Abstract:In
situ spectroscopic characterization of the interfacial structure
of an organic additive at a Cu electrode is essential for a mechanistic
understanding of Cu superfilling at the molecular level. In this work,
we demonstrate wide-frequency attenuated total reflection surface-enhanced
infrared absorption spectroscopy (wf-ATR-SEIRAS) to elucidate the
dissociative adsorption of bis(sodium sulfopropyl)-disulfide (a typical
accelerator) on a Cu electrode in conjunction with the electrochemical
quartz crystal micr… Show more
“…The IREs used in this work were micromachined Si substrates fabricated from ∼0.5 mm thick, standard Si wafers, diced into approximately 1 cm × 1 cm chips. The low path length through these Si IREs is advantageous when working below ∼1400 cm –1 and gives rise to so-called wide-frequency ATR–SEIRAS , and have convenient dimensions for physical deposition of conductive films. The majority of IREs in this work were first coated with a 15 nm thick film of ITO using a home-built RF magnetron sputtering unit at a base vacuum of 2 × 1 × 10 –5 Torr.…”
Ionic liquids (ILs)
nanostructuring at electrified interfaces is
of both fundamental and practical interest as these materials are
increasingly gaining prominence in energy storage and conversion processes.
However, much remains unresolved about IL potential-controlled (re)organization
under highly polarized interfaces, mostly due to the difficulty of
selectively probing both the distal and proximal surface layers of
adsorbed ions. In this work, the structural dynamics of the innermost
layer (<10 nm from the surface) were independently interrogated
from that of the ionic layers in the sub-surface region (>100 nm
from
the surface), using an infrared (IR) spectroscopy approach. By tuning
the metal fill factor of gold films deposited on conductive metal
oxide-modified IR internal reflection elements, the charge-driven
(re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium
trifluoromethanesulfonate is unveiled. Within a relatively wide potential
region (∼±1 V) bounding the potential of zero charges,
the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization
whereby the innermost layer of anions (cations) is exchanged by a
layer of cations (anions). Kinetically unhindered changes in the number
density of constituent cations and anions largely follow electrostatic
expectations in the subsurface region, whereas the innermost layer
exhibits a pronounced hysteresis and very slow relaxation. Under larger
negative potential bias, IL restructuring is characterized by a highly
irreversible (i.e., hard) and intense interfacial densification of
the BMPy+ cations, consistent with the formation of nanoscale
segregated liquids. The outcomes of this work reveal a plastic IL
nanostructuring under a strong electric field.
“…The IREs used in this work were micromachined Si substrates fabricated from ∼0.5 mm thick, standard Si wafers, diced into approximately 1 cm × 1 cm chips. The low path length through these Si IREs is advantageous when working below ∼1400 cm –1 and gives rise to so-called wide-frequency ATR–SEIRAS , and have convenient dimensions for physical deposition of conductive films. The majority of IREs in this work were first coated with a 15 nm thick film of ITO using a home-built RF magnetron sputtering unit at a base vacuum of 2 × 1 × 10 –5 Torr.…”
Ionic liquids (ILs)
nanostructuring at electrified interfaces is
of both fundamental and practical interest as these materials are
increasingly gaining prominence in energy storage and conversion processes.
However, much remains unresolved about IL potential-controlled (re)organization
under highly polarized interfaces, mostly due to the difficulty of
selectively probing both the distal and proximal surface layers of
adsorbed ions. In this work, the structural dynamics of the innermost
layer (<10 nm from the surface) were independently interrogated
from that of the ionic layers in the sub-surface region (>100 nm
from
the surface), using an infrared (IR) spectroscopy approach. By tuning
the metal fill factor of gold films deposited on conductive metal
oxide-modified IR internal reflection elements, the charge-driven
(re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium
trifluoromethanesulfonate is unveiled. Within a relatively wide potential
region (∼±1 V) bounding the potential of zero charges,
the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization
whereby the innermost layer of anions (cations) is exchanged by a
layer of cations (anions). Kinetically unhindered changes in the number
density of constituent cations and anions largely follow electrostatic
expectations in the subsurface region, whereas the innermost layer
exhibits a pronounced hysteresis and very slow relaxation. Under larger
negative potential bias, IL restructuring is characterized by a highly
irreversible (i.e., hard) and intense interfacial densification of
the BMPy+ cations, consistent with the formation of nanoscale
segregated liquids. The outcomes of this work reveal a plastic IL
nanostructuring under a strong electric field.
“…55°) served as the working electrode for in situ ATR-SEIRAS (for metal film preparation details, see the Supporting Information). − A Pt mesh and a Hg/Hg 2 SO 4 /K 2 SO 4(sat’d) (MSE) served the counter electrode and the reference electrode, respectively, and a thin slice of glass sand core was placed between the chambers of the working electrode and the counter electrode. Aliquots of a concentrated PEG or HCl solution were injected into the catholyte chamber under strong N 2 bubbling to attain the desired concentration.…”
Section: Methodsmentioning
confidence: 99%
“…In this work, the microscopic structure of the PEG-Cl – inhibition layer is further clarified by wide-frequency ATR-SEIRAS in conjunction with electrochemical quartz crystal microbalance (EQCM) measurement. In situ wide-frequency ATR-SEIRAS is able to detect the frequency range above 650 cm –1 while conventional ATR-SEIRAS can only detect above 1000 cm –1 , − providing richer spectral information to update the PEG-Cl – inhibition layer structure, and EQCM provides additional evidence in support of PEG on the underlying Cl – adstructure. Detailed analysis of time-evolved spectral features for C–O, C–H, and O–H vibration modes allows direct dynamic observation of PEG conformation change upon its adsorption on the underlying Cl – adlayer on the Cu electrode in response to the hydrophobic interaction between subunits of PEG and the Cl – adlayer.…”
Polyethylene glycol (PEG) is a typical suppressor in
the presence
of chloride anions for Cu interconnect electroplating in the field
of microelectronics manufacture, yet its adsorption structure and
its correlation with the inhibition effect remain controversial and
unclear. In this work, wide-frequency attenuated total reflection
surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is
utilized to clarify the interfacial adsorption structure of PEG with
Cl– on a Cu electrode, providing direct molecular-level
evidence for the inhibition effect. Time-resolved spectroscopic results
show that the OC–CO subunit of PEG transforms from trans to gauche conformation with the addition
of Cl– in a way favoring the hydrocarbon sections
of PEG to lean toward the Cl–-covered Cu surface,
as demonstrated by the evolution of characteristic peaks at 1134,
1090, and 848 cm–1 as well as that of interfacial
water stretching vibration bands (ca. 3400–3650 cm–1). Moreover, a comparison of spectra for adsorbed PEG and dissolved
PEG shows that more OC–CO and CC-OC gauche conformations are present in the former, in favor of PEG chain coiling
to form mounds on the Cl–-covered Cu electrode.
The steric hindrance of as-formed PEG mounds may account for the strong
interfacial inhibition effect of the PEG-Cl– adstructure,
as supported by the electrochemical quartz crystal microbalance (EQCM)
measurement. A series of potential-dependent ATR-SEIRAS spectra reveal
that with decreasing potential, the coiled PEG chains become loosened
due to gradual desorption of the underlying Cl– adlayer.
“…Owing to insufficient surface sensitivity and narrow frequency-detection range as well as the complication from additional Cu 2+ , the interfacial adsorption configuration of JGB at Cu electrodes was not well established then without in situ spectral evidence of two fragments. Recently, wide frequency attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), meriting a high surface sensitivity and an extended wavenumber detection range to the fingerprint region, − has been applied in studying adsorption structures of the accelerator SPS and the suppressor PEG at Cu electrodes. , This upgraded technique is expected to provide direct molecular insight into the adsorption structure of the leveler JGB at Cu electrodes.…”
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