Atom probe has been developed for investigating materials at the atomic scale and in three dimensions by using either high-voltage (HV) pulses or laser pulses to trigger the field evaporation of surface atoms. In this paper, we propose an atom probe setup with pulsed evaporation achieved by simultaneous application of both methods. This provides a simple way to improve mass resolution without degrading the intrinsic spatial resolution of the instrument. The basic principle of this setup is the combination of both modes, but with a precise control of the delay (at a femtosecond timescale) between voltage and laser pulses. A home-made voltage pulse generator and an air-to-vacuum transmission system are discussed. The shape of the HV pulse presented at the sample apex is experimentally measured. Optimizing the delay between the voltage and the laser pulse improves the mass spectrum quality.

Optimizing Atom Probe Analysis with Synchronous Laser Pulsing and Voltage Pulsing.

An RF electromagnetic (EM) characterization of high pulsed voltage electrode is investigated in the present paper. The electrode acts as an electric-or E-field pulse generator for atom probe tomography (APT) application. The proposed electrode device is essentially comprised of a microstrip transmission line (TL) combined with via hole. The challenging prediction of the electrode signal integrity and E-field emission is elaborated. The APT pulse generator equivalent model is established. The transient response of the voltage pulse generator EM into transient electric pulse is analyzed. The excitation signal is assumed as a square wave pulse voltage with 1-kV amplitude and 2-ns full width time duration. The electrode device S-parameter responses from DC to 8-GHz is computed. The behavior of the transient E-field response in function of the position inside the substrate via hole is analysed. The delivered harmonic input current and power optimal values are assessed.

Analysis of transient electric-field emitted by atom-probe tomography electrode

An uncommon circuit modelling of microelectrode for ultra-short signal propagation is developed. The proposed model is based on the Tensorial Analysis of Network (TAN) using the Kron–Branin (KB) formalism. The systemic graph topology equivalent to the considered structure problem is established by assuming as unknown variables the branch currents. The TAN mathematical solution is determined after the KB characteristic matrix identification. The TAN can integrate various structure physical parameters. As proof of concept, via hole ended microelectrodes implemented on Kapton substrate were designed, fabricated and tested. The 0.1-MHz-to-6-GHz S-parameter KB model, simulation and measurement are in good agreement. In addition, time-domain analyses with nanosecond duration pulse signals were carried out to predict the microelectrode signal integrity. The modelled microstrip electrode is usually integrated in the atom probe tomography. The proposed unfamiliar KB method is particularly beneficial with respect to the computation speed and adaptability to various structures.

Kron–Branin modelling of ultra-short pulsed signal microelectrode

The electrode constitutes the key element of the atom probe (AP) pulse signal generator. The AP parameter Monte Carlo (MC) analysis is introduced. The AP microelectrode is designed with 50-Ω loaded microstrip line centered by via hole. The excitation square wave pulse presents 300-ps duration and 1-kV amplitude. The worst cases of the signal integrity is performed with MC analysis applied to the electrode transmission line metallization width sensitivity. Computation results with commercial frequency analysis from DC to 10-GHz is presented. The worst-case analysis is necessary for the AP performance optimization by increasing the radiated pulsed electric-field.

Monte Carlo worst case analysis of atom probe tomography microelectrode

A signal integrity (SI) analysis of high voltage rectangular short pulses for the atom- probe system is explored in this paper. The operated RF transient pulse is considered for exciting on material sample inside an ultra-high vacuum (UHV) cryogenic chamber. The ns- duration pulse signal is injected into the cryogenic analysis chamber through the transmitting system mainly constituted by a microstrip interconnect line ended by optical controlled nonlinear load. The whole system frequency characterization is performed based on the S- parameter measurements. As expected, a challenging ultra-short rectangular shape pulse is exhibited by the pulser. Promising experimental results with the improvement of ion mass spectrum is demonstrated with the designed RF pulser.

http://iopscience.iop.org/article/10.1088/1757-899X/120/1/012006/pdf

RF Pulse Signal Integrity Analysis for Nonlinear Ended Microstrip Line Atom-Probe Tomography

Improvement of atom probe tomography requires the high voltage rectangular short pulses. This typical RF transient pulse must be applied on a sample inside an ultra-high vacuum (UHV) chamber. In this letter, we present a synthesis technique of rectangular pulse signal with full width ns-duration. The pulse signal was injected into the cryogenic analysis chamber through the transmitting system composed of a microstrip transmission line. The system frequency characterization based on the S-parameter analysis and RF engineering shows the transmitting system major deterrent. The preliminary experimental result demonstrates that the atom probe performance is improved.

http://ieeexplore.ieee.org/iel7/7317693/7323359/07323403.pdf

F. Delaroche

Papers

RF Pulse Signal Integrity Analysis for Nonlinear Ended Microstrip Line Atom-Probe Tomography

RF transient pulse signal integrity with ns-duration for atom-probe tomography