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1.
The reaction of CO 2 and H 2O to form bicarbonate (HCO −3) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO 2(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO 2 only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti 4+ sites (TPD peak at 137 K) typical of the nearly perfect TiO 2(110) surface. Vibrational HREELS indicates that CO 2 is linearly bound at the latter sites with a νa(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H 2O to bridging OH groups which recombine to liberate H 2O in TPD at 490 K. No evidence for a reaction between CO 2 and H 2O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO 2 adsorption is blocked by the presence of preadsorbed H 2O, adsorbed CO 2 is displaced by postdosed H 2O, and there is little or no evidence for bicarbonate formation in either case. However, when CO 2 and H 2O are simultaneously dosed, a new CO 2 TPD state is observed at 213 K, and the 166 K state associated with CO 2 at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO 2 TPD state to a bicarbonate species. The 213 K CO 2 TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO 2+H 2O exposure. Sticking coefficient measurements suggest that CO 2 adsorption at 110 K is precursor-mediated, as is known to be the case for H 2O adsorption on TiO 2(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H 2O–CO 2 van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO 2 and H 2O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO 2, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution. 相似文献
2.
The chemical reaction products of elemental sulfur (S), selenium (Se), and molecular hydrogen (H 2) at high pressures and room temperature are probed by Raman spectroscopy. Two known compounds H 2S and H 2Se can be synthesized after laser heating at pressures lower than 1 GPa. Under further compression at room temperature, an H 2S-H 2Se and an H 2S-H 2Se-H 2 van der Waals compounds are synthesized at 4 GPa and 6 GPa, respectively. The later is of guest-host structure and can be identified as (H 2S) x(H 2Se) (2-x)H 2. It can be maintained up to 37 GPa at least, and the stability of its H 2Se molecules is extended:the H-Se stretching mode can be detected at least to 36 GPa but disappears at 22 GPa in (H 2Se) 2H 2. The pressure dependence of S-H and Se-H stretching modes of this ternary compound is in line with that of (H 2S) 2H 2 and (H 2Se) 2H 2, respectively. However, its hydrogen subsystem only shows the relevance to (H 2S) 2H 2, indicating that this ternary compound can be viewed as H 2Se-replaced partial H 2S of (H 2S) 2H 2. 相似文献
3.
采用紫外波段吸收光谱检测技术,实现了SO 2和H 2S混合气体各组分浓度的实时监测。在实验中选用氘灯为测试光源,MAYA2000Pro光谱仪用于采集数据。基于光谱的峰谷特性,选择吸收光谱上波长非常接近的两个来推导SO 2气体的浓度公式,该方法可以忽略其他气体散射和吸收的影响。H 2S气体的吸收光谱可以通过减去混合气体中相应的SO 2气体吸收光谱获得。在常温常压下,H 2S气体的浓度可以从H 2S气体的吸收光谱的吸收峰获得。混合气体的测量精度约为1×10 -6(1 ppm)。基于上述方法,实现了混合气体SO 2和H 2S浓度的实时监测。 相似文献
4.
First-principles calculations based on density functional theory and the pseudopotential method have been used to investigate the energetics of H 2O adsorption on the (110) surface of TiO 2 and SnO 2. Full relaxation of all atomic positions is performed on slab systems with periodic boundary conditions, and cases of full and half coverage are studied. Both molecular and dissociative (H 2O→OH −+H −) adsorption are treated, and allowance is made for relaxation of the adsorbed species to unsymmetrica configurations. It is found that for both TiO 2 and SnO 2 an unsymmetrical dissociated configuration is the most stable. The symmetrical molecularly adsorbed configuration is unstable with respect to lowering of symmetry, and is separated from the fully dissociated configuration by at most a very small energy barrier. The calculated dissociative adsorption energies for TiO 2 and SnO 2 are in reasonable agreement with the results of thermal desorption experiments. Calculated total and local electronic densities of states for dissociatively and molecularly adsorbed configurations are presented, and their relation with experimental UPS spectra is discussed. 相似文献
5.
The surface chemical reactions of clean lithium with H 2S, SO 2 and SO 2Cl 2 have been studied by a combination of XPS and EELS. The reactions with H 2S lead entirely to the formation of sulfide product layers, which propagate only to the extent of a few monolayers. The reactions with SO 2 are more complicated, the first monolayer consists of oxide and sulfide from the full dissociation of the SO 2 molecule. Subsequent reaction occurs to form sulfide, sulfite and SO 2 (ads), probably as the radical anion form. At exposures of SO 2 up to atmospheric pressure, the product layer composition, within the XPS sampling depth, becomes exclusively sulfite. The reaction with SO 2Cl 2 occurs along similar pathways. The first monolayer is exclusively the oxide, sulfide and chloride, while subsequent reactions occur to form sulfite and SO 2 (ads), in the presence of additional chloride. These studies are important first steps toward the understanding of electrochemical processes of these interfaces. 相似文献
6.
将CuInSe 2薄膜在H 2S与Ar的混合气体中硫化是制备CuIn(S xSe 1-x) 2薄膜的一种常用方法。硫化所用到的CuInSe 2薄膜是用溶剂热法生成的CuInSe 2纳米颗粒旋涂而成。不同于其他真空条件下制备CuInSe 2薄膜的方法.溶剂热法的优点是其相对简单的制备工艺和较低廉的成本。对硫化过程进行研究后发现,硫化温度和时间直接影响CuIn(S xSe 1-x) 2薄膜的质量,诸如薄膜成分、结晶度、均匀性和带隙宽度都可以通过改变这些实验条件来进行控制。 相似文献
7.
The recent discovery of room temperature superconductivity (283 K) in carbonaceous sulfur hydride (C-S-H) has attracted much interest in ternary hydrogen rich materials. In this report, ternary hydride P-S-H was synthesized through a photothermal-chemical reaction from elemental sulfur (S), phosphorus (P) and molecular hydrogen (H 2) at high pressures and room temperature. Raman spectroscopy under pressure shows that H 2S and PH 3 compounds are synthesized after laser heating at 0.9 GPa, and a ternary van der Waals compound P-S-H is synthesized with further compression to 4.6 GPa. The P-S-H compound is probably a mixed alloy of PH 3 and (H 2S) 2H 2 with a guest-host structure similar to the C-S-H system. The ternary hydride can persist up to 35.6 GPa at least and shows two phase transitions at approximately 23.6 GPa and 32.8 GPa, respectively. 相似文献
8.
The temperature effects on sub-monolayers of V deposited at the TiO 2(001) surface have been studied by ultraviolet and X-ray photoelectron spectroscopies, UPS and XPS, from 300 up to 623 K. V coverages, Θv, between 0.2 and 0.7 monolayers (ML) were deposited by an e-beam evaporator at 300 K. The V 2p3/2 core line region exhibits two well-defined components whose relative intensity depends on Θv. These two components, assigned to different oxidation states of V, are correlated with two features, with a dominant V 3d character, detected within the TiO2(001) band gap of the UPS valence band spectra. UPS and XPS measurements performed after in-situ thermal treatments show unambiguous and reproducible changes of these spectral components. After annealing at 623 K only the higher binding energy component is present in the V 2p3/2 spectra; the Ti 2p core lines recover the typical symmetry of the clean and stoichiometric TiO2(001) surface and the higher binding energy feature only is detected in the TiO2 band gap. These data suggest that, within the volume probed by XPS and UPS, Ti ions have a mainly d0 configuration, while V has a single and stable open-shell configuration, as revealed by the significant intensity detected within the TiO2 band gap. These annealing-induced changes are due, as suggested by the O 1s/Ti 2p core line intensity trend, to an oxygen diffusion from the TiO2 bulk to the surface. Finally, a detailed analysis of the data indicates that different V/TiO2(001) interfaces exhibit different behaviours after annealing treatments, depending on Θv. For Θv = 0.7 ML, V interdiffuses into the TiO2 sub-surface layers, whereas for Θv = 0.2 ML it remains at the surface. This finding is consistent with a rearrangement of V atoms. which under annealing occupy first the energetically most favorable surface sites (Θv = 0.2 ML) before interdiffusing into the TiO2 lattice (Θv = 0.7 ML). 相似文献
9.
本文主要研究了基于SnO 2/CuO薄膜的声表面波(SAW)传感器(室温下,工作频率约为147.8 MHz)检测H 2S气体的特性。以36°YXLiTaO 3为基片制作声表面波器件,通过采用射频磁控溅射法在其表面淀积SnO 2/CuO的复合薄膜制作出H 2S气体传感器。由场发射电子扫描电镜观察薄膜,薄膜连续均匀且表面分布大量微气孔,因而具有良好的吸附性。然后本文在85℃~205℃范围内对传感器的吸附和脱附速率、灵敏度及选择性等进行了实验研究。实验结果表明,所制备的传感器在较低温度下同时具备快速吸附和脱附特性,工作在190℃时气体吸附和脱附速率最快,检测20ppm H 2S的响应和恢复时间分别为30s、15s;工作在160℃时,传感器检测20ppmH 2S的灵敏度最高,工作频率变化约230 kHz,且对于低浓度2 ppm H 2S,频率变化可达45 kHz。同时,传感器也表现出良好的重复性和选择性。 相似文献
10.
The electrical conductivity of Cr 2O 3 nominally doped with 2 mol% MgO has been studied by the four point a.c. technique as a function of the oxygen activity (O 2 + Ar, CO + CO 2 and H 2 + H 2O) in the temperature range 400–1200 °C. It is concluded that Cr 2O 3 doped with MgO is an extrinsic conductor and that the dissolved Mg-dopant is compensated by the formation of electron holes at near atmospheric oxygen pressures and by oxygen vacancies (or possibly interstitial chromium ions) at highly reduced oxygen activities (in CO + CO 2 and H 2 + H 2O gas mixtures). In H 2 + H 2O mixtures Mg-doped chromia also dissolves hydrogen as protons and significantly affects the defect structure and electrical conductivity. The defect structure of the oxide under various conditions is discussed. 相似文献
11.
利用混合物理化学气相沉积法(HPCVD)在MgO(111)衬底上制备了干净的MgB 2超导超薄膜. 在背景气体压强, 载气氢气流量以及沉积时间一定的情况下, 改变B 2H 6的流量, 制备得到不同厚度系列的MgB 2超导薄膜样品, 并测量了其超导转变温度 Tc, 临界电流密度 Jc等临界参量. 该系列超导薄膜沿c轴外延生长, 表面具有良好的连接性, 且有很高的超导转变温度 Tc(0) ≈ 35-38 K和很小的剩余电阻率 ρ(42 K) ≈ 1.8-20.3 μΩ·cm -1. 随着膜厚的减小而减小, 临界温度变低, 而剩余电阻率变大. 其中20 nm的样品在零磁场, 5K时的临界电流密度 Jc ≈ 2.3×10 7 A/cm 2. 表明了利用HPCVD在MgO(111)衬底上制备的MgB 2超薄膜有很好的性能, 预示了其在超导电子器件中广阔的应用前景.
关键词:
MgO(111)衬底
2超薄膜')" href="#">MgB 2超薄膜
混合物理化学气相沉积 相似文献
12.
随着社会经济的发展,环境空气品质已经成为研究热点。TiO 2是一种化学稳定性高,耐腐蚀性强,对人体无毒无害的N型半导体材料。利用TiO 2的光催化性能提高室内环境空气品质已经成为研究焦点,但是由于TiO 2只能在紫外光源下才具有较高的光催化效率,而在可见光源下的光催化效率较低,从而极大的限制了TiO 2在室内环境领域的发展。因此,研发在可见光源下具有良好光催化性能的TiO 2复合材料势在必行。利用元素掺杂改性技术与提高比表面积方法可以改善光催化反应过程中量子效率和对光能的利用率,以加快电子和空穴向表面迁移的速率同时降低光生载流子的复合机率。以二氧化硅SiO 2为模板、聚乙烯吡咯烷酮为成膜剂、硝酸铈Ce(NO 3) 3·6H 2O和硝酸铜Cu(NO 3) 2·3H 2O为改性剂采用溶胶-凝胶法制备均匀粒度分布的Ce-Cu/TiO 2空心微球,并将制备过程分为四个阶段,即纳米SiO 2球模板的制备、Ce-Cu/TiO 2-SiO 2复合微球凝胶的制备、Ce-Cu/TiO 2-SiO 2复合微球的制备和Ce-Cu/TiO 2空心微球的制备。利用傅里叶变换红外光谱仪(FTIR)与X射线衍射仪(XRD)对Ce-Cu/TiO 2空心微球的制备过程各阶段生成物进行测试与分析,即在纳米SiO 2球模板的制备阶段从微观角度研究纳米SiO 2球模板的搭建过程,在Ce-Cu/TiO 2-SiO 2复合微球凝胶的制备阶段研究TiO 2附着于纳米SiO 2球模板的过程,在Ce-Cu/TiO 2-SiO 2复合微球的制备阶段研究煅烧工艺对Ce-Cu/TiO 2-SiO 2复合微球中晶相与结构的影响,在Ce-Cu/TiO 2空心微球的制备阶段研究氢氧化钠溶液对Ce-Cu/TiO 2-SiO 2复合微球中纳米SiO 2球模板洗涤效果的影响。利用紫外-可见分光光度计(UV-Vis)对Ce-Cu/TiO 2空心微球的光响应性能进行测试与分析,以研究Ce-Cu/TiO 2空心微球对可见光源的利用效率。利用激光粒度分析仪(LPSA)与扫描电子显微镜(SEM)对Ce-Cu/TiO 2空心微球的粒度分布与微观形貌进行测试与分析,以研究Ce-Cu/TiO 2空心微球的均匀粒度分布效果。结果表明:以Si-O-Si基团构建非晶体结构的无定形态纳米SiO 2球模板,有利于聚乙烯吡咯烷酮在纳米SiO 2球模板表面附着,从而控制Ce-Cu/TiO 2空心微球的空腔结构。Ce-Cu掺杂基本进入TiO 2晶体,极少进入纳米SiO 2球模板晶体,从而抑制了Ce-Cu/TiO 2-SiO 2复合微球中TiO 2由锐钛矿相向金红石相的转变。Ce-Cu掺杂TiO 2可以促使TiO 2内部形成新的能级,实现能量较小的光子捕获e-和h+,从而提高Ce-Cu/TiO 2空心微球对可见光源的利用效率。Ce-Cu/TiO 2空心微球的表面光滑且不存在明显的缺陷,其形貌呈现良好的球体且粒径分布均匀,即 d90为219.54 nm, d50为151.60 nm、 d10为103.84 nm,以及 d90- d10为115.70 nm。研究结果为进一步获得可见光源下具有良好光催化性能的均匀粒度分布Ce-Cu/TiO 2空心微球提供理论依据和研究基础。 相似文献
13.
In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O + ions through discontinuous Au films adsorbed on TiO 2(110). A low energy (< 10 eV) O + ion beam is generated via electron stimulated desorption when an Au-dosed TiO 2(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO 2(110). As the Au coverage increases, the formation of Au clusters on TiO 2(110) blocks a fraction of the TiO 2 surface and the O + yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O + signal decreases at a faster rate than the TiO 2 open area fraction. We attribute the attenuation of the O + yield for high Au coverages mainly to blocking of O + by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O + and neighboring Au clusters. 相似文献
14.
采用基于密度泛函理论第一性原理GGA和GGA+U相结合的方法研究了不同掺杂浓度下锐钛矿相和金红石相Nb:TiO2的晶体结构、电子结构以及稳定性.结果表明:锐钛矿相Nb:TiO2能带结构与简并半导体类似,呈类金属导电机理.金红石相Nb:TiO2呈半导体导电机理.Nb原子比Ti原子电离产生出更多的电子.锐钛矿相Nb:TiO2中Nb原子的电离率比金红石相Nb:TiO2的大.以上结果说明锐钛矿相Nb:TiO2比金红石相Nb:TiO2更适宜用作TCO材料;掺杂浓度对其杂质能级,费米能级和有效质量都有影响.Nb原子掺杂浓度越高,材料电离率呈降低趋势;形成能计算结果显示:在富钛条件下不利于Nb原子的掺杂,而在富氧条件下有利于Nb原子的掺杂.对于金红石相和锐钛矿相Nb:TiO2,不论是在贫氧或富氧条件下,随着Nb原子掺杂浓度的提高,形成能均增大. 相似文献
15.
将单层二硫化钼用石墨烯进行封装,构造了石墨烯和二硫化钼的范德瓦耳斯异质结构,并且分别在氩气(Ar)和氢气(H 2)氛围下,详细研究了被封装的二硫化钼的热稳定性.结果表明:在氩气氛围中,石墨烯封装的二硫化钼在400–1000℃下一直保持稳定,而石墨烯和氧化硅上裸露的二硫化钼在1000℃时几乎全部分解;在氢气氛围中,石墨烯封装的二硫化钼在400–1000℃下一直稳定存在,而石墨烯和氧化硅上裸露的二硫化钼在800℃下已经完全分解.综上可得,在氩气和氢气的氛围下,被石墨烯封装的二硫化钼的热稳定性得到了显著的提高.该研究通过用石墨烯将单层的二硫化钼进行封装以提高其热稳定性,在未来以单层二硫化钼作为基础材料的电子器件中,可以保证其在高温下能够正常工作.该研究也为提高其他二维材料的热稳定性提供了一种可行的方法和思路. 相似文献
16.
本文采用第一性原理中基于密度泛函理论(DFT)的广义梯度近似(GGA)方法, 设计了一种新的(TiO 2) 12 量子环结构, 研究了它的几何结构、平均结合能及电子云分布等属性. 在此新型结构的基础上, 分别采用过渡金属化合物MoS 2, MoSe 2, MoTe 2, WS 2, WSe 2和WTe 2进行掺杂, 并分析了掺杂后体系的几何结构及电子属性(如平均结合能、能级结构、HOMO-LUMO轨道电子云密度分布和电子态密度等). 计算结果表明: (TiO 2) 12量子环直径为1.059 nm, 呈中心对称分布, 且所有原子组成一个二维平面结构, 使其几何结构比较稳定, 另外该量子环HOMO-LUMO轨道电子云分布均匀, 且能隙为3.17 eV, 与半导体材料TiO 2晶体的能隙的实验值(3.2 eV)非常接近. 掺杂后量子环的能隙均大幅减小, 其中WTe 2的掺杂结果能隙最小, 仅为0.61 eV, MoTe 2的掺杂结果能隙最大, 为1.16 eV, 也比掺杂前减小约2.0 eV. 其他掺杂结果的能隙都在1 eV左右, 变化不大. 这个能隙的TiO 2可以利用大部分的太阳光能, 使TiO 2具有更为广泛的应用. 相似文献
17.
介绍了一种氩、氢混合等离子体清洗GaAs基片的实验工艺,深入研究了氩、氢等离子体清洗GaAs表面污染物和氧化层,并活化表面性能的基本原理,同时讨论了气体流量、溅射功率和清洗时间等不同溅射参数对等离子体清洗效果的影响。结果表明,在氩气和氢气流量分别为10 cm 3/min和30 cm 3/min,溅射功率为20 W,清洗时间为15 min的条件下,GaAs样品的光致发光强度提高达139.12%,样品表面的As-O键和Ga-O键基本消失。 相似文献
18.
The adsorption and decomposition of H 2S on the Ge(100) surface is investigated. H 2S is a simple sulfur containing molecule that eventually decomposes to yield hydrogen gas and deposits sulfur on the germanium surface. The surface reactions of H 2S are investigated by ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and temperature programmed desorption. Room temperature exposure of H 2S to Ge(100) results in dissociative adsorption which can be followed easily by ultraviolet photoelectron spectroscopy. Warming the H 2S exposed surface results in some molecular desorption and further decomposition of the adsorbed species. At saturation, 0.25 ML of H 2S decomposes generating 0.5 ML of atomic hydrogen. Above the hydrogen desorption temperature some etching of the germanium surface is observed by sulfur. The etch product, GeS, is subsequently observed in temperature programmed desorption experiments. Exposure of H 2S to the Ge surface at elevated temperatures leads to higher sulfur coverages. A sulfur coverage approaching 0.5 ML can be deposited at the higher exposure temperatures. 相似文献
19.
The adsorption and desorption of in situ deposited glycine on Pt(111) were investigated with thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). Glycine adsorbs intact on Pt(111) at all coverages at temperatures below 250 K. The collected results suggest that the glycine molecules adsorb predominantly in the zwitterionic state both in the first monolayer and in multilayers. Upon heating, intact molecules start to desorb from multilayers around 325 K. The second (and possibly third) layer(s) are somewhat more strongly bound than the subsequent layers. The multilayer desorption follows zero order kinetics with an activation energy of 0.87 eV molecule −1. From the first saturated monolayer approximately half of the molecules desorbs intact with a desorption peak at 360 K, while the other half dissociates before desorption. Below 0.25 monolayer all molecules dissociate upon heating. The dissociation reactions lead to H 2, CO 2, and H 2O desorption around 375 K and CO desorption around 450 K. This is well below the reported gas phase decomposition temperature of glycine, but well above the thermal desorption temperatures of the individual H 2, CO 2, and H 2O species on Pt(111), i.e. the dissociation is catalyzed by the surface and H 2, CO 2, and H 2O immediately desorb upon dissociation. For temperatures above 500 K the remaining residues of the dissociated molecules undergo a series of reactions leading to desorption of, for example, H 2CN, N 2 and C 2N 2, leaving only carbon left on the surface at 900 K. Comparison with previously reported studies of this system show substantial agreement but also distinct differences. 相似文献
20.
以多孔氧化铝(AAO)和导电玻璃FTO为基底,用射频(RF)磁控溅射法和溶胶凝胶(Sol-gel)法分别制备了微纳结构的TiO 2,两种TiO 2沉积技术各自体现出其特质。从XRD衍射光谱和拉曼散射光谱可以看到,在相同退火条件下,RF和Sol-gel法制备的TiO 2晶相结构不同。在以导电玻璃FTO为基底时,RF制备的薄膜颗粒分布均匀,没有团簇现象;而Sol-gel制备的薄膜由密实的颗粒构成。在以AAO为模板时,Sol-gel制备的TiO 2溶胶粒子由于胶体溶液的流动性使其对孔的填充率保持较高的水平;而RF制备的TiO 2对孔的填充率则降低。光电流实验的结果表明,前者具有更好的光电特性。 相似文献
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