等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

Deposition of SiO2-Like Films by HMDSN/O2 Plasmas at Low Pressure in a MMP-DECR Reactor

The effects of process parameters such as O₂/HMDSN (hexamethyldisilazane) ratio, microwave discharge power and deposition pressure on the growth rate, chemical bonding nature, and refractive index of thin films deposited by microwave plasma from HMDSN with oxygen, have been investigated. The plasma was created in a Microwave Multipolar reactor excited by Distributed Electron Cyclotron Resonance. The films were deposited at room temperature and characterized by Fourier Transform Infrared spectroscopy and ellipsometry. Growth rate increased with the discharge power P or the deposition pressure but decreased significantly with increasing O₂/HMDSN ratio. A large change in the film composition was observed when the O₂/HMDSN ratio was varied: films deposited with only HMDSN precursor are polymer-like but as the O₂/HMDSN ratio increased, organic groups decreased. For relative pressure values over 70%, deposited films are SiO₂-like with refractive index values close to those found for thermal silicon dioxide.     

Role of positive ions in determining the deposition rate and film chemistry of continuous wave hexamethyl disiloxane plasmas

New data shed light on the mechanisms of film growth from low power, low pressure plasmas of organic compounds. These data rebalance the widely held view that plasma polymer formation is due to radical/neutral reactions only and that ions play no direct role in contributing mass at the surface. Ion reactions are shown to play an important role in both the plasma phase and at the surface. The mass deposition rate and ion flux in continuous wave hexamethyl disiloxane (HMDSO) plasmas have been studied as a function of pressure and applied RF power. Both the deposition rate and ion flux were shown to increase with applied power; however, the deposition rate increased with pressure while the ion flux decreased. Positive ion mass spectrometry of the plasma phase demonstrates that the dominant ionic species is the (HMDSO-CH(3))(+) ion at m/z 147, but significant fragmentation and subsequent oligomerization was also observed. Chemical analysis of the deposits by X-ray photoelectron spectroscopy and secondary ion mass spectrometry show that the deposits were consistent with deposits reported by previous workers grown from plasma and hyperthermal (HMDSO-CH(3))(+) ions. Increasing coordination of silicon with oxygen in the plasma deposits reveals the role of ions in the growth of plasma polymers. Comparing the calculated film thicknesses after a fixed total fluence of 1.5 × 10(19) ions/m(2) to results for hyperthermal ions shows that ions can contribute significantly to the total absorbed mass in the deposits.     

Design of experiment for optimization of plasma-polymerized octafluorocyclobutane coating on very high aspect ratio silicon molds

As-fabricated deep reactive ion etched (DRIE) silicon mold with very high aspect ratio (>10) feature patterns is unsuitable for poly(dimethylsiloxane) (PDMS) replication because of the strong interaction between the Si surface and the replica and the corrugated mold sidewalls. The silicon mold can be conveniently passivated via plasma polymerization of octafluorocyclobutane (C4F8), which is also employed in the DRIE process itself, to enable the mold to be used repeatedly. To optimize the passivation conditions, we have undertaken a Box-Behnken experimental design on the basis of three passivation process parameters (plasma power, C4F8 flow rate, and deposition time). The measured responses were fluorinated film thickness, demolding status/success, demolding force, and fluorine/carbon ratio on the fifth replica surface. The optimal passivation process conditions were predicted to be an input power of 195 W, a C4F8 flow rate of 57 sccm, and a deposition time of 364 s; these were verified experimentally to have high accuracy. Demolding success requires medium-deposited film thickness (66-91 nm), and the thickness of the deposited films correlated strongly with deposition time. At moderate to high ranges, increased plasma power or gas flow rate promoted polymerization over reactive etching of the film. It was also found that small quantities of the fluorinated surface were transferred from the Si mold to the PDMS at each replication, entailing progressive wear of the fluorinated layer.     

Initial Growth of Functional Plasma Polymer Nanofilms

To gain deeper insights into the initial growth mechanism, with respect to functional group density and cross-linking, plasma polymer films (PPFs) were deposited from C₂H₄/NH₃ discharges. Keeping gas phase processes and electrical discharge conditions constant all over the deposition process, the mass deposition rate of the PPF was found to be initially lower and regularly increasing before reaching steady-state conditions after a film thickness of about 5 nm on metal oxide substrates. The first gradient nano-layer, i.e. the first 5 nm deposited, were observed to possess less amino functional groups and to be more cross-linked and thus more stable compared to the film prepared in steady state conditions, in which the uniform film comprises more amino functional groups, yet is less cross-linked and thus less stable. Due to its sticking probability, the substrate thus influences the initial deposition rate. Over plasma exposure time, the substrate becomes covered by an initial layer of PPF and the film-forming species are no longer deposited onto the pristine substrate but onto the already deposited organic polymer film. The preparation of the highly stable functional nanofilm, i.e. the initial PPF layer, can lead to new possible applications and fast deposition processes.     

Low-Frequency Glow Discharge Deposition of a Silicon Dioxide Film onto the Surface of Glass Microspheres

Laser fusion research demands microsized hollow shells with a large diameter and a thick wall. Because these geometric parameters are difficult to provide by fabrication, the wall thickness was increased by deposition of a silicon dioxide film on the outer surface of glass microspheres. The film was obtained by decomposition of tetraethoxysilane vapor in a low-frequency discharge plasma in mixtures with argon and oxygen. The thickness of coating was shown to be a linear function of the deposition time and the consumption of the precursor organoelement compound. The composition of plasma-deposited layers was studied and their density and refractive index were determined. Elemental analysis data showed that the coating comprised silicon dioxide with carbon and hydrogen impurities.     

沉积温度对等离子增强化学气相沉积法制备的SiNx:H薄膜特性的影响

利用Centrotherm公司生产的管式等离子增强化学气相沉积(PECVD)设备在p型抛光硅片表面沉积SiN_x:H薄膜, 研究沉积温度对SiN_x:H薄膜的组成及光学特性、结构及表面钝化特性的影响. 然后采用工业化的单晶硅太阳电池制作设备和工艺制作太阳电池, 研究不同温度制备的薄膜对电池电性能的影响. 测试结果表明: SiN_x:H薄膜的折射率随着沉积温度的升高而变大, 分布在1.926-2.231之间, 这表明Si/N摩尔比随着沉积温度的增加而增加; 当沉积温度增加时, 薄膜中Si－H键和N－H键浓度呈现减小趋势, 而Si－N键浓度逐渐升高, 薄膜致密度增加; 随着沉积温度的升高, SiN_x:H薄膜中的氢析出导致了钝化硅片的有效少子寿命先升高后降低, 并且有效少子寿命出现明显的时间衰减特性. 当沉积温度为450 °C时, 薄膜具有最优的减反射和表面钝化效果. 采用不同温度PECVD制备的5组电池的电性能测试结果也验证了这一结果.     

Effect of Showerhead Configuration on Coherent Raman Spectroscopically Monitored Pulsed Radio Frequency Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Thin Films

The effect of showerhead design, number of holes and geometry, in a parallel plate reactor was studied by measuring the concentration of silane reactant by coherent anti-Stokes Raman scattering (CARS) spectroscopy as a function of radio frequency (rf) pulse width and peak power during pulsed power plasma enhanced chemical vapor deposition (PECVD) of silicon nitride thin films. Film deposition rate, stress, SiH/NH ratio, and thickness and index of refraction homogeneity were correlated with the change in silane concentration for each of the three head geometries: radial, square, and asymmetrical. The asymmetrical head caused plasma quality problems which affected the films' qualities. The square pattern showed good mixing qualities, but produced a film with high compressive stress. The radial head provided the most homogenous film, with respect to index of refraction and film thickness. With a 10 ms pulse width, however, the radial head plasma acted as a continuous plasma for depletion and stress data. The showerhead geometry affects plasma qualities, like stability and intensity, and reactant gas velocities, which in turn affect the nitride film thickness, nitride composition, and stress.     

直流负偏压对类金刚石薄膜结构的影响

在不同的直流负偏压下利用直流射频等离子体辅助化学气相沉积技术在单晶硅表面沉积得到了类金刚石薄膜,用拉曼光谱、红外光谱和原子力显微镜对薄膜的结构和形貌进行了表征.结果表明:无偏压时,沉积得到的薄膜呈现类聚合物结构且表面比较粗糙,而叠加了偏压后,薄膜表现出类金刚石薄膜的结构特征,随着偏压的增大,膜中的氢含量和sp3碳含量均逐渐减小,且薄膜的表面粗糙度逐渐减小.     

基于p-6P异质诱导生长酞菁铜薄膜的NO2传感器

为实现室温下低浓度NO₂气体检测,制作了p-六联苯(p-6P)诱导层的酞菁铜有机薄膜传感器。利用原子力显微镜(AFM)研究了不同沉积速率下p-6P薄膜的生长规律,慢速沉积提供足够的分子扩散时间,利于薄膜横向生长,形成高度低、尺寸大的晶畴。在p-6P薄膜上生长了酞菁铜薄膜,可以清晰看到晶畴上酞菁铜薄膜的有序排列。利用X射线衍射(XRD)仪,阐明了p-6P对酞菁铜薄膜具有很好的诱导效应。通过对比不同沉积速率p-6P薄膜诱导的酞菁铜传感器性能,发现慢速沉积诱导层的酞菁铜器件有高的响应强度和低的回复时间。异质诱导生长的酞菁铜传感器响应强度是直接生长在二氧化硅上的酞菁铜传感器的2倍,回复时间是3.2 min,对浓度为1.0 × 10^-5的NO₂气体灵敏。     

利用XPS研究Y-Ba-Cu-O超导体**(Ⅰ)

实验部分XPS数据来自英国VG公司ESCA LAB-5型电子能谱仪,对谱仪能量标度及样品荷电位移的校准,皆以文献的标准数据为准,为了使光电子峰具有较好的分辨卒,以及尽量避开俄歇峰的重叠干扰,本实验主要采用MgKα_(1,2)辐射。