一种基于石墨烯电场效应的软X射线探测器简

针对脉冲星导航对软X射线探测的实际要求,研究分析了一种基于石墨烯电场效应的软X射线探测器的性能.通过理论计算,并利用COMSOL Multiphysics有限元仿真软件,给出了探测器时间分辨率和能量分辨率的估值公式.在5.9 keV软X射线入射硅吸收层的情况下,时间分辨率的理论值可达7.2ns,能量分辨率的理论值约为90 eV(1.5％).结果表明,该探测器能够初步满足脉冲星软X射线的探测需求.     

多层铁磁二维材料电场效应研究

二维(2D)材料的出现由于其良好的物理特性及对未来纳米电子设备的潜在应用,而引起了研究者的关注。Cr₂Ge₂Te₆(CGT)中的二维铁磁性已得到证明,然而对于二维CGT,一直缺乏电子输运特性与电场效应的研究。文中制备并鉴定了厚度仅为几nm的CGT铁磁薄片,这为由各种2D材料组成的范德华结构提供了前提条件,并进一步的展示了通过电场效应对2D CGT设备通道电阻进行的大幅度调制。实验结果证明了2D CGT栅极电压的可调性,同时也证明了铁磁2D材料CGT作为新型功能量子材料的潜力。     

FeCl3‐Based Few‐Layer Graphene Intercalation Compounds: Single Linear Dispersion Electronic Band Structure and Strong Charge Transfer Doping

Graphene has attracted much attention since its first discovery in 2004. Various approaches have been proposed to control its physical and electronic properties. Here, it is reported that graphene‐based intercalation is an efficient method to modify the electronic properties of few‐layer graphene (FLG). FeCl₃ intercalated FLGs are successfully prepared by the two‐zone vapor transport method. This is the first report on full intercalation for graphene samples. The features of the Raman G peak of such FLG intercalation compounds (FLGIC) are in good agreement with their full intercalation structures. The FLGICs present single Lorentzian 2D peaks, similar to that of single‐layer graphene, indicating the loss of electronic coupling between adjacent graphene layers. First principle calculations further reveal that the band structure of FLGIC is similar to single‐layer graphene but with a strong doping effect due to the charge transfer from graphene to FeCl₃. The successful fabrication of FLGIC opens a new way to modify properties of FLG for fundamental studies and future applications.     

Cu-Phosphorus Eutectic Solid Solution for Growth of Multilayer Graphene with Widely Tunable Doping

A one-step chemical vapor deposition (CVD) is proposed to grow multilayer graphene (MLG) with tunable doping types using a copper–phosphorus eutectic system as a catalyst. At the growth temperature, the phosphorus-dissolved copper forms a liquid phase, which promotes the formation of phosphorus-doped MLG. With this method, the thickness and doping level of graphene are simultaneously controlled at the synthesis stage. Moreover, the proposed CVD method enables patterned growth of MLG at the microscale. The resultant phosphorus-doped graphene demonstrates a tunable doping state from large n-type doping to p-type doping because of the high affinity of phosphorus to water molecules. Finally, stable n-type doping of MLG by passivating it with a parylene thin film is demonstrated.     

2D Janus Hybrid Materials of Polymer‐Grafted Carbon Nanotube/Graphene Oxide Thin Film as Flexible,Miniature Electric Carpet

Ultrathin, freestanding polymer hybrid film with macroscopic sizes and molecular thicknesses have received significant interest due to their applications as functional devices, microsensors or nanoactuators. Herein, a 2D Janus hybrid of polymer‐grafted carbon nanotubes/graphene oxide (CNTs/GO) thin film is fabricated using microcontact printed CNTs/GO as photo active surface to grow polymer brushes by self‐initiated photografting and photopolymerization selectively from one side of CNTs/GO film. This achieved 2D Janus hybrid materials with grafted polymer layer as insulative carpet and supported CNTs/GO thin film as conductive element have the potential application as flexible and miniature electric carpet for heating micro‐/nano devices locally.     

Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene

The crystallization and electrical characterization of the semiconducting polymer poly(3‐hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X‐ray diffraction revealed that P3HT crystallizes with a mixture of face‐on and edge‐on lamellar orientations on graphene compared to mainly edge‐on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face‐on and edge‐on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with π–π stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.     

热光源和稳恒磁场对石墨烯阻值的影响

研究了热光源和稳恒磁场对石墨烯阻值的影响。首先分析了光致吸附作用,利用Drude形式,建立了温度与阻值之间的关系。然后利用哈伯德模型和微扰理论,找到稳恒磁场中石墨烯从金属态到绝缘态的临界相变条件。实验结果表明,热光源的光功率从0增加到0.88 mW时,石墨烯的阻值从38.44Ω减小到33.48Ω。稳恒磁场从0增加到122.70 mT时,石墨烯阻值从38.44Ω增加到44.24Ω。实验结果证明了磁场强度与石墨烯阻值之间有着良好的线性关系。这对于石墨烯在导电涂层、抗腐蚀涂层和锂离子电池领域的应用具有一定的指导意义。     

激光作用双层材料产生瞬态温度场的数值模拟

从经典热传导方程出发,建立了单个短脉冲激光作用双层材料的二维轴对称物理模型,在考虑材料热物理参数随温度变化的基础上,采用有限元方法模拟了材料的瞬态温度场,得到了激光作用中和作用后铝-玻璃系统的温度时空分布.数值研究结果表明,在激光作用期间,系统表面的温度分布主要取决于作用激光的能量分布特性,并且金属材料的趋肤效应导致系统在厚度方向的温升范围很浅;在激光作用后,系统内部的热量在热传导作用下从高温区移向低温区,并且厚度方向的温升范围随着表面温度降低而不断扩大,但由于铝的热传导系数比玻璃大得多,所以温升主要停留在铝膜层.     

石墨烯对波导耦合特性影响的研究

石墨烯材料因具有非常优异的电光特性而成为新一代光子器件中的重要材料.文章研究了石墨烯对于硅基、聚合物两种材料双矩形波导耦合特性的影响.研究结果表明,在双波导耦合器件中增加一层石墨烯能够起到改变耦合长度的作用,不同费米能级的石墨烯可以增大或减小双波导耦合器件的耦合长度.石墨烯对耦合特性的影响对于硅基和聚合物波导均适用.此研究结果对于基于石墨烯的波导器件的设计和应用具有一定的参考意义.     

PECVD生长垂直石墨烯的场发射特性研究

采用射频等离子体增强化学气相沉积(PECVD)技术,以甲烷为碳源,在金属铜箔上制备了三维垂直石墨烯。通过调节生长参数,进行了七组对比实验,利用扫描电子显微镜,拉曼光谱对垂直石墨烯的形貌、质量以及层数进行了表征,用二级结构的场发射仪器测试了垂直石墨烯的场发射特性,研究了垂直石墨烯的场发射特性与其形貌、质量和密度的关系,并获得了开启电场低至0.29V/μm的场发射特性。研究结果表明,垂直石墨烯是一种良好的场发射材料,未来在真空电子源中具有广阔的应用前景。     

Boosting the Electrical Double‐Layer Capacitance of Graphene by Self‐Doped Defects through Ball‐Milling

Improving the capacitance of carbon materials for supercapacitors without sacrificing their rate performance, especially volumetric capacitance at high mass loadings, is a big challenge because of the limited assessable surface area and sluggish electrochemical kinetics of the pseudocapacitive reactions. Here, it is demonstrated that “self‐doping” defects in carbon materials can contribute to additional capacitance with an electrical double‐layer behavior, thus promoting a significant increase in the specific capacitance. As an exemplification, a novel defect‐enriched graphene block with a low specific surface area of 29.7 m² g^?1 and high packing density of 0.917 g cm^?3 performs high gravimetric, volumetric, and areal capacitances of 235 F g^?1, 215 F cm^?3, and 3.95 F cm^?2 (mass loading of 22 mg cm^?2) at 1 A g^?1, respectively, as well as outstanding rate performance. The resulting specific areal capacitance reaches an ultrahigh value of 7.91 F m^?2 including a “self‐doping” defect contribution of 4.81 F m^?2, which is dramatically higher than the theoretical capacitance of graphene (0.21 F m^?2) and most of the reported carbon‐based materials. Therefore, the defect engineering route broadens the avenue to further improve the capacitive performance of carbon materials, especially for compact energy storage under limited surface areas.     

High Sensitivity Graphene Field Effect Transistor‐Based Detection of DNA Amplification

Enzymatic DNA amplification‐based approaches involving intercalating DNA‐binding fluorescent dyes and expensive optical detectors are the gold standard for nucleic acid detection. As components of a simplified and miniaturized system, conventional silicon‐based ion sensitive field effect transistors (ISFETs) that measure a decrease in pH due to the generation of pyrophosphates during DNA amplification have been previously reported. In this article, Bst polymerase in a loop‐mediated isothermal amplification (LAMP) reaction combined with target‐specific primers and crumpled graphene field effect transistors (gFETs) to electrically detect amplification by sensing the reduction in primers is used. Graphene is known to adsorb single‐stranded DNA due to noncovalent π–π bonds, but not double‐stranded DNA. This approach does not require any surface functionalization and allows the detection of primer concentrations at the endpoint of reactions. As recently demonstrated, the crumpled gFET over the conventional flat gFET sensors due to their superior sensitivity is chosen. The endpoint of amplification reaction with starting concentrations down to 8 × 10^?21 m in 90 min including the time of amplification and detection is detected. With its high sensitivity and small footprint, this platform will help bring complex lab‐based diagnostic and genotyping amplification assays to the point‐of‐care.     

Enhanced Sensitivity of Iontronic Graphene Tactile Sensors Facilitated by Spreading of Ionic Liquid Pinned on Graphene Grid

Iontronic graphene tactile sensors (i‐GTS) composed of a top floating graphene electrode and an ionic liquid droplet pinned on a bottom graphene grid, which can dramatically enhance the performance of capacitive‐type tactile sensors, are presented. When mechanical stress is applied to the top floating electrode, the i‐GTS operates in one of the following three regimes: air–air, air–electric double layer (EDL) transition, or EDL–EDL. Once the top electrode contacts the ionic liquid in the i‐GTS, the spreading behavior of the ionic liquid causes a capacitance transition (from a few pF to over hundreds of pF). This is because EDLs are formed at the interfaces between the electrodes and the ionic liquid. In this case, the pressure sensitivity increases to ≈31.1 kPa^?1 with a gentle touch. Under prolonged application of pressure, the capacitance increases gradually, mainly due to the contact line expansion of the ionic liquid bridge pinned on the graphene grid. The sensors exhibit outstanding properties (response and relaxation times below 80 ms, and stability over 300 cycles) while demonstrating ultimate signal‐to‐noise ratios in the array tests. The contact‐induced spreading behavior of the ionic liquid is the key for boosting the sensor performance.     

近红外单/多频石墨烯谐振腔吸波器研究

采用传输矩阵法研究了石墨烯谐振腔在一维周期结构中的吸波特性。在700~950 nm波段,通过改变不同介质的尺寸、入射角大小以及电磁波模式等参数,分析了吸收频点及吸收峰值的变化情况。研究结果表明,在改变缺陷层的尺寸时,可产生单频点或双频点吸收峰;入射角及电磁波模式的变化对吸收峰的峰值影响较大。以上分析结果可以为近红外石墨烯吸波器的设计提供理论依据。     

并五苯场效应管的电学特性

介绍了用高真空中热蒸发镀膜的方法制备并五苯薄膜场效应晶体管. 作为场效应管半导体层的并五苯薄膜沉积在p型Si (100) (14.0～20.0Ω·cm）衬底上. 场效应管中并五苯薄膜厚度为70nm，源极、漏极和栅极（Au）的厚度均为50nm，绝缘层SiO2的厚度为300nm，沟道宽度为190μm，沟道长度为15μm. 用AFM表征了并五苯薄膜表面形貌，并研究了薄膜生长速率对并五苯场效应晶体管电学特性的影响. 在薄膜生长速率为024和136nm/min时，场效应管的载流子迁移率分别为2.7E-4和2.2E-6cm2／(V·s) .     

Manipulation of Electric Field Effect by Orbital Switch

The semiconductor industry has seen a remarkable miniaturization trend, where the size of microelectronic circuit components is expected to reach the scale of atom even subatom. Here, an orbital switch formed at the interface between BaTiO₃ (BTO) and La_0.5Sr_0.5MnO₃ (LSMO) is used to manipulate the electric field effect in the LSMO/BTO heterostructure. The orbital switch is based on the connection or breakdown of interfacial Ti–O–Mn bond due to the ferroelectric displacement under external electric field. This finding would pave the way for the tuning of the material performance or device operation at atomic level and introducing the orbital degree of freedom into the terrain of microelectronics.     

Local Built‐In Electric Field Enabled in Carbon‐Doped Co3O4 Nanocrystals for Superior Lithium‐Ion Storage

In this work, a novel concept of introducing a local built‐in electric field to facilitate lithium‐ion transport and storage within interstitial carbon (C‐) doped nanoarchitectured Co₃O₄ electrodes for greatly improved lithium‐ion storage properties is demonstrated. The imbalanced charge distribution emerging from the C‐dopant can induce a local electric field, to greatly facilitate charge transfer. Via the mechanism of “surface locking” effect and in situ topotactic conversion, unique sub‐10 nm nanocrystal‐assembled Co₃O₄ hollow nanotubes (HNTs) are formed, exhibiting excellent structural stability. The resulting C‐doped Co₃O₄ HNT‐based electrodes demonstrate an excellent reversible capacity ≈950 mA h g^?1 after 300 cycles at 0.5 A g^?1 and superior rate performance with ≈853 mA h g^?1 at 10 A g^?1.