Superperiodic Feature on Silicon-Sputtered Highly Oriented Pyrolytic Graphite

Superperiodic feature was observed by scanning tunneling microscopy (STM) on the surface of highly oriented pyrolytic graphite (HOPG) on which silicon was sputtered. The superlattice was analyzed by the moire pattern hypothesis, and the lattice constant is 7.03 nm. For the superlattice, the observed boundaries between the superlattice and the normal graphite areas were zigzag, which was in good agreement with the result predicted theoretically. In addition, the observed lattice constants varied slightly in the superperiodic feature area. This implies the role of intralayer strain in the formation of the observed superlattice on the graphite surface.

EPITAXIAL CRYSTALLIZATION OF POLY(ε-CAPROLACTONE)ON HIGHLY ORIENTED ISOTACTIC POLYPROPYLENE

Electron microscope and electron diffraction have been used to study epitaxial crystallization of poly(ε-caprolactone)(PCL).on highly oriented film of isotactic polypropylene(iPP).The results obtained from bright field(BF)electron micrograph and electron diffraction indicate that the PCL can epitaxially grow on iPP substrate and form cross-hatched lamellar texture.The c axes of PCL are ±500 apart from the c axes of iPP. The contact planes of the two kinds of crystals are(010)of iPP and(100) of PCL,respectively.

A High-Efficiency X-Ray Crystal Spectrometer for X-Ray Thomson Scattering

Highly oriented pyrolitic graphite （HOPG） has high X-ray diffraction efficiency due to its unique mosaic crystal structure, and thus is very suitable for its application to X-ray Thomson scattering measurement of solid-density plasmas. In this article, by using the K-shell X-ray source from laser-produced Ti plasma, the properties of the HOPG spectrometer are characterized and compared with those of the flat Pentaerythritol （PET） spectrometer. The results show that the diffraction efficiency of the HOPG spectrometer under focusing condition is an order higher than that of the PET spectrometer, while the spectral resolution of the HOPG is about 320, high enough to be used in the measurement of X-ray Thomson scattering spectra.

Some Unusual Features of Highly Oriented Pyrolytic Graphite Observed by Electrochemical Scanning Tunneling Microscopy

Highly oriented pyrolytic graphite (HOPG) is the substrate often used in scanningtunneling Ancroscopy (STM). It is well known that STM images of the basal plane of HOPG showsome unusual structUral patterns. In this letter, we present in situ STM images of some unusualfeatures on HOPG in solutions, including normal or abnormal chain-like featUres and hexagonal oroblique superPeriodic structures. These features emerge both next to and apart from the step ofHOPG.

Orientation and mobility control of 4HCB organic film for flexible X-ray detectors with high performance

In comparison to inorganic counterparts,organic semiconducting(OSC)crystalline films are promising for building large-area and flexible ionizing radiation detectors for X-ray imaging or dosimetry due to their tissue equivalence,simple processing and large-scale production accessibility.Fabrication processes,how-ever,hinder the ability to generate aligned and large-area films with high carrier mobility.In this work,the space-confined melt process is used to produce highly orientated 4HCB(4-hydroxycyanobenzene)OSC films with a large area of 15×18 mm^(2).The out-of-plane direction of the 4HCB film is<001>,and the benzene rings are found to be extensively overlapped inside the in-plane direction,according to the XRD patterns.The film exhibits a high resistivity up to 1012cm,and high hole mobility of 10.62 cm^(2)V^(−1)s^(−1).Furthermore,the 4HCB(80μm-thick film)based X-ray detectors can achieve a sensitivity of 93μC Gy air^(−1) cm^(−2)and on/offratio of 157.The device also shows steady flexibility,with no degradation in detecting function after 100 cycles of bending.Finally,the proposed 4HCB film detectors demonstrated a high-resolution X-ray imaging capability.The imaging of several materials with sharp edges(copper and polytetrafluoroethylene)has been obtained.This work has developed a fast but efficient approach for producing large-area,highly oriented OSC films for high-performance X-ray detectors.

Macroscopic Electromagnetic Cooperative Network‑Enhanced MXene/Ni Chains Aerogel‑Based Microwave Absorber with Ultra‑Low Matching Thickness

Electromagnetic cooperative strategy has been presented as a mainstream approach that can effectively optimize the matching thickness of dielectric loss dominant system.However,it is still challenging for dielectric–magnetic loss coexisting-type absorber to develop electromagnetic wave(EMW)performance with ultra-low matching thickness(≤1 mm).Breaking the limitation of traditional electromagnetic response at microscopic/mesoscopic scale,a ficus microcarpa-like magnetic aerogel with macroscopical electromagnetic cooperative effect was fabricated through highly oriented self-assembly engineering.The highly oriented Ni chains with unique macroscopic morphology(~1 cm in length)were achieved via a special magnetic field-induced growth.Strong magnetic coupling was observed in the Ni chains confirmed by the micromagnetic simulation.The deductive calculation validates that maintaining high value of electromagnetic parameters at high frequencies is the prerequisites of ultrathin absorber.The electromagnetic cooperative networks with uninterrupted and dual pathways spread through the entire aerogel skeleton,resulting in the impressive permittivity even at high frequencies.Consequently,the aerogel exhibits a remarkable EMW performance at an ultrathin thickness of 1 mm.Thus,based on the modulation of electromagnetic parameters,this work proposed a macroscopic ordered structure with the electromagnetic cooperative effect useful to develop a suitable strategy for achieving ultrathin EMW absorbers.

Raman spectrum study of graphite irradiated by swift heavy ions

Highly oriented pyrolytic graphites are irradiated with 40.5-Me V and 67.7-Me V ^112Sn-ions in a wide range of fluences： 1×10^11 ions/cm^2–1×10^14ions/cm^2. Raman spectra in the region between 1200 cm^-1 and 3500cm^-1 show that the disorder induced by Sn-ions increases with ion fluence increasing. However, for the same fluence, the amount of disorder is greater for 40.5-Me V Sn-ions than that observed for 67.7-Me V Sn-ions, even though the latter has a slightly higher value for electronic energy loss. This is explained by the ion velocity effect. Importantly, ～ 3-cm^-1frequency shift toward lower wavenumber for the D band and ～ 6-cm^-1 shift toward lower wavenumber for the 2D band are observed at a fluence of 1×10^14 ions/cm^2, which is consistent with the scenario of radiation-induced strain. The strain formation is interpreted in the context of inelastic thermal spike model, and the change of the 2D band shape at high ion fluence is explained by the accumulation of stacking faults of the graphene layers activated by radiation-induced strain around ion tracks. Moreover,the hexagonal structure around the ion tracks is observed by scanning tunneling microscopy, which confirms that the strains near the ion tracks locally cause electronic decoupling of neighboring graphene layers.

Manipulation of the overall polarization orientation in the focal volume of high numerical objectives

We propose an approach for tuning the three-dimensional polarization of a focusing subwavelength spot by a high numerical aperture objective. The incident beams are composed of a radially polarized beam, an azimuthally polarized beam, and a linearly polarized beam with three different weighting factors, respectively. A specially designed adjustable amplitude angular selector is also inserted at the back aperture of the objective for tuning the polarization azimuthally. It is shown that any desired overall polarization orientation can be obtained. We calculated the overall polarization orientation in the focal volume. It is found that the polar angle of the overall polarization orientation can be arbitrarily tuned by the combination of a radially polarized beam and a linearly polarized beam with different weighting factors, and the azimuthal angle can be tuned by rotating the orientation of the linearly polarized beam azimuthally.

Continuous SiC skeleton reinforced highly oriented graphite flake composites with high strength and specific thermal conductivity

Highly oriented graphite-based composites have attracted great attention because of their high thermal conductivity(TC),but the low mechanical properties caused by the inhomogeneous distribution and discontinuity of reinforcements restrict the wide applications.Herein,continuous SiC ceramic skeleton reinforced highly oriented graphite flake(SiC/GF)composites were successfully prepared by combining vacuum filtration and spark plasma sintering.The effect of SiC concentration on the microstructure,flexural strength,and thermophysical properties of the composites was investigated.The GF grains in the composites exhibited high orientation with a Lotgering factor of>88%when the SiC concentration was≤30 wt%,and the SiC skeleton became continuous with the SiC concentration reaching 20 wt%.The formation of continuous SiC skeleton improved the flexural strength of the composites effectively while keeping the TC in a high level.Especially,the composites with 30 wt%SiC exhibited the flexural strength up to 105 MPa,and the specific TC reaching 0.118 W·m^(2)·K^(−1)·kg-1.The composites with excellent flexural strength and thermophysical properties showed significant promise for thermal management applications.

通过给桑蚕喂食稀土离子改性的饲料制备高强高韧的蚕丝纤维

蚕丝纤维具有优异的生物相容性和良好的力学性能,但以简单且大规模的方式生产强韧的蚕丝纤维仍是一项重大挑战.本文报道了一种通过给桑蚕喂食稀土离子改性桑叶饲料以制备强韧蚕丝纤维的方法.所得蚕丝纤维具有显著提高的拉伸强度和韧性,其平均值分别为0.85±0.07 GPa和156±13 MJ m^(-3),且最大值达到0.97±0.04 GPa和188±19 MJ m^(-3),这些性能接近蜘蛛牵引丝(自然界最强的丝纤维之一)的拉伸强度和韧性.研究结果表明,稀土离子(La^(3+)或En^(3+))成功掺入蚕丝纤维并与其形成相互作用.稀土离子减小了蚕丝纤维的直径,降低了其内部结晶组分的含量并提升了取向度.这些相互作用与结构演变同时提升了蚕丝纤维的强度和韧性.该研究提出了一种简单、可扩展且有效的生产超强韧丝纤维的策略,制备的蚕丝纤维有望应用于个人防护和航空航天等需要轻质结构材料的领域.

Spontaneous polarization enhanced bismuth ferrate photoelectrode:fabrication and boosted photoelectrochemical water splitting property

In this paper,the fabrication of a highly orientated Bi_(2)Fe_(4)O_(9)(BFO)photoelectrode in the presence of two-dimensional(2D)graphene oxide(GO)was reported.It was found that the GO can be used as a template for controlling the growth of BFO,and the nanoplate composites of BFO/reduced graphene oxide(RGO)with a high orientation can be fabricated.The thickness of the nanoplates became thinner as the ratio of GO increased.As a result,the ferroelectric spontaneous polarization unit arranges itself in the space in a periodic manner,leading to the formation of a polarization field along a special direction.Therefore,the created built-in electric field of the nanoplate composites of BFO/RGO is improved upon the increase of the amount of RGO.As expected,carrier separation is enhanced by the built-in electric field,therefore substantially enhancing the photoelectrochemical(PEC)activity of water splitting compared to pure BFO under the irradiation of visible-light.

Stratigraphic analysis of intercalated graphite electrodes in aqueous inorganic acid solutions

A detailed stratigraphic investigation of the intercalation mechanism when graphite electrodes are immersed inside diluted perchloric(HClO_(4))and sulfuric(H_(2)SO_(4))electrolytes is obtained by comparing results when graphite crystals are simply immersed in the same acid solutions.By combining time-of-flight secondary ion mass spectrometry(ToF-SIMS)and in-situ atomic force microscopy(AFM),we provide a picture of the chemical species involved in the intercalation reaction.The depth intensity profile of the ion signals along the electrode crystal clearly shows a more complex mechanism for the intercalation process,where the local morphology of the basal plane plays a crucial role.Solvated anions are mostly located within the first tens of nanometers of graphite,but electrolytes also diffuse inside the buried layers for hundreds of nanometers,the latter process is also aided by the presence of mesoscopic crystal defects.Residual material from the electrolyte solution was found localized in well-defined circular spots,which represent preferential interaction areas.Interestingly,blister-like micro-structures similar to those observed on the highly oriented pyrolytic graphite(HOPG)surface were found in the buried layers,confirming the equivalence of the chemical condition on the graphite surface and in the underneath layers.

Carbon nanodots:a new precursor to achieve reactive nanoporous HOPG surfaces

In the present work we develop an electrochemical assisted method to form nanopores on the surface of highly oriented pyrolytic graphite(HOPG),which was accomplished by a simple electrochemical route and a scalable nanomaterial,carbon nanodots,without applying high voltages,high temperatures or toxic reagents.HOPG electrodes are in a solution of N-enrich carbon nanodots in acidic media and the potential scans applied on HOPG lead to the formation of a spatially inhomogeneous porous surface.The diameter of the resulting nanopores can be tuned by controlling the number of electrochemical reduction cycles.The resulting nanoporous surfaces are characterized by atomic force microscopy,Raman spectroscopy,scanning electrochemical microscopy,electrochemical impedance spectroscopy and electrochemistry.These nanoporous HOPG showed high capacitance.Hence the potential of these surfaces to the development of energy storage devices is demonstrated.

The potentially crucial role of quasi-particle interferences for the growth of silicene on graphite

A comprehensive picture of the initial stages of silicene growth on graphite is drawn.Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene configurations.We propose,on one hand,that the charge modulations caused by those quantum interferences serve as templates and guide the incoming Si atoms to self-assemble to the unique(√3 x√3)R30°honeycomb atomic arrangement.On the other hand,their limited extension limits the growth to about 150 Si atoms under our present deposition conditions.The here proposed electrostatic interaction finally explains the unexpected stability of the observed silicene islands over time and with temperature.Despite the robust guiding nature of those quantum interferences during the early growth phase,we demonstrate that the window of experimental conditions for silicene growth is quite narrow,making it an extremely challenging experimental task.Finally,it is shown that the experimentally observed threedimensional silicon clusters might very well be the simple result of the end of the silicene growth resulting from the limited extent of the quasi-particle interferences.