An Atomically Resolved Schottky Barrier Height Approach for Bridging the Gap between Theory and Experiment at Metal-Semiconductor Heterojunctions.

We propose an atomically resolved approach to capture the spatial variations of the Schottky barrier height (SBH) at metal-semiconductor heterojunctions. This proposed scheme, based on atom-specific partial density of states (PDOS) calculations, further enables calculation of the effective SBH that aligns with conductance measurements. We apply this approach to study the variations of SBH at MoS2@Au heterojunctions, in which MoS2 contains conducting and semiconducting grain boundaries (GBs). Our results reveal that there are significant variations in SBH at atoms in the defected heterojunctions. Of particular interest is the fact that the SBH in some areas with extended defects approaches zero, indicating Ohmic contact. One important implication of this finding is that the effective SBH should be intrinsically dependent on the defect density and character. Remarkably, the obtained effective SBH values demonstrate good agreement with existing experimental measurements. Thus, the present study addresses two long-standing challenges associated with SBH in MoS2-metal heterojunctions: the wide variation in experimentally measured SBH values at MoS2@metal heterojunctions and the large discrepancy between density-functional-theory-predicted and experimentally measured SBH values. Our proposed approach points out a valuable pathway for understanding and manipulating SBHs at metal-semiconductor heterojunctions.

Recent Advances in In-Memory Computing: Exploring Memristor and Memtransistor Arrays with 2D Materials.

The conventional computing architecture faces substantial challenges, including high latency and energy consumption between memory and processing units. In response, in-memory computing has emerged as a promising alternative architecture, enabling computing operations within memory arrays to overcome these limitations. Memristive devices have gained significant attention as key components for in-memory computing due to their high-density arrays, rapid response times, and ability to emulate biological synapses. Among these devices, two-dimensional (2D) material-based memristor and memtransistor arrays have emerged as particularly promising candidates for next-generation in-memory computing, thanks to their exceptional performance driven by the unique properties of 2D materials, such as layered structures, mechanical flexibility, and the capability to form heterojunctions. This review delves into the state-of-the-art research on 2D material-based memristive arrays, encompassing critical aspects such as material selection, device performance metrics, array structures, and potential applications. Furthermore, it provides a comprehensive overview of the current challenges and limitations associated with these arrays, along with potential solutions. The primary objective of this review is to serve as a significant milestone in realizing next-generation in-memory computing utilizing 2D materials and bridge the gap from single-device characterization to array-level and system-level implementations of neuromorphic computing, leveraging the potential of 2D material-based memristive devices.

The effects of point defect type, location, and density on the Schottky barrier height of Au/MoS2 heterojunction: a first-principles study.

Using DFT calculations, we investigate the effects of the type, location, and density of point defects in monolayer MoS2 on electronic structures and Schottky barrier heights (SBH) of Au/MoS2 heterojunction. Three types of point defects in monolayer MoS2, that is, S monovacancy, S divacancy and MoS (Mo substitution at S site) antisite defects, are considered. The following findings are revealed: (1) The SBH for the monolayer MoS2 with these defects is universally higher than that for its defect-free counterpart. (2) S divacancy and MoS antisite defects increase the SBH to a larger extent than S monovacancy. (3) A defect located in the inner sublayer of MoS2, which is adjacent to Au substrate, increases the SBH to a larger extent than that in the outer sublayer of MoS2. (4) An increase in defect density increases the SBH. These findings indicate a large variation of SBH with the defect type, location, and concentration. We also compare our results with previously experimentally measured SBH for Au/MoS2 contact and postulate possible reasons for the large differences among existing experimental measurements and between experimental measurements and theoretical predictions. The findings and insights revealed here may provide practical guidelines for modulation and optimization of SBH in Au/MoS2 and similar heterojunctions via defect engineering.

Computational predictions of quantum thermal transport across nanoscale interfaces.

Interfaces are essential elements in nanoscale devices and their properties can differ significantly from their bulk counterparts. Because interfaces often act as bottlenecks in heat dissipation, the prediction and control of the interfacial thermal conductance is critical to the design of nanoscale devices. In this review, we examine the recent advances in quantum interfacial thermal transport from a theoretical and computational perspective. We discuss in detail recent advances in the Atomistic Green's Function method which is an important tool for predicting interfacial thermal transport. We also discuss recent progress in the understanding of interfacial transport mechanisms, including the role of interfacial modes, the role of anharmonic phonon-phonon coupling, the role of electron-phonon interaction, and the ways to tune the interfacial thermal conductance. Finally, we give an overview of the challenges and opportunities in this research field.

Three-Fold Enhancement of In-Plane Thermal Conductivity of Borophene through Metallic Atom Intercalation.

We studied the thermal conductivity of Al-intercalated bilayer δ4 borophene sheet by solving phonon Boltzmann transport equation based on density functional theory. Although the overall atomic density of Al-intercalated borophene is larger than that of δ4 borophene, it possesses significant enhancement in in-plane thermal conductivity. With metallic atom intercalation, the armchair-direction thermal conductivity increases from 53.8 to 160.2 W m-1 K-1 and that along the zigzag direction increases from 115.7 to 157.2 W m-1 K-1. This pronounced enhancement is attributed to the bunching of the acoustic branches in the Al-intercalated borophene, which decreases the phase space for the high frequency three acoustic phonon scattering processes. In addition to the pronounced increased thermal conductivity, the Al-intercalation also tunes the in-plane anisotropy. This study illustrates the importance of metallic atom intercalation in the in-plane thermal conductivity of 2D van der Waals materials and also has practical implications for fields ranging from thermal management to thermoelectrics design.

Neural network representation and optimization of thermoelectric states of multiple interacting quantum dots.

We perform quantum master equation calculations and machine learning to investigate the thermoelectric properties of multiple interacting quantum dots (MQD), including electrical conductance, Seebeck coefficient, thermal conductance and the figure of merit (ZT). We show that by learning from the data obtained from the QME, the thermoelectric states of the MQD can be represented well by a two-layer neural network. We also show that after training, the neural network was able to predict the thermoelectric properties of the MQD with much less computational cost compared to the QME approach. Based on the neural network, we further optimize the MQD to achieve a high ZT and power factor. This work presents a powerful route to study, represent, and optimize interacting quantum many-body systems.

The important role of strain on phonon hydrodynamics in diamond-like bi-layer graphene.

In this work, combining first-principles calculation and the phonon Boltzmann transport equation, we explored the diffusive thermal conductivity of diamond-like bi-layer graphene. The converged iterative solution provides high room temperature thermal conductivity of 2034 W mK-1, significantly higher than other 2D materials. More interesting, the thermal conductivity calculated by relaxation time approximation is about 33% underestimated, revealing a remarkable phonon hydrodynamic transport characteristic. Significant strain dependence is reported, for example, under 5% tensile strain, room temperature thermal conductivity (1081 W mK-1) of only about 50% of the strain-free sample, and under 20% strain, it reduces dramatically to only about 11% of the intrinsic one (226 W mK-1). Unexpectedly, in addition to the remarkable reduction in the absolute value of thermal conductivity, tensile strain can impact the hydrodynamic significance. For example, under 5% strain, the underestimation of relaxation time approximation in thermal conductivity is reduced to 20%. Furthermore, using a non-equilibrium Green's function calculation, high ballistic thermal conductance (2.95 GW m-2 K-1) is demonstrated, and the mean free path is predicted to be 700 nm at room temperature. The importance of the knowledge of phonon transport in diamond-like bi-layer graphene goes beyond fundamental physics owing to its relevance to thermal management applications due to the super-high thermal conduction.

Phonon stability and phonon transport of graphene-like borophene.

Recent decades have seen tremendous progress in quantitative understanding of phonon transport, which is critical for the thermal management of various functional devices and the proper optimization of thermoelectric materials. In this work, using a first-principles based calculation combined with the non-equilibrium Green's function and a phonon Boltzmann transport equation, we provide a systematic study of the phonon stability and phonon transport of a monolayer boron sheet with a honeycomb, graphene-like structure (graphene-like borophene) in both ballistic and diffusive regimes. For free-standing graphene-like borophene, phonon instabilities occur near the centre of the Brillouin zone, implying elastic instability. Investigation of the electronic structures shows that the phonon instability is due to the deficiency of electrons. Our first-principles results show that with net charge doping and in-plane tensile strain, graphene-like borophene becomes thermodynamically stable in ideal planar nature, because the bonding characteristic is modified. At room temperature, the ballistic thermal conductance of graphene-like borophene (7.14 nWK-1 nm-2) is higher than that of graphene (4.1 nWK-1 nm-2), due to high phonon transmission. However, its diffusive thermal conductivity is two orders of magnitude lower than graphene, because the phonon relaxation time is dramatically reduced compared with its carbon counterpart. Although the phonon group velocity and phonon anharmonicity are comparable with those of graphene, the suppressed phonon space results in dramatically strong phonon-phonon scattering. These thermal transport characteristics in both ballistic and diffusive regimes are of fundamental and technological relevance and provide guidance for applications of boron-based nanomaterials in which thermal conduction is the major concern.

High thermal conductivity driven by the unusual phonon relaxation time platform in 2D monolayer boron arsenide.

The cubic boron arsenide (BAs) crystal has received extensive research attention because of its ultra-high thermal conductivity comparable to that of diamond. In this work, we performed a comprehensive study on the diffusive thermal properties of its two-dimensional (2D) counterpart, the monolayer honeycomb BAs (h-BAs), through solving the phonon Boltzmann transport equation combined with first-principles calculation. We found that unlike the pronounced contribution from out-of-plane acoustic phonons (ZA) in graphene, the high thermal conductivity (181 W m-1 K-1 at 300 K) of h-BAs is mainly contributed by in-plane phonon modes, instead of the ZA mode. This result is explained by the unique frequency-independent 'platform' region in the relaxation time of in-plane phonons. Moreover, we conducted a comparative study of thermal conductivity between 2D h-BAs and h-GaN, because both of them have a similar mass density. The thermal conductivity of h-BAs is one order of magnitude higher than that of h-GaN (16 W m-1 K-1), which is governed by the different phonon scattering process attributed to the opposite wavevector dependence in out-of-plane optical phonons. Our findings provide new insight into the physics of heat conduction in 2D materials, and demonstrate h-BAs to be a new thermally conductive 2D semiconductor.

From Two- to Three-Dimensional van der Waals Layered Structures of Boron Crystals: An Ab Initio Study.

A remarkable recent advancement has been the successful synthesis of two-dimensional boron monolayers on metal substrates. However, although up to 16 possible bulk allotropes of boron have been reported, none of them possess van der Waals (vdW) layered structures. In this work, starting from the experimentally synthesized monolayer boron sheet (ß12 borophene), we explored the possibility for forming vdW layered bulk boron. We found that two ß12 borophene sheets cannot form a stable vdW bilayer structure, as covalent-like B-B bonds are formed between them because of the peculiar bonding. Interestingly, when the covalently bonded bilayer borophene sheets are stacked on top of each other, three-dimensional (3D) layered structures are constructed via vdW interlayer interactions, rather than covalent. The 3D vdW layered structures were found to be dynamically stable. The interlayer binding energy is about 20 meV/Å2, which is close to the weakly bound graphene layers in graphite (∼16 meV/Å2). Furthermore, the density functional theory predicted electronic band structure testifies that these vdW bulk boron crystals can behave as good conductors. The insights obtained from this work suggest an opportunity to discover new vdW layered structures of bulk boron, which is expected to be crucial to numerous applications ranging from microelectronic devices to energy storage devices.

Unusual phonon behavior and ultra-low thermal conductance of monolayer InSe.

Monolayer indium selenide (InSe) possesses numerous fascinating properties, such as high electron mobility, quantum Hall effect and anomalous optical response. However, its phonon properties, thermal transport properties and the origin of its structural stability remain unexplored. Using first-principles calculations, we show that the atoms in InSe are highly polarized and such polarization causes strong long-range dipole-dipole interaction (DDI). For acoustic modes, DDI is essential for maintaining its structural stability. For optical modes, DDI causes a significant frequency shift of its out-of-phase vibrations. Surprisingly, we observed that there were two isolated frequency regimes, which were completely separated from other frequency regimes with large frequency gaps. Within each frequency regime, only a single phonon mode exists. We further reveal that InSe possesses the lowest thermal conductance among the known two-dimensional materials due to the low cut-off frequency, low phonon group velocities and the presence of large frequency gaps. These unique behaviors of monolayer InSe can enable the fabrication of novel devices, such as thermoelectric module, single-mode phonon channel and phononic laser.

Phonon transport in a one-dimensional harmonic chain with long-range interaction and mass disorder.

Atomic mass and interatomic interaction are the two key quantities that significantly affect the heat conduction carried by phonons. Here, we study the effects of long-range (LR) interatomic interaction and mass disorder on the phonon transport in a one-dimensional harmonic chain with up to 10^{5} atoms. We find that while LR interaction reduces the transmission of low-frequency phonons, it enhances the transmission of high-frequency phonons by suppressing the localization effects caused by mass disorder. Therefore, LR interaction is able to boost heat conductance in the high-temperature regime or in the large size regime, where the high-frequency modes are important.

Boosting thermoelectric efficiency using time-dependent control.

Thermoelectric efficiency is defined as the ratio of power delivered to the load of a device to the rate of heat flow from the source. Till date, it has been studied in presence of thermodynamic constraints set by the Onsager reciprocal relation and the second law of thermodynamics that severely bottleneck the thermoelectric efficiency. In this study, we propose a pathway to bypass these constraints using a time-dependent control and present a theoretical framework to study dynamic thermoelectric transport in the far from equilibrium regime. The presence of a control yields the sought after substantial efficiency enhancement and importantly a significant amount of power supplied by the control is utilised to convert the wasted-heat energy into useful-electric energy. Our findings are robust against nonlinear interactions and suggest that external time-dependent forcing, which can be incorporated with existing devices, provides a beneficial scheme to boost thermoelectric efficiency.

Improved Dyson series expansion for steady-state quantum transport beyond the weak coupling limit: divergences and resolution.

We present a general theory to calculate the steady-state heat and electronic currents for nonlinear systems using a perturbative expansion in the system-bath coupling. We explicitly demonstrate that using the truncated Dyson-series leads to divergences in the steady-state limit, thus making it impossible to be used for actual applications. In order to resolve the divergences, we propose a unique choice of initial condition for the reduced density matrix, which removes the divergences at each order. Our approach not only allows us to use the truncated Dyson-series, with a reasonable choice of initial condition, but also gives the expected result that the steady-state solutions should be independent of initial preparations. Using our improved Dyson series we evaluate the heat and electronic currents up to fourth-order in system-bath coupling, a considerable improvement over the standard quantum master equation techniques. We then numerically corroborate our theory for archetypal settings of linear systems using the exact nonequilibrium Green's function approach. Finally, to demonstrate the advantage of our approach, we deal with the nonlinear spin-boson model to evaluate heat current up to fourth-order and find signatures of cotunnelling process.

High expression of TIMP-1 in human breast cancer tissues is a predictive of resistance to paclitaxel-based chemotherapy.

For breast cancer patients with lymph node metastasis, paclitaxel is the first-line chemotherapy drug. Clinical studies showed that some patients with breast cancer were insensitive to paclitaxel, which led to chemotherapy failure. Today, no validated markers exist for the prediction of chemotherapy sensitivity in this patient group. Tissue inhibitor of metalloproteinases-1 (TIMP-1) has been shown to protect against apoptosis. Epidemiological studies have also associated elevated tumor tissue TIMP-1 levels with a poor response to cyclophosphamide/methotrexate/5-fluorouracil and anthracycline-based chemotherapy. Additionally, our previous study proved that TIMP-1 significantly decreased the sensitivity of breast cancer cells to paclitaxel-induced apoptosis by enhancing degradation of cyclin B1. These data imply that TIMP-1 may be a useful predictive biomarker for chemotherapy resistance. In this retrospective study, we investigated the association between expression levels of TIMP-1 protein in the primary tumor and objective response to paclitaxel-based chemotherapy in 99 patients with breast cancer. With Kaplan-Meier survival analysis, the patients with high TIMP-1 levels were found to have significantly worse 5-year DFS (71.1 %) than the patients with low levels (88.5 %; P = 0.020). Similarly, the patients with high TIMP-1 levels had significantly worse 5-year OS (78.9 %) than patients with low levels (96.7 %; P = 0.004). In Cox's univariate and multivariate analyses, TIMP-1 was prognostic for both DFS and OS. Our data showed that elevated tumor tissue TIMP-1 levels were significantly associated with a poor response to paclitaxel-based chemotherapy, and TIMP-1 might be a potential biomarker for predicting response of breast cancer patients to paclitaxel-based chemotherapy.

[Male genitourinary system lymphoma: a clinicopathological analysis].

OBJECTIVE: To investigate the clinicopathological features and immunophenotypes of male genitourinary system lymphoma. METHODS: We retrospectively studied the histopathological characteristics and immunohistochemical markers of 35 cases of male genitourinary system lymphoma, and reviewed the relevant literature. RESULTS: The 35 patients of male genitourinary system lymphoma were aged from 4 to 83 (mean 56.5) years, 28 (80%) of them > or = 50 years. Twenty-eight cases (80%) involved the testis, 3 (8.6%) the prostate, 1 (2.9%) the spermatic cord, 1 the seminal vesicles, 1 the penis and 1 the epididymis. Histologically, 22 cases (62.9%) were diffused large B cell lymphoma (DLBCL), 6 (17.1%) mucosa associated lymphoid tissue (MALT) lymphoma, 4 (11.4%) Burkitt lymphoma, 2 (5.7%) peripheral T cell lymphoma, and 1 (2.9%) plasmacytoma. CONCLUSION: Male genitourinary system lymphomas are rare tumors clinically, which occur more often in the elderly. The majority of them are B cell lymphomas, of which the most common is DLBCL, followed by MALT lymphoma and Burkitt lymphoma. T cell lymphoma and plasmacytoma are rare. The diagnosis of male genitourinary system lymphoma relies on the histopathology, and immunohistochemical markers are of high value for its definite diagnosis, classification and differential diagnosis.

High thymidine kinase 1 (TK1) expression is a predictor of poor survival in patients with pT1 of lung adenocarcinoma.

In this study, we explore the association of thymidine kinase 1 (TK1) expression in tumour tissues with clinical pathological parameters and prognosis in patients with pathological T1 (pT1) lung adenocarcinoma. The expression of TK1 was studied by immunohistochemistry techniques in 80 patients with surgically resected pT1 lung adenocarcinoma, retrospectively and at >10-year follow-up. Compared to patients with low TK1 expression [labelling index (LI) <25.0%], patients with high TK1 expression (LI ≥ 25.0%) showed significantly increased lymphatic/vascular permeation and lymph node involvement and higher stromal invasion grade and pathological stage, and a greater number of patients had a tumour size of 2.1 to 3.0 cm. The 5-year survival and the mortality during follow-up for patients with high TK1 expression were significantly worse than that of patients with low TK1 expression. The prognoses of the cases with grade 0, grade 1 and grade 2 stromal invasions were similar and were better than those of cases with grade 3. In patients with stromal invasion grade 3, the 5-year survival and the mortality during follow-up were significantly worse for patients with high TK1 compared to patients with low TK1 expression. Univariate analyses showed that stromal invasion and TK1 expression were significant prognostic factors, while in the multivariate analysis, TK1 expression and tumour stage were found to be independent prognostic factors, but not stromal invasion. This is the first study showing that TK1 expression in combination with stromal invasion is a more reliable prognostic factor than stromal invasion classification itself in patients with pT1 lung adenocarcinoma. TK1 expression enables a further classification of the patients and opens opportunities for improved treatment outcome.

[Mucinous tubular and spindle cell carcinoma of kidney: a clinicopathological study].

OBJECTIVE: To investigate the clinicopathological features, histogenesis and prognosis of mucinous tubular and spindle cell carcinoma (MTSCC). METHODS: Five MTSCCs were studied with histochemical, immunohistochemical staining, electron microscopy, and review of the related literatures. RESULTS: Four cases of MTSCC were females and one was male. Three patients presented with flank discomfort and two were incidentally found with health examination. In gross examination, the tumors were circumscribed. The cut surface was solid, gray-white, yellow or red. Necrosis was present in one case of high-grade MTSCC. Microscopically, low-grade MTSCC was mainly consisted of tubular, spindle cell and mucinous stroma with relatively bland morphology, and mitoses were rare. While in the high-grade area of one case, the cells were spindle or polymorphic with severe atypia and high mitotic activity, without mucinous stroma and tubular structure. Mucin was positive for Alcian blue. The neoplastic cells were positive for vimentin (5/5), CKpan (5/5), CK7 (5/5), CK19 (5/5), 34betaE12 (1/5), EMA (5/5), E-cadherin (3/5), CD10 (1/5), P504S (5/5), and CAM5.2 (5/5). The Ki-67 index was low (< or = 5%) in the low-grade component, while it was high (15%) in the high-grade component. Ultrastructural study showed short microvilli along glandular lumens. The nuclear membrane was focally invaginated. Four cases were followed up for 3 to 52 months, and recurrence and metastasis were not found. CONCLUSIONS: MTSCC occurs predominantly in females and it is a rare kidney neoplasm. Most of MTSCCs are low-grade and the prognosis is relatively good. However, the patients of high-grade MTSCC should be closely followed up.