With thermal phase lag measurements, current paths are tracked in a Class A radio frequency (RF) power amplifier at 2¿GHz. The amplifier is heterodynally driven at 440¿MHz and 2¿GHz, and its resulting thermal field was inspected, respectively, at 1013 and 113¿Hz with an infrared lock-in thermography system. The phase lag maps evidence with a higher sensitivity than thermal amplitude measurements an input-output loop due to a substrate capacitive coupling. This limits the amplifier's performance, raising the power consumption in certain components. Other information relative to local power consumption and amplifier operation is also inferred. This approach allows the local non-invasive testing of integrated systems regardless of their operating frequency.
With thermal phase lag measurements, current paths are tracked in a Class A radio frequency (RF) power amplifier at 2 GHz. The amplifier is heterodynally driven at 440 MHz and 2 GHz, and its resulting thermal field was inspected, respectively, at 1013 and 113 Hz with an infrared lock-in thermography system. The phase lag maps evidence with a higher sensitivity than thermal amplitude measurements an input-output loop due to a substrate capacitive coupling. This limits the amplifier’s performance, raising the power consumption in certain components. Other information
relative to local power consumption and amplifier operation is also inferred. This approach allows the local non-invasive testing of integrated systems regardless of their operating frequency.
Ochoa, D. A.; Esteves, G.; Jones, J.L.; Rubio-Marcos, F.; Fernández, J.F; Garcia, J. E. Applied physics letters Vol. 108, num. 14, p. 142901-1-142901-5 DOI: 10.1063/1.4945593 Data de publicació: 2016-04-04 Article en revista
Polymorphic phase boundaries (PPBs) in piezoelectric materials have attracted significant interest in recent years, in particular because of the unique properties that can be found in their vicinity. However, to fully harness their potential as micro-nanoscale functional entities, it is essential to achieve reliable and precise control of their piezoelectric response, which is due to two contributions known as intrinsic and extrinsic. In this work we have used a (K,Na)NbO3-based lead-free piezoceramic as a model system to investigate the evolution of the extrinsic contribution around a PPB. X-ray diffraction measurements are performed over a wide range of temperatures in order to determine the structures and transitions. The relevance of the extrinsic contribution at the PPB region is evaluated by means of nonlinear dielectric response measurements. Though it is widely appreciated that certain intrinsic properties of ferroelectric materials increase as PPBs are approached, our results demonstrate that the extrinsic contribution also maximizes. An enhancement of the extrinsic contribution is therefore also responsible for improving the functional properties at the PPB region. Rayleigh’s law is used to quantitatively analyze the nonlinear response. As a result, an evolution of the domain wall motion dynamics through the PPB region is detected. This work demonstrates that the extrinsic contribution at a PPB may have a dynamic role in lead-free piezoelectric materials, thereby exerting a far greater influence on their functional properties than that considered to date.
We report the nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating immersed in water. In the linear regime, the system presents high focal gain (32 dB), with a narrow beam-width and intense side lobes as it is common in focusing by Fresnel-like lenses. Activating the nonlinearity of the host medium by using high amplitude incident waves, the focusing properties of the lens dramatically change. Theoretical predictions show that the focal gain of the system extraordinary increases in the strongly nonlinear regime (Mach number of 6.1 × 10-4). Particularly, the harmonic generation is locally activated at the focal spot, and the second harmonic beam is characterized by strongly reduced side-lobes and an excellent beam profile as experiments show in agreement with theory. The results can motivate applications in medical therapy or second harmonic imaging.
Stern-Taulats, E.; Gracia-Condal, A.; Planes, A.; Lloveras, P.; Del Barrio, M.; Tamarit, J. Ll.; Pramanick, Sabyasachi; Majumdar, Subham; Mañosa Carrera, Lluis Applied physics letters Vol. 107, num. 15, p. 152409-1-152409-4 DOI: 10.1063/1.4933409 Data de publicació: 2015-10-12 Article en revista
We report on the adiabatic temperature changes (Delta T) associated with the magnetocaloric and barocaloric effects in a Fe49Rh51 alloy, For the magnetocaloric effect, data derived from entropy curves are compared to direct thermometry measurements. The agreement between the two sets of data provides support to the estimation of Delta T for the barocaloric effect, which are indirectly determined from entropy curves. Large Delta T values are obtained at relatively low values of magnetic field (2 T) and hydrostatic pressure (2.5 kbar), It is also shown that both magnetocaloric and barocaloric effects exhibit good reproducibility upon magnetic field and hydrostatic pressure cycling, over a considerable temperature range. (C) 2015 AIP Publishing LLC
We demonstrate infrared femtosecond laser-induced inversion of ferroelectric domains. This process can be realised solely by using tightly focused laser pulses without application of any electric field prior to, in conjunction with, or subsequent to the laser irradiation. As most ferroelectric crystals like LiNbO3, LiTaO3, and KTiOPO4 are transparent in the infrared, this optical poling method allows one to form ferroelectric domain patterns much deeper inside a ferroelectric crystal than by using ultraviolet light and hence can be used to fabricate practical devices. We also propose in situ diagnostics of the ferroelectric domain inversion process by monitoring the Cerenkov second harmonic signal, which is sensitive to the appearance of ferroelectric domain walls.
Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.
An approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.
Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
We study the propagation of waves in a periodic array of absorbing layers. We report an anomalous increase of wave transmission through the structure related to a decrease of the absorption around the Bragg frequencies. The effect is first discussed in terms of a generic coupled wave model extended to include losses, and its predictions can be applied to different types of waves propagating in media with periodic modulation of the losses at the wavelength scale. The particular case of sound waves in an array of porous layers embedded in air is considered. An experiment designed to test the predictions demonstrates the existence of the enhanced transmission band.
Copyright 2014 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
Patterns are fabricated on 290 nm thick nanostructured porous silicon layers by phase-mask laser interference using single pulses of an excimer laser (193 nm, 20 ns pulse duration). The dynamics of pattern formation is studied by measuring in real time the intensity of the diffraction orders 0 and 1 at 633 nm. The results show that a transient pattern is formed upon melting at intensity maxima sites within a time <30 ns leading to a permanent pattern in a time <100 ns upon solidification at these sites. This fast process is compared to the longer one (>1-µs) upon melting induced by homogeneous beam exposure and related to the different scenario for releasing the heat from hot regions. The diffraction efficiency of the pattern is finally controlled by a combination of laser fluence and initial thickness of the nanostructured porous silicon layer and the present results open perspectives on heat release management upon laser exposure as well as have potential for alternative routes for switching applications.
This work exploits the mirage effect to analyze multiple heat sources thermally interacting in an integrated circuit (IC) by means of a probe IR laser beam, which strikes on the die lateral walls and passes through the die substrate. Under such conditions, the criteria for locating such hot spots, as well as their relative power dissipation, are discussed on the basis of a theoretical model inferred in this work. Finally, the technique feasibility is shown in a real application scenario, obtaining 5-mu m spatial lateral resolution and an error in power dissipation measurements below 5%. This method may become a practical alternative to usual off-chip techniques for inspecting hot spots in ICs and to experimentally characterize heat flow in the semiconductor substrate. (C) 2014 AIP Publishing LLC.
An electrospray technique has been used to deposit SiO2 nanoparticles as insulator layer of a metal-insulator-metal device. Impedance spectroscopy measurements show that a 4.4 factor increase in capacitance is achieved compared to a continuous dielectric layer of the same permittivity and dimensions.
We propose and experimentally show the mechanism of beam super-collimation by axisymmetric photonic crystals, specifically by periodic (in propagation direction) structure of layers of concentric rings. The physical mechanism behind the effect is an inverse scattering cascade of diffracted wave components back into on-and near-axis angular field components, resulting in substantial enhancement of intensity of these components. We explore the super-collimation by numerical calculations and prove it experimentally. We demonstrate experimentally the axial field enhancement up to 7 times in terms of field intensity.
Here, we introduce bimodal atomic force microscopy operated with sub-nm and ultra-small, i.e., sub-angstrom, first and second mode amplitudes in ambient conditions. We show how the tip can be made to oscillate in the proximity of the surface and in perpetual contact with the adsorbed water layers while the second mode amplitude and phase provide enhanced contrast and sensitivity. Nonlinear and nonmonotonic behavior of the experimental observables is discussed theoretically with a view to high resolution, enhanced contrast, and minimally invasive mapping. Fractions of meV of energy dissipation are shown to provide contrast above the noise level.
Here, we introduce bimodal atomic force microscopy operated with sub-nm and ultra-small, i.e., sub-angstrom, first and second mode amplitudes in ambient conditions. We show how the tip can be made to oscillate in the proximity of the surface and in perpetual contact with the adsorbed water layers while the second mode amplitude and phase provide enhanced contrast and sensitivity.
Nonlinear and nonmonotonic behavior of the experimental observables is discussed theoretically with a view to high resolution, enhanced contrast, and minimally invasive mapping. Fractions of meV of energy dissipation are shown to provide contrast above the noise level.
Formica, N.; Ghosh, D.S.; Martinez-Otero, A.; Chen, T.; Martorell, J.; Pruneri, V. Applied physics letters Vol. 103, num. 18, p. 183304-1-183304-6 DOI: 10.1063/1.4827877 Data de publicació: 2013-10-28 Article en revista
We propose a transparent electrode consisting of an aluminum doped zinc oxide (AZO) layer capped with an ultrathin oxidized Ti film for indium-free bulk-heterojunction polymer solar cells (PSCs). The oxidized Ti increases the chemical, environmental, stability and the surface smoothness of AZO while still maintaining its electrical and optical properties. The application potential of the proposed transparent electrode is demonstrated in an inverted PSC, which shows an efficiency of 6.3%, very close to the value (7%) obtained in a similar structure using indium tin oxide. This efficiency is the highest reported to date for PSCs incorporating AZO electrodes.
We investigate beam shaping in broad area semiconductor amplifiers induced by a 2-dimensional (longitudinal and lateral) periodic modulation of the pump on a scale of several microns. The study is performed by solving numerically a (2¿+¿1)-dimensional model for the semiconductor amplifier. We show that, under realistic conditions, the anisotropic gain induced by the pump periodicity can show narrow angular profile of enhanced gain of less than 1°, providing an intrinsic filtering mechanism and eventually improving the spatial beam quality.
During the last years, many techniques have been developed to obtain thin crystalline films from commercial silicon ingots. Large market applications are foreseen in the photovoltaic field, where important cost reductions are predicted, and also in advanced microelectronics technologies as
three-dimensional integration, system on foil, or silicon interposers [Dross et al., Prog.
Photovoltaics 20, 770-784 (2012); R.Brendel, Thin Film Crystalline Silicon Solar Cells
(Wiley-VCH, Weinheim, Germany 2003); J. N. Burghartz, Ultra-Thin Chip Technology and
Applications (Springer ScienceþBusiness Media, NY, USA, 2010)]. Existing methods produce “one at a time” silicon layers, once one thin film is obtained, the complete process is repeated to obtain the next layer. Here, we describe a technology that, from a single crystalline silicon wafer,
produces a large number of crystalline films with controlled thickness in a single technological step.
We propose and experimentally demonstrate a mechanism of sound wave concentration based on soft reflections in chirped sonic crystals. The reported controlled field enhancement occurs at around particular (bright) planes in the crystal and is related to a progressive slowing down of the sound wave as it propagates along the material. At these bright planes, a substantial concentration of the energy (with a local increase up to 20 times) was obtained for a linear chirp and for frequencies around the first band gap. A simple couple mode theory is proposed that interprets and estimates the observed effects. Wave concentration energy can be applied to increase the efficiency of detectors and absorbers.
This paper combines the infrared lock-in thermography (IR-LIT) and heterodyne excitation techniques to detect high-frequency capacitive currents due to intradie electrical coupling between microelectronic devices or more complex systems. Modulating the excitation with the heterodyne approach, we drive devices or complex systems with high frequency electrical signals in such a way that they behave as low frequency heat sources, modulating their temperature field at a frequency detectable by an IR-LIT system. This approach is analytically studied and extended to a bi-dimensional scenario, showing that the thermal information at low frequency depends on the electrical characteristics of the sample at high frequency.
A way to operate fundamental mode amplitude modulation atomic force microscopy is introduced which optimizes stability and resolution for a given tip size and shows negligible tip wear over extended time periods (~24¿h). In small amplitude small set-point (SASS) imaging, the cantilever oscillates with sub-nanometer amplitudes in the proximity of the sample, without the requirement of using large drive forces, as the dynamics smoothly lead the tip to the surface through the water layer. SASS is demonstrated on single molecules of double-stranded DNA in ambient conditions where sharp silicon tips (R¿~¿2–5¿nm) can resolve the right-handed double helix.
A way to operate fundamental mode amplitude
modulation atomic force microscopy is
introduced which optimizes stability and resolution for a given tip size and shows negligible tip
wear over extended time periods (
24 h). In small amplitude smal
l set-point (SASS) imaging,
the cantilever oscillates with sub-nanometer am
plitudes in the proximity of the sample, without
the requirement of using large drive forces, a
s the dynamics smoothly lead the tip to the surface
through the water layer. SASS is demonstrat
ed on single molecules of double-stranded DNA in
ambient conditions where sharp silicon tips (R
2–5 nm) can resolve the right-handed double
Hernandez, D.; Garin, M.; Trifonov, T.; Rodriguez, A.; Alcubilla, R. Applied physics letters Vol. 100, num. 9, p. 091901-1-091901-3 DOI: 10.1063/1.3688031 Data de publicació: 2012-02 Article en revista
Carboxylated multi-wall carbon-nanotubes (CNTs) monolayers are integrated on microfabricated all-polymer micro-electromechanical systems (pMEMS) resonator bridges on glass substrates. The structural layer of the MEMS bridges is a multilayer blended conductive polymer based on
poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) to which functionalized CNT monolayers are electrostatically attached. The resonance frequency (fres) of electrostatically
actuated pMEMS bridges was measured as a function of their length (32–67 lm) for different multilayer compositions. A significant increase in fres and quality factor (Q) with the addition of CNT monolayers to the PEDOT:PSS structural material is observed, demonstrating that CNT
monolayers can be used to modulate pMEMS resonator properties.
We report on the observation of Čerenkov emission of a third-harmonic frequency in a
two-dimensional nonlinear photonic crystal, where the second-order nonlinearity chi((2)) is spatially modulated by the reversal of ferroelectric domains. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions.
We demonstrate second and third harmonic generation from a GaP substrate 500 μm thick. The second harmonic field is tuned at the absorption resonance at 335 nm, and the third harmonic signal is tuned at 223 nm, in a range where the dielectric function is negative. These results show that a phase locking mechanism that triggers transparency at the harmonic wavelengths persists regardless of the dispersive properties of the medium, and that the fields propagate hundreds of microns without being absorbed even when the harmonics are tuned to portions of the spectrum that display
We show that the nonlinear optical activity of an organic molecule may be quenched by electron irradiation. Exploiting this effect, we inscribe periodic χ(2) patterns in the molecular films by means of a scanning electron microscope. The second harmonic diffraction efficiency of the resulting χ(2) gratings is measured. The relative intensity of the diffraction orders observed agrees with the expectations for a sheet of nonlinear dipoles with a periodic modulation. No linear diffraction is seen. The present method allows realizing any type of two-dimensional χ(2) pattern with a resolution only limited by the electron beam patterning capabilities.
Krautz, D.; Lunedei, E.; Puigdollers, J.; Badenes, G.; Alcubilla, R.; Cheylan, S. Applied physics letters Vol. 96, num. 3, p. 1-3 DOI: 10.1063/1.3276271 Data de publicació: 2010-01-18 Article en revista
A blend of the polymer poly 2- 2-ethylhexyloxy -5-methoxy-1,4-phenylenevinylene MEH-PPV
and the electron-transport molecule tris- 8-hydroxyquinoline aluminum Alq3 has been
investigated by means of electroluminescence and fluorescence spectroscopy, upon variation of the
Alq3 content in the blend.Adecreased interchain emission is observed upon increasing Alq3 content,
due to lower packing of the MEH-PPV chains which leads to a reduction in the interchain
interaction, excimer formation, and emission probability. A branching of MEH-PPV interchain and
intrachain emissive contributions is clearly time resolved and analyzed as a function of the Alq3
content. At high doping concentration, direct emission from Alq3 molecules is observed.
The following article appeared in Vuong, Luat T. ...[et al.]. Cavity-controlled radiative recombination of excitons in thin-film solar cells. Applied physics letters [en línia]. 2009, vol. 95 [Consulta 29/06/2010]. p. 233106-1/233106-3 and may be found at http://apl.aip.org/applab/v95/i23/p233107_s1?view=fulltext
We study the performance of photovoltaic devices when controlling the exciton radiative recombination time. We demonstrate that when high-quantum-yield fluorescent photovoltaic materials are placed within an optical cavity, the spontaneous emission of the radiative exciton is partially inhibited. The corresponding increase of the exciton lifetime results in an increase of the effective diffusion length and diffusion current. This performance maximizes when the thickness of the cell is comparable to the absorption length. We show that when typical parameter values of thin solar-cell devices are used, the efficiency may improve by as much as three times.
A vertical hybrid microcavity is fabricated by sandwiching a polymer layer between distributed Bragg reflectors (DBRs) composed of porous silicon photonic crystals. The DBRs are made by electrochemical etching of Si and consist of alternating porous Si layers of high and low porosity, the top DBR being a freestanding film. The hybrid microcavity demonstrates a deep microcavity
mode placed within a 200 nm wide photonic band gap, and reveals a many-fold enhancement of the third-order nonlinearity of the microcavity layer. The fabrication technique employed is rather simple, enabling the use of a variety of functional materials as the microcavity spacer.
Garin, M.; Trifonov, T.; Rodriguez, A.; Alcubilla, R.; Marquier, F.; Arnold, C.; Greffet, J. Applied physics letters Vol. 93, num. 8, p. 081913-1-081913-3 DOI: 10.1063/1.2976144 Data de publicació: 2008-08 Article en revista
We present a theoretical and experimental study on the effect of progressive porosity increase, through multiple oxidation/oxide removal steps, upon the optical characteristics in three-dimensional macroporous silicon. It is shown that, by increasing porosity, optical features can be pushed toward higher frequencies. Optimum porosities exist where normal or omnidirectional total reflection bandwidths are maximized, doubling the initial values. Results are confirmed experimentally through angle-resolved reflectance and thermal emission measurements.
Manosa, L.; Moya, X.; Planes, A.; Gutfleisch, O.; Lyubina, J.; Del Barrio, M.; Tamarit, J. Ll.; Aksoy, S.; Krenke, T.; Acet, M. Applied physics letters Vol. 92, num. 1, p. 2515.1-2515.3 Data de publicació: 2008-01 Article en revista
The capacitance system of a hyperboloidal tip and a rough surface is usually encountered in
analyzing electrostatic force microscopy images. In this letter, a perturbation approach has been
applied to solve for the electric potential of this system, in which the rough surface is treated as
perturbation from a flat one. For the first-variation solution, the boundary value problem is
represented in the prolate-spheroidal coordinate system and solved in terms of a generalized Fourier
series involving conical functions. Based on this solution, the tip-surface Coulombic interaction can
be computed. Sample calculations have been applied to sinusoidal surface profiles
In this paper we investigate the infrared thermal emission properties of macroporous silicon with modulated pore diameter. Samples with different pore modulation periodicities but fixed in-plane lattice constant are fabricated. Normal emission of these samples is measured between 373 and 673K673K. Room-temperature normal-incidence reflectance and transmission spectra are also measured and compared with the photonicband structure simulation. It is shown that thermal emission is suppressed due to photonic band gap effect along the pore axis in excellent agreement with the numerical calculations.