arXiv subjects

Zahra Shomali

Publications and source records attributed to Zahra Shomali.

14 recordsLinked to original sources

arXiv2025

Thermal Transport and Application Reassessment of ThSi$_2$N$_4$ Monolayer: From FET Channel to Thermoelectric Material

The two-dimensional M$_2$Z$_4$ materials are proposed as suitable replacements for silicon channels in field-effect transistors (FETs). In the present work, the ThSi$_2$N$_4$ monolayer from the family, with the very appropriate electron mobility, is thermally investigated using the non-equilibrium Monte Carlo simulation of the phonon Boltzmann transport equation. The reliability of the MOSFET with the ThSi$_2$N$_4$ channel has been reassessed and determined to be low due to the high maximum temperature achieved. The phonon analysis is performed and reveals that the dominant contribution of fast and energetic LA and also slow and low energy ZA phonons alongside the minor participation of the TA phonons is responsible for the peak temperature rise reaching 800 K. This finding presents that the ThSi$_2$N$_4$ monolayer is not a good candidate for replacing as silicon channel but alternatively is capable of generating a significant temperature gradient, which makes it, a suitable candidate for using as a thermoelectric material in thermoelectric generators.

cond-mat.mes-hall↗

arXiv2025

Heat Dissipation and Thermoelectric Performance of InSe-Based Monolayers: A Monte Carlo Simulation Study

Using nonequilibrium Monte Carlo simulations of the phonon Boltzmann transport equation, we study transient heat transfer in five indium-based two-dimensional monolayers: Janus monolayers In$_2$SeTe and In$_2$SSe, pristine InSe, and InSe under 4$\%$ and 6$\%$ tensile strain. In this work, the potential of these materials for energy conversion in thermoelectric generators and hotspot control in metal-oxide-semiconductor field-effect transistors is investigated. A promising option for an effective heat dissipation and enhanced transistor reliability is found to be a strained InSe, which shows the lowest peak temperature during the heating among the studied materials. On the other hand, with a high Seebeck coefficient, low thermal conductivity, and an improved figure of merit, the Janus In$_2$SeTe monolayer, compensates for its increased phonon scattering to reach the maximum temperature, making it a potent thermoelectric material. Our findings emphasis the importance of strain engineering and structural asymmetry in tuning phonon transport, enabling material optimization for next-generation nanoelectronic and energy-harvesting devices.

physics.app-ph↗

arXiv2025

The Non-Local Dual Phase Lag Model of Heat Conduction in a Silicon Metal-Oxide-Semiconductor Field-Effect Transistor

As the transistors and consequently the chips are getting smaller, the accurate investigation of heat transport at micro/nanoscale, becomes an important issue of concern. This is due to an increase in the energy consumption and the leakage currents as a result of the miniaturization which requires taking care of the thermal behavior to make sure that the device is working in the threshold temperature regime. The current work deals with a two-dimensional framework, incorporating the nonlocality in space, for more accurate investigation of the nanoscale heat transport using the lower computational cost phenomenological macroscopical Dual Phase Lag (DPL) method. The non dimensional non-locality parameter γ, which indicates the strength of the non-locality, is embedded through the modified DPL model named as nonlocal DPL. It is obtained that for the two-dimensional silicon transistor, the γ parameter in x and y direction has the same value and like its behavior at one-dimension, is linearly dependent on the Knudsen number, being 1.5 for Kn=10 and 0.015 for Kn=0.1. Also, the phase lagging ratio, B, is found to be 0.08. It should be mentioned that the non-locality effect is more pronounced for smaller systems with higher Knudsen number in which the non-Fourier behavior is more evident but contemplating the non-locality parameter in systems with lower Knudsen number, makes the results more precise. In brief, it is confirmed that taking into account the γ parameter is noteworthy for accurately predicting the thermal behavior in micro/nano scale systems using the classical macroscopical methods.

physics.app-ph↗

arXiv2024

Thermal transport in thermoelectric materials of SnSSe and SnS$_2$: a non-equilibrium Monte-Carlo simulation of Boltzmann transport equation

In the present work, thermal transport and energy conversation in two thermoelectrically efficient candidates of Janus SnSSe and SnS$_2$ are investigated within the non-equilibrium Monte Carlo simulation of phonon Boltzmann equation. The phonon analysis is performed to determine the contributed phonons in heat transport. The results present that the dominant participating phonons are longitudinal acoustic ones while the least belongs to the transverse acoustic (TA) mode. Both materials reached the very high maximum temperature in response to the implied wasted heat. This is attributed to the low presence of the critical TA phonons. Also, the temperature profile achieved during the heating and cooling of the materials is studied. It is obtained that the heat propagation through the SnS$_2$ is, at first, swifter, which results in a temperature gradient through the whole material which is less than that of the SnSSe. As the time passes, the heat transfer that is directly related to the material thermal conductivity, slows down. So, the behavior of the SnS$_2$ and SnSSe, in case of the heat propagation status, becomes similar. More, the behavior of the thermoelectric figure of merit (zT), the efficiency ($η$), and the generated voltage have been figured out. It is stated that the higher zT and $η$ do not guarantee a larger generated Seebeck voltage. This is true, while the generated Seebeck voltage is related to the temperature difference between the heated and the cold junction. Accordingly, how far the temperature of matter rises in response to the implied wasted heat is related to the obtained voltage. Mainly, it is presented that the maximum temperature that a material achieves, alongside the temperature gradient and material property Seebeck coefficient, are essential in introducing thermoelectrically efficient materials with reasonable thermal to electrical energy conversion.

cond-mat.mes-hall↗

arXiv2023

Implementation of nonlocal non-Fourier heat transfer for semiconductor nanostructures

The study of heat transport in micro/nanoscale structures due to their application, especially in Nanoelectronics, is a matter of interest. In other words, the precise simulation of the temperature distribution inside the transistors is consequential in designing and building more reliable devices reaching lower maximum temperatures during the operation. The present study constitutes a framework for micro/nanoscale heat transport study which leads to the calculation of accurate temperature/heat flux profiles with low computational cost. The newly non-dimensional parameter γ, presenting the strength of the nonlocality, is utilized through the nonlocal DPL modeling (NDPL). Alongside the calculating nonlocality coefficient, the factors also appearing in DPL, including the temperature jump, phase lagging ratio, are revisited. The factor γ is found to have a linear relationship with Knudsen (Kn) number, being 3.5 for Kn=10 and 0.035 for Kn=0.1. Although the nonlocality is bold for the large Knudsen numbers, it also plays a vital role for low Knudsen number structures especially at earlier times. Further, It is obtained that intruding γ is critical for obtaining accurate temperature and heat flux distributions which are very close to the practical results of Phonon Boltzmann equation.

cond-mat.mes-hall↗

arXiv2023

An investigation into the reliability of newly proposed MoSi$_2$N$_4$/WSi$_2$N$_4$ field-effect transistors: A monte carlo study

Recently, the two dimensional complex MA$_2$Z$_4$ structures have been suggested as suitable replacements for silicon channels in field-effect transistors (FETs). Specifically, two materials of MoSi$_2$N$_4$ and WSi$_2$N$_4$ due to their very desirable electrical and thermal properties are noticed. On the other hand, the reliability of transistors, which is determined by the maximum temperature they obtain during the performance, specifies the usefulness of the newly proposed channels for thermal management solution. In this work, the FETs, including MoSi$_2$N$_4$ and WSi$_2$N$_4$ channels, are investigated using Monte Carlo simulation of the phonon Boltzmann equation. In particular, the phonon analysis has been carried out to investigate the peak temperature rise. Our calculations confirm that MoSi$_2$N$_4$ and WSi$_2$N$_4$ present lower maximum temperature than the previously suggested candidate, the blue phosphorene (BP) which itself reaches a shallow temperature. Concretely, the phonon exploration shows that the competition between the dominant heat carrier velocity, and its related frequency settles the maximum temperature value. The material WSi$_2$N$_4$ with much more phonons in TA mode, with almost high velocity and relatively low-frequency, shows adequate thermal condition, and its peak temperature is very low, say 110 K, less than that of BP. The material MoSi$_2$N$_4$ attains the maximum temperature of only 10 K less than BP peak temperature. This behavior attributes to the dominant LA phonons which are fast but also have high frequency and consequently make the temperature get larger than that of the WSi$_2$N$_4$. In summary, WSi$_2$N$_4$, with very low peak temperature, and in the next step MoSi$_2$N$_4$, both with beneficial electrical/thermal properties, are suggested as very suitable candidates for producing more reliable FETs, fulfilling the thermal management.

cond-mat.mtrl-sci↗

arXiv2022

A time-fractional dual-phase-lag framework to investigate transistors with TMTC channels (TiS3, In4Se3) and size-dependent properties

In this study, a time fractional dual-phase-lag model with temperature jump boundary condition as a choice for the Fourier's law replacement in thermal modeling of transistors, is utilized. In more details, the numerical simulation of heat transfer in newly proposed TMTC field effect transistors using fractional DPL equation has been investigated. Moreover, the Caputo fractional derivative is employed to formulate the finite difference scheme for discretization of the fractional DPL model. In order to obtain more precise results for the peak temperature rise, the temperature and heat flux profiles, the size-dependent thermal properties are taken into account. Also, the temperature jump boundary condition has been also applied by means of a mixed-type boundary condition. It is obtained that considering size-dependent thermal characteristics for transistors under study, results in increase of the peak temperature rise up to 250 percent. Furthermore, considering constant bulk thermal properties for the silicon MOSFET, certain oscillations are observed in the time-variation of the peak temperature rise for alpha= 0.7, 0.9 and 1. This presents the so-called negative bias temperature instability appearing in electronic nano-semiconductor devices. Finally, the hotspot temperature has been researched in transistors containing two-dimensional materials with quasi one-dimensional band structure channels. It is obtained that among the studied FETs, titanium trisulfide with maximum temperature increase of 19.63 K exhibits the least peak temperature rise. This presents that TiS3 may be an acceptable silicon channel replacement as far as the thermal issues are concerned.

cond-mat.mes-hall↗

arXiv2022

Lagging Heat Models in Thermodynamics and Bioheat Transfer: a Critical Review

The accuracy of the classical heat conduction model, known as Fourier's law, is highly questioned, dealing with the micro and nanosystems and biological tissues. In other words, the results obtained from the classical equations deviate from the available experimental data. It means that the continuum heat diffusion equation is insufficient and inappropriate for modeling heat transport in these cases. There are several techniques for modeling non-Fourier heat conduction. In the present paper, we place our focus on the dual-phase-lag (DPL) approach. The DPL model, as a popular modification of Fourier's law, has already been utilized in numerous situations, such as simulating ultrafast laser heating and heat conduction in carbon nanotubes. There has been a sharp increase in research on non-Fourier heat conduction in recent years. Several studies have been performed in the fields of thermoelasticity, thermodynamics, transistor modeling, and bioheat transport. This review presents the most recent non-Fourier bioheat conduction works and the related thermodynamics background. The various mathematical tools, modeling different thermal therapies, and relevant criticisms and disputes are discussed. Finally, the novel and other possible studies are also presented to provide a better overview, and the roadmap to the future research and challenges ahead is drawn up.

physics.app-ph↗

arXiv2021

Combined active-passive heat transfer control using slotted fins and oscillation in turbulent flow: the cases of single cylinder and tube banks

In heat transfer augmenting methods such as radial fins, the heat transfer enhancement commonly leads to the drag force increment. In the present paper, slots are inserted over the fins to simultaneously reduce the drag coefficient. Turbulent convection heat transfer around a cylinder, as well as oscillating bundle of tubes including the slotted radial fins have been investigated. The governing equations are solved in two-dimension utilizing OpenFOAM software based on k-ω SST closure model. The cases with various slot location, slot width, the number of the slots, the fin height, and oscillation frequencies are examined. In all cases, the Reynolds number is taken to be equal to 5000. Presence of three slots on the fins reduces the drag coefficient by 23% and augments the Nusselt number by 76%. In order to enhance the heat transfer from the bundle of tube, oscillation of tubes and utilization of the slotted fins are applied. The optimum situation occurs for a sample with the oscillating third column that shows 3% increment in heat transfer relative to that of the fixed case. This is while adding the slotted fins to the oscillating tube bank increases the heat transfer up to 2.5 times.

physics.flu-dyn↗

arXiv2019

Spin transfer torque and exchange coupling in Josephson junctions with ferromagnetic superconductor reservoirs

In this paper, the spin transfer torque (STT) and the exchange coupling of the Josephson junctions containing interesting cases of diffusive/ballistic-triplet/singlet ferromagnetic superconductor materials together with diffusive Josephson junction of the form S$_{1}$/F$_{1}$/I$_1$/N/I$_2$/F$_2$ with I being insulating barrier are investigated. Using the Nazarov quantum circuit theory, it is found that for the diffusive FS$_1$/N/FS$_2$ structure the only emerged torque in normal direction to the plane of the exchange fields of F$_1$ and F$_2$ results in antiparallel/parallel or vice versa parallel/antiparallel transition of favorable exchange coupling depending on the considered parameters of the system, including the nonmagnetic spacer thickness, the superconducting phase difference, the length and the exchange field of the ferromagnets. Furthermore, the analyze of the width of the transitions, the phase difference interval in which an interlayer length-induced antiparallel/parallel transition can be occurred, is performed. For instance, as the exchange field or the temperature increases, the interval of phase difference gets larger. On the other hand, ballistic Josephson junction containing the triplet ferromagnetic superconductor reservoirs solving the 16$\times$16 Bogoliubov-de-Gennes equation is studied. It is found that although the exchange fields of the FS are laid in the z and y direction, the STT interestingly exists in all three directions of x, y and z. This exciting finding suggests that the favorable equilibrium configuration concerning the least exchange coupling occurs in the relative exchange field direction different from 0 or $π$. To the best of our knowledge it is for the first time that the occurrence of the in-plane STT is reported. Moreover, the occurrence of the beat like behavior with two oscillation period for the out-of-plane STT is interestingly acquired.

cond-mat.mes-hall↗

arXiv2018

Effects of low-dimensional material channels on energy consumption of Nano-devices

It is commonly believed that the significant energy saving advantages are belonged to the logic circuits which operate at low temperature as less enegy is needed for cooling them to the treshold temperature after operation. Also, nanoscale thermal management, efficient energy usage in nanoscale and especially thermal optimization are the most challenging issues, while dealing with the new generation of transistors as the miniaturizing unlimitedly the silicon channels of the transistors has resulted in an increase in the energy consumption of computers and the leakage currents. In this paper, the non-Fourier thermal attitudes of well-known two-dimensional crystalline materials of graphene, blue phosphorene, germanene, silicene and MoS$_2$ as the silicon channels replacements are studied by using the phonon Monte-Carlo method. We show that graphene and blue phosphorene have the least maximum temperature, representer of the reliability of the transistors, among the all five investigated nano-channels during the Monte-Cralo simulation. The established hotspots of these two materials are always cooler, not reaching the temperature threshold level, and they lose the heat much faster as the heat generation zone is switched off. The obtained results considered along with the electrical disadvantages of the graphene layer, suggests the blue phosphorene as the more thermally appropriate and optimal choice for the silicon channel replacement in new designed field effect transistors. That is to say that the limit of the energy and economic cost of the producing the advanced blue phosphorene chips meets the value of the product for the computing enterprise.

cond-mat.mes-hall↗

arXiv2012

Spin-Transfer and Exchange Torques in Ferromagnetic Superconductors

We consider how superconducting correlations influence spin-transfer torques in ferromagnetic superconductors. It is demonstrated that there is a novel torque arising from particle-hole interference that depends on the U(1) phase associated with the superconducting order parameter. We also show that there is an equilibrium exchange torque between two ferromagnetic superconductors in contact via a normal metal mediated by Andreev states. The latter equilibrium magnetic torque is also sensitive to spin-resolved phase differences in the superconducting order parameters as well as to an externally applied phase difference.

cond-mat.supr-con↗

arXiv2011

Spin supercurrent in Josephson contacts with noncollinear ferromagnets

We present a theoretical study of the Josephson coupling of two s-wave superconductors which are connected through a diffusive contact consisting of noncollinear ferromagnetic domains. First, we consider a contact with two domains with magnetization vectors misoriented by an angle $θ$. Using the quantum circuit theory, we find that in addition to the charge supercurrent, a spin supercurrent, which is even in $ϕ$ and odd in $θ$, with a spin polarization normal to the magnetization vectors flows between the domains. Furthermore, with asymmetric insulating barriers at the interfaces of the junction, the system may experience an antiferromagnetic-ferromagnetic phase transition for $ϕ=π$. Secondly, we discuss the spin supercurrent in an extended magnetic texture with multiple domainwalls. We find the position-dependent spin supercurrent. The magnitude of the spin supercurrent strongly depends on the phase difference between the superconductors and the number of domain walls. Our results demonstrate the possibility to couple the superconducting phase to the magnetization dynamics.

cond-mat.supr-con↗

arXiv2008

Width of the $0-π$ phase transition in diffusive magnetic Josephson junctions

We investigate the Josephson current between two superconductors (S) which are connected through a diffusive magnetic junction with a complex structure (F$_{c}$). Using the quantum circuit theory, we obtain the phase diagram of 0 and $π$ Josephson couplings for F$_{c}$ being a IFI (insulator-ferromagnet-insulator) double barrier junction or a IFNFI structure (where N indicates a normal metal layer). Compared to a simple SFS structure, we find that the width of the transition, defined by the interval of exchange fields in which a $0-π$ transition is possible, is increased by insulating barriers at the interfaces and also by the presence of the additional N layer. The widest transition is found for symmetric F$_{c}$ structures. The symmetric SIFNFIS presents the most favorable condition to detect the temperature induced $0-π$ transition with a relative width, which is five times larger than that of the corresponding simple SFS structure.

cond-mat.mes-hall↗