Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO2)n Cluster

doi:10.21203/rs.3.rs-975265/v1

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Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO₂)_n Cluster

https://doi.org/10.21203/rs.3.rs-975265/v1

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The structural and electronic properties of pure and nitrogen-doped TiO₂ nanoclusters are investigated using density functional theory (DFT) with vibrational modes. We performed numerical simulation using two methods based on theories at the Quantum Espresso/PBE and Gaussian/B3LYP/631G (d) levels. The properties of a single nitrogen-doped (TiO₂)_n nanocluster are also computed in this study. In both cases, interstitial and substitutional Nitrogen doping at all accessible sites was examined. For the experiment, Supersonic Cluster Beam Deposition (SCBD) was used to create pure and nitrogen-doped TiO₂ films of nanocluster assemblies. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and Raman techniques were used to characterize these samples. The binding energies (Np, O2s, Ti 2p1/2, and Ti 2p3/2) of N-doped TiO₂ were estimated using XPS spectral results. The UV-Vis measurement confirmed the previously stated reasoning about the quantum size effect on the band gap of the pure and nitrogen doped TiO₂ nanocluster. The theoretical vibrational modes frequencies are calculated using the B3LYP/6-31G (d) functional via the Gaussian16 code's implementation algorithm. The good agreement between simulation and experimental results implies that a significant advantage of interstitial over substitutional positions. N-O vibration modes appeared in interstitial doped TiO₂, and each vibration was dependent on a different cluster structure.

Electronic Materials and Devices

Electrical Engineering

Magnetics Materials and Devices

N doping

(TiO2)nnanocluster

interstitial

DFT

vibrational mode

Nitrogen doped titanium dioxide is gaining popularity due to its potential as a material for environmental photo catalysis. In the last year, numerous theoretical and experimental studies on doped TiO₂ have been published. Controlling the size of the nanostructure, on the other hand, is both a problem and a pipe dream for many researchers. The following papers, published in recent years, investigate the physical and chemical properties of TiO₂ nanoclusters experimentally and theoretically. I. Shyjumon et al. (Shyjumon et al. 2006) created titanium clusters on a silicon substrate using magnetron sputtering, followed by aggregation in an argon gas flow. Clusters typically range in size from 8 to 13 nm. M. Drabik et al. (Drabik et al. 2011) investigated the design and fabrication of titanium nanocluster films using a magnetron-sputtering gas-aggregation cluster source. S. Srivastava et al.(Srivastava et al. 2014) successfully manufactured and collected size-selected TiO₂ nanoclusters at room temperature on three distinct substrates: Si, glass, and quartz. They used a special magnetron-sputtering source followed by a quadrupole mass filter. Transmission electron microscopy revealed that NCs larger than a primary size (eight nanometers) have a translucent center with a shapeless shell. M. Chiodi et al.(Chiodi et al. 2012) used Supersonic Cluster Beam Deposition (SCBD) to create co-doped Cr-N TiO₂ films with significantly improved absorbance in the visible and near infrared. The Cr and N dopants are involved in substitution sites. According to the spectroscopic data, the general impact of N and Cr substitution co-doping results in the presence of new electronic states at the highest point of the Valence band (VB). Many researchers have reported TiO₂ clusters in theory: DFT was used by A. Arab et al., (Arab et al. 2016) to investigate the electronic structure and reactivity of (TiO₂)_n (n=1-10) nano-clusters. The binding energy per atom, second-order energy difference, and fragmentation energy were all used to discuss cluster stability.

M. Fronzi et al. (Fronzi et al. 2016) demonstrated the effect of TiO₂ nanocluster alteration providing valuable guidelines for further developing TiO₂ photo catalytic (UV and visible light) movement, which will be useful for oxidative degradation of organic pollutants or CO₂ reduction by utilizing combined DFT recreation and experimentation. The optical absorption spectra of (TiO₂)_n (n = 1-20) nanoclusters and (n= 35, 84) nanoparticles have been computationally investigated in gas phase and in water as solvent by A. R. Valero et al., (Valero et al. 2018) based on the analysis of the frequency-dependent dielectric function in the independent particle approximation within the framework of the density functional theory. Villanueva et al. (2015)(Salazar-Villanueva et al. 2015) used DFT to investigate the underlying and electronic properties of Ti₉XO₂₀ (X = Ti, C, Si, Ge, Sn, and Pb) clusters in order to provide an alternative to experimental strategies for developing new materials with high synergist applications. Kroes and Qu et al.(Qu and Kroes 2006) investigated the electronic structure and steadiness of both nonpartisan and independently charged (TiO₂)_n groups with n=19 using the DFT with B3LYP/LANL2DZ strategy. The steady construction of TiO₂ nanoclusters resulted in a general frame with a minimal design and a couple of Ti–O terminal bonds. A few researchers have also theoretically and experimentally focused on the band gap of TiO₂ as a function of particle size. S. Monticone et al (Monticone et al. 2000). investigated the TiO₂ anatase crystalline phase and discovered that the band gap energy did not vary with size down to 2R=1.5 nm. According to UV–vis absorbance measurements, Lin et al.(Lin et al. 2006) believe there is no variation in band gap energy with size. Besides that, they used the MOCVD method to create TiO₂ crystalline with varying particle sizes (particle size ranged between 12 and 29 nm). The band gap of TiO₂ nanoparticles varies with primary particle size. M. Karkare (Karkare 2014) proved that the band gap increased with particle size. With decreasing particle size, the absorption edge shifted to higher energy (blue shift). They demonstrated that a smaller crystallite size (8.4–10.6 nm) should have a larger band gap of 3.4 eV. S. Mandal et al. (Mandal et al. 2019) investigated the optical band gap of these nano composites for pure TiO₂, using 3.7 eV as a reference.

In this study, Ab initio calculations are performed and electronic properties for pure N-doped TiO₂ are investigated in order to assess the change in properties with respect to the N content. The formation energies of pure and N-doped TiO₂ were computed using two different DFT models: Quantum Espresso/PBE and Gaussian/B3LYP/6-31G (d). The results were analyzed and compared to the experimental. Based on these theoretical observations, pure and N-doped TiO₂ samples synthesized using Supersonic Cluster Beam Deposition (SCBD) were characterized, with particular emphasis on the analysis of particle size by AFM (Stylus profilometer KLA Tencor P6), band gap energy values obtained by UV–vis spectroscopy (Agilent Cary 100 UV-Vis spectrophotometer), and the chemical composition analysis by XPS (Leybold LHS 10/12 ) ,and the vibration mode by Raman spectroscopy.

2.1. Experimental: Synthesis of nitrogen-Doped TiO₂ cluster

SCBD was employed to prepare pure and nitrogen-doped TiO₂ nanostructured films on silicon and quartz substrates, using a Pulsed Micro-Plasma Cluster Source (PMCS) from LGM laboratory at CIMaINa (Università degli Studi di Milano)(Barborini et al. 1999; Milani et al. 2001; Piseri et al. 1998): a pulsed electric-discharge between the target-material (Ti) - as the cathode - and a second electrode – as the anode - vaporizes the target via sputtering ablation. The discharge is confined to a micro-plasma region at the cathode surface through controlled injection of a process gas (inert: typically He or Ar for metallic clusters, or an oxygen-containing mixture for oxide nanoparticles) with a pulsed solenoid valve. precise control of the gas mixture allows fine tuning on the composition of the nanoparticles that are formed upon condensation of the vapor(D’Elia et al. 2020): for N-doped TiO₂, 99.80% (Ar), 0.015% (O₂), and 0.05% (N₂) were used. The thus-formed nanoparticles suspension is evacuated from the PMCS via a nozzle, generating a seeded supersonic beam of nanoparticles that can be deposited on any substrate intercepting the beam along the propagation direction.

2.2 Theoretical: Computational methods (DFT)

To obtain the optimized structure, the configuration is geometrically fully relaxed using the DFT model. To compute the electronic and vibrational properties of pure and N-doped TiO₂, we used quantum chemical calculations DFT (Gaussian 16 program package) and Quantum ESPRESSO. The PBE functional(Giannozzi et al. 2009), ultra soft Vanderbilt pseudopotentials(Kresse and Joubert 1999), and a plane-wave (PWs) basis set with a cut off of charge density (30 Ry and 300 Ry) were used to perform structural relaxations with the code Quantum ESPRESSO simulation package. We used Gaussian 16 (Frisch et al. 2020) with hybrid B3LYP(Lee et al. 1988) functional basis sets 6-31G(d) to compute the electric and vibrational modes other than plane waves (PWs). Fig. 1 depicts an optimized structure of (TiO₂)_n :Ti₉O₁₈ and Ti₂₈O₅₆. It was chosen from among the structures determined by global optimization using interatomic potentials in recent works(Lamiel-Garcia et al. 2017).

3.1 Bond lengths and formation energies: substitutional and interstitial case of (Ti ₂₈ O ₅₅ N ₁ ) and TiO ₂ (Ti₂₈O₅₆N₁) cluster in different configuration

When the nitrogen substituents incorporate into the TiO₂, the formation energy altered function of impurity position and Ti–N bond lengths are of course altered compared to the pristine Ti–O bonds. Several additional publications have noted the effect of impurity location on TiO₂ electronic characteristics. Giovanni Di Liberto et al. (Di Liberto et al. 2019) investigated nitrogen doping that is exposed to (001)-(101) Anatase TiO₂ Surfaces and discovered that N001 is the most stable doping arrangement, with the nitrogen atom on the (001) side of the interface. kakil et al. (Kakil et al. 2020) demonstrated that nitrogen doping in TiO₂ anatase is subsurface depth dependent in substitution and interstitial doped forms, and that nitrogen impurity locations are dependent on nanocrystal facet (Kakil et al. 2021). They also investigated the formation of nitrogen impurity in TiO₂ nanoparticles and how the mid-gap state of TiO₂ nanocrystal is generated, as well as how the nitrogen impurity locations depend on facet of nanocrystal.

Figure 2 shows the optimal structure of Ti₂₈O₅₅N₁ obtained by inserting one substitution N atom in an O lattice location in various configurations using DFT/PBE. Each number in Table 1 corresponds to the formation energies of nitrogen doped TiO₂ (Ti₂₈O₅₅N₁) at various sites. Ns-Cl.n Ns is for Nitrogen substitution doped, and Cl.n stands for impurity at various positions in the cluster, with n ranging from 1 to 9, corresponding to each location in Figure 2. Equation 1 was used to calculate the formation energies of nitrogen substitution sites.

$${E}_{f}={E}_{1N nanocluster}\text{-}{E}_{nanocluster}+{\frac{1}{2}E}_{{O}_{2}}-{\frac{1}{2}E}_{{N}_{2}} \left(1\right)$$

Table 1 shows the formation energy and defect gap of a substitution-N-doped (Ti₂₈O₅₅N₁) nanocluster at various positions. The formation energy varied from 5.321-4.685 eV, whereas the defect energy varied from 1.314 to 0.696 eV. As seen in (Ns-Cl6, Ns-Cl7, Ns-Cl8, and Ns-Cl9), the nitrogen atom inside the cluster has lower formation energy than the nitrogen atom outside the cluster. The formation energy of cluster Ns-Cl9 is 4.685, which is lower than the formation energy of another cluster impurity position. The electronic structure of a cluster is affected by the location of nitrogen impurities. According to Table 1, the energy differences are around 0.625 eV, although in the case of clusters, the majority of atoms are at the surface and Atom clusters have considerably different physical and chemical properties than bulk solids of the same composition. The discrepancy arises from the fact that a high proportion of their component atoms are situated at the surface. Fig. 4 depicts the influence of impurity position on bond-length change of various substitution positions of nitrogen dopants in the (Ti₂₈O₅₅N1) cluster.

We doped TiO₂ in four distinct sites for nitrogen to explore interstitial N doping, as illustrated in Fig. 3. Equation 2 is used to compute the formation energy.

$${E}_{f}={E}_{1Nnanocluster}\text{-}{E}_{nanocluster}-{\frac{1}{2}E}_{{N}_{1}} \left(2\right)$$

The formation energy, defect gap, and N-O bond length of interstitial -N-doped (Ti₂₈O₅₆N₁) clusters at different positions are shown in Table 2. The influence of impurity position on defect gap and the N-O bond produced in the case of interstitial have different lengths depending on impurity position. Because of the low formation energy, interstitial is more beneficial than substitution in terms of impurity position. We studied (Ni-Cl.4) for the electronic structure investigation because it has a lower formation.

Table 1

Formation energy (E_f) and the defect gap (E_IL -E_{V B}) of substitutional-N-doped (Ti₂₈O₅₅N₁) nanocluster ata differentposition.

Ti₂₈O₅₅N₁	E_f[eV]	E_IL -E_{V B}[eV]
Ns-Cl.1	5.321	1.0456
Ns-Cl.2	5.152	0.977
Ns-Cl.3	5.125	0.696
Ns-Cl.4	5.070	1.041
Ns-Cl.5	5.080	1.326
Ns-Cl.6	5.018	1.259
Ns-Cl.7	5.052	0.965
Ns-Cl.8	4.869	1.270
Ns-Cl.9	4.685	1.314

3.2 Electronic properties of pure Ti₂₈O₅₆ and nitrogen doped (Ti₂₈O₅₆N₁)

The density of State (DOS) was computed using Gaussian16 software to investigate the electrical characteristics of the examined structures. Any material's electronic density of states provides enough information to comprehend its electronic characteristics fully. A density-of-state (DOS) diagram can be used to visualize the energy level distribution (Gui et al. 2019). TiO₂ and N-doped TiO₂ ,nanocluster wave function was calculated using Density Functional Theory (DFT), B3LYP at 6-31G(d) basis set. Fig. 5 compares the density of states (DOS) for pure (Ti₂₈O₅₆) and nitrogen doped (Ti₂₈O₅₅N₁) Nano clusters. Significant impurity states are introduced into the gap as a result of doping. Following the addition of one nitrogen, the states emerge at the top of the conduction band. N's action defines the creation of the ionic N–O bond as a p dopant. N (p) helps to narrow the gap by producing the valence and conduction bands.

After the Nitrogen atom was inserted into the TiO₂ structure, the HUMO-LUMO gap was reduced from 3.772 eV to 2.389 eV. A significant change can be seen in these graphs. UV absorption spectra, which will be examined in the next section, revealed this behavior. Because the band gap of the Quantum Espresso/PBE-GGA method was underestimated, we employed the Gaussian/B3LYP approach. The gap energy reduces from 2.826 to 1.257 eV calculated by Quantum Espresso /PBE-GGA, as shown in Table 3. The electronic band and defect band in [eV] for pure Ti₂₈O₅₆ and nitrogen doped TiO₂ (Ti₂₈O₅₆N₁) were calculated using both Quantum Espresso /PBE-GGA and Gaussian/B3LYP/6-31G(d) approaches, and the results were compared to previous literature(Cao et al. 2021; Lundqvist et al. 2006; Oprea and Gîrțu 2019; Persson et al. 2000; Selli et al. 2017).

Table 2

Formation energy (E_f), the defect gap (E_IL -E_{V B}),and N-O bond length of interstitial -N-doped (Ti₂₈O₅₆N₁) cluster at a different position.

Ti₂₈O₅₆N₁	E_f[eV]	E_IL -E_{V B}[eV]	N-O[pm]
Ni-Cl.1	3.910	1.617	137
Ni-Cl.2	3.820	0.914	133
Ni-Cr.3	3.527	1.291	135
Ni-Cl.4	2.9	1.253	134

Table 3

TheBandgap and defect gap inunit [eV] for pure Ti₂₈O₅₆ and nitrogen doped TiO₂ (Ti₂₈O₅₆N₁) utilizing Q.E espresso /PBE-GGA and Gaussian/B3LYP /6-31G (d)methods.

Cluster	Method	Band gap [eV]	Defect band gap[eV]
Ti₂₈O₅₆	PBE	2.826^{[this work]}	1.257
Ti₂₈O₅₆	B3LYP/6-31G(d)	3.772^{[ this work]}	2.893
Ti₂₈O₅₆	B3LYP/VDZ//PW/SZ	3.67^[27]
(TiO₂)₁₀₁·6H2O	DFT(B3LYP)	3.81^[28]
Ti₂₄O₅₀H	B3LYP/LANL2DZ	3.8^[29]
(TiO₂)₁₀₁·6H2O	DFTB	3.2^[28]
Ti₂₉O₅₈	Gaussian03/B3LYP/6311G	3.33^[30]
Ti₃₈O₇₆	INDO/S-CI	3.5^[31]

3.3. Surface morphology of N-doped TiO₂ nanocluster

Atomic force microscopy AFM was used to analyze the surface morphology of nanostructured Nitrogen-doped TiO₂. Fig. 6 shows the surface morphology of the N doped TiO₂ cluster layer formed on silicon and a histogram of particle size distribution. As seen in the histogram, the clusters appear to be almost spherical, with an average lateral size of less than (2 nm) and some of them having an average size of 5 nm. The smallest visible grains (2 nm) are primeval clusters created in the source, while larger grains produce smaller clusters aggregating and coalescing.

3.4. X-ray Photoelectron Spectroscopy (XPS)

XPS analysis was used to analyze the chemical composition and chemical state of the TiO₂ nanoclusters. Fig. 7 shows the XPS spectra of N-doped TiO₂, where the peaks at 401.7, 459, 464, and 530.17 eV correspond to the binding energy of N1s, Ti2P_1/2, Ti2P_3/2, and O 1s peaks. The N1s reveal the presence of nitrogen in the nanostructured material (inset Fig. 7). The peaks are in the range (396-404 eV) seen by numerous other writers, although Di Valentin et al (Di Valentin et al. 2007) detected a peak at higher binding energy (400 eV). This peak at this energy represents the interstitial-site nitrogen (Ti–O–N) in which the N atoms are bound to lattice oxygen atoms. This peak at this energy represents the interstitial-site nitrogen.

3.5. Optical properties of the pure and nitrogen-doped TiO₂

A UV- visible absorption spectrum was performed to analyze the optical absorbance of pure and nitrogen-doped TiO₂ nanoclusters. If the semiconductor size is smaller than the Bohr radius of the excited state, the quantum confinement effect is expected, and the absorption edge will be shifted to higher energy. More study is being done on the quantum confinement effect of TiO₂ as well as direct and indirect band gaps. Yin Zhao and Chunzhong Li et al (Zhao et al. 2007)found that the band gap of as-prepared TiO₂ nanoparticles is 3.28 eV, which is somewhat higher than the value of 3.2 eV for bulk TiO₂ due to the quantum size impact of the present TiO₂. In anatase TiO₂ nanoparticles, K. Madhusudan Reddy et al (Madhusudan Reddy et al. 2003) indicated that the direct, rather than indirect, transition is more beneficial, as shown in Table 4. Fig. 8 shows the UV–vis spectra of pure and Nitrogen-doped (TiO₂) nanostructures. The plots of (α.hν) ² vs the energy level of the absorbed light are shown in the inset Fig. 8. The Wood and Tauc equation, which is defined as follows, is used to estimate the band gap value.

Table 4

Experimental Band Gap in unit [eV] forpure and Nitrogen-doped TiO₂compared with previous works.

Nano composites	Size [nm]	Bandgap [eV]	Ref
TiO₂ nanocluster N-TiO₂ nanocluster	2-5 2-5	3.75 3.56	This work This work
Quantum dot	5	~3.76	[37]
Quantum dot	3-7	3.79	[38]
Nanoparticle	11	3.4	[12]
Nanoparticle N-doped nanoparticle	10 10	3.35 3.05	[35]
Nanoparticle	20	3.75	[13]

${\alpha }\text{h}{\nu }={\text{K}(\text{h}{\nu }-{\text{E}}_{\text{g}})}^{\text{n}}$ ( 3)

Where K, hv, and Eg are constant, photon energy, and optical band gap, respectively. n is equal to 1/2 for allowed direct optical transitions, and α is the absorption coefficient. The band gap values were determined by extrapolating the linear region of the plot to hν = 0. From the Tauc plots of (αhν)² versus hν. The direct band gap of TiO₂ nanopartical observed (Jia et al. 2018; Karkare 2014; Mahmoud et al. 2021; Mandal et al. 2019) With the addition of nitrogen atom, the band gap decreased from 3.75 to 3.560 eV, and the results were summarized in Table 4. It displays the experimental measurements of band gap in [eV] units and compares them with previous works (Gnanasekaran et al. 2015; Javed et al. 2019; Jia et al. 2018; Karkare 2014; Mandal et al. 2019). Because its p states contribute to band gap narrowing by mixing with O 2p and N (p) states, the N atom's lowered band gap was the most effective. The excitation wavelengths were found by DFT (B3LYP/6-31G(d)) for pure and nitrogen-doped TiO₂ (350.96 and 411.00 nm), respectively.

3.6. Experimental and theoretical DFTB3LYP/6-31G (d) investigation of Raman spectra for pure and nitrogen doped TiO₂

3.6.1. Raman analysis

The following representation for optical vibrational modes at the Γ point of bulk TiO₂ was derived from a group theoretical analysis:

A_1g + 1 A_2u + 2 B_1g + 1 B_2u + 3 E_g + 2 E_u

It consists of three Raman active modes (A_1g+ 1 B_1g+3 E_g), two modes are infrared active (1 A_2u+2 E_u), and one mode (1 B_2u) is inactive in both Raman and infrared(Ohsaka 1980). The vibration mode of TiO₂ was impacted by size, annealing, architectures, and other factors; Xu et al. (Xu et al. 2001) explained the variation in the Raman bands with a phonon confinement model based on the Heisenberg uncertainty principle. They showed that the phonon becomes increasingly confined within the particle and the phonon momentum distribution as particle size decreases.

Flavio Della Foglia et al. (Della Foglia et al. 2009) synthesized the TiO₂ nanostructured film via (SCBD). Raman spectroscopy indicated no crystalline structure after annealing at 200^oC, indicating that the film is predominantly amorphous. They also demonstrated that the shape of nanostructured TiO₂ films could improve annealing for photocatalytic applications. Hengzhong Zhang (Zhang et al. 2008) reported a combination of experimental and computational modeling to investigate amorphous titanium made up of 2 nm TiO₂ nanoparticles. The nanoparticles contain a severely deformed shell and a stretched anatase-like core, according to the researchers. The weak Raman scattering in these films is attributed to the low phonon density of states in the amorphous phase, as seen in Fig. 9, which exhibits Raman spectra of pure and Nitrogen-doped TiO₂ clusters without annealing. The no observed Raman bands in an amorphous solid are no longer related to traveling waves or wave vectors, as are no longer phonons.

3.6.2. Theoretical vibrational properties of pure and N-doped (TiO2)n by DFT / B3LYP/6-31G(d)

Ogata et al. (Ogata et al. 1999) employed modified variable charge interatomic potential to examine the structural and physical features of nano size TiO₂ clusters of 1050 and 672 atoms at 100 K using molecular dynamics (MD) simulations. We reveal the Ti–O bonding characteristics that play a key role in replicating macroscopic and microscopic values with accuracy comparable to that of first-principles computations. Kulbir Kaur Ghuman et al.(Ghuman et al. 2013) investigated the vibrational characteristics of rutile supercells and rutile and amorphous TiO₂ nanoparticles using the Matsui and Akaogi rigid ion model with effective charges on Ti and O atoms. They demonstrated that the phonon bandwidth and dispersive character of optical phonon modes in higher frequency ranges agree with experimental results. However, the calculated and experimental findings are within 15% of each other in the intermediate energy range, while the calculated results are higher than the experimental values in the lower energy range.

In a (TiO₂)_n cluster, if n changes, the majority of physical properties change as well. The clusters were constructed by Brandon Bukowski et al. (Bukowski and Deskins 2015) with n = 1, 3, 5, 8, and 15 total atoms, or 3, 9, 15, 24, and 45 total atoms, respectively. For each cluster size, there are a number of possible structural isomers. When a result, as cluster sizes get larger, atoms tend to adopt higher coordination, eventually embracing bulk coordination with the correct cluster size.

The vibrational modes of Ti₉O₁₈and Ti₂₈O₅₆ clusters were calculated in this study. Except for Ti₂O₄ spectral investigation (Majid and Bibi 2017), none of the above physical attributes have been explored by any other researcher.

Because there are multiple coordinates of Ti (1Ti, 2Ti, 3Ti....) for any given cluster size, we have 74 modes of vibration in Ti₉O₁₈ clusters, the majority of which are different from Ti₂O₄ due to different structures. As cluster sizes rise, the atoms tend to adopt higher coordination, as shown in Fig. 10, which shows the Raman activity spectra of Ti₉O₁₈ and Ti₂8O₅₆ computed using Gaussian/ B3LYP 6-31G (d), with two strong peaks appearing about 1040.92 cm⁻¹ and 1045.45 cm⁻¹. These two vibrations do not exist in the cluster (Ti₂₈O₅₆) because both cluster sides have 1Ti coordinates, as shown in Fig. 11. The arrow represents the O-1Ti vibration mode. We believe all clusters cannot have the same vibration, which is dependent on cluster structure. The Raman spectrum activity of pure (Ti₂₈O₅₆) and nitrogen doped (Ti₂₈O₅₆N₁) Nano clusters are displayed in Fig. 12 using Gaussian/ B3LYP/6-31G (d). The (*) peak of pure Ti-O demonstrates the stretched bonds (Ti₂₈O₅₆). The vibrational mode N-O of nitrogen doped (Ti²⁸O5⁶N¹) at approximately 1013.9 cm⁻¹ is depicted in the inset Fig. 13. This is a stretching mode that has been investigated in N-doped TiO₂.

The following goals are pursued using experimental and theoretical studies (DFT/B3LYP/6-31G (d) techniques and the Quantum espresso code).

Structural and Electronic characteristics of pure and nitrogen doped (TiO₂)_n clusters were examined using two DFT level theories: Quantum Espresso/PBE and Gaussian/B3LYP/6-31G (d).
The synthesis of TiO₂ and nitrogen doped TiO₂ nanoclusters was achieved using Supersonic Cluster Beam Deposition (SCBD). The size of the particles is estimated to be in the range of (2-5 nm).
We discovered the effect of impurity position on formation energy and electronic characteristics in both interstitial and substitution cases in an optimized structure. We assumed that doped nitrogen in TiO₂ clusters is positioned at the interstitial site of the TiO₂ lattice based on formation energy, which is compatible with XPS data (O-Ti-N).
The band gap energy dropped for the N-doped TiO₂ clusters, according to UV-Vis spectroscopy. As a result of the theoretical conclusions, the band gap is predicted to decrease when N is doped.
The addition of N as a dopant result in forming a new N–O band with the vibration of (1013.91cm^-1) at Gaussian/B3LYP/6-31G (d), implying the emergence of states in band states with a narrowing of the bandgap.
The quantum confinement effect was observed using UV- Vis Spectroscopy, with a significant band gap energy of pure TiO₂ (3.753 eV) and the theoretical band gap (3.772 eV) via DFT/B3LYP/6-31G (d) basis set.
Raman spectral activity of Ti₉O₁₈ and Ti₂₈O₅₆ nano clusters has been studied using Gaussian/ B3LYP/6-31G (d) basis set.
We believe this research is important because it has the potential to aid in the study and characterization of the physics and materials science of TiO₂. This material that has received a lot of attention in recent years. Due to its significance for titanium nanocluster, it may also have an impact on nanoscience.

Acknowledgments

The authors would like to thank Nicola Manini from UniversitadegliStudi di Milano-Italy for providing computational facilities and outstanding scientific advice. Special thanks to Alessandro Podestà and Paolo Piseri from CIMaIna laboratories at UniversitàdegliStudi di Milano (Milano, Italy), for their facilities to access samples and perform characterization. The scientific support in the etsfmi group, especially Elena Molteni and Guido Fratesi are acknowledged.

Conflict of Interest

The authors declare no conflict of interest.

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You are reading this latest preprint version

Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO₂)_n Cluster

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material And Method

2.1. Experimental: Synthesis of nitrogen-Doped TiO₂ cluster

2.2 Theoretical: Computational methods (DFT)

3. Results And Discussions

3.2 Electronic properties of pure Ti₂₈O₅₆ and nitrogen doped (Ti₂₈O₅₆N₁)

3.3. Surface morphology of N-doped TiO₂ nanocluster

3.4. X-ray Photoelectron Spectroscopy (XPS)

3.5. Optical properties of the pure and nitrogen-doped TiO₂

3.6. Experimental and theoretical DFTB3LYP/6-31G (d) investigation of Raman spectra for pure and nitrogen doped TiO₂

3.6.1. Raman analysis

3.6.2. Theoretical vibrational properties of pure and N-doped (TiO2)n by DFT / B3LYP/6-31G(d)

4. Conclusions

Declarations

References

Status:

Version 1

Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO2)n Cluster

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material And Method

2.1. Experimental: Synthesis of nitrogen-Doped TiO2 cluster

2.2 Theoretical: Computational methods (DFT)

3. Results And Discussions

3.2 Electronic properties of pure Ti28O56 and nitrogen doped (Ti28O56N1)

3.3. Surface morphology of N-doped TiO2 nanocluster

3.4. X-ray Photoelectron Spectroscopy (XPS)

3.5. Optical properties of the pure and nitrogen-doped TiO2

3.6. Experimental and theoretical DFTB3LYP/6-31G (d) investigation of Raman spectra for pure and nitrogen doped TiO2

3.6.1. Raman analysis

3.6.2. Theoretical vibrational properties of pure and N-doped (TiO2)n by DFT / B3LYP/6-31G(d)

4. Conclusions

Declarations

References

Status:

Version 1

Theoretical and Experimental Investigation of the Electronic and Optical Properties of Pure and Interstitial Nitrogen -Doped (TiO₂)_n Cluster

2.1. Experimental: Synthesis of nitrogen-Doped TiO₂ cluster

3.2 Electronic properties of pure Ti₂₈O₅₆ and nitrogen doped (Ti₂₈O₅₆N₁)

3.3. Surface morphology of N-doped TiO₂ nanocluster

3.5. Optical properties of the pure and nitrogen-doped TiO₂

3.6. Experimental and theoretical DFTB3LYP/6-31G (d) investigation of Raman spectra for pure and nitrogen doped TiO₂