TY - JOUR
T1 - Ligand-free Ni nanocluster formation at atmospheric pressure via rapid quenching in a microplasma process
AU - Kumar, Ajay
AU - Kang, Seungkoo
AU - Larriba-Andaluz, Carlos
AU - Ouyang, Hui
AU - Hogan, Christopher J.
AU - Sankaran, R. Mohan
PY - 2014/9/26
Y1 - 2014/9/26
N2 - The production of metal nanoclusters composed of less than 103 atoms is important for applications in energy conversion and medicine, and for fundamental studies of nanomaterial nucleation and growth. Unfortunately, existing synthesis methods do not enable adequate control of cluster formation, particularly at atmospheric pressure wherein formation typically occurs on sub-millisecond timescales. Here, we demonstrate that ligand-free, unagglomerated nickel nanoclusters can be continuously synthesized at atmospheric pressure via the decomposition of bis(cyclopentadienyl)nickel(II) (nickelocene) in a spatially-confined microplasma process that rapidly quenches particle growth and agglomeration. The clusters were measured on line by ion mobility spectrometry (IMS) and further analyzed by atomic force microscopy (AFM). Our results reveal that stable clusters with spherical equivalent mean diameters below 10 are produced, and by controlling the nickelocene concentration, the mean diameter can be tuned up to ∼50 . Although diameter is often the sole metric used in nanocluster and nanoparticle characterization, to infer the number of atoms in AFM and IMS detected clusters, we compare measured AFM heights and IMS inferred collision cross sections to theoretical predictions based on both bulk matter approximations and density functional theory and Hartree-Fock calculated Ni nanocluster structures (composed of 2-15 atoms for the latter). The calculations suggest that Ni nanoclusters composed of less than 102 atoms can be produced repeatably with simple microplasma reactors.
AB - The production of metal nanoclusters composed of less than 103 atoms is important for applications in energy conversion and medicine, and for fundamental studies of nanomaterial nucleation and growth. Unfortunately, existing synthesis methods do not enable adequate control of cluster formation, particularly at atmospheric pressure wherein formation typically occurs on sub-millisecond timescales. Here, we demonstrate that ligand-free, unagglomerated nickel nanoclusters can be continuously synthesized at atmospheric pressure via the decomposition of bis(cyclopentadienyl)nickel(II) (nickelocene) in a spatially-confined microplasma process that rapidly quenches particle growth and agglomeration. The clusters were measured on line by ion mobility spectrometry (IMS) and further analyzed by atomic force microscopy (AFM). Our results reveal that stable clusters with spherical equivalent mean diameters below 10 are produced, and by controlling the nickelocene concentration, the mean diameter can be tuned up to ∼50 . Although diameter is often the sole metric used in nanocluster and nanoparticle characterization, to infer the number of atoms in AFM and IMS detected clusters, we compare measured AFM heights and IMS inferred collision cross sections to theoretical predictions based on both bulk matter approximations and density functional theory and Hartree-Fock calculated Ni nanocluster structures (composed of 2-15 atoms for the latter). The calculations suggest that Ni nanoclusters composed of less than 102 atoms can be produced repeatably with simple microplasma reactors.
KW - aerosol
KW - atomic force microscopy
KW - cluster
KW - ion mobility measurement
KW - microplasma
KW - nanocluster
KW - nanoparticles
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U2 - 10.1088/0957-4484/25/38/385601
DO - 10.1088/0957-4484/25/38/385601
M3 - Article
AN - SCOPUS:84930654563
SN - 0957-4484
VL - 25
JO - Nanotechnology
JF - Nanotechnology
IS - 38
M1 - 385601
ER -