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It has been a long-standing challenge to produce air-stable few- or monolayer samples of phosphorene because thin phosphorene films degrade rapidly in ambient conditions. Here we demonstrate a new highly controllable method for fabricating high quality, air-stable phosphorene films with a designated number of layers ranging from a few down to monolayer. Our approach involves the use of oxygen plasma dry etching to thin down thick-exfoliated phosphorene flakes, layer by layer with atomic precision. Moreover, in a stabilized phosphorene monolayer, we were able to precisely engineer defects for the first time, which led to efficient emission of photons at new frequencies in the near infrared at room temperature. In addition, we demonstrate the use of an electrostatic gate to tune the photon emission from the defects in a monolayer phosphorene. This could lead to new electronic and optoelectronic devices, such as electrically tunable, broadband near infrared lighting devices operating at room temperature.

The mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form. It is shown that at high intensities when the ionization of the target material is complete before the end of the pulse, the ablation mechanism is the same for both metals and dielectrics. The physics of this new ablation regime involves ion acceleration in the electrostatic field caused by charge separation created by energetic electrons escaping from the target. The formulae for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data. The calculated dependence of the ablation thresholds on the pulse duration is in agreement with the experimental data in a femtosecond range, and it is linked to the dependence for nanosecond pulses.

Extremely high pressures ( 10 TPa) and temperatures (5 10 5 K) have been produced using a single laser pulse (100 nJ, 800 nm, 200 fs) focused inside a sapphire crystal. The laser pulse creates an intensity over 10 14 W=cm 2 converting material within the absorbing volume of 0:2 m 3 into plasma in a few fs. A pressure of 10 TPa, far exceeding the strength of any material, is created generating strong shock and rarefaction waves. This results in the formation of a nanovoid surrounded by a shell of shock-affected material inside undamaged crystal. Analysis of the size of the void and the shock-affected zone versus the deposited energy shows that the experimental results can be understood on the basis of conservation laws and be modeled by plasma hydrodynamics. Matter subjected to record heating and cooling rates of 10 18 K=s can, thus, be studied in a well-controlled laboratory environment. DOI: 10.1103/PhysRevLett.96.166101 PACS numbers: 81.07.ÿb, 47.40.Nm, 62.50.+p, 81.40.ÿz The study of matter in conditions of extreme pressure and temperature is an exciting area of condensed matter physics relevant to the formation of new materials and modeling the state of matter inside stars and planets. Creation of such extreme conditions in the laboratory is, however, a formidable experimental task. So far, pressures in excess of 0.1 TPa have been obtained using a diamond anvil in stationary conditions, while transient pressures behind shock waves generated by chemical or nuclear explosions or generated using powerful lasers up to 50 TPa have been reported [1,2]. Here we present experimental evidence that one can create TPa pressures, many times the strength of any material, using low energy pulses from a conventional tabletop laser.Recent studies have demonstrated [3][4][5][6][7][8] that sub-ps laser pulses tightly focused inside transparent dielectrics (glasses, crystals, and polymers) can produce detectable sub-micrometer-sized structural modifications, including voids. This requires intensities in excess of 10 14 W=cm 2 which results in a highly nonlinear light-matter interaction with most dielectrics being ionized early in the laser pulse. To achieve such high intensities the laser beam should be tightly focused using high numerical aperture optics into a spot whose dimensions are of the order of the laser wavelength ( ).Previously the formation of voids in silica was associated with self-focusing of the laser beam [3]. In fact void formation can occur in conditions favorable for selffocusing if the beam is weakly focused into the sample [9]. Previously, however, there has been no systematic study of void formation by single fs pulses in conditions when self-focusing cannot occur. We demonstrate here that in such conditions nanovoids are formed by the extreme temperatures and pressures created by optical breakdown and these drive shock and rarefaction waves in the surrounding material. It is possible that new materials [10 -12] with altered chemical properties [13] could be formed by such micro-explosions.The inte...