Pt/Cu(001)-p(2×2)-O表面吸附结构的总能计算

采用密度泛函理论(DFT)研究了氧吸附后Pt/Cu(001)表面合金的原子结构和表面性质. 计算结果表明, 在Pt/Cu(001)-p(2×2)-O表面最稳定结构中, 衬底表面原子层不发生再构, 氧原子吸附于4重对称的Pt原子谷位, 每个氧原子吸附能约为2.303 eV. 吸附结构的Cu—O和Pt—O键键长分别为0.202和0.298 nm, 氧原子的吸附高度ZCu—O约为0.092 nm. 吸附前后Pt/Cu(001)-1ML(monolayer)表面合金的表面功函数分别为4.678和5.355 eV. 吸附表面氧原子和衬底的结合主要来自氧原子2p轨道和衬底金属原子d轨道的杂化作用, 氧原子吸附形成的表面电子态主要位于费米能级以下约-2.7 eV 处.     

金属-半导体催化剂Pt/TiO2的表面微观结构

用透射电镜(TEM)技术研究了Pt/TiO_2催化剂的表面形貌。经高温下氢处理的Pt/TiO_2,表面上原来高分散的不规则的Pt微粒发生迁移并构成多边形粒子。暗场TEM照片上的“蝶”形图象说明多边构形实际是外延生长的Pt多面体微晶。确定了在氢气氛中加热是造成TiO_2半导体表面缺陷,并导致Pt粒子规整构形的重要条件。还发现Pt/TiO_2的表面微观形貌和催化性能之间有并行关系。用金属-半导体相互作用的观点可以合理地解释这些结果。     

Pt/Cu(001)-p(2×2)-O表面吸附结构的总能计算

采用密度泛函理论(DFT)研究了氧吸附后Pt/Cu(001)表面合金的原子结构和表面性质.计算结果表明,在Pt/Cu(001)-p(2×2)-O表面最稳定结构中,衬底表面原子层不发生再构,氧原子吸附于4重对称的Pt原子谷位,每个氧原子吸附能约为2.303 eV.吸附结构的Cu-O和Pt-O键键长分别为0.202和0.298 nm,氧原子的吸附高度Zcu-O约为0.092 nm.吸附前后Pt/Cu(001)-1ML(monolayer)表面合金的表面功函数分别为4.678和5.355 ev.吸附表面氧原子和衬底的结合主要来自氧原子2p轨道和衬底金属原子d轨道的杂化作用,氧原子吸附形成的表面电子态主要位于费米能级以下约-2.7 eV处.     

Pt/Cu（001）-p（2×2）-O表面吸附结构的总能计算

采用密度泛函理论（DFT）研究了氧吸附后Pt/Cu（001）表面合金的原子结构和表面性质.计算结果表明,在Pt/Cu（001）-p（2×2）-O表面最稳定结构中,衬底表面原子层不发生再构,氧原子吸附于4重对称的Pt原子谷位,每个氧原子吸附能约为2.303 eV.吸附结构的Cu—O和Pt—O键键长分别为0.202和0.298 nm,氧原子的吸附高度ZCu—O约为0.092 nm.吸附前后Pt/Cu（001）-1ML（monolayer）表面合金的表面功函数分别为4.678和5.355 eV.吸附表面氧原子和衬底的结合主要来自氧原子2p轨道和衬底金属原子d轨道的杂化作用,氧原子吸附形成的表面电子态主要位于费米能级以下约-2.7 eV处.     

铂/{还原氧化石墨烯/硅钨酸盐}_n复合物的制备及其电催化性能

利用层层自组装(LBL)结合原位光照还原法,制备了一系列{还原氧化石墨烯/多金属氧酸盐}n多层复合膜({rGO/POMs}_n),并以此作为载体,再通过恒电势法将Pt纳米粒子电沉积到复合膜载体上,得到一种P t/{rGO/SiW_(12)}_n燃料电池阳极纳米复合膜催化剂。用紫外可见分光光度计(UV-Vis)、原子力显微镜(AFM)以及扫描电子显微镜(SEM)等技术手段对载体复合多层膜的生长情况以及负载Pt纳米簇的表面形貌进行表征。结果表明,载体多层膜{rGO/SiW_(12)}_6被连续均匀地组装到了不同基底(氧化铟锡,ITO或玻碳,GC)表面且多层膜表面平整,在选定恒电势下,沉积于其表面的Pt纳米粒子具有花簇状形貌且分布均匀。比较研究了分别引入3种不同的多金属氧酸盐(硅钨酸盐SiW_(12),磷钼酸盐PMo_(12),磷钨酸盐PW_(12))制得的多层复合膜催化剂,即Pt/{rGO/SiW_(12)}_6、Pt/{rGO/PMo_(12)}_6和Pt/{rGO/PW_(12)}_6。电化学实验研究表明,在甲醇酸性溶液中,Pt/{rGO/SiW_(12)}_6复合膜相较于Pt/{rGO/PMo_(12)}_6、Pt/{rGO/PW_(12)}_6和Pt作为催化剂对甲醇氧化具有更好的电催化活性、电化学稳定性以及更优异的抗CO毒化性能,是一种颇有应用前景的燃料电池阳极催化剂。     

蓝宝石衬底上化学气相沉积法生长石墨烯

化学气相沉积(CVD)法是制备大面积、高质量石墨烯材料的主要方法之一,但存在衬底转移和碳固溶等问题,本文选用蓝宝石衬底弥补了传统CVD法的不足。利用CVD法在蓝宝石衬底上生长石墨烯材料,研究生长温度对石墨烯表面形貌和晶体质量的影响。原子力显微镜(AFM)、光学显微镜(OM)、拉曼光谱和霍尔测试表明,低温生长有利于保持材料表面的平整度,高温生长有利于提高材料的晶体质量。研究氢气和碳源对蓝宝石衬底表面刻蚀作用机理,发现氢气对蓝宝石衬底有刻蚀作用,而单纯的碳源不能对衬底产生刻蚀效果。在1200 ℃下,直径为50 mm的晶圆级衬底上获得平整度和质量相对较好的石墨烯材料,室温下载流子迁移超过1000 cm²·V^-1·s^-1。     

Cu在ZrO_2(111)薄膜载体上的生长与界面相互作用

采用分子束外延法在Pt(111)单晶表面上制备有序的ZrO2(111)薄膜,利用低能电子衍射谱、同步辐射光电子能谱和X射线光电子能谱研究了Cu纳米颗粒在ZrO2(111)薄膜表面的生长模式和界面相互作用.结果表明,室温下Cu先以二维模式生长到0.15单层(ML),接着以三维模式生长.随着Cu覆盖度的减小,Cu2p3/2峰逐渐向高结合能位移,可归因于初态效应和终态效应共同作用的结果.Cu最初沉积到ZrO2表面时,两者间存在较强的相互作用,Cu向ZrO2衬底传递电荷,以Cu(Ⅰ)形式出现.当Cu覆盖度增加到1ML以后,Cu开始表现出金属特征.     

石墨烯负载Pt催化剂的制备及催化氧还原性能

采用直接化学还原法, 以金属钠为还原剂, 四氯乙烯为碳源, 在石蜡油中不经氧化石墨(GO)和氧化石墨烯(GrO)而直接制备石墨烯(Gr), 然后将Pt纳米粒子担载在Gr基体上, 得到Pt/Gr催化剂, 并对其催化氧还原(OR)性能进行了研究. 通过X射线衍射(XRD), 透射电镜(TEM)和电化学测试对合成催化剂的结构、形貌和电化学性质进行了表征. 实验结果表明: 所制备的Pt/Gr催化剂具有较好的分散性, 平均粒径为3.1 nm; 氧还原起始电位比商业JM-Pt/C催化电极正移了24 mV; 交换电流密度达到1×10^-3 mA·cm^-2, 是商业JM-Pt/C催化电极的2.5倍.     

石墨烯负载Pt催化剂的制备及催化氧还原性能

采用直接化学还原法, 以金属钠为还原剂, 四氯乙烯为碳源, 在石蜡油中不经氧化石墨(GO)和氧化石墨烯(GrO)而直接制备石墨烯(Gr), 然后将Pt纳米粒子担载在Gr基体上, 得到Pt/Gr催化剂, 并对其催化氧还原(OR)性能进行了研究. 通过X射线衍射(XRD), 透射电镜(TEM)和电化学测试对合成催化剂的结构、形貌和电化学性质进行了表征. 实验结果表明: 所制备的Pt/Gr催化剂具有较好的分散性, 平均粒径为3.1 nm; 氧还原起始电位比商业JM-Pt/C催化电极正移了24 mV; 交换电流密度达到1×10^-3 mA·cm^-2, 是商业JM-Pt/C催化电极的2.5倍.     

石墨烯/聚苯胺复合材料的制备及其电化学性能

以苯胺和氧化石墨烯(GO)为原料, 采用电化学方法制备了石墨烯/聚苯胺(GP)复合材料. 利用X射线衍射(XRD)、扫描电镜(SEM)、拉曼(Raman)光谱、X射线光电子能谱分析(XPS)对其结构、微观形貌进行了表征,并对复合材料电化学性能进行了测试. 结果表明, 复合材料保持了石墨烯的基本形貌, 聚苯胺颗粒均匀地分散在石墨烯表面, 复合材料在500 mA·g^-1的电流密度下比电容达到352 F·g^-1, 1000 mA·g^-1下比电容为315 F·g^-1, 经过1000 次的充放电循环后容量保持率达到90%, 远大于石墨烯和聚苯胺单体的比电容. 复合材料放电效率高, 电解质离子易于在电极中扩散和迁移.     

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

Large area single and bilayer graphene are grown on Pt/Ti/SiO₂ substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO₂ substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO₂ substrate at a low filament temperature. The approach paves a novel pathway towards the layer-controlled growth of graphene on Pt/Ti/SiO₂ substrates by HFCVD for frontier applications.     

Can a Procedure for the Growth of Single-layer Graphene on Copper be used in Different Chemical Vapor Deposition Reactors?

In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a “showerhead” cold-wall type, whereas the other represented the popular “tubular” hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm²-scale SLG growth that differed only by the carrier gas flow rate used in the two reactors.     

Nanoscale imaging of oxidized copper foil covered with chemical vapor deposition-grown graphene layers

Characterization of the geometrical and structural characteristics of oxidized Cu area in high resolution is crucial for tracking the change in morphology, exploring interactions between graphene layers and Cu substrates and revealing the mechanism for the orientation-dependent oxidation of Cu. Here, we reported experimental results on nanoscale imaging of natural oxidation of the polycrystalline Cu substrate coated by partial-coverage chemical vapor deposition (CVD)-grown graphene stored in dryer under ambient conditions for up to 10 months. Scanning electron microscope (SEM), together with atomic force microscope (AFM), Raman, and X-ray photoelectron spectroscopy (XPS), was used for systematically studying the morphological and compositional changes at nanoscale during oxidation. The appearance of oxidized Cu substrates could be unambiguously distinguished from the unoxidized regions based on their distinctly different morphologies in SEM images, and the underlying mechanism was discussed in detail. By analyzing a millimeter-seized polycrystalline Cu substrate, we found that the oxidation of polycrystalline Cu substrate depends sensitively on both orientation of graphene layers and Cu substrates. Furthermore, the time-dependent oxidation evolution of Cu substrate was also established, and the oxidation rate was readily determined. The findings reported here will have important implications for developing protection coatings for Cu.     

Bestimmung des oberflächensauerstoffs auf metallen durch aktivierung im reaktor

Surface oxygen on metal foils was determined by activation analysis on the basis of the reaction sequence ⁶Li(n,α)t, ¹⁶O(t,n) ¹⁸F. The metal foils were placed between foils consisting of lithium fluoride and polystyrene, sealed in evacuated ampoules, and irradiated in the reactor. The produced ¹⁸F was radiochemically separated, and measured by its annihilation radiation at 0.51 MeV. The overall cross-sections of such foil arrangements were computed by simple formulas and compared with experimental data. Instructions are given for the chemical treatment of irradiated foils of Au, Pt, Ni, Cu, Al, Fe and Zr. The following values of oxygen coverage were found on rolled foils; Pt 1.4, Ni 1.4, Cu 2.9, Al 4.9 and Fe 7.5 μg O/cm² of geometrical surface, Other oxygen values refer to Au, Zr and to different pretreatments of the metal surfaces. The lower limit of determination is about 0.1 μg O/cm².     

金属衬底在石墨烯化学气相沉积生长中的作用

以过渡金属为催化衬底的化学气相沉积法(Chemical Vapor Deposition，CVD)已经可以制备与机械剥离样品相媲美的石墨烯，是实现石墨烯工业应用的关键技术之一。原子尺度理论研究能够帮助我们深刻理解石墨烯生长机理，为实验现象提供合理的解释，并有可能成为将来实验设计的理论指导。本文从理论计算的角度，总结了各种金属衬底在石墨烯CVD生长过程中的各种作用与相应的机理，包括在催化碳源裂解、降低石墨烯成核密度等，催化加快石墨烯快速生长，修复石墨烯生长过程中产生的缺陷，控制外延生长石墨烯的晶格取向，以及在降温过程中石墨烯褶皱与金属表面台阶束的形成过程等。在本文最后，我们对当前石墨烯生长领域中亟需解决的理论问题进行了深入探讨与展望。     

Fast growth of graphene on SiO2/Si substrates by atmospheric pressure chemical vapor deposition with floating metal catalysts

Graphene on dielectric substrates is essential for its electronic applications. Graphene is typically synthesized on the surface of metal and then transferred to an appropriate substrate for fabricating device applications. This post growth transfer process is detrimental to the quality and performance of the as-grown graphene. Therefore, direct growth of graphene films on dielectric substrates without any transfer process is highly desirable. However, fast growth of graphene on dielectric substrates remains challenging. Here, we demonstrate a transfer-free chemical vapor deposition (CVD) method to directly grow graphene films on dielectric substrates at fast growth rate using Cu as floating catalyst. A large area (centimeter level) graphene can be grown within 15 min using this CVD method, which is increased by 500 times compared to other direct CVD growth on dielectric substrate in the literatures. This research presents a significant progress in transfer-free growth of graphene and graphene device applications.     

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

Ultrathin carbon films were grown on different types of metallic substrates. Free‐standing foils of Cu and Ni were prepared by electroforming, and a pure Ni film was obtained by galvanic displacement on a Si wafer. Commercial foil of Ni 99.95% was used as a reference substrate. Carbon films were grown on these substrates by chemical vapour deposition in a CH₄‐H₂ atmosphere. Obtained films were characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ultraviolet photoemission spectroscopy. The XPS at grazing collection angle was used to determine the thickness of carbon films. Depending on the deposition parameters, the films of graphene or graphite were obtained on the different substrates. The uniformity of graphene and its distribution over the sample area were investigated from Raman data, optical images, and XPS chemical maps. The presence of graphene or graphite in the films was determined from the Raman spectra and Auger peak of C KVV. For this purpose, the D parameter, which is a fingerprint of carbon allotropes, was determined from C KVV spectra acquired by using X‐rays and electron beam. A formation of an intermediate layer of metal hydroxide was revealed in the samples with graphene overlayer.     

Surface‐Confined Self‐Assembled Janus Tectons: A Versatile Platform towards the Noncovalent Functionalization of Graphene

A general strategy for simultaneously generating surface‐based supramolecular architectures on flat sp²‐hybridized carbon supports and independently exposing on demand off‐plane functionality with controlled lateral order is highly desirable for the noncovalent functionalization of graphene. Here, we address this issue by providing a versatile molecular platform based on a library of new 3D Janus tectons that form surface‐confined supramolecular adlayers in which it is possible to simultaneously steer the 2D self‐assembly on flat C(sp²)‐based substrates and tailor the external interface above the substrate by exposure to a wide variety of small terminal chemical groups and functional moieties. This approach is validated throughout by scanning tunneling microscopy (STM) at the liquid–solid interface and molecular mechanics modeling studies. The successful self‐assembly on graphene, together with the possibility to transfer the graphene monolayer onto various substrates, should considerably extend the application of our functionalization strategy.     

Controlled hydrothermal synthesis and growth mechanism of various nanostructured films of copper and silver tellurides

Various nanostructured films of copper and silver tellurides were hydrothermally grown on the corresponding metal substrates through reactions between metal foils and tellurium powder in different media. Interesting morphologies including nanowires, nanorods, nanobelts, nanosheets, and hierarchical dendrites were obtained. The nanostructured films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). A growth mechanism was proposed based on the characterization results. This study provides a low-temperature, solution-phase approach to grow low-dimensional, nanostructured metal tellurides with controllable morphologies.