Photoresist Research Articles

Highly Durable Chemoresistive Micropatterned PdAu Hydrogen Sensors: Performance and Mechanism.

Hydrogen (H2) is a promising alternative energy source for Net-zero, but the risk of explosion requires accurate and rapid detection systems. As the use of H2 energy expands, sensors require high performance in a variety of properties. Palladium (Pd) is an attractive material for H2 detection due to its high H2 affinity and catalytic properties. However, poor stability caused by volume changes and reliability due to environmental sensitivity remain obstacles. This study proposes a micropatterned thin film of PdAu with optimized composition (Pd0.62Au0.38) as a chemoresistive sensor to overcome these issues. At room temperature, the sensor has a wide detection range of 0.0002% to 5% and a fast response time of 9.5 s. Significantly, the sensor exhibits excellent durability for repeated operation (>35 h) in 5% H2 and resistance to humidity and carbon monoxide. We also report a negative resistivity change in PdAu, which is opposite to that of Pd. Density functional theory (DFT) calculations were performed to investigate the resistance change. DFT analysis revealed that H2 penetrates specific interstitial sites, causing partial lattice compression. The lattice compression causes a decrease in electrical resistance. This work is expected to contribute to the development of high-performance H2 sensors using Pd-based alloys.

Impact of passivation on GaS nanoflakes: A study on stability, electronic, spectroscopy, and photocatalytic properties

This study uses first-principle calculations to investigate the properties of pristine and passivated gallium sulfide nanoflakes. Passivation significantly enhances stability, with fluorinated nanoflakes being the most stable and pristine nanoflakes the least stable, having formation energies of −0.058 eV/atom and −0.009 eV/atom, respectively. The pristine and passivated nanoflakes show semiconducting band gap, which lies in a visible region. Hydrogenated nanoflakes exhibit the largest band gap of 3.62 eV, making them highly suitable for photocatalysis, while fluorine and chlorine passivation result in band gaps of 3.16 eV and 3.01 eV. Scanning tunneling microscopy reveals distinct topographical features for each passivated nanoflake, affecting their electronic properties, including negative differential conductance, making it suitable for advanced switching devices and sensors. The quantum capacitance value of 815 µF/cm2 for chlorinated nanoflakes suggests that passivated nanoflakes could be beneficial for supercapacitor applications. Spectroscopic studies show that passivation changes the infrared spectrum and moves absorption spectra from the ultraviolet to the visible range. The hydrogenated nanoflakes are found ideal for water splitting, and adjusting the pH can further optimize its photocatalytic performance. These findings highlight the potential of passivated nanoflakes in photovoltaics, biomedical imaging, photocatalysis, and advanced technological devices.

Resistance to anti-smoking messages related to the higher smoking stigma of Korean female smokers.

The degree of perceived smoking stigma can differ, based on various factors such as gender; this may influence the effect of smoking cessation interventions, including denormalization. This study investigates the gender differences in smoking stigma recognized by Korean smokers and explores the effect of these differences on the success of smoking cessation messages that aim to initiate an identity crisis among smokers. It aims to contribute to effective smoking cessation intervention strategies for female smokers. The smoker-gender Implicit Association Test (IAT) was used to measure gender-based smoking stigma; the test comprised photos of people smoking, with positive and negative descriptors. Participants were 120 smokers aged 19-35 years (60 males and 60 females). Participants' cognitive attitudes toward smoking and cessation intentions were assessed at baseline. To investigate the effect of social stigmatization on smokers, participants were asked to watch anti-smoking campaigns that stigmatized either smoking behavior or smokers' self-identity. Cognitive attitudes and cessations intention were used to show differences in gender and message conditions. The IAT D-score showed that female smokers perceived other female smokers significantly more negatively than they did male smokers, suggesting a higher level of smoking stigma. Female smokers in the socially stigmatizing condition reduced their negativity toward smoking less than those who were not stigmatized. Moreover, cessation intentions did not improve when female smokers received identity-threatening messages, indicating that female smokers tended to resist stigmatizing messages. These findings provide empirical evidence that the gender of Korean smokers is significantly related to differences in smoking stigma. The negative perception and resistance responses of female smokers shown in this study are consistent with the findings of previous studies on the stigma of substance use disorders and addiction. High smoking stigma can also be a risk factor in anti-smoking interventions, including health communication; therefore, these findings should be interpreted with caution.

Sub-Boltzmann Switching, Hysteresis-Free Charge Modulated Negative Differential Resistance FinFET.

The ever-increasing power consumption in integrated circuits has raised concerns about the relentless doubling of transistor density in chips and cost drop per combinational/sequential circuits. To address the physical limit of thermionic emission carrier transport (i.e., subthreshold swing >60 mV/decade at 300 K), alternative charge-transport mechanisms or the implementation of functional substances have been attempted but without appreciable success. One such choice is to take advantage of negative differential resistance with the activation of localized electrons or migration of atom and oxygen vacancies to extend the capabilities of Si-transistors. However, inconsistency in current during forward/reverse bias sweep is confronted as a notable weak point. This work proposes an eye-catching solution to modulating potential distribution between a resistance switching layer and a transistor by employing charge trapping within a hafnium zirconium oxide layer. This approach introduces features advancing the potential of "More Moore" technologies.

Negative Differential Resistance with Ultralow Peak-to-Valley Voltage Difference in Td-WTe2/2H-MoS2 Heterostructure.

Negative differential resistance (NDR) devices with a low peak-to-valley voltage difference (ΔV) exhibit a high cut off frequency and low power consumption efficiency, which is significant for fabricating high-performance oscillators. However, achieving an ultralow ΔV is challenging. In this work, we report the first construction of an NDR device utilizing a van der Waals heterostructure composed of semimetallic Td-WTe2 and semiconducting 2H-MoS2. Our findings reveal that the narrow energy region of the decreasing density of states (DOS) above the Fermi level of WTe2 acts as a narrow band gap, facilitating type-III band alignment with MoS2 and enabling band-to-band tunneling-based NDR transport. Notably, the NDR device exhibits an ultralow ΔV of approximately 0.01 V, which is at least an order of magnitude lower than previously reported values. This work not only introduces a new approach for NDR device fabrication but also provides new insights into the pivotal role of Td-WTe2 in NDR transport.

Observation of voltage dependent negative differential resistance (NDR) in SnS2-GO nanocomposites

This study investigates the structural, optical, and electrical properties of tin disulfide (SnS2) and SnS2-graphene oxide (GO) nanosheets synthesized via chemical bath deposition method (CBD). Structural characterization confirms the formation of hexagonal crystal phases with nanosheet morphology. It shows a well distribution of nanosheet average square sizes of 10 nm for SnS2 and 6 nm for SnS2-GO. Optical analysis shows blue shifts in absorption edges compared to bulk SnS2, attributed to quantum confinement effects. Photoluminescence emission peaks exhibit different energy levels in SnS2-GO originated to native defects. The composites show a sharp reduced of PL intensity due to enhanced charge carrier separation. Electrical measurements on SnS2-GO thin films demonstrate negative differential resistance (NDR) behavior in both planar and sandwich contact configurations, suggesting electron injection/extraction mechanisms. The NDR phenomenon exhibits a dependence on voltage scan rate, indicating the involvement of electronic and ionic elements in charge transport mechanisms. Overall, this study provides insights into the NDR properties of SnS2-GO nanocomposite, laying the groundwork for their potential applications in optoelectronics and nanoelectronics.

Effect of Cl2 Radical on Dry Development of Spin-Coated Metal Oxide Resist.

In this study, the effects of Cl2 radicals on dry development of spin-coated metal oxide resist (MOR) and changes in its surface binding states were investigated to verify the mechanism of dry development. Dry development characteristics of tin hydroxide (Tin OH), which is one of the MOR candidates for next generation lithography, were investigated as functions of process time and temperature using a Cl2 radicals source. Non-UV-exposed Tin OH film showed a linear etch rate (1.77 nm/min) from the initial thickness of ∼50 nm, while the UV-exposed film showed slower etch behavior (1.46 nm/min) in addition to the increase of film thickness for up to 3 min during the Cl2 radical dry development. UV-exposed photoresist (PR) contained more oxygen (Sn-O bonding) in the film due to the removal of butyl compounds from the clusters during the UV exposure process. Therefore, due to the lower reaction of chlorine radicals with Sn-O in the UV-exposed Tin OH than the other bindings, the non-UV-exposed PR was preferentially removed compared to the UV-exposed PR. As the temperature decreases, the overall etch rate decreases, but the difference in etch rate between exposed and unexposed Tin OH becomes larger. Finally, at a substrate temperature of -20 °C, the non-UV-exposed Tin OH with a thickness of 50 nm was completely removed, while ∼30 nm thick PR remained for UV-exposed Tin OH. Eventually, a negative tone development was possible with Cl2 radical plasma due to the difference in activation energy between the UV-exposed and non-UV-exposed films. It is believed that dry development using Cl2 radicals will be one of the most important process techniques for next-generation patterning to remove problems such as pattern leaning, line edge roughness, residue, etc., caused by wet development.

Upheaval of Negative Dielectric Permittivity and Semiconductor to Metallic Transition in a Thermally Induced Sn-Doped β-Ga2O3 (-201) Single Crystal.

Thermally induced dielectric and conductivity properties of an Sn-doped β-Ga2O3 (-201) single crystal were investigated by frequency-domain impedance spectroscopy in the frequency window from 100 Hz to 1 MHz with temperatures between 293 and 873 K. The (-201) plane-orientated single crystalline nature and the presence of an Sn dopant in β-Ga2O3 were confirmed by X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy. Two different trends of impedance spectra have been discussed by the modulation of relaxation times and semiconductor to metallic transition after ∼723 K due to activation of a significant number of Sn dopants and their movements with temperature. The negative impedance values were encountered in the Nyquist plots (Z' vs Z″) after 573 K and constitute a reverse movement after 723 K with temperature. The average normalized change (ΔZ'/Δf)/Z0 of impedance exhibits a broad downward relaxation plateau near 723 K, indicating a weak electrical transition. The increases in the positive value of the dielectric constant (εr') below a percolating threshold temperature 573 K is attributed to the interfacial and dipolar polarizations, and the plasma oscillation of delocalized electrons governed by the Drude theory is responsible for the negative dielectric constant above 573 K. The 3D projections of the real dielectric constant create a sharp downward sinkhole near 723 K, indicating the existence of negative dielectric permittivity. The electrical conductivity dramatically changes its trends after 523 K and confirms a transition from hopping conduction (dielectric or semiconductor) following Jonscher's power law to metallic conduction by Drude theory. Below the percolating threshold temperature, a nonoverlapping small polaron tunneling conduction mechanism was unveiled with defect-induced activation energy of 0.21 eV. The Sn-doped β-Ga2O3 exhibits unique and tailored electromagnetic responses with temperatures that can be associated with a variety of applications in electromagnetic wave manipulations, cloaking devices, antennas, sensors, medical imaging, seismic wave propagation, etc.

Axon-like active signal transmission

Any electrical signal propagating in a metallic conductor loses amplitude due to the natural resistance of the metal. Compensating for such losses presently requires repeatedly breaking the conductor and interposing amplifiers that consume and regenerate the signal. This century-old primitive severely constrains the design and performance of modern interconnect-dense chips1. Here we present a fundamentally different primitive based on semi-stable edge of chaos (EOC)2,3, a long-theorized but experimentally elusive regime that underlies active (self-amplifying) transmission in biological axons4,5. By electrically accessing the spin crossover in LaCoO3, we isolate semi-stable EOC, characterized by small-signal negative resistance and amplification of perturbations6,7. In a metallic line atop a medium biased at EOC, a signal input at one end exits the other end amplified, without passing through a separate amplifying component. While superficially resembling superconductivity, active transmission offers controllably amplified time-varying small-signal propagation at normal temperature and pressure, but requires an electrically energized EOC medium. Operando thermal mapping reveals the mechanism of amplification—bias energy of the EOC medium, instead of fully dissipating as heat, is partly used to amplify signals in the metallic line, thereby enabling spatially continuous active transmission, which could transform the design and performance of complex electronic chips.

The negative differential resistance of nitrogen implanted TiO2

The microstructure and negative differential resistance (NDR) effect of nitrogen implanted rutile TiO2 were investigated by measuring the XPS, Raman spectra and current voltage curves. It was found that the light illumination has large influence on the NDR effect. Under the illumination of 60 mW laser light, a large NDR with a small electric field (1250 V/cm) is obtained. This electric field is about three orders smaller than that reported in literature (1×106 V/cm). The electric field induced tunneling is the possible mechanism of electric transport at higher field region. The NDR is thought to be related to the light and nitrogen dopant induced reaction including the destroying of water, the scavenging of electron, and the surface oxidation transform of non-stoichiometric TiO2−x to stoichiometric insulating state. The results of this paper are not only useful in understanding the mechanism of NDR, but also useful in providing an effective method in manipulation NDR.

The transport properties and new device design: A case of doped armchair blue phosphorene nanoribbons

We design two p-n nanojunctions based on S- and Si- atoms doped armchair blue phosphorene nanoribbons (aBPNRs) including two semi-infinite electrodes and a scattering region and investigate their electronic and transport properties. Our calculations are based on density functional theory incorporated non-equilibrium Green's function approach. In impure aBPNRs, S/Si atoms substituted doping could greatly enhance the conductivity, and the S/Si doped aBPNRs show metallic properties. Based on the doped aBPNRs, devies D1 and D2 are constructed where the scattering region of D1 is formed by direct expansion of two electrodes, while the scattering region of D2 includes two undoped unit cells as buffer. The transport calculations show that both of D1 and D2 show excellent negative differential resistance (NDR) effect at low bias and significant rectification effects at high bias. Moreover, whether there is buffer in the scattering region has a great influence on the magnitude of current of the devices. Although the current of the device D1 without buffer is generally higher than that of the device D2, the NDR and rectification effects of D2 are better than D1 in terms of peak-to-valley ratio and rectification rate. These transport behaviors can be explained by the evolution of the transmission spectra, frontier molecular orbital and the symmetry matching between the band structures of the electrodes. This indicates that aBPNRs are a promising candidate for the future application of multi-functional electronic devices.

Photoinduced Negative Differential Resistance at a Graphene/Silicon Interface: A Nonadiabatic Quantum Molecular Dynamics Study.

The oscillatory retinal neuron (ORN) is a promising technology for achieving in-sensor cognitive image computing without external power. While its operation is based on photoinduced negative differential resistance (NDR) at a graphene/silicon interface to directly convert the incident optical signal into voltage oscillations, the optoelectronic mechanism of the NDR remains elusive. Here, nonadiabatic quantum molecular dynamics simulations show that the interplay of band alignment and charge transfer rates of photoexcited carriers at varying applied voltages gives rise to NDR at a graphene/silicon interface under illumination. Such intrinsic NDR at an interface, along with extrinsic circuit-level factors, could enable the much needed rational design of desired image computing functionality of ORN devices in the era of ubiquitous AI on edge devices.

Diffusion across a concentration step: Strongly nonmonotonic evolution into thermodynamic equilibrium

Dynamical and statistical behaviour of the ionic particles in dissolved salts have long been known, but their hydration shells still raise unsettled questions. We engineered a “diffusion tunnel diode” that is structurally analogous to the well-known Esaki diode, but now concentration gradients serve as generalized voltages and the current means particle flow. In an equipartition sense, the hydrated ions enter a cavity as individual particles and later, upon increase of their concentration therein, they lose water molecules that henceforth are particles of their own. These temporarily attached water molecules thus are the tunnel current analogue. Unlike the original tunnel diode, our negative differential resistance has implications for the second law of thermodynamics, due to thermal effects of changes in the hydration shells.

Design and test of a contactless damper for HTS maglev systems via electromagnetic shunt dampers

High-temperature superconducting (HTS) maglev system is promising to become the future high-speed transport due to its numerous advantages. However, the low-damping dynamic characteristics of superconductors make the system vulnerable to external disturbances, which present a significant challenge to its implementation. To enhance the vibration attenuation effect of the HTS maglev system, a non-contact damper that employs electromagnetic shunt damping (EMSD) and negative resistance is incorporated into the HTS maglev system. This study elucidates the principles of EMSD and negative resistance, and establishes the governing equations to describe the behavior of the HTS maglev model equipped with EMSD. Subsequently, the EMSD coupling coefficients are analysed via the finite element method (FEM) under varying conditions. Finally, a dedicated vibration test rig is designed and fabricated to validate the effectiveness of the proposed damper. The results demonstrate that the proposed damper, in combination with negative resistance, is capable of effectively suppressing vibration in HTS maglev systems. The maximum acceleration of the test model can be reduced by 86% compared with the original system without the damper. This work may provide valuable guidance for future practical implementations.

Sensing-performance improvement of 2D MoSH based gas sensors for detecting NO, NO2, and NH3 gas molecules

Nitrogen group oxide is one of the major pollutants in the air, and its accurate and rapid detection is essential for environmental protection and human health. Therefore, it is of great significance to develop high-performance new line sensor for Nitrogen group oxide. Here, we investigate the potential of monolayer 2D MoSH materials as candidates for NO gas sensing using a combination of density functional theory and non-equilibrium functions to construct nanodevices based on MoSH monolayer, and theoretically study the adsorption behavior of MoSH monolayer to NO, NO2, and NH3 gas molecules. The results indicate that MoSH monolayer exhibit metallicity, and nanodevices based on 2D MoSH monolayer exhibit anisotropic transport properties and significant negative differential resistance effects(NDR). More interestingly, gas sensors based on MoSH monolayers exhibit typical chemical adsorption of NO, NO2, and NH3 gas molecules, and the anisotropic transport properties still maintain, but significant differences of sensitivity appear for these three gas molecules. Specifically, the MoSH based gas sensor has the highest sensitivity to NO, reaching 93.1% and 76.3% along the armchair and zigzag directions, respectively. These results show that 2D MoSH monolayer is an excellent gas-sensing material with excellent application prospects for NO gas detection.

Analysis of the Stability and System Participation Factors of Grid-Connected Converters

When the sources of renewable energy and numerous power electronic gadgets are introduced into the power system, which is related to the negative resistance features of power electronic gadgets, the power system with high power electronics often exhibits weak inertia. Also the stability of multi-converter grid-connected systems is adversely affected. To address these issues, a process of small disturbance stability analysis is proposed in this paper for the grid-connected systems of multiple grid-forming converters based on impedance ratio criterion. The Nyquist trajectory map of the system ratio of impedance in the complex plane is used in the suggested analytical method to estimate the quantity of RHPs in the right half-plane of the system, and the stability at the common points of the system is evaluated against the Nyquist criterion. In addition, the instability of grid-forming converters in grid-connected systems is reproduced by using grid-forming converters state space equation. Unlike the traditional methods of analysis, the method proposed in this paper can be applied to specifically judge the key equipment or control link of instability of the system, which provides guidance on optimizing the parameters of the system. Finally, simulation analysis is conducted to confirm that the model is accurate and that the proposed approach is applicable.

Dry etch performance of Novolak-based negative e-beam resist

Electron beam lithography (EBL) is pivotal for micro- and nanoscale fabrication, offering sub-micron precision. This study explores the utilization of the Novolac-based negative resist AR-N 7520 for EBL and its potential as an etch mask for reactive ion etching (RIE) of silicon. Recent comparisons of negative EBL resists have revealed promising results for AR-N 7520 in terms of resolution and adaptability with other lithography techniques. In this article, we conduct an exploration of patterning of AR-N 7520 (new) for EBL, addressing key parameters in achieving optimal patterning fidelity. Furthermore, we investigate its compatibility with RIE processes, aiming to provide insights into its effectiveness as an etch mask for creating sub-micron silicon structures. Experimental results show that optimal e-beam dose with 100 kV exposure is 300–350 μC/cm2. Selectivity of around 9:1 can be achieved by optimizing etching parameters for a continuous etch and higher than 14:1 for a cyclic etch process.

The features of magnetotransport properties of the Mn δ-doped GaAs structure with multiple conduction channels

The work examines the features of the magnetotransport and magnetooptical properties of a GaAs structure with a Mn δ-layer located near an In0.25Ga0.75As/GaAs quantum well with high charge carrier mobility. It is shown that in the initial structure, conduction occurs predominantly in the quantum well region, that leads to the dominance of magnetotransport phenomena of a Lorentzian nature (ordinary Hall effect and positive magnetoresistance). After suppression of the conduction channel through the quantum well using ion irradiation, an anomalous Hall effect and negative resistance are observed. It has been established that the experimental magnetic field dependences of the Hall resistance in ferromagnetic nanostructures with multiple conduction channels may not reflect the real magnetic properties of the structures.

Simulation study on temperature characteristics of AlN/ β-Ga2O3 HEMT

This paper reports a comprehensive analysis of temperature on DC and AC characteristics of AlN/β-Ga2O3 HEMT. As the temperature increases from 300 °C to 500 °C, the drain current (IDS) decreases by 50 %, leading to a 50 % decrease in transconductance (gm) without self heating effect. This decrease in maximum gm further resulted in a significant reduction of 49 % in the cut-off frequency (fT). Incorporating the self-heating effect, while the threshold voltage (Vth) remains unaffected, the maximum gm experiences a marked decrease. At 300 °C, the decrease reaches 58 %, while at 500 °C, the decrease is 36 %. Additionally, the saturation IDS shows a negative differential resistance phenomenon. Furthermore, the decrease at 300°Cin fT reaches 45 %, while at 500 °C, the decrease is 30 %. The main reason for the performance degradation caused by self heating effect at low temperatures is that the peak temperature at the channel of the device increases more significantly at low temperatures, resulting in a more significant decrease in mobility.

Bioinspired polydopamine coated nanopore nanofluidic unijunction transistor exhibiting negative differential resistance and ion current oscillation

Bioinspired polydopamine coated nanopore nanofluidic unijunction transistor exhibiting negative differential resistance and ion current oscillation