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Nadzeya Khinevich, Domantas Peckus, Asta Tamulevičienė, Gerda Klimaitė, [Joel Henzie](https://orcid.org/0000-0002-9190-2645), Tomas Tamulevičius, Sigitas Tamulevičius

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[Size and crystallinity effect on the ultrafast optical response of chemically synthesized silver nanoparticles](https://mdr.nims.go.jp/datasets/9afcf5cd-38d5-4fa4-a224-12ec703e753e)

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Size and crystallinity effect on the ultrafast optical response of chemically synthesized silver nanoparticlesilable at ScienceDirectJournal of Materiomics 10 (2024) 594e600Contents lists avaJournal of Materiomicsjournal homepage: www.journals .elsevier .com/journal-of-mater iomics/Research paperSize and crystallinity effect on the ultrafast optical response ofchemically synthesized silver nanoparticlesNadzeya Khinevich a, Domantas Peckus a, b, *, Asta Tamulevi�cien _e a, b, Gerda Klimait _e b,Joel Henzie c, Tomas Tamulevi�cius a, b, Sigitas Tamulevi�cius a, b, **a Institute of Materials Science of Kaunas University of Technology, K. Bar�sausko St. 59, LT-51423, Kaunas, Lithuaniab Department of Physics, Kaunas University of Technology, Studentų St. 50, LT-51368, Kaunas, Lithuaniac International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, 305-0044, Japana r t i c l e i n f oArticle history:Received 3 July 2023Received in revised form21 August 2023Accepted 22 August 2023Available online 17 September 2023Keywords:Silver nanospheresSilver nanocubesElectron-phonon couplingTransient absorption spectroscopyCrystallite sizePolycrystalline structure* Corresponding author. Institute of Materials ScieTechnology, K. Bar�sausko St. 59, LT-51423, Kaunas, Lit** Corresponding author. Institute of Materials ScieTechnology, K. Bar�sausko St. 59, LT-51423, Kaunas, LitE-mail addresses: domantas.peckus@ktu.lt (D. Pktu.lt (S. Tamulevi�cius).Peer review under responsibility of The Chinese Chttps://doi.org/10.1016/j.jmat.2023.08.0092352-8478/© 2023 The Authors. Published by Elseviecreativecommons.org/licenses/by-nc-nd/4.0/).a b s t r a c tThe excited localized surface plasmon (LSP) in metallic nanoparticles is known to relax through severalprocesses such as electron-electron scattering, electron-phonon coupling, and phonon-phonon scat-tering. In the current research, the ultrafast electron-phonon (e-ph) coupling relaxation processes fordifferent average sizes and crystallinity of chemically synthesized silver nanoparticles were evaluatedutilizing transient absorption spectroscopy. The nanoparticle size and crystallinity of similar lineardimension polycrystalline spherical and monocrystalline cubic nanoparticles ranging from ca. 30e60 nmwas related to their electron relaxation time constants and revealed very different dependencies. For themonocrystalline nanocubes, the electron-phonon coupling was not dependent on the cube edge length,while for the polycrystalline nanospheres, it was linearly decreasing with diameter. We demonstrate thatthe e-ph coupling time constant could be used to evaluate crystallinity and crystallite size in plasmonicmetal nanoparticles when the size (surface area) of the nanoparticle is known.© 2023 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an openaccess article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).1. IntroductionMetal nanoparticle synthesis and optical characterization havebecome an important focus in diverse fields from catalysis tosensing and medicine. Special attention is paid to noble metal (Au,Ag, and Pt) nanostructures because they support plasmon reso-nance. Due to their unique physicochemical properties, Ag NPs areused as biosensor material, additives to composite fibres, cosmeticproducts, and electronic and optical components [1]. Ag NPs havebeen one of the most attractive nanomaterials in biomedicine,where they are used for antimicrobial and anticancer therapy,promote wound repair and bone healing, or as an adjuvant tovaccines as an antidiabetic agent [2]. Ag NPs also find multipleapplications ranging from heterogeneous catalysis [3] to gasnce of Kaunas University ofhuania.nce of Kaunas University ofhuania.eckus), sigitas.tamulevicius@eramic Society.r B.V. on behalf of The Chinese Cersensing and nonlinear optics [4,5]. Metallic nanoparticles act as afunctional base component of nanoscale devices or sensors withhigh selectivity and sensitivity in these applications. These nano-particles can also be applied in spectroscopic systems to enhanceRaman scattering spectroscopy signal [6]. Nanoscale metal featuressupport localized surface plasmon resonances (LSPs) associatedwith strong electromagnetic (EM) hotspots. These EM fieldsenhance the Raman scattering of adsorbed molecules and can beused for chemical sensing [4].One of the key issues to consider during a variety of applicationsof metallic NPs includes developments and novel applications inphotovoltaics, photodetection, photocatalysis, etc. where the LSPexcitation of NPs is employed, is their ultrafast optical user-designed response. Currently, there is knowledge of the temporalevolution of hot electrons excited by light and its dependence onthe size, composition, and morphology of metal NPs. The excitedLSP in metallic NPs is known to relax through several processessuch as electron-electron scattering (e-e, typical time scale ca. 100fs), electron-phonon coupling (e-ph, 1e5 ps), and phonon-phononscattering (ph-ph, 10e100 ps) [7]. When the excitation source isfaster than the expansion/contraction period, the light-heatedparticles can form coherent vibrations called optomechanicalamic Society. This is an open access article under the CC BY-NC-ND license (http://http://creativecommons.org/licenses/by-nc-nd/4.0/mailto:domantas.peckus@ktu.ltmailto:sigitas.tamulevicius@ktu.ltmailto:sigitas.tamulevicius@ktu.lthttp://crossmark.crossref.org/dialog/?doi=10.1016/j.jmat.2023.08.009&domain=pdfwww.sciencedirect.com/science/journal/23528478www.journals.elsevier.com/journal-of-materiomics/https://doi.org/10.1016/j.jmat.2023.08.009http://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/https://doi.org/10.1016/j.jmat.2023.08.009https://doi.org/10.1016/j.jmat.2023.08.009N. Khinevich, D. Peckus, A. Tamulevi�cien _e et al. Journal of Materiomics 10 (2024) 594e600oscillations that decay together with ph-ph [7e9]. One of thepump-probe spectroscopy variants, transient absorption spectros-copy (TAS) is a primary choice for studying the kinetics of the LSPeffect of different processes taking place in femto e to picosecondtime scales. Despite intensive research in this field, the thermali-zation effect of hot electrons in metal NPs with the lattice viaelectron-phonon coupling, especially the NPs size and shape de-pendency of the process, has been controversially discussed inrecent literature [8,10]. For example, theoretical studies [11] doneon the temporal evolution of optically excited conduction electronsin small plasmon-supporting gold and silver NSs predict that thecontribution of surface states (and the effect of the size of the NPs)to hot electron dynamics should be relatively small, as surfaceelectrons only make a small fraction of the total conduction elec-trons for the particle sizes under consideration. In Refs. [8,12] it wasexperimentally shown that gold and silver NPs do not demonstratea dependence of hot electron dynamics on size and shape, whilecopper NPs have shown some dependence on size [13]. Otherstudies indicated that the e-ph coupling time constants of Ag andAu NPs stop depending on size and shape if the diameter of the NPsbecomes greater than 10 nm [8,14,15]. The importance of bulkphonons dependence on the degree of crystallinity of gold NPs wasrevealed e it was demonstrated that the e-ph coupling time con-stant increases when polycrystalline gold nanoprisms are annealedand transformed into nearly single-crystal nanospheres (NSs). Onthe other hand, a size-dependent e-ph coupling time constant wasexperimentally demonstrated in goldmonocrystalline NSs [10]. Thelarger monocrystalline gold NPs have demonstrated a lower e-phcoupling time constant, which was explained as a result of thedecreasing effect of electron-surface scattering and e-ph couplingconstants approaching the values reported for bulk gold. Further-more, the size dependences were outweighed by the effectivescattering at grain boundaries [10]. Similar results were reportedfor gold NPs in Ref. [16] showing no influence of crystallinity onelectron-phonon equilibration dynamics. It was suggested that thecrystal twins present in the polycrystalline gold NPs do notsignificantly enhance the e-ph scattering.Despite the manifold plasmonics-related applications of Ag NPs,the dependence of the e-ph interaction on crystallinity are almostnot considered in the literature for Ag NPs in comparison to Au NPs.Studies of the dependence of e-ph coupling on size have been donefor a long time [13,17,18] and in most cases no significant size effectwas found [13,17e20]. This indicates that e-ph coupling depen-dence on size is very unlikely in Ag NPs. Nevertheless, in thesearticles, the crystalline structure was not examined; therefore, it ishard to discriminate between the size and crystallinity influence,which is being tackled in this work. In our studies, the difference inAg NPs crystallinity was implied by the use of two different wetchemistry methods (reduction of silver salt and polyol synthesis).Different preparation methods have been reported for the pro-duction of Ag NPs, including physical (laser ablation, sputtering,etc.), chemical (chemical reduction, green synthesis), photochem-ical methods, and microwave processing [1]. One of the popularmethods used to produce silver nanospheres (Ag NSs) is thereduction of silver salt. In this method, monodisperse Ag NSs aresynthesized via the reduction of silver nitrate using a mixture oftwo chemical agents: sodium citrate (SC) and tannic acid (TA).Combining SC and TA forms a complex with better reducing andstabilizing properties than SC and TA alone [21e23]. Whereas thepolyol synthesis method is frequently utilized when non-sphericalgeometries are preferred, such as nanocubes (NCs), nanowires [24],etc. The method provides better control of the crystallinity andgeometry of monocrystalline nanocubes (NC) and various poly-hedrons were obtained [25,26].In the current research, we have performed a systematic595analysis of ultrafast processes taking place in highlymonodispersedpolycrystalline and monocrystalline Ag NPs colloids, investigatingtheir LSP relaxation kinetics empowering TAS as a perspective toolfor nanomaterial characterization. We explored the dependence ofAg nanoparticle shape, average size, and crystallinity on e-phcoupling. The e-ph coupling of single-crystal Ag NCs was size-invariant while e-ph coupling in polycrystalline Ag NSs had alinear size dependence.2. Experimental section2.1. MaterialsSilver salt (AgNO3), tannic acid (TA, C76H52O46), and trisodiumcitrate (TC, Na3C6H5O7), 1,5-pentanediol, copper (II) chloride dihy-drate (CuCl2$2H2O), poly (vinylpyrrolidone) (PVP, Mw ¼ 55,000amu) were purchased from Sigma Aldrich and used without furtherpurification. All solutions were prepared with Milli-Q water.The synthesis of silver nanospheres (sequence a) was carried outaccording to the procedure developed by N. Bastus [23], where acomplex of TA and TC is used and allows control over the nucle-ation, growth, and stabilization processes, leading to reproduciblemonodisperse Ag NSs. The method consists of two preparationsteps: synthesis of silver seeds followed by growth of Ag NSs.Synthesis of silver seeds. An aqueous solution (100 mL) con-taining 5 mmol/L TC and 0.0125 mmol/L of TAwas heated at 100 �Сdegrees for about 15 min under vigorous stirring. Subsequently,1 mL of the silver salt solution (25 mmol/L) was injected. Thesynthesis lasted for 70 min.Growth of Ag NSs. 19.5 mL of seeds were mixed with 16.5 mL ofwater and heated under 90 �С, 250 mL of 2.5 mmol/L TA, 100 mL of25 mmol/L TC, and 250 mL of 25 mmol/L AgNO3 were sequentiallyinjected. After 30 min of heating, 1 mL of aliquots was extracted forfurther characterization. The solution produced was used as theseed solution for the subsequent synthesis step. The growth pro-cess was repeated four times. Aliquots were centrifuged at 7,000 r/min.Monodisperse solutions of Ag nanocubes (sequence b) wereprepared using a modified procedure based on the polyol synthesismethod described in Refs. [26,27]. A copper chloride solution wasprepared by dissolving 80 mg of CuCl2 in 10 g of 1,5-pentanediol(PD; Acros). Then the two precursor solutions were prepared bydissolving 0.4 g of polyvinylpyrrolidone (PVP; Sigma-Aldrich) in20 g of PD, and dissolving 35 mL of the above CuCl2 solution and0.4 g of AgNO3 into 20 g of PD. Next, a 100 mL round bottom flask(RBF) was filled with 20 g of PD and heated to an internal tem-perature of 130 �C. Once the PD reached this temperature, 500 mL ofthe AgNO3 solution was added to the RBF, then 30 s later 500 mL ofthe PVP solution was added to the RBF. This process was repeatedevery minute (i.e. Add the Agþ solution at 0:00, the PVP solution at0:30, then Agþ at 1:00 and so on) until the desired nanocube sizewas achieved.2.2. Analysis methodsUVeVis absorbance spectra of the studied nanoparticles wererecorded using a fibre-optic spectrometer AvaSpec-2048 (Avantes,The Netherlands) with a resolution of 1.2 nm in the 400e800 nmspectral range.Transmission electron microscope (TEM) Tecnai G2 F20 X-TWIN(FEI, The Netherlands) with an FE source operated at 200 kV wasused for the visualization of Ag NSs. 20 mL of the precipitates aftercentrifugation were dropped onto a TEM copper mesh and left todry at room temperature. While Ag NCs were inspected with 2100F(JEOL) TEM operating at 200 kV.N. Khinevich, D. Peckus, A. Tamulevi�cien _e et al. Journal of Materiomics 10 (2024) 594e600The images were analyzed with ImageJ software and used forthe estimation of the mean diameter/edge length and size distri-bution. For each sample, at least 50 NPs were measured to evaluatethe mean diameter (DM) and standard deviation (SD) - dispersity ofthe ensemble.The X-ray diffraction method was used to study the crystallinestructure of synthesized Ag NPs. The D8 Discover (Bruker AXSGmbH) diffractometer with a Cu Ka1 (l ¼ 0.154 nm) radiationsource and parallel beam focusing geometry was used. Peak in-tensities were measured in the 30�e90� 2qeqwith 0.012� step size.The DIFFRAC.EVA software was used to process the diffractograms.Considering that in all cases single-phase compounds were ob-tained, we performed the Rietveld refinement using X'pert High-Score Plus software to calculate crystallite sizes and latticeparameters based on Scherrer formula.Transient absorption spectroscopy was used to study the ul-trafast electron dynamics of Ag NPs. The HARPIA spectrometer(Light Conversion, Lithuania) was used for the TAS measurements.For the sample excitation with an ultrafast 290 fs pulse length and1,030 nm wavelength Yb:KGW laser Pharos (Light Conversion, LT)with a regenerative amplifier at a 66.7 kHz repetition ratewas used.Collinear optical parametric generator Orpheus and harmonicgenerator Lyra (Light Conversion, LT) were used to tune the pumpbeam wavelength to 350 nm with an excitation intensity of0.6e13.6 mJ/cm2, and a pulse width of about 290 fs. The samples ofAg NPs were probed with a white-light supercontinuum generatedusing a 2 mm thickness sapphire plate excited with the secondharmonic (515 nm) of fundamental laser wavelength. The spectralrange of the supercontinuum probe, as well as the detection rangeof the TAS signal relaxation dynamics, spanned wavelengths from370 nm to 674 nm. The excitation beam was focused on a ca.700 mm diameter spot, while the diameter of the spatially over-lapped supercontinuum probe was ca. 500 mm [28].3. Results and discussion3.1. Properties of synthesized Ag NPsThe process of seeded growth chemical synthesis was repeatedand after each growth cycle, Ag nanospheres of different sizes wereobtained. Themethod based on a seed-growth approach allowed usthe production of long-term stable aqueous colloidal Ag NS dis-persions with narrow size distribution. The homogeneous growthof Ag seeds was kinetically controlled by adjusting the reactionparameters: concentrations of reducing agents, temperature, a sil-ver precursor-to-seed ratio, and pH value as it was proposed inRef. [23]. From the TEM analysis (Fig. 1) it was determined that AgNSs diameters after the 1st growth process were 27.8 nm (noted assample a1) and ranged to 56.6 nm (a4) after the 4th cycle. TEMmicroscopy analysis also revealed the polycrystalline structure ofthe Ag NSs (Fig. 1 aed), while Ag nanocubes are monocrystallinestructures (Fig. 1 eeh).The increasing linear dimension was accompanied by the ex-pected redshift of the absorbance peak (Fig. 2 a, c) related to thedipolar LSP resonance mode and the emergence of the second peakin the UV region associated with the quadrupole mode in larger AgNSs (Fig. 2a) and Ag NCs (Fig. 2c). The mean diameter (DM) andstandard deviation (SD) of the synthesized Ag NSs, Ag NCs alongwith their size distribution are depicted in Fig. 2b and d,respectively.3.2. Crystallinity analysis of Ag NPsFor each sample, the crystallite size and its standard deviation ofthe NPs were evaluated from the XRD patterns (Fig. 3) which show596the diffraction peaks at 2q¼ 38.2�, 44.5�, 64.6�, and 77.6�, 81.7� thatcorrespond to the planes (111), (200), (220), (311), and (222)respectively of the face-centered cubic (FCC) silver structure, ac-cording to the standard powder diffraction card Joint Committee onPowder Diffraction Standards (JCPDS 04e0783).The crystallite size was calculated using the Scherrer formula[29], and the results are presented in Table 1. The table includes themean diameter of NSs and mean edge length of NCs with standarddeviations defined from TEM analysis. One can see that for Ag NSs,the Ag NSs crystallite size increases together with the diameter(Table 1) and this is in good agreement with the applied synthesisapproach where during the seeds-growth process, Ag ions reduceon the surface of Ag NPs avoiding new nucleation or agglomeration[23]. The growth mechanism enabled the formation of NPs with acontrolled crystallite size, which is important in the quantitativestudies of electron-phonon scattering, elucidating the effects ofelectron scattering in grain boundaries. The crystallite size of AgNCs was bigger than their spherical counterparts and much closerto the linear dimension of the nanoparticles, a similar result wasobtained for the monocrystalline silver nanocubes in Ref. [30] andgold nanospheres in Ref. [31].3.3. Nonlinear optical spectroscopyTAS measurements were employed to characterize Ag NPs,including defectiveness and structure. The TAS measurement datafor Ag NSs at different probe wavelengths and different pumpexcitation intensities are shown in Figs. S1eS5. Electron-phononcoupling (e-ph, t1) and phonon-phonon (ph-ph, t2) scatteringtime constants were calculated from the TAS signal decay traces(Figs. S2eS5) by fitting traces at the negative and positive peaks ofthe TAS spectra using the exponential decay function with one ortwo components (1) [26,32].IðtÞ ¼ A1e� tt1 þ A2e� tt2 þ I0 (1)where A1; A2 and t1; t2 are the amplitudes and time constants ofdecay, respectively, while I0 represents the background of the TASsignal [32]. The fitting results for Ag NSs are summarized inTable S1, while the Ag NCs data analysis depicted in Figs. S7eS10 arecompiled in Table S2.For the investigation of coupling time constants, pump excita-tion intensity measurements were performed (Fig. S6 and Fig. S11).From these measurements, the e-ph coupling time constant (te-ph)was extrapolated from t1 under 0 excitation intensity as [13,33,34].The extrapolated e-ph coupling time constants are shown inTable 1.Damping of the excited state depends on e-ph couping. It variedfrom 0.69 ps to 0.96 ps for Ag NSs and from 0.85 ps to 1.05 ps for AgNCs (Table S1). A relatively weak TAS signal relaxation componentwas observed and that can be attributed to ph-ph scattering whosedurations ranged from 10 ps to 206 ps for Ag NSs (Table S1) and22e73 ps for Ag NCs (Table S2).The two-temperature model was used for the calculation of theelectron-phonon coupling constant [8] and the electron-phononcoupling constant G was found based on the equation [13,33,35]:G ¼ gT0/te-ph (2)where g equals 65 J$m�3$K�2 [36]; T0 is the ambient temperature(293 K); te-ph is hot-electron lifetimes (provided in Table 1).The polycrystalline Ag NSs indicated a decrease in the e-phcoupling time constant with increasing mean diameter (Fig. 4a)while the monocrystalline Ag NCs seem to be independent of theFig. 1. TEM analysis of the Ag NPs. Top row: Ag nanospheres after 1st process of growth (a1); after 2nd (a2); after 3rd (a3), and after 4th (a4). Bottom row: Ag nanocubes with edgelengths of 32 nm (b1), 35 nm (b2), 37 nm (b3), and 55 nm (b4). The scale bar is 25 nm.Fig. 2. UVeVis absorbance spectra (a, c) and size distribution (b, d) of Ag NSs (a, b) and Ag NCs (c, d).N. Khinevich, D. Peckus, A. Tamulevi�cien _e et al. Journal of Materiomics 10 (2024) 594e600597Fig. 3. XRD patterns of Ag NPs: nanospheres (a) and nanocubes (b). The peaks areassigned to diffraction from the planes (111), (200), (220), (311) and (222) of silver(spectra are offset for clarity).N. Khinevich, D. Peckus, A. Tamulevi�cien _e et al. Journal of Materiomics 10 (2024) 594e600edge length (Fig. 4a). We also calculated the e-ph coupling timeconstant dependence on volume of Ag NSs and Ag NCs that cor-responds well with data in Fig. 4a (Fig. S12). According to theo-retical predictions, the absence of size-dependent e-ph coupling inAu and Ag NPs is due to the relatively small contributions of surfacephonon modes to the e-ph coupling process [13] (in case they havea polycrystalline structure [31]). On the other hand, the depen-dence of the time constant of e-ph coupling on the NPs size hasbeen reported for Cu NPs [13,37] and monocrystalline Au NPs [31].In these cases, the dependence of the e-ph time constant wasattributed to the stronger influence of surface phonon modes onthe e-ph coupling process, and the increase in the size of NP has ledto longer e-ph coupling time constants. However, this contradictsour obtained dependencies presented in Fig. 4 a. It is also knownthat the e-ph coupling time depends on the crystallinity of the NPs[33], and the grain boundaries are important to consider in allmodes of plasmon damping [31]. To verify this hypothesis, wechose the ratio (Crystallite size/Linear dimension of Ag NPs)2(Table 1) for the analysis of the decay time constant of the e-phcoupling, assuming that the higher ratio of crystallite size to thesize of NPs corresponds to a more pronounced monocrystallinestructure and fewer grain boundaries of the NPs. In this ratio:Table 1The mean sizes of Ag NSs (a1ea4) and Ag NCs (b1eb4) based on TEM analysis, crystallite sTAS data (eq (1)), e-ph coupling constant G based on eq. (2).Sample Linear dimension (Diameter/Edgelength) (nm)Crystallite size(nm)Ratio (Crystallite sizdimension)a1 27.8 ± 4.1 9.8 ± 3.1 0.349a2 35.7 ± 4.9 10.5 ± 3.8 0.310a3 44.7 ± 4.4 13.0 ± 4.8 0.291a4 56.6 ± 5.6 15.0 ± 6.6 0.272b1 31.3 ± 1.7 27.1 ± 1.4 0.869b2 35.1 ± 1.7 27.8 ± 1.9 0.792b3 37.2 ± 2.2 30.9 ± 4.5 0.831b4 55.8 ± 3.6 32.1 ± 3.8 0.575598(Crystallite size/Linear dimension of Ag NPs)2 (3)Crystallite size e parameter calculated with Scherrer formulafrom Ag NPs sample XRD data; Linear dimension of Ag NPs e lineardimension is the length picked to evaluate size of Ag NPs. It isdiameter for Ag NSs and edge length for Ag NCs. We use Eq. (3) todescribe generally both types Ag NPs e for Ag NSs we use eq.(Crystallite size/Diameter of Ag NSs)2 while for Ag NCs - (Crystallitesize/Edge Length of Ag NCs)2.The linear dependence of the e-ph coupling decay time constanton (Crystallite size/Diameter of Ag NSs)2 (Fig. 4b) shows that the e-ph coupling time constant for NSs is size-dependent, and thisdependence correlates with the crystallinity of the NP. Thesefindings support the results of other researchers who have shownthat the grain boundaries in polycrystalline Au NCs increase theefficiency of coupling of hot electrons with phonons, making the e-ph coupling process faster [12,31]. In this way, the reviled depen-dence on the time constant e-ph coupling on (Crystallite size/Lineardimension of Ag NP)2 could in the future be used for control of thecrystalline structure of plasmonic metal NPs.The analysis of e-ph coupling time constants was done for theAg nanoparticles with sizes that provided us with the most reliableTAS data and therefore the most reliable e-ph coupling time con-stants. The extension of the range of sizes of samples becomesproblematic, because smaller nanoparticles absorb more andscatter less light leading to a strong TAS signal but the smallestsamples (below linear size 28 nm) are unstable therefore their timeresolved spectroscopy becomes complicated. Investigation of sizesabove 60 nm is also challenging because both the absorption andscattering from the nanoparticles prevail and lead to a decrease inTAS signal amplitude and larger noises whichmakes the calculationof e-ph coupling with huge error margins especially for Ag NSssamples. For comparison we used only Ag NCs that have mostsimilar sizes/volume to Ag NSs. All in all, in our studies we chose toinvestigate the most reliable results demonstrating Ag nanoparticlesizes for the e-ph coupling time constant analysis. Although webelieve that the size range could be extended in the study but someimprovements to the synthesis and stability of Ag NSs need to beimproved in the future.4. ConclusionThe chemical synthesis method based on a seed-growthapproach applied for the production of long-term stable aqueouscolloidal dispersions of spherical silver nanoparticles with narrow,controlled size distribution (mean diameter 28e57 nm), and vari-able crystallinity proven by TEM, XRD and TAS measurements,allowed systematic studies of the e-ph coupling process in plasmonrelaxation dynamics. Comparing similar mean linear dimensions ofchemically synthesized polycrystalline and monocrystalline silverparticles it was obtained that their electron-phonon relaxationize based on XRD data, electron-phonon coupling time constant te-ph calculated frome/Linear Ratio (Crystallite size/Lineardimension)2te-ph (ps) G � 1016 (W/(m3$K))0.122 0.96 ± 0.020 1.980.096 0.90 ± 0.002 2.120.085 0.77 ± 0.003 2.470.074 0.69 ± 0.020 2.760.755 0.86 ± 0.040 2.210.627 0.94 ± 0.010 2.030.690 0.85 ± 0.010 2.240.331 0.85 ± 0.020 2.24Fig. 4. Dependence of the e-ph coupling time constant (te-ph) on the diameter of Ag NSs and the edge length of the NCs (a). Estimated based on the negative TAS signal, (a), e-phcoupling time constant dependence on (Crystallite size/diameter of Ag NSs)2 (b); (Crystallite size/edge length of Ag NCs)2 (c). The black and red lines show the guide for eyes. D ediameter of Ag NSs, EL e edge length of Ag NCs. The insets show schematic image of Ag NSs samples (b) and Ag NCs samples (c).N. Khinevich, D. Peckus, A. Tamulevi�cien _e et al. Journal of Materiomics 10 (2024) 594e600time constants follow different dependencies. The polycrystallinenanoparticles indicated faster relaxationwith increasing size, whilethe decaying of monocrystalline counterparts was indifferent to thesize. We have demonstrated that the e-ph coupling decay timeconstant depends linearly on (Crystallite size/Linear dimension ofAg NPs)2 for polycrystalline Ag nanospheres, while monocrystallineAg nanocubes do not show any clear dependence on this ratio. Thisfact illustrates that e-ph coupling time could be used to evaluatecrystallinity and crystallite size in plasmonic metal nanoparticleswhen the size (surface area) of the nanoparticle is known.Declaration of competing interestThe authors declare that they have no known competingfinancial interests or personal relationships that could haveappeared to influence the work reported in this paper.AcknowledgmentsThe studies were performed within the LaSensA project carried599out under the M-ERA.NET 2 scheme (European Union’s Horizon2020 Research and Innovation Program, grant No. 685451) and co-funded by the Research Council of Lithuania (LMTLT), agreementNo. S-M-ERA.NET-21-2, the National Science Centre of Poland,project No. 2020/02/Y/ST5/00086, and the Saxon State Ministry forScience, Culture and Tourism (Germany), grant No. 100577922, aswell as from the tax funds on the basis of the budget passed by theSaxon state parliament.Appendix A. 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J Electron Mater 2006;35:1715e21.[36] Bigot J-Y, Halt�e V, Merle J-C, Daunois A. Electron dynamics in metallic nano-particles. Chem Phys 2000;251:181e203.[37] Peckus D, Tamulevi�cius T, Me�skinis �S, Tamulevi�cien _e A, Vasiliauskas A,Ul�cinas O, et al. Linear and nonlinear absorption properties of diamond-likecarbon doped with Cu nanoparticles. Plasmonics 2016;12:47e58.Dr. Domantas Peckus, senior researcher at the Institute ofMaterials Science of Kaunas University of Technology. Hehas been working with ultrafast transient differential ab-sorption spectroscopy of organic semiconductors,diamond-like carbon, graphene, and plasmonic materialsfor more than ten years. His research field covers ultrafastexcited state relaxation dynamics in organic semiconduc-tors, plasmonic metal nanoparticles, diamond-like carbonand graphene.Prof. Dr. Habil. Sigitas Tamulevi�cius, an academician ofthe Academy of Sciences of Lithuania, a full professor atthe Physics Department and Research Director of theInstitute of Materials Science of Kaunas University ofTechnology, obtained the Physics Engineer degree fromthe Moscow Engineering Institute of Physics (formerUSSR) in 1979 and a Ph.D. degree from the University ofVilnius in 1984. From 1990 to 1991, he was a postdoctoralresearcher at the Royal Institute of Technology (Stock-holm, Sweden). In 1994 he was Research Scholar at theMassachusetts Institute of Technology (USA). He hascofounded a spin-off company and co-authored approxi-mately 250 peer-reviewed publications in the field of vac-uum and plasma technologies and optical technologiesand spectroscopy with more than 2500 citations (h-index:26 (WoS)). He has received series of awards including theSoros Foundation Research Grant, (1993), Fulbright certif-icate (1997), National Award for Science (2000 and 2019),Honorary Professor of Southern Denmark University(2020), Laureate of Kaunas City Scientist Award (2017).During 2010e2012, he was a representative member ofLithuania in the EU FP7 committee “Nanoscience, nano-techno log ies , mate r i a l s and nove l produc t iontechnologies“.http://refhub.elsevier.com/S2352-8478(23)00157-0/sref3http://refhub.elsevier.com/S2352-8478(23)00157-0/sref3http://refhub.elsevier.com/S2352-8478(23)00157-0/sref3http://refhub.elsevier.com/S2352-8478(23)00157-0/sref3http://refhub.elsevier.com/S2352-8478(23)00157-0/sref3http://refhub.elsevier.com/S2352-8478(23)00157-0/sref4http://refhub.elsevier.com/S2352-8478(23)00157-0/sref4http://refhub.elsevier.com/S2352-8478(23)00157-0/sref4http://refhub.elsevier.com/S2352-8478(23)00157-0/sref5http://refhub.elsevier.com/S2352-8478(23)00157-0/sref5http://refhub.elsevier.com/S2352-8478(23)00157-0/sref5http://refhub.elsevier.com/S2352-8478(23)00157-0/sref5http://refhub.elsevier.com/S2352-8478(23)00157-0/sref5http://refhub.elsevier.com/S2352-8478(23)00157-0/sref6http://refhub.elsevier.com/S2352-8478(23)00157-0/sref6http://refhub.elsevier.com/S2352-8478(23)00157-0/sref6http://refhub.elsevier.com/S2352-8478(23)00157-0/sref7http://refhub.elsevier.com/S2352-8478(23)00157-0/sref7http://refhub.elsevier.com/S2352-8478(23)00157-0/sref7http://refhub.elsevier.com/S2352-8478(23)00157-0/sref7http://refhub.elsevier.com/S2352-8478(23)00157-0/sref8http://refhub.elsevier.com/S2352-8478(23)00157-0/sref8http://refhub.elsevier.com/S2352-8478(23)00157-0/sref8http://refhub.elsevier.com/S2352-8478(23)00157-0/sref9http://refhub.elsevier.com/S2352-8478(23)00157-0/sref9http://refhub.elsevier.com/S2352-8478(23)00157-0/sref9http://refhub.elsevier.com/S2352-8478(23)00157-0/sref9http://refhub.elsevier.com/S2352-8478(23)00157-0/sref9http://refhub.elsevier.com/S2352-8478(23)00157-0/sref10http://refhub.elsevier.com/S2352-8478(23)00157-0/sref10http://refhub.elsevier.com/S2352-8478(23)00157-0/sref10http://refhub.elsevier.com/S2352-8478(23)00157-0/sref10http://refhub.elsevier.com/S2352-8478(23)00157-0/sref11http://refhub.elsevier.com/S2352-8478(23)00157-0/sref11http://refhub.elsevier.com/S2352-8478(23)00157-0/sref11http://refhub.elsevier.com/S2352-8478(23)00157-0/sref11http://refhub.elsevier.com/S2352-8478(23)00157-0/sref12http://refhub.elsevier.com/S2352-8478(23)00157-0/sref12http://refhub.elsevier.com/S2352-8478(23)00157-0/sref12http://refhub.elsevier.com/S2352-8478(23)00157-0/sref12http://refhub.elsevier.com/S2352-8478(23)00157-0/sref12http://refhub.elsevier.com/S2352-8478(23)00157-0/sref13http://refhub.elsevier.com/S2352-8478(23)00157-0/sref13http://refhub.elsevier.com/S2352-8478(23)00157-0/sref13http://refhub.elsevier.com/S2352-8478(23)00157-0/sref13http://refhub.elsevier.com/S2352-8478(23)00157-0/sref14http://refhub.elsevier.com/S2352-8478(23)00157-0/sref14http://refhub.elsevier.com/S2352-8478(23)00157-0/sref14http://refhub.elsevier.com/S2352-8478(23)00157-0/sref15http://refhub.elsevier.com/S2352-8478(23)00157-0/sref15http://refhub.elsevier.com/S2352-8478(23)00157-0/sref16http://refhub.elsevier.com/S2352-8478(23)00157-0/sref16http://refhub.elsevier.com/S2352-8478(23)00157-0/sref16http://refhub.elsevier.com/S2352-8478(23)00157-0/sref16http://refhub.elsevier.com/S2352-8478(23)00157-0/sref17http://refhub.elsevier.com/S2352-8478(23)00157-0/sref17http://refhub.elsevier.com/S2352-8478(23)00157-0/sref17http://refhub.elsevier.com/S2352-8478(23)00157-0/sref17http://refhub.elsevier.com/S2352-8478(23)00157-0/sref18http://refhub.elsevier.com/S2352-8478(23)00157-0/sref18http://refhub.elsevier.com/S2352-8478(23)00157-0/sref18http://refhub.elsevier.com/S2352-8478(23)00157-0/sref19http://refhub.elsevier.com/S2352-8478(23)00157-0/sref19http://refhub.elsevier.com/S2352-8478(23)00157-0/sref19http://refhub.elsevier.com/S2352-8478(23)00157-0/sref20http://refhub.elsevier.com/S2352-8478(23)00157-0/sref20http://refhub.elsevier.com/S2352-8478(23)00157-0/sref20http://refhub.elsevier.com/S2352-8478(23)00157-0/sref20http://refhub.elsevier.com/S2352-8478(23)00157-0/sref21http://refhub.elsevier.com/S2352-8478(23)00157-0/sref21http://refhub.elsevier.com/S2352-8478(23)00157-0/sref21http://refhub.elsevier.com/S2352-8478(23)00157-0/sref22http://refhub.elsevier.com/S2352-8478(23)00157-0/sref22http://refhub.elsevier.com/S2352-8478(23)00157-0/sref22http://refhub.elsevier.com/S2352-8478(23)00157-0/sref23http://refhub.elsevier.com/S2352-8478(23)00157-0/sref23http://refhub.elsevier.com/S2352-8478(23)00157-0/sref23http://refhub.elsevier.com/S2352-8478(23)00157-0/sref23http://refhub.elsevier.com/S2352-8478(23)00157-0/sref24http://refhub.elsevier.com/S2352-8478(23)00157-0/sref24http://refhub.elsevier.com/S2352-8478(23)00157-0/sref24http://refhub.elsevier.com/S2352-8478(23)00157-0/sref24http://refhub.elsevier.com/S2352-8478(23)00157-0/sref24http://refhub.elsevier.com/S2352-8478(23)00157-0/sref25http://refhub.elsevier.com/S2352-8478(23)00157-0/sref25http://refhub.elsevier.com/S2352-8478(23)00157-0/sref25http://refhub.elsevier.com/S2352-8478(23)00157-0/sref25http://refhub.elsevier.com/S2352-8478(23)00157-0/sref26http://refhub.elsevier.com/S2352-8478(23)00157-0/sref26http://refhub.elsevier.com/S2352-8478(23)00157-0/sref26http://refhub.elsevier.com/S2352-8478(23)00157-0/sref26http:/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Size and crystallinity effect on the ultrafast optical response of chemically synthesized silver nanoparticles 1. Introduction 2. Experimental section 2.1. Materials 2.2. Analysis methods 3. Results and discussion 3.1. Properties of synthesized Ag NPs 3.2. Crystallinity analysis of Ag NPs 3.3. Nonlinear optical spectroscopy 4. Conclusion Declaration of competing interest Acknowledgments Appendix A. Supplementary data References