Table of contents

Polariton lasers are coherent emitters in which the fundamental constituents are not photons amplified by a gaining medium but hybrid, part exciton and part photon, quasi-particles named polaritons. In this review we discuss some of the main topics in the field of polariton lasing: we start from an introduction to the concepts of strong coupling regime and polaritons, we then discuss the mechanism of polariton lasing and the main difficulties in achieving it. Some of the main results on polariton lasing reported in the literature, from 2D samples to confined structures, are then reviewed. This latter case will allow us to discuss some of the peculiarities of polariton lasing with respect to traditional lasers. Polariton lasing mostly occurs at cryogenic temperatures, but we will see that it can also be observed at room temperature with a proper choice of materials. To conclude, we will discuss some perspectives for the field.

Pr_0.5Sr_0.5MO₃ (PSMO) films with tetragonal and orthorhombic structures were epitaxially grown on a [0 0 1]-oriented LaAlO₃ substrate (LAO) and a BaTiO₃ substrate (BTO), respectively. It was found that the M(T) curves of the tetragonal PSMO films exhibit one/two distinguished magnetic transition peaks depending on the thickness of the film, which is related to the competition between ferromagnetic (FM) and antiferromagnetic (AFM) interactions in the films. The tetragonal film shows an insulator-to-metal transition (MIT) as well as a metal-to-semiconductor transition with increasing temperature from 10 to 300 K, and the AFM insulating state of the film can be transformed into the metallic state under a magnetic field of 5 T due to the collapse of the AFM insulator state. For the orthorhombic film on BTO substrate, only a FM metallic state is observed without MIT from 10 to 300 K. In addition, a significant colossal magnetoresistance effect is observed with a wide temperature range from T_C (182 K) to 10 K for the tetragonal films, while only around T_C (240 K) for the orthorhombic films.

ε-Fe₃N films on c-plane GaN are fabricated through nitridation of amorphous Fe films. From x-ray diffraction, the structures of these ε-Fe₃N films are found to consist of two crystal orientations of ε-Fe₃N, i.e. (0 0 2) and (1 1 1). The binding energies of Fe ions in the samples are analysed by x-ray photoelectron spectroscopy, both Fe–N and Fe–O–N peaks are observed. Scanning electron microscopy shows that the surface morphology of the ε-Fe₃N films is island-like. In particular, these films are ferromagnetic at room temperature, with a coercivity of about 200 Oe according to the measured magnetic hysteresis loop. The ferromagnetism is further studied by ferromagnetic resonance spectra. With increasing angle between the incident field and the sample plane, the resonance magnetic fields of Fe and ε-Fe₃N films exhibit different behaviours; the difference can be interpreted by Kittel's theory. In addition, the I–V curves and Hall measurement indicate that the ε-Fe₃N films are good conductors at room temperature. On the whole, these magnetic and electrical properties demonstrate that the ε-Fe₃N films are appropriate for GaN-based spintronic devices.

Highly doped n-type ZnO films have been grown on n-type and p-type Si substrates by atomic layer deposition (ALD). Transmission electron microscopy shows columnar growth of the ZnO films with randomly oriented grains and a very thin interfacial layer of SiO_x(x ⩽ 2) with a thickness below 0.4 nm to the Si substrate. Current–voltage and capacitance–voltage measurements performed at temperatures from 50 to 300 K reveal a strong rectifying behaviour on both types of substrates with an ideality factor close to unity between 180 and 280 K. Using the classical approach of thermionic emission, the barrier heights of the ZnO/n-Si and ZnO/p-Si junctions have been deduced and consistent values are obtained yielding a work function of n-type ZnO close to 4.65 eV.

Infrared (IR) emission spectroscopy was performed on N₂ + H₂ microwave discharges at pressures ranging between 300 and 3000 mTorr. The relative atomic density of N and H was measured by optical actinometry in the IR region at various total gas pressures. The effect of relative hydrogen partial pressure (between 10 and 90% in the discharge) on N and H relative density was also investigated. Although rarely studied, optical actinometry in the IR region has nevertheless provided numerous advantages over traditional techniques performed in the UV–visible (UV–VIS) spectral region. Results show that despite the decrease in the radiative state of the N and H atoms as a function of pressure, their ground state density increased. With increased relative hydrogen concentration under constant pressure, both the ground and the radiative state density of the H atoms increased similarly to that recorded by actinometry, whereas those of the N atoms decreased as expected. In comparing the results of the H-atom density measured in the well-documented UV–visible region and the IR region, optical actinometry confirms the accuracy of the IR method.

It is shown that a metallic state can be induced on the surface of SrTiO₃ crystals by the electron beam evaporation of oxygen deficient alumina or insulating granular aluminium. No special preparation nor heating of the SrTiO₃ surface is needed. Final metallic or insulating states can be obtained depending on the oxygen pressure during the evaporation process. Photoconductivity and electrical field effect are also demonstrated.

Two theoretical models describing photoelectron transport in multilayer samples were developed: (i) the Monte Carlo simulation strategy, in which the photoelectron elastic scattering events are accounted for, and (ii) the common x-ray electron spectroscopy (XPS) formalism adjusted to multilayer systems, in which the photoelectron elastic scattering events are ignored. Calculations were performed for Au/Ni and Si/Au multilayer systems with layers of different thicknesses. The emission depth distribution function (EMDDF) calculated for a layer deposited at a surface turns out to be identical to that for the bulk of the layer material; however, it may differ considerably when the layer is buried at a certain depth. The EMDDFs for buried layers are found to be considerably affected by elastic photoelectron scattering, however, in a different way from the EMDDF of the bulk material. The XPS depth profiles calculated for multilayer materials in the considered geometry are noticeably affected by elastic photoelectron collisions. However, in contrast with Auger electron spectroscopy depth profiling, the shape of the profile due to a given layer is not affected by the structure beneath that layer.

Molybdenum thin films on glass substrates play an important role as contact layer for thin film solar cells. They can be ablated by picosecond laser pulses irradiated from the substrate side at low laser fluences of less than 1 J cm⁻², while structured trenches remain free from thermal damage and residues. The fluence for that so-called direct induced ablation from the substrate side is in contrast to metal side ablation reduced by approximately one order of magnitude and is far below the thermodynamic limit for heating, melting and evaporating the complete layer. For an extended investigation of the direct induced laser ablation and the underlying mechanism, further thin film materials, chromium, titanium and platinum, with thicknesses between 200 nm and 1 µm were examined. Finally, a simple thermo-dynamical model is able to connect the observed ablation energetics with the mechanical ductility and stress limit of the metal thin films.

We have measured the electrical resistance of inkjet printed multiwall carbon nanotube networks and found that it depends strongly on the temperature of the substrate during the printing process, with both the resistance and its anisotropy decreasing as temperature increases. A parallel investigation of the surface morphology of the printed networks found long raised ridges running parallel to the printing direction, with the height of the ridges decreasing with increasing substrate temperature. Both these observations are shown to be associated with segregation of the nanotubes during drying (coffee staining) and that this segregation is suppressed at higher substrate temperatures, with the lowest resistance values and anisotropy found with a substrate temperature of 70 °C. Network conductance was found to increase with increasing layer thickness and similar results are obtained through a reduction in drop spacing or by printing multiple layers.

Nanoparticle growth in arc discharges is analysed numerically. An analysis is carried out for the root growth method of nanotubes in plasmas. The existing models for estimating the growth of nanoparticles in stationary plasmas are extended to plasmas with variable properties. The distributions of velocity, species density and temperature from numerical simulations are used as input to the growth models. The nickel particle diameter obtained from the numerical model is 9.2 nm and the frequency of finding this size in the experiment is 26 on the larger side. The length of the single-walled carbon nanotube obtained from the model is 2.1 µm, which falls in the upper 10% of the size distribution from experiment. Parametric studies are carried out varying the arc current, inter-electrode gap and background pressure. Results showed 40–95% increment in the nanotube length by increasing the background pressure and the inter-electrode gap. A hot-chamber arc discharge method is proposed to maximize the growth of nanoparticles subjected to the conditions identical to those existing in convectional arc discharges.

This paper introduces a facile method to fabricate magnetoelectric (ME) composites with microscale lead-free piezoceramic pillars embedded in a ferrite matrix without high-temperature co-sintering. The microscale piezoceramic pillars with a sectional width of about 150 µm were obtained from lead-free piezoceramic discs by a dicing method. The spacing between the pillars was backfilled with cobalt ferrite (CFO) nanoparticles, and then a liquid epoxy was infiltrated into the backfilled spacing to bond the filled particles and the pillars. The ME property of the resultant 1–3-type piezoelectric/ferrite composites was verified and found to be significantly dependent on the filling density of the CFO powder, which could be adjusted by repeating the filling step. A maximum ME voltage response of up to 302 µV Oe⁻¹ was obtained in a 700 µm high composite with pillars of 150 µm width and 200 µm spacing. The present method provides a potential way to fabricate finescale multiferroic composites for microdevice applications.