Te 3d Research Articles

Influence of HfO2 oxide layer on crystallization properties of In3SbTe2 phase change material

Phase Change Memory (PCM) represents a potential paradigm in the realm of non-volatile memory technologies, and several phase change materials are studied for utilization in PCM devices. This work employs a less explored In3SbTe2 (IST) phase change material (active layer) integrated with an oxide (HfO2) layer and investigates the influence of the oxide layer on the active layer. The oxide layer remains amorphous when annealed at 400 °C, and it doesn’t alter the crystallization temperature (290 °C) of the active layer in IST with HfO2 thin-film. However, after crystallization, the grain size of the active layer is reduced to ∼8.23 nm in IST with HfO2 thin-film, compared to only IST thin-film. XPS core-level spectra (In 3d, Sb 3d, Te 3d) of IST active layer reveal the peak shifting towards higher binding energy at 300 °C and 400 °C annealed films, implying bond energy increase with crystallization and film stability improves. The Hf or O atoms of the oxide layer don’t diffuse into the active layer with annealing, suggesting no interference with the phase switching property of IST. A higher optical bandgap of 1.154 eV in as-deposited IST with HfO2 thin-film compared to the only IST thin-film illustrates better stability of the amorphous state in the film with the oxide layer. In addition, the fabricated PCM device using the IST with the oxide layer demonstrates phase switching at a lower threshold voltage of (2.1 ± 0.1) V, compared to the IST-based device. The findings indicate that the enhanced structural and electrical switching characteristics of IST phase change layer coupled with an oxide layer make it beneficial for data storage PCM applications.

Downfield Proton MRSI at 3 Tesla: A Pilot Study in Human Brain Tumors.

To investigate the use of 3D downfield proton magnetic resonance spectroscopic imaging (DF-MRSI) for evaluation of tumor recurrence in patients with glioblastoma (GBM). Seven patients (4F, age range 44-65 and mean ± standard deviation 59.3 ± 7.5 years) with previously treated GBM were scanned using a recently developed 3D DF-MRSI sequence at 3T. Short TE 3D DF-MRSI and water reference 3D-MRSI scans were collected with a nominal spatial resolution of 0.7 cm3. DF volume data in eight slices covered 12 cm of brain in the cranio-caudal axis. Data were analyzed using the 'LCModel' program and a basis set containing nine peaks ranging in frequency between 6.83 to 8.49 ppm. The DF8.18 (assigned to amides) and DF7.90 peaks were selected for the creation of metabolic images and statistical analysis. Longitudinal MR images and clinical history were used to classify brain lesions as either recurrent tumor or treatment effect, which may include necrosis. DF-MRSI data were compared between lesion groups (recurrent tumor, treatment effect) and normal-appearing brain. Of the seven brain tumor patients, two were classified as having recurrent tumor and the rest were classified as treatment effect. Amide metabolite levels from recurrent tumor regions were significantly (p < 0.05) higher compared to both normal-appearing brain and treatment effect regions. Amide levels in lesion voxels classified as treatment effect were significantly lower than normal brain. 3D DF-MRSI in human brain tumors at 3T is feasible and was well tolerated by all patients enrolled in this preliminary study. Amide levels measured by 3D DF-MRSI were significantly different between treatment effect and tumor regrowth.

Photo-induced lattice distortion in 2H-MoTe2 probed by time-resolved core level photoemission.

The technological interest in MoTe2 as a phase engineered material is related to the possibility of triggering the 2H-1T' phase transition by optical excitation, potentially allowing for an accurate patterning of metallic areas into a semiconducting canvas via laser irradiation. In this paper, we investigate the photo-induced modifications of a bulk 2H-MoTe2 crystal by means of time-resolved X-ray photoemission spectroscopy. We observe that in the microsecond timescale, the core levels shift to higher kinetic energies due to surface photovoltage fields, while in the sub-nanosecond range, the photoemission peaks shift in the opposite direction. With the support of DFT calculations, we ascribe the latter effect to the deformation of the lattice in the out-of-plane direction, which is along the pathway for the 2H-1T' phase transition. Our data indicate an intermediate lattice excitation state with a measured lifetime in the order of 600 ps, in which the displacement of Mo and Te atoms causes the Te 4d electrons to shift towards higher binding energies.

Effect of Fe on Bi2Te3: Structure, magnetic properties, and XPS valence band

The crystal structure and magnetic properties of Fe doped Bi2Te3 are presented. The samples were studied by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Rietveld refinement results show a decrease in volume due to the decrease in c lattice parameter as iron is introduced. By XPS measurements, the Te 3d, Bi 4f, Bi 5d, Te 4d, and Fe 3d core levels were identified, and the XPS valence band (VB) was measured. The deconvolution process of high resolution XPS spectra in Fe 3d orbital shows that the Fe3+ ion is present in the samples. Theoretical calculations by DFT reveal that the Bi2Te3 compound is a semiconductor with a narrow energy band gap in agreement with experimental results. DOS analysis shows that the main contributions to the valence band are the Te 5p, Bi 6p, and Fe 3d states. XPS VB shows a decrease in the intensity at zero eV due to increased Fe 3d states and good correspondence with DOS calculated for Bi2Te3. Finally, magnetic susceptibility measurements on Bi2Te3 do not show a magnetic behavior; however, for the doped sample with x = 0.2, a weak ferromagnetic behavior (WFM) below 14 K is observed.

1T′-MoTe2 and 2H-MoTe2 by XPS

Two different phases of the transition-metal dichalcogenide and molybdenum ditelluride (1T′-MoTe2 and 2H-MoTe2) were grown by chemical vapor transport. Oxygen-free surfaces were generated by exfoliation in air and then analyzed by x-ray photoelectron spectroscopy. High-resolution core and valence and Auger spectra were acquired for both materials including Te 3d, Te 4d, Te MNN, Mo 3d, and valence band spectra. Differences in Te 3d and Mo 3d peak positions that were previously reported were confirmed, and asymmetry on the metallic 1T′-phase was documented in the Te 3d, Te 4d, and Mo 3d spectra that could prove useful in identifying mixtures of these materials.

Nonparabolicity effects on carrier lifetimes in bulk Hg1-xCdxTe alloys and Mid-Infrared 2D Hg1-xCdxTe/CdTe Single Quantum Well Lasers

We report on a theoretical study of nonparabolicity (NP) effects on carrier lifetimes in narrow energy bandgap bulk (3D) Hg 1-x Cd x Te ternary alloys and their related 2D Hg 1-x Cd x Te/CdTe Single Quantum Well (SQW) nanostructures for Mid-infrared (MIR) Laser applications. Carrier lifetime (τ) calculations are performed within both the parabolic and the 4-band CB + HH + LH + SO nonparabolic models. We show that NP affects strongly all three main scattering processes: Auger, Schockley-Read-Hall (SRH), and radiative recombination (RR). At 300 K and in mid-Cd contents (0.4 < x < 0.6) 3D Hg 1-x Cd x Te alloys, Auger 1 is shown to be the dominant τ limiting factor. In 2D Hg 1-x Cd x Te/CdTe SQW nanostructures, we show that RR turns out to be the dominant τ limiting process. This strongly reduced influence of Auger1 process in 2D Hg 1-x Cd x Te/CdTe SQW nanostructures is the result of the strong 2D quantum confinement induced amplification of NP effects via much stronger electron (CB) and all three hole (HH, LH, SO) energy subbands interactions and mixing. As a consequence, NP effects are finally shown to significantly improve all main 2D Hg 1-x Cd x Te/CdTe SQW Laser parameters in the MIR λ range with an optimum at x = 0.45 and for wide enough QW with L z ≥ 100 Å. • Nonparabolicity effects on carrier lifetimes in Hg 1-x Cd x Te 3D and 2D MIR Lasers. • Auger scattering processes are dominant at 300 K in 3D Hg 1-x Cd x Te alloys (0.3 < x < 0.6). • Radiative recombination is dominant 300 K in 2D Hg 1-x Cd x Te/CdTe QW (x ≥ 0.40). • NP affects strongly carrier lifetimes, and consequently, all main laser parameters. • NP improves Laser emission wavelength, optical gain and threshold current densities.

XPS analysis of bridging and non-bridging oxygen in Yb3+-Er3+-Tm3+-doped zinc-tellurite glasses

Influence of Er3+, Yb3+ and Tm3+ on the network structure of zinc-tellurite glasses is investigated by refraction index and high-resolution X-ray photoelectron spectroscopy (XPS) in order to clarify the role of rare-earth ions in the formation of non-bridging and bridging oxygens (NBO and BO, respectively). The NBO atoms were responsible for high polarizability, as confirmed from the correlations between the local structure and polarizability, where have been tentatively established high linear fit r2=0.96 and 0.98 when the excitation wavelengths are 532 and 632.8 nm, respectively. The structural origin of the NBO atoms into the zinc-tellurites glasses is discussed by analysis of the component number from the deconvolution in the XPS spectra. In this analysis, Te 3d peaks shift by about 0.23 eV towards higher binding energy from TZ1 to TZ4, and spin-orbit splitting between Te 3d5/2 and Te 3d3/2 to all glasses remain unchanged, ΔE ≈10.4 eV. While Zn 2p peaks shift by about 1.08, eV towards higher binding energy, and spin-orbit splitting between Zn 2p3/2 and Zn 2p1/2 increase of 23.08 eV (TZ1 to TZ3) to 24.09 eV (TZ4) whit the increase REI. The O 1s spectra suggest that the increase of REI concentration produces additional environments for REI with bonds through lone-pair electrons, favoring the formation of NBOs. It was observed that the increasing the concentrations of REI has a high linear dependence with increased of NBO atoms in the glass network, r2=0.87.

Simultaneous Observation of Carrier-Specific Redistribution and Coherent Lattice Dynamics in 2H-MoTe2 with Femtosecond Core-Level Spectroscopy.

We employ few-femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy to reveal simultaneously the intra- and interband carrier relaxation and the light-induced structural dynamics in nanoscale thin films of layered 2H-MoTe2 semiconductor. By interrogating the valence electronic structure via localized Te 4d (39-46 eV) and Mo 4p (35-38 eV) core levels, the relaxation of the photoexcited hole distribution is directly observed in real time. We obtain hole thermalization and cooling times of 15 ± 5 fs and 380 ± 90 fs, respectively, and an electron-hole recombination time of 1.5 ± 0.1 ps. Furthermore, excitations of coherent out-of-plane A1g (5.1 THz) and in-plane E1g (3.7 THz) lattice vibrations are visualized through oscillations in the XUV absorption spectra. By comparison to Bethe-Salpeter equation simulations, the spectral changes are mapped to real-space excited-state displacements of the lattice along the dominant A1g coordinate. By directly and simultaneously probing the excited carrier distribution dynamics and accompanying femtosecond lattice displacement in 2H-MoTe2 within a single experiment, our work provides a benchmark for understanding the interplay between electronic and structural dynamics in photoexcited nanomaterials.

In Situ Dynamics during Heating of Copper-Intercalated Bismuth Telluride

Summary The presence of a van der Waals gap within layered materials enables the intercalation of guest species, which can be used for tuning properties. The introduction of intercalant species may also lead to structural transformations across a range of temperatures and use conditions, but we have a limited understanding of the high-temperature evolution of intercalated layered materials. Here, we use in situ transmission electron microscopy to investigate temperature-dependent structural evolution of Bi2Te3, a layered material with well-known application as a thermoelectric, which contains intercalated Cu. As temperature is increased, the initially disordered Cu undergoes local ordering within the van der Waals gap, along with anisotropic sublimation behavior of the crystals. As the temperature is raised further, layered Cu2Te crystals nucleate and grow with a crystallographic relationship to the Bi2Te3 lattice. Notably, the presence of Cu decreases the thermal stability of the Bi2Te3 and substantially alters the transformation pathways during heating.

Effect of core size on the luminescence properties of cadmium telluride/zinc sulphide core-shell quantum dots

In the present work, cadmium telluride/zinc sulphide (CdTe/ZnS) Core-Shell Quantum Dots (QDs) were prepared and the effects of core size on the luminescence possessions of CdTe QDs were investigated. For this purpose, the CdTe QDs was coated with ZnS from aqueous phase. Post growths, the synthesized QDs (CdTe & CdTe/ZnS) were characterized by photo-physical spectra for analyzing the characteristic changes in the samples. The photo-physical analysis revealed the shifts in absorption peaks of both the samples (CdTe and CdTe/ZnS). In UV–Visible analysis, due to increase in particle size, the absorption peak of CdTe QDs red shifts to higher wavelength with respect to the refluxing time. Even in the case of CdTe/ZnS core-shell QDs, the emission wave length red shifts to longer wavelength. X-Ray Diffraction (XRD) revealed the crystal structure of the synthesized CdTe QDs and CdTe/ZnS core-shell QDs. The peaks of CdTe/ZnS QDs shift towards greater angles and it is the development of shell structure ZnS over CdTe QDs. HRTEM studies revealed the presence of core and shell from the synthesized materials In HRTEM images, the additional stretch everywhere from the core particles confirmed the compressive strain developed from ZnS. This was qualitatively considered and attributed into the successive establishment of ZnS shells on the core CdTe QDs surface. And these prepared CdTe/ZnS core-shell QDs are having the increase of average size. In XPS analysis for the CdTe/ZnS Core-Shell layering were confirmed, through the intensity signal of Cd (3d), Te (3d), Zn (2p) and S (2s).

2D bismuth telluride analyzed by XPS

Bismuth telluride (Bi2Te3) was analyzed using x-ray photoelectron spectroscopy. A freshly exfoliated, oxygen-free flake was analyzed. Spectral regions for O 1s, Te 3d, C 1s, Bi 4f, Bi 5d, and Te 4d were acquired. Bulk quantitative analyses by x-ray fluorescence, inductively coupled plasma-mass spectrometry, and x-ray diffraction indicated that the material was stoichiometric, contained low concentrations of impurities, and was phase pure, respectively.

Structure and low field magnetic properties in phosphate-tellurite glasses

Phosphate-tellurite glasses exhibit magnetic properties, due to the presence of the small metallic Te colloids which were revealed in low field magnetic circular dichroism. These metallic colloids induce the red coloring of these glasses together with the absorbance in the visible region. The temperature dependence of the absorption spectrum and the A-term in magnetic circular dichroism are specific for Te metallic nanoparticles, which results during the melting procedure over 10000C due to the conversion of Te4+ in Te0 atoms. The X-ray photoelectron spectroscopy supports this fact due to the presence of small peaks as satellites in the region of Te 3d core-level spectrum. Quantification of these satellites compared with Te 3d3/2 and 3d5/2 peaks suggests a 14% concentration of Te metallic nanoparticles in these phosphate-tellurite glasses. The presence of metallic particles induces the crystallization effects of Te micrograins upon thermal treatments at higher temperatures.

Spray pyrolysis-coated nano-clustered CdTe on amorphous Si thin films for heterojunction solar cells

Heterojunction solar cells are demonstrated employing spray pyrolysis-processed nano-clustered cadmium telluride (CdTe) on DC-sputtered amorphous silicon (a-Si) as p- and n-type layers, respectively. CdTe and a-Si films were subjected to X-ray photoelectron spectroscopic measurements showing Cd 3d (404.9 eV) and Te 3d (575.8 eV) peaks corresponding to CdTe while the peaks Si 2p (98.3 eV) and Si 2 s (148.3 eV) represent a-Si. Heterojunction solar cells with a stacked structure of FTO/a-Si/CdTe/Al resulted in a photo-conversion efficiency of 2.7% for an optimized thickness values of a-Si (1 µm) and CdTe (6 µm) films.

X-ray photoelectron spectroscopy (XPS) and radiation shielding parameters investigations for zinc molybdenum borotellurite glasses containing different network modifiers

Zinc molybdenum borotellurite glasses containing different network modifiers with the nominal composition of 60 TeO2–10 B2O3–10 MoO3–10 ZnO–10 MO (MO = Li2O, Na2O, K2O, MgO, CaO, and PbO) were prepared by melt quenching method. The X-ray photoelectron spectroscopy (XPS) studies allow to monitor the structural modifications leading to the formation of bridging oxygens (Te–O–Te, B–O–B, Mo–O–Mo, and Te–O–Mo bonds) and nonbridging oxygens (Te = O, Te–O−M+, Mo–O− bonds in the MoO6 octahedral units, Zn–O bonds from ZnO4) with the addition of alkali (Li, Na, and K), alkaline (Mg, Ca), or heavy metal (Pb) oxides. The Te 3d localized core-levels spectra show an asymmetry due to the existence of different Te-based structural clusters and were fitted with three contributions such as Te ions in TeO4 trigonal bipyramid configuration, Te ions in TeO3 − trigonal pyramid configuration and TeO3+1 polyhedra, respectively. The analysis of the Mo 3d spectra indicates prevailingly Mo6+ ions only. The Zn 2p core-level XPS spectra demonstrate that the zinc is mainly coordinated by four oxygen atoms. The essential radiation shielding parameters were studied for the prepared glasses in the photon energy range 1 keV to 100 GeV using WinXCom software program. Parameters like mass attenuation coefficient (μ/ρ), effective atomic number (Z eff), and mean free path (MFP) are evaluated. Further, by using geometric progression method, exposure buildup factor (EBF) values were also calculated in the incident photon energy range 0.015–15 MeV, up to penetration depth of 40 mfp (mean free path). The macroscopic effective removal cross sections (∑R) for fast neutrons have been calculated. The maximum values of μ/ρ and Z eff were found for PbO-introduced glass though it possesses a lower value for MFP and EBF. The obtained results indicate that PbO-based glass is the best radiation shielding material among the studied glasses.

Direct evidence of reactive ion etching induced damages in Ge2Sb2Te5 based on different halogen plasmas

Chalcogenide glasses based on Ge-Te-Sb are processed using reactive ion etching (RIE) in the fabrication of phase change memory (PCM). These materials are known to be halogenated easily and apt to be damaged when exposed to halogen gas based plasmas which can cause severe halogenation-induced degradation. In this paper, we investigate the RIE induced damage of popular phase change material Ge2Sb2Te5 (GST) in different halogen based plasmas (CF4, Cl2 and HBr) highly diluted by argon. After blanket etching, results of scanning electron microscopy and atomic force microscopy directly showed that the surface of Cl2 etched samples were roughest with a Ge deficient damaged layer. X-ray photoelectron spectroscopy was performed to investigate the chemical shift of constituent elements. Selected scans over the valence band peaks of Te 3d revealed that electrons were transferred from chalcogenide to halogen and the highest halogenation was observed on the GST etched by CF4. The GST films masked with patterned TiN were also etched. High-resolution transmission electron microscopy and surface scan directly showed the line profile and the damaged layer. Almost vertical and smooth sidewall without damaged layer makes HBr a promising gas for GST etch in the fabrication of high-density memory devices.

Etching Characteristics and Mechanisms of Ti-Sb-Te Phase Change Material in CHF3/O2/Ar Plasma for Nano-Devices

The investigation of reactive-ion-etching (RIE) characteristics and mechanisms for Ti-Sb-Te (TST) new phase change material in CHF3/O2/Ar plasmas was carried out in this paper. The effects of three experimental parameters, gas ratio, gas pressure and input radio frequency (RF) power on variations of etch rate, surface root-mean-square (RMS) roughness and profile were investigated. Within the range of our experimental conditions, the maximum etch rate with ∼83 nm/min, a smooth surface with RMS less than 1 nm and a highly anisotropic profile are obtained using the optimized process conditions (8% oxygen content, input power of 300 W, gas pressure of 30 mTorr). The surface roughness is strongly reduced with the addition of oxygen, but sharply increased at higher gas pressure. Surface analysis using X-ray photoelectron spectroscopy (XPS) reveal that surface of etched TST film is mainly fluorinated by forming TiFx, SbFx, and TeFx. According to spectra of Sb 3d and Te 3d, a slight shift of peaks to a higher energies (∼0.6 eV) on the etched surface can be seen, indicting the surface degradation after etching process.

Measurement of core level and band offsets at the interface of ITO/Hg3In2Te6(1 1 0) heterojunction by synchrotron radiation photoelectron spectroscopy

The Indium Tin Oxide (ITO) film was deposited on the surface of Hg3In2Te6 (short for MIT) (110) for the fabrication of ITO/MIT(110) heterojunction by using the pulsed laser deposition method. In situ X-ray photoelectron spectroscopy was utilized to examine the band offsets and core level of ITO/MIT(110) heterojunctions. The result showed that the valence band maximum of ITO films and MIT(110) were 1.6eV and 0.6eV, respectively. Meanwhile, it was found that the binding energy of Te 3d, Sn 3d and Hg 4f remained unchanged during the ITO deposition process. However, the binding energy of O 1s and In 3d5/2 increased about 0.3eV and 0.2eV, respectively, with the thickness increasing of ITO film from 3.5nm to 5nm. This may due to the elements diffusion at the interface region during the film growing process. According to the core level spectrum, it can be speculated that no significant chemical reaction occurred at the interface of ITO/MIT(110). In addition, the valence band offset of the ITO/MIT(110) heterojunction can be calculated to be −1±0.15eV by the means of the photoelectron spectroscopy methods. The conduction band offset is deduced to be −3.96±0.15eV from the known valence band offset value, indicating that the band offsets of ITO/MIT(110) heterojunction is a type-II band alignment.

Investigation of oxide layer on CdTe film surface and its effect on the device performance

In this work, the chemical evolution of CdTe crystal and thin film under air exposure was investigated by X-ray Photoelectron Spectroscopy (XPS). In particular, the analysis of Te 3d core level allowed us to characterize the surface oxidation. Indeed, in both cases and after a short air exposure, the Te 3d peaks exhibited clearly two components corresponding to Te–Cd and Te–O, i.e. bulk CdTe and native oxide. The later one was used to estimate an equivalent oxide layer thickness. Only a weak oxide amount could be observed on both fresh surfaces, whereas after two days of air exposure, the native oxide thickness was estimated to 2.2nm and 0.9nm for CdTe crystal and thin film respectively. For a longer exposition time of one month, the oxide layer thickness increased in both cases up to 7.2 and 5.9nm, for CdTe crystal and thin film respectively. Even, if the oxidation kinetic appeared slower in the case of CdTe thin film, such insulating oxide layer formation at CdTe surface under air exposure might have negative effect on the ohmic back contact formation and further electrical characteristics of solar cells. Next to this study, aged CdTe samples were submitted to a chemical etching after several days of air exposure and before solar cell fabrication. It appeared that solar cell based on ‘aged CdTe layer’ after etching exhibit electrical performances similar to those obtained with a freshly elaborated CdTe device. Therefore, CdTe chemical etching appears as an effective way to remove the surface oxide layer and retrieve good cell performances. As a result, it is possible to store CdTe films for long duration before solar cells fabrication.

Ab initio study of the structural, vibrational and thermal properties of Ge2Sb2Te5

The structural, vibrational and thermal properties of hexagonal as well as cubic Ge 2 Sb 2 Te 5 (GST) have been calculated from first principles. The relative stability of the possible stacking sequences of hexagonal GST has been confirmed to depend on the choice for the exchange-correlation (XC) energy functional. It is apparent that without the inclusion of the Te 4d orbitals in the valence states, the lattice parameters can be underestimated by as much as 3.9% compared to experiment and all-electron calculations. From phonon dispersion curves, it has been confirmed that the hexagonal phase is, indeed, stable whereas the cubic phase is metastable. In particular, calculations based on the quasi-harmonic approximation (QHA) reveal an extra heat capacity beyond the Dulong–Petit limit at high temperatures for both hexagonal and cubic GST. Moreover, cubic GST exhibits a residual entropy at 0 K, in agreement with experimental studies which attribute this phenomenon to substitutional disorder on the Sb / Ge / v sublattice.

Effect of Sm2O3 on structural and thermal properties of zinc fluoroborate glasses

Glasses based on Sm3+ doped zinc fluoroborate were synthesized and characterized. Formations of glasses were investigated in the 30ZnF2–20TeO2–(50–x)B2O3–xSm2O3 matrix. Fast quenching and adequate heat treatment are required to prevent melt crystallization and to diminish thermal stress, which result in an efficient amorphous material. The differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS) were employed to record, calculate, measure and analyze the stability, density and refractive index of the glass samples with different concentrations of Sm3+ ranging between 0 to 2.5% (mass fraction). XPS result shows the values of core-level binding energy (Zn 3s, Sm 4d, Te 3d, B 1s, O 1s and F 1s) of (ZnF2–TeO2–B2O3–Sm2O3) glass matrix and indicates the good fusibility of the present glass samples. Density of the glass samples increases as dopant concentration increases and glass transition temperature tg ranges between 395 °C and 420 °C.