Visualization and Estimation of 0D to 1D Nanostructure Size by Photoluminescence

At a Glance

Metadata	Details
Publication Date	2024-12-12
Journal	Nanomaterials
Authors	Artūrs Medvids, Artūrs Plūdons, A. Vaitkevičius, S. Miasojedovas, Patrik Ščajev
Institutions	Vilnius University, Riga Technical University
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nanostructure Sizing via Photoluminescence

This document analyzes the research on using Photoluminescence (PL) to estimate the size of 0D-1D nanostructures (nanocones and AFM tips). It highlights the technical requirements of the study and maps them directly to the advanced MPCVD diamond solutions offered by 6CCVD, positioning our materials for next-generation quantum and nanomechanical applications.

Executive Summary

The following points summarize the core technical achievements and the resulting value proposition for advanced material engineering:

Novel Sizing Method: A simple, non-destructive optical procedure was developed to visualize and estimate the sharpness (top diameter) of nanocones and AFM tips using their Photoluminescence (PL) emission spectrum.
Quantum Confinement Validation: The method leverages the blue-shift in PL spectra, directly correlating the emission energy ($E_g$) with the nanostructure diameter (d) via the quantum confinement effect.
Precision Measurement: The top diameter of a sharp Si AFM tip (SuperSharpSilicon™ SSS-NCL) was precisely determined to be 1.5 nm, validating the technique against traditional SEM measurements.
Kinetic Analysis: Time-resolved PL (TRPL) confirmed a stretched-exponent decay ($\tau_0 = 1.0$ ns), indicating that exciton decay is dominated by surface and radiative recombination, crucial for understanding quantum emitter stability.
Material Relevance: The technique is applicable to wide-bandgap materials like Diamond-Like Carbon (DLC) and Silicon (Si) nanocones, demonstrating a clear pathway for characterizing high-performance diamond-based nanoprobes.
Operational Advantage: This optical method allows for in situ sharpness determination without requiring the high vacuum and specialized equipment necessary for SEM analysis.

Technical Specifications

The following hard data points were extracted from the analysis of DLC and Si nanocone structures:

Parameter	Value	Unit	Context
Si AFM Tip Top Diameter	1.5	nm	Calculated from PL blue cutoff ($E_{gmax} = 2.8$ eV)
DLC Nanocone Top Diameter	2.0	nm	Calculated from blue-shifted PL
DLC Film Thickness	400	nm	Formed by magnetron sputtering on Si substrate
DLC Annealing Temperature	1060	°C	Thermal treatment in N atmosphere
PL Excitation Wavelength	405	nm	Used for confocal PL imaging (0.25 mW power)
Time-Resolved PL Excitation	350	nm	Used for kinetic analysis (200 fs pulses)
Average Exciton Lifetime ($\tau_0$)	1.0	ns	Fitted using stretched exponent decay ($\beta = 0.58$)
Si Tip Radiative Efficiency ($\Phi$)	$\sim 15$	%	Confirms high quality for optical applications
Si Tip Surface Recombination Velocity (S)	1.1	cm/s	Calculated for Tip No. 1 (indicates high surface quality)
Si Tip Resistivity	0.01 - 0.025	$\Omega \cdot$cm	N-type doped silicon probe
Si Tip Electron Density ($n_{dop}$)	$\sim 10^{19}$	cm^-3	High doping level for static charge dissipation

Key Methodologies

The experimental procedure focused on material synthesis, structural characterization, and advanced optical spectroscopy:

DLC Film Synthesis: Diamond-Like Carbon (DLC) films were deposited via magnetron sputtering of Carbon onto a Si substrate.
Nanocone Formation: Subsequent thermal annealing of the DLC films at 1060 °C in a Nitrogen atmosphere induced the formation of 80 nm-high DLC nanocones (Stranski-Krastanow model).
AFM Probe Selection: Commercial SuperSharpSilicon™ (SSS-NCL) AFM probes were selected. These probes feature n-type doped silicon for conductivity and a typical top radius of less than 2 nm.
Confocal Photoluminescence (PL): Measurements were performed using a WITec Alpha 300S microscope (100× objective, NA = 0.9). Excitation was performed at 405 nm with 0.25 mW power.
Time-Resolved PL (TRPL): Kinetics were measured using a Hamamatsu streak camera system. Excitation was provided by 200 fs laser pulses at 350 nm (10-kHz frequency).
Size Calculation: Nanocone diameter (d) was estimated by fitting the blue-shifted PL spectrum using a quantum confinement model that includes the exciton binding energy ($E_{ex}$) and quantum confinement energy ($E_{Qc}$).

6CCVD Solutions & Capabilities

The research demonstrates the critical need for materials with precise dimensional control, controlled doping, and superior surface quality for quantum confinement applications. 6CCVD’s expertise in MPCVD diamond growth provides ideal solutions for replicating and advancing this research, particularly in high-performance probe and quantum emitter development.

Applicable Materials for Advanced Nanoprobes and Quantum Confinement

Material Solution	Application Relevance	Key 6CCVD Capability
Optical Grade Single Crystal Diamond (SCD)	Ideal replacement for DLC/Si in quantum confinement studies. Provides a stable, ultra-wide bandgap host for robust quantum emitters (e.g., NV centers).	SCD thickness control (0.1 µm - 500 µm) and ultra-low defect density for high radiative efficiency.
Heavy Boron-Doped Diamond (BDD)	Direct replacement for the n-type doped Si AFM tip. BDD offers superior hardness, chemical inertness, and conductivity for robust scanning probes.	Precise BDD doping control to match or exceed the required conductivity (0.01-0.025 $\Omega \cdot$cm) for static charge dissipation.
Polycrystalline Diamond (PCD)	Suitable for large-area nanocone arrays or robust substrates requiring high thermal conductivity and mechanical strength.	Large area growth up to 125 mm diameter, with thicknesses up to 500 µm.

Customization Potential for Nanostructure Engineering

6CCVD offers specialized services critical for manufacturing and characterizing materials used in this type of nanostructure research:

Custom Dimensions and Thickness: The paper utilized 400 nm thick films. 6CCVD routinely delivers SCD and PCD plates/wafers with precise thickness control, ranging from 0.1 µm to 500 µm, enabling tailored quantum confinement layers.
Ultra-Low Roughness Polishing: Achieving low surface recombination velocity (S = 1.1 cm/s in the paper) is critical for high radiative efficiency. 6CCVD guarantees ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, minimizing surface defects that cause non-radiative decay.
Advanced Metalization Services: While the Si tip was undoped, many advanced probes require contact layers. 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for creating custom electrical contacts or protective layers on diamond substrates.
Feature Fabrication Support: For creating sharp nanoconic structures or arrays, 6CCVD provides custom laser cutting and etching services to define precise geometries on diamond substrates.

Engineering Support

6CCVD’s in-house PhD team specializes in the characterization and optimization of wide-bandgap materials. We can assist researchers in material selection, doping optimization, and surface preparation for similar quantum confinement and nanomechanical probe projects, ensuring optimal performance metrics like radiative efficiency and exciton lifetime.

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

View Original Abstract

We elaborate a method for determining the 0D-1D nanostructure size by photoluminescence (PL) emission spectrum dependence on the nanostructure dimensions. As observed, the high number of diamond-like carbon nanocones shows a strongly blue-shifted PL spectrum compared to the bulk material, allowing for the calculation of their top dimensions of 2.0 nm. For the second structure model, we used a sharp atomic force microscope (AFM) tip, which showed green emission localized on its top, as determined by confocal microscopy. Using the PL spectrum, the calculation allowed us to determine the tip size of 1.5 nm, which correlated well with the SEM measurements. The time-resolved PL measurements shed light on the recombination process, providing stretched-exponent decay with a τ0 = 1 ns lifetime, indicating a gradual decrease in exciton lifetime along the height of the cone from the base to the top due to surface and radiative recombination. Therefore, the proposed method provides a simple optical procedure for determining an AFM tip or other nanocone structure sharpness without the need for sample preparation and special expensive equipment.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano14241988

References

2004 - Optical fiber probe for biomedical Raman spectroscopy [Crossref]
1984 - Electron-electron and electron-hole interactions in small semiconductor crystallites: The size dependence of the lowest excited electronic state [Crossref]
1993 - Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites [Crossref]
1993 - Absorption and intensity-dependent photoluminescence measurements on CdSe quantum dots: Assignment of the first electronic transitions [Crossref]
2022 - High-Performance Deep Red Colloidal Quantum Well Light-Emitting Diodes Enabled by the Understanding of Charge Dynamics [Crossref]
2007 - Quantum confinement effect in nanohills formed on a surface of Ge by laser radiation [Crossref]
2008 - Properties of Nanostructure Formed on SiO2/Si Interface by Laser Radiation
2011 - Properties of nanocones formed on a surface of semiconductors by laser radiation: QC effect of electrons, phonons, and excitons [Crossref]
2010 - Mechanism of nano-cone formation on Cd0.9Zn0.1Te crystal by laser radiation [Crossref]