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Materials Science in Additive Manufacturing Biodegradable sustainable electronics

was suggested by Li et al. to calculate the rates at which pH, temperature, concentration, doping level, and the
[2]
bioresorbable metal degrades. types of ions and proteins present in the solution, have a
substantial impact on the dissolving rates [12-15] . Higher
M kh 2 temperatures and pH levels were shown to speed up the
v kD 0 tanh 0 (I)

20
qM HO2 D dissolution process, but doping levels more than 10 cm −3
had the reverse effect [12,13] . Similar to Mg dissolution, the
Where, k is the reaction constant, D is the diffusivity of presence of chlorides and phosphates above a certain level
water phosphate-buffered saline (PBS), ω is the initial water at approximately pH = 7.5 accelerates the Si dissolution
o
concentration, q is the number of water molecules that (Figure 2D) . In another study, researchers found that
[14]
react with each atom of the material, ρ is the mass density extremely thin Si NMs hydrolyze to form orthosilicic acid,
of the dissolution material, and M and M H2O are the molar Si(OH) [16] . These NMs with variable thickness from 35 to
4
mass of the dissolution material and water, respectively. By 100 nm dissolve in PBS at 37°C in ~ 8 – 22 days with the
adjusting the pH of the solution and observing the time- approximate rate of 4.5 nm/day . The dissolution rate (R)
[17]
dependent changes in electrical resistance, Rogers et al. of Si at temperature T with molar concentrations of water
[3]
investigated the dissolution rates of several bioresorbable and hydroxide ions was given by Equation II [13,18] .
metallic films. The metallic films degraded in DI water and
E A
in Hanks’ Balanced Salt Solution (HBSS), which has a pH Rk HO 2 OH x e kBT (II)
4

range of 5-8. Chloride ions (Cl ) caused Mg to deteriorate 0
-
10 times more quickly in HBSS than in DI water. Regardless Where, k is the Boltzmann constant, E is the activation
B
A
of pH or temperature, the presence of Cl ions speeds up energy, and fitted values of x fall in the range of 0.46 – 0.9.
-
the degradation of Mg by removing its surface protective The dissolution rate increased with increase in the pH value.
layer . Zn exhibits an 8.2, 2.6, and 3.3 times greater EDR Change in the concentration of PBS solution from 0.05 to 1
[4]
in salt solution with pH values of 5, 7.4, and 8, respectively, M increased the dissolution rate from 10 to 20 times. Besides
following the same trend. Zinc hydroxide, Zn(OH) , for Si NMs, above equation can be used to determine the
2
a metabolite, is produced when zinc oxide (ZnO) is dissolution rate of other semiconducting materials such as
solubilized in water . In a dissolution test in DI water and polycrystalline amorphous Si (a-Si), Si (poly-Si), Si-Ge alloy
[5]
[6]
at room temperature, conducted by Dagdeviren et al., it (SiGe), and Ge. Their dissolution rate was found to be 4.1,
was discovered that 200 nm thick ZnO vanished entirely 2.8, 0.1, and 3.1 nm/day, respectively, in a buffer solution
in 15 h. W has 4 times higher EDR in salt solution with a of pH 7.4 at 37°C. Studies using molecular dynamics (MD)
pH value ranging from 7.4 to 8 as compared to a solution simulations and density functional theory (DFT) indicated
with pH value of 5. This is attributed to the sensitivity of that silicon dissolution initiates by the nucleophilic attack
W toward deposition conditions. The EDR of W deposited on silicon surface bonds, weakening the inner bonds. This
using the sputtering technique was higher than the one makes them even more prone to subsequent ion attacks .
[14]
formed using chemical vapor deposition (CVD). Mo has a The dissolution rates of a-Si, poly-Si, and Ge increased by
greater EDR in DI water than in salt solution, in contrast to 10 – 10 times, and those of SiGe increased by 10 times,
3
2
Mg and Zn. The greater concentration of dissolved oxygen with a rise in pH from 7 to 10 . Kang et al. examined
19
[20]
in aqueous solution is responsible for this difference . It the SiO and Si N dissolving rates in various pH solutions.
[7]
3
2
4
showed slower dissolution rates at higher pH in HBSS, as The room temperature dissolution rates for SiO and Si N
3
4
2
[3]
shown in Figure 2A and B . Although, Fe has the highest are around 0.13 and 0.0044 nm/h in a buffer solution of
EDR at pH 5, but due to the development of passive oxide pH = 7.4, respectively. The dissolution rates were increased
layer in DI water, its dissolution ceases after 120 h . Within by one or two orders in magnitude with increase in pH value
[8]
a few days, 300 nm thick oxides on Mg, AZ31B Mg alloy, and to 12. Another study found that a 150 nm thick MgO film
Zn completely vanished in DI water, while residual oxides created using electron beam evaporation may disintegrate
were detected on Mo (40 nm) and W (150 nm) substrate in deionized water at a rate of about 50 nm/h . Thus, the
[21]
for a few weeks, which makes the degradation process dissolution rate of metals gets affected by the change in
slower [3,9-11] . As stated earlier, pure Si is a non-degradable conditions and deposition method of the film.
material. However, nanostructured Si may have dissolution
kinetics that can be varied. Its dissolution kinetics was 3. Biodegradable conducting materials
studied by monitoring the change in Si nanomembranes
(NMs) thickness with time using profilometer or atomic 3.1. Metals
force microscopy (AFM) in bovine serum . As shown Metal has widely been used as interconnects and electrodes
[12]
in Figure 2C and D, a variety of variables, including in electronic devices. They have found their wide usage in
Volume 1 Issue 3 (2022) 4 https://doi.org/10.18063/msam.v1i3.15