New device for operando strain engineering at ID01

Imposing and controlling strain in materials such as semiconductors or ferroelectrics is a promising way to obtain new or enhanced properties. Despite significant advancements in the field of strain engineering over the past two decades, straining semiconductor membranes across large areas remains challenging. Imposing high elastic strain on a material is limited by rupture, typically occurring at its weakest point, and is usually far from the elastic limit sustainable by atomic bonds. Nevertheless, theoretical studies suggest that elastic strain levels feasible on the atomic level (although often unachievable in practice) significantly influence most properties of solid-state materials. Consequently, the search for effective methods to manipulate strain in materials continues. 

In this context, researchers from beamline ID01 partnered with engineers from local company Nelumbo Digital to develop an innovative method and novel device for uniformly imposing extreme strain levels across large surfaces. Dubbed the ‘strainoscope’, this new device is mechanically similar to the principle of a hydraulic press.

Leveraging the unique properties of elastomers – high deformability coupled with strong resistance to volume reduction under compression – the device converts simple vertical compression forces into strong, laterally expansive forces, thereby inducing biaxial strain in a chosen material membrane (Figure 1).

Fig. 1: Straining of rigid membranes by compression of a rubber slab. a) The rigid membrane (grey) is sandwiched between two polydimethylsiloxane (PDMS) slabs of total height h (i). Upon loading with a vertical pressure σ_V, the PDMS slabs expand laterally (ii), leading to a biaxial expansion of the membrane (red) by the biaxial strain ε_L sketched by the lateral expansion of the atomic lattice. Rigid metal plates (black) that compress the sandwich are equipped with acrylic-based X-ray and UV/visible light windows in the centre. b) X-ray diffracted intensity as a function of scattering angle 2θ gives a direct measure of the in-plane expansion of the lattice, indicated by the Bragg diffraction curves shifting to lower angles. c) Operando press mounted at ID01 for diffraction in transmission geometry. 

Importantly, the device’s geometry can be tailored to specific sample requirements, guided by a comprehensive analytical model for predicting the requisite forces. Consequently, researchers can investigate strain in thin films and membranes at levels beyond the limitations of epitaxial growth or other post-growth straining methods.

To validate its efficacy, the strainoscope was employed to strain silicon membranes spanning thicknesses from 0.2 to 4.0 μm and areas ranging from 2.0 × 2.0 to 5.0 × 5.0 mm². Through in-situ X-ray diffraction and Raman spectroscopy experiments conducted at beamline ID01, researchers confirmed the successful tuning of biaxial elastic strain in the membranes, achieving levels of up to 2.1% (Figure 2). 

Fig. 2: X-ray diffracted intensity of biaxially strained membranes as a function of a cubic lattice parameter extracted from the 220-diffraction angle for (a), 200 nm Si and (b), 2 µm-thick Si during the operando straining process. Both samples are supported by 75 µm-thick polyimide layers.

As a dynamic, substrate-free straining method, this new tool presents opportunities in fields where strain engineering typically relies on custom-designed substrates, or where epitaxial growth conditions impose limits on achievable elastic strain. The tunability is complemented by the potential for in-situ X-ray diffraction, while the optical transparency of the siloxane elastomers enables observations via Raman spectroscopy and photoluminescence under strain.

Notably, this method has successfully strained silicon sheets several micrometres thick up to 1%, suggesting potential applications in straining full device stacks while concurrently monitoring their functionality or conducting electrical mobility measurements in response to strain variations. 

Benefitting from ID01’s status as a leading strain imaging beamline, the user community possesses extensive expertise in strain engineering, positioning them as early adopters poised to leverage the new opportunities for strain tuning and investigation. This development is expected to pave the way for new studies in the field of strain-related physics, from semiconductors to perovskite oxide multiferroics. 

Principal publication and authors
Dynamic and controlled stretching of macroscopic crystalline membranes towards unprecedented levels, T.U. Schülli (a), E Dollekamp (a), Z Ismaili (b,f), N. Nawaz (a,f), T. Januel (a,d), T. Billo (a), P. Brumund (a), H. Djazouli (a), S.J. Leake (a), M. Jankowski (a), V. Reita (c), M. Rodriguez (f), L. André (e), A. Aliane (e), Y.M. Le Vaillant (f), Mater. Today Adv. 22, 100489 (2024); https://doi.org/10.1016/j.mtadv.2024.100489
(a) ESRF 
(b) Laboratoire des Technologies de la Microélectronique, Grenoble (France)
(c) Institut NÉEL, Grenoble (France)
(d) Phelma, Grenoble INP – Université Grenoble Alpes, Grenoble (France)
(e) CEA-LETI, Grenoble (France)
(f) Nelumbo Digital SAS, Crolles (France)