Imperial College London

DrPeterPetrov

Faculty of EngineeringDepartment of Materials

Principal Research Scientist
 
 
 
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Contact

 

+44 (0)20 7594 8156p.petrov

 
 
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Location

 

B333Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

107 results found

Petrov P, Altynnikov A, Platonov R, Tumarkin A, Kozyrev Aet al., 2021, Formation of millimeter waves with electrically tunable orbital angular momentum, Coatings, Vol: 11, Pages: 1-9, ISSN: 2079-6412

A method for forming electromagnetic waves with a tunable nonzero orbital angular momentum (OAM) is proposed. The approach is based on transforming an incident plane wave into a helical one using an electrically tunable ferroelectric lens. It uses high-resistive thin/thick film electrodes with a special discrete topology. The correlation between film electrodes topology and the highest order of OAM modes that the lens can form is described. A lens prototype based on Ba0.55Sr0.45TiO3 ferroelectric material and operating at a frequency of 60 GHz was designed, manufactured, and tested. The amplitude and phase distribution of the OAM wave with l = +1 formed by prototype were measured to confirm the effectiveness of the proposed method. The proposed lens has a combination of advantages such as low dimensions, electrical control over the OAM modes, and the possibility to operate in the millimeter wavelength range.

Journal article

Berenov A, Petrov P, Moffat B, Phair J, Allers L, Whatmore Ret al., 2021, Pyroelectric and photovoltaic properties of Nb doped PZT thin films, APL Materials, Vol: 9, ISSN: 2166-532X

Nb-doped lead zirconate titanate (PZT) films with up to 12 at. % of Nb were co-sputtered from oxide PZT and metallic Nb targets at a substrate temperature of 600 °C. Up to 4 at. % of Nb was doped into the perovskite structure with the formation of B-site cation vacancies for charge compensation. The preferential (111) PZT orientation decreased with Nb-doping within the solid solution region. The ferroelectric response of the films was affected by the large values of the internal field present in the samples (e.g., −84.3 kV cm−1 in 12 at. % Nd doped films). As-deposited unpoled films showed large values of the pyroelectric coefficient due to self-poling. The pyroelectric coefficient increased with Nb-doping and showed a complex dependence on the applied bias. The photovoltaic effect was observed in the films. The value of the photocurrent increased with the A/B ratio. The combined photovoltaic–pyroelectric effect increased the values of the measured current by up to 47% upon light illumination.

Journal article

Ramadan S, Lobo R, Zhang Y, Xu L, Shaforost O, Tsang DKH, Feng J, Yin T, Qiao M, Rajeshirke A, Jiao LR, Petrov PK, Dunlop IE, Titirici M-M, Klein Net al., 2021, Carbon-dot-enhanced graphene field-effect transistors for uitrasensitive detection of exosomes, ACS Applied Materials and Interfaces, Vol: 13, Pages: 7854-7864, ISSN: 1944-8244

Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.

Journal article

Ramadan S, Zhang Y, Tsang DKH, Shaforost O, Xu L, Bower R, Dunlop IE, Petrov PK, Klein Net al., 2021, Enhancing structural properties and performance of graphene-based devices using self-assembled HMDS monolayers, ACS Omega, Vol: 6, Pages: 4767-4775, ISSN: 2470-1343

The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.

Journal article

Bower R, Loch DAL, Ware E, Berenov A, Bin Z, Hovsepian PE, Ehiasarian AP, Petrov PKet al., 2020, Complementary Metal-Oxide-Semiconductor Compatible Deposition of Nanoscale Transition-Metal Nitride Thin Films for Plasmonic Applications, ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 45444-45452, ISSN: 1944-8244

Journal article

Petrova NL, Cai Q, Petrov PK, Saiz E, Shanahan CM, Edmonds MEet al., 2020, Can novel bone substitutes withstand the enhanced resorbing activity of Charcot osteoclasts?, Publisher: WILEY, Pages: 48-48, ISSN: 0742-3071

Conference paper

Petrova NL, Petrov PK, Shanahan CM, Edmonds MEet al., 2020, Clinical care: Technology, Publisher: WILEY, Pages: 6-6, ISSN: 0742-3071

Conference paper

Doiron B, Gusken NA, Lauri A, Li Y, Mihai A, Matsui T, Bower R, Huettenhoffer L, Regoutz A, Forno SD, Fearn S, Petrov PK, Cortes E, Cohen LF, Alford NM, Lischner J, Petrov P, Maier SA, Oulton RFet al., 2020, Hot Carrier Optoelectronics with Titanium Nitride, Lasers and Electro-Optics Society Annual Meeting-LEOS, ISSN: 1092-8081

© 2020 OSA. Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.

Conference paper

Gusken NA, Lauri A, Li Y, Jacassi A, Matsui T, Doiron B, Bower R, Regoutz A, Mihai A, Petrov PK, Oulton RF, Cohen LF, Maier SAet al., 2020, IR hot carrier based photodetection in titanium nitride oxide thin film-Si junctions, MRS Advances, Vol: 5, Pages: 1843-1850, ISSN: 2059-8521

Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.

Journal article

Doiron B, Güsken NA, Lauri A, Li Y, Mihai A, Matsui T, Bower R, Huettenhoffer L, Regoutz A, Forno SD, Fearn S, Petrov PK, Cortés E, Cohen LF, Alford NM, Lischner J, Petrov P, Maier SA, Oulton RFet al., 2020, Hot carrier optoelectronics with titanium nitride

Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.

Conference paper

Cohen L, Boldrin D, Johnson F, Thompson R, Mihai AP, Zou B, Griffiths J, Gubeljak P, Ormandy KL, Manuel P, Khalyavin DD, Ouladdiaf B, Petrov P, Branford W, Cohen LFet al., 2019, The biaxial strain dependence of magnetic order in spin frustrated mn3nin thin films, Advanced Functional Materials, Vol: 29, ISSN: 1616-301X

Multi-component magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetisation for energy efficient memory, data storage and cooling applications. Strong spin-lattice coupling extends this functionality further by allowing electric-field-control of magnetisation via strain coupling with a piezoelectric . Here we explore the magnetic phase diagram of piezomagnetic Mn3NiN thin films, with a frustrated non-collinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρxy, at low temperature, that transforms at a well-defined Néel transition temperature (TN) into a soft ferrimagnetic-like (FIM) state at high temperatures. In stark contrast, under tensile strain the low temperature canted AFM phase transitions to a state where ρxy is an order of magnitude smaller and therefore consistent with a low magnetisation phase. Neutron scattering confirms that the high temperature FIM-like phase of compressively strained films is magnetically ordered and the transition at TN is 1st-order. Our results open the field towards future exploration of electric-field driven piezospintronic and thin film caloric cooling applications in both Mn3NiN itself and the broader Mn3AN family.

Journal article

Cohen L, Boldrin D, 2019, Anomalous Hall effect in noncollinear antiferromagnetic Mn 3NiN thin films, Physical Review Materials, Vol: 3, ISSN: 2475-9953

We have studied the anomalous Hall effect (AHE) in strained thin lms of the frustrated anti-ferromagnet Mn3NiN. The AHE does not follow the conventional relationships with magnetizationor longitudinal conductivity and is enhanced relative to that expected from the magnetization inthe antiferromagnetic state belowTN= 260 K. This enhancement is consistent with origins fromthe non-collinear antiferromagnetic structure, as the latter is closely related to that found in Mn3Irand Mn3Pt where a large AHE is induced by the Berry curvature. As the Berry phase inducedAHE should scale with spin-orbit coupling, yet larger AHE may be found in other members of thechemically exible Mn3AN structure.

Journal article

Doiron B, Li Y, Mihai A, Bower R, Alford NM, Petrov PK, Maier SA, Oulton RFet al., 2019, Plasmon-enhanced electron harvesting in robust titanium nitride nanostructures, The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces, Vol: 123, Pages: 18521-18527, ISSN: 1932-7447

Titanium nitride (TiN) continues to prove itself as an inexpensive, robust, and efficient alternative to gold in plasmonic applications. Notably, TiN has improved hot electron-harvesting and photocatalytic abilities compared to gold systems, which we recently attributed to the role of oxygen in TiN and its native semiconducting TiO2–x surface layer. Here, we explore the role of localized surface plasmon resonances (LSPRs) on electron harvesting across the TiN/TiO2–x interface and probe the resilience of TiN nanostructures under high-power laser illumination. To investigate this, we fabricate TiN strips, in which the lateral confinement allows for the polarization-selective excitation of the LSPR. Using ultrafast pump–probe spectroscopy, optical characterization, and Raman vibrational spectroscopy, we relate the differences and changes observed in the electron behavior to specific material properties. We observe plasmon-enhanced electron harvesting beyond what is expected resulting from the enhanced absorption of the plasmonic mode. We accredit this to the surface oxide damping the plasmon resonance, providing additional nonradiative loss channels. Subsequently, we show that low-power annealing of the surface oxide layer reduces the trap density at the interface and increases the initial harvested electron concentration. The unique properties of TiN make it important in the future development of plasmonic electron-harvesting applications.

Journal article

Pang JS, Theodorou IG, Centeno A, Petrov PK, Alford NM, Ryan MP, Xie Fet al., 2019, Tunable three-dimensional plasmonic arrays for large near-infrared fluorescence enhancement, ACS Applied Materials and Interfaces, Vol: 11, Pages: 23083-23092, ISSN: 1944-8244

Metal-enhanced fluorescence (MEF), resulting from the near-field interaction of fluorophores with metallic nanostructures, has emerged as a powerful tool for dramatically improving the performance of fluorescence-based biomedical applications. Allowing for lower autofluorescence and minimal photoinduced damage, the development of multifunctional and multiplexed MEF platforms in the near-infrared (NIR) windows is particularly desirable. Here, a low-cost fabrication method based on nanosphere lithography is applied to produce tunable three-dimensional (3D) gold (Au) nanohole–disc arrays (Au-NHDAs). The arrays consist of nanoscale glass pillars atop nanoholes in a Au thin film: the top surfaces of the pillars are Au-covered (effectively nanodiscs), and small Au nanoparticles (nanodots) are located on the sidewalls of the pillars. This 3D hole–disc (and possibly nanodot) construct is critical to the properties of the device. The versatility of our approach is illustrated through the production of uniform and highly reproducible Au-NHDAs with controlled structural properties and tunable optical features in the NIR windows. Au-NHDAs allow for a very large NIR fluorescence enhancement (more than 400 times), which is attributed to the 3D plasmonic structure of the arrays that allows strong surface plasmon polariton and localized surface plasmon resonance coupling through glass nanogaps. By considering arrays with the same resonance peak and the same nanodisc separation distance, we show that the enhancement factor varies with nanodisc diameter. Using computational electromagnetic modeling, the electric field enhancement at 790 nm was calculated to provide insights into excitation enhancement, which occurs due to an increase in the intensity of the electric field. Fluorescence lifetime measurements indicate that the total fluorescence enhancement may depend on controlling excitation enhancement and therefore the array morphology. Our findings provide important in

Journal article

Gusken NA, Lauri A, Li Y, Matsui T, Doiron B, Bower R, Regoutz A, Mihai A, Petrov PK, Oulton RF, Cohen LF, Maier SAet al., 2019, TiO2-x-enhanced IR hot carrier based photodetection in metal thin film-si junctions, ACS Photonics, Vol: 6, Pages: 953-960, ISSN: 2330-4022

We investigate titanium nitride (TiN) thin film coatings on silicon for CMOS-compatible sub-bandgap charge separation upon incident illumination, which is a key feature in the vast field of on-chip photodetection and related integrated photonic devices. Titanium nitride of tunable oxidation distributions serves as an adjustable broadband light absorber with high mechanical robustness and strong chemical resistivity. Backside-illuminated TiN on p-type Si (pSi) constitutes a self-powered and refractory alternative for photodetection, providing a photoresponsivity of about ∼1 mA/W at 1250 nm and zero bias while outperforming conventional metal coatings such as gold (Au). Our study discloses that the enhanced photoresponse of TiN/pSi in the near-infrared spectral range is directly linked to trap states in an ultrathin TiO2–x interfacial interlayer that forms between TiN and Si. We show that a pSi substrate in conjunction with a few nanometer thick amorphous TiO2–x film can serve as a platform for photocurrent enhancement of various other metals such as Au and Ti. Moreover, the photoresponse of Au on a TiO2–x/pSi platform can be increased to about 4 mA/W under 0.45 V reverse bias at 1250 nm, allowing for controlled photoswitching. A clear deviation from the typically assumed Fowler-like response is observed, and an alternative mechanism is proposed to account for the metal/semiconductor TiO2–x interlayer, capable of facilitating hole transport.

Journal article

Doiron B, Mota M, Wells MP, Bower R, Mihai A, Li Y, Cohen LF, Alford NM, Petrov PK, Oulton RF, Maier SAet al., 2019, Quantifying figures of merit for localized surface plasmon resonance applications: a materials survey, ACS Photonics, Vol: 6, Pages: 240-259, ISSN: 2330-4022

Using localized surface plasmon resonances (LSPR) to focus electromagnetic radiation to the nanoscale shows the promise of unprecedented capabilities in optoelectronic devices, medical treatments and nanoscale chemistry, due to a strong enhancement of light-matter interactions. As we continue to explore novel applications, we require a systematic quantitative method to compare suitability across different geometries and a growing library of materials. In this work, we propose application-specific figures of merit constructed from fundamental electronic and optical properties of each material. We compare 17 materials from four material classes (noble metals, refractory metals, transition metal nitrides, and conductive oxides) considering eight topical LSPR applications. Our figures of merit go beyond purely electromagnetic effects and account for the materials’ thermal properties, interactions with adjacent materials, and realistic illumination conditions. For each application we compare, for simplicity, an optimized spherical antenna geometry and benchmark our proposed choice against the state-of-the-art from the literature. Our propositions suggest the most suitable plasmonic materials for key technology applications and can act as a starting point for those working directly on the design, fabrication, and testing of such devices.

Journal article

Maslakov K, Teterin YA, Popel AJ, Teterin AY, Ivanov KE, Kalmykov SN, Petrov VG, Petrov PK, Farnan Iet al., 2018, XPS study of ion irradiated and unirradiated CeO2 bulk and thin film samples, APPLIED SURFACE SCIENCE, Vol: 448, Pages: 154-162, ISSN: 0169-4332

Journal article

Maslakov KI, Teterin YA, Ryzhkov MV, Popel AJ, Teterin AY, Ivanov KE, Kalmykov SN, Petrov VG, Petrov PK, Farnan Iet al., 2018, The electronic structure and the nature of the chemical bond in CeO2, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 20, Pages: 16167-16175, ISSN: 1463-9076

Journal article

Wells M, Bower R, Kilmurray B, Zou B, Mihai AP, GOBALAKRICHENANE G, Alford NM, Oulton RFM, Cohen L, Maier SA, ZAYATS A, Petrov PKet al., 2018, Temperature stability of thin film refractory plasmonic materials, Optics Express, Vol: 12, Pages: 15726-15744, ISSN: 1094-4087

Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their stability at high operational temperatures. However, investigation of the reproducibility of the optical properties after thermal cycling between room and elevated temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, SrRuO3 and SrNbO3 are investigated to assess their viability for robust refractory plasmonic applications. These results are further compared to the performance of SrMoO3 reported in literature. Films ranging in thickness from 50 to 105 nm are deposited on MgO, SrTiO3 and Si substrates by e-beam evaporation, RF magnetron sputtering and pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 to 1000° C for one hour, to establish the maximum cycling temperature and potential longevity at elevated temperatures for each material. It is found that SrRuO3 retains metallic behaviour after annealing at 800° C, while SrNbO3 undergoes a phase transition resulting in a loss of metallic behaviour after annealing at 400° C. Importantly, the optical properties of TiN and TiON are degraded as a result of oxidation and show a loss of metallic behaviour after annealing at 500° C, while the same is not observed in Au until annealing at 600° C. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.

Journal article

Petrov PK, Wells M, Zou B, Mihai A, Bower R, Doiron B, Regoutz A, Fearn S, Maier S, Alford Net al., 2018, Multiphase strontium molybdate thin films for plasmonic local heating applications, Optical Materials Express, Vol: 8, Pages: 1806-1817, ISSN: 2159-3930

In the search for alternative plasmonic materials SrMoO3 has recently been identified as possessing a number of desirable optical properties. Owing to the requirement for many plasmonic devices to operate at elevated temperatures however, it is essential to characterize the degradation of these properties upon heating. Here, SrMoO3 thin films are annealed in air at temperatures ranging from 75 - 500{\deg} C. Characterizations by AFM, XRD, and spectroscopic ellipsometry after each anneal identify a loss of metallic behaviour after annealing at 500{\deg} C, together with the underlying mechanism. Moreover, it is shown that by annealing the films in nitrogen following deposition, an additional crystalline phase of SrMoO4 is induced at the film surface, which suppresses oxidation at elevated temperatures.

Journal article

Boldrin D, Mihai A, Zou B, Zemen J, Thompson R, Ware E, Neamtu B, Ghivelder L, Esser B, McComb DW, Petrov PK, Cohen LFet al., 2018, Giant Piezomagnetism in Mn3NiN., ACS Appl Mater Interfaces, Vol: 10, Pages: 18863-18868

Controlling magnetism with electric field directly or through strain-driven piezoelectric coupling remains a key goal of spintronics. Here we demonstrate that giant piezomagnetism, a linear magneto-mechanic coupling effect, is manifest in antiperovskite Mn3NiN, facilitated by its geometrically frustrated antiferromagnetism opening the possibility of new memory device concepts. Films of Mn3NiN with intrinsic biaxial strains of ±0.25% result in Néel transition shifts up to 60K and magnetisation changes consistent with theory. Films grown on BaTiO3 display a striking magnetisation jump in response to uniaxial strain from the intrinsic BaTiO3 structural transition, with an inferred 44% strain coupling efficiency and a magnetoelectric coefficient α (where α=dB/dE) of 0.018 G cm/V. The latter agrees with the 1000-fold increase over Cr2O3 predicted by theory. Overall our observations pave the way for further research into the broader family of Mn-based antiperovskites where yet larger piezomagnetic effects are predicted to occur at room temperature.

Journal article

Mignuzzi S, Mota M, Coenen T, Li Y, Mihai A, Petrov PK, Oulton RF, Maier SA, Sapienza Ret al., 2018, Energy-momentum cathodoluminescence spectroscopy of dielectric nanostructures, ACS Photonics, Vol: 5, Pages: 1381-1387, ISSN: 2330-4022

Precise knowledge of the local density of optical states (LDOS) is fundamental to understanding nanophotonic systems and devices. Complete LDOS mapping requires resolution in energy, momentum, and space, and hence a versatile measurement approach capable of providing simultaneous access to the LDOS components is highly desirable. Here, we explore a modality of cathodoluminescence spectroscopy able to resolve, in single acquisitions, the dispersion in energy and momentum of the radiative LDOS. We perform measurements on a titanium nitride diffraction grating, bulk molybdenum disulfide, and silicon to demonstrate that the technique can probe and disentangle the dispersion of coherent and incoherent cathodoluminescence signals. The approach presented raises cathodoluminescence spectroscopy to a versatile tool for subwavelength design and optimization of nanophotonic devices in the reciprocal space.

Journal article

Ptashnik SV, Mikhailov AK, Yastrebov AV, Petrov PK, Liu W, Alford N, Hirsch S, Kozyrev ABet al., 2017, Ferroelectric thin film acoustic devices with electrical multiband switching ability, Scientific Reports, Vol: 7, ISSN: 2045-2322

Design principles of a new class of microwave thin film bulk acoustic resonators with multiband resonance frequency switching ability are presented. The theory of the excitation of acoustic eigenmodes in multilayer ferroelectric structures is considered, and the principle of selectivity for resonator with an arbitrary number of ferroelectric layers is formulated. A so called “criterion function” is suggested that allows to determine the conditions for effective excitation at one selected resonance mode with suppression of other modes. The proposed theoretical approach is verifiedusing thepreexisting experimental data published elsewhere. Finally, the possible application of the two ferroelectric layers structures for switchable microwave overtone resonators, binary and quadrature phase-shift keying modulators are discussed. These devices could play a pivotal role in the miniaturization of microwave front-end antenna circuits.

Journal article

Wells MP, Zou B, Doiron BG, Kilmurray R, Mihai AP, Oulton RF, Gubeljak P, Ormandy K, Mallia G, Harrison N, Cohen LF, Maier S, Petrov PKet al., 2017, Tunable, Low Optical Loss Strontium Molybdate Thin Films for Plasmonic Applications, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071

Strontium molybdate (SrMoO3) thin films are grown epitaxially on strontium titanate (SrTiO3), magnesium oxide (MgO), and lanthanum aluminate (LaAlO3) substrates by pulsed laser deposition and possess electrical resistivity as low as 100 µΩ cm at room temperature. SrMoO3 is shown to have optical losses, characterized by the product of the Drude broadening, ΓD, and the square of the plasma frequency, ωpu2, significantly lower than TiN, though generally higher than Au. Also, it is demonstrated that there is a zero-crossover wavelength of the real part of the dielectric permittivity, which is between 600 and 950 nm (2.05 and 1.31 eV), as measured by spectroscopic ellipsometry. Moreover, the epsilon near zero (ENZ) wavelength can be controlled by engineering the residual strain in the films, which arises from a strain dependence of the charge carrier concentration, as confirmed by density of states calculations. The relatively broad tunability of ENZ behavior observed in SrMoO3 demonstrates its potential suitability for transformation optics along with plasmonic applications in the visible to near infrared spectral range.

Journal article

Doiron B, Li Y, Mihai AP, Cohen LF, Pretrov PK, Alford NM, Oulton RF, Maier SAet al., 2017, Comparison of the ultrafast hot electron dynamics of titanium nitride and gold for plasmonic applications, SPIE Optics + Photonics Conference on Plasmonics - Design, Materials, Fabrication, Characterization, and Applications XV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

With similar optical properties to gold and high thermal stability, titanium nitride continues to prove itself as a promising plasmonic material for high-temperature applications in the visible and near-infrared. In this work, we use transient pump probe differential reflection measurements to compare the electron energy decay channels in titanium nitride and gold thin films. Using an extended two temperature model to incorporate the photoexcited electrons, it is possible to separate the electron-electron and electron-phonon scattering contributions immediately following the arrival of the pump pulse. This model allows for incredibly accurate determination of the internal electronic properties using only optical measurements. As the electronic properties are key in hot electron applications, we show that titanium nitide has substantially longer electron thermalization and electron-phonon scattering times. With this, we were also able to resolve electron thermal conduction in the film using purely optical measurements.

Conference paper

Braic L, Vasilantonakis N, Mihai A, Villar-Garcia I, Fearn S, Zou B, Alford N, Doiron B, Oulton R, Maier S, Zayats A, Petrov Pet al., 2017, Titanium oxynitride thin films with tuneable double epsilon-near-zero behaviour for nanophotonic applications, ACS Applied Materials and Interfaces, Vol: 9, Pages: 29857-29862, ISSN: 1944-8244

Titanium oxynitride (TiOxNy) thin films are fabricated using reactive magnetron sputtering. The mechanism of their growth formation is explained, and their optical properties are presented. The films grown when the level of residual oxygen in the background vacuum was between 5 nTorr to 20 nTorr exhibit double epsilon-near-Zero (2-ENZ) behavior with ENZ1 and ENZ2 wavelengths tunable in the 700–850 and 1100–1350 nm spectral ranges, respectively. Samples fabricated when the level of residual oxygen in the background vacuum was above 2 × 10–8 Torr exhibit nonmetallic behavior, while the layers deposited when the level of residual oxygen in the background vacuum was below 5 × 10–9 Torr show metallic behavior with a single ENZ value. The double ENZ phenomenon is related to the level of residual oxygen in the background vacuum and is attributed to the mixture of TiN and TiOxNy and TiOx phases in the films. Varying the partial pressure of nitrogen during the deposition can further control the amount of TiN, TiOx, and TiOxNy compounds in the films and, therefore, tune the screened plasma wavelengths. A good approximation of the ellipsometric behavior is achieved with Maxwell–Garnett theory for a composite film formed by a mixture of TiO2 and TiN phases suggesting that double ENZ TiOxNy films are formed by inclusions of TiN within a TiO2 matrix. These oxynitride compounds could be considered as new materials exhibiting double ENZ in the visible and near-IR spectral ranges. Materials with ENZ properties are advantageous for designing the enhanced nonlinear optical response, metasurfaces, and nonreciprocal behavior.

Journal article

Adabi M, Lischner J, Hanham SM, Shaforost O, Wang R, Mihai, Hao L, Petrov P, Klein Net al., 2017, Microwave study of field-effect devices based on graphene/aluminum nitride/graphene structures, Scientific Reports, Vol: 7, ISSN: 2045-2322

Metallic gate electrodes are often employed to control the conductivity of graphene based field effect devices. The lack of transparency of such electrodes in many optical applications is a key limiting factor. We demonstrate a working concept of a double layer graphene field effect device that utilizes a thin film of sputtered aluminum nitride as dielectric gate material. For this system, we show that the graphene resistance can be modified by a voltage between the two graphene layers. We study how a second gate voltage applied to the silicon back gate modifies the measured microwave transport data at around 8.7 GHz. As confirmed by numerical simulations based on the Boltzmann equation, this system resembles a parallel circuit of two graphene layers with different intrinsic doping levels. The obtained experimental results indicate that the graphene-aluminum nitride-graphene device concept presents a promising technology platform for terahertz- to- optical devices as well as radio-frequency acoustic devices where piezoelectricity in aluminum nitride can also be exploited.

Journal article

Yu H, Sidiropoulos T, Liu W, Ronning C, Petrov P, Oh S, Maier SA, Jin P, Oulton Ret al., 2017, Influence of silver film quality on the threshold of plasmonic nanowire lasers, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071

Plasmonic nanowire lasers are nanoscopic sources of light operating at deep subwavelength scales with ultrafast dynamics.[1-6] Such lasers enable the investigation of enhanced light-matter interactions and can have large impact on applications in the fields of non-linear optics, sensing, and optical communications.[7-12] However, metal-based lasers suffer from high losses, caused by the inherent electron scattering in metals, which leads to an increased lasing threshold and limits their use in applications. To minimise losses and thus improve their performance, it has been suggested to use metal films of high quality which ideally have an ultra-flat surface with a high crystalline perfection.[1, 13-16] However, investigating the effects of Ag film quality on the performance of hybrid-plasmonic zinc oxide (ZnO) nanowire lasers this work finds that such a laser geometry is dominated by losses in the gain material.

Journal article

Pang J, Theodorou I, Centeno A, Petrov P, Alford N, Ryan M, Xie Fet al., 2016, Gold nanodisc arrays as near infrared metal-enhanced fluorescence platforms with tuneable enhancement factors, Journal of Materials Chemistry C, Vol: 5, Pages: 917-925, ISSN: 2050-7534

Metal enhanced fluorescence (MEF) is a physical effect through which the near-field interaction of fluorophores with metallic nanoparticles can lead to large fluorescence enhancement. MEF can be exploited in many fluorescence-based biomedical applications, with potentially significant improvement in detection sensitivity and contrast enhancement. Offering lower autofluorescence and minimal photoinduced damage, the development of effective and multifunctional MEF platforms in the near-infrared (NIR) region, is particularly desirable. In this work, the enhancement of NIR fluorescence caused by interaction with regular arrays of cylindrical gold (Au) nanoparticles (nanodiscs), fabricated through nanosphere lithography, is reported. Significant MEF of up to 235 times is obtained, with tuneable enhancement factors. The effect of array structure on fluorescence enhancement is investigated by semi-quantitatively de-convoluting excitation enhancement from emission enhancement, and modelling the local electric field enhancement. By considering arrays of Au nanodiscs with the same extinction maximum, it is shown that the excitation enhancement, due to increased electric field, is not significantly different for the particle sizes and separation distances considered. Rather, it is seen that the emission from the fluorophore is strongly enhanced, and is dependent on the topography, in particular particle size. The results show that the structural characteristics of Au nanodisc arrays can be manipulated to tune their enhancement factor, and hence their sensitivity.

Journal article

Popel A, Le Solliec S, Lampronti GI, Day J, Petrov PK, Farnan Iet al., 2016, The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2 matrix, Journal of Nuclear Materials, Vol: 484, Pages: 332-338, ISSN: 1873-4820

This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO2 matrix in water, as a simulant for the UO2 matrix of spent nuclear fuel. For this purpose, thin films of CeO2 on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO2 samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO2 matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO2 films after the dissolution experiment.

Journal article

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