Supporting Information: Experimental Details and Spectral Analysis NaCl (99.999% trace metals basis), KCl (99.999% trace metals basis), NaNO 3 (99.995% trace metals basis), NH 4 Cl (99.998% trace metals basis), Na 2 SO 4 (99.99% trace metals basis), and (NH 4 ) 2 SO 4(99.999% trace metals basis) were purchased from Sigma-Aldrich. NaCl, KCl and Na 2 SO 4 were baked at 500 o C before use. For the aqueous solutions, proper amount of salts were dissolved in ultra-pure distilled water (with resistivity of 18.3 MΩ/cm, Thermo Fisher-EASYpure). Hydrophobic PTFE syringe filter (VWR) was then used to filter out residue particles from solutions. All glassware was soaked in concentrated H 2 SO 4 mixed with NoCromix, and then rinsed thoroughly with ultra-pure water.The details of our PS-SFVS setup have been described elsewhere. 1 We used collinear geometry with an incident angle of 45 o for the green (532nm, 20ps) and IR (3000-3800 cm -1 , 20ps) beams with input energies of ~300 µJ/pulse and ~120 µJ/pulse, respectively. The two beams overlapped in time and space at the sample surface, one focused to an area of 0.2 mm 2 and the other to 0.1 mm 2 . The SF output was collected after proper filtering by a gated detection system. The signal is proportional to χ eff

We demonstrate efficient terahertz (THz) modulation by coupling graphene strongly with a broadband THz metasurface device. This THz metasurface, made of periodic gold slit arrays, shows near unity broadband transmission, which arises from coherent radiation of the enhanced local-field in the slits. Utilizing graphene as an active load with tunable conductivity, we can significantly modify the local-field enhancement and strongly modulate the THz wave transmission. This hybrid device also provides a new platform for future nonlinear THz spectroscopy study of graphene.

The key factor in long-term use of batteries 9 is the formation of an electrically insulating solid layer that 10 allows lithium ion transport but stops further electrolyte 11 redox reactions on the electrode surface, hence solid 12 electrolyte interphase (SEI). We have studied a common 13 electrolyte, 1.0 M LiPF 6 /ethylene carbonate (EC)/diethyl 14 carbonate (DEC), reduction products on crystalline silicon 15 (Si) electrodes in a lithium (Li) half-cell system under 16 reaction conditions. We employed in situ sum frequency 17 generation vibrational spectroscopy (SFG-VS) with inter-18 face sensitivity in order to probe the molecular 19 composition of the SEI surface species under various 20 applied potentials where electrolyte reduction is expected. 21 We found that, with a Si(100)-hydrogen terminated wafer, 22 a Si-ethoxy (Si-OC 2 H 5) surface intermediate forms due to 23 DEC decomposition. Our results suggest that the SEI 24 surface composition varies depending on the termination 25

A phase transition within the ligand shell of core/shell quantum dots is studied in the prototypical system of colloidal CdSe/CdS quantum dots with a ligand shell composed of bound oleate (OA) and octadecylphosphonate (ODPA). The ligand shell composition is tuned using a ligand exchange procedure and quantified through proton NMR spectroscopy. Temperaturedependent photoluminescence spectroscopy reveals a signature of a phase transition within the organic ligand shell. Surprisingly, the ligand order to disorder phase transition triggers an abrupt increase in the photoluminescence quantum yield (PLQY) and full-width at half maximum (FWHM) with increasing temperature. The temperature and width of the phase transition shows a clear dependence on ligand shell composition, such that QDs with higher ODPA fractions have sharper phase transitions that occur at higher temperatures. In order to gain a molecular understanding of the changes in ligand ordering, fourier-transform infrared and vibrational sum frequency generation spectroscopies are performed. These measurements confirm that an order/disorder transition in the ligand shell tracks with the photoluminescence changes that accompany the order disorder ligand phase transition. The phase transition is simulated through a lattice model that suggests that the ligand shell is well-mixed, and does not 1 have completely segregated domains of OA and ODPA. Furthermore, we show that the unsaturated chains of OA seed disorder within the ligand shell.

The hydrogenation of crotonaldehyde by platinum nanoparticles supported on cobalt oxide was used as a reaction to probe the effect of the interface between the two materials on the activity and selectivity of the catalyst. Four potential products can be formed by this reaction: propylene, butyraldehyde, crotyl alcohol, and butanol. When Pt nanoparticles are supported on SiO 2 , an inert support, only propylene and butyraldehyde are formed. However, when Pt is supported on cobalt oxide, the alcohols make up roughly 40% of the total activity, indicating that cobalt oxide plays a pivotal role in the reaction, much like other active supports such as TiO 2 . To elucidate the mechanism of alcohol formation, in situ sum frequency generation vibrational spectroscopy (SFG) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were utilized to probe the reactant adsorption and intermediate formation and the chemical state of the materials under working catalytic conditions. The SFG data indicate that crotonaldehyde adsorbs on the oxide surface, likely through the aldehyde oxygen as well as on the Pt surface through the alkene group. AP-XPS results show that the surface of the Co 3 O 4 support becomes partially reduced under the reaction conditions and Pt exists in its metallic state. Taking these results together, we propose that the crotonaldehyde adsorbs at reduced oxide surface sites and that this adsorption mode is responsible for the production of alcohol products. A platinum nanoparticle density dependence study was also undertaken to change the abundance of interface sites and study their effect on the reaction. The selectivity between the two alcohol products was altered as a function of the Pt nanoparticle density: higher selectivity toward butanol and lower selectivity toward crotyl alcohol was obtained with increasing density, while propylene and butyraldehyde selectivities were constant with respect to density. On the basis of the data presented, we propose that butanol is preferentially formed at the metal−oxide interface, while crotyl alcohol is formed at oxide surface sites by reaction with spillover hydrogen.

Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities.

The present review discusses the current state of the art microscopic and spectroscopic characterization techniques available to study surfaces and interfaces under working conditions. Microscopic techniques such as environmental transmission electron microscopy and in situ transmission electron microscopy are first discussed showing their applications in the field of nanomaterials and catalysis. Next sum frequency generation vibrational spectroscopy is discussed, giving probing examples of surface studies in gaseous conditions. Synchrotron based X‐ray techniques are also examined with a specific focus on ambient pressure X‐ray photoelectron and absorption techniques such as near and extended X‐ray absorption fine structure. Each of the techniques is evaluated, whilst the pros and cons are discussed in term of surface sensitivity, spatial resolution and/or time resolution. The second part of the articles is articulated around the future of in situ characterization, giving examples of the probable development of the discussed techniques as well as an introduction of emerging tools such as scanning transmission X‐ray microscopy, ptychography, and X‐ray photon correlation spectroscopy.

In-situ X-ray Absorption Spectroscopy (XAS), Raman Spectroscopy, AFM and XPS have been used to investigate the effect of reactions occurring in aqueous electrolytes on the structure of a single-layer graphene produced by CVD. It was found that defects are readily and irreversibly produced by application of electrode voltages. The defects and the products were identified also by new features in the XAS spectra. Our findings show the poor stability of the CVD graphene, which could be a challenge in applications such as super-capacitors, fuel-cells, batteries and photo-catalysis.