Temperature-dependent Measurements Research Articles

Unveiling novel drug delivery mechanism : Cisplatin's bonding behaviour with BC4N Nanostructure

Abstract Recent advancements in nanotechnology have opened avenues to address the selectivity challenges in targeted drug delivery systems, minimizing adverse effects. While carbon nanotubes (CNTs) have gained traction as drug carriers, their B, N-containing counterpart, pristine boron carbonite (p-BC4N), remains underexplored. This study investigates the possibility of pristine boron carbonite (p-BC4N) nanotubes as a drug carrier for the anticancer medication cisplatin (CPT). Using first-principles Density Functional Theory (DFT) simulations, we examined the interaction between CPT and p-BC4N nanotubes, revealing favourable adsorption energies (-0.523 eV) due to orbital interactions and charge transfer between the C 2p orbitals of BC4N and the 1s orbitals in H of CPT. Ab initio molecular dynamics (AIMD) simulations confirmed the stability of the system at room temperature. Furthermore, pH and temperature-dependent desorption measurements demonstrated the effectiveness of p-BC4N nanotubes as a promising candidate for CPT drug delivery, highlighting their potential in targeted cancer therapy. This work opens up new avenues for the development of nanotechnology-based drug delivery systems.

Impact of the Ge-Si interfacial barrier on the temperature-dependent performance of PureGaB Ge-on-Si p + n photodiodes

A temperature-dependent study of the near-infrared (NIR) responsivity of Ge-on-Si photodiodes is presented. The diodes, formed as n-Ge islands within oxide windows on n-Si and capped with Ga and B layers (PureGaB), exhibit low dark current of ∼2 × 10−13 A/µm2 and broadband responsivity. Temperature-dependent measurements reveal an inherent potential barrier at the low-doped n-Ge on the n-Si heterointerface. This leads to a decrease in responsivity with decreasing temperatures for wavelengths above 1100 nm. The Al-migration process along the Ge-Si interface, associated with the sidewall passivation and found to be a means of reducing dark current, increases the barrier height. Irrespective of the barrier height, room-temperature responsivity is fully recovered by applying a reverse bias to lower the interface barrier. In the devices with the highest barrier, the responsivity at 1310 nm increased from 4.8 to 164 mA/W, at 0 V and 18 V reverse bias, respectively. An additional increase in maximum responsivity at 1550 nm is attributed to Al-sidewall passivation leading to a measured responsivity of 126.4 mA/W at 18 V reverse bias.

Growth of VO2-ZnS thin film cavity for adaptive thermal emission

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. In this study, we used a thin film coating with the Fabry–Pérot (FP) effect to enhance emissivity contrast (Δε) between VO2 phase-change states. This coating utilizes a hybrid material architecture that combines VO2 with a mid- and long-wave infrared transparent chalcogenide, zinc sulfide (ZnS), as a cavity spacer layer. We simulated the design parameter space to obtain a theoretical maximum Δε of 0.63 and grew prototype devices. Using x-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), we determined that an intermediate buffer layer of TiO2 is necessary to execute the crystalline growth of monoclinic VO2 on ZnS. Through temperature-dependent FTIR measurements, our fabricated devices demonstrated FP-cavity enhanced adaptive thermal emittance.

Isostructural Series of a Cyclometalated Iron Complex in Three Oxidation States.

An isostructural series of FeII, FeIII, and FeIV complexes [Fe(ImP)2]0/+/2+ utilizing the ImP 1,1'-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene) ligand, combining N-heterocyclic carbenes and cyclometalating functions, is presented. The strong donor motif stabilizes the high-valent FeIV oxidation state yet keeps the FeII oxidation state accessible from the parent FeIII compound. Chemical oxidation of [Fe(ImP)2]+ yields stable [FeIV(ImP)2]2+. In contrast, [FeII(ImP)2]0, obtained by reduction, is highly sensitive toward oxygen. Exhaustive ground state characterization by single-crystal X-ray diffraction, 1H NMR, Mössbauer spectroscopy, temperature-dependent magnetic measurements, a combination of X-ray absorption near edge structure and valence-to-core, as well as core-to-core X-ray emission spectroscopy, complemented by detailed density functional theory (DFT) analysis, reveals that the three complexes [Fe(ImP)2]0/+/2+ can be unequivocally attributed to low-spin d6, d5, and d4 complexes. The excited state landscape of the FeII and FeIV complexes is characterized by short-lived 3MLCT and 3LMCT states, with lifetimes of 5.1 and 1.4 ps, respectively. In the FeII-compound, an energetically low-lying MC state leads to fast deactivation of the MLCT state. The distorted square-pyramidal state, where one carbene is dissociated, can not only relax into the ground state, but also into a singlet dissociated state. Its formation was investigated with time-dependent optical spectroscopy, while insights into its structure were gained by NMR spectroscopy.

Freezing of short-range ordered antiferromagnetic clusters in the CrFeTi2O7system.

We report on the CrFeTi2O7(CFTO) system using a combination of x-ray diffraction, dc magnetization, ac susceptibility, specific heat and neutron diffraction measurements. CFTO is seen to crystallize in a monoclinic P21/a symmetry. It shows a glassy freezing at Tf ~ 22 K, characterized by the observation of bifurcation between ZFC and FC χ (T) curves, frequency dispersion across Tf in ac susceptibility, and follows Vogel-Fulcher and power law type critical dynamics, very slow relaxation of iso-thermal remanent magnetization with time and the absence of an anomaly in the temperature dependence of specific heat measurements. The microscopic neutron diffraction analysis of CFTO not only confirms the absence of long-range antiferromagnetic ordering but also exhibits diffuse scattering due to the presence of short-range ordered antiferromagnetically correlated spin clusters.&#xD.

Coexistence of multiple magnetic interactions in oxygen-deficient V2O5 nanoparticles

This paper reports on the spin glass-like coexistence of competing magnetic orders in oxygen-deficient V2O5 nanoparticles with a broad size distribution. X-ray photoelectron spectroscopy yields the surface chemical stoichiometry of nearly V2O4.65 due to significant defect density. Temperature-dependent electrical conductivity and thermopower measurements demonstrate a polaronic conduction mechanism with a hopping energy of about 0.112 eV. The V2O5-δ sample exhibits strong field as well as temperature-dependent magnetic behaviour when measured with a SQUID magnetometer, showing positive magnetic susceptibility across the temperature range of 2-350 K. Field-cooled and zero-field-cooled data indicate hysteresis, suggesting glassy behaviour. The formation of small polarons due to oxygen vacancy defects, compensated by V4+ charge defects, results in Magneto-Electronic Phase Separation (MEPS) and various magnetic exchanges, as predicted by first-principle calculations. This is evidenced by the strong hybridisation of V orbitals in the vicinity of vacant oxygen site. An increase in V4+ defects shows an antiferromagnetic (AFM) component. The magnetic diversity in undoped V2O4.9 originates from defect density and their random distribution, leading to MEPS. This involves localised spins in polarons and ferromagnetic (FM) clusters on a paramagnetic (PM) background, while V4+ dimers induce AFM interactions. Electron paramagnetic resonance spectra measured at different temperatures indicate a dominant paramagnetic signal at a g-value of 1.97 due to oxygen defects, with a broad FM resonance-like hump. Both signals diminish with increasing temperature. Neutron diffraction data rules out long-range magnetic ordering, reflecting the composition as V2O4.886. Despite the FM hysteresis, no long-range order is observed in neutron diffraction data, consistent with the polaron cluster-like FM with MEPS nature. This detailed study shall advance the understanding of the diverse magnetic behaviour observed in undoped non-magnetic systems.

Temperature-dependent charge transport measurements unveil morphological insights in non-fullerene organic solar cells

The morphological analysis of bulk heterojunction (BHJ) active layer stands as a critical imperative for advancing the performance of future organic solar cells. Conventional characterization tools employed for morphological investigation often require substantial resources, both in cost and physical space, thereby imposing restraints on research endeavors in this domain. Here, we extend the application of charge carrier transport characterization beyond conventional mobility assessments, utilizing it as a table-top method for preliminary morphological screening in organic thin films. The investigation focuses on several high-performance BHJ systems that utilize typical “Y” non-fullerene acceptors. It involves in-depth transport studies, including temperature- and field-dependent transport characterizations. The resulting transport data are analyzed in detail using the Gaussian disorder model to extract key transport parameters, specifically the high-temperature limited mobility (μ∞) and positional disorder (∑). Integrating these transport parameters with morphological insights obtained through various characterization tools—including x-ray scattering, sensitive spectroscopy, and quantum chemistry simulation—provides a deep understanding of the intricate interplay between charge transport properties and morphological characteristics. The results reveal explicit relationships, associating μ∞ with the degree of molecular stacking in BHJs and ∑ with the structural disorder in molecule skeleton. Our findings point to the promising potential of utilizing a simple transport characterization technique for the early stage evaluation of thin film packing and geometric properties of organic materials.

Elucidation of amphoteric nature of Pr2O3 using XPS and conductivity measurement in lead-free NKBT host lattice

The study of the piezoelectric response in praseodymium-doped (Na0.41K0.09Bi0.5)TiO3 (NKBT) revealed an unusual behaviour at doping level near 0.5 and 1.0 at%. Although there is a marginal increment in the piezoelectric charge coefficients for samples with praseodymium doping of 0.5–1.0 at% compared to undoped NKBT, importantly, the response drastically diminishes for doping concentrations exceeding 1.0 at%. To comprehend the observed anomaly, X-ray photoelectron spectroscopy (XPS) and temperature dependent conductivity measurement was carried out. These investigations provided critical insights into the role of oxygen vacancy and the behaviour of praseodymium ions in the NKBT matrix. The XPS analysis revealed the presence of core level peak corresponding to O-1s with asymmetric broadening at higher energy side implying the presence of oxygen bound to the perovskite lattice (binding energy: 529.2±0.3 eV) along with oxygen vacancy (binding energy: 531.5±0.4 eV). The XPS study further revealed that the concentration of the oxygen vacancy is lowest around 0.5 at% of praseodymium doping and beyond this the oxygen vacancy increases. The high temperature conductivity measurement supported these findings by showing similar trends in the electrical conductivity. Both the XPS and conductivity measurements further corroborate the conjecture that praseodymium behaves as amphoteric ion. The praseodymium occupies the A-site of perovskite (Na0.41K0.09Bi0.5)TiO3 for lower praseodymium concentration (<1.0 at%), whereas for higher doping concentration (>1.0 at%) it occupies the B-site exhibiting acceptor like behavior that deteriorates the piezoelectric response.

Magnon excitation-induced spin memory loss in epitaxial L10-FePt/MgO/L10-FePt magnetic tunnel junctions

This work investigates the interplay between interfacial spin–orbit coupling (SOC) and magnon excitation-induced spin memory loss in epitaxial L10-FePt/MgO/L10-FePt magnetic tunnel junctions, which is crucial for advancing spintronic technologies. By employing systematic temperature-dependent transport measurements and inelastic electron tunneling spectroscopy, our study reveals that interfacial SOC at the Pt-terminated FePt/MgO interface significantly enhances magnon excitation during electron tunneling. This process results in a pronounced loss of spin memory in the spin-polarized current, diminishing the tunnel magnetoresistance ratio. Our findings provide critical insights into the mechanisms of spin memory loss, offering directions for optimizing spintronic device performance in the context of pronounced SOC environments.

Perpendicular magnetic anisotropy in multilayers arising from the interplay of thermal strains and diffusion-driven plastic deformation

Magnetic films with perpendicular magnetic anisotropy (PMA) are the basis for efficient memory-storage and future spintronic devices. PMA predominantly stems from surface effects, e.g., symmetry reduction, at the magnetic-layer interface and quickly decays with increasing layer thickness. Strong PMA is thus typically observed in sub-nanometer multilayers with alternating magnetic and noble metals. Using in-situ temperature-dependent measurements of ferromagnetic resonance it is demonstrated that strong PMA can be achieved in Si/Ni multilayers with individual layer as thick as 16 nm. Here, PMA is imposed by thermal strains acting via magnetoelastic coupling and directly depends on the annealing temperature and time, which regulate the diffusion-driven plastic deformation. This opens a way to PMA-film fabrication that avoids complex and resource-intensive production of atomically thin multilayers.

All-2D CVD-grown semiconductor field-effect transistors with van der Waals graphene contacts

Two-dimensional (2D) semiconductors and van der Waals (vdW) heterostructures with graphene have generated enormous interest for future electronic, optoelectronic, and energy-harvesting applications. The electronic transport properties and correlations of such hybrid devices strongly depend on the quality of the materials via chemical vapor deposition (CVD) process, their interfaces and contact properties. However, detailed electronic transport and correlation properties of the 2D semiconductor field-effect transistor (FET) with vdW graphene contacts for understanding mobility limiting factors and metal-insulator transition properties are not explored. Here, we investigate electronic transport in scalable all-2D CVD-grown molybdenum disulfide (MoS2) FET with graphene contacts. The Fermi level of graphene can be readily tuned by a gate voltage to enable a nearly perfect band alignment and, hence, a reduced and tunable Schottky barrier at the contact with good field-effect channel mobility. Detailed temperature-dependent transport measurements show dominant phonon/impurity scattering as a mobility limiting mechanisms and a gate-and bias-induced metal-insulator transition in different temperature ranges, which is explained in light of the variable-range hopping transport. These studies in such scalable all-2D semiconductor heterostructure FETs will be useful for future electronic and optoelectronic devices for a broad range of applications.

Combining electron transfer, spin crossover, and redox properties in metal-organic frameworks

Hofmann coordination polymers (CPs) that couple the well-studied spin transition of the FeII central ion with electron-responsive ligands provide an innovative strategy toward multifunctional metal-organic frameworks (MOFs). Here, we developed a 2D planar network consisting of metal-cyanide-metal sheets in an unusual coordination mode, brought about by infinitely π-stacked redox-active bipyridinium derivatives as axial ligands. The obtained family of materials show vivid thermochromism attributed to electron transfer and/or electronic spin state change processes that can occur either independently or concomitantly. Importantly, the redox activity of the ligands within the structure leads to the quasi-reversible electrochemical reduction reaction on a spin-crossover complex at solid state. These observations have been confirmed via temperature-dependent single-crystal X-ray diffraction, magnetic measurements, Mössbauer, EPR, optical and vibrational spectroscopies as well as quantum chemical calculations.

Tunable Doping Strategy for Few-Layer MoS2 Field-Effect Transistors via NH3 Plasma Treatment.

Molybdenum disulfide (MoS2) is a promising candidate for next-generation transistor channel materials, boasting outstanding electrical properties and ultrathin structure. Conventional ion implantation processes are unsuitable for atomically thin two-dimensional (2D) materials, necessitating nondestructive doping methods. We proposed a novel approach: tunable n-type doping through sulfur vacancies (VS) and p-type doping by nitrogen substitution in MoS2, controlled by the duration of NH3 plasma treatment. Our results reveal that NH3 plasma exposure of 20 s increases the 2D sheet carrier density (n2D) in MoS2 field-effect transistors (FETs) by +4.92 × 1011 cm-2 at a gate bias of 0 V, attributable to sulfur vacancy generation. Conversely, treatment of 40 s reduces n2D by -3.71 × 1011 cm-2 due to increased nitrogen doping. X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence analyses corroborate these electrical characterization results, indicating successful n- and p-type doping. Temperature-dependent measurements show that the Schottky barrier height at the metal-semiconductor contact decreases by -31 meV under n-type conditions and increases by +37 meV for p-type doping. This study highlights NH3 plasma treatment as a viable doping method for 2D materials in electronic and optoelectronic device engineering.

Charge density wave transition and unusual resistance hysteresis in vanadium disulfide (1T-VS2) microflakes

We report existence of charge density wave (CDW) transition with unusual resistivity hysteresis in stable micro-flakes of 2D transition metal dichalcogenide (TMDC) vanadium disulfide (1T-VS2) as ascertained by structural studies, Raman spectroscopy, heat capacity, resistivity measurements and supported by phonon calculations based on density functional theory. The CDW transition occurs at around 296 K on cooling and manifests itself by the onset of resistivity with a negative temperature coefficient, which we identify as the transition temperature (TCDW). The transition is identified by a distinct peak in the heat capacity at T ≈ T CDW along with anomalies in temperature variation of the lattice parameters and complimentary signatures in electron diffraction and temperature-dependent Raman spectroscopy. The temperature-dependent resistivity measurements done with different ramp rates of cooling and heating show strong hysteresis and a low temperature relaxation pointing to the existence of metastable states below the transition. The Raman spectroscopy data show a hysteresis loop below the onset of the CDW transition. The phonon band structure calculations carried out on the 1T-VS2 system show the existence of the phonon mode softening along the diagonal of the Brillouin zone, which is pronounced near the transition temperature implying the prominent role of the mode softening as a driver of the transition. The results imply that the formation of CDW is sensitive to phonon mode softening rather than energy gap opening at the Fermi level.

Remote plasma-enhanced chemical vapor deposition of GeSn on Si (100), Si (111), sapphire, and fused silica substrates

GeSn films were simultaneously deposited on Si (100), Si (111), c-plane sapphire (Al2O3), and fused silica substrates to investigate the impact of the substrate on the resulting GeSn film. The electronic, structural, and optical properties of these films were characterized by temperature-dependent Hall-effect measurements, x-ray diffractometry, secondary ion mass spectrometry, and variable angle spectroscopic ellipsometry. All films were polycrystalline with varying degrees of texturing. The film on Si (100) contained only GeSn (100) grains, 40.4 nm in diameter. The film deposited on Si (111) contained primarily GeSn (111) grains, 36.4 nm in diameter. Both films deposited on silicon substrates were fully relaxed. The layer deposited on Al2O3 contained primarily GeSn (111) grains, 41.3 nm in diameter. The film deposited on fused silica was not textured, and the average grain size was 35.0 nm. All films contained ∼5.6 at. % Sn throughout the layer, except for the film deposited on Al2O3, which contained 7.5% Sn. The films deposited on Si (111), Al2O3, and fused silica exhibit p-type conduction over the entire temperature range, 10–325 K, while the layer deposited on the Si (100) substrate shows a mixed conduction transition from p-type at low temperature to n-type above 220 K. From ∼175 to 260 K, both holes and electrons contribute to conduction. Texturing of the GeSn film on Si (100) was the only characteristic that set this film apart from the other three films, suggesting that something related to GeSn (100) crystal orientation causes this transition from p- to n-type conduction.

Hofmann Clathrates: A "Blue Box" Approach to Modulate Spin-Crossover Properties.

Hofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing p-electron-rich aromatic molecules - similar to the "little blue box". In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox-active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23% increase in volume, caused by the strong donor-acceptor p-p stacking interaction formed between the ligands and the guest molecule. These findings have been confirmed through temperature-dependent single crystal X-ray diffraction, magnetic measurements and optical reflectivity measurements.

Effects of K excess in microstructure of (Ba0.6K0.4)Fe2As2 superconducting powders

Abstract Iron-based superconductors (IBSs) are promising for high-field applications due to their exceptional characteristics, like ultrahigh upper critical field and minimal electromagnetic anisotropy. Creating multifilamentary superconducting wires with elevated transport critical current density is essential for practical use. The Powder in Tube (PIT) technique is commonly used for this purpose, but achieving optimal results requires careful exploration of powder microstructural properties. This is particularly crucial for superconductors like (Ba,K)122, the IBS most promising from an applicative point of view, where factors such as reactivity, volatility, and toxicity of constituent elements affect phase formation. Potassium volatility often leads to nonstoichiometric conditions, introducing excess potassium in the formulation. This study focuses on the impact of potassium excess δ on the microstructural properties of the ‘optimally doped’ (Ba0.6K0.4+δ )Fe2As2 phase (0 ⩽ δ ⩽ 0.08). Using techniques like Scanning Electron Microscopy, x-ray diffraction, and temperature-dependent magnetization measurements, we demonstrate the ability to produce nearly pure powders of the superconducting phase with controlled grain size. Our findings are relevant for PIT wire fabrication, where grain size strongly affects mechanical deformation. Grain size also influences transport properties, as observed in previous studies, where reducing grain size enhanced current-carrying capability at high magnetic fields.

Ln3+ Induced Thermally Activated Delayed Fluorescence of Chiral Heterometallic Clusters Ln2Ag28.

A series of TADF-active compounds: 0D chiral Ln-Ag(I) clusters L-/D-Ln2Ag28-0D (Ln=Eu/Gd) and 2D chiral Ln-Ag(I) cluster-based frameworks L-/D-Ln2Ag28-2D (Ln=Gd) has been synthesized. Atomic-level structural analysis showed that the chiral Ag(I) cluster units {Ag14S12} in L-/D-Ln2Ag28-0D and L-/D-Ln2Ag28-2D exhibited similar configurations, linked by varying numbers of [Ln(H2O)x]3+ (x=6 for 0D, x=3 for 2D) to form the final target compounds. Temperature-dependent emission spectra and decay lifetimes measurement demonstrated the presence of TADF in L-Ln2Ag28-0D (Ln=Eu/Gd) and L-Gd2Ag28-2D. Experimentally, the remarkable TADF properties primarily originated from {Ag14S12} moieties in these compounds. Notably, {Ag14S12} in L-Eu2Ag28-0D and L-Gd2Ag28-2D displayed higher promote fluorescence rate and shorter TADF decay times than L-Gd2Ag28-0D. Combined with theoretical calculations, it was determined that the TADF behaviors of {Ag14S12} cluster units were induced by 4 f perturbation of Ln3+ ions. Specially, while maintaining ΔE(S1-T1) small enough, it can significantly increase k(S1→S0) and reduce TADF decay time by adjusting the type or number of Ln3+ ions, thus achieving the purpose of improving TADF for cluster-based luminescent materials.

Phonon-assisted leakage current of InGaN light emitting diode

We report on the leakage current mechanism in a blue GaN-based light-emitting diode (LED). The device structure was grown by the MOCVD technique on a sapphire substrate. The LED was characterized through various measurements including current-voltage, electroluminescence, and secondary ion mass spectroscopy (SIMS). Capacitance-voltage measurements were employed to calculate the depletion layer thickness at different bias voltages and to analyze the doping profile in the active layer. The reverse temperature-dependent current-voltage measurements were carried out to study the leakage mechanism. The leakage current was explained by phonon-assisted tunneling of charge carriers through deep trap states. The trap energy and density of states were extracted from the application of the introduced model. Cathodoluminescence measurements were performed to evaluate the density of dislocations, which were then compared to x-ray diffraction measurements. The determined value was close to the density of states obtained from the tunneling model.

Unraveling carrier distribution in far-UVC LEDs by temperature-dependent electroluminescence measurements

The hole transport and the carrier distribution in AlGaN-based far-ultraviolett (UVC) light emitting diodes (LEDs) emitting around 233 nm was investigated. Temperature-dependent electroluminescence measurements on dual wavelength AlGaN multiple quantum well (MQW) LEDs show a strong shift in the spectral power distribution from 250 to 233 nm with decreasing temperature. Comparing experimental data with simulation shows that the hole mobility and the electron to hole mobility ratios have a significant influence on the carrier injection efficiency (CIE) and that the change in the spectral power distribution is originating from a change in the hole distribution in the MQWs. Poor hole injection and charge carrier confinement in the AlGaN MQW active region was identified as one of the main reasons for the low CIE in far-UVC LEDs.