Periodic Reporting for period 1 - AttoPES (Attosecond time-and angle resolved PhotoEmission Spectroscopy (AttoPES))
Reporting period: 2022-03-01 to 2024-02-29
Quantum material (QM) such as topological materials (TM), transition metal dichalcogenides (TMD), superconductors, and charge density wave materials have shown novel properties to be the next generation materials for ultrafast electro-optical electronic devices. These materials show properties such as relatively small band gaps, good electron mobility and even robust surface states, especially in the case of TM. Even the effects which do not exist at equilibrium are being unearthed and are leading to new applications of these materials. Thus, it is necessary to understand the phenomena related to electron-electron, electron-spin and electron-phonon interactions occurring at ultrafast timescale and the nanoscopic level. One of the difficulties in developing these novel materials is the limited availability of techniques to characterize and measure their ultrafast non-equilibrium state dynamics. Angle-Resolved Photoemission Spectroscopy (ARPES) is the technique offers these unique capabilities (both static and dynamic). ARPES is based on the photoelectric effect and is one of the most powerful methods for probing the electronic band structure of solids through the direct and simultaneous measurement of the energy and the momentum of the electron.
The primary goal of the AttoPES project was to develop and establish the metrology solution at AttoLab for TM and TMD as well as novel materials developed at IMEC for efficient electronic devices. The research conducted within the framework utilized the ARPES technique in static as well as time-resolved manner to probe the band structure of the TM and TMD.
During the 24 months, the AttoPES project was able to address most of the subobjective and goals as described in the three work packages (WPs) although with minor deviation and corrective action were also taken. AttoLab was the new facility at IMEC and the ARPES tool required baseline characterization. Thus, in the first step, WP1 focused on static measurements of topological properties and band structure of TM. Tool benchmarking was achieved using Bismuth based TM (Bi2Se3), as well as transition metal dichalcogenides (TMD). Second, WP 2 & 3 we used the tunable high harmonic generation (HHG) laser source (25-120 eV) and combined it with ARPES tool to build a pump-probe set up for time-resolved ARPES experiment on QM. To access the full tunability in probe wavelength (25-120 eV) the beamline optics was also upgraded. However, it was found that to resolve and capture the ultrafast dynamics on QM, a system upgrade (high-repetition rate HHG laser source) was required. To circumvent this challenge, as defined in the risk mitigation plan of the description on the action (DoA), we extended static VUV and laser HHG source based ARPES on 2D materials and TMDs as well as on photoresist materials which play an essential role in fabrication of next generation electronic devices.
The primary goal of the AttoPES project was to develop and establish the metrology solution at AttoLab for TM and TMD as well as novel materials developed at IMEC for efficient electronic devices. The research conducted within the framework utilized the ARPES technique in static as well as time-resolved manner to probe the band structure of the TM and TMD.
During the 24 months, the AttoPES project was able to address most of the subobjective and goals as described in the three work packages (WPs) although with minor deviation and corrective action were also taken. AttoLab was the new facility at IMEC and the ARPES tool required baseline characterization. Thus, in the first step, WP1 focused on static measurements of topological properties and band structure of TM. Tool benchmarking was achieved using Bismuth based TM (Bi2Se3), as well as transition metal dichalcogenides (TMD). Second, WP 2 & 3 we used the tunable high harmonic generation (HHG) laser source (25-120 eV) and combined it with ARPES tool to build a pump-probe set up for time-resolved ARPES experiment on QM. To access the full tunability in probe wavelength (25-120 eV) the beamline optics was also upgraded. However, it was found that to resolve and capture the ultrafast dynamics on QM, a system upgrade (high-repetition rate HHG laser source) was required. To circumvent this challenge, as defined in the risk mitigation plan of the description on the action (DoA), we extended static VUV and laser HHG source based ARPES on 2D materials and TMDs as well as on photoresist materials which play an essential role in fabrication of next generation electronic devices.
Work Package 1 (WP1): Baseline characterization of new ARPES tool using TM
The main goal of the WP1 was to establish the experimental protocol for material characterization using ARPES tool with VUV light source. This was a new tool at the host institution thus required benchmarking and calibration. At the end of the WP the tool was fully commissioned, and a measurement protocol was established. The band dispersion measurement was done on a home-grown TM (Bi2Se3) fabricated using molecular beam epitaxy method (MBE). In these experiments Fermi surface, Dirac cone, and surface states were measured. Furthermore, the effect of the different transfer process on the electronic structure of material was also understood.
Work Package 2 (WP2): Achieving laser based ARPES on semiconductor materials
In this WP a new beamline was constructed and combined with the KRIEOS 150 spectrometer to achieve HHG laser source based ARPES. The beamline consisted a vacuum chamber with an EUV grating for dispersing the broadband light from the HHG-source, as well as providing a way of selecting particular harmonic peaks in the EUV spectrum for PES studies. Following energy selection, a focusing mirror was also installed to focus the EUV into the photoelectron spectrometer. Additionally, a pump beamline was also installed adjacent to the EUV beam line for performing time-resolved photoemission measurements. Laser HHG based ARPES was achieved for TMD at various wavelengths. The time resolved pump-probe experiment was set up, however the signal from excited state was not detected owing to lower repetition rate of the laser and lack of tunability in the pump beamline.
Work Package 3 (WP3): Application of laser based ARPES on novel material developed at host institution
In this part of the project the developed technique was applied to TMD (MoS2). The valence band spectrum and band dispersion measurements were done on single monolayer and three monolayer samples. Furthermore, defect analysis was performed on the material by measuring the photoelectron spectra and the effect of sulfur vacancies on electronic structure was understood.
Moreover, at IMEC, one of fundamental pillars is to push development of new photoresist material for improved lithography performance. Thus, besides the work on TM and TMD materials this work was extended to explore the photoresist materials as well. To support this development at IMEC, fellow also undertook work on unravelling the exposure driven chemistry using 92eV EUV HHG photon source on chemically amplified photoresist (CAR). In this work a model CAR material was exposed to 92 eV EUV light source and photoelectron spectrum was measured to capture the EUV exposure driven chemical changes.
The main goal of the WP1 was to establish the experimental protocol for material characterization using ARPES tool with VUV light source. This was a new tool at the host institution thus required benchmarking and calibration. At the end of the WP the tool was fully commissioned, and a measurement protocol was established. The band dispersion measurement was done on a home-grown TM (Bi2Se3) fabricated using molecular beam epitaxy method (MBE). In these experiments Fermi surface, Dirac cone, and surface states were measured. Furthermore, the effect of the different transfer process on the electronic structure of material was also understood.
Work Package 2 (WP2): Achieving laser based ARPES on semiconductor materials
In this WP a new beamline was constructed and combined with the KRIEOS 150 spectrometer to achieve HHG laser source based ARPES. The beamline consisted a vacuum chamber with an EUV grating for dispersing the broadband light from the HHG-source, as well as providing a way of selecting particular harmonic peaks in the EUV spectrum for PES studies. Following energy selection, a focusing mirror was also installed to focus the EUV into the photoelectron spectrometer. Additionally, a pump beamline was also installed adjacent to the EUV beam line for performing time-resolved photoemission measurements. Laser HHG based ARPES was achieved for TMD at various wavelengths. The time resolved pump-probe experiment was set up, however the signal from excited state was not detected owing to lower repetition rate of the laser and lack of tunability in the pump beamline.
Work Package 3 (WP3): Application of laser based ARPES on novel material developed at host institution
In this part of the project the developed technique was applied to TMD (MoS2). The valence band spectrum and band dispersion measurements were done on single monolayer and three monolayer samples. Furthermore, defect analysis was performed on the material by measuring the photoelectron spectra and the effect of sulfur vacancies on electronic structure was understood.
Moreover, at IMEC, one of fundamental pillars is to push development of new photoresist material for improved lithography performance. Thus, besides the work on TM and TMD materials this work was extended to explore the photoresist materials as well. To support this development at IMEC, fellow also undertook work on unravelling the exposure driven chemistry using 92eV EUV HHG photon source on chemically amplified photoresist (CAR). In this work a model CAR material was exposed to 92 eV EUV light source and photoelectron spectrum was measured to capture the EUV exposure driven chemical changes.
The research activities from AttoPES project resulted in development of state-of-the-art metrology tool for novel materials being fabricated at IMEC.
1. Development and commissioning of the ARPES technique for robust and fast metrology of semiconductor materials. Furthermore, extending the technique to characterize and support the device fabrication process.
2. Development of table-top laser-based photoemission spectroscopy setup to explore the excited state dynamics of QM.
The progress achieved during the AttoPES project will profoundly impact the development of semiconductor material at host institution. Moreover, it will enable the fundamental studies and fast metrology on these materials. The tool developed in this project will also be commissioned for the external users enabling room for future collaborations.
1. Development and commissioning of the ARPES technique for robust and fast metrology of semiconductor materials. Furthermore, extending the technique to characterize and support the device fabrication process.
2. Development of table-top laser-based photoemission spectroscopy setup to explore the excited state dynamics of QM.
The progress achieved during the AttoPES project will profoundly impact the development of semiconductor material at host institution. Moreover, it will enable the fundamental studies and fast metrology on these materials. The tool developed in this project will also be commissioned for the external users enabling room for future collaborations.