Temperature Dependence Of Contrast Research Articles

Excited-state spin-resonance spectroscopy of V{}_{{{{{{{{rm{B}}}}}}}}}^{-} defect centers in hexagonal boron nitride

The recently discovered spin-active boron vacancy (V{}_{{{{{{{{rm{B}}}}}}}}}^{-}) defect center in hexagonal boron nitride (hBN) has high contrast optically-detected magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state that shows promise as a quantum sensor. Here we report temperature-dependent ODMR spectroscopy to probe spin within the orbital excited-state. Our experiments determine the excited-state spin Hamiltonian, including a room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that of the ground-state. We confirm that the resonance is associated with spin rotation in the excited-state using pulsed ODMR measurements, and we observe Zeeman-mediated level anti-crossings in both the orbital ground- and excited-state. Our observation of a single set of excited-state spin-triplet resonance from 10 to 300 K is suggestive of symmetry-lowering of the defect system from D3h to C2v. Additionally, the excited-state ODMR has strong temperature dependence of both contrast and transverse anisotropy splitting, enabling promising avenues for quantum sensing.

Effect of ambient temperature on respiratory tract cells exposed to SARS-CoV-2 viral mimicking nanospheres-An experimental study.

The novel coronavirus caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has reached more than 160 countries and has been declared a pandemic. SARS-CoV-2 infects host cells by binding to the angiotensin-converting enzyme 2 (ACE-2) surface receptor via the spike (S) receptor-binding protein (RBD) on the virus envelope. Global data on a similar infectious disease spread by SARS-CoV-1 in 2002 indicated improved stability of the virus at lower temperatures facilitating its high transmission in the community during colder months (December-February). Seasonal viral transmissions are strongly modulated by temperatures, which can impact viral trafficking into host cells; however, an experimental study of temperature-dependent activity of SARS-CoV-2 is still lacking. We mimicked SARS-CoV-2 with polymer beads coated with the SARS-CoV-2 S protein to study the effect of seasonal temperatures on the binding of virus-mimicking nanospheres to lung epithelia. The presence of the S protein RBD on nanosphere surfaces led to binding by Calu-3 airway epithelial cells via the ACE-2 receptor. Calu-3 and control fibroblast cells with S-RBD-coated nanospheres were incubated at 33 and 37 °C to mimic temperature fluctuations in the host respiratory tract, and we found no temperature dependence in contrast to nonspecific binding of bovine serum ablumin-coated nanospheres. Moreover, the ambient temperature changes from 4 to 40 °C had no effect on S-RBD-ACE-2 ligand-receptor binding and minimal effect on the S-RBD protein structure (up to 40 °C), though protein denaturing occurred at 51 °C. Our results suggest that ambient temperatures from 4 to 40 °C have little effect on the SARS-CoV-2-ACE-2 interaction in agreement with the infection data currently reported.

Contrasting temperature dependences of isostructural one-dimensional ferroelectric crystals NH4HSO4 and RbHSO4 in terms of thermal conductivities.

Temperature-dependent thermal conductivities are reported for one-dimensional (1D) hydrogen-bonding ferroelectric crystals of isostructural compounds NH4HSO4 and RbHSO4. As the temperature was decreased from 300 K, at which point they were paraelectric in the P21/n space group, their thermal conductivities decreased, similar to those of glassy materials. At the ferroelectric transition points (T1A = 270 K for NH4HSO4 and T1R = 264 K for RbHSO4), a change from P21/n to Pn space groups was observed, and the thermal conductivity of the NH4HSO4 crystal decreased without any anomalies, whereas that of RbHSO4 increased, similar to that of crystalline materials. At the second ferroelectric-to-paraelectric transition point of NH4HSO4 (T2A = 154 K), the thermal conductivity increased from 1.00 W m-1 K to 1.32 W m-1 K and increased with a subsequent decrease in temperature, similar to that of crystalline materials. Single-crystal x-ray structure analyses revealed that the thermal conductivity transition of RbHSO4 at T1R = 264 K corresponds to the rotational motion excitation of the HSO4 - chains. The abrupt thermal conductivity jump of NH4HSO4 was likely related to the order-disorder type transition in NH4 + ions, accompanied by lattice vibration excitation, coupled with internal rotation. At the T2A ferroelectric-to-paraelectric phase transition of NH4HSO4, 21 crystal symmetry recovery was observed, similar to the Rochelle salt, and the space group at low temperatures was P21/n. For the RbHSO4 crystals, the thermal conductivity parallel to the 1D chains was 1.5-times higher than the corresponding perpendicular orientation.

Anomalous 2D-Confined Electronic Transport in Layered Organic Charge-Glass Systems.

To get insight into the nature of the electronic fluid in the frustration-driven charge glasses, we investigate in-plane and out-of-plane charge transport for several quasitriangular-lattice organic systems: θ-(BEDT-TTF)_{2}X [X=RbZn(SCN)_{4}, CsZn(SCN)_{4}, and I_{3}]. These compounds host a charge order, charge glass, and Fermi liquid, depending on the strength of the charge frustration. We find that the resistivity exhibits extreme 2D anisotropy and contrasting temperature dependence between the in-plane and out-of-plane directions in the charge-glass phase, unlike in the charge order and metallic states. The experimental features indicate that the frustration-induced charge glass carries an anomalous 2D-confined electronic fluid with possible charge excitations other than conventional quasiparticles.

Thermal stability and dynamics of soft nanoparticle membranes: role of entropy, enthalpy and membrane compressibility.

Nanoparticle based ultra-thin membranes have been shown to have remarkable mechanical properties while also possessing novel electrical, optical or magnetic properties, which could be controlled by tailoring properties at the level of individual nanoparticles. Since in most cases the ultra-thin membranes are coupled to some substrates, the role of membrane-substrate interactions, apart from nanoparticle-nanoparticle interactions become very crucial in understanding their mechanical and thermal stability, as well as their plethora of applications. However, systematic studies in this direction have been conspicuously absent. Here we report thermal stability and the corresponding microscopic dynamics of polymer supported ultra-thin membranes comprising of self-assembled, ordered grains of polymer grafted nanoparticles having tunable mechanical properties. The initially ordered membranes show distinct pathways for temperature induced disordering depending on membrane flexibility as well as on interfacial entropic and enthalpic interactions with the underlying polymer thin film. We also observe contrasting temperature dependence of microscopic dynamics of these membranes depending on whether the graft polymer-substrate polymer interactions are predominantly entropic or enthalpic in nature. Our results suggest that apart from their varied applications, the soft nanoparticle-polymer hybrid membranes are a playground for rich physics involving subtle entropic and enthalpic effects along with the nanoparticles softness, which eventually determine their thermo-mechanical stability.

Polaronic effect in the x-ray absorption spectra of La1−xCaxMnO3 manganites

X-ray absorption spectroscopy (XAS) is performed to study changes in the electronic structures of colossal magnetoresistance (CMR) and charged ordered (CO) La1−xCaxMnO3 manganites with respect to temperature. The pre-edge features in O and Mn K-edge XAS spectra, which are highly sensitive to the local distortion of MnO6 octahedral, exhibit contrasting temperature dependence between CMR and CO samples. The seemingly counter-intuitive XAS temperature dependence can be reconciled in the context of polarons. These results help identify the most relevant orbital states associated with polarons and highlight the crucial role played by polarons in understanding the electronic structures of manganites.

Critical Comparison of FAPbX3 and MAPbX3 (X = Br and Cl): How Do They Differ?

Dielectric measurements on formamidinium lead halide perovskites, FAPbCl3 and FAPbBr3, compared to those of MAPbCl3 and previously reported MAPbBr3, reveal the strongly suppressed temperature dependence of dielectric constants in FA compounds in the temperature range of approximately 140–300 K. Although the behavior of dielectric constants of FA compounds for temperatures <140 K resembles that of the MAPbX3 system, the absence of any strong temperature dependence in sharp contrast to MA analogues in the higher temperature range up to room temperature suggests that the formamidinium (FA) dipoles are in a deep-frozen glassy state unlike the MA dipoles that rotate nearly freely in the temperature range relevant for any photovoltaic application. This observation is further supported by the temperature-dependent single-crystal X-ray diffraction (XRD) results.

Temperature and Parasitic Photocurrent Effects in Dynamic Vision Sensors

The effect of temperature and parasitic photocurrent on event-based dynamic vision sensors (DVS) is important because of their application in uncontrolled robotic, automotive, and surveillance applications. This paper considers the temperature dependence of DVS threshold temporal contrast (TC), dark current, and background activity caused by junction leakage. New theory shows that if bias currents have a constant ratio, then ideally the DVS threshold TC is temperature independent, but the presence of temperature dependent junction leakage currents causes nonideal behavior at elevated temperature. Both measured photodiode dark current and leakage induced event activity follow Arhenius activation. This paper also defines a new metric for parasitic photocurrent quantum efficiency and measures the sensitivity of DVS pixels to parasitic photocurrent.

Temperature dependence of viscosity, relaxation times (T1, T2) and simulated contrast for potential perfusates in post-mortem MR angiography (PMMRA)

Developments in post-mortem imaging increasingly focus on addressing recognised diagnostic weaknesses, especially with regard to suspected natural deaths. Post-mortem MR angiography (PMMRA) may offer additional diagnostic information to help address such weaknesses, specifically in the context of sudden cardiac death. Complete filling of the coronary arteries and acceptable contrast with surrounding tissue are essential for a successful approach to PMMRA. In this work, the suitability of different liquids for inclusion in a targeted PMMRA protocol was evaluated. Factors influencing cooling of paraffinum liquidum + Angiofil® (6 %) in cadavers during routine multiphase post-mortem CT angiography were investigated. The temperature dependence of dynamic viscosity (8–20 °C), longitudinal (T1) and transverse (T2) relaxation (1–23 °C) of the proposed liquids was quadratically modelled. The relaxation behaviour of these liquids and MR scan parameters were further investigated by simulation of a radiofrequency (RF)-spoiled gradient echo (GRE) sequence to estimate potentially achievable contrast between liquids and post-mortem tissue at different temperatures across a forensically relevant temperature range. Analysis of the established models and simulations indicated that based on dynamic viscosity (27–33 mPa · s), short T1 relaxation times (155–207 ms) and a minimal temperature dependence over the investigated range of these parameters, paraffin oil and a solution of paraffin oil + Angiofil® (6 %) would be most suitable for post-mortem reperfusion and examination in MRI.

Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen

Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.8 to 4.3 K temperature range. Upon short-term in situ irradiation the NO readily undergoes photolysis to yield HNO, NOH, NH, NH3, H2O, and H atoms. We map the postphotolysis reactions of mobile H atoms with NO and document first-order growth in HNO and NOH reaction products for up to 5 h after photolysis. We perform three experiments at 4.3 K and one at 1.8 K to permit the temperature dependence of the reaction kinetics to be quantified. We observe Arrhenius-type behavior with a pre-exponential factor of A = 0.036(2) min(-1) and Ea = 2.39(1) cm(-1). This is in sharp contrast to previous H atom reactions we have studied in solid pH2 that display definitively non-Arrhenius behavior. The contrasting temperature dependence measured for the H + NO reaction is likely related to the details of H atom quantum diffusion in solid pH2 and deserves further study.

Thermal Expansion, Anharmonicity and Temperature‐Dependent Raman Spectra of Single‐ and Few‐Layer MoSe2 and WSe2

We report the temperature-dependent Raman spectra of single- and few-layer MoSe2 and WSe2 in the range 77-700 K. We observed linear variation in the peak positions and widths of the bands arising from contributions of anharmonicity and thermal expansion. After characterization using atomic force microscopy and high-resolution transmission electron microscopy, the temperature coefficients of the Raman modes were determined. Interestingly, the temperature coefficient of the A(2)(2u) mode is larger than that of the A(1g) mode, the latter being much smaller than the corresponding temperature coefficients of the same mode in single-layer MoS2 and of the G band of graphene. The temperature coefficients of the two modes in single-layer MoSe2 are larger than those of the same modes in single-layer WSe2. We have estimated thermal expansion coefficients and temperature dependence of the vibrational frequencies of MoS2 and MoSe2 within a quasi-harmonic approximation, with inputs from first-principles calculations based on density functional theory. We show that the contrasting temperature dependence of the Raman-active mode A(1g) in MoS2 and MoSe2 arises essentially from the difference in their strain-phonon coupling.

Non-intrusive measurement of microscale temperature distribution by spontaneous Raman imaging

A non-intrusive and spatially resolved temperature measurement technique based on spontaneous Raman imaging was developed to measure two-dimensional temperature distributions in microfluidic systems. Raman scattering arising from OH stretching vibrations of H2O molecules was used to measure the local channel flow temperature because of its high sensitivity to temperature. The OH stretching band has two parts with contrasting temperature dependences: hydrogen-bonded (HB) and non-hydrogen-bonded (NHB) modes. Raman images of HB and NHB modes were separately captured by an electron-multiplying charge-coupled device camera using two bandpass filters with center wavelengths of 642 and 660 nm, respectively. The two-dimensional temperature distributions were obtained from the intensity ratio of the two images by applying a calibration curve, which showed that there was a linear relationship between the temperature and the intensity ratio of HB to NHB modes for temperatures in the range 293–333 K. Temperature distribution measurements were demonstrated in the mixing flow field in the junction area of a T-shaped channel composed of a poly(dimethylsiloxane) chip and borosilicate glass slides. Non-uniform temperature distributions were quantitatively visualized at a spatial resolution of 12.8 × 12.8 μm2 for three different heating conditions.

A band-pass filter approach within molecular dynamics for the prediction of intrinsic quality factors of nanoresonators

The temperature and frequency dependence of the flexural mode quality factors (Q) of doubly clamped single wall carbon nanotube resonators are calculated using classical molecular dynamics simulations. The validity of the various methods available in the literature for calculating Q based on the temporal response of the system during ring-down is discussed and the discrepancies associated with the methods are explained. A new approach based on band-pass filtering is proposed for calculating Q, which reveals classical temperature dependence (Q ∼ T−1) in contrast to the previously reported results (Q ∼ T−β, 0 &amp;lt; β &amp;lt; 1). It is shown that the Q estimated from the temporal response is in good agreement with the Q estimated from frequency response. This work also demonstrates that the proposed method is particularly advantageous when multiple modes are simultaneously excited within the linear regime.

Thermoelectric Power at Low Temperatures in Ce(Ni1-xPdx)2Ge2and CeCu5.9Au0.1in the Vicinity of Antiferromagnetic Quantum Critical Point

We present experimental results of thermoelectric power S and magnetic specific heat C m down to 0.2 K for Ce(Ni 1- x Pd x ) 2 Ge 2 ( x = 0- 0.12) and CeCu 5.9 Au 0.1 , being located in the vicinity of antiferromagnetic quantum critical point (AFM-QCP). S / T for Ce(Ni 1- x Pd x ) 2 Ge 2 shows complicated temperature dependence in contrast to a monotonic increase in the C m / T with decreasing temperatures. The correlation parameter q , equivalent to the ratio S / C m , decreases below 10 K attaining a considerably smaller value than unity at the lowest temperature for CeNi 2 Ge 2 . On the other hand, the q for CeCu 5.9 Au 0.1 deviates upward below 0.6 K from the saturation around 1 K, and reaches unity at the lowest temperature. The contrastive observation in the q between the both systems at low temperatures seems to reflect the difference in the AFM-QCP type.

Effect of threading screw and edge dislocations on transport properties of 4H–SiC homoepitaxial layers

Local recombination properties of threading screw and edge dislocations in 4H–SiC epitaxial layers have been studied using electron beam induced current (EBIC). The minority carrier diffusion length in the vicinity of dislocations was found to vary with dislocation type. Screw dislocations had a more pronounced impact on diffusion length than the edge dislocations, evidencing stronger recombination activity. Temperature dependence of EBIC contrast of dislocations suggests that their recombination activity is controlled by deep energy levels in the vicinity of dislocation cores. This paper shows that the type of dislocation (screw or edge) can be identified from analysis of EBIC contrast.

Dual-[formula omitted] assignment policies in ITD-aware synthesis

Traditionally, the effects of temperature on delay of CMOS devices have been evaluated using the highest operating temperature as a worst-case corner. This conservative approach was based on the fact that, in older technologies, CMOS devices systematically degraded their performance as temperature increases.With the progressive scaling of technology, however, there has been a continuous reduction of the gap between supply and threshold voltages of devices, mostly due to low-power constraints. The latter have accelerated this trend by using libraries containing multiple instances of a cell with different ranges of threshold voltages; in particular, the use of high-Vt cells to control sub-threshold leakage currents has made this gap smaller and smaller.The consequence of this trend is the occurrence of the so-called inverted temperature dependence (ITD), under which cells get faster as temperature increases. This new thermal dependence has made the old worst-case design approach obsolete, posing new EDA challenges. Beside complicating timing analysis, in particular, ITD has important and unforeseeable consequences for power-aware design, especially in dual-Vt logic synthesis. Due to a contrasting temperature dependence between low-Vt cells (which enjoy the classical, direct temperature dependence) and high-Vt cells (for which an inverted temperature dependence holds), a single-temperature worst-case design approach fails to generate netlists that are compliant with timing constraints for the entire temperature range.In this work, we first validate the relevance of ITD on an industrial 65nm CMOS multi-Vt library. Then, we describe an ITD-aware, dual-Vt assignment algorithm that guarantees temperature-insensitive operation of the circuits, together with a significant reduction of both leakage and total power consumption. The algorithm has been tested over standard benchmarks using three different replacement policies.Experimental results show an average leakage power savings of 50% w.r.t. circuits synthesized with a standard, commercial flow that does not take ITD into account and thus, to ensure that no temperature-induced timing faults occur, needs to resort to over-design (i.e., over-constraining the timing bound so as to make sure that temperature fluctuations never make the circuits violating the specified required time for all paths).

Manifestation of the electrode-contact effect on the dielectric response and impedance spectra of CaSiO3-doped CaCu3Ti4O12

Undoped and CaSiO3-doped CaCu3Ti4O12 (CCTO) ceramics were prepared by solid-state reaction. The structures and compositions were characterized by a field-emission transmission electron microscope, equipped with Gatan image filter and high angle annular dark filed detector. We observed the low-frequency plateaus of frequency dependence of permittivity in CaSiO3-doped CCTO with Au electrode revealing an opposite temperature dependence in contrast to In–Ga electrode, which is evidenced to be related to the grain-boundary capacitance and contact resistance. Impedance spectra of CaSiO3-doped CCTO with In–Ga and Au electrodes can be modeled by an equivalent circuit with series combination of four parallel RC elements including domains, domain boundaries, grain boundaries, and the electrode contacts. We also confirm that the Si ions segregate to either grain boundaries or pore surface and develop an amorphous phase; most of the excess Cu ions are prevented by the segregated Si ions from being along the grain boundaries and form CuO particles in triple-junction pores.

NMR Spin-Lattice Relaxation Rates in Cuprates

An analysis of nuclear spin-lattice relaxation data in the normal state of cuprates that appropriately accounts for the highly anisotropic structures shows no contrasting temperature dependence of the Cu, O, and Y relaxations, which suggests that all nuclei relax by the same mechanism of the spin liquid. To investigate the temperature dependence of this mechanism, the model of fluctuating fields is used in which the rates are expressed in terms of hyperfine interaction energies and an effective correlation time τ eff characterizing the dynamics of the spin fluid. The former contain the effects of the antiferromagnetic static spin correlations, which cause the hyperfine field constants to be added more coherently at low temperature but incoherently at high temperature. At low temperatures, τ eff grows linearly with temperature as in ordinary metals. At high temperatures, however, the nuclear spin-lattice relaxation rates in various cuprates unequivocally reflect local moment features. This behavior is similar to that observed for the magnetic transition metals Fe, Co, and Ni, where also some properties show a cross-over from an itinerant behavior of delocalized electrons at low to that of localized moments at high temperatures.

Luminescence of dislocation network in directly bonded silicon wafers

AbstractThe luminescence behaviors of dislocation network in directly bonded silicon wafers have been investigated in this paper. The individual dislocations were observed in the sample bonded with extreme small misorientation angles by electron beam induced current (EBIC) technique. The temperature dependence of EBIC contrast of the dislocation lines showed that its contamination degree was smaller than 104/cm. The cathodoluminescence (CL) from the dislocation networks showed D1‐line existed in all the bonded samples, often along with D2‐line. The D3/D4‐lines could also be obtained by tuning the misorientations. Meanwhile, the application of an external bias can effectively enhance the luminescence. Furthermore, a metal‐insulator (SiOx, x &lt; 2)‐semiconductor light‐emitting diode (MOS‐LED) based on the bonded silicon wafer was demonstrated. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Two-impurity Anderson model for the transport through two quantum dots coupled via a quantum wire

We study the problem of transport through two quantum dots coupled via a finite-length quantum wire. In the limit where each dot acts essentially as a localized Kondo impurity, the geometry allows us to study various questions in the many-impurity problem like the interplay of Kondo and RKKY interactions, the average interimpurity distance beyond which the single-impurity model becomes valid, etc. We model the system in terms of the two-impurity Anderson model and study the transport behavior using a perturbative (in the Coulomb interaction $U$) approach, restricting ourselves to the ``symmetric'' case. It can be seen that (antiferromagnetic) ferromagnetic correlations develop between the impurities for (``odd'') ``even'' distances between the impurities. We analyze the antiferromagnetic case in detail and show that the linear conductance for the coupled dot system has a nonmonotonic temperature dependence in contrast to the monotonic temperature dependence for the single-dot system. A temperature scale emerges in the problem\char22{}the coherence temperature\char22{}below which the two impurities develop strong correlations. The emergence of this scale is also reflected in the behavior of the impurity Green functions. In particular, the zero-temperature diagonal impurity density of states shows a splitting of the Kondo resonance with the splitting width being of the same order as the coherence temperature. The coherence temperature decreases with an increase in the distance between the impurities and increases with an increase in $U$. Finally, we also study transport in the ``side'' geometry where the dots are side coupled to a long wire at a finite distance and show that essentially the same physics is observed for the antiferromagnetic case as in the ``chain'' geometry.