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Synthesis of (BiSe) <sub/> 1+ <i>δ</i> </sub> (Bi <sub/>2</sub> Se <sub/>3</sub> ) <sub/> 1+ <i>γ</i> </sub> (BiSe) <sub/> 1+ <i>δ</i> </sub> TiSe <sub/>2</sub> by Directed Self-Assembly of a Designed Precursor
摘要： The synthesis, structure and properties of a new three constituent heterostructure containing BiSe, Bi2Se3, and TiSe2 layers, each with a different structural motif, is reported. (BiSe)1+δ(Bi2Se3)1+γ(BiSe)1+δTiSe2, where δ and γ are the misfit parameters representing the differences in the in-plane packing density of the constituents, forms via a self-assembly process during low-temperature annealing from precursors with a range of compositions and repeat period thicknesses. This indicates that the compound exists in a relatively broad and deep free-energy minima in the energy landscape. The formation was followed as a function of annealing temperature using X-ray diffraction to determine optimum annealing temperatures and stability range. High-resolution electron microscopy images revealed the layering sequence of the constituents and a supercell within the BiSe layers created by periodic anti-phase boundaries. Temperature dependent electrical transport measurements show unexpected changes in carrier mobility and concentration relative to (BiSe)1.15TiSe2. This study suggests that new ternary and multinary phases containing fragments of known binary phases can be synthesized via precursors that mimic the desired product and that the properties of these new phases with ultrathin constituent thicknesses will probably be different from that expected based on composite behavior.
关键词： X-ray diffraction,electron microscopy,heterostructure,BiSe,self-assembly,TiSe2,Bi2Se3,electrical transport
更新于2025-09-04 15:30:14
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Electron Transport in Nanoporous Graphene: Probing the Talbot Effect
摘要： Electrons in graphene can show diffraction and interference phenomena fully analogous to light thanks to their Dirac-like energy dispersion. However, it is not clear how this optical analogy persists in nanostructured graphene, for example, with pores. Nanoporous graphene (NPG) consisting of linked graphene nanoribbons has recently been fabricated using molecular precursors and bottom-up assembly (Moreno et al. Science 2018, 360, 199). We predict that electrons propagating in NPG exhibit the interference Talbot effect, analogous to photons in coupled waveguides. Our results are obtained by parameter-free atomistic calculations of real-sized NPG samples based on seamlessly integrated density functional theory and tight-binding regions. We link the origins of this interference phenomenon to the band structure of the NPG. Most importantly, we demonstrate how the Talbot effect may be detected experimentally using dual-probe scanning tunneling microscopy. Talbot interference of electron waves in NPG or other related materials may open up new opportunities for future quantum electronics, computing, or sensing.
关键词： multiscale modeling,electron transport,Nanoporous graphene,scanning probe microscopy,Talbot interference
更新于2025-09-04 15:30:14
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Charge transport layers manage mobility and Carrier density balance in light-emitting layers influencing the operational stability of organic light emitting diodes
摘要： Organic light emitting diodes (OLEDs) consist of several organic layers, including the charge injection layer, charge transport layer, and light emitting layer (EML). Of these layers, the charge transport layer is crucial for ensuring device longevity, but its overall effects on charge transport and corresponding device stability are poorly understood. Herein we report the factors influencing differences in lifetime between two OLEDs with different hole transporting layers (HTLs). Comprehensive electrical analysis of the materials and the devices reveals that the mobility, accumulation, trapping, and the transport path of holes in the EML are totally changed by the HTLs. The charge transport layers affect mobility and carrier density balance in the EML through the modification of the charge transport path and the energetic barrier. This results in a reduction of overbalanced polaron density, which is critical for bond dissociation in excitonic interactions. Consequently, device lifetime is increased sevenfold through modification of the HTL structure without any alteration of the EML. These results imply that the analysis of polaronic transport through impedance spectroscopy is a crucial step in determining the requisite electrical properties for charge transport layers, with a view to maximizing the operational stability of OLEDs.
关键词： charge transport,Organic light-emitting diodes,device stability,impedance spectroscopy
更新于2025-09-04 15:30:14
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Solid-state order and charge mobility in [5]-[12] cycloparaphenylenes
摘要： We report a computational study of mesoscale morphology and charge transport properties of radially π-conjugated cycloparaphenylenes [n]CPPs of various ring sizes (n = 5-12, where n is the number of repeating phenyl units). These molecules are considered as structural constituents of fullerenes and carbon nanotubes. [n]CPP molecules are nested in a unique fashion in the solid state. Molecular dynamics simulations show that while intramolecular structural stability (order) increases with system size, intermolecular structural stability reduces. Density functional calculations reveal that reorganization energy, an important parameter in charge transfer, decreases as n is increased. Intermolecular charge-transfer electronic couplings in the solid state are relatively weak (due to curved π-conjugation and loose intermolecular contacts) and are on the same order of magnitude (i.e., ~10 meV) for each system. Intrinsic charge-carrier mobilities were simulated from kinetic Monte Carlo simulations; hole mobilities increased with system size and scaled as ~n4. We predict that disordered [n]CPPs exhibit hole mobilities as high as 2 cm2/Vs. A strong correlation between reorganization energy and hole mobility, i.e. μ~λ?4, was computed. Quantum mechanical calculations were performed on co-facially stacked molecular pairs for varying phenyl units and revealed that orbital delocalization is responsible for both decreasing reorganization energies and electronic couplings as n is increased.
关键词： kinetic Monte Carlo simulations,charge transport,density functional calculations,molecular dynamics,cycloparaphenylenes
更新于2025-09-04 15:30:14
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Force-noise spectroscopy by tunneling current deflection sensing
摘要： An electro-mechanical setup for the measurement of force-noise properties in a low-temperature tunneling microscope has been utilized to enable extremely high resolution and acquire force-noise spectra as function of the applied voltage bias. The direct crosstalk of vibrations onto the tunneling current is used to measure the de?ection of a force-sensing cantilever. We demonstrate its capability to measure the mechanical energy of the cantilever, caused by the noise of the force from vacuum tunneling between polycrystalline Iridium electrodes. We observe peak levels of the induced cantilever energy at polarity-symmetric voltages corresponding to dominant peaks of the phonon density of states, which suggests that inelastic transport processes contribute to force ?uctuations.
关键词： inelastic transport processes,force-noise spectroscopy,cantilever deflection,tunneling current,phonon density of states
更新于2025-09-04 15:30:14
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Single-crystal investigation of the proposed type-II Weyl semimetal CeAlGe
摘要： We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction con?rms that CeAlGe forms in a noncentrosymmetric I 41md space group, in line with predictions of nontrivial topology. Magnetization, speci?c heat, and electrical transport measurements were used to con?rm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of (cid:2) = 9.11 K from heat capacity and hole-like carrier density of 1.4 × 1020 cm?3 from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal ab plane below 7 K. A spin-?op transition to less than 1 μB /Ce is observed to occur below 30 kOe at 1.8 K in the M (H ) (H(cid:2)a) data. Small magnetic ?elds of 3 and 30 kOe are suf?cient to suppress magnetic order when applied along the a and c axes, respectively, resulting in a complex T –H phase diagram for H(cid:2)a and a simpler one for H(cid:2)c.
关键词： Weyl semimetal,CeAlGe,electrical transport measurements,single-crystal x-ray diffraction,antiferromagnetic order,magnetization,specific heat
更新于2025-09-04 15:30:14
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Electric field modified Arrhenius description of charge transport in amorphous oxide semiconductor thin film transistors
摘要： While it is known that the charge-carrier mobility in amorphous metal oxide semiconductor thin ?lm transistors (TFT) deviates from Arrhenius temperature dependence, we found that the Hall mobility measured in amorphous In-Ga-Zn-O (a-IGZO) follows an Arrhenius relation surprisingly well. We explain these observations by the effect of strong vertical electric ?eld created by the gate voltage, which facilitates direct tunneling of trapped carriers into the conductive band and leads to virtually temperature independent mobility. We present a generalized Arrhenius model based on the effective temperature concept. We show that our model allows quantitative description of the temperature dependence of the mobility in a-IGZO TFTs over a broad temperature range.
关键词： charge transport,thin film transistors,Arrhenius relation,amorphous oxide semiconductor,electric field
更新于2025-09-04 15:30:14
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Machine Learning-Based Charge Transport Computation for Pentacene
摘要： Insight into the relation between morphology and transport properties of organic semiconductors can be gained using multiscale simulations. Since computing electronic properties, such as the intermolecular transfer integral, using quantum chemical (QC) methods requires a high computational cost, existing models assume several approximations. A machine learning (ML)–based multiscale approach is presented that allows to simulate charge transport in organic semiconductors considering the static disorder within disordered crystals. By mapping ?ngerprints of dimers to their respective transfer integral, a kernel ridge regression ML algorithm for the prediction of charge transfer integrals is trained and evaluated. Since QC calculations of the electronic structure must be performed only once, the use of ML reduces the computation time radically, while maintaining the prediction error small. Transfer integrals predicted by ML are utilized for the computation of charge carrier mobilities using o?-lattice kinetic Monte Carlo (kMC) simulations. Bene?ting from the rapid performance of ML, microscopic processes can be described accurately without the need for phenomenological approximations. The multiscale system is tested with the well-known molecular semiconductor pentacene. The presented methodology allows reproducing the experimentally observed anisotropy of the mobility and enables a fast estimation of the impact of disorder.
关键词： machine learning,multiscale approach,organic semiconductors,charge transport,pentacene
更新于2025-09-04 15:30:14
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Performance and Reliability Improvement under High Current Densities in Black Phosphorus Transistors by Interface Engineering
摘要： Few-layer Black phosphorus (BP) has recently emerged as a promising two-dimensional (2D) material for electronic and optoelectronic devices due to its high mobility and tunable bandgap. However, BP is known to have quick degradation and oxidize in ambient conditions by breaking of the P-P bonds. As a result, there is a growing need to encapsulate BP that avoids oxygen and water while retaining the high electric performance of the devices. Here we demonstrate a hydrophobic polymer encapsulation technique with improved thermal conductivity for high current density, which preserves the electrical properties of BP back-gate transistors compared to the commonly used Al2O3 encapsulation with improved mobility and minimal traps. The on-off ratio increases for more than an order of magnitude at room temperature and more than four orders of magnitude at cryogenic temperatures. High field transport shows the first systematic study on unprecedented breakdown characteristics up to -5.5 V for the 0.16 μm transistors with a high current of 1.2 mA/μm at 20 K. These discoveries open up a new way to achieve high-performance 2D semiconductors with significantly improved breakdown voltage, on-off ratios, and stability under ambient conditions for practical applications in electronic and optoelectronic devices.
关键词： encapsulation,polymer,Black phosphorus,high-field transport,field-effect transistors,breakdown voltage,reliability
更新于2025-09-04 15:30:14