Advanced Material Characterization Service
In-house Service
MONSTR Sense Technologies’ advanced material characterization is the first of its kind. Based on our patented nonlinear imaging and spectroscopy technology, this characterization service is the Swiss army knife of characterization services. We can image samples with sub-micron resolution. At the same time, we can employ numerous nonlinear spectroscopic techniques to characterize your sample.
This is a great way to test whether or not MONSTR Sense products would be a good fit for your lab, or to acquire some useful ultrafast imaging data for a paper.
We currently offer both imaging and spectroscopy characterization.
Imaging capabilities
Static Images
- Resonant linear reflectance data for field-of-views of up to 4″ and spatial resolution of up to 1 um (smaller field-of-view).
- Four-wave mixing data for field-of-views of up to 4″ and spatial resolution of up to 1 um (smaller field-of-view).
Decay images
- Pump-probe decay images with temporal resolution down to 100 fs and delay range up to 1.3 ns
- Spectrally-resolved pump-probe images with 10 nm bandwidth for fixed laser wavelength or up to 600 nm bandwidth with tuned laser excitation.
Dephasing images
- Dephasing (photon-echo) images with temporal resolution up to 100 fs and delay range up to 250 ps, corresponding to a homogeneous linewidth resolution down to 0.01 meV.
Hyperspectral images
- Resonant linear reflection with selectable range spanning 350 nm-950 nm
- Four-wave mixing image with selectable range spanning 350 nm-950 nm
Spectroscopy capabilities
Linear reflection and nonlinear emission spectroscopy
- High-resolution (<10 GHz) linear reflection and four-wave mixing emission spectroscopy for a selectable 10 nm bandwidth between 350-950 nm.
- Low-resolution (<5 nm) linear reflection and four-wave mixing emission spectroscopy for a selectable wavelength range between 350-950 nm.
- Nonlinear spectroscopy with high dR/R sensitivity (1e-7)
Transient Absorption Spectroscopy
- Transient Absorption Spectroscopy with <100 fs resolution and delay times up to 1.3 ns.
- High-resolution and high-bandwidth options for spectroscopy
- Two color pump-probe options upon request
- High dR/R sensitivity (1e-7)
Multidimensional Coherent Spectroscopy
- Zero-quantum, single-quantum, and double-quantum capabilities
- Coherence times up to 250 ps, decay times up to 1.3 ns
- 10 nm tunable bandwidth across 350 nm-950 nm wavelength range
| Samples | Transition metal dichalcogenides, quantum dots, quantum wells, perovskites, cuprous oxides, j-Aggregates, micro-LEDs, etc. | |
| Sample size | Up to 120×100 mm | |
| Spatial resolution | <1 um | |
| Temporal resolution | <100 fs | |
| Delay range | 1.3 ns | |
| Wavelength range | 350-950 nm | |
| Provided data | Image files containing spectra and images (depending on requested measurements, see Capabilities). Raw imaging and spectroscopy data with Python template files for analysis. |
A universal characterization technique
Our imaging and spectroscopy characterization of advanced materials is rooted in our past as scientists in the University of Michigan Physics Department. Stuck between inconsistent results depending on sample position and a desire to have a more tunable and versatile arsenal of spectroscopic techniques, we came up with an idea: A device, combining nonlinear spectroscopy and imaging. This is how BIGFOOT and NESSIE were born. Now, we have extended the capabilities of BIGFOOT and NESSIE to cover larger samples and integrated them with a tunable laser to cover larger wavelength ranges. Thinking of all those late nights in the lab, we now open this advanced material characterization service to scientist at universities, national labs, and industry.
Our ultrafast nonlinear imaging and spectroscopy techniques are rather versatile – we work with tunable excitation lasers that currently allow us to study materials with bandgaps between 350-500 nm and 690-950 nm.
This makes the technique perfectly suitable for many “hot” materials, including transition metal dichalcogenides, quantum dots and quantum wells for different materials, perovskites, cuprous oxides, j-Aggregates, etc. See below for some of the results demonstrated with BIGFOOT and/or NESSIE.
Transition Metal Dichalcogenides
Transition metal dichalcogenides (TMDs) are a promising materials platform for optoelectronic applications due to their strong light-matter interaction. Understanding the homogeneity of promising physical properties across the sample and getting to the bottom of the fundamentals of these light-matter interactions is of crucial importance for scientists in academia and industry alike.
Linear (a) and pump-probe image (b) of a MoSe2 mono to quad-layer on a sapphire substrate. The pump-probe image has several zoomed-in images, highlighting the combination of high spatial resolution and large field-of-view for MONSTR Sense’s ultrafast microscope. (c) Decay time map of the multilayer sample.
Our inspection service can help you with material characterization “from scratch”: Take a large area overview scan with linear reflection or pump-probe (four-wave mixing) imaging to find your sample, then proceed to more detailed analysis such as decay time maps, plotted in (c) above. Our spectroscopic service enables the study of exciton interactions in these materials. In the work shown below, our optical research scientist Dr. Torben Purz highlighted the large inhomogeneity of coherence (dephasing) times across an MoSe2 monolayer using multidimensional coherent spectroscopy (MDCS).
(a) Low-power, low-temperature MDCS spectrum of a MoSe2 monolayer. (b) Low-power, low-temperature MDCS spectrum for a different location on the same sample. Figures adapted from T. L. Purz et al., J Chem. Phys. 156 (21). (c) Characteristic low-temperature, low-power MDCS spectrum of an MoSe2/WSe2 heterostructure at a pump-probe delay T =600 fs, measured using a BIGFOOT. Figure adapted from T. L. Purz et al., Phys. Rev. B. 104 (24) (2021).
MDCS can also be used to study coupling between excitons in different TMD materials. An example of this is shown above where a heterostructure of MoSe2/WSe2 was studied using broadband MDCS. The two off-diagonal peaks are clear indicators of coupling between the MoSe2 and WSe2 excitons. By studying the time-dependence of the MDCS spectra, the authors of this publication show that at early times, the excitons are coherently coupled together, while at later times electrons tunneling from the WSe2 to the MoSe2 and holes tunneling from the MoSe2 to the WSe2 dominate the coupling between excitons.
Quantum Wells
Four-wave mixing characterization, measured using BIGFOOT and NESSIE, of a GaAs multiple quantum well. The sample consists of four quantum wells with a 10 nm quantum well width and 10 nm AlGaAs cladding in between the wells. Defects with sub-10-um size can be found on areas spanning tens of millimeters.
Similar to quantum dots, quantum wells are already in our everyday devices, from diode lasers for DVDs and laser pointers to high electron mobility transistors. These days, quantum wells are grown at the wafer scale with both large-scale inhomogeneities due to varying growth conditions and small defects. Characterization of any quantum well device thus requires both the large and small scale, together with spectroscopic resolution, to better distinguish defects. On the left, we show several images measured with our in-house characterization service. Large scale inhomogeneity due to varying quantum well thickness shows up as radially symmetric fringes across the wafer, while small defects on the order of 10 um and below glow brightly in the nonlinear image. Some defects, such as crystallographic defects, surface defects, localized defects, and pits, are highlighted.
Perovskites
Perovskites are seen as another viable candidate for next-generation solar cells. As such, much effort has been devoted to understanding the carrier dynamics using techniques such as transient absorption spectroscopy.
Apart from understanding the general dynamics, defect inspection is hugely important for these types of applications.
Four-wave mixing image, measured using BIGFOOT and NESSIE, of a Methylammonium Lead Iodide (MAPbI3) perovskite over a large area. Clear large-scale inhomogeneities such as scratches, as well as small-area inhomogeneities, including varying four-wave mixing strengths, are evident.
On the left is an image of a perovskite uni-crystal over a large area. Varying spatial scales of sample inhomogeneity are evident. While the most dominant inhomogeneities such as scratches and cracks are accessible with simpler characterization techniques such as brightfield microscopy, the more subtle inhomogeneities that show up with varying four-wave mixing strengths here, are often not evident from those simpler techniques. Moreover, our characterization technique has the option to perform transient absorption spectroscopy in specific areas afterwards, correlating findings from the rapidly acquirable nonlinear images with information about the carrier dynamics.
Quantum Dots
Quantum Dots (QDs) have already made it from the lab to the production floor in the form of quantum dot displays. Nonetheless, they are still being explored for other applications, including quantum information sciences.
(a) One-Quantum spectrum of core-shell colloidal quantum dots. (b) shows two quadrature and the magnitude of the spectrum along the red line plotted in (a). (c) shows the Fourier transform of the two sidebands in (a) as a function of T-delay. Figure adapted from A. Liu et al., Phys. Rev. Lett. 123, 5 (2019).
Spectroscopy of quantum dots has shed much light on the extraordinary properties of these nanometer-sized particles. MDCS and transient absorption properties have helped researchers understand the intricate dynamics of exciton-phonon interactions and coherence transfer, and unravel the band structure dynamics of the materials.
Measuring electrical properties without probes
Ultrafast spectroscopy techniques measure charge transfer and energy transfer in materials. Ultrafast imaging microscopy measurements therefore identify regions where electrical energy is lost. For finding defects in semiconductors that impede device performance, this is everything. Regions of a semiconductor with uncharacteristically long optical decay constants will have correspondingly high nonradiative decay. For LEDs these regions will have reduced efficiency, and for detectors and solar cells these regions will have weak absorption.
Emission and absorption efficiency is typically determined with electrical measurements, requiring construction of an entire device around the semiconductor for testing. Our measurements can perform these tests 100% non-contact saving manufacturers time and process steps.
Capabilities are separated into imaging and spectroscopic capabilities. One powerful aspect our characterization system is the symbiosis of imaging and spectroscopy: We conventionally start with imaging to identify areas of interest on which more advanced spectroscopic techniques can be deployed subsequently. We maintain active communication with our customers throughout the data acquisition process to ensure that you get the data you need.
Imaging capabilities:
Linear reflectance and four-wave mixing imaging
A picture is worth a thousand words, but the combination of resonant linear reflectance and four-wave mixing imaging is worth even more. Our resonant linear reflectance is somewhat similar to conventional brightfield microscopy – with one major difference: It is resonant. This means any changes in the absorption of the sample show up in the linear reflectance image. However, the linear reflectance alone does not tell the full story:
If an area of the sample is dark in linear reflectance, it could, for example, be because of strain, or a localized defect. It could equally be just a piece of dust or some other particulate that might or might not alter the band structure. This is where the four-wave mixing image comes in. Many defects will glow brightly in the nonlinear image, making them clearly distinguishable, and further spectroscopic analysis of certain sample areas can help shed light on the underlying physics.
Figure adapted from T. L. Purz et al., Opt. Express 30, 45008-45019 (2022)
Decay images
Studying the decay (or lifetime) dynamics of your sample can be both interesting for fundamental physics reasons and for quality characterization. Changes in decay times across the sample can be indicators of many things – fundamentally, your carriers (or excitons) experience a change in lifetime. For transition metal dichalcogenides for example, it has been shown that the decay time can be an indicator of dark states, charge transfer, energy transfer, or interlayer exciton lifetime. On the other hand, a locally altered lifetime can also be a good indicator of defect states, rendering decay images a useful tool for defect characterization and inspection.
Figure adapted from T. L. Purz et al., Opt. Express 30, 45008-45019 (2022)
Dephasing images
Figure adapted from T. L. Purz et al., Opt. Express 30, 45008-45019 (2022)
Dephasing (or decoherence) is crucial for many material applications, especially quantum information sciences. The most precise way to access dephasing is to use multidimensional coherent spectroscopy and perform linewidth fits to extract the homogeneous linewidth which is inversely related to the dephasing time. However, this is not always feasible, especially when trying to do spatial studies. Luckily, for most samples, the dephasing time can be extracted by one-dimensional measurements in the time domain by recording the photon-echo and performing an exponential decay fit.
Hyperspectral images (linear and nonlinear)
Hyperspectral imaging is one of the most useful imaging tools. Studying resonance shifts across a sample can give vast insight into strain, doping, changes in chemical composition, or even sample thickness in the case of transition metal dichalcogenides and quantum wells. With the broad wavelength range of our tunable ultrafast lasers, we can characterize the spatial response of samples across hundreds of nanometers with nanometer spectral resolution.
Hyperspectral image of a TMD mono-/bi-/quad-layer sample, measured using BIGFOOT and NESSIE. While strain still plays a significant role in shifting resonance energies, the layer transitions can clearly be seen by the resonance energy shift.
Spectroscopy capabilities:
Our in-house inspection service is equipped with the full spectroscopic might of the BIGFOOT spectrometer. You can find out more about the different spectroscopic techniques on our resources page.
Linear and nonlinear emission spectroscopy
We can perform linear reflectance spectroscopy with high sensitivity across a large wavelength range. Similarly, we can look at the four-wave mixing emission as a function of energy/wavelength.
Transient Absorption Spectroscopy
Also often known as “pump-probe”, this technique is used to detect any changes to the (spectral) response of the sample after “pumping” the sample with an ultrafast laser. It is great for studying sample dynamics and can be spectrally resolved to disentangle the dynamics of different resonances.
Multidimensional Coherent Spectroscopy
The most general form of third-order nonlinear spectroscopy, this technique is particularly useful to disentangle the homogeneous and inhomogeneous contributions to spectral linewidth – yielding information about true dephasing and spatial inhomogeneity of the system. It is also useful for studying coupling between different resonances, whether that’s coherent coupling (e.g., dipole-dipole interactions) or incoherent (e.g., charge or energy transfer). Many other things, from spectral diffusion to non-Markovian exciton-phonon interactions to name a few, can be understood by careful study of a system with multidimensional coherent spectroscopy.
Is your sample or device ready to move from the lab to the fab? MONSTR Sense Technologies also offers wafer-scale characterization of advanced semiconductor materials.
This characterization also uses four-wave mixing imaging, but without the spectroscopic sophistication of a BIGFOOT spectrometer.
This has the advantage of accelerated imaging for wafers up to 6″.