Related Experiment Video
Updated: Jun 14, 2026
10:40
High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
Published on: June 28, 2016
Layer-Dependent Phonon Polaritons in hBN Resolved by Photo-Induced Force Spectroscopy
Amin Hajarian1, Jiwoo Seo1, SungWoo Nam1,2
1Department of Mechanical and Aerospace Engineering, University of California, Irvine, California, USA.
Advanced Science (Weinheim, Baden-Wurttemberg, Germany)
|June 12, 2026
Summary
Hexagonal boron nitride (hBN) layer number tunes phonon polariton resonance frequencies. Increasing layers blue-shift in-plane resonances and red-shift out-of-plane resonances, impacting nanophotonic applications.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanophotonics
Background:
- Hexagonal boron nitride (hBN) is a van der Waals material supporting confined phonon polaritons.
- Previous studies focused on phonon polariton wavelength and propagation, not resonance energy dependence on hBN layer number.
Purpose of the Study:
- To systematically investigate the layer-dependent phonon polariton resonance frequencies in hBN.
- To analyze the spectral behavior of phonon polaritons as a function of hBN thickness.
Main Methods:
- Photo-induced force microscopy (PiFM) was employed for spectroscopic analysis.
- hBN samples with layer numbers ranging from approximately 10 to 60 were probed.
Main Results:
- Observed opposing trends in resonance frequencies for in-plane and out-of-plane phonon polaritons.
- In-plane resonance blue-shifted, while out-of-plane resonance red-shifted with increasing hBN layer number.
- Out-of-plane band intensity increased, while in-plane resonance weakened and broadened with layer number.
Conclusions:
- Layer number is a critical tuning parameter for phonon polariton behavior in hBN.
- Findings provide insights into the optical response of hBN across different layer regimes.
- Results are significant for developing nanophotonic devices utilizing hBN.
Related Concept Videos
01:23IR Spectrum Peak Broadening: Hydrogen Bonding
The vibrational frequency of a bond is directly proportional to its bond strength. As a result, stronger bonds vibrate at higher frequencies, while weaker bonds vibrate at lower frequencies. The stretching vibration of the strong O–H bond in alcohols and phenols (very dilute solution or gas phase) appears as a sharp peak at 3600–3650 cm−1.
However, the extent of hydrogen bonding influences the observed stretching frequency and band broadening. Intermolecular or intramolecular hydrogen bonding...
However, the extent of hydrogen bonding influences the observed stretching frequency and band broadening. Intermolecular or intramolecular hydrogen bonding...
01:16IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to the...
According to Hooke's law, the vibrational frequency is directly proportional to the...
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:12Double Resonance Techniques: Overview
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...