skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Magnetic Ordering in Gold Nanoclusters

Abstract

Here, several research groups have observed magnetism in monolayer-protected gold-cluster samples, but the results were often contradictory and thus a clear understanding of this phenomenon is still missing. We used Au 25(SCH 2CH 2Ph) 18 0, which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors by electron paramagnetic resonance (EPR). As a film, Au 25(SCH 2CH 2Ph) 18 0 displays paramagnetic behavior but, at low temperature, ferromagnetic interactions are detectable. One or few single crystals undergo physical reorientation with the applied field and display ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit coupling and crystal distortion are important to determine the observed magnetic behaviors. DFT calculations carried out on single cluster and periodic models predict values of spin6orbit coupling and crystal6splitting effects in agreement with the EPR derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balancemore » of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodispersed with atomic precision, (ii) of known charge state, and (iii) well defined also in terms of crystallinity and experimental conditions. This study highlights the efficacy of EPR spectroscopy to provide a molecular understanding of these phenomena« less

Authors:
 [1];  [1];  [1];  [1];  [1]; ORCiD logo [2];  [2]; ORCiD logo [3];  [3]; ORCiD logo [4]
  1. Univ. of Padova, Padova (Italy)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. CNR-ICCOM & IPCF, Pisa (Italy)
  4. Univ. of Padova, Padova (Italy); Univ. of Connecticut, Storrs, CT (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1363986
Report Number(s):
PNNL-SA-125554
Journal ID: ISSN 2470-1343; 49645; KP1704020
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Omega
Additional Journal Information:
Journal Volume: 2; Journal Issue: 6; Journal ID: ISSN 2470-1343
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Environmental Molecular Sciences Laboratory; Crystal structure; Magnetic properties; Mechanical properties; Nanoclusters; Physical and chemical processes

Citation Formats

Agrachev, Mikhail, Antonello, Sabrina, Dainese, Tiziano, Ruzzi, Marco, Zoleo, Alfonso, Apra, Edoardo, Govind, Niranjan, Fortunelli, Alessandro, Sementa, Luca, and Maran, Flavio. Magnetic Ordering in Gold Nanoclusters. United States: N. p., 2017. Web. doi:10.1021/acsomega.7b00472.
Agrachev, Mikhail, Antonello, Sabrina, Dainese, Tiziano, Ruzzi, Marco, Zoleo, Alfonso, Apra, Edoardo, Govind, Niranjan, Fortunelli, Alessandro, Sementa, Luca, & Maran, Flavio. Magnetic Ordering in Gold Nanoclusters. United States. doi:10.1021/acsomega.7b00472.
Agrachev, Mikhail, Antonello, Sabrina, Dainese, Tiziano, Ruzzi, Marco, Zoleo, Alfonso, Apra, Edoardo, Govind, Niranjan, Fortunelli, Alessandro, Sementa, Luca, and Maran, Flavio. 2017. "Magnetic Ordering in Gold Nanoclusters". United States. doi:10.1021/acsomega.7b00472. https://www.osti.gov/servlets/purl/1363986.
@article{osti_1363986,
title = {Magnetic Ordering in Gold Nanoclusters},
author = {Agrachev, Mikhail and Antonello, Sabrina and Dainese, Tiziano and Ruzzi, Marco and Zoleo, Alfonso and Apra, Edoardo and Govind, Niranjan and Fortunelli, Alessandro and Sementa, Luca and Maran, Flavio},
abstractNote = {Here, several research groups have observed magnetism in monolayer-protected gold-cluster samples, but the results were often contradictory and thus a clear understanding of this phenomenon is still missing. We used Au25(SCH2CH2Ph)180, which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors by electron paramagnetic resonance (EPR). As a film, Au25(SCH2CH2Ph)180 displays paramagnetic behavior but, at low temperature, ferromagnetic interactions are detectable. One or few single crystals undergo physical reorientation with the applied field and display ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit coupling and crystal distortion are important to determine the observed magnetic behaviors. DFT calculations carried out on single cluster and periodic models predict values of spin6orbit coupling and crystal6splitting effects in agreement with the EPR derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balance of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodispersed with atomic precision, (ii) of known charge state, and (iii) well defined also in terms of crystallinity and experimental conditions. This study highlights the efficacy of EPR spectroscopy to provide a molecular understanding of these phenomena},
doi = {10.1021/acsomega.7b00472},
journal = {ACS Omega},
number = 6,
volume = 2,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • Ge nanostructures grown by molecular beam epitaxy on a vicinal Si(111) surface with atomically well-defined steps are studied by means of scanning tunneling microscopy and spectroscopy. When the substrate temperature during deposition is around 250 degree sign C, Ge nanoclusters of diameters less than 2.0 nm form a one-dimensional array of the periodicity 2.7 nm along each step. This self-organization is due to preferential nucleation of Ge on the unfaulted 7x7 half-unit cells at the upper step edges. Scanning tunneling spectroscopy reveals localized electronic states of the nanoclusters.
  • Electron paramagnetic resonance (EPR) is used to probe the spin dynamics in two-dimensional (2D) quantum dot (QD) arrays with local ordering of nanoclusters. A careful examination of EPR line shape, width and g-factor values allow us to attribute this signal to the electrons localized in the strain-induced potential wells in Si in the vicinity of the Ge dots. The strong orientation dependence of EPR line width is defined by changing localization degree of electrons at different magnetic field directions. The theoretical approximation of orientation dependence of EPR line width allows estimating the effective radius of electron localization, as {approx}80 nm.
  • Nanometer-sized gold particles were encapsulated in the micropores of xerogels and aerogels. The synthesis involves the sequential reduction of a gold salt followed by sol-gel processing in an inverse micelle solution. The inverse micelle solution solubilizes the metal salt and provides a microreactor for the nucleation, growth, and stabilization of the nanometer-sized clusters. Hydrolysis and condensation of an added siloxane precursor produces a wet gel embedding the particles. Characterization of the particle size and composition and the particle growth process was completed with transmission electron microscopy (TEM), electron diffraction, and UV-visible absorption spectrometry. Characterization of the gel surface areas wasmore » completed with N{sub 2} porosimetry. Material properties determined as a function of the gel precursor (TEOS vs a prehydrolyzed form of TEOS), the water to gel precursor reaction stoichiometry, and surfactant concentration are discussed in terms of the unique solution chemistry occurring in the microheterogeneous inverse micelle solutions. 73 refs., 7 figs., 1 tab.« less
  • The authors report high pressure liquid chromatography, (HPLC), and transmission electron microscopy, (TEM), studies of the size distributions of nanosize gold clusters dispersed in organic solvents. These metal clusters are synthesized in inverse micelles at room temperature and those investigated range in diameter from 1--10 nm. HPLC is sensitive enough to discern changes in hydrodynamic volume corresponding to only 2 carbon atoms of the passivating agent or metal core size changes of less than 4 {angstrom}. The authors have determined for the first time how the total cluster volume (metal core + passivating organic shell) changes with the size ofmore » the passivating agent.« less
  • No abstract prepared.