Session Z05: Nanoscale and Atomic Materials

Magnetic Field Enhancement from a Single Split Ring Resonator using Optically Detected Magnetic Resonance of the Nitrogen Vacancy Center in Diamond at 4.2 T and 115 GHz

Electron Paramagnetic Resonance (EPR) is an invaluable spectroscopic technique for characterizing materials with applications in biology, chemistry, physics, material science and medicine. EPR uses microwaves (MW) to resonantly excite transitions between different spin states and detects the oscillating magnetic fields generated by the evolution of these states. In principle, EPR at high magnetic fields is very advantageous because of high spectral resolution and high sensitivity. However, the sensitivity is often limited by the technical difficulties in generating strong resonant microwave excitation in the sub-THz and THz bandgap regimes, prohibiting the careful study of many interesting samples like 2-dimensional materials, thin films, or spin-limited biological samples. Cavity resonators are often used in HF-EPR to improve the sensitivity, but as the resonant frequency increases, the size of these resonant cavities becomes prohibitively small for fabrication and sample accommodation. The use of surface resonators for HF-EPR is relatively unexplored.[1]

In this work, we report on the development and characterization of a planar metamaterial, the edge-coupled split-ring resonator (SRR), used to enhance the local magnetic field at 115 GHz on a microscopic scale. Electromagnetic field simulation show that a single resonator structure improves the transverse magnetic field strength by a factor of 11 with -15.11 dB absorptive coupling at 113.2 GHz and an unloaded Q factor of 43. Initial experiments agree with this very well. As a subsequent demonstration, we aim to show this magnetic field enhancement from a single SRR through Optically Detected Magnetic Resonance (ODMR) experiments of the Nitrogen Vacancy (NV) center in diamond at 4.2 T. We expect the MW pi pulse to be between 5-10 ns at 4.2 T based on the simulation results. Combining the MW enhancement of a planar resonator with the advantages ODMR of the NV-center at high magnetic fields[2] may offer further improvements in sensitivity and resolution and help realize highly interesting studies of 2-dimensional materials and spin-limited samples on the micro- and nano-scale.   

Atomic Scale Synthesis using Scanning Transmission Electron Microscopy

Point defects and regular arrays of point defects in otherwise pristine materials can imbue a material with new and useful functional properties. Nanopores, single-atom catalysts, and color and spin centers for quantum applications are examples. In particular, quantum defects are central in several nascent technologies for quantum optics and sensing. However, their full potential cannot be realized until these defects can be created and placed exactly where and how they are needed. Current lithographic techniques are orders of magnitude too imprecise. The scanning transmission electron microscope (STEM), a workhorse instrument in materials characterization, can not only be used to observe dynamic processes with atomic resolution, but also drive and control synthesis with atomic precision. Through custom control of the electron beam position that actively feeds back on image, spectroscopy, and other data streams, it’s possible to use focused beam energy to precisely initiate and interrupt desired transformations. This can be used for generating point defects, drilling and milling materials, changing phase, modifying bond coordination, and positioning dopants. Presented here are recent results highlighting advancements towards such a “synthescope”[1], insights into beam drilling processes [4,5], demonstration of patterning of arrays of dopants [3], and methods to deliver dopant atoms to the sample, in situ [2]. Developing this combination of experimental methods provides a window into dynamic synthesis processes at fundamental length scales and a path towards fabricating materials and devices with atomically precise components for quantum information science applications.  

Closed-Loop Spectroscopy and Nanofabrication Around Individual Quantum Emitters

Diamond color centers, with a particular focus on nitrogen vacancy (NV) and tin-vacancy (SnV), have assumed pivotal roles in the realm of quantum information technology. These color centers function as interfaces for photons to interact with electron and nuclear spin ground states, propelling explorations into diverse quantum applications, including quantum networks, quantum computing, and quantum sensing. Yet, a substantial hurdle within this domain pertains to the fabrication of photonic nanostructures like waveguides and photonic crystal nanocavities, which are essential for the efficient control and interaction of photons with color center spins. To tackle these challenges, we introduce a novel approach that combines in-situ maskless etching with high-resolution hyperspectral cathodoluminescence (CL) measurements conducted concurrently. Specifically, we harness electron beam-induced surface chemistry to etch through diamond precisely at the color center's location, all the while capturing emission properties. Our work has successfully achieved remarkable fabrication precision, achieving resolutions as fine as 20 nm creating predefined patterns, and enabling the production of perforations in suspended waveguides. Furthermore, we continuously monitor color center intensity throughout the etching process in terms of both time and depth using cathodoluminescence and free-space laser techniques. Our findings underscore the spatial precision needed to pattern diamond structures, shaping cavities or exposing quantum emitters, while simultaneously tracking optical properties like peak position and brightness enhancement.   

Investigating Circular Dichroism in Distorted Double Gyroids

Circular dichroism (CD, the differential absorption of left and right circularly polarized light) offers significant applications in anti-counterfeit as well as molecular and protein sensing. 3D network materials, and specifically double gyroids, are of particular interest for circular dichroism as they can possess a number chiral elements (surface structure, bulk helices) that can be tuned for a particular CD response. These structures can also be readily generated via self-assembly. While many optical simulations of gyroids assume a perfect cubic structure, experimentally created gyroids often include distortions, especially Z-compression due to processing. In this work, the CD of distorted double gyroids is explored systematically with finite difference time domain (FDTD) simulations. When varied from 0-45%, the volume conserved, uniform Z-compression of (110) oriented silver double gyroids with a 0.52 volume fraction yields both enhanced CD (g-factors of 0.15) as well as the emergence and disappearance of CD peaks. Many of these optical behaviors are found only at certain surface terminations of the double gyroid unit cell. In this talk, both the surface structure and bulk features leading to these spectral features will be discussed. Overall, this talk will elucidate the impact of uniform distortions on the CD of double gyroids offering improved understanding and possible recommendations for structural design.   

Selective Area Grown DNA origami Superlattice Assembly for Scalable Device Synthesis

DNA nanotechnology enables precise nanoscale material assembly, including creating superlattices with 3D organization of materials. However, creating devices based on these materials is challenging due to the difficulty in growing and placing DNA superlattices on surfaces. We demonstrate a scalable technique using nanofabrication and inorganic templating for controlled superlattice growth and conversion into inorganic 3D structures that could bridge the gap between DNA self-assembly and nanoelectronics. This technique allows precise placement, orientation and material composition. We prove its functionality by templating nanolattices on silicon substrate and converting it to a 3D tin-oxide networks. Electrical characterization demonstrates a Poole-Frenkel conductivity behavior that is typical for disordered semiconductors.   

Energy and time-resolved NIR to Visible Upconversion Luminescence from Single NaYF4:Yb3+,Tm3+Nanoparticles on Nanowire Substrates

Tm-doped energy transfer upconversion (ETU) NaYF4:Yb3+:Tm3+ nanoparticles have potential applications in deep tissue imaging and energy conversion devices due to their visible (450nm) and infra-red (800nm) upconversion emission, but suffer from low quantum efficiency. We use energy and time-resolved single particle imaging to assess the plasmonic enhancement of NIR-to-visible upconversion luminescence (UCL) from single β-NaYF4:Yb3+:Tm3+ upconverting nanoparticles (UCNPs) supported on substrates consisting of sparse arrangements of Ag nanowires. By examining the effects at the single particle level, for UCNPs strongly-coupled to nanowires, isolated UCNPs, and intermediate cases, we obtain a statistical description of UCL emission enhancement in the Tm-doped UCNPs and map out the statistical distribution of excitation and luminescence enhancement on the plasmonic substrates. We use both wide field and confocal spectroscopic imaging of single UCNPs on and off the plasmonic substrates in combination with energy and time resolved spectroscopy and compare these results to a coupled rate equation analysis to elucidate the energy transfer upconversion enhancement mechanisms.   

Simultaneous Characterization of In-plane and Cross-plane Resistivities in Highly Anisotropic (PbSe)1(VSe2)1 Heterostructures

We present a method to measure and model contact and lead resistances through a series of in-plane measurements with different contact area and at various temperatures. The contact and lead resistances are obtained by fitting the width dependence of the contact end voltages of top and bottom electrodes of different linewidths to a model based on current crowding, which are then used to eliminate the contribution of contacts in cross-plane measurements without needing multiple devices and/or etching steps. The effective contact area of the cross-plane measurements is also corrected for lateral current spreading to obtain the cross-plane resistivity from the cross-plane resistance. This approach was used to measure both in-plane and cross-plane resistivities of a (PbSe)₁(VSe₂)₁ heterostructure containing alternating layers of PbSe and VSe₂ with random in-plane rotational disorder. Several samples measured exhibited a 4 order of magnitude difference between cross-plane and in-plane resistivities over the 6 – 300 K temperature range. The similar temperature dependencies of the resistivities reflect a large difference in the density of states, mobilities, and/or tunneling between metallic VSe₂ layers. The device fabrication process is fully lift-off compatible, and the method developed enables the straightforward measurement of the resistivity anisotropy of most thin film materials with nm thicknesses.   

Gate-tunable magnetism in monolayer graphene on a nanoscale-patterned ferroelectric substrate

Ferroelectric thin films have many desirable characteristics that are important for information science and nanoelectronics. The recent discovery of ferroelectricity in boron-doped AlN thin films is especially interesting because of the large polarization achievable, of order 10¹⁵ cm^-2. Here we use ultra-low voltage electron beam (ULV-EBL)¹ to program nanoscale ferroelectric domains in Al_1-xB_xN thin films. We demonstrate ferroelectric field effects on a graphene/AlBN device using the programmed ferroelectric polarization. Under a patterned square mesh lattice of period ~33 nm, the graphene shows an emergent gate-tunable magnetism and a giant magnetoresistance tuning over 100%. The suggested explanation may relate to the flat band ferromagnetism and the Stoner criteria. This can be a new platform for solid-state-based 2D quantum simulators.

¹Appl. Phys. Lett. 117, 253103 (2020)