Level Splitting Research Articles

Effect of Chlorine Inclusion in Wide Band Gap FAPbBr3 Perovskites

AbstractWide bandgap perovskites have recently gained attention owing to their physical properties, versatility, and potential in various optoelectronic devices including LEDs, detectors, and building‐integrated photovoltaics (BIPV). However, BIPV materials must meet conflicting requirements, necessitating high performance, high transparency in the visible spectrum and color neutrality. This study investigates the controlled addition of chlorine in FAPb(Br1‐xClx)3 perovskites to achieve band gaps exceeding 2.4 eV. Increasing chlorine content from xCl = 0.00 to xCl = 0.25 widens the band gap from 2.37 to 2.52 eV, effectively improving the visible light transparency. Advanced characterization techniques including X‐ray diffraction, synchrotron radiation photoelectron spectroscopy, photoluminescence imaging, and fast transient absorption spectroscopy, complemented by density functional theory, reveal insights into absorption properties, electronic structure, and ultrafast recombination dynamics as a function of the thin film chemical composition. Furthermore, this study evaluates energetic disorder, carrier recombination rates, and non‐radiative losses for different compositions by extracting quantitative parameters such as Urbach energy and quasi‐Fermi level splitting, offering novel insights and guidelines for the design and optimization of emerging photovoltaic (PV) materials. Optimal PV performance metrics are achieved with a wide bandgap bromine perovskite containing 14% chlorine, striking a balance between morphology, transparency, and voltage losses.

Dual efficacy of potassium-doping in perovskite solar cells: Reducing hysteresis and boosting open-circuit voltage

The incorporation of potassium into perovskite solar cells (PSCs) has been empirically validated to mitigate hysteresis phenomena and boost the power conversion efficiency (PCE). However, the doping mechanism of potassium ions in the perovskite film and their effect on photocarrier recombination remains a topic of debate. Here, we grew doped MAPbI3: K single crystals by inverse temperature crystallization using KI as a dopant, and then perovskite thin films were spin-coated with dissolved MAPbI3: K crystals as a precursor. The doped MAPbI3: K perovskite films exhibit better crystal quality with large columnar grains and lower defect density. Employing Hall effect, ultraviolet photoelectron spectroscopy, and Kelvin probe force microscopy measurements, we definitively demonstrate that K-doping transforms the conductivity type of the perovskite film from a marginally N-type to a distinct P-type semiconductor. Furthermore, this doping strategy induces a concurrent downward shift in both the conduction band minimum and valence band maximum. As a result, the PCE of the PSCs increases from 15.15% to an impressive 20.66%, and the J–V curve hysteresis almost disappears. Additionally, theoretical simulations using SCAPS-1D software reveal a profound modification in the device's energy band diagram after K+-doping. Specifically, the energy level offset between the perovskite layer and the electron transport layer diminishes from 0.24 to 0.14 eV, with a result of bigger quasi-Fermi energy level splitting. This, in turn, elevates the open-circuit voltage (Voc) of the doped perovskite solar cell, underscoring the profound impact of potassium doping on enhancing PSC performance.

DISSOCIATION, SPLITTING AND COMPARTMENTALIZATION IN TRAUMA-RELATED DISORDERS

The article is devoted to the analysis of actual scientific views and theoretical research on the participation of the phenomena of dissociation, splitting, and compartmentalization in disorders associated with mental trauma, in particular, PTSD and addictions. It is shown that the understanding of the concepts of dissociation and splitting developed in parallel and that both concepts emerged from research on trauma. Empirical studies show a clear correlation between dissociation, splitting, and compartmentalization with trauma-related disorders. However, there is considerable confusion in the differentiation of these concepts: some authors use them as synonyms, other authors consider dissociation to be a more basic process underlying splitting, and some distinguish two separate types of dissociation - separation, and compartmentalization. In this article, the concept of dissociation and splitting into separate independent phenomena is chosen, where dissociation is defined as the separation of mental processes or mental systems from consciousness, and splitting is defined as the division of consciousness itself into several independent centers of self-consciousness, with the phenomenon of compartmentalization referring to a shallow level of splitting. Both dissociation and splitting can exist in the spectrum from normal to deep pathology of the (sub)psychotic level. The article analyzes how dissociation and splitting can participate in the formation of trauma-related disorders such as PTSD and addiction. In the formation of PTSD, a part of the human psyche system associated with traumatic experiences is detached from consciousness as a result of protection from unbearable experiences (dissociation). Further, due to unsuccessful attempts to integrate the trauma, a negative self-concept with feelings of shame/guilt is formed, which splits off from the core self (splitting). As a result, a triadic structure is formed: the normative Ego-state, the split traumatic Ego-state, and the dissociated traumatic Self-state. When addiction is formed based on early trauma, a dissociated self-state exists since childhood, but while using psychoactive substances, it is integrated with a state of altered consciousness, which is why a person is experiencing a state of high, similar to a miracle. In this case, a system is formed of a normative Ego state, a dissociated traumatic Self-state, and a detached addictive Ego state, which is activated exclusively in a state of altered consciousness, and during activation, integration with the dissociated Self-state occurs. This addictive integration is the real motive for the use of this group of addictive drugs. The proposed concept can be used in the psychotherapy of trauma-related disorders as a conceptualization of cases and conceptualization of loci of therapeutic contact. Keywords: dissociation, splitting, compartmentalization, mental trauma, PTSD, addiction

Isomeric diammonium passivation for perovskite-organic tandem solar cells.

In recent years, perovskite has been widely adopted in series-connected monolithic tandem solar cells (TSCs) to overcome the Shockley-Queisser limit of single-junction solar cells. Perovskite/organic TSCs, comprising a wide-bandgap (WBG) perovskite solar cell (pero-SC) as the front cell and a narrow-bandgap organic solar cell (OSC) as the rear cell, have recently drawn attention owing to the good stability and potential high power conversion efficiency (PCE)1,2,3,4. However, WBG pero-SCs usually exhibit higher voltage losses than regular pero-SCs, which limits the performance of TSCs5,6. One of the major obstacles comes from interfacial recombination at the perovskite/C60 interface, and it is important to develop effective surface passivation strategies to pursue higher PCE of perovskite/organic TSCs7. Here we exploit a new surface passivator cyclohexane 1,4-diammonium diiodide (CyDAI2), which naturally contains two isomeric structures with ammonium groups on the same or opposite sides of the hexane ring (denoted as cis-CyDAI2 and trans-CyDAI2, respectively), and the two isomers demonstrate completely different surface interaction behaviors. The cis-CyDAI2 passivation treatment reduces the Quasi-Fermi level splitting (QFLS)-open circuit voltage (Voc) mismatch of the WBG pero-SCs with a bandgap of 1.88 eV and enhanced its Voc to 1.36 V. Combining the cis-CyDAI2 treated perovskite and the organic active layer with a narrow-bandgap of 1.24 eV, the constructed monolithic perovskite/organic TSC demonstrates a PCE of 26.4% (certified as 25.7%).

Enhanced Electric Field Minimizing Quasi-Fermi Level Splitting Deficit for High-Performance Tin-Lead Perovskite Solar Cells.

The quasi-Fermi level splitting (QFLS) deficit caused by the non-radiative recombination at the interface of perovskite/electron transport layer (ETL) can lead to severe open-circuit voltage (VOC) loss and thus decreases the efficiency of perovskite solar cells (PSCs), however, has received limited attention in inverted tin-lead PSCs. Herein, the strategy of constructing an extra-electric field is presented by introducing ferroelectric polymer dipoles (FPD)-β-poly(1,1-difluoroethylene)-to suppress the QFLS deficit. The directional polarization of FPD can enhance the built-in electric field (BEF) and thus promote the charge transfer at the perovskite/ETL interface, which effectively suppresses non-radiative recombination. Furthermore, the incorporation of FPD facilitates high-quality crystallization of perovskite and reduces the surface energetic disorder. Therefore, the QFLS deficit in the perovskite/ETL half-stacked device is reduced from 62 to 27 meV after incorporating FPD, and the optimized device achieves an efficiency of 23.44% with a high VOC of 0.88V. Additionally, the addition of FPD increases the activation energy for ion migration, which can reduce the effect of ion migration on the long-term stability of the device. Consequently, the FPD-incorporated device retains 88% of the initial efficiency after 1100h of continuous illumination at the maximum power point (MPP).

Three-dimensional assessment of root canal morphology of primary dentition using cone beam computed tomography.

Root canal therapy in primary teeth is exceedingly complex due to the unique internal geometry of the pulp cavity. The purpose of this study was to evaluate variations in primary teeth root canal morphology and applicability of the Ahmed etal. (Int Endod J, 50, 2017, 761) alphanumeric system for classifying them. A retrospective analysis of 2024 primary teeth from an existing CBCT database was performed for assessing variations in root canal morphology. Descriptive statistics and the chi-squared test were used for data analysis. The maxillary canines exhibited splitting levels of 5.9% (right) and 6.6% (left), and merging levels of 1% (both sides); maxillary lateral incisors showed splitting levels of 2.6% (right) and 0.8% (left), with no merging observed; mandibular second molars had splitting levels of 1.5% (right) and 0.8% (left), with no merging observed; and mandibular lateral incisors exhibited a merging level of 0.9% (right), with no splitting observed. This study provides new insights into the variations in root canal morphology of primary teeth, particularly highlighting the variations found in primary canines. The Ahmed etal. (Int Endod J, 50, 2017, 761) classification system was found to be a useful tool for categorizing these variations.

Magnetic field-engineered optical nonlinearity in germanene nanotubes

Abstract The linear and nonlinear optical properties of germanene nanotubes (GeNTs) under the influence of magnetic fields are investigated through theoretical analysis. By employing a tight-binding model beyond the Dirac cone approximation, the electronic band structure, density of states, dipole matrix elements, and third-order nonlinear optical susceptibilities are calculated. The application of a magnetic field induces a Zeeman splitting of the energy levels, breaking the band degeneracy. Consequently, the dipole matrix elements exhibit a magnetic field dependence, altering the intensity and number of allowed transitions. In the infrared and ultraviolet energy regions, the linear optical absorption spectrum displays the splitting of peaks into dual neighboring peaks, with the splitting distance linearly dependent on the magnetic field strength. The third-order nonlinear optical susceptibilities, χTHG(3)3ω and χIDIR(3)ω, reveal the emergence of multiple resonance peaks in different energy regions due to two-photon and three-photon absorption processes. The magnetic field significantly influences the number, position, and height of these optical peaks, enabling effective control over the nonlinear optical response. By investigating the scaled energy (E/E_g) dependence, a universal behavior is observed for the three- and two photon resonance peaks, where their positions remain constant, but their peak intensities are significantly enhanced under the influence of the magnetic field. These findings demonstrate the potential of GeNTs as tunable nonlinear optical materials, with the magnetic field serving as an effective parameter for engineering their optical properties for various applications in optoelectronics, photonics, and related fields.

CdWO4 Sub‐1 nm Nanowires for Visible‐light CO2 Photoreduction

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO4 sub‐1 nm nanowires (SNWs) with oleylamine adsorption, PO43‐‐doping and oxygen defects are synthesized by combining Cd(CH3COO)2, H3PW12O40 (PW12) and oleylamine (abbreviated as PO43‐‐CdWO4‐X SNWs). Compared with bulk CdWO4, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and bandgap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible‐light CO2 photoreduction activity. Under 410 nm LED light irradiation, PO43‐‐CdWO4‐40 SNWs exhibit the highest photocatalytic performance with a CO2‐to‐CO generation rate of 1685 µmol g‐1 h‐1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO43‐‐doping and oxygen defects will generate defect energy band below the conduction band of PO43‐‐CdWO4‐40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO2 reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub‐nano materials.

Enhanced Infrared Emission from Rare-Earth Double Perovskite Embedded in Fluoride Glass with Different B-Site Cation Structures for N2O Sensing in a Hydrogen Stream.

Rare-earth halide perovskites can lead to a distinctive infrared luminescence. However, achieving tunable infrared luminescence presents significant challenges. The leptons of their f-f ubiquitous forbidden ring influence the energy level splitting, and the substitution of atoms in perovskite by rare-earth ions also distorts the crystal structure. The research on achieving tunable mid-infrared emission by altering the crystal structure of rare-earth perovskites is limited. The crystal structure can be modified by changing the matrix B-site cation for a series of Cs2MIn1-xHoxCl6-ZBLAY (M = Na and Ag) rare-earth perovskites coated with a glass matrix that have been prepared. On this basis, we revealed the local electronic structure of Cs2MInCl6 (M = Na and Ag) perovskites and proposed an effective charge transfer strategy to achieve an efficient infrared emission of Ho3+ ions at 1.2 and 2.87 μm. The contribution of Na s and Na p is minor in Cs2NaIn1-xHoxCl6, which leads to poor interactions between Na+ and Cl- and promotes charge transfer of Ho3+-Cl- in the [HoCl6]3- octahedron. The charge transfer mechanism of Cs2NaInCl6:Ho3+-Cl- is validated by executing density functional theory calculations. Furthermore, a device that identifies N2O gas levels in hydrogen energy was built using the Cs2NaIn1-xHoxCl6-ZBLAY sample. These findings provide a new perspective on how to achieve effective infrared emission.

CdWO4 Sub-1 nm Nanowires for Visible-light CO2Photoreduction.

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO4 sub-1 nm nanowires (SNWs) with oleylamine adsorption, PO43--doping and oxygen defects are synthesized by combining Cd(CH3COO)2, H3PW12O40 (PW12) and oleylamine (abbreviated as PO43--CdWO4-X SNWs). Compared with bulk CdWO4, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and bandgap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible-light CO2 photoreduction activity. Under 410 nm LED light irradiation, PO43--CdWO4-40 SNWs exhibit the highest photocatalytic performance with a CO2-to-CO generation rate of 1685 µmol g-1 h-1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO43--doping and oxygen defects will generate defect energy band below the conduction band of PO43--CdWO4-40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO2 reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub-nano materials.

How symmetry helps to improve the estimation of the hyperfine splitting of torsional levels due to tunneling. The case of the HSSSH molecule

In this study, we analyze a series of molecules belonging to the C2V(M) molecular symmetry group which are characterized by several conformers. The use of molecular symmetry at each stage of calculating the energy of stationary torsional states is demonstrated. In particular, the importance is shown of preliminary symmetrization of physical characteristics of the molecules obtained by quantum chemical calculations. For the first time, symmetry-adapted basis functions for the diagonal kinetic coefficients are presented, which for the analyzed molecules do not satisfy all symmetry operations of the C2V(M) group. Using the HSSSH molecule as an example, it is shown how the full or partial accounting for molecular symmetry influences the calculated values of ultra-small tunneling splittings of the ground torsional states of the trans- and cis-conformers. It has also been established that the Hamiltonian matrix is characterized by symmetry which, when taken into account, makes it possible to halve the time of calculation of its elements.

Infrared optical spectra of a silicene quantum dot modulated by spin-orbit coupling and uniaxial strain

Abstract We theoretically study the electronic structure and light absorption spectra of a triangular silicene quantum dot (TZSQD) modulated by spin-orbit coupling (SOC) and the uniaxial strain from a symmetry point of view. After considering the SOC, the symmetry of the system decreases and the degenerate energy level split, creating the absorption peaks in the far infrared region and some multimodal structures in the near-infrared region and visible region. In addition, the intensity of the SOC also affects the degree of splitting of the energy levels, which makes the absorption peaks in the far infrared region are blueshifted to the mid-infrared region, and absorption edge in the near infrared region is redshifted to the mid-infrared region. We also find that when a uniaxial strain and SOC coexist at the same time, the symmetry of the system is further reduced, and the number of absorption peaks is increased. Moreover, the uniaxial strain intensity can efficiently regulate the frequency position of the absorption edge in the near-infrared region, and make its spectral range greatly expanded.

Unraveling the Positive Effects of Glycine Hydrochloride on the Performance of Pb–Sn‐Based Perovskite Solar Cells

Additives are commonly used to increase the performance of metal‐halide perovskite solar cells, but detailed information on the origin of the beneficial outcome is often lacking. Herein, the effect of glycine hydrochloride is investigated when used as an additive during solution processing of narrow‐bandgap mixed Pb–Sn perovskites. By combining the characterization of the photovoltaic performance and stability under illumination, with determining the quasi‐Fermi level splitting, time‐resolved microwave conductivity (TRMC), and morphological and elemental analysis a comprehensive insight is obtained. Glycine hydrochloride is able to retard the oxidation of Sn2+ in the precursor solution, and at low concentrations (1–2 mol%) it improves the grain size distribution and crystallization of the perovskite, causing a smoother and more compact layer, reducing non‐radiative recombination, and enhancing the lifetime of photogenerated charges. These improve the photovoltaic performance and have a positive effect on stability. By determining the quasi‐Fermi level splitting on perovskite layers without and with charge transport layers it is found that glycine hydrochloride primarily improves the bulk of the perovskite layer and does not contribute significantly to passivation of the interfaces of the perovskite with either the hole or electron transport layer (ETL).

Supported Au single atoms and nanoparticles on MoS2 for highly selective CO2-to-CH3COOH photoreduction

Effectively controlling the selective conversion of CO2 photoreduction to C2 products presents a significant challenge. Here, we develop a heterojunction photocatalyst by controllably implanting Au nanoparticles and single atoms into unsaturated Mo atoms of edge-rich MoS2, denoted as Aun/Au1-CMS. Photoreduction of CO2 results in the production of CH3COOH with a selectivity of 86.4%, which represents a 6.4-fold increase compared to samples lacking single atoms, and the overall selectivity for C2 products is 95.1%. Furthermore, the yield of CH3COOH is 22.4 times higher compared to samples containing single atoms and without nanoparticles. Optical experiments demonstrate that the single atoms domains can effectively capture photoexcited electrons by the Au nanoparticles, or the local electric field generated by the nanoparticles promotes the transfer of photogenerated electrons in MoS2 to Au single atoms, prolonging the relaxation time of photogenerated electrons. Mechanistic investigations reveal that the orbital coupling of Au5d and Mo4d strengthens the oxygen affinity of Mo and carbon affinity of Au. The hybridized orbitals reduce energy splitting levels of CO molecular orbitals, aiding C–C coupling. Moreover, the Mo−Au dual-site stabilize the crucial oxygen-associated intermediate *CH2CO, thereby enhancing the selectivity towards CH3COOH. The cross-scale heterojunctions provide an effective strategy to simultaneously address the kinetical and thermodynamical limitations of CO2-to-CH3COOH conversion.

Amphipathic Astaxanthin Additive for Low Voltage-loss Perovskite Solar Cells With Enhanced Quasi-Fermi Level Splitting and Solar Hydrogen Production Application.

Even though the power conversion efficiency (PCE) of perovskite solar cells (PSCs) is nearly approaching the Schottky-Queisser limit, low open-circuit voltage (Voc) and severe Voc loss problems continue to impede the improvement of PCEs. Astaxanthin (ASTA) additive is introduced in the formamidinium lead triiodide (FAPbI3)perovskite film as an additive, which can facilitate the transportation of charge carriers and interact with Pb2+ by its distinctive groupings. Furthermore, the addition of ASTA decreases the defect's active energy, regulates the deep-level defect by filling up the grain boundaries (GBs), and promotes the crystallization of perovskite film. Remarkably, an enhanced quasi-Fermi level splitting (QFLS) of 1.164eV and a reduced Voc loss of only 96mV are realized. The champion PCE of 24.56% is attained by ASTA-modified PSCs on the basis of 22.75% PCE. Moreover, the PSCs that underwent ASTA modification demonstrate improved operational stability, ensuring consistent output in real-world scenarios. Furthermore, PSCs with an active area of 1 cm2 are used for water electrolysis to produce hydrogen and exhibit a PCE of 22.41%. This work offers an environmentally benign solution to address the inherent issues of FAPbI3 PSCs and lays the groundwork for the development of a prospective solar hydrogen production application.

Study on the effects caused by defect LaK in KH2PO4 crystal

Based on first-principles calculations, we have investigated the effects of different charged states of LaK on the defect formation energies (DFE), lattice distortions, electronic structures, and optical properties of paraelectric phase (PE-KDP) and ferroelectrical phase (FE-KDP) crystals. Our calculations indicate that LaK·· is readily formed in both crystal structures, and the degree of H–O bond distortion is more pronounced in PE-KDP. This could explain the formation of small growth mounds on the surface of La-doped crystals observed in the experiments, as well as the large decrease in the hardness of La-doped crystals. Furthermore, the band gap value of La-doped crystals is smaller than that of perfect crystals. This can be attributed to the fact that the 5d orbitals of La affect the 2p orbitals of O located in the conduction band minimum (CBM), resulting in a splitting of the energy levels and the formation of a defective energy level that enters the forbidden band. The optical spectra have been obtained considering the electron-phonon coupling. Large stokes redshift and nonradiative jump will lower the crystal laser damage threshold. The La-doped PE-KDP has an absorption band at 3.03 eV (409 nm) in good agreement with the experimentally observed absorption band at 390 nm.

Imaging Spin-Orbit Excitation of Yttrium through High-Energy Collisions with Rare Gas Atoms.

The energy required for spin-orbit excitation plays a critical role in understanding translational-to-electronic energy conversion, particularly in chemical reactions involving changes in spin states. This is particularly important for transition metal atoms possessing d-orbitals, which result in multiple spin-orbit split energy levels at low energies. The accurate identification and characterization of spin-orbit transitions in such species require advanced experimental techniques and theoretical support. In this study, the spin-orbit excited collisions of Y(2D3/2) with rare gas atoms Ne, Ar, and Kr leading to Y(2D5/2) were observed using laser-ablated crossed-beam and time-sliced ion velocity mapping imaging techniques. Through a comparison of the forward angular distributions of Y(2D3/2) to the backward and sideway scattering distributions of Y(2D5/2) from elastic and inelastic collisions of Y(2D) with rare gas atoms, this study reveals that the spin-orbit electronic excitation occurs with high collision energy and low impact parameters from backward and sideway collisions. The effectiveness of the spin-orbit excitation process is strongly dependent on the collision energy or temperature, suggesting that energy requirements of the process have to be considered in chemical reactions involving changes in spin states.

Spin-Degeneracy Breaking and Parity Transitions in Three-Terminal Josephson Junctions

Hybrid Josephson junctions (JJs) realized in superconductor-semiconductor heterostructures host fermionic modes known as Andreev bound states (ABSs). In these structures, a promising and yet unexplored avenue for harnessing spin and parity degrees of freedom is offered by JJs with three or more superconducting terminals, where phase-induced spin polarization and transitions of the ground state to an odd parity were predicted to arise. Here we spectroscopically probe the two-dimensional band structure of ABSs in a phase-controlled InAs/Al three-terminal JJ. Andreev bands show signatures of spin-degeneracy breaking, with level splitting in excess of ∼9 GHz, and zero-energy crossings associated to ground state fermion parity transitions. Spin splitting and parity transitions are enabled and controlled by locally applied magnetic fluxes, in the absence of Zeeman effect or Coulomb blockade. Our results underscore the potential of multiterminal hybrid devices for phase engineering ABSs, with significant implications for spin- and parity-based quantum devices. Published by the American Physical Society 2024

Symmetry properties, tunneling splittings of some vibrational energy levels and torsional IR spectra of the trans – and cis – conformers of hydroquinone molecule

Torsional vibrational states of trans − and cis − conformers belonging to point symmetry groups C2H and C2V, respectively, of hydroquinone molecules are classified according to the irreducible representations of the molecular symmetry group D2H(M). A correspondence has been established between the symmetry elements of the D2H(M) group and the symmetry elements on the torsional coordinate plane for two-dimensional surfaces of potential energy, wave functions, kinetic coefficients and dipole moment projections. A correspondence has been established between the symmetry species of the point symmetry groups C2H, C2V and the symmetry species of the molecular symmetry group D2H(M). Conformational states, barriers to internal rotation and the above-mentioned characteristics of the hydroquinone molecule were calculated at the MP2/Aug-cc-pVDZ, MP2/Aug-cc-pVQZ, MP2/Aug-cc-pVTZ, MP2/CBS(aD,aT,aQ), and CCSD(T)/dAug-cc-pVDZ levels of theory. The calculated data sets were approximated using symmetry-adapted sets of basis functions. Using a numerical solution of the vibrational Schrödinger equation of restricted dimensionality, the energies and wave functions of 50 stationary torsional states of the hydroquinone molecule were determined for the first time. The values of tunneling splittings of the ground vibrational and a number of excited torsional states of trans − and cis − conformers were determined. In particular, when calculating at the MP2/CBS(aD,aT,aQ) level of theory, the values of tunneling splittings of the ground vibrational states of trans − and cis − conformers turned were 1.32*10-6 and 1.62*10-6 cm−1, which is consistent with the experimentally established upper limit for this value in the cis − conformer by authors of [W. Caminati, S. Melandri, L. B. Favero, J.Chem.Phys., 100 (1994) 8569 – 8572] (0.2 MHz or 6.67*10-6 cm−1). The calculations of the matrix elements of the dipole moment operator and the partition function made it possible to simulate the torsional IR spectra of the molecule’s conformers at different temperatures. The frequencies of fundamental torsional vibrations in the trans – (267.1 and 269.0 cm−1) and cis – (269.5 and 270.9 cm−1) conformers, calculated at the MP2/CBS(aD,aT,aQ) level of theory, are in good agreement with the experimental value of frequency of this vibration (266 cm−1), established in [W.G. Fateley, G.L. Carlson, F.F. Bentley, J.Phys.Chem., 79 (1975) 199–204.].

Unveiling Sub-60 mV/decade Subthreshold Swing in The Oxide Local Thinning (OLT) Gated MIS Tunnel Diodes by TCAD Simulations

Metal-insulator-semiconductor (MIS) tunnel diodes (TD) are widely used in the modern integrated circuit, for its ease of fabrication and low cost. Recently, we have reported that the gated MIS TDs can exhibit sub-60 mV/decade subthreshold swing (SS) [1], which can be further reduced by introducing oxide local thinning (OLT) regions. SSs could be as low as 9.7 and 8.4 mV/decade in gated MIS TDs with the OLT regions formed by soft breakdown and photolithography, respectively [2,3]. The reason is unclear and the feasibility of scaling is of interest. In this work, we unveiled the mechanism and designed the scaled devices with ultra-low SS by TCAD simulation.We performed Silvaco TCAD with the 2-D cylindrical structure identical to [2] (Fig. 1). Models of direct tunneling and quantum confinement were included. The OLT region at the center TD is 100 nm. The OLT region at the gate is 400 μm from the inner gate edge, and the width (W GOLT) varies from 100 to 1000 nm.Fig. 2(a) shows the simulated I TD-V G curves of the OLT gated MIS TDs, denoted as TDOLT+GOLT, with different W GOLT, compared to the one without an OLT region at the gate, denoted as TDOLT, and Fig. 2(b) shows the corresponding SS. TDOLT+GOLT turns-on steeply, with SS approaching 10 mV/decade, close to the value observed in [2,3]. The electron densities n e at 2 nm depth in the silicon under different V G are examined for TDOLT and TDOLT+GOLT with W GOLT = 100 nm in Fig. 3(a) and (b) respectively. n e near the inner gate of the latter case increases abruptly from -0.8 to -0.7 V, due to the injection of the extra electrons from the gate OLT region. Fig. 3(c) shows the electron densities at 2 μm inside the gate edge for different devices, following the similar trend with the I TD-V G curves, indicating that the magnitude of the TD current is determined by n e near the gate edge. Fig. 4 shows the mechanism of TD current under different situations. For V G = -1 V, I TD is off and comes from the generation of electrons under the TD. For V G = -0.5 V, I TD is in the stage 1 and comes from the injection of electrons through the gate OLT region. The injection of electrons results in the steep increase of I TD and subsequently the ultra-low SS. For V G = 0.2 V, I TD is in stage 2 and collects the electrons generated in the whole substrate. The rapid increase of n e at the gate edge can be understood in another point of view. Fig. 5 shows the band diagram laterally near the silicon surface. Since n e depends on the difference between the conduction band energy (E C) and the electron quasi-Fermi level (E Fn), when V G increases from -0.8 to -0.7 V, E C is pushed down while E Fn at the gate edge is pulled up due to the injection of electrons through the gate OLT region. Therefore, the device can have SS lower than 60 mV/dec.To test whether the ultra-low SS characteristics can maintain when scaling down, we performed the simulation of the sub-micro device shown in Fig. 6. We find the TD cannot be turned off if we still use substrate thickness t sub = 5 μm (Fig. 7(a)), since the injection of electrons are too strong. However, by reducing t sub, I TD can be turned off and shows superior performance with on-off ratio over 8 orders and SS lower than 60 mV/decade (Fig. 7(b)). Since the electron diffusion current flowing to the substrate of an MIS TD with the substrate much shorter than the diffusion length can be expressed as J n = (qD n n i 2/t sub N A) e qΔΦ n/kT where q, D n, n i, N A, ΔΦ n, k, T are the elementary charge, electron diffusion coefficient, intrinsic carrier concentration, p-type doping concentration, electron quasi-Fermi level splitting, Boltzmann constant, and temperature, respectively, reducing t sub can lead to a stronger diffusion of electrons to the substrate, and there will be fewer electrons flowing to the gate edge (Fig. 8). Therefore, the electron densities can be lower near the gate edge when V G is negative enough, as shown in Fig. 9, leading to the effective turn-off of the TD.REFERENCES[1] Liao, et al., IEEE Trans. on Electron Devices, 62(6), 2061, (2015).[2] Yang, et al., IEEE Trans. Electron Devices, 66(1), 279, (2018).[3] Chiang, et al., IEEE Trans. Electron Devices, 67(4), 1887, (2020).ACKNOWLEDGEMENTThis work was supported by the Ministry of Science and Technology of Taiwan, ROC, under Contract No. MOST 111-2221-E-002-192-MY3 and NSTC 111-2622-8-002-001. Figure 1