Manipulation of Glassy State in Amorphous Selenium by Low-temperature Internal Friction Measurements

Abstract

We have studied the thickness and quench-rate dependent internal friction of amorphous selenium (a-Se) thin films deposited at room temperature. The internal friction of a-Se films exhibit a temperature independent plateau below 1 K followed by a broad maximum at 10 K. The plateau, which is seen in almost all amorphous solids, is caused by dissipation by two-level tunneling systems (TLS), whose origin is still unknown. The maximum is caused by thermal relaxation over the same energy barrier that induces TLS. The internal friction and shear modulus are almost thickness independent from 100 nm to 10 µm. Unlike other elemental amorphous materials, the sufficiently low glass transition temperature (T g ) of a-Se (only about 10 K above room temperature) allows in-situ quench-rate dependent study of TLS. The amorphous structure resets itself by a thermal equilibration cycle above T g . We show that a faster quench rate freezes a-Se to a lower density structure with a higher TLS density and vice versa. The changes are reversible supporting a relationship between different quenched states and the density of TLS. Our study shows that a-Se can be a simple monatomic amorphous system to constrain models for the origin of TLS in amorphous solids.

Sound absorption in glasses

“…There is another measurement [61] at 228 Hz which shows an even lower C as the 5400 Hz data [57] and the 20 MHz data [58], so there must be a calibration error by a factor of 2.1 in the 180 kHz measurement. The factor is too large to be ascribed to annealing effects, in selenium [57] of the order of twenty percent.…”

“…Again, one has to change the soft potential parameters [9], the W to a factor 4/3 higher value. The factor for C is different for the two measurements; the measurements at 5400 Hz [57] and 20 MHz [58] require a C of 4.4 10 −4 , the one at 180 kHz [46] a C of 9.3 10 −4 .…”

“…FIG. 9: Comparison of measured low temperature sound absorption data at 5.4 kHz [57], 180 kHz [46], and at 20 MHz [58] in amorphous selenium with the soft potential calculation, using eq. ( 45) with a=0.07 (parameters see Table I, but note that the 180 kHz data are calculated with a factor 2.1 larger C).…”

“…The last example is selenium in Fig. 16, with l(V ) from paddle oscillator data [57] at 5.4 kHz and longitudinal ultrasonic data [83] at 15 and 25 MHz in the glass phase, another case where uniaxial and shear distortion provide the same l(V ). The equilibrium liquid values are from J r (t)-data [31] at 304.7 and 308.3 K, evaluated with G = 3.4 and 3.3 GPa, respectively, values taken from an ultrasonic determination [84] which shows excellent agreement with an earlier one [85].…”

“…This is again a case where one finds essentially only low-barrier relaxations and Kohlrausch tail, in this sub- FIG. 16: Barrier density l(V ) in selenium from measurements at 5.4 kHz [57], 15 and 25 MHz [83] and from Jr(t)-data [31] in the undercooled liquid at 304.7 and 308.3 K.…”