Unannealed State Research Articles

Stable α-FAPbI3 via porous PbI2 for efficient perovskite solar cells.

Black-phase formamidinium lead iodide (FAPbI3), with a narrow bandgap and high thermal stability, has emerged as an in-demand material for highly efficient perovskite solar cells (PSCs). In a two-step sequential deposition, the PbI2 film plays an important role in the formation of a perovskite film with desirable qualities. This paper explores using N-methyl-2-pyrrolidone (NMP), a strong Lewis base, and N,N-dimethylformamide (DMF) as a mixed precursor solvent (DMF/NMP) of PbI2 and reports on preparing PbI2 films with a porous morphology by thermal treatment. Porous PbI2 films ensure the diffusion and sufficient reaction of the formamidinium iodide solution to form a smooth perovskite film. In addition, a dynamic spin coating method is also introduced to improve the uniformity of the perovskite film. Both methods yield a pure α-phase FAPbI3 film immediately in the unannealed state, which is necessary for the perovskite film to maintain phase stability. Finally, PSCs with a power conversion efficiency of 21.20% (0.13cm2) are fabricated and optimized. The unencapsulated PSCs retain 90% of the initial efficiency for 1000 hours in dry air and exhibit a good thermal stability when heated to 85 °C.

Graphene growth on the textured copper surface

The effect of mechanical processing of copper foil on the single-layer graphene growth is studied. The deformation of the foil in the annealed and unannealed state is carried out by rolling between rollers with varying degrees of roughness. It is shown that the formed single-layer graphene coating on the foil deformed in the unannealed state has a larger number of defects, which is associated with the heterogeneity of the copper texture formed upon annealing. In the case of rolling the copper foil after the annealing stage, the quality of graphene coatings only slightly deteriorates in the deformed areas of foil.

Influence of large amount Zn on mechanical properties and corrosion resistance of 5083 hot rolled aluminum alloy

The influence of three kinds of alloy adding 0.3–1.8 wt% Zn on the mechanical properties and corrosion resistance of medium Mg content 4.0–4.5 wt% (5083 type) hot rolled alloy was investigated. The results showed that the addition of Zn content could further dissolve the second phases into the matrix. The hardness and tensile strength were reduced when annealing at 250 °C × 2 h. The mechanical behavior of the alloys showed a tendency that increases first and then decreases and the peak reached its maximum when 1.6 wt% Zn is added at both annealed and unannealed states. Through quantitative analysis, the improvement of mechanical properties mainly comes from dislocation strengthening and Al–Mg–Zn ternary strengthening phases. Meanwhile, with the increase of Zn content, the intergranular corrosion (IGC) of the alloy improved greatly after annealing at 250 °C × 2 h. The electrochemical corrosion potential (ECP) of the alloys increased first and then decreased.

Experimental Investigation of the Secondary and Backscatter Electron Emission from Spacecraft Materials

The emission of secondary and backscattered electrons influences spacecraft surface potentials and the surrounding plasma. Modern spacecraft use new materials for which secondary emission properties have been unavailable. In this work, the total electron yield (i.e., the sum of secondary and backscattered electron yields) was measured for niobium-C103 alloy, molybdenum Titanium, Zirconium, Molybdenum (TZM) alloy, tantalum-tungsten alloy, Elgiloy®, graphite lubricant (DAG 213®), and titanium nitride. The surface properties of tungsten were also measured for comparison with past test data. The materials were readied as spacecraft flight materials and temperature-treated (“annealed”) to predicted peak flight temperatures. The yield properties for 10 eV–5 keV incident electron energies for all samples were measured. Both unannealed and annealed states were tested, except DAG 213, which was only tested annealed. Three-parameter and four-parameter models were used to fit the secondary and backscattered electron yield data, respectively. The emitted electron energy distributions are also obtained and fit with a Chung-Everhart model for secondary electrons and a Gaussian function for backscattered electrons. The secondary and backscattered electrons’ current densities were calculated for different ambient plasma conditions. For ready reference, the normalized primary electron, secondary electron, and backscattered electron current densities versus ambient electron temperature were computed and plotted from 1 eV to 8 keV.

Operation corrosion test of austenitic steel bends for supercritical coal boilers

Abstract Corrosion tests of both annealed and not annealed bends of HR3C and S304H steels in operation conditions of black and brown coal combustion boilers in EPRU and EDE. After a long-term exposure, the samples were assessed gravimetrically and metallographically. The comparison of annealed and unannealed states showed higher corrosion rates in the annealed state; corrosion of the sample surface did not essentially differ for compression and tensile parts of the beams. Detailed assessment of both steels is described in detail in this study.

Shrinking water's no man's land by lifting its low-temperature boundary

Investigation of the properties and phase behavior of noncrystalline water is hampered by rapid crystallization in the so-called ``no man's land.'' We here show that it is possible to shrink the no man's land by lifting its low-temperature boundary, i.e., the pressure-dependent crystallization temperature ${T}_{x}(p)$. In particular, we investigate two types of high-density amorphous ice (HDA) in the pressure range of $0.10--0.50\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and show that the commonly studied unannealed state, uHDA, is up to 11 K less stable against crystallization than a pressure-annealed state called eHDA. We interpret this finding based on our previously established microscopic picture of uHDA and eHDA, respectively [M. Seidl et al., Phys. Rev. B 88, 174105 (2013)]. In this picture the glassy uHDA matrix contains ice ${\mathrm{I}}_{\mathrm{h}}$-like nanocrystals, which simply grow upon heating uHDA at pressures $\ensuremath{\le}0.20\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. By contrast, they experience a polymorphic phase transition followed by subsequent crystal growth at higher pressures. In comparison, upon heating purely glassy eHDA, ice nuclei of a critical size have to form in the first step of crystallization, resulting in a lifted ${T}_{x}(p)$. Accordingly, utilizing eHDA enables the study of amorphous ice at significantly higher temperatures at which we regard it to be in the ultraviscous liquid state. This will boost experiments aiming at investigating the proposed liquid-liquid phase transition.

Annealing-induced softening of copper and molybdenum for high strain rate deformation

The effect of annealing on the high strain rate deformation properties of copper and molybdenum was studied. Samples were extracted using spark erosion and were annealed under various conditions. High strain rate stress-strain curves at ∼700 s−1 and 1500 s−1 were measured using a split Hopkinson pressure bar. Recrystallization occurred for the copper and molybdenum at annealing temperatures of 300 °C and 1200 °C, respectively, and resulted in a significant softening of the samples compared to their unannealed state. Generally, copper and molybdenum are annealed at much higher temperatures and it is suggested that lower temperature annealing may provide cost savings during the manufacturing processes.

Effects of annealing on amorphous GdxSi1−x near the metal-insulator transition

Annealing of amorphous Gd–Si films produces large changes in magnetic and magnetotransport properties. The materials have spin-glass freezing and enormous negative magnetoresistance (MR) in the unannealed state but show drastically reduced MR and magnetization on annealing. These changes can be explained by high resolution transmission electron micrographs and energy-dispersive x-ray analysis which show the appearance of nanocrystalline clusters of GdSi and GdSi2 in an amorphous background. A comparison with the nonmagnetic analog Y–Si shows similar modification of electrical properties.

Electrical, CL, EPR and RBS study of annealed SiC implanted with Al or Al and C

Lightly n-doped, 4H-SiC films implanted with 1020 cm−3 Al or co-implanted with 1020 cm−3 Al and 1020 cm−3 C were examined in the unannealed state or annealed at 1300, 1400, 1500, 1600 or 1650 °C after they had been coated with an AlN cap. For a given annealing temperature, TA, the sheet resistance, Rsh, is smaller in the co-implanted samples at the lower TA's, but not at the higher ones because the C catalyzes the chemical reactions for the incorporation of Al into a Si site, and at the higher TA's the activation energies for these reactions no longer control the reaction kinetics. The CL peak created by a free electron recombining with a hole bound to an Al acceptor decreases in intensity as TA increases because the Al acceptors can be trapped by the deep donors related to the DI defect that increase in number as TA increases. However, the process must be more complicated because the temperature dependence of Rsh implies that the activation energy for conduction is much less than that of the 0.35 eV hole trap. The excellent temperature stability of the DI defect suggests it is likely to be associated with defects that nucleate and grow such as dislocation loops and/or stacking faults. This is consistent with decreased ion beam channeling at the higher TA's, and the small anisotropy of the EPR peak associated with implant damage. The higher energy peak in the DI doublet increases in intensity relative to the lower energy peak as TA increases, and for the same TA the relative intensity of the higher energy peak is larger in the co-implanted samples. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of annealing on the dielectric properties of PZN–PT–BT ceramics

The dielectric behaviors of Pb(Zn 1/3Nb 2/3)O 3–PbTiO 3–BaTiO 3 (PZN–PT–BT) ceramics of several compositions have been systematically studied in as-prepared (unannealed) condition as well as after annealing (at 880 °C for 16 h). The general trend seems to indicate that the annealed samples become more ferroelectric-like as opposed to relaxor type in the unannealed state. It also shows a shift of T m, the temperature at dielectric maximum, toward higher value after annealing. Both behaviors are composition dependent. X-ray diffraction patterns reveal changes of crystalline structure after annealing, which can be correlated to the accompanied changes in dielectric properties. Those experimental results may be understood using a model of paraelectric BZN nano-phase particles embedded in the PZN–PT–BT matrix.

Thermal dimensional stability of glass substrates for poly‐Si TFT‐LCD application

Abstract— Thermal dimensional stability of Fusion‐drawn Corning Code 1737 glass was investigated at simulated thermal cycles for low‐temperature poly‐Si TFT fabrication. For low‐temperature poly‐Si TFT processes between 550 and 600°C, annealed Code 1737 is required to meet a typical thermal shrinkage requirement of less than 20 ppm. For super‐low‐temperature poly‐Si TFT processes between 400 and 450°C, Code 1737 meets the requirement in the unannealed state. Code 1737 glass having a high strain point of 666°C provides thermal capabilities as a substrate for low‐temperature poly‐Si TFT‐LCD applications.

A study of positional disorder in strontium barium niobate

The first systematic examination of trends in the site occupancies of strontium and barium ions in strontium barium niobate (SBN) at three compositions across the phase range is presented. X-ray powder diffraction and Rietveld structure refinement were used to obtain refined structures for SBN. Some problems were encountered in the structure refinement due to the domain structure in the material. Barium was found only at the A2 site for each composition. Ba/Sr occupancy for the A2 site varied from 91% for SBN (72-28) to 99% for SBN (50-50) in the unannealed state, while strontium occupancy of the A1 site varied from 70% to 54%. In annealed SBN (50-50), the A2 site occupancy decreased to 95%, while the A1 site occupancy increased to 62%. It is proposed that a twisting of the structure in the unannealed state decreases the sizes of the cages at the A1, A2 and C sites. After annealing, the structure becomes more regular, enlarging the A1, A2 and C sites and allowing more strontium atoms to occupy the A1 site. Cation distribution is controlled by the twisting of the octahedral framework. The overall properties of the material are modified by this distortion of the structure.

Damage characterization of ion beam exposed metal–oxide–semiconductor varactor cells by charge to breakdown measurements

Damage in thin (10 nm) oxide layers of metal–oxide–semiconductor varactor cells caused by exposures with ions, electrons, and x rays has been electrically characterized by constant-current stress time-dependent dielectric breakdown and capacitance-voltage measurements. The time-dependent dielectric breakdown investigations show measurable damage if the ions (H+; 74 keV) are allowed to penetrate the resist (300 nm PMMA) and the poly-Si layer (250 nm) to reach the oxide. This is not the case if the ions (H+2; 74 keV) are stopped inside the poly-Si layer by use of a thicker (450 nm) resist. Also for electrons and x rays the exposure with lithographic doses did not change the time-dependent dielectric breakdown curves. The capacitance-voltage measurements demonstrate that electrons and x rays which do penetrate the gate oxide cause a flatband voltage shift of nearly 400 mV. This shift could not be observed if the H+2 ions were stopped in the poly-Si buffer layer. Ions seem to create no secondary effects like x-ray generation which reach beyond the penetration depth. The measurements were performed in the unannealed state to detect all possible damage effects including those which can be removed by annealing.

Thermal annealing effect on cellulose acetate reverse osmosis membrane structure

The structure variation of cellulose acetate (CA) reverse osmosis (RO) membranes due to thermal annealing was investigated by using gas adsorption. When the CA membranes were dehydrated by freeze-drying, the morphology of the unannealed membrane was similar to that of the annealed membrane. On the contrary, with air-drying which induced structure collapse of the CA membranes, gas adsorption behavior of the unannealed membrane showed a significant difference from that of the annealed membrane. The CA RO membrane in an unannealed state totally collapsed during air-drying, but the membrane that was annealed for 10 min at 90°C showed significantly reduced collapsing compared to the unannealed one. However, even though the CA membranes were annealed, use of methanol as the wetting agent caused complete collapsing during air-drying.

Vibrational Analysis of 1,2-Dibromopropane and 1,2-Dibromopropane-D6

Abstract Infrared spectra were obtained for 1,2-dibromopropane-d6 in the liquid and in the unannealed and annealed solid states. Vibrational assignments were made for the three conformers of 1,2-dibromopropane and the three conformers of 1,2-dibromopropane-d6 with the aid of normal coordinate calculations. All three possible conformers of CD2BrCDBrCD3 were found to be present in the liquid and unannealed solid, but the PHSHH conformer was absent in the annealed solid.

Effect of physical annealing on the dynamic mechanical properties of a high‐Tg amine‐cured epoxy system

AbstractPhysical annealing of a fully cured amine/epoxy system has been investigated using the freely oscillating TBA torsion pendulum technique. The material densifies spontaneously during annealing in an attempt to reach equilibrium, thereby changing material behavior. The dynamic mechanical behavior of a film specimen (Tg = 174°C, 0.3 Hz) and of a glass braid composite specimen (Tg = 182°C, 0.9 Hz) was monitored during isothermal annealing at sub‐Tg temperatures (ranging to 230°C below Tg); after annealing, the behavior was measured vs. temperature and compared with that of the unannealed state. Isothermally, the storage modulus (G′) of the film specimen and the relative rigidity (1/P2) of the composite specimen increased almost linearly with log time, whereas the logarithmic decrement (Δ) decreased with time. The isothermal rates of annealing were determined from the rates of changes in G′ and in 1/P2 for the film and composite specimens, respectively. In a wide temperature range between Tg and the secondary transition temperature, Tsec (≈ −30°C, 2.3 Hz by TBA), the isothermal rates of annealing at the same annealing time appeared to be the same. Thermomechanical spectra of the isothermally annealed material revealed a maximum deviation in thermomechanical behavior from the unannealed material in the vicinity of the annealing temperature. The effects of physical aging were the same for the film and composite specimens. Effects of sequential annealing at two isothermal temperatures on the thermomechanical behavior were also investigated; when the second temperature was higher than the first, the effect of only the high‐temperature annealing was evident, whereas the effect of annealing at both temperatures was revealed when the second temperature was lower than the first. Results suggest that physical annealing at different temperatures involves different length scales of chain segment relaxation and that the effects of isothermal aging can be eliminated by heating to below Tg.

Interaction of hydrogen and deuterium with CoTi surfaces.

The interaction of ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ with polycrystalline CoTi in the annealed and unannealed states, and at 300 and 80 K, has been studied using ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy, electron-energy-loss spectroscopy (EELS), thermal desorption spectroscopy, and measurement of work function. The two surface conditions, annealed and unannealed, were found to be slightly enriched in Ti and Co, respectively. Both ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ were found to react readily with CoTi at both 300 and 80 K, causing changes in the UPS spectra that could be explained from density-of-states calculations on CoTi and (by extension) on ${\mathrm{FeTiH}}_{\mathrm{x}}$. The surface stoichiometry was unaltered by the interaction, indicating no adsorbate-induced segregation, and there was no evidence from EELS of the formation of a separate hydride phase. However, EELS was able to demonstrate the presence of ${\mathrm{H}}_{2}$ or ${\mathrm{D}}_{2}$ at the surface by virtue of the rapid quenching of a surface loss feature on initial exposure. On heating above \ensuremath{\approxeq}500 K ${\mathrm{H}}_{2}$ or ${\mathrm{D}}_{2}$ were desorbed, the desorption threshold temperature increasing progressively with successive cycles of heating. For both ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ interaction the work function increased on exposure, but reached different saturation levels at 300 and 80 K, respectively. All these results are consistent with a mechanism of ${\mathrm{H}}_{2}$ or ${\mathrm{D}}_{2}$ chemisorption followed by inward diffusion and the formation of an \ensuremath{\alpha}-phase solid solution, but not with formation of a hydride phase.

Effect of the cooling rate from austenitization temperature on the crack resistance of 15Kh2N3MDFTChA steel

1. Reduction of the cooling rate from austenitization temperature (VCOO) leads to a reduction in the hardness of the 15Kh2N3MDFTChA steel in unannealed state. The dependence of HRC=f(VCOO) in annealed state is of an extremal nature with the hardness maximum moving towards lower VCOO with rising annealing temperatures. 2. The 15Kh2N3MDFTChA steel has the lowest crack resistance after annealing. The steel hardened to a structure of martensite+lower bainite after medium and high annealing is with regard to hardenss and crack resistance practically no worse than a steel with a martensite structure. 3. The dependence of mechanical characteristics of hardened as well as of normalized steel 15Kh2N3MDFTChA on the duration of low annealing is of a pulsating character caused by the processes of formation, coagulation, and dissolution of metastable carbides of three types. 4. In the low-annealed condition after tann>6 the normalized 15Kh2N3MDFTChA steel with an initial martenisite-bainite structure has an advantage over a steel hardened for martenisite with regard to crack resistance both after single as well as after cyclic loading without being less hard. 5. The maximum level of crack resistance of the low-annealed 15Kh2N3MDFTChA steel (both the normalized and the hardened) under single or cyclic loading is reached at tann=15 and 35 h, respectively.

ChemInform Abstract: VIBRATIONAL SPECTRA OF 1‐CHLORO‐2‐METHYLPROPANE AND 1‐CHLORO‐2,2‐DIMETHYLPROPANE

Abstract Infrared and Raman spectra are obtained for 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane. The former compound exists as a mixture of PC and PH' conformers in the liquid and unannealed solid states, but only the PC conformer is present in the crystalline solid. Vibrational assignments are made for both conformers of 1-chloro-2-methylpropane and for 1-chloro-2,2-dimethylpropane with the aid of normal coordinate calculations.

Vibrational spectra of 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane

Infrared and Raman spectra are obtained for 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane. The former compound exists as a mixture of P C and P H' conformers in the liquid and unannealed solid states, but only the P C conformer is present in the crystalline solid. Vibrational assignments are made for both conformers of 1-chloro-2-methylpropane and for 1-chloro-2,2-dimethylpropane with the aid of normal coordinate calculations.