Improvement of the high-k/Ge interface thermal stability using an in-situ ozone treatment characterized by conductive atomic force microscopy

In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO_2/Al_2O_3 gate stack on germanium（Ge） substrate. The micrometer scale level of HfO_2/Al_2O_3 gate stack on Ge is studied using conductive atomic force microscopy（AFM） with a conductive tip. The initial results indicate that comparing with a non insitu ozone treated sample, the interface thermal stability of the sample with an in-situ ozone treatment can be substantially improved after annealing. As a result, void-free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ/Ge are obtained. A detailed analysis is performed to confirm the origins of the changes.All results indicate that in-situ ozone treatment is a promising method to improve the interface properties of Ge-based three-dimensional（3D） devices in future technology nodes.

Effect of diode size and series resistance on barrier height and ideality factor in nearly ideal Au/n type-GaAs micro Schottky contact diodes

Small high-quality Au/n type-GaAs Schottky barrier diodes （SBDs） with low reverse leakage current are produced using lithography. Their effective barrier heights （BHs） and ideality factors from current-voltage （I-V） characteristics are measured by a Pico ampere meter and home-built I-V instrument. In spite of the identical preparation of the diodes there is a diode-to-diode variation in ideality factor and barrier height parameters. Measurement of topology of a surface of a thin metal film with atomic force microscope （AFM） shows that Au-n type-GaAS SD consists of a set of parallel-connected micro and nanocontacts diodes with sizes approximately in a range of 100-200 nm. Between barrier height and ideality factor there is an inversely proportional dependency. With the diameter of contact increasing from 5 μm up to 200 μm, the barrier height increases from 0.833 up to 0.933 eV and its ideality factor decreases from 1.11 down to 1.006. These dependencies show the reduction of the contribution of the peripheral current with the diameter of contact increasing. We find the effect of series resistance on barrier height and ideality factor.

Local leakage current behaviours of BiFeO_3 films

The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeOa films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films.

Analysis of the resistive switching behaviors of vanadium oxide thin film

We demonstrate the polarization of resistive switching for a Cu/VOx/Cu memory cell.The switching behaviors of Cu/VOx/Cu cell are tested by using a semiconductor device analyzer（Agilent B1500A）,and the relative micro-analysis of I-V characteristics of VOx/Cu is characterized by using a conductive atomic force microscope（CAFM）.The I-V test results indicate that both the forming and the reversible resistive switching between low resistance state（LRS） and high resistance state（HRS） can be observed under either positive or negative sweep.The CAFM images for LRS and HRS directly exhibit evidence for the formation and rupture of filaments based on positive or negative voltage.The Cu/VOx/Cu sandwiched structure exhibits reversible resistive switching behavior and shows potential applications in the next generation of nonvolatile memory.

Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

Polycrystalline tungsten（W）and molybdenum（Mo）materials both non-annealed and annealed at temperatures of 800-1750~C have been irradiated with low-energy（220 eV）,high-flux（~10^（21）ions/m^2.s）He~＋at an irradiation temperature of 600℃and at a dose of1.0×10^（25）ions/m^2.This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials.A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He＋dose of 1.0×10^（25）ions/m^2.Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W.Compared to W,Mo suffered much less surface damage after being irradiated at various He~＋doses.

In situ strain electrical atomic force microscopy study on two-dimensional ternary transition metal dichalcogenides

Atomically thin two-dimensional(2D)alloys have attracted wide interests of study recently due to their potential in flexible electronic and optoelectronic applications.In particular,monolayer transition metal dichalcogenide(TMD)alloys have emerged as unique 2D semiconductors with tunable bandgaps,by means of alloying.However,response of surface electrical potential and barrier height to strain for 2D TMD alloys–electrode interface is rarely explored.Apparently,revealing such strain-dependent evolution of electrical properties is crucial for developing advanced 2D TMD based flexible electronics and opto-electronics.Here we performed in situ strain Kelvin probe force microscopy(KPFM)and conductive atomic force microscopy(C-AFM)investigations of monolayer Mo_(0.4)W_(0.6)Se_(2) on Au coated flexible substrate,where controlled uni-axial tensile strain is applied.Both contact potential difference(CPD)and Schottky barrier heights(SBH)of monolayer Mo_(0.4) W_(0.6)Se_(2) show obvious decreases with the increase of strain,which is mainly due to the strain-induced increment of TMD electron affinity.Our in situ strain photoluminescence(PL)measurements also indicate the changes of electronic band structures under strain.We further exploit the substrate effects on CPD by study the monolayer alloy on the mostly used substrates of SiO 2/Si and indium tin oxide(ITO)/glass.Our findings could strengthen the foundation for the potential applications of 2D TMD and their alloys in the fields of strain sensors,flexible photodetectors,and other wearable electronic devices.

Origin mechanism of pitting corrosion induced by cerium inclusions

In this paper,the origin mechanism of pitting corrosion induced by Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions in a microalloyed steel was investigated by field emission scanning electron microscopy with energy dispersive spectroscopy and electron backscattered diffraction,conductivity atomic force microscopy,immersion test,and first-principles calculation.The results show that the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions are non-conductive,which are impossible to form corrosion couples with the steel matrix.There are no obvious lattice distortion zones in the steel matrix around the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions,so it is difficult to form micro-galvanic corrosion near the Ce inclusion.The order of work functions of the Ce inclusions and the steel matrix from small to large is Ce_(2)O_(2)S<Ce_(2)O_(3)<CeAlO_(3)<steel matrix,which is consistent with their dissolution sequence in the immersion test in _(3).5 wt%NaCl solution.Consequently,it is effective and reliable to use work function to predict or judge the dissolution behaviors of the Ce inclusions or steel matrix in corrosive solution.The Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions have the tendency of self-dissolution and dissolve preferentially to the steel matrix in the solution by the salt effect,which lead to pitting corrosion of Ce-containing microalloyed steel.

半导体薄膜表面粘附的非对称性偏压调控

电调控表面粘附对微机电系统是至关重要的,同时相对于外加电压极性常具有对称性.本文以二硫化钼为研究对象,以石墨烯、氮化硼和n型硅为参照组展示半导体薄膜表面的非对称粘附行为.研究主要通过导电原子力显微镜和理论模拟来揭示金探针与金基底上二硫化钼之间的偏压调控粘附力的行为.结果反映二硫化钼表面偏压对粘附的调控能力远大于参照组材料,这种非对称行为主要来源于半导体薄膜与背电极之间形成的肖特基结中的内建电场.

Structure and Electrical Characteristics of Zinc Oxide Thin Films Grown on Si (111) by Metal-organic Chemical Vapor Deposition

ZnO thin films were grown on Si （111） substrates by low-pressure metal-organic chemical vapor deposition. The crystal structures and electrical properties of as-grown sample were investigated by scanning electron microscopy （SEM） and conductive atomic force microscopy （C-AFM）. It can be seen that with increasing growth temperature, the surface morphology of ZnO thin films changed from flake-like to cobblestones-like structure. The current maps were simultaneously recorded with the topography, which was gained by C-AFM contact mode. Conductivity for the off-axis facet planes presented on ZnO grains enhanced. Measurement results indicate that the off-axis facet planes were more electrically active than the c-plane of ZnO flakes or particles probably due to lower Schottky barrier height of the off-axis facet planes.

Barrier height and ideality factor dependency on identically produced small Au/p-Si Schottky barrier diodes

Small high-quality Au/P-Si Schottky barrier diodes（SBDs） with an extremely low reverse leakage current using wet lithography were produced.Their effective barrier heights（BHs） and ideality factors from current-voltage （Ⅰ-Ⅴ） characteristics were measured by a conducting probe atomic force microscope（C-AFM）.In spite of the identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters.By extrapolating the plots the built in potential of the Au /p-Si contact was obtained as V_（bi）=0.5425 V and the barrier height valueΦ_（b（c-V）） was calculated to beΦ_（B（C-V））=0.7145 V for Au/p-Si.It is found that for the diodes with diameters smaller than 100μm,the diode barrier height and ideality factor dependency to their diameters and correlation between the diode barrier height and its ideality factor are nonlinear,where similar to the earlier reported different metal semiconductor diodes in the literature,these parameters for the here manufactured diodes with diameters more than 100μm are also linear.Based on the very obvious sub-nanometer C-AFM produced pictures the scientific evidence behind this controversy is also explained.

A universal calibration method for eliminating topographydependent current in conductive AFM and its application in nanoscale imaging

The topography and electrical properties are two crucial characteristics that determine the roles and functionalities of materials.Conductive atomic force microscopy(CAFM)is widely recognized for its ability to independently measure the topography and conductivity.The increasing trend towards miniaturization in electrical devices and sensors has encouraged an urgent demand for enhancing the accuracy of CAFM characterization.However,when performing CAFM tests on Bi_(0.5)Na_(0.5)TiO_(3)bulk ceramic,it is interesting to observe significant currents related to the topography.Why do insulators exhibit“conductivity”in CAFM testing?Herein,we thoroughly investigated the topography-dependent current during CAFM testing for the first time.Based on the linear dependence between the current and the first derivative of topography,the calibration method has been proposed to eliminate the topographic crosstalk.This method is evaluated on Bi_(0.5)Na_(0.5)TiO_(3)bulk ceramic,one-dimensional(1D)ZnO nanowire,twodimensional(2D)NbOI_(2)flake,and biological lotus leaf.The corresponding results of negligible topography-interference current affirm the feasibility and universality of this calibration method.This work effectively addresses the challenge of topographic crosstalk in CAFM characterization,thereby preventing the erroneous estimation of the conductivity of any unknown sample.