Quantitative Mapping Of Charge Distribution By In-line Holography

Mapping the charge distribution in nano scale systems still is a difficult task,but is important to provide fundamental insights into the properties of materials.Knowledge on the charge distribution in nanostructures,such as catalysts,doped semiconductors and surface plasmon resonance,is highly beneficial to understand the relationship between internal microstructure,defects and functional properties.In practice charge distribution is always modulated by various external conditions(atmosphere,temperature,bias),investigation into the dynamic process of charges is therefore essential to understand the coupling mechanism between charge and external field.In order to do so,it is necessary to find a simple and efficient method to acquire the charge information in nanostructures.Some of these methods are based on low-energy electron point source microscope(LEEPS),where charge density is usually measured from the borders of the Fresnel fringes;however these data cannot be related to the structure of(nano)material.Other methods are based on scanning probe technologies or off-axis electron holography;these allow for indirectly imaging of the charge distribution,but the response to charge variation is slow and this limits their time resolution.We are seeking for a fast and intuitive approach that allows for a dynamic observation of the charge process and that can be generally used in TEM.We propose a method allowing for the simple and direct acquisition of charges.Combined with various in-situ technologies developed for electron microscopy,it provides a fast probing tool for charge variation.Moreover,it can acquire information of the potential over a broad range of dimensions from micrometer to nanometer,while it is usually smaller in the off-axis holography(within lum).In this work,we demonstrate how high energy electrons can be used to visualize the charge density distribution along one-dimensional wires with a sensitivity as low as several tenths of elementary charges per nanometer,which is sufficient for the measurement of electrical properties of materials.Besides,charge distribution in the particle-nanowire coupling system is also imaged and the relationship between the fringe features and the local charge can be determined.Furthermore,we could observe real-time charge redistributions under in-situ heating and biasing.In addition,the measured charge density provides information on the electrical resistivity of individual nanowires and this avoids the common issue of contact conditions in traditional electrical measurements.