284
S. Papazoglou and I. Zergioti
9.3 Mechanism of Transfer in LIFT
The dynamics of the liquid and solid deposits that are transferred during LIFT have
been studied by several groups through time-resolved imaging with the aim to provide
a deeper understanding of the phenomena that occur at different timescales starting
from the moment that the laser pulse irradiates the donor substrate until the material
finally impacts the receiver substrate. In the next paragraphs, these studies will be
presented including the jetting dynamics of different materials namely metallic NP
inks, pastes, and biological materials.
9.3.1 Mechanism of Liquid Phase LIFT
Many research groups have been involved in the study of LIFT dynamics so as to
investigate the jetting mechanism regarding various materials and viscosities [31–
33]. Briefly, the mechanism in liquid phase LIFT can be described as follows: (1)
at the low laser fluence regime, the free surface of the coated material is displaced
due to the formation of a bubble of vaporized material that consequently collapses
back on the donor substrate and no transfer is observed, (2) at an intermediate—
above threshold—laser fluence regime successful transfer of well-defined droplets is
observed and the released material is confined within a narrow jet, while no satellite
droplets and material debris are observed, (3) finally above a certain laser fluence
threshold (high fluence regime) the vapor bubble bursts violently and the released jet
can be described as divergent leading to splashing and uncontrolled deposition [32].
The ejection mechanism and dynamics of a viscous nanopowder transferred by
MAPLE have been investigated in an early attempt using time-resolved microscopy
[34]. In this work, an Nd:YAG laser source using the 3rd harmonic (355 nm) has been
employed for the investigation of the transfer process at different laser fluences. In
another work, the ejection dynamics of the nanosecond laser transfer of a 200 nm thick
gold layer have been demonstrated [35], revealing two jetting regimes with single
droplet ejection at low fluences (>140 mJ/cm
2 ) and undesirable multiple droplet
formation at higher fluences (>400 mJ/cm
2 ). Moreover, the ejection mechanism of
complex solutions (Ag NP inks) [36] and metallic pastes [37] has also been reported,
whereas for low viscosity Ag NP inks, the incorporation of a metallic (Ti) DRL
lead to a “low velocity” jetting behavior ranging between 9 and 77 m/s for a fluence
window between 100 and 230 mJ/cm
2 . Regarding high viscosity pastes (>500 cP)
the jetting behavior resembles that of solid-phase LIFT, where the ejected material
from the donor substrate travels rather slowly (<1 m/s) towards the receiver substrate
resulting in a smooth landing and avoiding the formation of fragments and debris upon
impact. Jetting dynamics studies during printing at high repetition rates (500 kHz)
has been also demonstrated for the transfer of Ag Np ink using a frequency tripled
fiber laser (λ = 343 nm, τ = 30 ps). An intriguing observation in this work was
that for a given spacing of 20 µm or smaller between adjacent pulses, interaction
S. Papazoglou and I. Zergioti
9.3 Mechanism of Transfer in LIFT
The dynamics of the liquid and solid deposits that are transferred during LIFT have
been studied by several groups through time-resolved imaging with the aim to provide
a deeper understanding of the phenomena that occur at different timescales starting
from the moment that the laser pulse irradiates the donor substrate until the material
finally impacts the receiver substrate. In the next paragraphs, these studies will be
presented including the jetting dynamics of different materials namely metallic NP
inks, pastes, and biological materials.
9.3.1 Mechanism of Liquid Phase LIFT
Many research groups have been involved in the study of LIFT dynamics so as to
investigate the jetting mechanism regarding various materials and viscosities [31–
33]. Briefly, the mechanism in liquid phase LIFT can be described as follows: (1)
at the low laser fluence regime, the free surface of the coated material is displaced
due to the formation of a bubble of vaporized material that consequently collapses
back on the donor substrate and no transfer is observed, (2) at an intermediate—
above threshold—laser fluence regime successful transfer of well-defined droplets is
observed and the released material is confined within a narrow jet, while no satellite
droplets and material debris are observed, (3) finally above a certain laser fluence
threshold (high fluence regime) the vapor bubble bursts violently and the released jet
can be described as divergent leading to splashing and uncontrolled deposition [32].
The ejection mechanism and dynamics of a viscous nanopowder transferred by
MAPLE have been investigated in an early attempt using time-resolved microscopy
[34]. In this work, an Nd:YAG laser source using the 3rd harmonic (355 nm) has been
employed for the investigation of the transfer process at different laser fluences. In
another work, the ejection dynamics of the nanosecond laser transfer of a 200 nm thick
gold layer have been demonstrated [35], revealing two jetting regimes with single
droplet ejection at low fluences (>140 mJ/cm
2 ) and undesirable multiple droplet
formation at higher fluences (>400 mJ/cm
2 ). Moreover, the ejection mechanism of
complex solutions (Ag NP inks) [36] and metallic pastes [37] has also been reported,
whereas for low viscosity Ag NP inks, the incorporation of a metallic (Ti) DRL
lead to a “low velocity” jetting behavior ranging between 9 and 77 m/s for a fluence
window between 100 and 230 mJ/cm
2 . Regarding high viscosity pastes (>500 cP)
the jetting behavior resembles that of solid-phase LIFT, where the ejected material
from the donor substrate travels rather slowly (<1 m/s) towards the receiver substrate
resulting in a smooth landing and avoiding the formation of fragments and debris upon
impact. Jetting dynamics studies during printing at high repetition rates (500 kHz)
has been also demonstrated for the transfer of Ag Np ink using a frequency tripled
fiber laser (λ = 343 nm, τ = 30 ps). An intriguing observation in this work was
that for a given spacing of 20 µm or smaller between adjacent pulses, interaction