Optical trapping of optical nanoparticles:Fundamentals and applications

Optical nanoparticles are nowadays one of the key elements of photonics.They do not only allow optical imaging of a plethora of systems(from cells to microelectronics),but,in many cases,they also behave as highly sensitive remote sensors.In recent years,it has been demonstrated the success of optical tweezers in isolating and manipulating individual optical nanoparticles.This has opened the door to high resolution single particle scanning and sensing.In this quickly growing field,it is now necessary to sum up what has been achieved so far to identify the appropriate system and experimental set-up required for each application.In this review article we summarize the most relevant results in the field of optical trapping of individual optical nanoparticles.After systematic bibliographic research,we identify the main families of optical nanoparticles in which optical trapping has been demonstrated.For each case,the main advances and applications have been described.Finally,we also include our critical opinion about the future of the field,identifying the challenges that we are facing.

Low-Cost and Biodegradable Thermoelectric Devices Based on van der Waals Semiconductors on Paper Substrates

We present a method to fabricate handcrafted thermoelectric devices on standard office paper substrates.The devices are based on thin films of WS_(2),Te,and BP(P-type semiconductors)and TiS_(3)and TiS_(2)(N-type semiconductors),deposited by simply rubbing powder of these materials against paper.The thermoelectric properties of these semiconducting films revealed maximum Seebeck coefficients of(+1.32±0.27)mV K^(-1)and(-0.82±0.15)mV K^(-1)for WS_(2)and TiS_(3),respectively.Additionally,Peltier elements were fabricated by interconnecting the P-and N-type films with graphite electrodes.A thermopower value up to 6.11 mV K^(-1)was obtained when the Peltier element were constructed with three junctions.The findings of this work show proof-of-concept devices to illustrate the potential application of semiconducting van der Waals materials in future thermoelectric power generation as well as temperature sensing for low-cost disposable electronic devices.

Gold nanoshells： Contrast agents for cell imaging by cardiovascular optical coherence tomography

Optical coherence tomography （OCT） has gained considerable attention in interventional cardiovascular medicine and is currently used in clinical settings to assess atherosclerotic lesions and to optimize stent placement. Artery imaging at the cellular level constitutes the first step towards cardiovascular molecular imaging, which represents a major advance in the development of personalized noninvasive therapies. In this work we demonstrate that cardiovascular OCT can be used to detect individual cells suspended in biocompatible fluids. Importantly, the combination of this catheter-based clinical technique with gold nanoshells （GNSs） as intracellular contrast agents led to a substantial enhancement in the backscattered signal produced by individual cells. This cellular contrast enhancement was attributed to the large backscattering cross-section of GNSs at the OCT laser wavelength （1,300 nm）. A simple intensity analysis of OCT cross-sectional images of suspended cells makes it possible to identify the sub-population of living cells that successfully incorporated GNSs. The generalizability of this method was demonstrated using two different cell lines （HeLa and Jurkat cells）. This work provides novel insights into cardiovascular molecular imaging using specifically modified GNSs.

Scalable and low-cost fabrication of flexible WS_(2) photodetectors on polycarbonate

We present a low-cost and easy-to-implement technique to fabricate large-area WS_(2) photodetector devices onto transparent and flexible polycarbonate substrates.The method relies on the deposition of large-area(in the cm scale)thin films(~30 nm thick)of WS_(2) by a recently introduced abrasion-induced method.Interdigitated electrical contacts are then deposited by thermal evaporation through a shadow mask.The photodetectors present well-balanced performances with an good trade-off between responsivity(up to 144 mA/W at a source-drain voltage of 10 V and illumination power of 1μW)and response time(down to~70µs)and a detectivity value of 10^(8) Jones.We found that the devices perform very reversibly upon several illumination and straining cycles and we found a moderate device-to-device variation.

Heavy ion ranges from first-principles electron dynamics

The effects of incident energetic particles,and the modification of materials under irradiation,are governed by the mechanisms of energy losses of ions in matter.The complex processes affecting projectiles spanning many orders of magnitude in energy depend on both ion and electron interactions.Developing multi-scale modeling methods that correctly capture the relevant processes is crucial for predicting radiation effects in diverse conditions.In this work,we obtain channeling ion ranges for tungsten,a prototypical heavy ion,by explicitly simulating ion trajectories with a method that takes into account both the nuclear and the electronic stopping power.The electronic stopping power of self-ion irradiated tungsten is obtained from first-principles timedependent density functional theory(TDDFT).Although the TDDFT calculations predict a lower stopping power than SRIM by a factor of three,our result shows very good agreement in a direct comparison with ion range experiments.These results demonstrate the validity of the TDDFT method for determining electronic energy losses of heavy projectiles,and in turn its viability for the study of radiation damage.

Orbital magneto-optical response of periodic insulators from first principles

Magneto-optical response,i.e.optical response in the presence of a magnetic field,is commonly used for characterization of materials and in optical communications.However,quantum mechanical description of electric and magnetic fields in crystals is not straightforward as the position operator is ill defined.We present a reformulation of the density matrix perturbation theory for time-dependent electromagnetic fields under periodic boundary conditions,which allows us to treat the orbital magneto-optical response of solids at the ab initio level.The efficiency of the computational scheme proposed is comparable to standard linearresponse calculations of absorption spectra and the results of tests for molecules and solids agree with the available experimental data.A clear signature of the valley Zeeman effect is revealed in the continuum magneto-optical spectrum of a single layer of hexagonal boron nitride.The present formalism opens the path towards the study of magneto-optical effects in strongly driven low-dimensional systems.