ANGLE-RESOLVED POLARIZED RAMAN SPECTROSCOPY STUDY OF BLACK PHOSPHORUS AND BLACK ARSENIC– PHOSPHORUS NANORIBONSCITATION

Abstract

The discovery of graphene in 2004 introduced a new class of materials known as two-dimensional (2D) materials, which exhibit unique surface properties and pronounced anisotropy compared to their bulk counterparts. One of the most widely studied 2D materials, owing to its promising applications and significant research interest, is phosphorene, the monolayer or few-layer form of black phosphorus (BP). Theoretical studies suggest that intercalating alkali atoms into the layers of phosphorene can enhance its versatility and expand its potential applications. In 2D layered materials, intercalation has shown itself to be an effective method for synthesis, modification, transformation, and phase transitions. Furthermore, phosphorene's stability problems, which have hindered its widespread use in device, were addressed by alloying it with grey arsenic. The first part of this dissertation focused on the synthesis of black phosphorus (BP) under laboratory conditions. Thus, high quality BP crystals were grown in our lab using chemical vapor transport (CVT) technique and characterized for its quality using several characterization techniques. The electrochemical intercalation of sodium (Na) and Lithium (Li) into BP flakes which eventually produced phosphorene nanoribbons (PNRs). PNRs have inspired strong research interests to explore their exciting properties that are associated with the unique 2D structure of phosphorene. A systematic angle-resolved polarized Raman spectroscopy (ARPRS) was conducted on the PNRs. Sodium intercalation leads to bundles of densely packed, highly uniform phosphorene nanoribbons (PNRs) separated by parallel amorphous channels, whereas lithium intercalation results in shorter, irregular nanoribbon-like segments with lower aspect ratios. In both cases, six additional Raman peaks (P1–P6) appear alongside the three primary Raman-active modes of BP (A1g, B2g, and A2g). These peaks are attributed to the amorphous regions, as confirmed by their isotropic angular dependence in ARPRS measurements. The three BP modes show pronounced angular variations that differ significantly between the two intercalated samples. In sodium-intercalated BP, A1g and A2g modes retain a dumbbell-like angular dependence under parallel polarization with enhanced anisotropy and reduced symmetry under crossed polarization. At the same time, the B2g mode transitions from four-lobed (cloverleaf) polar plot to a butterfly-like one. In contrast, lithium-intercalated BP exhibits weaker anisotropy and less distinct angular polar plots for all three modes. These differences reflect the sensitivity of phonon behavior to underlying nanostructure morphology. The vibrational frequencies density of states (FDOS) calculations attributes the B2gmode transformation to phonon band folding and mode mixing in PNRs. This study demonstrates the power of ARPRS in probing phonon-structure relationships and highlights the influence of edge geometry and quantum confinement on phonon dispersion in PNRs The next part of this dissertation focused on the synthesis of two b-AsₓP₁₋ₓ (x = 0.4 and 0.8) alloys under controlled laboratory conditions using the chemical vapor transport (CVT) method. Then a systematic ARPRS study on the two bAsxP1-x nanostructures (x=0.4 and 0.8) formed via electrochemical sodium (Na) intercalation was conducted. Sodium intercalation in both samples is found to lead to bundles of densely packed, highly uniform AsxP1-x nanoribbons separated by parallel amorphous channel. In addition to the amorphous Raman peak (P1), which is attributed to grey-As in AsₓP₁₋ₓ, an additional Raman peak (P2) is observed alongside the three primary Raman-active modes of P-P vibrations (A1g, B2g, and A2g), three primary Raman-active modes of As-As vibrations (A1g, B2g, and A2g), and two primary Raman-active modes of As-P vibrations (A1g, B2g + A2g). This P2 peak is attributed to the amorphous regions, as confirmed by their isotropic angular dependence in ARPRS measurements. The eight modes corresponding to P-P, As-As, and As-P vibrational modes show pronounced angular variations for each intercalated sample. In sodium-intercalated AsxP1-x sample, A1g and A2g modes retain a dumbbell-like angular dependence under parallel polarization while exhibiting enhanced anisotropy and reduced symmetry under crossed polarization.At the same time, the B2g mode transitions from four-lobed (cloverleaf) polar plot to a butterfly-like one, similar as found in bulk AsₓP₁₋ₓ. These differences reflect the sensitivity of phonon behavior to underlying nanostructure morphology. The final part of this dissertation was the study of GeSe alloy which was a layered material with a BP-analog structure that is a significant component of 2D group IV-VIA semiconductors. Firstly, the synthesis of GeSe alloy via CVT then electrochemical intercalation by Na ion. A systematic ARPRS study of pristine GeSe alloy and its nanostructure. In the pristine GeSe spectrum, three Raman peaks are clearly observed at around 150, 170, and 188 cm-1, corresponding to the B3g, A2g, and A3g modes, respectively. In contrast, the Raman spectrum of nanostructure containing material exhibits additional peak (P1) after electrochemical sculpting. The amorphous channels created during the sculpting process are the source of disorder-induced vibrational modes that are responsible for this peak. These new modes' existence indicates structural changes driven on by localized disorder and bond breakage. These findings give insight into how GeSe's structure changed during the electrochemical sculpting process. However, the nanorods resulted from Na-intercalation are pure Se without any incorporation of Ge. It is believed the reaction of Ge with Na causes depletion of Ge in the nanorods and requires further investigation