ADVERTISEMENT

Visualizing Layer-By-Layer Growth Of LaTiO3 On SrTiO3

The atomic stacking sequence of materials known as the complex oxides can be critical to material properties. For instance, the oxide YBa2Cu3O7 is superconducting only when the stacking sequence is precisely Y-CuO2-BaO- CuO-BaO-CuO2. One can test this by growing an oxide film with the same composition but a different layer sequence using a technique called molecular beam epitaxy (MBE): this deposition technique is unique in that it allows the chemical control of each and every deposited layer (similar to spray painting but on the atomic level).

In more recent years, such growth techniques have been key to the discovery of exotic properties present at oxide interfaces. For instance, while SrTiO3 is an insulator and LaTiO3 is an insulator, it was found that the interface between them is metallic.1

ADVERTISEMENT

For the growth of high-quality films, one must start with a high-quality substrate, and TiO2-terminated SrTiO3 is the standard crystalline substrate used for deposition of oxide thin films.

As was recently discussed here, SrTiO3 is one of the few oxide crystals that can be fabricated in large sizes with such high quality. And the ability to produce surfaces with only the TiO2 composition (rather than SrO) means that one can control the sequence of layers grown atop it.

Figure courtesy Dillon D. Fong

In work performed by researchers at Argonne National Laboratory, synchrotron x-rays were used to visualize how layer-by-layer growth of LaTiO3 takes place on SrTiO3 by MBE. With the aid of “x-ray vision,” they were able to see that MBE deposition is not quite so simple as “atomic spray painting” scenario described above. First, the top of the SrTiO3 crystal exhibits two layers of TiO2 rather than one. Furthermore, the same film structure is obtained regardless if it was grown in the sequence LaO-TiO2 or TiO2-LaO. In the first case, the LaO layer exchanges places with the TiO2 layer immediately beneath it; in the second case, the LaO layer digs through two TiO2 layers to find its favored position.

This means that even when using MBE to achieve the desired stacking sequence, one must necessarily account for atomic redistribution: no matter how sophisticated our synthesis technique, the material has its own idea of how to stack the atomic layers. In addition, this study shows the importance of using in situ synchrotron techniques for the investigation of materials. The Advanced Photon Source at Argonne National Laboratory, where this work was carried out, is one of only four third-generation hard X-ray sources in the world and will soon undergo a major upgrade, making it the world’s brightest hard X-ray source. In situ experiments such as this will benefit tremendously from the upgrade, allowing improved time resolution and studies on a wider range of materials.

ADVERTISEMENT

These findings are described in the article entitled How heteroepitaxy occurs on strontium titanate, recently published in the journal Science Advances.

Reference:

  1. A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang, Nature 419, 378 (2002).

Comments

READ THIS NEXT

Stem Cells Need Centrosome To Retain Their Stem Cell Properties

Centrosome is an organelle responsible for the organization of microtubule arrays, typically implicated in the organization of cell division, cell […]

When Non-Conventional Research Organisms Drive Change For Standard Laboratory Techniques

In situ hybridization is a common laboratory technique, widely employed to visualize gene expression or chromosomal location of DNA sequences. […]

“Rogue” Sunspots Spoil Chances For Long-Term Space Weather Forecasting

The number of solar spots and eruptive phenomena connected to them show cyclical variations with a mean period of 11 […]

What Is Molarity? With Examples

Molarity is how chemists measure the concentration of a solution, allowing them to relate concentrations to one another when calculating […]

Ambient Air Temperature And Cognitive Performance

The earliest writings in history report the damaging and extreme impact of the thermal environment on human performance. The Bible […]

New Approaches To Old Problems: Integrating Disciplines To Understand Lodging In Oats

Oats have been grown in Ireland since the Bronze age and once occupied a land area of over 1.5 million […]

Bizarre Fossil Wasps Found In Amber From Myanmar From Ca. 99 Mio. Years Ago Point Toward Later Plate Collision Of Asia And The West Burma Plates Than Previously Assumed

Fossil amber from present-day Myanmar – commonly called Burmese amber – continuingly yields amazing new discoveries. Among these are three […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?