arXiv subjects

Giacomo Mariani

Publications and source records attributed to Giacomo Mariani.

6 recordsLinked to original sources

arXiv2026

The SPHEREx Instrument: Calibration, testing and performance measurements of the NIR spectroscopic surveyor from the laboratory to in-orbit commissioning

The SPHEREx near-infrared space telescope is an all-sky spectroscopic survey mission launched on March 12th, 2025 UTC. In addition to providing the community with a spectral database applicable to a wide range of investigations, it is optimized to address three core science goals: to survey the large scale structure of the Universe for signatures of non-Gaussianity during inflation; to conduct intensity mapping studies of the extragalactic background light for probing the history of galaxy evolution; and to survey the plane of the Milky Way for the prevalence and distribution of water and other biogenic ices. Each of these science goals imposes unique requirements on the performance of the instrument. We detail the design and testing strategies and report the performance results for the full instrument test campaign, ranging from component-level screening to in-orbit tests during the commissioning phase. The instrument, currently operating in full science survey mode, meets all of its driving requirements including optical performance, point source sensitivity, thermal stability and correlated noise minimization.

astro-ph.IM↗

arXiv2026

Uniform Narrow Excitonic Spectrum in Large-Area Suspended WSe2 Monolayers

Uniformity in the excitonic spectrum is a key requirement for accessing intrinsic excitonic physics in two-dimensional semiconductors; however, in transition-metal dichalcogenide (TMD) monolayers supported on substrates, exciton energies and linewidths can vary spatially due to inhomogeneities from contact with other materials or fabrication residues. Suspended TMD monolayers provide a route to minimizing substrate-induced disorder, although conventional transfer processes can introduce contamination. Here we demonstrate the spatially uniform excitonic spectrum from optically high-quality WSe2 suspended monolayers fabricated by gold-assisted exfoliation directly onto an Au contact electrode of a gate-tunable device. The resulting membranes span narrow suspended regions up to ~80 um and show spatially uniform photoluminescence at cryogenic temperatures with neutral-exciton linewidths as low as ~4.5 meV. Spectral reproducibility supports an intrinsic optical response, while gate-dependent measurements resolve multiple excitonic species. This approach provides a route to electrically tunable potential landscapes in suspended TMD monolayers with a highly uniform excitonic response.

cond-mat.mes-hall↗

arXiv2025

The SPHEREx Satellite Mission

SPHEREx, a NASA explorer satellite launched on 11 March 2025, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 um with a resolving power ranging from 35 to 130 in 6.2 arcsecond pixels. The observatory obtains a 5-sigma depth of 19.5 - 19.9 AB mag for 0.75 to 3.8 um and 17.8 - 18.8 AB mag for 3.8 to 5.0 um after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky, intended to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that will use intensity mapping to probe the evolution of galaxies over cosmic history. By mapping the depth of infrared absorption features over the Galactic plane, SPHEREx will comprehensively survey the abundance and composition of water and other biogenic ice species in the interstellar medium. The initial data are rapidly released in the form of spectral images to the public. The project will release specialized data products over the life of the mission as the surveys proceed. The science team will also produce specialized spectral catalogs on planet-bearing and low-mass stars, solar system objects, and galaxy clusters 3 years after launch. We describe the design of the instrument and spacecraft, which flow from the core science requirements. Finally, we present an initial evaluation of the in-flight performance and key characteristics.

astro-ph.IM↗

arXiv2024

Enhanced interlayer electron transfer by surface treatments in mixed-dimensional van der Waals semiconductor heterostructures

We investigate the excitonic species in WS$_{2}$ monolayers transferred onto III-V semiconductor substrates with different surface treatments. When the III-V substrates were covered with amorphous native oxides, negatively charged excitons dominate the spectral weight in low-temperature near-resonance photoluminescence (PL) measurements. However, when the native oxides of the III-V substrates were reduced, neutral excitons begin to dominate the spectral weight, indicating a reduction in the electron density in the WS$_{2}$ monolayers. The removal of the native oxides enhanced the electron transfer from the WS$_{2}$ monolayer to the III-V substrate. In addition, an additional shoulder-like PL feature appeared $\sim$50 meV below the emission of neutral excitons, which can be attributed to the emission of localized excitons. When the III-V substrate surface was passivated by sulfur after the reduction of the native oxides, neutral excitons still dominated the spectral weight. However, the low energy PL shoulder disappeared again, suggesting the effective delocalization of excitons through the substrate surface passivation. Surface engineering of the semiconductor substrates for two-dimensional (2D) materials can provide a novel approach to control the carrier density of the 2D materials, to implement deterministic carrier localization or delocalization for the 2D materials, and to facilitate the interlayer transfer of charge, spin, and valley currents. These findings open the avenue for novel device concepts and phenomena in mixed-dimensional semiconductor heterostructures.

cond-mat.mtrl-sci↗

arXiv2018

Imaging of microwave field distribution over a non-fed gold pattern by using NV centers in diamond

Nitrogen-vacancy (NV) centers in diamond have been widely used as platforms for quantum information, magnetometry and imaging of microwave (MW) fields. High-precision spatial control of the MW field necessary to drive the electronic spin of NV centers is essential for these applications. Here, we report a controlled MW field distribution by excitation of a micrometer-scale gold pattern in vicinity of the diamond surface. The gold pattern excited by a planar ring MW antenna, acts as a receiving antenna and redistribute the MW field in a localized area, without a direct feed of electrical current. The planar ring MW antenna is designed to generate a uniform MW field on diamond substrate in an area of 0.785 mm$^{2}$, providing a useful tool for detecting the MW variations. We performed the imaging of the localized MW intensity on the micrometer-scale gold pattern by direct observation of electron spin Rabi oscillations, showing also the potential application of NV centers for imaging MW field and characterization of MW devices. We achieved an enhancement of about 19 times for the Rabi frequency on a scale of few micrometers for the gold pattern, compared to the bulk Rabi frequency in presence of the single planar ring MW antenna. Compared to previous methods, our method has been shown as a fast and easy tool for the spatial control of MW fields and spin manipulation of NV centers in diamond.

quant-ph↗

arXiv2013

The Dependence of Alloy Composition of InGaAs Inserts in GaAs Nanopillars on Selective-Area Pattern Geometry

GaAs nanopillars with 150 nm - 200 nm long axial InGaAs inserts are grown by MOCVD via catalyst-free selective-area-epitaxy (SAE). The alloy composition of the InGaAs region, as determined by room-temperature photoluminescence (PL), depends critically on the pitch and diameter of the selective-area pattern geometry. The PL emission varies based on pattern geometry from 1.0 \{mu}m to 1.25 \{mu}m corresponding to a In to Ga ratio from 0.15 to > 0.3. This In enrichment is explained by a pattern dependent change in the incorporation rate for In and Ga. Capture coefficients for Ga and In adatoms are calculated for each pattern pitch. As the pitch decreases, these data reveal a contest between a synergetic effect (related to nanopillar density) that increases the growth rate and a competition for available material that limits the growth rate. Gallium is more susceptible to both of these effects, causing the observed changes in alloy composition.

cond-mat.mtrl-sci↗