Quantitative measurement of the charge carrier concentration using dielectric force microscopy

The charge carrier concentration profile is a critical factor that determines semiconducting material properties and device performance.Dielectric force microscopy(DFM)has been previously developed to map charge carrier concentrations with nanometer-scale spatial resolution.However,it is challenging to quantitatively obtain the charge carrier concentration,since the dielectric force is also affected by the mobility.Here,we quantitative measured the charge carrier concentration at the saturation mobility regime via the rectification effect-dependent gating ratio of DFM.By measuring a series of n-type GaAs and GaN thin films with mobility in the saturation regime,we confirmed the decreased DFM-measured gating ratio with increasing electron concentration.Combined with numerical simulation to calibrate the tip–sample geometry-induced systematic error,the quantitative correlation between the DFM-measured gating ratio and the electron concentration has been established,where the extracted electron concentration presents high accuracy in the range of 4×10^(16)–1×10^(18)cm^(-3).We expect the quantitative DFM to find broad applications in characterizing the charge carrier transport properties of various semiconducting materials and devices.

Probe the Effects of Surface Adsorbates on ZnO Nanowire Conductivity using Dielectric Force Microscopy

Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode contacts in FET devices heavily influences the device performance, which makes it difficult to obtain the intrinsic electric properties of nanomaterials. Dielectric force microscopy （DFM）, a contactless method developed recently, can detect the low-frequency dielectric responses of nanomaterials without electric contact, which avoids the influence of electric contact and can be used to study the intrinsic conductivity of nanomaterials. Here we study the influences of surface adsorbates on the conductivity of ZnO nanowires （NWs） by using FET and DFM methods. The conductivity of ZnO NW is much larger in N2 atmosphere than that in ambient environment as measured by FET device, which is further proven by DFM measurement that the ZnO NW exhibits larger dielectric response in N2 environment, and the influence of electrode contacts on measurement can be ruled out. Based on these results, it can be concluded that the adsorbates on ZnO NW surface highly influence the conductivity of ZnO NW rather than the electrode contact. This work also verifies the capability of DFM in measuring electric properties of nanomaterials.

Effect of the Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection

In this paper,the effect of Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection(RBC)in a dielectric liquid layer contained between two parallel electrode plates has been numerically investigated.Two different operating conditions have been considered in electrohydrodynamic(EHD)conduction:ohmic and saturation,and variations in the physical properties of the dielectric fluid with temperature.The electric equations and the state equations based on the Boussinesq approximation are integrated in the framework of OpenFOAM buoyantBoussinesqPimpleFoam program.The results show that in the ohmic regime,the combined effect of Coulomb and dielectric forces promotes the onset of RBC flow,while in the saturation state,the inhibition of RBC flow by Coulomb force is more significant.The value of the critical Rayleigh number Ra decreases with increasing electric Reynolds number ReE in the ohmic regime,whereas in the saturation state,the critical Ra increases with increasing ReE.In the saturation regime,the flow field always has a steady flow in the range of parameters considered.However,the onset of the RBC flow promoted by the dielectric force is more pronounced in the ohmic state.Due to the presence of the dielectric force,the flow field exhibits periodic oscillatory flow at low electric Reynolds numbers for the range of parameters considered.

Optical forces exerted on a graphene-coated dielectric particle by a focused Gaussian beam

In this paper, we derive the analytical expression for the multipole expansion coefficients of scattering and interior fields of a graphene-coated dielectric particle under the illumination of an arbitrary optical beam. By using this arbitrary beam theory, we systematically investigate the optical forces exerted on the graphene-coated particle by a focused Gaussian beam. Via tuning the chemical potential of the graphene, the optical force spectra could be modulated accordingly at resonant excitation. The hybridized whispering gallery mode of the electromagnetic field inside the graphene-coated polystyrene particle is more intensively localized than the pure polystyrene particle, which leads to a weakened morphology-dependent resonance in the optical forces. These investigations could open new perspectives for dynamic engineering of optical manipulations in optical tweezers applications.

A Comparison between Abraham and Minkowski Momenta

In this paper I compare the Abraham and the Minkowski forms for the momentum pertaining to an electromagnetic wave inside a dielectric or a magnetic material. The discussion is based on a careful treatment of the surface charges and currents and of the forces acting on them. While in the dielectric case the Abraham momentum is certainly more appealing from the physical point of view, for a magnetic material it suggests an interpretation in terms of magnetic charges and related magnetic currents. The Minkowski momentum for magnetic non conducting materials, on the contrary, has a natural interpretation in terms of an amperian model, in which the dynamics is determined by the Lorentz force acting on bulk and surface electric currents.

Contactless probing of the intrinsic carrier transport single-walled carbon nanotubes

Intrinsic carrier transport properties of single-walled carbon nanotubes have been probed by two parallel methods on the same individual tubes： The contactless dielectric force microscopy （DFM） technique and the conventional field-effect transistor （FET） method. The dielectric responses of SWNTs are strongly correlated with electronic transport of the corresponding FETs. The DC bias voltage in DFM plays a role analogous to the gate voltage in FET. A microscopic model based on the general continuity equation and numerical simulation is built to reveal the link between intrinsic properties such as carrier concentration and mobility and the macroscopic observable, i.e. dielectric responses, in DFM experiments. Local transport barriers in nanotubes, which influence the device transport behaviors, are also detected with nanometer scale resolution.

Avalanche boron fusion by laser picosecond block ignition with magnetic trapping for clean and economic reactor

Measured highly elevated gains of proton–boron(HB11) fusion(Picciotto et al., Phys. Rev. X 4, 031030(2014))confirmed the exceptional avalanche reaction process(Lalousis et al., Laser Part. Beams 32, 409(2014); Hora et al.,Laser Part. Beams 33, 607(2015)) for the combination of the non-thermal block ignition using ultrahigh intensity laser pulses of picoseconds duration. The ultrahigh acceleration above 10^(20) cm s^(-2)for plasma blocks was theoretically and numerically predicted since 1978(Hora, Physics of Laser Driven Plasmas(Wiley, 1981), pp. 178 and 179) and measured(Sauerbrey, Phys. Plasmas 3, 4712(1996)) in exact agreement(Hora et al., Phys. Plasmas 14, 072701(2007)) when the dominating force was overcoming thermal processes. This is based on Maxwell's stress tensor by the dielectric properties of plasma leading to the nonlinear(ponderomotive) force f_(NL)resulting in ultra-fast expanding plasma blocks by a dielectric explosion. Combining this with measured ultrahigh magnetic fields and the avalanche process opens an option for an environmentally absolute clean and economic boron fusion power reactor. This is supported also by other experiments with very high HB11 reactions under different conditions(Labaune et al., Nature Commun.4, 2506(2013)).