Time-resolved cathodoluminescence in an ultrafast transmission electron microscope

At a Glance

Metadata	Details
Publication Date	2021-08-09
Journal	Applied Physics Letters
Authors	Sophie Meuret, Luiz H. G. Tizei, Florent Houdellier, Sébastien Weber, Yves Auad
Institutions	Laboratoire de physique des Solides, Centre d’Élaboration de Matériaux et d’Études Structurales
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Analysis: Time-Resolved Cathodoluminescence in an Ultrafast Transmission Electron Microscope

Executive Summary

This research paper details a significant breakthrough in nanoscale characterization, successfully implementing time-resolved Cathodoluminescence (CL) within an Ultrafast Transmission Electron Microscope (UTEM). This achievement is highly relevant to engineers developing diamond-based quantum and opto-electronic devices.

Methodological Breakthrough: Reports the first time-resolved CL measurements in a UTEM, combining sub-picosecond temporal resolution with the high spatial resolution of TEM.
Material Focus: Demonstrated spatially-resolved lifetime mapping of Nitrogen-Vacancy (NV) centers in nano-diamonds, a critical material system for quantum sensing and photonics.
Resolution Achieved: Achieved exceptional spatial resolution of 12 nm and sub-nanosecond temporal resolution (Instrumental Response Function, IRF, of ~873 ps).
Key Finding: Measured NV center lifetimes showed strong spatial variation (ranging from 23.4 ± 0.7 ns down to 15.8 ± 0.8 ns) over distances less than 50 nm, highlighting the necessity of nanoscale characterization.
Excitation Source: Utilized a high-brightness, laser-driven cold-field emission source generating 400 fs electron pulses accelerated to 150 keV.
Future Applications: This technique enables correlative studies, linking atomic-scale structural, morphological, and chemical analysis (TEM/EELS) directly with light emission dynamics (CL) in complex nanoscale systems.

Technical Specifications

The following hard data points were extracted from the experimental results and setup description:

Parameter	Value	Unit	Context
Spatial Resolution (Lifetime Map)	12	nm	Effective pixel size after binning
Temporal Resolution (IRF)	873	ps	Measured Instrumental Response Function
Electron Pulse Width	400	fs	Generated by femtosecond laser
Electron Beam Energy	150	keV	Acceleration voltage in UTEM
Repetition Rate	2	MHz	Electron pulse frequency
NV Center Lifetime (Maximum, T₁)	23.4 ± 0.7	ns	Measured on nano-diamond cluster
NV Center Lifetime (Minimum, T₂)	15.8 ± 0.8	ns	Measured on nano-diamond cluster
Nano-Diamond Mean Diameter	~100	nm	Material studied
NV° Zero-Phonon Line (ZPL)	575	nm	Characteristic emission wavelength
Electron Probe Size (Decay Trace)	5	nm	Spot size used for 200 s decay trace acquisition

Key Methodologies

The time-resolved Cathodoluminescence (CL) measurements were performed using a modified Ultrafast Transmission Electron Microscope (UTEM) setup:

Electron Source Generation: A femtosecond laser (515 nm) triggered the emission of 400 fs electron pulses from a sharp Tungsten tip (cold-field emission source).
Acceleration: Electrons were accelerated to 150 keV, with a pulse repetition rate set to 2 MHz.
Beam Focusing and Scanning: The pulsed electron beam was focused to a nanometric probe (as small as 5 nm for decay traces) and scanned over the nano-diamond sample cluster.
CL Collection: A high numerical aperture parabolic mirror collected the CL generated by the electron-sample interaction, ensuring efficient photon flux capture despite the low current (~100 fA).
Signal Routing: The collected light was coupled via an optical fiber to either an optical spectrometer (for spectrum acquisition) or a Single Photon Counting Module (SPCM) connected to a correlator.
Time-Resolved Acquisition: The correlator recorded the delay histogram between the laser trigger (excitation) and the detected CL photons, yielding the excited state decay trace.
Data Analysis: Lifetime (τ) was extracted by fitting the decay trace with the convolution of an exponential decay and a Gaussian function (accounting for the instrument response). Spatially-resolved maps were generated by fitting binned data (12 nm effective pixel size) from scanned regions.

6CCVD Solutions & Capabilities

The successful implementation of UTEM-CL relies fundamentally on high-quality diamond material with precisely engineered defect centers. 6CCVD, as an expert supplier of MPCVD diamond, offers the necessary materials and processing capabilities to replicate, optimize, and scale this advanced research.

Applicable Materials

To replicate or extend this research into functional quantum devices, high-purity Single Crystal Diamond (SCD) is essential for controlled NV center formation.

Material Grade	6CCVD Offering	Relevance to UTEM-CL Research
SCD (Single Crystal Diamond)	Optical Grade, Low Strain. Available in Type IIa (ultra-high purity) or Type Ib (nitrogen-rich precursor).	Provides the ideal crystalline lattice for creating stable, high-coherence NV centers, essential for reliable lifetime measurements.
BDD (Boron-Doped Diamond)	Heavy Boron Doped PCD/SCD.	Relevant for future correlative studies requiring integrated electrical contacts or plasmonic structures on the diamond surface, leveraging BDD’s metallic conductivity.
PCD (Polycrystalline Diamond)	Large Area Wafers (up to 125 mm).	Suitable for large-scale device prototyping or use as robust, high-thermal-conductivity heat spreaders in integrated opto-electronic systems studied by UTEM.

Customization Potential

6CCVD’s in-house processing capabilities directly address the needs of advanced nanoscale characterization and device integration:

Research Requirement	6CCVD Customization Service	Technical Benefit
Specific Defect Engineering	Custom Nitrogen Doping. Precise control over nitrogen concentration during MPCVD growth (Type Ib) to optimize NV center density and distribution.	Ensures material consistency for high-density NV ensembles or low-density single-photon emitter studies.
Device Integration & Contacts	Custom Metalization. Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu films.	Enables the fabrication of integrated plasmonic antennas or electrical contacts directly onto the diamond surface for correlative electron/optical studies.
High-Resolution Imaging Prep	Ultra-Precision Polishing. SCD polished to Ra < 1 nm; inch-size PCD polished to Ra < 5 nm.	Provides atomically smooth surfaces critical for minimizing background noise and maximizing signal collection efficiency in high-resolution TEM/CL experiments.
Unique Sample Geometry	Custom Dimensions and Laser Cutting. Plates/wafers up to 125 mm, with custom shapes and thicknesses (SCD up to 500 µm).	Supports the creation of specific micro- or nanostructures (e.g., diamond membranes, pillars) required for advanced UTEM sample preparation.

Engineering Support

6CCVD recognizes that UTEM-CL is a highly specialized technique requiring optimized material inputs.

Material Selection for Quantum Photonics: 6CCVD’s in-house PhD team can assist researchers in selecting the optimal diamond grade (e.g., low-strain SCD) and processing route (e.g., post-growth annealing protocols) necessary to achieve the desired NV charge state stability and coherence time for similar Time-Resolved Cathodoluminescence projects.
Global Logistics: We offer reliable global shipping (DDU default, DDP available) to ensure sensitive, high-value diamond materials reach advanced research facilities worldwide without delay.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Ultrafast transmission electron microscopy (UTEM) combines sub-picosecond time-resolution with the versatility of TEM spectroscopies. It allows us to study the ultrafast materials’ response using complementary techniques. However, until now, time-resolved cathodoluminescence was unavailable in UTEM. In this paper, we report time-resolved cathodoluminescence measurements in an ultrafast transmission electron microscope. We mapped the spatial variations of the emission dynamics from nano-diamonds with a high density of NV centers with a 12 nm spatial resolution and sub-nanosecond temporal resolution. This development will allow us to study the emission dynamics from quantum emitters with a unique spatiotemporal resolution and benefit from the wealth of complementary signals provided by transmission electron microscopes. It will further expand the possibilities of ultrafast transmission electron microscopes, paving the way to the investigation of the quantum aspects of an electron/sample interaction.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0057861

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