Transverse Optical Phonon Research Articles

Quasiparticle and Nonquasiparticle Transport in Doped Quantum Paraelectrics.

Charge transport in doped quantum paraelectrics (QPs) presents a number of puzzles, including a pronounced T^{2} regime in the resistivity. We analyze charge transport in a QP within a model of electrons coupled to a soft transverse optical (TO) mode via a two-phonon mechanism. For T above the soft-mode frequency but below some characteristic scale (E_{0}), the resistivity scales with the occupation number of phonons squared, i.e., as T^{2}. The T^{2} scattering rate does not depend on the carrier number density and is not affected by a crossover between degenerate and nondegenerate regimes, in agreement with the experiment. Temperatures higher than E_{0} correspond to a nonquasiparticle regime, which we analyze by mapping the Dyson equation onto a problem of supersymmetric quantum mechanics. The combination of scattering by two TO phonons and by a longitudinal optical mode explains the data quite well.

Electron-phonon contribution in aluminene: Superconductive and transport properties

Abstract Density functional and many-body perturbation theories have been employed to investigate the superconductive character and transport properties in 2D buckled aluminene. The examination of superconductivity at low temperature reveals a huge dependence on the electron phonon coupling (EPC), especially in the calculation of the critical temperature by the Allen-Dynes theory. It is found that the EPC strength is dominated by the longitudinal and transversal optical phonon. The superconducting gap equals to 1.5 meV at 0 K, drops to 0 meV for temperatures above the critical temperature. Transport properties calculations reveals a carrier's mobility of 8842.6 c m 2 V − 1 s − 1 at 100 K which decreases to 620 c m 2 V − 1 s − 1 at room temperature. The findings of this work highlight the importance of aluminene as a promising candidate for future advanced applications.

Limits of the quasiharmonic approximation in MgO: Volume dependence of optical modes investigated by infrared reflectivity and ab initio calculations

Experimental and numerical investigation of phonon optical modes of MgO as a function of temperature (from 300 to 1400 K) and pressure (from 0 to 21 GPa) are here presented. Infrared reflectivity measurements were performed to probe energies and widths of the optical phonons, as well as of the multiphonon processes affecting the spectral shape, over a variation of the unit-cell volume exceeding 20%. Calculations within quasiharmonic approximation (QHA) account well for the volume dependence of the optical phonon energies observed in high-pressure experiments, while they fail at larger volumes, corresponding to the highest investigated temperatures. Moreover, QHA calculations more closely predict energies of transverse optical (TO) modes than those of longitudinal optical (LO) ones. This can be ascribed to known limitations in the modeling of the effective charges (${Z}^{*}$) and dielectric constant (${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$) that lead to an underestimation of the LO-TO splitting. Based on the comparison of our experimental and theoretical results, we propose an empirical analytical expression for ${{Z}^{*}}^{2}/{\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$ as a function of the atomic cell volume. Density-functional perturbation theory including phonon-phonon scattering up to the third order of the lattice potential expansion is used to calculate phonon widths. These calculations reproduce and explain remarkably well the nontrivial volume dependence of both TO and LO phonons linewidths determined by the experiments.

Equation of State of TiN at High Pressures and Temperatures: A Possible Host for Nitrogen in Planetary Mantles

AbstractNitrogen, the most abundant element in Earth's atmosphere, is also a primary component of solid nitride minerals found in meteorites and on Earth's surface. If they remain stable to high pressures and temperatures, these nitrides may also be important reservoirs of nitrogen in planetary interiors. We used synchrotron X‐ray diffraction to measure the thermal equation of state and phase stability of titanium nitride (TiN) in a laser‐heated diamond anvil cell at pressures up to ∼70 GPa and temperatures up to ∼2,500 K. TiN maintains the cubic B1 (NaCl‐type) crystal structure over the entire pressure and temperature range explored. It has K0 = 274 (4) GPa, K0′ = 3.9 (2), and γ0 = 1.39 (4) for a fixed V0 = 76.516 (30) Å3 (based on experimental measurements), q = 1, and θ0 = 579 K. Additionally, we collected Raman spectra of TiN up to ∼60 GPa, where we find that the transverse acoustic (TA), longitudinal acoustic (LA), and transverse optical phonon modes exhibit mode Grüneisen parameters of 1.66(17), 0.54(15), and 0.93 (4), respectively. Based on our equation of state, TiN has a density of ∼5.6–6.4 g/cm3 at Earth's lower mantle conditions, significantly more dense than both the mantle of the Earth and the estimated densities of the mantles of other terrestrial planets, but less dense than planetary cores. We find that TiN remains stable against physical decomposition at the pressures and temperatures found within Earth's mantle, making it a plausible reservoir for deep planetary nitrogen if chemical conditions allow its formation.

Terahertz optics-driven phase transition in two-dimensional multiferroics

Displacive martensitic phase transition is potentially promising in semiconductor-based data storage applications with fast switching speed. In addition to traditional phase transition materials, the recently discovered two-dimensional ferroic materials are receiving a lot of attention owing to their fast ferroic switching dynamics, which could tremendously boost data storage density and enhance read/write speed. In this study, we propose that a terahertz laser with an intermediate intensity and selected frequency can trigger ferroic order switching in two-dimensional multiferroics, which is a damage-free noncontacting approach. Through first-principles calculations, we theoretically and computationally investigate optically induced electronic, phononic, and mechanical responses of two experimentally fabricated multiferroic (with both ferroelastic and ferroelectric) materials, β-GeSe and α-SnTe monolayer. We show that the relative stability of different orientation variants can be effectively manipulated via the polarization direction of the terahertz laser, which is selectively and strongly coupled with the transverse optical phonon modes. The transition from one orientation variant to another can be barrierless, indicating ultrafast transition kinetics and the conventional nucleation-growth phase transition process can be avoidable.

Critical Coupling and Perfect Absorption Using α‐MoO3 Multilayers in the Mid‐Infrared

Abstractα‐Phase molybdenum trioxide(α‐MoO3) is a biaxial van der Waals semiconductor that can naturally support anisotropic phonon polaritons with elliptic and hyperbolic in‐plane dispersion. α‐MoO3 can meet critical coupling (CC) condition for both transverse magnetic (TM) and transverse electric (TE) polarizations along the x and y directions and exhibit high absorption in the mid‐infrared region due to strong phonon polaritons. In this study, an absorber composed of few‐layer α‐MoO3 and one‐dimensional photonic crystal separated by a cavity is proposed. Perfect absorption for TE and TM polarized light is achieved at the longitudinal and transverse optical phonon frequencies, respectively. The underlying mechanism of perfect absorption is investigated by using coupled mode theory and simulating electric field and power dissipation profiles. The results prove that CC is responsible for the perfect absorption. Moreover, the influence of the thickness of α‐MoO3 layer, width of cavity between α‐MoO3 and photonic crystal, and angle of incident light on the CC and absorption performance are examined. Accordingly, the rules for realizing perfect absorption at different operation frequencies are established. Overall, this study provides useful insights on designing a perfect absorber based on α‐MoO3 for detection and sensing applications in the mid‐infrared region.

The Correlation between Structural and Optical Properties of Zinc Hydroxide Nanoparticle in Supports Photocatalytic Performance

- Green synthesized Zn(OH)2 mediated by Coleus blumei Benth leaf for pH: 4, 7, 10 and for calcination temperature: 400 °C, 450 °C, 500 °C, 550 °C, and 600 °C have been characterized by using Fourier transform infra-red (FTIR), ultraviolet–visible (Uv–Vis), and X-ray diffraction (XRD). The bonding formation present Zn– O –H, H– O –H, O –H, and Zn–O indicated Zn(OH)2 nanocrystal successfully synthesized. The optical, dielectric properties, and energy loss function were quantitatively determined from the FTIR spectra by using Kramers-Kronig (KK) dispersion relation. The distance between longitudinal (LO) and transverse (TO) optical phonon vibration mode Δ (LO-TO) and the bandgap increases with increasing the calcination temperature for all pH due to the amount of covalent bond is increase. The best calcination temperature is 600 °C and pH 7 indicated by the rate of the degradation performance is faster than the other temperature and pH. In this study shows FTIR spectra effective ways for determining the optical and dielectric properties, optical phonon vibration mode, and energy loss function of Zn(OH)2 material. • The Zn-O-H, H-O-H, O-H, and Zn-O bonding indicated formed of Zn(OH) 2 nanocrystal. • The n and k , ε 1 and ε 2 (ω), Im ( - 1 / ε 1 ( ω ) ) determined from FTIR spectra by applying K-K relation. • Distance optical phonon vibration (D(LO-TO)) is increases with increasing the calcination temperature for all pH. • The band gap increase with increasing the calcination temperature. • The best calcination temperature for photocatalyst is 600 o C.

Towards a stoichiometric electrodeposition of SnS

SnS films have been grown at room temperature by electrochemical deposition technique on to ITO (indium-tin-oxide) coated glass substrates. Tin chloride (SnCl2) and sodium thiosulphate (Na2S2O3) were used in aqueous solution as precursors and ethylenediamine tetraacetic acid (C10H16N2O8, EDTA) or triethanolamine (C6H15NO3, TEA) was added to slow the deposition rate of Sn. The pH of each solution was adjusted to 1.8. The deposition time was 60 min and the potential was maintained to − 1 V vs Ag/AgCl electrode. The structural, morphological and optical properties of the electrodeposited films were investigated. X-ray diffraction patterns confirm the polycrystalline samples’ nature as the α-SnS orthorhombic structure. A clear change in the preferential growth direction was observed when adding TEA. Raman spectroscopy spectra exhibit five bands belonging to both transversal and longitudinal optical phonons modes that match with the α-SnS prototype ones. Scanning electron microscopy images show that the films morphology was highly influenced by the complexing agent. The addition of EDTA leads to significant decrease in particle size, while that of TEA results in a mixture of both small and large particles. Energy-dispersive X-ray spectroscopy measurements demonstrate that the addition of complexing agent, TEA or EDTA, leads to a close stoichiometry with better crystallographic properties for TEA addition. The optical characterization shows that the addition of EDTA results in a blue shift of the band gap energy, while the addition of TEA rather causes its red shift.

Effect of Sugar Palm Fiber (SPF) to the Structural and Optical Properties of Bioplastics (SPF/Starch/Chitosan/Polypropylene) in supporting Mechanical Properties and Degradation Performance

Recycling plastic waste by mix with natural polymers for bio-plastic packaging produces plastics with high mechanical properties and easily degradable. In this study, the relation between the structural and the optical properties of composite SPF/starch/chitosan/polypropylene to the mechanical properties and degradation performance were analyzed. Structural and optical properties of composite bioplastic SPF/Starch/Chitosan/Polypropylene have analyzed using X-Ray diffraction (XRD), and Fourier transforms infrared (FTIR) spectroscopy, respectively. The composition was varied: the ratio between starch and chitosan are 35/65, 50/50, and 65/35 with additional SPF for each ratio is 1%, 3%, and 5%. The SPF effectively enhances the tensile strength due to the SPF's better dispersion and interaction in the starch/chitosan/polypropylene matrix. For SPF's effect on the degradation performance, the ratio starch/chitosan 50/50 increase for 1% SPF is 87.23%, for 3% SPF is 92.59%, and for 5 SPF is 94.12%. The refractive index (n), extinction coefficient (k), dielectric functions (e), and energy loss function (Im (−1/ e)) determined from the quantitative analysis of FTIR spectra by using Kramers–Kronig (K–K) relations. The crystalline phase increases with increasing the amount of SPF in composite bioplastic SPF/Starch/Chitosan /Polypropylene for ratio starch/chitosan is 35/65, which consistent with the distance between the wavenumber (D) of transversal and longitudinal optical phonon vibration mode become wider. We found that a good correlation between optical properties, structural properties, mechanical properties, and degradation performance for ratio starch/chitosan 35/65 and 50/50 with SPF 1% and 3% in the composite. Besides, the FTIR spectra could be useful for determining the optical phonon vibration, dielectric function, and energy loss function of composite bioplastic SPF/Starch/Chitosan /Polypropylene. The degradation performance by additional polypropylene from plastic waste shows a potential solution for decreasing plastic waste in the world.

Phase analysis of tungsten and phonon behavior of beryllium layers in W/Be periodic multilayers.

In periodic W/Be multilayers, thickness-dependent microstructural and phase modifications were investigated in W and Be layers. In X-ray diffraction, α-W was predominant for the ultrathin layer of W, while β-W evolved along with the α-W phase for higher film thickness. For the thicker layers, the thermodynamically metastable β-W vanished and a single well-defined preferably oriented stable α-W phase was observed. The lattice spacing revealed that these phases exist in the tensile stressed condition. With the increase in thickness of Be layers, the blueshift and narrow linewidth of the transverse optical (TO) phonon mode was observed in Raman scattering studies. However, the TO mode was redshifted and the linewidth was further narrowed consistently with an increase in the thermal annealing temperature of the multilayers. The investigation has quantified an increase in compressive strain and reduction of defects with an increase in thickness of the Be layers. However, for thermally annealed samples, the compressive strain in the Be layers was relaxed and crystalline quality was improved.

Dielectric and vibrational properties of CdTe studied by first-principles and terahertz time-domain spectroscopy

The optical phonon frequency and damping factor of Cadmium telluride (CdTe) have been investigated by using both the first-principles calculation and terahertz time-domain spectroscopy (TDS) system. The temperature dependence of transverse and longitudinal optical phonon frequency obtained by using the quasi-harmonic approximation is consistent with experimental results at the lower temperature range. Finally, the damping factors estimated from the three phonon contributions deviate from the extracted experimental data in the higher temperature range, which indicates the scattering process of four phonon plays an important role in anharmonic phenomena.

Resonant Raman scattering of anthracene‐based carbons in the secondary carbonization stage

AbstractThe Raman spectra of graphene‐based matter exhibit a set of defect/disorder‐induced bands. The D band, which exhibits a strong dispersion up to ~50 cm−1/eV, comes from transverse optical phonons around K or K′ in the first Brillouin zone and involves an intervalley double resonance (DR) Raman process. In the present work, resonant Raman scattering (lines ranging from 1.58 to 3.81 eV) is used to study the unusual behavior of the one‐phonon Raman band of a carbonaceous material (anthracene‐based carbon which is one of the graphitizable carbons) upon its secondary carbonization stage (450°C–1000°C). While the G band appears to be nondispersive, the D band exhibits a change in both position and intensity. Its dispersion progressively rises from ~6 cm−1/eV to values close to what is usually observed in defected graphene‐based systems when anthracene‐based carbon becomes almost pure. This evolution appears to be correlated with a release of hydrogen (fixed on the edges of polyaromatic layers) questioning their role in changing the D band resonance conditions.

Study of Grass Shoot-Shape Silicon Nanowires Grown by Thermal Chemical Vapor Deposition

Grass shoot-shape silicon nanowires (SiNWs) with sharp tip have been successfully synthesized on an n-type Si (111) substrates at temperatures of 700 °C and various times using a thermal chemical vapor deposition (TCVD) technique. Au thin film (~10 nm thick) as catalyst were deposited on Si (111) substrates by a radio frequency magnetron sputtering system. Effect of the growth time on morphology of SiNWs has been reported. The morphologies, growth mechanism, homogeneity and crystalline structure of the nanowires were studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffractometer (XRD) and Raman spectroscopy. SEM images depict morphology of wires in form of nanoneedles (NNs) with base diameter of 60 nm, tip diameter of ∼5 nm and length up to 3 μm. TEM analysis revealed that the nanowires have core-shell structure with Au nanoparticles on the tip. Raman spectrum of as-grown SiNNs exhibited a transverse optical (TO) phonon mode. The obtained results have shown radius and length of the SiNNs increased with increase in growth time.

Raman LO phonon signal and two dimensional AFM studies on GaAs implanted by Mn ions and impact of irradiation with 5 MeV Si++ ions on it

In the present work, gallium arsenide samples implanted with 325 keV Mn+ ions for the fluence of 5 × 1015, 1 × 1016 and 2 × 1016 ions cm−2, have been investigated using Raman scattering and Atomic force microscopy measurements. The sample implanted with the fluence of 1 × 1016 ions cm−2 was further irradiated using 5 MeV Si++ ion beams for the fluence of 1 × 1016 ions cm−2 at a substrate temperature of 350°C for recrystallization. Raman peaks obtained at 293.51 and 269.35 cm−1 were assigned to longitudinal optical (LO) phonon mode and transverse optical (TO) phonon mode of gallium arsenide, respectively. The shift in the Raman peaks towards higher wave-number with respect to ion fluence indicated the presence of residual compressive stress within the samples. The Mn and (MnAs) like mode were observed after implantation. The additional mode like GaMn was also seen in sample after irradiation with 5 MeV Si++ ions. The composition of manganese atoms in gallium arsenide estimated from the Raman spectra for the ion fluence 5 × 1015, 1 × 1016 and 2 × 1016 ions cm−2 were found to be 0.74%, 1.40% and 2.80%, respectively. The Phonon coherence length estimated from the Phonon Confinement Model by fitting the LO phonon signal was found to increase from 39.40 to 47.10 nm with respect to ion fluence. AFM images of non-implanted sample showed the smooth micrograph with root mean square surface roughness of 0.41 nm. After implantation, the different sizes of clusters were observed on the surfaces of GaAs. The shape and size of the clusters were found to depend on the ion fluence.

Spin–phonon coupling in NiO nanoparticle

Nickel oxide (NiO) has a cubic rock salt crystal structure at room temperature. Raman scattering of the transverse optical (TO) and longitudinal optical (LO) phonon in NiO is Raman inactive. Thus, it is difficult to employ the Raman scattering technique to study the lattice vibration dynamics and spin–phonon coupling in NiO. In this work, crystalline stoichiometry of NiO nanoparticles with different nanocrystalline sizes was tuned to make the Raman scattering selection rules dramatically relaxed. Well-defined Raman scattering peaks of the two zone-boundary folded modes TO(Δ) and LO(Δ) were observed. These two modes are situated at the midpoint along the Γ–Δ–X direction in the Brillouin zone. The Raman scattering of these two modes are induced by magnetostriction and nonstoichiometric Ni–O stretching, respectively. The well-defined Raman peaks of TO(Δ) and LO(Δ) allow us to study the spin–phonon coupling effect in NiO. It is found that spin–phonon coupling is responsible for the Raman scattering anomalies, namely, the relatively large Raman shift hardening and peak width narrowing below the Néel temperature for LO and its overtone 2LO phonons.

Temperature-Dependent Cationic Doping-Driven Phonon Dynamics Investigation in CdO Thin Films Using Raman Spectroscopy

In the present work, undoped cadmium oxide (CdO)- and 1% Tin (Sn)-doped CdO thin films were prepared by the sol–gel route. These samples have been analyzed by temperature (T)-dependent (80–500 K) Raman spectroscopy and studied for their lattice dynamics and vibrational density of states. Results indicate that the room T synthesized pure CdO thin film manifests two prime second order features, that is, 300.5 cm–1 transverse optical (TO) and 488 cm–1 longitudinal optical (LO) phonon modes. However, incorporation of cationic-assisted impurity (Sn) with larger ionic radii results in a softening of the high-frequency LO (480.5 cm–1) mode via lattice deformation scattering potential. In fact, selective Sn doping increases the carrier concentration in the host CdO matrix which subsequently mitigates intraionic anharmonicity owing to increased Coulomb screening, leading to disappearance of the low-frequency TO mode (300.5 cm–1). In the case of pure CdO thin films, surface electron-induced electron–LO phonon coupling causes the intensity enhancement in LO modes, while negligible four-phonon anharmonic coupling results in lowering of full width at half maxima below Debye T. On the other hand, Frühlich interaction in the polar LO phonon mode supersedes the impact of anharmonic decay and dominates the overall phonon decay process by impurity incorporation, via appropriate Sn doping. Theoretical phonon dispersion profiles throughout the Brillouin zone with increasing T suggests stronger TO phonon mode softening along with optical branch broadening followed by LO–TO splitting. The acoustic branch barely suffers any shift with changing T which cannot be observed in experimental spectra. However, the flexural phonon modes confer a direct indication of changed rigidity and bond stiffness with varying T. Overall, the present investigation provides experimental evidence regarding the significance of Debye T, below and above which the three- and four-phonon anharmonicity are feasible in phonon scattering in conjunction with theoretical insights.

Elastic constants and optical phonon frequencies of BX (X= P, As, and Sb) semiconductors: Semi-empirical prediction

Based on some simple empirical formulas established by Adachi in, Properties of group-IV, III-V and II-VI semiconductors, John Wiley & Sons, Chichester (2005), and the experimental lattice constants reported in the literature; the present work aims to predict the elastic constants and some other significant properties of cubic zinc-blende boron compounds (BP, BAs and BSb). The obtained values of C12and C44 are in general good agreement with other data of the literature, while C11 and B are slightly lower. The zone-center longitudinal optical (LO) and transverse optical (TO) phonon frequencies are also obtained. The LO and TO phonon frequencies of BP compound were found at 866.6and 834.5 cm–1, respectively; these of BAs were found at 731.3 and 727.1 cm–1, respectively; while for the BSb narrow-gap semiconducting compound were found at around 598.3and 586.2 cm–1, respectively. These two later values are in general slightly lower than the calculated values, and the observed Raman spectroscopy values reported in the literature.Â

Temperature dependence of dynamic dipole formation in PbTe

PbTe-based thermoelectric materials remain of great interest due to their peculiar dynamic behavior and high thermoelectric performance. The true structure of pristine PbTe has been widely discussed, since the average rocksalt structure does not adequately account for the low lattice thermal conductivity. Single crystals of PbTe exhibit large amounts of x-ray diffuse scattering, which along with additional experimental observations has led to a series of structural models containing different types of disorder. Recently, analysis of the x-ray diffuse scattering from single-crystal PbTe confirmed the formation of local dynamic dipoles proposed earlier based on inelastic neutron scattering (INS) and one-dimensional pair distribution function (PDF) experiments. Here, we study the single-crystal diffuse x-ray scattering over a wider temperature range from 30 to 622 K in order to investigate the temperature dependence of the dynamic dipole formation. We observe that the longitudinal displacement correlations along the ⟨100⟩ directions form pairwise plateaus which results in a steplike decay of the correlations with increasing interatomic distance. This is consistent with previous observations from single-crystal diffuse scattering experiments on PbTe where the same steplike trend for the correlations was observed. However, upon lowering the temperature we observe a larger relative antiphase displacement contribution to the correlations proposed to originate from the softening of the transverse optical (TO) branch. As the local dipole formation depends on the absolute amplitude of antiphase displacements, and not the relative antiphase contribution to atomic displacements, it is found that the local dipole formation increases upon heating consistent with previous INS and PDF studies. The underlying mechanism responsible for the softening of the TO branch, and thereby the formation of dynamic dipoles, is investigated by comparison to the isostructural KCl system. The different dynamics in KCl and PbTe can be explained from the different bonding mechanism, where the metavalent bonding and ability to dynamically express a stereochemically active lone pair in PbTe gives rise to long-range interactions and TO phonon softening.

Growth and characterization of ZnSe nanocrystals synthesized using solvothermal process

ZnSe nanocrystals with zinc blende structure are synthesized by solvothermal process at 1-h, 3-h and 5-h reaction times in a mixed solvent of hydrazine hydrate [H6N2O], ammonia [NH3] and de-ionized water. Zinc acetate [(CH3COO)2 Zn; 2H2O] and sodium selenite [Na2SeO3] are, respectively, used as precursors for zinc and selenium ions. X-ray diffraction (XRD) and scanning electron microscope (SEM) study show that the crystallinity and the chemical purity of the compound improve with increase in reaction duration. SEM images show formation of bulk rod-shaped ZnO particles in samples prepared at 1-h and 3-h reaction times, which is absent in the 5-h sample. TGA measurements also show that the ZnSe nanocrystals synthesized in this process have high purity and the nanocrystals prepared for longer duration have improved purity as well as higher thermal stability. In Raman measurements, nanocrystalline nature such as surface phonon (SP) mode and phonon line width broadening are observed. The observed variation of the relative intensities of the phonon modes follows the differences in the size of nanocrystals, in which the relative strength of the transverse optical (TO) phonon mode is found to increase with nanocrystals size and the SP phonon relative strength on the other hand decreases.

Collective near-field coupling and nonlocal phenomena in infrared-phononic metasurfaces for nano-light canalization

Polaritons – coupled excitations of photons and dipolar matter excitations – can propagate along anisotropic metasurfaces with either hyperbolic or elliptical dispersion. At the transition from hyperbolic to elliptical dispersion (corresponding to a topological transition), various intriguing phenomena are found, such as an enhancement of the photonic density of states, polariton canalization and hyperlensing. Here, we investigate theoretically and experimentally the topological transition, the polaritonic coupling and the strong nonlocal response in a uniaxial infrared-phononic metasurface, a grating of hexagonal boron nitride (hBN) nanoribbons. By hyperspectral infrared nanoimaging, we observe a synthetic transverse optical phonon resonance (strong collective near-field coupling of the nanoribbons) in the middle of the hBN Reststrahlen band, yielding a topological transition from hyperbolic to elliptical dispersion. We further visualize and characterize the spatial evolution of a deeply subwavelength canalization mode near the transition frequency, which is a collimated polariton that is the basis for hyperlensing and diffraction-less propagation.