時間分解顕微法の開発とオペランド時空間解析への応用
Development of time-resolve microscopy
and its application to operando
桑原研究室、桑原真人、池永英司、小川智史
spatiotemporal analysis
Advanced Measurement Technology Center, Kuwahara Lab.
The temporal evolution of phenomena occurring in nanomaterials provides important information on phasetransitions, optical coupling, and energy relaxation. Ultrafast measurements in electron microscopy using
pulsed electron beams is a promising method for investigating high-speed phenomena on the nanoscale.
Furthermore, the use of a high-brightness pulsed beam in transmission electron microscopy (TEM) is expected
to enable one-shot electron imaging in projection mode, allowing observations of organic materials or
biological specimens without electron-beam damage.

High-quality pulsed beam

Nano particles, XAFSA GaAs-type photocathode having anegative electron affinity surface(NEA-PC) was applied to the electron
source to generate a picosecond pulse
electron beam with high brightness.
We have developed a spin-polarized
pulse-TEM (SPTEM) system, whichHigh brightness w/ high pol.
comprises an NEA-PC as a polarized
electron source and a 30-keV transmission
electron microscope. Evaluation of this0.24 eV @FWHM
system showed that it was capable of0.03 eV
producing a highquality electron beam with@756 nm
a high brightness, a high spinpolarization,a long coherence length, a picosecond
Defference from the center energy (eV)response time and a narrow energy width.
Narrow energy width

Coherent wave

Polarization-maintaining
optical fiber
Pulse generator
24 ns, 8 MHz

Linear polarizer

24ns
125 nsLiquid crystal
controller

LCModulated
RF generator

Circularly polarized laser

AOM

Photocathode

Linearpolarizer
Half-wave
plate2020(a)00-20-20-40-40-60-0.8(b)Polarization -80%

Polarization +83%-0.6

-0.4

-0.2

00.2

0.4

-60
0.8
-0.8

0.6

-0.6

-0.4

Coincidence time (ns)

-0.2

00.2

0.4

0.6

0.8

Coincidence time (ns)Spin-polarized electrons

ATi:Sap. CW laser
λ : 710 - 910 nm

PC

Difference in coincidence
counts Npol−Nnon (a. u.)

The first-order interference was clearly observed in the SPTEM,
which showed long coherence length was realized by the NEA-PC.
The intensity interference between pairs of electrons,
second-order intergerence, was investigatedVacuumusing a spin-polarized electron beam having ahigh polarization and a narrow energy width.
Spin-dependent antibunching was observed,
Carbondemonstrating that the antibunching wasassociated with fermionic statistics. The
coherent spin-polarized electron beam facilitated
100nm
Biprism +4V
the extraction of intrinsic quantum interference.

targetinterface

Specimen holder
Electron biprism

Multi-channel
analyzer

Main amp.
DelayMCPs

Pre-amp.

Coincidence detector

Pre-amp.

Time-toamplitude
converterMain amp.

Holography

Phosphor screen

CCDcamera

1.21Counts (a.u.)

Coherence w/ spin polarized

We synthesized metal nano-particles (NPs) Color reaction of NPs for pHwith solution plasma process (SPP) method
which can realize arbitrary composition ofmetals without surface modifications.
Our group uses X-ray absorption finestructure (XAFS) analysis to clarify thechemical information of the NPs, which issimilar to TEM-EELS but high precise
analysis method. XAFS of NPs revealed
atomic distances and thevalence information.
Development of high-voltage
CMA was started to analyseinterface of NPs, which
contributes to improve thephotocatalytic reaction.

0.8
0.6
0.4

Energy width

0.20-0.5

00.5Electron Energy (eV)1Energy spectrometer

M. Kuwahara et al., Phys. Rev. Lett. 126, 125501 (2021).

Time-resolved measurement
We have developed a time-resolved TEM (TRTEM) system by combining an NEA-PC with a 100-kV TEM instrument. Combination of thepulsed electron beam with electron energy-loss spectroscopy (EELS) in TRTEM realized a transient EELS (TEELS) technique with atemporal resolution of 8 ps and an energy resolution of 0.38 eV. Ultrafast phenomena in gold nanotriangles (AuNTs) stimulated by apulsed laser beam were investigated using the TEELS technique. Coincidentally, an increment in the energy loss in the EEL spectrum isobserved at approximately 0 s. The TEELS data showed two decay processes with a time constant of 7.8 ps and longer than 100 ps.
The results indicate that excited electrons on the surface and in the bulk underwent the same relaxation processes during bothelectron-phonon and phonon-phonon interactions.
Specimen holder

Optical fiberΔt11ps

Bunched electrons

Variable delay line

Half-wave plate

Specimen

Linear polarizer
Photocathode

Pump laser

Mode-locked
Ti:Sapphier laser
780 nm, 180 fs, 80MHz

Bunched electrons

Time-resolved EELS
50A

43 x1040

SpecimenholderGold nanoplates
on membrane

PhosphorscreenNPs on membrane

CCDcamera

50 nm

ADF STEM image

Schematics of 100-kV TRTEM

030

3205 ps

21100
20-15 ps10-10-20

Energy spectrometer

1Intensity of EELS (arb. u.)

Electron beam
trajectory

Laserbtrajec eam
tory35 ps

20204060

80

Electron energy loss (eV)1003001020304050

Electron energy loss (eV)602010×103

A semiconductor with an NEA surface is equipped in the photocathode-typee-gun. The extra-high vacuum and high acceleration field in the electron gun
was realized simultaneously.

Optical system for pump-probe method in TRTEM, which
consists of a modelocked Ti:Sapphire laser,
pulse picker, power
control system with EO,
and a delay system.We!"# $%&'(can select the free
4$.5 06
space path or opticalfiber path for driving thephotocathode.

Pulse laser fordriving probe beam

Delay time (ps)Stroboscopic measurement (cw ~ few ps)
Time-resolved TEM imaging
Time-resolved EELS
Ultrafast-Electron-Diffraction
Time-resolved STEM imaging
Single-shot measurement
Single-shot TEM imaging (> 500 ns)
Single-shot UED (> 100 ns)

Polarized half-wave
beam splitter plate

Bunched electrons and pump laser at specimen

0M. Kuwahara et al., Appl. Phys. Lett. 121, 143503 (2022).