H. Tang
Please Note
21 records found
1
Two-dimensional materials (2DMs)-based devices exhibit aerospace potential due to their superior properties. However, the operational reliability of 2DMs-based devices in space environments is significantly influenced by charged-particle radiation, necessitating rigorous ground-based radiation tolerance assessments. Current research on radiation effects in 2DMs is primarily experimental, yet such methodologies are inherently time-consuming, resource-intensive, and limited in throughput. To address these challenges, computational modeling and simulation techniques are increasingly being integrated with experimental characterization to accelerate materials design and unravel underlying physical mechanisms. This review systematically evaluates the state-of-the-art multiscale computational frameworks for 2DMs research, focusing on recent advancements, technical challenges, and emerging opportunities. A novel integrative approach is proposed, combining density functional theory, molecular dynamics, Monte Carlo, finite element analysis, and machine learning techniques. Particular emphasis is placed on addressing challenges in multiscale modeling, including accurate representation of complex phenomena across spatial and temporal scales under extreme environmental conditions. Conversely, opportunities for enhancing predictive capabilities are highlighted, with implications for expediting materials discovery in electronics, photonics, energy storage, catalysis, and nanomechanical systems. This comprehensive survey provides a strategic roadmap for future research directions in multiscale computational modeling of 2DMs, emphasizing interdisciplinary methodologies that bridge atomistic simulations with macroscale engineering applications. The insights presented herein aim to advance the development of radiation-hardened 2DMs-based devices for next-generation aerospace systems.
Corrosion protection is one of the most important issues when copper is applied in power electronics packaging as bonding wire, die attachment, interconnection, and DBC substrate. Covering a layer of corrosion-resistant encapsulation material is a worthy consideration to protect copper. In this paper, the corrosion-resistant effects of two organic encapsulation materials, polydimethylsiloxane (PDMS) and hexamethyldisiloxane (HMDSO), on the copper surface were performed by molecular dynamics simulations. Firstly, the Cu-coating bilayer models were constructed, and the binding performances of the encapsulation material/copper interface were evaluated through calculating their interaction energy, proving that the organic coatings can form interconnection on copper surface. Then, the diffusion processes of corrosive gas molecules (H2S, H2O and O2) into the copper layer under different coating conditions were simulated, and both coatings exhibited good corrosion protection performances. The above results indicate that both PDMS and HMDSO have promising potential for copper corrosion protection in power electronics packaging. This may provide some guidance for corrosion protection of copper material used in power electronics packaging.
Double-sided packages for heat dissipation are an efficient thermal management mechanism for power semiconductor devices. A fan-out panel-level packaging (FOPLP), as one of the double-sided forms, exhibits excellent electro–thermal characteristics and provides low stray inductance and thermal resistance. Besides, the temperature at each point within the structure is closely related to its thermo–mechanical properties and device reliability. However, thermal resistance is limited in describing the temperature distribution. Finite element analysis (FEA) requires time-consuming construction of 3D models. Therefore, to depict the temperature distribution of FOPLP rapidly and accurately, a numerical heat transfer model was proposed for the double-sided package structure. The solution was obtained from the steady-state thermal balance Laplace equation using the separation of variables method. Several boundaries were analyzed to determine the specific parameters in the model. Finally, the temperature field predicted by the derived numerical model was compared with finite element simulation results. The proposed model was consistent with both Silicon (Si) and Silicon Carbide (SiC) FOPLP structures within the error of 15 % at the center of the device, which verified the validity and accuracy of the numerical model for double-sided heat dissipation. The proposed models and results could contribute to the development of effective thermal design tools for double-sided thermal power modules.
In this paper, tin oxidation (SnO x )/tin-sulfide (SnS) heterostructures are synthesized by the post-oxidation of liquid-phase exfoliated SnS nanosheets in air. We comparatively analyzed the NO2 gas response of samples with different oxidation levels to study the gas sensing mechanisms. The results show that the samples oxidized at 325 °C are the most sensitive to NO2 gas molecules, followed by the samples oxidated at 350 °C, 400 °C and 450 °C. The repeatabilities of 350 °C samples are better than that of 325 °C, and there is almost no shift in the baseline. Thus this work systematically analyzed the gas sensing performance of SnO x/SnS-based sensor oxidized at 350 °C. It exhibits a high response of 171% towards 1 ppb NO2, a wide detecting range (from 1 ppb to 1 ppm), and an ultra-low theoretical detection limit of 5 ppt, and excellent repeatability at room temperature. The sensor also shows superior gas selectivity to NO2 in comparison to several other gas molecules, such as NO, H2, SO2, CO, NH3, and H2O. After X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscope, and electron paramagnetic resonance characterizations combining first principle analysis, it is found that the outstanding NO2 sensing behavior may be attributed to three factors: The Schottky contact between electrodes and SnO x/SnS; active charge transfer in the surface and the interface layer of SnO x/SnS heterostructures; and numerous oxygen vacancies generated during the post-oxidation process, which provides more adsorption sites and superior bandgap modulation. Such a heterostructure-based room-temperature sensor can be fabricated in miniaturized size with low cost, making it possible for large-scale applications.
Effects of Defect and Temperature on the Mechanical Performance of WS2
A Multiscale Analysis
This paper analyzes the mechanical properties of tungsten disulfide (WS2) by means of multiscale simulation, including density functional theory (DFT), molecular dynamic (MD) analysis, and finite element analysis (FEA). We first conducted MD analysis to calculate the mechanical properties (i.e., Young's modulus and critical stress) of WS2. The influence of different defect types (i.e., point defects and line defects) on the mechanical properties are discussed. The results reveal that WS2 has a high Young's modulus and high critical stress. Next, the effects of defect density and temperature on the mechanical properties of the material were analyzed. The results show that a lower defect density results in improved performance and a higher temperature results in better ductility, which indicate that WS2 can potentially be a strain sensor. Based on this result, FEA was employed to analyze the WS2 stress sensor and then fabricate and analyze the device for benchmarking. It is found that the FEA model proposed in this work can be used for further optimization of the device. According to the DFT results, a narrower band gap WS2 is found with the existence of defects and the applied strain. The proposed multiscale simulation method can effectively analyze the mechanical properties of WS2 and optimize the design. Moreover, this method can be extended to other 2D/nanomaterials, providing a reference for a rapid and effective systematic design from the nanoscale to macroscale.
Recent advances in 2D/nanostructured metal sulfide-based gas sensors
Mechanisms, applications, and perspectives
2D and nanostructured metal sulfide materials are promising in the advancement of several gas sensing applications due to the abundant choice of materials with easily tunable electronic, optical, physical, and chemical properties. These applications are particularly attractive for gas sensing in environmental monitoring and breath analysis. This review gives a systematic description of various gas sensors based on 2D and nanostructured metal sulfide materials. Firstly, the crystal structures of metal sulfides are introduced. Secondly, the gas sensing mechanisms of different metal sulfides based on density functional theory analysis are summarised. Various gas-sensing concepts of metal sulfide-based devices, including chemiresistors, functionalized metal sulfides, Schottky junctions, heterojunctions, field-effect transistors, and optical and surface acoustic wave sensors, are compared and presented. It then discusses the extensive applications of metal sulfide-based sensors for different gas molecules, including volatile organic compounds (i.e., acetone, benzene, methane, formaldehyde, ethanol, and liquefied petroleum gas) and inorganic gas (i.e., CO2, O2, NH3, H2S, SO2, NOx, CH4, H2, and humidity). Finally, a strengths-weaknesses-opportunities-threats (SWOT) analysis is proposed for future development and commercialization in this field. This journal is
Humidity sensors based on flexible sensitive nanomaterials are very attractive in noncontact healthcare monitoring. However, the existing humidity sensors have some shortcomings such as limited sensitivity, narrow relative humidity (RH) range, and a complex process. Herein, we show that a tin sulphide (SnS) nanoflakes-based sensor presents high humidity sensing behaviour both in rigid and flexible substrate. The sensing mechanism based on the Schottky nature of a SnS-metal contact endows the as-fabricated sensor with a high response of 2491000% towards a wide RH range from 3% RH to 99% RH. The response and recovery time of the sensor are 6 s and 4 s, respectively. Besides, the flexible SnS nanoflakes-based humidity sensor with a polyimide substrate can be well attached to the skin and exhibits stable humidity sensing performance in the natural flat state and under bending loading. Moreover, the first-principles analysis is performed to prove the high specificity of SnS to the moisture (H2O) in the air. Benefiting from its promising advantages, we explore some application of the SnS nanoflakes-based sensors in detection of breathing patterns and non-contact finger tips sensing behaviour. The sensor can monitor the respiration pattern of a human being accurately, and recognize the movement of the fingertip speedily. This novel humidity sensor shows great promising application in physiological and physical monitoring, portable diagnosis system, and noncontact interface localization.
Two-dimensional transition-metal dichalcogenides (TMDCs) such as MoS2 are potential channel materials for thin film transistor. Here, we report the effects of strain on the performance of the back-gated few-layer MoS2 thin film transistors (FL-MoS2 TFTs) with poly(acrylic acid) (PAA) dielectric layer. The devices exhibit high on/off ratio of 5600 and mobility of 7.07 cm/Vs. The electrical and optical characterizations were affected by the strain under bending conditions. The results show that the device exhibits quite stable mobility and photoswitching behavior under different bending radius, which is owing to the high deformability of MoS2 and PAA dielectric layer. Big bending radius enable improved photoresponsitivity due to the change of band gap of MoS2. The excellent bending performance of FL-MoS2 transistor presents potential applications in flexible and wearable electronics and optoelectronics.
In this paper, four composite coatings of nano-SnS/polyvinylbutyral (PVB), nano-MoS2/PVB, nano-SnS-Zn/PVB, and nano-MoS2-Zn/PVB were prepared, and their anti-corrosion mechanism was analyzed by experimental and theoretical calculations. The results of the electrochemical experiments show that the effect of nano-MoS2 on the corrosion protection performance of PVB coating is better than that of nano-SnS in 3% NaCl solution, and that the addition of Zn further enhances this effect, which is consistent with the results of weight loss measurements. Furthermore, the observation of the corrosion matrix by the field emission scanning electron microscope (FESEM) further confirmed the above conclusion. At last, the molecular dynamics (MD) simulation were carried out to investigate the anti-corrosion mechanism of the nanofillers/PVB composites for the copper surface. The results show that both nano-SnS and nano-MoS2 are adsorbed strongly on the copper surface, and the binding energy of nano-MoS2 is larger than that of nano-SnS.
This paper presents the anti-corrosion application of polyvinylbutyral/tin sulfide (PVB/SnS) composites for the first time, where the liquid-phase exfoliated (LPE) SnS nanosheets are uniformly embedded in the PVB matrix. The measurement results of the potentiodynamic polarization, the electrochemical impedance spectroscopy (EIS) and the scanning electronic microscopy (SEM) show that PVB/SnS composite coatings show the excellent corrosion protection behavior for copper under 3.0% NaCl solution. Besides, we investigated the anti-corrosion performance with different contents of SnS nanosheets. The results show that embedding 0.1 wt% SnS nanosheets in the PVB matrix can greatly improve the anti-corrosion properties of the coating due to the enhanced "Labyrinth effect" of the coatings. In addition, the results of the molecular dynamic analysis further show the high interaction energy between PVB/SnS composites and copper, which is attributed to the high aspect-ratio of LPE-SnS nanosheets. Moreover, the scratch tests reveal that the PVB/SnS composite coatings exhibit weak corrosion-promotion activity, indicating a promising potential application in the corrosion protection of the metal surface for ocean engineering. The methods for enhancing the inhibited corrosion-promotion activity of the semiconductor material SnS-based composite coatings could be expanded to other n-type and p-type semiconductors.
In this study, the structural, electronic and optical properties of a tungsten disulfide (WS2) hybrid with indium-gallium-zinc-oxide (IGZO) heterostructures were investigated based on density functional theory (DFT) calculations. According to the results of binding energy, charge density difference and electron localization function of heterostructures, we found that the WS2 and IGZO monolayers were bound to each other via non-covalent interactions with large binding energy. The calculated results illustrate that the AAii stacking pattern has an indirect band gap of 1.643 eV, while AAi and AB stacking patterns have maximum direct-gaps of 1.102 eV and 1.234 eV, respectively. Under an external E-field and mechanical strain, the response of the energy gap of the WS2/IGZO heterostructure monotonically decreased over a wide range, even with a semiconductor-metal transition. In addition, we investigated the optical properties of the heterostructure and found that it exhibits a much broad spectral responsivity (from visible light to deep UV light) and a more pronounced optical absorption than WS2 and IGZO monolayers. Moreover, the tensile strain could weaken the photoresponse of the heterostructure to the UV light and enhance the response for the visible light; under compressive strain, the heterostructure showed a strong absorption peak in the UV light. Meanwhile, a red-shift was observed under an external strain. All these unique and tunable properties indicate that the WS2/IGZO heterostructure is a good candidate for nanoelectronic and photoelectronic devices, such as field-effect transistors, flexible sensors, photodetectors and photonic devices.
In this work, a thin-film transistor gas sensor based on the p-N heterojunction is fabricated by stacking chemical vapor deposition-grown tungsten disulfide (WS2) with a sputtered indium-gallium-zinc-oxide (IGZO) film. To the best of our knowledge, the present device has the best NO2 gas sensor response compared to all the gas sensors based on transition-metal dichalcogenide materials. The gas-sensing response is investigated under different NO2 concentrations, adopting heterojunction device mode and transistor mode. High sensing response is obtained of p-N diode in the range of 1-300 ppm with values of 230% for 5 ppm and 18 170% for 300 ppm. On the transistor mode, the gas-sensing response can be modulated by the gate bias, and the transistor shows an ultrahigh response after exposure to NO2, with sensitivity values of 6820% for 5 ppm and 499 400% for 300 ppm. Interestingly, the transistor has a typical ambipolar behavior under dry air, while the transistor becomes p-type as the amount of NO2 increases. The assembly of these results demonstrates that the WS2/IGZO device is a promising platform for the NO2-gas detection, and its gas-modulated transistor properties show a potential application in tunable engineering for two-dimensional material heterojunction-based transistor device.
SnS monolayer has sparked intensive attention due to its unique electronic and optical properties. We systemically investigate the electronic properties of SnS by first-principles calculation. Our results show that the monolayer possesses indirect bandgap. We further perform mechanical strain to adjust the electronic structure of SnS, corresponding results display an indirect-direct transition of band gap when subjected to proper external strain. Interestingly, the bandgap can be linearly increase under tensile strain from 0% to 7%, while the bandgap reduced under compressive strain. For biaxial strain, the band gap changes more remarkable compared with that under uniaxial strain (zigzag x or armchair y direction). Furthermore, we demonstrate that the gas molecules (CO2, H2S, C2H4 and NO2) adsorption property on SnS monolayer can be modulated through biaxial strain. Especially, the NO2 adsorption is further enhanced on the SnS monolayer under biaxial tensile strain. These results may provide guidance for fabricating SnS-based strained gas sensor.
Germanene on single-layer ZnSe substrate
Novel electronic and optical properties
In this work, the structural, electronic and optical properties of germanene and ZnSe substrate nanocomposites have been investigated using first-principles calculations. We found that the large direct-gap ZnSe semiconductors and zero-gap germanene form a typical orbital hybridization heterostructure with a strong binding energy, which shows a moderate direct band gap of 0.503 eV in the most stable pattern. Furthermore, the heterostructure undergoes semiconductor-to-metal band gap transition when subjected to external out-of-plane electric field. We also found that applying external strain and compressing the interlayer distance are two simple ways of tuning the electronic structure. An unexpected indirect-direct band gap transition is also observed in the AAII pattern via adjusting the interlayer distance. Quite interestingly, the calculated results exhibit that the germanene/ZnSe heterobilayer structure has perfect optical absorption in the solar spectrum as well as the infrared and UV light zones, which is superior to that of the individual ZnSe substrate and germanene. The staggered interfacial gap and tunability of the energy band structure via interlayer distance and external electric field and strain thus make the germanene/ZnSe heterostructure a promising candidate for field effect transistors (FETs) and nanoelectronic applications.
In this paper, the heat transfer performance of the multi-chip (MC) LED module is investigated numerically by using a general analytical solution. The configuration of the module is optimized with genetic algorithm (GA) combined with a response surface methodology. The space between chips, the thickness of the metal core printed circuit board (MCPCB), and the thickness of the base plate are considered as three optimal parameters, while the total thermal resistance (Rtot) is considered as a single objective function. After optimizing objectives with GA, the optimal design parameters of three types of MC LED modules are determined. The results show that the thickness of MCPCB has a stronger influence on the total thermal resistance than other parameters. In addition, the sensitivity analysis is performed based on the optimum data. It reveals thatRtot increases with the increased thickness of MCPCB, and reduces as the space between chips increases. The effect of the thickness of base plate is far less than that of the thickness of MCPCB. After optimization, three types of MC LED modules obtain lower Tj andRtot. Moreover, the optimized modules can emit large luminous energy under high-power input conditions. Therefore, the optimization results are of great significance in the selection of configuration parameters to improve the performance of the MC LED module.
Thermal conductivity of functionalized graphene-polymer nanocomposite
A non-equilibrium molecular dynamics study
Heat transfer across thermal interface material, such as graphene-polymer composite, is a critical issue for microelectronics thermal management. To improve its thermal performance, we use chemical functionalization on the graphene with hydrocarbon chains in this work. Molecular dynamics simulations are used to identify the thermal conductivity of monolayer graphene and graphene-polymer nanocomposites with and without grafted hydrocarbon chain. The influence of functionalization with hydrocarbon chains on the interfacial thermal conductance of graphene-polyethylene nanocomposites was investigated using a non-equilibrium molecular dynamics (NEMD) simulation. We also study the effects of the graft density (number of hydrocarbon chain) on the thermal conductivity of graphene and the nanocomposite.
Overdriving reliability of chip scale packaged LEDs
Quantitatively analyzing the impact of component
Nitrogen Dioxide Gas Sensor Based on Monolayer SnS
A First-Principle Study
The sensing behavior of monolayer tin sulfide (SnS) for four gas molecules (NH3, NO2, CO, and H2O) are studied by the first-principle calculation based on density-functional theory. We calculate adsorption energy, adsorption distance, and Hirshfeld charge to estimate the adsorption ability of monolayer SnS for these gas molecules. The results demonstrate that all the gas molecules show physisorption nature. We further calculate the current-voltage (I -V ) curves using the nonequilibrium Green's function formalism for evaluating the NO2 gas sensing properties. The monolayer SnS is found to be strongly sensitive to NO2 molecule dependent on moderate adsorption energy, excellent charge transfer, and significant change of I -V property before and after gas adsorption. Therefore, we suggest that monolayer SnS can be a prominent candidate for application as NO2 gas sensor.