Perspective oxide epitaxy

The main challenges for the epitaxy of high-quality oxide layers are identified as the high oxidization potentials needed to achieve many desired compounds, the high temperatures required for numerous oxide phases to form, and the high temperatures necessary to grow films in adsorption-controlled growth modes. To overcome these challenges, various possibilities exist. Thermal laser epitaxy and CO2 laser heaters are deemed especially promising in this regard, because with this technology growth in extreme environments is possible.

This work was recently published in Applied Physics Letters Materials.

Sapphire Surfaces

Heating c-plane sapphire to a temperature of 1700 °C results in a perfect surface for subsequent epitaxy. These surfaces are characterized by atomically flat double-stepped terraces with widths exceeding 1 μm. The atoms on the surface rearrange in a singular in-plane orientation of the (√31x√31)R9° surface reconstruction, as shown in the reflection high-energy electron diffraction (RHEED) image on the right. The observation of up to 20 Laue circles indicates the high crystal quality of the surface.

This work was recently published in Advanced Materials.

Evaporation of All Elements

We have explored the deposition of elemental metal films with TLE. So far we have succeeded in depositing films with thicknesses ranging from 1 to 500 nm on 2 inch Si wafers. All elemental sources could be evaporated in the same setup with growth rates between 0.01 and 1 Å/s by varying the laser power. Due to the inherent efficiency of the TLE process, significantly less power is required compared to high-temperature effusion cells and e-beam evaporators. A set of sample examples is shown below. The films are dense and homogeneous and have a very smooth surface morphology. These results show that laser evaporation is well-suited for the growth of complex compounds with excellent control.

In situ surface preparation

Oxide substrate surfaces can be prepared simply by high-temperature annealing in the growth chamber. This removes the need for chemical treatments and ex situ annealing. The process takes only a few minutes. Specifically, the successful surface preparation of doped SrTiO3 (001), LaAlO3 (001), NdGaO3 (001), DyScO3 (110), TbScO3 (110), MgO (001), and Al2O3 (0001) surfaces is demonstrated.


TLE publications

An overview of the key scientific publications about thermal laser epitaxy.
1The very first TLE paper
Description of the principle method and key features of the technology.
2019-05 / AIP Advances 9: Film deposition by thermal laser evaporation
2The TLE periodic table
Demonstration of thin film growth with 43 elements from the periodic table.
2021-02 / Journal of Laser Applications 33: Thermal laser evaporation of elements from across the periodic table
3Oxide evaporation
4Oxide epitaxy
Demonstration of epitaxial growth of metal oxide films NiO, VO2, and RuO2 on Al2O3 or MgO substrates.
2021-08 / Journal of Vacuum Science & Technology A 39: Epitaxial film growth by thermal laser evaporation
6Metal sources in oxygen
A systematic, experimental study of the role of source oxidation on source evaporation.
2022-12 / Journal of Applied Physics 132: Thermal laser evaporation of elemental metal sources in oxygen
7Aluminum sources
8Evaporation of carbon
The effectiveness of TLE in synthesizing a broad spectrum of carbon films.
2023-10 / Crystal Growth and Design 23: Thermal Laser Epitaxy of Carbon Films
9Perspective oxide epitaxy
A discussion of the implications of ongoing developments and the future of oxide epitaxy, focussing on TLE and CO2 laser substrate heating.
2024-04 / Applied Physics Letters Materials. 12: State of the art, trends, and opportunities for oxide epitaxy
10Ruthenium films on sapphire
Using TLE ruthenium films of unprecedented quality were grown. The three-step process involving high-temperature substrate preparation, low-temperature growth and high-temperature annealing is reminiscent of solid-phase epitaxy.
2024-07 / Journal of Vacuum Science and Technology A. 42: Growth of high-quality ruthenium films on sapphire

CO2 laser heating publications

An selection of publications enabled by direct substrate heating using a CO2 laser.
1In situ termination of strontium titanate surfaces
The first example of using the high temperatures enabled by direct CO2 laser heating for the preparation of atomically smooth surfaces for epitaxy.
2018-03 / Applied Physics Letters 112: Independence of surface morphology and reconstruction during the thermal preparation of perovskite oxide surfaces
2Substrate surface preparation
Description of the advantages of our THERMALAS substrate heater for surface termination.
2020-03 / Applied Physics Letters Materials 8: In situ thermal preparation of oxide surfaces
3Investigation of the strontium titanate surface
A TiO2 double layer is found to be present on terminated SrTiO3 surfaces.
2022-03 / Applied Physics Letters 120: Engineering the stoichiometry of a TiO2-rich SrTiO3(001) surface
4Nanostructure self-assembly
Self-assembly of nanocrystalline oxide structures enabled by our THERMALAS substrate heating system.
2023-01 / Advanced Materials 35: Self-Assembly of Nanocrystalline Structures from Freestanding Oxide Membranes
5High-temperature grown buffer layers
The reduced dislocation density in the SrZrO3 buffer layers results in improved electron mobility in the electronically active materials.
2023-05 / Applied Physics Letters 122: Employing high-temperature-grown SrZrO3 buffer to enhance the electron mobility in La:BaSnO3-based heterostructures
6The surface of sapphire (0001)
The surface of sapphire reconstructs at high temperatures into a double-terrace structure with a single orientation of the surface reconstruction.
2024-03 / Advanced Materials 23: Long-Range Atomic Order on Double-Stepped Al2O3(0001) Surfaces
7Perspective oxide epitaxy
A discussion of the implications of ongoing developments and the future of oxide epitaxy, focussing on TLE and CO2 laser substrate heating.
2024-04 / Applied Physics Letters Materials. 12: State of the art, trends, and opportunities for oxide epitaxy
8Interface Design beyond Epitaxy
Membrane-based interface formation enables heterostructures with symmetry-forbidden interfaces. A crucial step in obtaining atomically sharp interfaces is high-temperature annealing using a CO2 laser.
2024-06 / Advanced Materials 24: Interface Design beyond Epitaxy: Oxide Heterostructures Comprising Symmetry-Forbidden Interfaces