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Moldovan, Nicolaie

Publications and source records attributed to Moldovan, Nicolaie.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Freestanding high-aspect-ratio gold masks for low-energy, phase-based x-ray microscopy

High-resolution, x-ray phase contrast microscopy, a key technique with promising potential in biomedical imaging and diagnostics, is based on narrow-slit high-aspect-ratio gold gratings. Here we present the development, fabrication details, and experimental testing of the freestanding 10 μm thick gold membrane masks with an array of 0.9–1.5 μm void slit apertures for a novel low-energy x-ray microscope. The overall mask size is 4 mm × 4 mm, with a grating pitch of 7.5 μm, 6.0–6.6 μm wide gold bars are supported by 3 μm wide crosslinks at 400 μm intervals. The fabrication process is based on gold electroplating into a silicon mold coated with various thin films to form a voltage barrier, plating base, and sacrificial layer, followed by the mold removal to obtain the freestanding gold membrane with void slit apertures. We discuss key aspects for the materials and processes, including gold structures homogeneity, residual stresses, and prevention of collapsing of the grid elements. We further demonstrate the possibility to obtain high-resolution, high contrast 2D images of biological samples using an incoherent, rotating anode x-ray tube.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Low-Z FIB Grids for Reducing Spurious Fluorescence and X-ray Overlaps

Low-Z nanocrystalline diamond (NCD) grids have been developed to reduce spurious fluorescence and avoid X-ray peak overlaps or interferences between the specimen and conventional metal grids. Here, the low-Z NCD grids are non-toxic and safe to handle, conductive, can be subjected to high-temperature heating experiments, and may be used for analytical work in lieu of metal grids. Both a half-grid geometry, which can be used for any lift-out method, or a full-grid geometry that can be used for ex situ lift-out or thin film analyses, can be fabricated and used for experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Brain-implantable multifunctional probe for simultaneous detection of glutamate and GABA neurotransmitters

We report Glutamate (GLU) and gamma-aminobutyric acid (GABA) are neurotransmitters (NTs) with an essential role in signal transmission in the brain. Brain disorders, such as epilepsy, Alzheimer's and Parkinson's diseases, and traumatic brain injury can be linked to imbalances in the GLU-GABA homeostasis that occurs in sub-second to seconds time frames. Current measurement techniques can detect these two NT concentrations simultaneously only in vitro. The present work reports on the fabrication of a silicon multifunctional biosensor microarray probe for sub-second simultaneous GLU-GABA detection in real-time, with excellent analyte sensitivity and selectivity and in vivo capabilities. The novel Si probes feature four surface-functionalized platinum ultramicroelectrodes (UMEs) for simultaneous amperometric detection of GLU and GABA with a sentinel, and a built-in microfluidic channel for the introduction of neurochemicals in the proximity of the UMEs. The microchannel also allows functioning of an On-Demand In-situ Calibrator that runs in-situ biosensor calibration. The probe exhibited excellent robustness at insertion in agarose-gel brain-tissue-mimicking test, and remarkably high hydrogen peroxide sensitivity (a by-product of GLU-GABA enzyme biosensor) with values on the order of 5000 nA μM -1 cm -2 and maximum sensitivities of 204 ± 15 nA μM -1 cm -2 and 37 ± 7 nA μM -1 cm -2 for GLU and GABA, respectively. Furthermore, the limit of detection of the biosensors reached as low as 7 nM, 165 nM and 750 nM for H 2 O 2 , GLU and GABA, respectively and a temporal resolution of hundreds of milliseconds during in vivo studies using freely moving rats.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Approaching the Strain-Free Limit in Ultrathin Nanomechanical Resonators

Ultrathin mechanical structures are ideal building platforms to pursue the ultimate limit of nanomechanical resonators for applications in sensing, signal processing, and quantum physics. Unfortunately, as the thickness of the vibrating structures is reduced, the built-in strain of the structural materials plays an increased role in determining the mechanical performance of the devices. As a consequence, it is very challenging to fabricate resonators working in the modulus-dominant regime, where their dynamic behavior is exclusively determined by the device geometry. In this Letter, we report ultrathin doubly clamped nanomechanical resonators with aspect ratios as large as L/t similar to 5000 and working in the modulus-dominant regime. Here, we observed room temperature thermomechanically induced motion of multiple vibration modes with resonant frequencies closely matching the predicted values of Euler-Bernoulli beam theory under an axial strain of 6.3 x 10 -8 . The low strain of the devices enables a record frequency tuning ratio of more than 50 times. These results illustrate a new strategy for the quantitative design of nanomechanical resonators with unprecedented performance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Nonlinear Mode Coupling and One-to-One Internal Resonances in a Monolayer WS 2 Nanoresonator

Nanomechanical resonators make exquisite force sensors due to their small footprint, low dissipation, and high frequencies. Because the lowest resolvable force is limited by ambient thermal noise, resonators are either operated at cryogenic temperatures or coupled to a high-finesse optical or microwave cavity to reach sub aN Hz -1/2 . sensitivity. Here, we show that operating a monolayer WS 2 nanoresonator in the strongly nonlinear regime can lead to comparable force sensitivities at room temperature. Cavity interferometry was used to transduce the nonlinear response of the nanoresonator, which was characterized by multiple pairs of 1:1 internal resonance. Some of the modes exhibited exotic line shapes due to the appearance of Hopf bifurcations, where the bifurcation frequency varied linearly with the driving force and forms the basis of the advanced sensing modality. The modality is less sensitive to the measurement bandwidth, limited only by the intrinsic frequency fluctuations, and therefore, advantageous in the detection of weak incoherent forces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Scientific/Technical Report – Phase IIA Final

This project developed advanced focusing devices for high-photon-energy X-rays, up to 25 keV, and up to 20 nm resolution, which can be used to analyze complex composite materials, biological structures, and nano-electronic circuits. The advancement is made possible through the use of ultrananocrystalline diamond as a structural material and Platinum or Iridium deposited by atomic layer deposition as an X-ray absorber in a highly innovative device design for Fresnel zone plates and suited nanofabrication approach based on electron beam lithography.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Atomic layer deposition frequency-multiplied Fresnel zone plates for hard x-rays focusing

The design and fabrication of Fresnel zone plates for hard x-ray focusing up to 25 keV photon energies with better than 50 nm imaging half-pitch resolution is reported as performed by forming an ultrananocrystalline diamond (UNCD) scaffold, subsequently coating it with atomic layer deposition (ALD) with an absorber/phase shifting material, followed by back side etching of Si to form a diamond membrane device. The scaffold is formed by chemical vapor-deposited UNCD, electron beam lithography, and deep-reactive ion etching of diamond to desired specifications. The benefits of using diamond are as follows: improved mechanical robustness to prevent collapse of high-aspect-ratio ring structures, a known high-aspect-ratio etch method, excellent radiation hardness, extremely low x-ray absorption, and significantly improved thermal/dimensional stability as compared to alternative materials. Central to the technology is the high-resolution patterning of diamond membranes at wafer scale, which was pushed to 60 nm lines and spaces etched 2.2-mu m-deep, to an aspect ratio of 36:1. The absorber growth was achieved by ALD of Ir, Pt, or W, while wafer-level processing allowed to obtain up to 121 device chips per 4 in. wafer with yields better than 60%. X-ray tests with such zone plates allowed resolving 50 nm lines and spaces, at the limit of the available resolution test structures.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Development of Diamond Membrane-Based X-Ray Optics: Fresnel Zone Plates, Beam Stops, and Grids

This project was proposed to develop the design and fabrication of zone plates for hard X-ray focusing up to 25 keV photon energies with 20 nm resolution (with zone doubling), based on diamond membranes. The benefits of using diamond are: improved mechanical robustness which among other advantages prevents collapse of high-aspect-ratio ring structures, a known high-aspect-ratio etch method, and excellent compatibility with other processes, excellent radiation hardness, extremely low X-ray absorption, and significantly improved thermal/dimensional stability as compared to alternative materials. The Phase I findings enable Phase II goals as well as significant progress in other diamond-membrane devices, such as diamond-supported X-ray optics (beam stops, apertures, phase shift disks for phase contrast X-ray microscopy, grids, resolution targets, coded apertures for coherence measurements, etc), X-ray windows and membrane–based detectors. Zone plates with outermost zones of 60 nm were written in 500 nm electron resist and transferred to a depth of up to 1.8 mm (exceeding the expectations) into a stack of engineered multilayer ultra-nano-crystalline diamond alternating non-conductive and conductive layers. The active material for focusing was added on top (Au and Ir). Several processes were investigated and validated to enable in Phase II the enhancement of the thickness of the structures, including polishing the over-plated zone plates and growing diamond on top of Ir-coated zone plates without the destruction of the nanostructures underneath. The zone plates were geometrically characterized.

07 ISOTOPE AND RADIATION SOURCES↗