend T. Jonker, Angela R. Hight Walker, and Christina A. Hacker. "Control of the Schottky barrier height in monolayer WS₂ FETs using molecular doping." AIP Advances 12, no. 8 (August 1, 2022): 085222. http://dx.doi.org/10.1063/5.0101033.

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Developing controllable doping processes for two-dimensional (2D) semiconductors is critical to developing next-generation electronic and optoelectronic devices. Understanding the nature of the contacts is an essential step in realizing efficient charge injection in transition metal dichalcogenides. In this study, post-growth n-doping of chemical vapor deposition grown monolayer (1 L) WS2 is achieved through molecular reductant solution treatment. The doping level can be effectively controlled by the treatment time and dopant solution concentrations. The doped WS2 field-effect transistors showed profound threshold voltage shifts and tunable channel currents. This molecular n-doping technique is beneficial for the selective area doping needed for electrical contacts and reduces the contact resistance ( Rc) in 1 L WS2 by more than two orders of magnitude. The significant reduction of Rc is attributed to the high electron-doping density achieved in WS2, which leads to a significant reduction of the Schottky barrier height. The dependence of mobility on temperature indicates clear evidence of the strong suppression of charge-impurity scattering after doping. High levels of doping allow the observation of a metal–insulator transition in monolayer WS2 due to strong electron–electron interactions. This doping technique provides a viable route for tailoring the electrical properties and improving the contacts in transition metal dichalcogenides, paving the way for high-performance 2D nanoelectronic devices.

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Journal articles on the topic 'Electron doping induced metal-insulator transition'

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