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Surface characterization of nanomaterials and nanoparticles: Important needs and challenging opportunities
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Image of FIG. 1.
FIG. 1.

(Color online) All “nanomaterials” publications identified by a Web of Science topic search (including: nanomaterials AND nanoparticles AND nanostructure) by year.

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FIG. 2.

(Color online) Percentage of publications in JVST A and B that include “nano” as a topic, ♦ as identified in the Web of Science and those focused on nanomaterials ▲.

Image of FIG. 3.
FIG. 3.

(Color online) (a) Schematic representation of the regenerative capability and oxidation state switching of ceria nanoparticles in an aqueous environment. The pictures of the bottles containing the nanoparticle suspension in DI water indicate color and oxidation state changes after different aging periods. (b) XPS Ce 3d spectra from particles removed from solution after one day and three weeks. Consistent with the optical measurements and solution color, the particles were mostly Ce after one day and mostly Ce after three weeks. When HO was added to the aged nanoparticles in solution, they switched from Ce back to Ce. Adapted with permission from Kuchibhatla , J. Phys. Chem. C , 14108 (2012). Copyright 2012, American Chemical Society.

Image of FIG. 4.
FIG. 4.

Three categories of synthesis and processing approaches used to produce ceria particles: high-temperature processing (a)–(c) (Refs. ), indirect heating of precursors or nanoparticles in solution (d)–(f) (Refs. ), and room-temperature synthesis of nanoparticles (g)–(i) (Refs. ). Adapted from Ref. .

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FIG. 5.

(Color online) Summary of the relationships among synthesis categories and biological impacts, showing that synthesis routes have a significant impact of biological outcomes. Adapted from Ref. .

Image of FIG. 6.
FIG. 6.

(Color online) XPS spectra from Cu oxide nanoparticles and clean PTFE reference: (a) XPS survey spectra with unexpected F lines; (b) High-energy resolution F 1s region, showing photoelectron peaks consistent with the presence of PTFE and CuF; (c) High-energy resolution spectrum C 1s region from clean PTFE, showing a photoelectron peak consistent with CF bonds in PTFE; and d) High-energy resolution C 1s, showing the presence of breakdown products from PTFE (e.g., CF, CF, CF-CHF, CHF-CHF, along with CH from advantageous surface contamination; a small amount of C-O and C = O is possible but not included in this peak fit). XPS identified the presence of F that was not expected or desired on these particles.

Image of FIG. 7.
FIG. 7.

(Color online) Sputter depth profiles of plasma processed p-OSG film before and after exposure to IPA. Based on comparison to the sputter rate for SiO the apparent thickness was approximately 157 nm with no IPA exposure and 205 nm after IPA exposure. From Gaspar , Surf. Interface Anal. , 417 (2005), Copyright 2005, John Wiley & Sons, Ltd.

Image of FIG. 8.
FIG. 8.

(Color online) (a) Image of filter and pump arrangement used to “flash dry” nanoparticles removed from aqueous solution for detailed. (b) Graph showing percent weight (moisture) loss as a function of drying time under −20 mm Hg vacuum (open circles). Without the vacuum assist, variable amounts of moisture often were retained in the collection of particles. As shown by the horizontal line, an additional 2 to 3% of moisture could be removed by storing the particles for 24 h in a desiccator filled with 50:50 anhydrous calcium sulfate and activated charcoal. Reprinted with the permission from Nurmi , J. Nanopart. Res. , 1937 (2010). Copyright 2010, Springer Science and Business Media.

Image of FIG. 9.
FIG. 9.

(Color online) Properties of nanoparticles that often introduce characterization challenges; also see Table I .

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FIG. 10.

(Color online) Ce 3d XPS spectra from ceria nanoparticles deposited on a Si substrate. Based on optical data, we would expect the ceria to be mostly Ce. The deposition process produced regions of high (a) and low (b) particle density. The XPS photoelectron spectrum from the higher density of particles differed (some Ce) from the lower density region (only Ce).

Image of FIG. 11.
FIG. 11.

(Color online) Changes in the Ce 3d XPS spectra collected as a function of time for (a) particles formed in an aqueous solution, containing some amount of organic (toluene) (after Ref. ), or (b) particles synthesized in a solution with no added organic. The 3–5 nm diameter particles produced in the solution with toluene (a) tended to become reduced upon x-ray exposure, while 10–14 nm particles formed in aqueous solution without added organics (b) tended to become oxidized upon x-ray exposure.

Image of FIG. 12.
FIG. 12.

(Color online) Schematic model for the carboxylic-terminated SAM on a flat gold surface that was used in the SESSA calculations. Reprinted with permission from Techane , Anal. Chem. , 6704 (2011). Copyright 2011, American Chemical Society.

Image of FIG. 13.
FIG. 13.

(Color online) For application of SESSA to predict the signal strengths from SAM-coated Au nanoparticles, the particles were modeled as multiconcentric cylinders, where each cylinder surface has an average photoelectron take-off angle of a. The XPS detector is positioned at 0° from the central axis of the AuNP. (a) The sphere is divided into nine concentric cylinders. (b) The end of each cylinder is modeled as a flat surface tiled relative to the axis of the spectrometer with infinite thickness of gold, and (c) the surface composition of each flat Au sample is weighted by its geometric factor then summed together to find the AuNP surface composition. Reprinted with permission from Techane , Anal. Chem. , 6704 (2011). Copyright 2011, American Chemical Society.

Image of FIG. 14.
FIG. 14.

(Color online) Schematic diagram showing the relationships of peak intensity ratios (a) and shell thickness' of nanoparticles based upon knowledge of the radius of the nanoparticles. Reprinted with permission from Shard, J. Phys. Chem. C , 16806 (2012). Copyright 2012, American Chemical Society.

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FIG. 15.

STEM dark field images of Ag-shell Au-core nanoparticles clearly show the presence of Au cores in most particles.

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FIG. 16.

(Color online) Illustration of the SFG liquid cell and experimental geometry. The cell body was made of Teflon. The nanoparticles were deposited on the flat bottom of a CaF 1 in. diameter hemisphere, which served as the optical window. The liquid flowed through ports sealed by Teflon plugs for studies not requiring the following liquid. The visible and infrared beams were propagated through the CaF hemisphere and overlap at the center of the flat surface of the CaF hemisphere. The SFG signals were collected in a reflective geometry.

Image of FIG. 17.
FIG. 17.

(Color online) SFG-VS spectra (2-cm-step scan) of (a) partially reduced ceria nanoparticles and (b) oxidized ceria nanoparticles in contact with CDCOH solutions. The vertical dashed lines reveal the shift of peak positions. The two major peaks are identified as bidentate bridging and chelating species of deprotonated acetic acid adsorbed on the particle surfaces. The relative ratio of the type of bonding varies for reduced and oxidized surfaces. There are two lines for each set of data related to the polarization combinations of the incident and SFG signals. The series ssp identifies s-polarizations for the SFG and visible beams and p-polarization for the IR beam, and ppp indicates p-polarizations for the SFG, visible, and IR beams.

Image of FIG. 18.
FIG. 18.

(Color online) H/C cross-polarization MAS NMR spectrum of 1-C-ethanol dosed onto a sample of titania (anatase) nanoparticles, exhibiting two bonding environments for the ethanol molecules reacted with the anatase surface. Data were obtained at a C resonance frequency of 188.657 MHz, and a H resonance frequency of 750.198 MHz with TPPM H decoupling after a 2 ms cross-polarization contact time, using a H 90° pulse of 6.5 s and a 5 s recycle delay. A total of 8192 transients were collected, and the data processing included 50 Hz of Lorentzian broadening.

Image of FIG. 19.
FIG. 19.

(Color online) Surface characterization of a PtFe alloy using 1 keV Ne LEIS to collect data from mildly sputtered and annealed surfaces. As indicated by the schematic model, no Fe is observed for the annealed surface, indicating the formation of a thin Pt skin, which is destroyed upon even very mild sputtering. Reprinted with permission from Stamenkovic , Nat. Mater. , 241 (2007). Copyright 2007, Macmillan Publishers Nature Publishing Group.

Image of FIG. 20.
FIG. 20.

(a TOF-MEIS spectrum of 6 nm Pt/V/Cu nanoparticles soft landed onto Si(100). The spectrum shows the composition of the particles, but the large peak associated with Si makes it difficult to detect low energy peaks from the particles, such as oxygen. (b) TOF-MEIS spectrum of 4 nm Pt/V/Cu nanoparticles soft landed onto RF plasma cleaned HOPG. The new peak appearing after deposition on the HOPG substrate was from Mo that was unintentionally deposited on the substrate during the cleaning process.

Image of FIG. 21.
FIG. 21.

(a XPS spectrum of HOPG placed in vacuum for 90 min. (b) XPS spectrum of HOPG RF plasma cleaned in Ar for 10 min. XPS data demonstrates that Mo was introduced into the soft landing process during the sputter cleaning of the HOPG substrate.

Image of FIG. 22.
FIG. 22.

(Color online) Comparison of the relative rates of application of a wide range of analysis tools to nanomaterials based on a Web of Science search as described in the text. The most widely used surface analysis tools are XPS and AFM. Techniques not previously discussed in this paper include: Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), ultraviolet–visible spectroscopy (UV-VIS), x-ray adsorption spectroscopy (XAS), extended x-ray adsorption fine structure (EXAFS), and x-ray absorption near edge structure (XANES).


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Challenges associated with characterization of nanoparticles.

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Characteristics of common surface analysis methods and types of information available for nanomaterials.

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Strengths and limitations of primary methods discussed in this review.

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Parameters used to calculate the shell thickness for Ag-shell Au-core nanoparticles using XPS signal strengths.

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Examples of measurements that can be used to collect or i real-time information about nanomaterials. The importance depends on the property of interest. Techniques not otherwise discussed in this paper include: attenuated total reflectance FTIR (ATR-FTIR), optical fluorescence, scanning x-ray transmission microscopy (STXM), and infrared-scattering scanning near-field optical microscopy (IR-sSNOM).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Surface characterization of nanomaterials and nanoparticles: Important needs and challenging opportunities