Dear John Peter Isaqu,

According to the conventional Mott-Schottky (MS) model, contacts are expected to be ohmic when the work function of the metal is close to the HOMO or LUMO level of the semiconductor, depending on whether the semiconductor is p or n type.

The HOMO is the orbital of highest energy that is still occupied, so

energetically it is the easiest to remove electrons from this orbital. This could be simply donating electron density to form a bond (act as a Lewis base) or it could be oxidation.

The LUMO is the lowest lying orbital that is empty, so energetically it is the

easiest to add more electrons into this orbital…Lewis acid; reduction.

It isn’t always the HOMO and/or LUMO involved in chemical reactivity.

Symmetry plays a role, too. If the HOMO or LUMO isn’t of the correct

symmetry, it might be the HOMO-1 or the LUMO+1 that is involved in the

reaction.

For organic semiconductors, HOMO represents the energy required to

extract an electron from a molecule, which is an oxidation process, and LUMO is the energy necessary to inject an electron to a molecule, thus implying a reduction process. These processes can be measured using

cyclic voltammetry method by measuring the redox potentials Ered and Eox.

Ferrocence is used as a known reference to calculate the energy of the HOMO and LUMO levels, including the ferrocene value of -4.4 eV. The energy levels were calculated using the following empirical Bredas et all equations:

E (HOMO) =-e [Eoxonset + 4.4], (1)

E (LUMO) =-e [Eredonset + 4.4] (2)

The energy band configuration of photocatalysts has crucial effect on their properties, such as the wavelength of excitation, redox ability of the photogenerated holes and electrons, and the separation efficiency of the charge carriers. These energies are estimated by applying the Mullikan electronegativity theory for atoms using Eqs. (a) and (b) :

EVB = X – Ee + ‏ 0.5Eg  ... (a)                                                                                                           

ECB = EVB − Eg           ... (b)

where,

EVB & ECB present valence band (VB) and conduction band (CB) edge potentials, respectively;

Ee is the energy of free electrons on the hydrogen scale ca. 4.50 eV;

χ is electronegativity of the semiconductor expressed as the geometric mean of the absolute electronegativity of the constituent atoms.

HOMO is level cyclic voltammetry,

Eg is fluorescence,  &

LUMO = HOMO - Eg

The HOMO and LUMO levels approximated from CV as well as the band

gap (optical and the one obtained from CV)

With Best Wishes,

Samir G. Pandya

Dear John Peter Isaqu,

According to the conventional Mott-Schottky (MS) model, contacts are expected to be ohmic when the work function of the metal is close to the HOMO or LUMO level of the semiconductor, depending on whether the semiconductor is p or n type.

The HOMO is the orbital of highest energy that is still occupied, so

energetically it is the easiest to remove electrons from this orbital. This could be simply donating electron density to form a bond (act as a Lewis base) or it could be oxidation.

The LUMO is the lowest lying orbital that is empty, so energetically it is the

easiest to add more electrons into this orbital…Lewis acid; reduction.

It isn’t always the HOMO and/or LUMO involved in chemical reactivity.

Symmetry plays a role, too. If the HOMO or LUMO isn’t of the correct

symmetry, it might be the HOMO-1 or the LUMO+1 that is involved in the

reaction.

For organic semiconductors, HOMO represents the energy required to

extract an electron from a molecule, which is an oxidation process, and LUMO is the energy necessary to inject an electron to a molecule, thus implying a reduction process. These processes can be measured using

cyclic voltammetry method by measuring the redox potentials Ered and Eox.

Ferrocence is used as a known reference to calculate the energy of the HOMO and LUMO levels, including the ferrocene value of -4.4 eV. The energy levels were calculated using the following empirical Bredas et all equations:

E (HOMO) =-e [Eoxonset + 4.4], (1)

E (LUMO) =-e [Eredonset + 4.4] (2)

The energy band configuration of photocatalysts has crucial effect on their properties, such as the wavelength of excitation, redox ability of the photogenerated holes and electrons, and the separation efficiency of the charge carriers. These energies are estimated by applying the Mullikan electronegativity theory for atoms using Eqs. (a) and (b) :

EVB = X – Ee + ‏ 0.5Eg  ... (a)                                                                                                           

ECB = EVB − Eg           ... (b)

where,

EVB & ECB present valence band (VB) and conduction band (CB) edge potentials, respectively;

Ee is the energy of free electrons on the hydrogen scale ca. 4.50 eV;

χ is electronegativity of the semiconductor expressed as the geometric mean of the absolute electronegativity of the constituent atoms.

HOMO is level cyclic voltammetry,

Eg is fluorescence,  &

LUMO = HOMO - Eg

The HOMO and LUMO levels approximated from CV as well as the band

gap (optical and the one obtained from CV)

With Best Wishes,

Samir G. Pandya

Thank you Dr. Samir G. Pandya to share the valuable suggestion.