Bottom-up Cu deposition in metallized through silicon vias (TSV) depends
on a co-adsorbed polyether–Cl
−
suppressor layer that
selectively breaks down within recessed surface features. This work explores Cu
deposition when formation of the suppressor blocking layer is limited by the
flux of Cl
−
. This constraint leads to a transition from
passive surfaces to active deposition partway down the via sidewall due to
coupling between suppressor formation and breakdown as well as surface
topography. The impact of Cl
−
concentration and hydrodynamics
on the formation of the suppressor surface phase and its potential-dependent
breakdown is examined. The onset of suppression breakdown is related to the
local Cl
−
coverage as determined by the adsorption isotherm or
transport limited flux. A two-additive co-adsorption model is presented that
correlates the voltammetric potential of suppression breakdown with the depth of
the passive-active transition during TSV filling under conditions of transport
limited flux and incorporation of Cl
−
. The utility of
potential waveforms to optimize the feature filling process is demonstrated. At
higher Cl
−
concentrations (≥80 μmol/L), sidewall
breakdown during Cu deposition occurs near the bottom of the via followed by a
shift to bottom-up growth like that seen at higher Cl
−
concentrations.
The
novel ternary Zn(II)-thiourea–urea ionic cocrystal [Zn(thiourea)(urea)Cl2], (ZnTU) has been prepared by both solution and mechanochemical
processes and structurally characterized by solid-state methods. ZnTU
exhibited improved response properties to water as relative humidity
as inherited from thiourea. The results of enzymatic activity measurements
provide evidence that ZnTU is effective in modulating urea hydrolysis
both in vitro (negatively impacting on the activity of isolated urease)
and in vivo (decreasing the ureolytic activity of Sporosarcina
pasteurii, a widespread soil bacterium), and that Zn(II)
is the component of the cocrystal acting as the actual urease inhibitor.
Concomitantly, the analysis of the ammonia monooxygenase (AMO) enzymatic
activity in Nitrosomonas europaea, taken as a representative
of soil ammonia-oxidizing bacteria, in the presence of ZnTU reveals
that thiourea is the only component of ZnTU able to inhibit ammonia
conversion to nitrite. It has also been shown that ZnTU maintains
these capabilities when applied to bacterial cultures containing both S. pasteurii and N. europaea working in
tandem. The compound can thus act both as a fertilizer via urea and
via the Zn(II) and thiourea components, as a dual action inhibitor
of the activities of the enzymes urease and AMO, which are responsible
for the negative environmental and economic impact of the agricultural
use of urea as soil fertilizer. These results indicate that ZnTU should
be considered a novel material to improve N fertilization efficiency,
toward a more environment-friendly agricultural practice.
Population
growth is necessitating a significant increase in crop
production, while regulations require less use of nitrogen (N) (as
fertilizers, such as urea) to minimize its environmental influx. A
large fraction of applied N fertilizers is currently lost with significant
negative environmental effects. The urea decomposition pathways explored
in the literature chiefly concern the gas emissions but provide less
mechanistic insights into the urea particle/soil interface after deposition
and during their environmental processing (aging). The present work
investigated the mechanistic role of relative humidity (RH) at the
model humic material (salicylic acid)–urea interface and the
resulting surface reactions using dynamic vapor sorption and in situ spatially resolved Raman spectroscopy, combined
with ab initio thermodynamic calculations. The formation
of a reaction product between urea and salicylic acid, used as a model
compound of humic substances, was observed, resulting in the profoundly
different response to RH, with the hysteresis due to the bulk urea
no longer apparent. Ab initio and resulting NH3 emission measurement experiments suggest a decreased propensity
of such reaction products to hydrolyze due to the formation of strong
molecular bonds between urea and salicylic acid at the interface.
The reaction was facilitated by the formation of a supersaturated layer of aqueous urea
on the surface, which is likely the driving force behind the new product
formation due to its higher vapor pressure. The results suggest that
RH-driven reactions of urea and humic substances of soil could profoundly
influence gas-phase emissions and thus affect the global nitrogen
cycle. The impact of the stabilizing structure and the properties
of the resulting urea reaction products on organic moieties needs
to be further studied in the future to better understand the implications
toward global N cycle.
Nutrient - nitrogen (N) and phosphorus (P) - recovery from wastewater is an important challenge for enhanced environmental sustainability. Herein we report the synthesis and properties of mesoporous MgO nanoparticles...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.