Understanding Nanoplasma Creation.

A plasma is a state of matter (like solid, liquid and gas)in which ionized gases have high enough electrical conductivity that long-range electromagnetic fields dominate its behavior. A nanomaterial is a substance that is between around 1 to 100 nanometers (a nanometer (nm) is a billionth of a meter). Scientists have learned how to create nanoscale plasmas by bombarding nanoparticles with high-powered xrays. Using x-ray free-electron lasers (XFELs), scientists can learn much about the structures of nanoscale objects like proteins, but these matter-energy interactions are little understood. Because they happen so rapidly, it has been difficult to know just what is occurring.

Now, scientists at Tohoku University in Japan, have developed a time-sensitive technique for determining what is happening when an x-ray pulse first strikes a cluster of atoms to create nanoplasma. This technique is sensitive down to the femtosecond resolution. Yoshiaki Kumagai and colleagues blasted a cluster of ~5000 xenon atoms with an x-ray pulse, then a near-infrared (NIR) pulse to ionize additional atoms, with a controlled delay time between the pulses. They then measured the created ion fragments versus the delay time. Using this method they discovered that the number of Xe ionsinitially spiked within 12 fs then dropping over the next several hundred femtoseconds. this data was then compared with theoretical models as well as data ionization of single xenon atoms.

The researchers concluded that the observed increase in Xe ions during delay times contribute many more Xe ions to the plasma on their own through multitudes of extra collisions. They thoerize that the first plasma-producing x-ray pulse quickly generates many neutral and highly excited xenon atoms that are easily ionized by the following low-energy NIR photons. The team described these events as "gateway states driving the birth of the nanoplasma".