Yachin Ivry

Nanometer resolution piezoresponse force microscopy to study deep submicron ferroelectric and ferroelastic domains

Understanding ferroelectricity at the deep submicron regime is desirable in utilizing it for next generation nonvolatile memory devices, medical imaging systems, and rf filters. Here we show how piezoresponse force microscopy can be enhanced (1 nm resolution). Using this method, we have investigated ferroelectric and ferroelastic domains at the deep submicron regime in polycrystalline lead zirconium titanate thin films. We demonstrate that in the clamped films, periodic pairs of 90° domains are stable even at 10 nm width, challenging recent predictions of minimum domain size, and suggesting ferroelectricity for high-density storage devices (≥10 Tbyte/in2).

Bundles of polytwins as meta-elastic domains in the thin polycrystalline simple multi-ferroic system PZT

We used enhanced piezo-response force microscopy (E-PFM) to investigate both ferroelastic and ferroelectric nanodomains in thin films of the simple multi-ferroic system PbZr(0.3)Ti(0.7)O(3) (PZT). We show how the grains are organized into a new type of elastic domain bundles of the well-known periodic elastic twins. Here we present these bundle domains and discuss their stability and origin. Moreover, we show that they can arrange in such a way as to release strain in a more effective way than simple twinning. Finally, we show that these bundle domains can arrange to form the macroscopic ferroelectric domains that constitute the basis of ferroelectric-based memory devices.

Unexpected Controllable Pair-Structure in Ferroelectric Nanodomains

The imminent inability of silicon-based memory devices to satisfy Moores Law is approaching rapidly. Controllable nanodomains of ferroic systems are anticipated to enable future high-density nonvolatile memory and novel electronic devices. We find via piezoresponse force microscopy (PFM) studies on lead zirconate titanate (PZT) films an unexpected nanostructuring of ferroelectric-ferroelastic domains. These consist of c-nanodomains within a-nanodomains in proximity to a-nanodomains within c-domains. These structures are created and annihilated as pairs, controllably. We treat these as a new kind of vertex-antivertex pair and consider them in terms of the Srolovitz-Scott 4-state Potts model, which results in pairwise domain vertex instabilities that resemble the vortex-antivortex mechanism in ferromagnetism, as well as dislocation pairs (or disclination pairs) that are well-known in nematic liquid crystals. Finally, we show that these nanopairs can be scaled up to form arrays that are engineered at will, paving the way toward facilitating them to real technologies.

Eight-fold signal amplification of a superconducting nanowire single-photon detector using a multiple-avalanche architecture

Superconducting nanowire avalanche single-photon detectors (SNAPs) with n parallel nanowires are advantageous over single-nanowire detectors because their output signal amplitude scales linearly with n. However, the SNAP architecture has not been viably demonstrated for n > 4. To increase n for larger signal amplification, we designed a multi-stage, successive-avalanche architecture which used nanowires, connected via choke inductors in a binary-tree layout. We demonstrated an avalanche detector with n = 8 parallel nanowires and achieved eight-fold signal amplification, with a timing jitter of 54 ps.

High-frequency programmable acoustic wave device realized through ferroelectric domain engineering

Surface acoustic wave devices are extensively used in contemporary wireless communication devices. We used atomic force microscopy to form periodic macroscopic ferroelectric domains in sol-gel deposited lead zirconate titanate, where each ferroelectric domain is composed of many crystallites, each of which contains many microscopic ferroelastic domains. We examined the electro-acoustic characteristics of the apparatus and found a resonator behavior similar to that of an equivalent surface or bulk acoustic wave device. We show that the operational frequency of the device can be tailored by altering the periodicity of the engineered domains and demonstrate high-frequency filter behavior (>8 GHz), allowing low-cost programmable high-frequency resonators.

Superconductor–superconductor bilayers for enhancing single-photon detection

Here, we optimized ultrathin films of granular NbN on SiO2 and of amorphous αW5Si3. We showed that hybrid superconducting nanowire single-photon detectors (SNSPDs) made of 2 nm thick αW5Si3 films over 2 nm thick NbN films exhibit advantageous coexistence of timing (<5 ns reset time and 52 ps timing jitter) and efficiency (>96% quantum efficiency) performance. We discuss the governing mechanism of this hybridization via the proximity effect. Our results demonstrate saturated SNSPDs performance at 1550 nm optical wavelength and suggest that such hybridization can significantly expand the range of available superconducting properties, impacting other nano-superconducting technologies. Lastly, this hybridization may be used to tune properties, such as the amorphous character of superconducting films.

Imaging of Quantum Materials

1. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138. 2. Quantum Nanostructures and Nanofabrication, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139. 3. Institut für Materialwissenschaften, Lehrstuhl 3, Universität Stuttgart, Stuttgart, Germany 4. Max Planck Institute for Condensed Matter Science, Stuttgart, Germany 5. Department of Physics, Harvard University, Cambridge, MA 02138 6. College of Engineering Architecture and Computer Science, Howard University, Washington, D.C. 20059.

On-fiber assembly of membrane-integrated superconducting-nanowire single-photon detectors

We directly assemble membrane-integrated superconducting-nanowire single- photon detectors (SNSPDs) on optical fiber-ferrule facets, yielding extremely compact, fiber-coupled SNSPD systems. Our initial demonstration shows 1% system detection efficien- cy, which can be further improved significantly.