Low Work Function Research Articles

Low-Power Design of Fully Digital BPSK Modulator and Demodulator Utilizing Nanoscale FinFET for Smart Implants

This study aims to create a high-speed, low-power data transmission solution for implantable medical devices based on cutting-edge FinFET technology. The work examines the application of Binary Phase Shift Keying (BPSK) modulation through a transmission gate design, which provides an optimal blend of low resistance, high-speed performance, and minimal power consumption. Additionally, the work includes the design of a sine-to-square wave converter and a modulating signal generator. FinFET is employed owing to its high switching speed, low power consumption, low leakage current, and excellent tolerance of short channel effects. The design exhibits a steady electric field at the source end, a high electrostatic potential, and an improved ON current at low work function values using Sentaurus TCAD simulations of a 20nm FinFET, allowing high-speed data modulation in smart implants. A nonoverlapping phase generator, a low-power, current-starved gated ring oscillator, a frequency divider utilizing a True Single Phase Clock D-Flip-flop, and an XOR gate serving as a pulse counter are all featured in the design of the BPSK demodulator. This work is significant for its ability to drastically reduce power consumption to 1.75μW while retaining high data transmission speeds, making it perfect for next-generation implantable medical devices. With a 0.9 V power supply, this FinFET-based BPSK modulator and demodulator achieve a far lower power consumption than conventional CMOS-based designs, which increases device longevity and efficiency in settings with limited resources.

Ag:MoO3:Yb semi-transparent electrode for top emission organic light-emitting didoes

Silver (Ag) is widely used as a cathode in top-emission organic light-emitting diodes (TEOLEDs) for its high reflectivity and conductivity. However, its high absorption, thickness-dependent transmittance, and high work function require further improvement. While Ag:MoO3 alloy has emerged as an alternative, it still needs further enhancement. In this study, we developed a ternary Ag:MoO3:Yb semi-transparent electrode, improving both the optical and electrical properties of the existing binary system. For example, The 30 nm-thick Ag:MoO3:Yb 4:3:3 film exhibited average transmittance, reflectance, and absorption of 64%, 12%, and 24%, respectively. Additionally, the Ag:MoO3:Yb showed a uniform transmittance spectrum in the visible wavelength range. The photoelectron spectroscopy results showed Ag:MoO3:Yb 4:3:3 film has a low work function of 3.69eV. Despite relatively high sheet resistance around 82~130 Ω/sq, the red phosphorescence TEOLEDs incorporating Ag:MoO3:Yb as cathode showed improved device performances compared to the control device with Ag:MoO3 30% where the current efficiency increased by up to 1.7 times and the power efficiency by up to 2.6 times. Furthermore, the optimized Ag:MoO3:Yb devices with good charge balance resulted in a relatively longer lifetime up to 80% of initial luminance (LT80) of 166hr, which are higher performance than those of the device with Ag:MoO3 30%.

A X-bit optimized 2D solid solution Ti3CNTx MXene as the electron transport layer toward high-performance perovskite solar cells

Electron transport layer (ETL) materials need to have good photoelectric properties and suitable energy levels to match the perovskite layer. Ti3CNTx MXene, a typical two dimensional (2D) solid solution, is a potential ETL material due to excellent conductivity and appropriate work function (WF). Herein, Ti3CNTx is obtained by optimizing the X-bit inside MXene, and is firstly used as a new ETL for perovskite solar cells (PSCs). Compared with Ti3C2Tx, Ti3CNTx possesses lower WF due to the existence of N-H bonds. And the energy level between Ti3CNTx and the perovskite layer is more suited to reduce energy loss. Moreover, Ti3CNTx interacts with I- ions to passivate defects, enhancing the quality of the perovskite film. As expected, the better power conversion efficiency (PCE) of Ti3CNTx-PSC reaches 20.16 %, which is one of the most outstanding PCE among 2D materials used as ETLs. More interestingly, the Ti3CNTx-PSC possesses better stability (the PCE retention rate is 70.3 % after 600 h in the air), as a stronger Pb-O bond can reduce Pb0 formation. This work not only reveals the mechanism of interaction between 2D solid solution materials and perovskite, but also explores the vast application prospect of solid solution MXene in PSCs.

Improvement of biocompatible TA9/ZrO2 joint by AuSn20 filler: Interfacial microstructure, mechanical properties, and corrosion resistance

We propose employing AuSn20 filler to improve the bonding strength and corrosion resistance of TA9/Sn-6Zr/ZrO2 joint. To assess its feasibility, the interfacial microstructure, mechanical properties, and corrosion resistance of two TA9/ZrO2 joints were investigated. The results indicate that the addition of AuSn20 filler transforms the brazing seam from brittle and lower work function β-Sn and ZrSn2 phases to ductile and higher work function AuSn2 and AuSn4 phase, significantly improving the shear strength and corrosion resistance of the TA9/ZrO2 joint. The corrosion products of TA9/ZrO2 joints are mainly SnO and SnO2, with traces of SnCl2, SnCl4, and Zr(HPO4)2.

Unique S-scheme structures in electrostatic self-assembled ReS2-TiO2 for high-efficiency perfluorooctanoic acid removal

Perfluorinated compounds (PFCs), recognized as persistent organic pollutants, resist degradation in the environment due to the high bond energy of the C–F. Increasing carrier density via adopting electrostatic self-assembly strategy has been shown to effectively cleave C–F bonds. In this work, a unique S-scheme structure was fabricated by combining oppositely charged semiconductors, TiO2 and ReS2, through electrostatic self-assembly. The resulting 2 % ReS2-TiO2 composite achieved a photodegradation efficiency of 98 % for perfluorooctanoic acid (PFOA), considerably higher than the 62 % efficiency observed for pure TiO2. Additionally, the 2 % ReS2-TiO2 composite demonstrated broad applicability for the removal of other PFCs. The introduction of ReS2, with a lower work function than TiO2, could generate an internal electric field (IEF) to facilitate electron transfer from TiO2 to ReS2 under continuous irradiation and thereby enhance charge separation efficiency.

Improvement of N-type carbon nanotube field effect transistor performance using the combination of yttrium diffusion layer in HfO2 dielectrics and metal contacts

In this paper, we obtained n-type top-gate carbon nanotube (CNT) thin film field effect transistors (FET) with source/drain extensions structure through dielectrics optimization strategy, combining the yttrium layer with HfO2dielectric argon annealing process, and metal contacts. The mechanism for enhanced n-type conduction was explained as being due to the vertical diffusion of yttrium to the HfO2dielectric during argon annealing. This diffusion causes a bending of the energy band, which results in more positive fixed charges, and a reduction in the electron injection barrier between the low work function source/drain Cr electrode and CNT thin film. The optimized technology has great prospects for the low cost, large scale and high performance n-type CNT thin film FET to be used in integrated electronic devices.

Reversible Redox Probes to Determine Band‐Edge Locations and Dopant Concentrations of Nano‐TiO2 Thin‐Films: Settling the Mott‐Schottky Conundrum

AbstractKnowing the exact location of the semiconductor band‐edges is key for mechanistic insights into their use for water and CO2 photo/electrocatalysis. In this regard, a reliable strategy for nano‐semiconductors did not exist yet. We demonstrate the use of reversible redox probes on nano‐semiconductor electrodes to determine their band‐edge locations in aqueous solutions. Rectifying current‐potential (i‐U) characteristics with the high work function (i.e. more positive formal potential) Fe(CN)63−/Fe(CN)64− redox couple yielded the exact flatband potential at various pH whereas the reversible i‐U characteristics with the low work function (i.e. more negative formal potential) Ru(NH3)63+/Ru(NH3)62+ redox couple provided the conduction band‐edge location and dopant concentration for a 30 nm thin‐film n‐TiO2. The methodology can be extended to other nano‐semiconductors and serves as an alternative to and goes beyond the capabilities of the Mott‐Schottky procedure for bulk semiconductor electrodes.

Fine-Tuning Conformation of PEDOT Chains Enables Simultaneously Enhanced Conductivity, Work Function, Transmittance, and Waterproofness in PEDOT:PSS Interlayer for Highly Efficient and Stable Organic Photovoltaics.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely utilized as the hole transport layer (HTL) inorganic photovoltaics (OPVs) because of its low-temperature solution processing peculiarity, high optical transmittance, and excellent mechanical flexibility. However, the core-shell structure of PSS coated PEDOT results in relatively low conductivity, work function, transmittance and waterproofness of PEDOT:PSS interlayer, limiting the photovoltaic performance and stability of OPVs. Here, the conformation of PEDOT chains are regulated from helical benzoyl to linear quinone structure via incorporation of 2D Cd0.85PS3Li0.15H0.15dopant into the conventional PEDOT:PSS interlayer, promoting an interpenetrating network structure in PEDOT:PSS interlayer and forming an efficient hole transport channel from active layer to ITO electrode. Such features significantly improve the electrical conductivity, work function, and transmittance of PEDOT:PSS interlayer. In consequence, the maximum power conversion efficiency (PCE) of D18:L8-BO, PBDB-T:ITIC, as well as PTzBI-dF:L8-BO based OPVs ameliorated from 18.37%, 8.94%, and 15.80% to 19.26%, 10.00%, and 16.83%, respectively. The application of Cd0.85PS3Li0.15H0.15 doping PEDOT:PSS strategy demonstrates great potential for the development of strongly conductive, large-work-function, highly transparent, and excellent-waterproof PEDOT:PSS interlayer toward highly efficient and stable OPVs.

Modulation on Surface Termination Groups to Optimize the Adsorption Energy and Work Function of Nb2CTx for Enhanced Hydrogen Storage in Magnesium Hydride

AbstractExploring high‐performance catalysts for hydrogen storage in magnesium hydride (MgH2) is crucial but still a challenge. Herein, Nb2CTx with controllable surface termination groups is developed as an efficient catalyst and the bifunctional modulation (adsorption energy and work function) of different surface termination groups (F, O, OH, or defects) is explored. First, compared to F and O, the introduction of OH on the surface or the direct removal of functional groups both leads to a significant increase in the adsorption of H by Nb2CTx. Second, compared to the surface bare, OH‐rich Nb2CTx has a lower work function, making it easier for hydrogen to enter Mg/MgH2 from the Nb2CTx surface or escape from the Mg/MgH2 surface into the Nb2CTx, thus facilitating the hydrogen ad/desorption properties of MgH2, i.e., the rate‐determining step (RDS) shifts from penetration to diffusion. The Nb2CTx‐KOH‐catalyzed MgH2 with optimal surface termination groups, therefore exhibits a release of 6.56 wt.% H2 in 5 min at 250 °C, and 6.46 wt.% H2 uptake within 5 min at 150 °C. The dehydrogenation and hydrogen uptake activation energies show 49.5% and 60.1% enhancements over pristine MgH2. In addition, a storage capacity of 5.51 wt.% is maintained after 50 dehydrogenation/hydrogenation cycles.

Self-Diffusion Effect Assisted TiO2/Li3PO4 Electron Selective Passivating Contact in Silicon Solar Cells Approaching 23% Efficiency.

Carrier selective contacts with passivation effects are considered to have a significant influence on the performance of crystalline silicon (c-Si) solar cells. It is essential for electron selective contact materials to meet the requirements of ultra-low contact resistance and excellent passivation effects. This work introduces a stack layer of Lithium Phosphate (Li3PO4) /Titanium Dioxide (TiO2) as a new electron selective passivating contact. It is found that the stack achieves an impressive contact resistivity (ρc) of 0.128mΩcm2 on n-type c-Si substrates with resistivity ranging from 1 to 3Ωcm (14.6mΩcm2 for the n-Si/a-Si:H/Li3PO4/TiO2/Al contact). Furthermore, it effectively reduces the surface recombination parameter (J0) to less than 4fA by incorporating a 6nm a-Si:H(i) layer. The characterization of the n-Si/Li3PO4/TiO2 interface reveals that phosphorus diffusion into silicon plays a crucial role in achieving the ultra-low contact resistivity, while the presence of PO4 3- groups helps in fixing hydrogen atoms to maintain the desired chemical passivation effect. Finally, a silicon heterojunction solar cell (SHJ) with a rear full-area configuration of a-Si:H/Li3PO4/TiO2/Al is successfully demonstrated achieving an impressive power conversion efficiency of 22.89%. The result proves the efficacy of employing hydrogen-rich low-work function metal oxide stacks as electron selective passivating contacts.

Reversible Redox Probes to Determine Band-Edge Locations and Dopant Concentrations of Nano-TiO2 Thin-Films: Settling the Mott-Schottky Conundrum.

Knowing the exact location of the semiconductor band-edges is key for mechanistic insights into their use for water and CO2 photo/electrocatalysis. In this regard, a reliable strategy for nano-semiconductors did not exist yet. We demonstrate the use of reversible redox probes on nano-semiconductor electrodes to determine their band-edge locations in aqueous solutions. Rectifying current-potential (i-U) characteristics with the high work function Fe(CN)63-/Fe(CN)64- redox couple yielded the exact flatband potential at various pH whereas the reversible i-U characteristics with the low work function Ru(NH3)63+/Ru(NH3)62+ redox couple provided the conduction band-edge location and dopant concentration for a 30nm thin-film n-TiO2. The methodology can be extended to other nano-semiconductors and serves as an alternative to and goes beyond the capabilities of the Mott-Schottky procedure for bulk semiconductor electrodes.

Analysis and optimization of cesium dynamics for the HUST negative ion source

The high-density beam in the NBI negative ion source relies on surface production on the converter with low work function, which is facilitated by cesium injection. Maintaining the appropriate cesium conditions during the source operation sequence is essential for achieving optimal cesium coverage on the converter. To better understand cesium cycle in the source and to enhance beam production performance during operation sequences, analysis of cesium dynamics and optimization of cesium operation have been carried out. The analysis model is established based on the Monte-Carlo method with cesium sources, cesium transport and surface process during the operation sequence considered. Cesium distribution and converter surface coverage can be obtained from the model using input parameters from the HUST negative ion source. For the operation in the HUST negative ion source, the influence of temperature settings and time sequence is discussed, with suggested parameters for cesium injection proposed to achieve appropriate cesium coverage on converter surface through operation sequences.

Spontaneous built-in electric field in W-W2C@C heterostructure: Accelerating Sn2- directed migration in Li-S batteries

The commercialization of Li-S batteries is severely hindered by shuttle effect and sluggish redox reaction kinetics of LiPSs. Heterostructure can resolve the above shortcomings through the synergistic effect of adsorption and catalysis. However, long-chain LiPSs dissolving in electrolyte tend to cluster, resulting in low sulfur utilization and preventing kinetic conversion Thus, it is necessary to regulate the diffusion of Sn2− to achieve the directional diffusion from adsorbent to catalyst. Nevertheless, the design principle has not yet been clarified. W-W2C@C heterostructure with W of strong adsorption ability and high work function and W2C of excellent catalytic activity and low work function is designed by theoretical screening. Due to work function difference, this heterostructure controls the direction of the interface built-in electric field (BIEF), realizing the directional migration process of Sn2− from adsorptive W to catalytic W2C, thereby achieving a continuous “trapping-directional migration-conversion” reaction mechanism. The batteries have an excellent Li+ diffusion rate, high initial discharge specific capacity (1400.6 mAh/g at 0.2C), excellent rate capability (853.2 mAh/g at 2C), high reversible capacity (977.9 mAh/g after 150 cycles at 0.2C) and an extremely low capacity decay rate of 0.09 % per cycle after 300 cycles at 1C.

Electrochemical production of ammonia: Nitrate reduction over novel Cu-Ni-Al metallic glass nanoparticles used as highly active and durable catalyst

It is a great challenge to design and synthesize catalysts that can regulate both adsorption and desorption processes for electrocatalytic nitrate reduction to ammonia (NRA). Herein, amorphous Cu-Ni-Al nanometallic glasses (NG) were synthesized using a facile thermal evaporation coupled Joule heating method. The Cu50Ni25Al25-NG exhibits remarkable Faradaic efficiency (98.81 %) and NH3 yield-rate (211.14 μmol h−1cm−2) at an outstanding positive potential of −0.15 V vs. RHE. Aluminum atoms of low work-function when intercalated at different positions in Cu50Ni25Al25-NG enhance both adsorption and desorption processes during NRA. The oscillatory properties of surface potential detected by Kelvin-probe force microscopy demonstrate the diversity of active sites on Cu50Ni25Al25-NG. Two potential-regulated reaction mechanisms in NRA on the surface of Cu50Ni25Al25-NG were proposed using in-situ electrochemical Raman spectra. This work provides a new method for the preparation of multi-element NG enriched with low work-function metals and a new idea for the synthesis of synergistic catalytic-sites for NRAs.

Application Of Vanadyl Alkoxoacetylacetonate In Formation Of v2O5 Electrochromic Films

Crystal structure, morphology and electrochromic properties of V2O5 film, prepared using vanadyl alkoxoacetylacetonate as precursor, were studied. We have shown that the obtained vanadium pentoxide contains significant amount of V4+ cations, which is indicated by low electron work function among other things. This results in material possessing anodic electrochromism – coloring upon oxidation – with rapid bleaching process (1 s upon necessary potential application). Anodic coloration is observed in the whole visible light spectrum, as well as in near IR region up to 1100 nm. Obtained data show high prospects for approach to formation of V2O5-based films using vanadyl acetylacetonate as precursor and application of such films as components of smart windows and displays, optical properties of which could be controlled by electrical current application.

Synergistic promotion of reaction kinetics for LiPSs at high loadings by interfacial built-in electric field and sulfur vacancies of ternary heterostructure for high-performance Li-S batteries

The practical application of lithium-sulfur batteries is significantly impeded by the chaotic migration of lithium polysulfides, sluggish redox-reaction kinetics, and pronounced shuttle effect. Herein, a ternary heterostructure (MoS2-x/MoO2/CoP) is developed with a spontaneous built-in electric field (BIEF) and enriched sulfur vacancies. This heterostructure comprises MoS2-x, which has a high adsorption capability and work function; CoP, noted for its low work function and potent catalytic properties; and MoO2, which features a work function between that of MoS2-x and CoP and serves as a bridge with excellent electronic conductivity. An appropriate combination of the catalyst and adsorbent with sulfur vacancies controls the direction of the BIEF, realizing the “adsorption-directed migration-catalytic” reaction mechanism for sulfur species. Specifically, the synergetic effect of the BIEF and sulfur vacancies enhances electron migration from CoP to MoS2-x, which improves the lithium polysulfide (LiPSs) trapping and accelerates the directional migration of LiPSs to CoP, thereby enabling the efficient catalytic conversion of sulfur species. Consequently, batteries equipped with MoS2-x/MoO2/CoP interlayers that contain sulfur vacancies demonstrate an ultrahigh initial specific capacity of 1356.2 mA h g−1 at 0.2 C, maintaining a capacity of 708.3 mAh g−1 after 1000 cycles at 2 C. Even with sulfur loading increased to 7.13 mg cm−2, these batteries display an initial specific capacity of 7.2 mAh cm−2. This work provides a feasible approach for the rational design of vacancy-containing ternary heterostructure catalysts for commercial lithium-sulfur batteries.

Tip-induced local Fermi level alignment: A Stark shift in vacuum level in scanning tunneling microscope configurations

Electric fields in the junction of a scanning tunneling microscope (STM) are generally considered to have a negligible impact on the vacuum level (VL) of materials. We employed field emission resonance (FER) in the STM, combined with the triangular potential model, to measure the VL of the Ag(100) surface under varying electric currents. Unexpectedly, our results reveal that the VL exhibits a linear positive energy shift with increasing electric field strength. We suggest that this Stark shift in the VL arises from local Fermi level alignment induced by the STM tip. Additionally, we examined the VL of Ag islands grown on Cu(111) and Au(111) surfaces under different currents. Despite the Ag island having a lower work function than the Cu(111) and Au(111) surfaces, the energy shift in the VL with respect to the electric field on the Ag island is almost identical to that on the substrate under the same tip structure. This suggests that the Stark shift of the VL is insensitive to the work function. These findings are crucial for utilizing FER to measure local work function variations on surfaces, as the measured value is not influenced by the STM tip structure or the tunneling current, both of which can alter the electric field.

Cs/O, Cs/NF3, and Cs/Li/NF3 coadsorption on GaAs0.5P0.5 (001) β2(2×4) reconstruction surface: A first principle study

The activation process of p-type doped GaAs0.5P0.5 (001) β2(2 × 4) reconstruction surface is investigated based on first principle calculations. For Cs-only adsorption, the adsorption energy rises as the Cs coverage increases, and when the Cs coverage is at 0.75 ML, the work function hits its minimum. Cs/O and Cs/NF3 concurrent adsorption are conducive to increasing steadiness and lowering the work function of the reconstruction surface during the phase of high Cs coverage. The work function reaches its minimum when Cs coverage is 0.75 ML in Cs/O coadsorbed models while that occurs when Cs coverage is 1.00 ML in Cs/NF3 coadsorbed models. Results indicate that the Li atoms intercalation with low coverage in Cs/NF3 coadsorbed models is conducive to establishing dipole moments, strengthening stability, and lowering the work function. The optimal adsorption recipe is 6Cs/2Li/NF3, with which the surface owns the lowest work function and shows the most stable property.

Scaling of N-Type Field-Effect Transistors Based on Aligned Carbon Nanotube Arrays.

Wafer-scale aligned carbon nanotubes (A-CNTs) are promising candidate semiconductors for building high-performance complementary metal-oxide-semiconductor (CMOS) transistors for future integrated circuits (ICs). A-CNT-based p-type field-effect transistors (P-FETs) have demonstrated excellent performance and scalability down to sub-10 nm nodes. However, the development of A-CNT n-type FETs (N-FETs) lags far behind, in regard to their electronic performance and device scaling. In this work, we fabricated top-gated N-FETs based on A-CNTs with a scandium (Sc)-contacted source and drain. High-performance A-CNT N-FETs were demonstrated with record on-state current (Ion) exceeding 1 mA/μm and peak transconductance (gm) of 0.4 mS/μm. Interestingly, the A-CNT N-FETs exhibited abnormal scaling behavior owing to the lateral oxidation of low-work function source/drain contacts, leading to formidable challenges to scale both the gate length (Lg) and the contact length (Lc) at the same time. Understanding of the abnormal scaling behavior contributes to seeking solutions for high-performance A-CNT N-FETs, and it paves the way for future CNT CMOS digital IC technology.

Experimental Verification of Inter Relation between Fowler–Nordheim and Millikan–Lauritsen Plot in Chemically Synthesized Zinc Oxide System

AbstractCold cathode emission or cold field emission (CFE) is a purely quantum mechanical phenomenon and a phenomenon of wonder. The exact science behind the observed current (I)–voltage (V) is yet to be pin pointed. For instance, a good cold emitter is very reasonably supposed to have low work function and good conductivity whereas a carbon allotropes like diamonds have just the reverse in both the cases, i.e., it is insulating in nature having very wide band gap as well as high work function yet it is considered to be an efficient field emitter. Since early of 20th century, till its middle a number of groups have suggested different equations or relations that can adequately describe the experimental CFE I–V characteristics adequately. Although they all fundamentally follow an exponential law, but so far, the relation suggests by Fowler and Nordheim (F–N) is the most accepted one. However, there is another relationship suggested by Millikan and Lauritsen (M–L) which is in spite of being reasonable not so common now a day to use. This work revisits different popular approaches for analyzing cold emission data. With this aim, the experimental CFE data obtained for chemically synthesized zinc oxide nanorods are chosen. The proper phase formation of ZnO is confirmed by XRD study whereas FESEM shows the rod like morphology. EDX confirms the proper stoichiometric ratio for the sample. After detail analysis it is confirmed that the theoretically proposed relation between F–N and M–L experimentally holds good as well and thus it would not be wrong to analyze the CFE data by simple M–L theory.