Mohammadreza Khodabakhsh

Koc University · Department of Chemistry

Lets say we have a substrate without any background noise which is coated plasmonic nanomaterials (Au or Ag N.P) just like the schematic image below. Since In Raman measurements 3 lasers with different wavelengths (532nm/633nm/780nm) can be used, based on absorption wavelength of both organic analyte and plasmonic nanoparticles, Does absorption of Light by N.P can contribute to the SERS enhancement? which of the following conditions is ideal for SERS measurement and can give us better peak enhancement ?

Condition 1: wavelength of laser should be close to absorption wavelength of Analyte

Condition 2: wavelength of laser should be close to absorption wavelength of Plasmonic Nanoparticles

Condition 3: it is better that both analyte and N.P have similar absorption wavelength

Condition 4: There is no overlap of absorption wavelength of analyte and N.P

In order to synthesize silver nanoparticles with specific shapes such as triangular or decahedron, we usually add capping agents such as PVP or citrate to the solution. for higher concentration solution the amount of these organic compounds should be increased inevitably. After drying one droplet of the final solution, thick layer of organic materials covers the nanoparticles (as shown in the attached figure).

I have seen that in many papers people suggest using "dialysis bag" or "centrifuge tube with filtration membrane" but both of these techniques may destroy unstable nanoparticles (specially triangular shaped N.Ps). Do you have any suggestion for getting rid of any organic materials form the final solution with out sacrificing the nanoparticles?

Aurivillius layered perovskites are consist of positively charged [Bi₂O₂]²⁺ interlayers, separating negatively charged Perovskite sheets. By performing acid washing , we can selectively wash away [Bi₂O₂]²⁺ layers and exfoliated the layered structure into single perovskite nanosheets. In the case of my sample with [Bi₂O₂][SrTa₂O₇] formula, evaluation of Tantalum (4f) XPS bands before and after exfoliation step shows small peak shift to lower bonding energy. On the other hand and according to literature, standard separation value for 4f_7/2 and 4f_5/2 bands of Tantalum should be 1.91 eV. In the case of our sample, when we have [Bi₂O₂]²⁺ sheets between [SrTa₂O₇]^2- perovskite sheet, energy separation of 4f_7/2 and 4f_5/2 is equal to 2.98 eV. However, after removing [Bi₂O₂]²⁺ layers, energy separation of 4f_7/2 and 4f_5/2 for [SrTa₂O₇]^2- perovskite has become 1.9 eV. (shown in the attached image)

Is it possible to generalize chemical stability of group of materials versus the others? For instance, can we arrange oxides, fluorides and haloids in an order from most to least chemically stable ?

The term "Chemically stable" sounds confusing too. When we say a material is chemically stable, are we including factors such as Temperature, Pressure, pH of medium, etc all at the same time ? I'm asking this question because I saw in a reference that they said Oxides are more chemically stable than Fluorides. While, in another paper the exact opposite claim was mentioned without any condition explanation.

"Phonon energy" is typically used to describe the resonance energy of lattice vibrations. As the host phonon energy decreases , we need more number of phonons to bridge the energy gap between excited state and ground state. Consequently, in host materials with low phonon energy, chance of radiative relaxation (upconversion efficiency) increases by lowering probability of non-radiative relaxation.

In order to decide the best host for upconversion measurements among several candidates, lattice phonon energy of the material should be measured (or calculated). So the question is that whether it's value should be calculate theoretically or is there any experimental technique to directly/indirectly measure this value ?

For example, should "Cerium oxide" be used instead of "Cerium nitrate"?

Upon doping of some elements in materials like BiFeO3 we see dramatic change in Ferroelectric properties of our material, like reduction in Transition Temperature. If we say that Bismuth has "6s2" lone pair, How can we explain that Tc reduction by stereochemical activity of Lone Pair ? Does this "Lone pair" have the ability to impact on volume distortion in our structure?

I am trying to coat "Bismuth Ferrite" solution (0.5 Molar) on "Nb doped Strontium Titanate". The solution is prepared by Sol-Gel method, and "Ethylene glycol" and "Acetic acid" are used as solvents. After cleaning the surface of "SrTiO3" by Distilled water and acetone and drying it by "Nitrogen Gas". I used spin coating to coat only single drop of the solution on the surface of the substrate, but during and after the calcination there are always tiny air bubbles on the surface of the sample (only visible in higher magnification).