Physica Status Solidi B: Basic Solid State Physics

Fang, D. Q.

doi: 10.1002/pssb.202500592pmid: N/A

Semiconductor heterostructures capable of separating photogenerated electrons and holes have a wide range of optoelectronic applications, including photodetectors, solar cells, and photocatalysts. β‐Ga2O3 and rutile GeO2 are both ultrawide‐bandgap semiconductors, with bandgaps of 4.85 eV and 4.68 eV, respectively, which have attracted increasing interest due to promising applications in next‐generation high‐power electronics and deep ultraviolet optoelectronics. Here, using first‐principles calculations, we investigate the interfacial property and band alignment of the β‐Ga2O3/rutile GeO2 heterojunction and explore the effect of interfacial oxygen vacancy. Calculations using the PBE0 hybrid functional based on an interface model show that a type‐II band alignment emerges at the β‐Ga2O3/rutile GeO2 interface, which facilitates the separation of photogenerated carriers. The valence band maximum of β‐Ga2O3 lies 0.38 eV below that of rutile GeO2, and its conduction band minimum lies 0.36 eV below. The presence of an interfacial oxygen vacancy in the stable configuration leads to a reduction in the band offset. Our results suggest that the β‐Ga2O3/rutile GeO2 heterojunction holds significant promise for application in strictly solar‐blind photodetectors.

Antil, Rachna; Kumar, Devendra; Lakhani, Archana

doi: 10.1002/pssb.202500362pmid: N/A

Single crystal of BiSbSe3 is synthesized in order to explore its topological characteristics and magneto‐transport behavior. The material system, known for its narrow bandgap and sensitivity to defect‐induced conduction, makes it an ideal platform to investigate the interplay between surface and bulk transport channels. Structural, optical, and magneto‐transport studies are carried out to understand the underlying mechanisms governing low‐temperature conduction. The transport data exhibit the low‐temperature upturn arising from the variable range hopping and weak antilocalization (WAL) effect as analyzed through the 2D Hikami–Larkin–Nagaoka (HLN) model. The observed WAL effect is attributed to a 2D multichannel quantum coherent transport mechanism, where the electron–electron interactions govern the phase coherence. These findings position BiSbSe3 as a promising candidate for next‐generation spintronics and low‐dimensional quantum device applications.

Tanaka, Keiji

doi: 10.1002/pssb.70172pmid: N/A

It is known that chalcogenide glasses such as Se and As2S3 exhibit transitory volume expansion under light excitation. We consider its mechanism through numerical analyses, the result being interpreted using simple ideas. Ab initio molecular‐orbital calculations reveal that one‐dimensional H–nS(Se)–H chains (n = 2–14) and crown‐shaped S/Se rings, when excited, undergo marked atomic changes; bond‐distance lengthening and angular widening, which could work as essential origins of the macroscopic photoexpansion. We grasp these changes, taking Mulliken‐charge variations under excitation into account, as exciton self‐trapping (polaronic) effects in molecular wires. The photoexpansion may be universal to one(or low)‐dimensional systems.

Zhang, Yun‐Xiao; Liu, Hai‐Tao

doi: 10.1002/pssb.202500632pmid: N/A

This study focuses on designing and validating a novel negative stiffness cylindrical metamaterial (NSCM), which is driven by the synergistic interaction between compression–torsion metamaterial (CTM) and curved beams. The proposed NSCM exhibits two salient mechanical characteristics that originate from the tailored design of its deformable unit cells: controllable compression–torsion deformation and stable negative stiffness behavior. The NSCM comprises CTM, an array of circumferentially arranged curved beams, and an annular outer frame. It achieves negative stiffness through “compression–torsion‐curved beam” coupling. The emergence of negative stiffness is conclusively demonstrated through both finite element analysis (FEA) and uniaxial compression experiments (EXP), with strong agreement between FEA and EXP results. Furthermore, a systematic parametric study is conducted to evaluate the influence of key geometric variables on the overall mechanical response, such as the dimensionless parameter (K), curved beam height (h), axial height (H), and misalignment angle (α). These investigations have clarified underlying performance regulation trends and established feasible design boundaries for each parameter. The findings offer theoretical insights and practical design guidelines for the application of negative stiffness metamaterials in engineering contexts, highlighting the potential of such mechanical metamaterials in complex functional scenarios.

Madana, Venkata Sai Teja; Manikandan, Subramanian; Akash, Akash; Pandey, Sanjeev Kumar; Naveen Kumar, Kumaran; Sairam, Tiruvachi Natarajan; Subbiah, Sathyan; Arunachalam, Narayanaperumal; Rao, Mamidanna Sri Ramachandra

doi: 10.1002/pssb.202500320

Elhadfi, Soufiane; Chenouf, Jamal; Arbaoui, Zakariya; Fakrach, Brahim; Abdelhai, Rahmani; Chadli, Hassane; Rahmani, Abdelali

doi: 10.1002/pssb.202500382pmid: N/A

Lead halide perovskites, particularly hybrid compounds based on germanium and methylammonium, offer a compelling combination of nontoxicity, environmental stability, and high efficiency, making them promising absorber materials for photovoltaic and thermoelectric applications. In this work, the optoelectronic and thermoelectric properties of methylammonium germanium halide perovskites CH3NH3Ge(Br,Cl)3 are investigated through comprehensive first‐principles calculations. The electronic band structure results reveal that both CH3NH3GeCl3 and CH3NH3GeBr3 are direct bandgap semiconductors, with bandgaps of 2.95 and 2.10 eV, respectively. These compounds also exhibit remarkable optical properties, with absorption coefficients reaching 3.06 × 105 cm−1 for CH3NH3GeCl3 and 3.24 × 105 cm−1 for CH3NH3GeBr3 in the visible regions. Such strong absorption highlights their potential as efficient candidates for optoelectronic and photovoltaic applications. Furthermore, the figure of merit attains values of 0.99 for CH3NH3GeCl3 and 0.98 for CH3NH3GeBr3 near room temperature, underscoring their strong promise for thermoelectric applications.

Şimşek, Telem; Keleş, Mervenur; Uçar, Enis Furkan; Bayram, Cem; Şimşek, Tuncay; Kaynar, Mehmet Burak; Özcan, Şadan

doi: 10.1002/pssb.202500393pmid: N/A

Superparamagnetic iron oxide nanoparticles are widely used for magnetic hyperthermia, yet their modest saturation magnetization limits heating efficiency. Here, a simple route to graphitic carbon–coated iron–cobalt (FeCo) nanocrystals that retain near‐bulk saturation magnetization and deliver competitive heating is reported. Single‐phase FeCo ingots are arc‐melted, crushed, mechanically milled with graphite for 5 h under argon and annealed at 400–800 °C in forming gas to form protective graphitic shells. X‐ray diffraction and transmission electron microscopy confirm body‐centered cubic FeCo cores encapsulated by a continuous carbon shell. After annealing at 400 °C, the sample achieves a saturation magnetization of 240 emu g−1 and a specific absorption rate (SAR, a measure of heating efficiency) of 191.5 W g−1 at 300 kHz and 325 Oe. Higher annealing temperatures increase graphitization and coarsening and reduce both saturation magnetization and SAR. Optimum performance at 400 °C is attributed to oxidation‐limiting shells of near‐optimal thickness. These results identify graphitic carbon–coated FeCo nanocrystals as a promising platform for magnetic hyperthermia. Although ethanol is nonphysiological, it was used to benchmark intrinsic heating capacity; biocompatibility and colloidal stability in aqueous media will be addressed in future work.

Qi, Xin; Du, Jiayu; Wu, Yong; hu, Guoming; Ma, Yanzhao; Peng, Weiping

doi: 10.1002/pssb.202500646pmid: N/A

Polyimide materials (PIs) are extensively used in aerospace applications due to their superior mechanical and thermal properties. However, their high secondary electron emission yield (SEY) poses significant challenges. To decrease the SEY of material, this study employed the magnetron sputtering technique to deposit TiN coatings of varying thicknesses onto PI surface. The results indicated that TiN coatings significantly reduced the secondary electron emission (SEE) of PI materials. Specifically, a 400‐nm TiN coating decreased the maximum SEY from 1.72 to 1.07. The results demonstrate that TiN coatings are effective in suppressing SEE, thereby indicating their considerable potential for aerospace technological applications.

Qiu, Chengyu; Xiao, Bin; Zhang, Weijie; Zeng, Hui

doi: 10.1002/pssb.202500374pmid: N/A

Using density functional theory combined with the nonequilibrium Green's function method, the modulation of the interface structure between single‐walled carbon nanotube (SWCNT) arrays and the HfO2 dielectric layer, which impacts electron transport in field‐effect transistor (FET) devices, is investigated. The results demonstrate that the array density of the SWCNTs affects device performance. Excessive array density enhances the interaction between adjacent CNTs, while low density results in a relatively higher total energy of the structure. The balance between array geometry and interface structure is crucial to device performance. Furthermore, as a high‐k dielectric layer, the HfO2 can effectively modulate the interface characteristics and enhance drain current and transport performance. This study reveals the intrinsic relationship between SWCNT array structure, the CNT/HfO2 interface, and electron transport in CNT field‐effect transistor. This work proposes a strategy to enhance transport performance and provides valuable insights for the practical application of carbon‐based integrated circuits.

Anchal, Neha; Kowachi, Lakhansingh; Javvaji, Srivani; Pathipati, Srinivasa Rao; Rambabu, Pachineela

doi: 10.1002/pssb.202500333pmid: N/A

The growing demand for alternative energy solutions has driven interest in thermoelectric materials for waste heat recovery. Zintl phases are promising thermoelectric candidates, yet the transport properties of Ca2ZnN2 remain largely unexplored. In this work, we combine density functional theory and semiclassical Boltzmann transport calculations to predict the intrinsic thermoelectric properties of Ca2ZnN2. The compound crystallizes in a tetragonal structure and exhibits intrinsic p‐type behavior, with high electrical conductivity (σ =  1.63 × 104 S cm)−1 and hole mobility of (μh ≈ 10 cm2 V−1 s)−1 at 300 K. Polaroptical phonon scattering dominates carrier relaxation, yielding lifetimes around 10−15 s. The lattice thermal conductivity is relatively large (kL =  14.0 W m−1 K−1 for p‐type and 13.0 W m−1 K−1 for n‐type), resulting in modest room‐temperature figures of merit: ZT =  0.017 (p‐type) and ZT =  0.018 (n‐type). However, ZT increases with temperature and carrier concentration, reaching 0.07 (p‐type) and 0.08 (n‐type) at 500 K for n =  1 × 1020 cm−3. Notably, p‐type doping benefits from higher mobility and power factor despite n‐type having larger Seebeck coefficients, making Ca2ZnN2 a promising candidate for p‐type thermoelectric applications.