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The self-organization of strongly interacting electrons into superlattice structures underlies the properties of many quantum materials. How these electrons arrange within the superlattice dictates what symmetries are broken and what ground states are stabilized. Here we show that cryogenic scanning transmission electron microscopy (cryo-STEM) enables direct mapping of local symmetries and order at the intra-unit-cell level in the model charge-ordered system Nd1/2Sr1/2MnO3. In addition to imaging the prototypical site-centered charge order, we discover the nanoscale coexistence of an exotic intermediate state which mixes site and bond order and breaks inversion symmetry. We further show that nonlinear coupling of distinct lattice modes controls the selection between competing ground states. The results demonstrate the importance of lattice coupling for understanding and manipulating the character of electronic self-organization and that cryo-STEM can reveal local order in strongly correlated systems at the atomic scale., In this paper, the authors demonstrate that cryogenic scanning transmission electron microscopy allows for the direct mapping of the local arrangements and symmetries of electronic order, providing a useful method for studying strongly correlated systems. They show this using the example of Nd1/2Sr1/2MnO3, a model charge ordered material.

The self-organization of strongly interacting electrons into superlattice structures underlies the properties of many quantum materials. How these electrons arrange within the superlattice dictates what symmetries are broken and what ground states are stabilized. Here we show that cryogenic scanning transmission electron microscopy enables direct mapping of local symmetries and order at the intra-unit-cell level in the model charge-ordered system Nd1/2Sr1/2MnO3. In addition to imaging the prototypical site-centered charge order, we discover the nanoscale coexistence of an exotic intermediate state which mixes site and bond order and breaks inversion symmetry. We further show that nonlinear coupling of distinct lattice modes controls the selection between competing ground states. The results demonstrate the importance of lattice coupling for understanding and manipulating the character of electronic self-organization and highlight a novel method for probing local order in a broad range of strongly correlated systems.

Combining multiple fast image acquisitions to mitigate scan noise and drift artifacts has proven essential for picometer precision, quantitative analysis of atomic resolution scanning transmission electron microscopy (STEM) data. For very low signal-to-noise ratio (SNR) image stacks – frequently required for undistorted imaging at liquid nitrogen temperatures – image registration is particularly delicate, and standard approaches may either fail, or produce subtly specious reconstructed lattice images. We present an approach which effectively registers and averages image stacks which are challenging due to their low-SNR and propensity for unit cell misalignments. Registering all possible image pairs in a multi-image stack leads to significant information surplus. In combination with a simple physical picture of stage drift, this enables identification of incorrect image registrations, and determination of the optimal image shifts from the complete set of relative shifts. We demonstrate the effectiveness of our approach on experimental, cryogenic STEM datasets, highlighting subtle artifacts endemic to low-SNR lattice images and how they can be avoided. High-SNR average images with information transfer out to 0.72 A are achieved at 300 kV and with the sample cooled to near liquid nitrogen temperature.

Incorporating oxides with radically different physical and chemical properties into heterostructures offers tantalizing possibilities to derive new functions and structures. Recently, we have fabricated freestanding 2D oxide membranes using the water-soluble perovskite Sr3Al2O6 as a sacrificial buffer layer. Here, with atomic-resolution spectroscopic imaging, we observe that direct growth of oxide thin films on Sr3Al2O6 can cause complete phase transformation of the buffer layer, rendering it water-insoluble. More importantly, we demonstrate that an ultrathin SrTiO3 layer can be employed as an effective barrier to preserve Sr3Al2O6 during subsequent growth, thus allowing its integration in a wider range of oxide heterostructures.

The structural perfection and defect microstructure of epitaxial (001) $\mathrm{SrTi}{\mathrm{O}}_{3}$ films grown on (001) Si was assessed by a combination of x-ray diffraction and scanning transmission electron microscopy. Conditions were identified that yield 002 $\mathrm{SrTi}{\mathrm{O}}_{3}$ rocking curves with full width at half-maximum below 0.03\ifmmode^\circ\else\textdegree\fi{} for films ranging from 2 to 300 nm thick, but this is because this particular peak is insensitive to the $\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--2}$ density of threading dislocations with pure edge character and extended defects containing dislocations and out-of-phase boundaries. Our results show that one narrow rocking curve peak is insufficient to characterize the structural perfection of epitaxial films.

The use of a sacrificial layer of water-soluble Sr3Al2O6 allows the release of freestanding 2D heterostructures and superlattices of epitaxially grown perovskite oxides while preserving their structural and physical properties. The ability to create and manipulate materials in two-dimensional (2D) form has repeatedly had transformative impact on science and technology. In parallel with the exfoliation and stacking of intrinsically layered crystals1,2,3,4,5, atomic-scale thin film growth of complex materials has enabled the creation of artificial 2D heterostructures with novel functionality6,7,8,9 and emergent phenomena, as seen in perovskite heterostructures10,11,12. However, separation of these layers from the growth substrate has proved challenging, limiting the manipulation capabilities of these heterostructures with respect to exfoliated materials. Here we present a general method to create freestanding perovskite membranes. The key is the epitaxial growth of water-soluble Sr3Al2O6 on perovskite substrates, followed by in situ growth of films and heterostructures. Millimetre-size single-crystalline membranes are produced by etching the Sr3Al2O6 layer in water, providing the opportunity to transfer them to arbitrary substrates and integrate them with heterostructures of semiconductors and layered compounds13,14.

Emergent properties in transition metal oxide superlattices are traditionally tuned as functions of stoichiometry, reduced dimensionality, and epitaxial strain. Here the authors introduce a new tuning parameter, the connectivity of the $M$O${}_{6}$ octahedra ($M=$ transition metal), as a means to manipulate the electronic structure, symmetry, and competing ground states of oxide superlattices. They demonstrate this by the epitaxial growth of alternating layers of the high spin-orbit metal IrO${}_{2}$ and the band insulator TiO${}_{2}$, both of which have the rutile structure.

A reliable method to apply biaxial strain over a wide range of values with minimal dislocation generation is critical for the study of strain dependent physical properties in oxide thin films and heterostructures. In this work, we systematically controlled the strain state in a perovskite manganite thin film by as much as 1% using a new ultrathin strain‐releasing buffer layer Sr3Al2O6, and observed signatures of accompanying magnetic and metal–insulator transitions. The near‐zero strain state is achieved within five nanometers of buffer layer thickness, substantially thinner than any oxide epitaxial buffer layers that can continuously tune the film strain states. Furthermore, the majority of misfit dislocations were confined to the Sr3Al2O6 layer, structurally decoupling defects in the film from the substrate.

Interfaces between complex oxides constitute a unique playground for two-dimensional electron systems (2DESs), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO

Interfaces between complex oxides constitute a unique playground for two-dimensional electron systems (2DESs), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO3/SrTiO3 interface is one of the most studied in this regard, and its origin is determined by the polar field in LaAlO3 as well as by the presence of point defects, like oxygen vacancies and intermixed cations. These defects usually reside in the conduction channel and are responsible for a decrease of the electronic mobility. In this work, we use an amorphous WO3 overlayer to obtain a high-mobility 2DES in WO3/LaAlO3/SrTiO3 heterostructures. The studied system shows a sharp insulator-to-metal transition as a function of both LaAlO3 and WO3 layer thickness. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 900% at 10 T and 1.5 K, the presence of multiple conduction channels with carrier mobility up to 80 000 cm2 V-1 s-1, and quantum oscillations of conductance.

We report the growth of thin films of the mixed valence compound YbAl$_{3}$ on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer, epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray diffraction, in situ low-energy electron diffraction and aberration-corrected scanning transmission electron microscopy we establish that the films are ordered in the bulk as well as at the surface. Our films show a coherence temperature of 37 K, comparable to that reported for bulk single crystals. Photoelectron spectroscopy reveals contributions from both $\textit{f}^{13}$ and $\textit{f}^{12}$ final states establishing that YbAl$_{3}$ is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level., Comment: 4 pages, 6 figures

Direct electrical detection of the binding of antibody and antigen of avian influenza virus was demonstrated through a biosensor derived from a double-gate FinFET. A simple detection method was employed in which the charge effect coming from the biomolecules was observed through the threshold voltage $V_{T}$ shift. Due to the presence of a local backgate, the proposed device is individually addressable and the operating voltage is markedly low compared with similar nanowire-type biosensors. Furthermore, its unique structure allows for the channel to be immune to the noise from the biomolecules, which can be problematic for nanogap field-effect-transistor biosensors. The proposed device is complementary metal–oxide–semiconductor compatible and highly reproducible, and monolithic integration with the readout circuits is achievable. Hence, this approach provides a step toward the large-scale development of sensor chips for their potential use in medicine and biotechnology.

We report the growth of superconducting Sr2RuO4 thin films by molecular-beam epitaxy on (110) NdGaO3 substrates with transition temperatures of up to 1.8 K. We calculate and experimentally validate a thermodynamic growth window for the adsorption-controlled growth of superconducting Sr2RuO4 epitaxial thin films. The growth window for achieving superconducting Sr2RuO4 thin films is narrow in growth temperature, oxidant pressure, and ruthenium-to-strontium flux ratio.

Epitaxial SrRuO3 and CaRuO3 films were grown under an excess flux of elemental ruthenium in an adsorption-controlled regime by molecular-beam epitaxy (MBE), where the excess volatile RuOx (x = 2 or 3) desorbs from the growth front leaving behind a single-phase film. By growing in this regime, we were able to achieve SrRuO3 and CaRuO3 films with residual resistivity ratios (ρ300 K/ρ4 K) of 76 and 75, respectively. A combined phase stability diagram based on the thermodynamics of MBE (TOMBE) growth, termed a TOMBE diagram, is employed to provide improved guidance for the growth of complex materials by MBE.

Recent advances in the synthesis of oxide thin films have led to the discovery of novel functionalities that are not accessible in bulk structures. However, their physical properties are vulnerable to the presence of crystal defects, which can give rise to structural, chemical, and electronic modifications. These issues are central to optimizing the opportunities to create freestanding oxide films using the recently developed buffer layer Sr3Al2O6, which is soluble in room temperature water. To evaluate the general possibility to create atomic scale freestanding oxide heterostructures, it is critical to understand the formation, structure, and role of defects as this buffer layer is employed. Here, using aberration-corrected scanning transmission electron microscopy in combination with electron energy loss spectroscopy, we reveal cation segregation and diffusion along crystal defects that form during growth of an oxide multilayer structure on the Sr3Al2O6 buffer layer. We demonstrate that mass transport of film material can occur either through open dislocation core channels or site-specifically in the crystal lattice, causing local variations in stoichiometry. However, by reducing the thermal driving force for diffusion during growth, we suppress the role of extended defects as cation segregation sites, thereby retaining the inherent properties of the overlaying film.

Complex oxide heterostructures display some of the most chemically abrupt, atomically precise interfaces, which is advantageous when constructing new interface phases with emergent properties by juxtaposing incompatible ground states. One might assume that atomically precise interfaces result from stoichiometric growth, but here we show that the most precise control is obtained for non-stoichiometric growth where differing surface energies can be compensated by surfactant-like effects. For the precise growth of Sr$_{n+1}$Ti$_n$O$_{3n+1}$ Ruddlesden-Popper (RP) phases, stoichiometric deposition leads to the loss of the first RP rock-salt double layer, but growing with a strontium-rich surface layer restores the bulk stoichiometry and ordering of the subsurface RP structure. Our results dramatically expand the materials that can be prepared in epitaxial heterostructures with precise interface control---from just the $n=\infty$ end members (perovskites) to the entire RP family---enabling the exploration of novel quantum phenomena at a richer variety of oxide interfaces., 9 pages, 5 figures

A nanoforest structure for surface-enhanced Raman scattering (SERS) active substrates is fabricated and analyzed. The detailed morphology of the resulting structure can be easily controlled by modifying the process parameters such as initial gold layer thickness and etching time. The applicability of the nanoforest substrate as a label-free SERS immunosensor is demonstrated using influenza A virus subtype H1N1. Selective binding of the H1N1 surface antigen and the anti-H1 antibody is directly detected by the SERS signal differences. Simple fabrication and high throughput with strong in-plane hot-spots imply that the nanoforest structure can be a practical sensing component of a chip-based SERS sensing system.

We present a sugar-templated polydimethylsiloxane (PDMS) sponge for the selective absorption of oil from water. The process for fabricating the PDMS sponge does not require any intricate synthesis processes or equipment and it is not environmentally hazardous, thus promoting potential in environmental applications. The proposed PDMS sponge can be elastically deformed into any shape, and it can be compressed repeatedly in air or liquids without collapsing. Therefore, absorbed oils and organic solvents can be readily removed and reused by simply squeezing the PDMS sponge, enabling excellent recyclability. Furthermore, through appropriately combining various sugar particles, the absorption capacity of the PDMS sponge is favorably optimized.

A novel method for reducing the pull-in voltage and achieving a steep sub-threshold slope has been studied on a FinFET-based NEMS switch. By decreasing the gap between the gate electrode and the fin (beam) with a process compatible with the CMOS fabrication, the proposed device showed a pull-in voltage of 2 V and a sub-threshold slope of 5 mV/dec, which can be further improved. Along with this method, it is a viable candidate for future low-power electronic devices.

A pH sensor composed of a double-gate silicon nanowire field-effect transistor (DG Si-NW FET) is demonstrated. The proposed DG Si-NW FET allows the independent addressing of the gate voltage and hence improves the sensing capability through an application of asymmetric gate voltage between the two gates. One gate is a driving gate which controls the current flow, and the other is a supporting gate which amplifies the shift of the threshold voltage, which is a sensing metric, and which arises from changes in the pH. The pH signal is also amplified through modulation of the gate oxide thickness.

An analytical technique is proposed that uses an asymmetric double-gate field-effect transistor (FET) structure to characterize the electrical properties of biomolecules, including their permittivity and charge density. Using a simple measurement with the proposed FET structure, we are able to extract the physical properties (i.e., permittivity and charge density) of biomolecules. A reliable analytical tool for the characterization of biomolecules can be provided by the proposed FET structure without a complex measurement system. It is expected that the proposed method will be expanded into a universal analysis technique for the electrical evaluation of biomolecules in applications beyond biosensing.

In this work, nanowire field-effect transistors (NW-FETs) constructed from a top-down approach has been utilized for the detection of biomolecules. Here, we demonstrate that the sensitivity of NW-FET sensors can be greatly enhanced when the same dopant type is used for both channel region and source and drain. This type of FET, known as accumulation mode field-effect transistors (AM-FETs), functions under different operating principle compared with conventional inversion mode FETs. The improved sensitivity is attributed to the different conduction mechanism and current components of AM devices. The results have been verified through a direct comparison with a conventional FET.

Through the structural modification of a three-dimensional silicon nanowire field-effect transistor, i.e., a double-gate FinFET, a structural platform was developed which allowed for us to utilize graphene oxide (GO) as a charge trapping layer in a nonvolatile memory device. By creating a nanogap between the gate and the channel, GO was embedded after the complete device fabrication. By applying a proper gate voltage, charge trapping, and de-trapping within the GO was enabled and resulted in large threshold voltage shifts. The employment of GO with FinFET in our work suggests that graphitic materials can potentially play a significant role for future nanoelectronic applications.