Rotationally induced luminescence of nanoclusters immersed in superfluid helium
We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission of nitrogen atoms (²D→⁴S transition) in nanoclusters which correlated with...
Gespeichert in:
| Datum: | 2019 |
|---|---|
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2019
|
| Schriftenreihe: | Физика низких температур |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/175950 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Rotationally induced luminescence of nanoclusters immersed in superfluid helium / P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, V.V. Khmelenko // Физика низких температур. — 2019. — Т. 45, № 3. — С. 356-362. — Бібліогр.: 32 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-175950 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1759502021-02-04T01:31:16Z Rotationally induced luminescence of nanoclusters immersed in superfluid helium McColgan, P.T. Sheludiakov, S. Rentzepis, P.M. Lee, D.M. Khmelenko, V.V. Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission of nitrogen atoms (²D→⁴S transition) in nanoclusters which correlated with the increasing of rotational speed of the beaker. Increasing luminescence was also observed by increasing the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. We suggest that this effect is caused by the change of the density of quantum vortices in He II initiated by variation of rotational speed of the beaker. When the density of the vortices is increased, the probability for the nanoclusters to become trapped in the vortex cores is also increased. The collisions in the vortex cores of trapped nanoclusters with nitrogen atoms stabilized mostly on the surfaces of the nanoclusters initiate the recombination of nitrogen atoms resulting in luminescence. Досліджено вплив швидкості обертання склянки з надплинним гелієм (He II) на інтенсивність люмінесценції нанокластерів, які знаходяться всередині He II. Спостерігається збільшення емісії α-групи атомів азоту (перехід ²D→⁴S) в нанокластерах, яке корелювало зі збільшенням швидкості обертання склянки. Збільшення люмінесценції також спостерігалося при збільшенні вмісту молекулярного азоту в азотно-гелієвій газовій суміші, яку використовували для отримання нанокластерів молекулярного азоту. Ми припускаємо, що цей ефект пов'язаний зі зміною щільності квантових вихорів в He II при зміні швидкості обертання склянки. При збільшенні щільності вихорів ймовірність захоплення нанокластеров в серцевинах вихорів також підвищується. Усередині серцевин вихорів відбувається зіткнення нанокластерів, внаслідок цього відбувається рекомбінація атомів азоту, що знаходяться на поверхні нанокластерів, та їх люмінесценція. Исследовано влияние скорости вращения стакана со сверхтекучим гелием (He II) на интенсивность люминесценции нанокластеров, находящихся внутри He II. Наблюдается увеличение эмиссии α-группы атомов азота (переход ²D→⁴S) в нанокластерах, которое коррелировало с увеличением скорости вращения стакана. Увеличение люминесценции также наблюдалось при повышении содержания молекулярного азота в азотно-гелиевой газовой смеси, используемой для получения нанокластеров молекулярного азота. Мы предполагаем, что этот эффект связан с изменением плотности квантовых вихрей в He II при изменении скорости вращения стакана. При увеличении плотности вихрей вероятность захвата нанокластеров в сердцевинах вихрей также увеличивается. Внутри сердцевин вихрей происходит столкновение нанокластеров, в результате которого происходит рекомбинация атомов азота, находящихся на поверхности нанокластеров, и их люминесценция. 2019 Article Rotationally induced luminescence of nanoclusters immersed in superfluid helium / P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, V.V. Khmelenko // Физика низких температур. — 2019. — Т. 45, № 3. — С. 356-362. — Бібліогр.: 32 назв. — англ. 0132-6414 http://dspace.nbuv.gov.ua/handle/123456789/175950 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) |
| spellingShingle |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) McColgan, P.T. Sheludiakov, S. Rentzepis, P.M. Lee, D.M. Khmelenko, V.V. Rotationally induced luminescence of nanoclusters immersed in superfluid helium Физика низких температур |
| description |
We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of
luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission
of nitrogen atoms (²D→⁴S transition) in nanoclusters which correlated with the increasing of rotational speed of
the beaker. Increasing luminescence was also observed by increasing the concentration of molecular nitrogen in
the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. We suggest that
this effect is caused by the change of the density of quantum vortices in He II initiated by variation of rotational
speed of the beaker. When the density of the vortices is increased, the probability for the nanoclusters to become
trapped in the vortex cores is also increased. The collisions in the vortex cores of trapped nanoclusters with nitrogen atoms stabilized mostly on the surfaces of the nanoclusters initiate the recombination of nitrogen atoms
resulting in luminescence. |
| format |
Article |
| author |
McColgan, P.T. Sheludiakov, S. Rentzepis, P.M. Lee, D.M. Khmelenko, V.V. |
| author_facet |
McColgan, P.T. Sheludiakov, S. Rentzepis, P.M. Lee, D.M. Khmelenko, V.V. |
| author_sort |
McColgan, P.T. |
| title |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| title_short |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| title_full |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| title_fullStr |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| title_full_unstemmed |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| title_sort |
rotationally induced luminescence of nanoclusters immersed in superfluid helium |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2019 |
| topic_facet |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/175950 |
| citation_txt |
Rotationally induced luminescence of nanoclusters immersed in superfluid helium / P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, V.V. Khmelenko // Физика низких температур. — 2019. — Т. 45, № 3. — С. 356-362. — Бібліогр.: 32 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT mccolganpt rotationallyinducedluminescenceofnanoclustersimmersedinsuperfluidhelium AT sheludiakovs rotationallyinducedluminescenceofnanoclustersimmersedinsuperfluidhelium AT rentzepispm rotationallyinducedluminescenceofnanoclustersimmersedinsuperfluidhelium AT leedm rotationallyinducedluminescenceofnanoclustersimmersedinsuperfluidhelium AT khmelenkovv rotationallyinducedluminescenceofnanoclustersimmersedinsuperfluidhelium |
| first_indexed |
2025-07-15T13:33:36Z |
| last_indexed |
2025-07-15T13:33:36Z |
| _version_ |
1837720057244811264 |
| fulltext |
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3, pp. 356–362
Rotationally induced luminescence of nanoclusters
immersed in superfluid helium
P.T. McColgan1, S. Sheludiakov1, P.M. Rentzepis2, D.M. Lee1, and V.V. Khmelenko1
1Texas A&M University, Department of Physics and Astronomy, Institute of Quantum Science and Engineering
4242 TAMU, 77843-4242 College Station, Texas, United States
E-mail: seshel@physics.tamu.edu
2Texas A&M University, Department of Electrical and Computer Engineering
3127 TAMU, 77843-3127, College Station, Texas, United States
Received October 24, 2018
We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of
luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission
of nitrogen atoms (2D→4S transition) in nanoclusters which correlated with the increasing of rotational speed of
the beaker. Increasing luminescence was also observed by increasing the concentration of molecular nitrogen in
the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. We suggest that
this effect is caused by the change of the density of quantum vortices in He II initiated by variation of rotational
speed of the beaker. When the density of the vortices is increased, the probability for the nanoclusters to become
trapped in the vortex cores is also increased. The collisions in the vortex cores of trapped nanoclusters with ni-
trogen atoms stabilized mostly on the surfaces of the nanoclusters initiate the recombination of nitrogen atoms
resulting in luminescence.
Keywords: luminescence, quantized vortices, optical spectroscopy, nanoclusters.
1. Introduction
Fascination with quantum vortices in superfluid helium
(He II) started with their discovery in the 1950s, and contin-
ues today [1]. Investigations of quantum vortices in super-
fluid helium have recently attracted great attention [2–4]. The
visualization of vortex cores [1] has led to the observation of
the reconnection of vortices and direct observation of Kelvin
waves excited by quantized vortex reconnections [5,6], char-
acterization of the probability density function representing
particle velocity [7] and acceleration in thermal counterflow
[8]. Metastable helium molecules were used as tracers in
superfluid helium [9], providing the possibility for studying
quantum turbulence in He in the T = 0 limit [10] and examine
the normal fluid behavior in thermal counterflow [11,12].
The technique of nanowire formation by ablating metallic
nanoparticles from a target in He II was realized on the basis
of coalescence of the nanoparticles in the vortex cores
[13,14]. The luminescence of ensembles of molecular nitro-
gen nanoclusters containing stabilized nitrogen atoms was
initiated in He II by quantum vortices [15]. In this latter case
the dependence of luminescence intensity on temperature
was correlated with that of the vortex density in the tempera-
ture range 1.2–2.1 K. These nanoclusters are created by the
injection of nitrogen-helium gas mixtures into bulk He II
after passing through a radio-frequency discharge zone [16].
In this work we studied the influence of vortex density
in He II on the intensity of luminescence accompanied by
the process of injection of molecular nitrogen nanoclusters
into a rotating beaker with He II. During these measure-
ments, the nanoclusters continued to enter into the bulk He
II inside the rotating beaker. Nitrogen atoms stabilized on
the surfaces of nanoclusters [17] provide an excellent op-
portunity for visualization of the process of capturing
nanoclusters into vortex cores. When two nanoclusters are
captured into a vortex core, they can collide and two nitro-
gen atoms residing on the surfaces of these nanoclusters
can then recombine, starting processes which lead to lumi-
nescence of nitrogen atoms in nanoclusters. We observed
the influence of rotation speed of the beaker with He II on
the intensity of luminescence from the ensembles of
nanoclusters.
We found that increasing the rotation speed of the
beaker with He II led to an increase in luminescence of the
injected nanoclusters. We explained this effect by an effi-
cient capturing of nanoclusters in quantum vortex cores
when the density of vortices was increased. Increasing the
© P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, and V.V. Khmelenko, 2019
Rotationally induced luminescence of nanoclusters immersed in superfluid helium
density of vortices with increasing the rotational speed of
the beaker with He II results in more chemical reactions of
pairs of nitrogen atoms on the surfaces of neighboring
nanoclusters in vortex cores leading to increasing the in-
tensity of luminescence.
2. Experimental setup
Our experimental setup contains two concentric glass
Dewars. The inner Dewar is filled with liquid helium, the
outer Dewar with liquid nitrogen. The inner Dewar is
pumped with an Edwards model 80 vacuum pump, achie-
ving liquid helium temperatures as low as 1.1 K.
The top flange of the cryogenic system houses all of the
connections to room-temperature equipment, including a
vacuum feed-through for our cryogenic fiber assembly,
and a vacuum feed-through for all electrical connections.
Gas mixtures are prepared at room temperature using a
gas handling system. This system consists of a manifold
connecting pressurized gas cylinders to mixing tanks, a
pressure gauge and connections to the cryostat and a vacu-
um pump. The flow of the gas mixture to the cryostat is
regulated by a Brooks Model 5850 flux controller.
Samples are created by passing a gas mixture through an
atomic source. The atomic source consists of a stainless steel
vacuum jacket housing a quartz discharge tube. The dis-
charge tube is made of an outer quartz tube with a concentric
quartz capillary. At the bottom of the quartz capillary there
are electrodes for a radio-frequency (RF) discharge. The RF
discharge is provided by a HP 8656B signal generator ampli-
fied by an E&I 3100L. The outer quartz tube is filled with
liquid nitrogen (LN2) which simultaneously cools the incom-
ing gas mixture in the capillary, and the discharge electrodes.
After passing through the RF discharge zone, excited at-
oms and molecules exit the orifice, diameter 0.75 mm, of the
quartz capillary. The pressure gradient ∼ 2 Torr between the
discharge zone and the cryostat creates a well-formed jet of
discharge products which is injected into the beaker filled
with superfluid helium (He II). The level of the He II in the
beaker is maintained constant (22 mm below the orifice)
using a thermo-mechanical (fountain-effect) pump. The
temperature during sample preparation (T ∼ 1.54 K) is
measured using a germanium thermometer.
One unique feature of this setup is the ability to rotate
our beaker at cryogenic temperatures. The possibility of
rotating a beaker containing He II was demonstrated in
previous work [18,19]. In our setup, rotation of the beaker
is accomplished by mounting the quartz beaker to the out-
put shaft of a stepper motor (see Fig. 1). The quartz beaker
sits in a teflon holder which is attached to a brass flange
with screws. The brass flange is secured to the output shaft
of the stepper motor with a set screw.
The electric motor is powered by a 24 VDC power sup-
ply controlled by a stepper motor driver and an Arduino
microcontroller. The Arduino microcontroller is running a
program which enables the motor, controls the direction of
rotation, and “ramps up” the rotational speed from zero to
the desired speed, as well as displaying this speed on a
seven-segment display. The Arduino microcontroller pro-
vides a chain of TTL pulses to the DM320T stepper motor
driver. This driver has built-in current limiting capabilities,
which reduces heating inside the stepper motor coils, as
well as providing the microstepping. These are controlled
by dip-switches located on the side of the stepper motor
driver.
The motor is a standard NEMA 8 motor with 200 steps
per revolution, or 1.8 deg. per step. With the microstepping
from the driver, there are a total of 1600 microsteps per rev-
olution (13.5 arcmin per microstep). Each TTL pulse from
the microcontroller advances the motor one step. The use of
microstepping allows for smoother rotation of the beaker.
Fig. 1. Rotating beaker assembly. Atomic source (1), Nitrogen-
helium jet (2), Fountain pump line (3), Quartz beaker (4), Teon
beaker holder (5), Brass ange (6), NEMA 8 stepper motor (7),
Fountain pump body (8), Optical liber (9).
Fig. 1. Rotating beaker assembly: atomic source (1), nitrogen-
helium jet (2), fountain pump line (3), quartz beaker (4), teflon
beaker holder (5), brass flange (6), NEMA 8 stepper motor (7),
fountain pump body (8), optical fiber (9).
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3 357
P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, and V.V. Khmelenko
The motor itself is an off-the shelf part, which was modi-
fied to perform in cryogenic conditions. The two bearings
connected to the rotor were removed and thoroughly cleaned
using an aerosol solvent. This solvent is generally used to
remove oil and debris from automotive sensors, and it is safe
for sensitive electronics. The liquid oil lubricants would be
frozen at cryogenic temperatures. The bearings were then
lubricated using a molybdenum disulfide (MbS2) dry lubri-
cant applied with an aerosol solvent. After application, the
solvent is evaporated, leaving a thin film of dry MbS2.
The operation of the motor provided an additional heat
load so that all experiments were performed at a slightly
elevated temperatures 1.53–1.54 K compared to the opti-
mal condition (T = 1.5 K).
The emission of the ultraviolet (UV) and visible (VIS)
light is collected using a cryogenic fiber assembly which
terminates at a vacuum-tight optical feed-through on the
top flange. A bifurcated optical fiber connects this feed-
through to the Andor Shamrock 500i and Ocean Optics
HR2000+ spectrometers. The emission of the near-infrared
(NIR) light is collected through the slits in the silvering of
the Dewars by a focusing lens located outside of the
Dewars, onto the entrance of a collimating lens mounted at
the end of an optical fiber connected to an Avantes NIR
512-1.7 TEC spectrometer.
We recorded the luminescence during the injection of the
products of a discharge in nitrogen-helium gas mixtures into
bulk superfluid helium contained in the cylindrical quartz
beaker (see Fig. 1). During these recordings the beaker was
rotated at various speeds. The rotation speeds were equal to
3, 4, and 7.5 rad/s. These speeds were similar to those used
for measurements of the attenuation of second sound in uni-
formly rotating He II [18]. For each rotation speed the re-
cording of luminescence lasted for 5 minutes. We performed
investigations for three different nitrogen-helium gas mix-
tures: N2:He = 1:400, 1:200, and 1:100.
3. Experimental results
We recorded the luminescence spectra and their intensity
during the injection of nanoclusters into bulk superfluid he-
lium while the beaker with helium was rotating uniformly.
The spectra were obtained over a broad range. The Ocean
Optics spectrometer provided spectra in the 200–1100 nm
range, the Andor spectrometer in 240–480 nm range, and the
Avantes spectrometer in the 900–1700 nm range.
Figure 2 shows the spectra obtained by the Andor spec-
trometer during the condensation of gas mixture N2:He =
= 1:200 for three different rotational speeds of the beaker
filled with He II. From the comparison of these spectra one
can see that the intensities of emission assigned to the mo-
lecular nitrogen bands and helium atomic lines which were
collected from the gas phase jet are almost the same for all
three rotation speeds of the beaker.
In contrast, the α-group emission of nitrogen atoms in
nanoclusters immersed into superfluid helium depends on the
rotation speed of the beaker with He II. Increasing the rota-
tion speed of the beaker from 3 rad/s to 7.5 rad/s resulted in a
substantial increase of the α-group emission. Figure 3 shows
a comparison of intensities of α-group emission during the
injection of two different gas mixtures (N2:He = 1:100 and
1:200) for three different rotational speeds of the beaker
filled with liquid helium. These spectra were obtained by the
Andor spectrometer using the first grating with a resolution
of 0.5 nm.
Fig. 2. (Color online) Spectra observed with the Andor spectrome-
ter during condensation of the mixture N2:He = 1:100 and 1:200
into a beaker filled with He II for different rotational speeds: 3 rad/s
(black, 1), 4 rad/s (red, 2), 7.5 rad/s (blue, 3). Each spectrum was
obtained by integration of the emission during a 5 minute time
interval.
Fig. 3. (Color online) Comparison of α-group emission observed
during condensation of gas mixtures N2:He = 1:100 (solid line)
and 1:200 (dashed line) for different rotational speeds: 3 rad/s
(black, 1), 4 rad/s (red, 2), 7.5 rad/s (blue, 3). Each spectrum was
obtained by integration of the emission during a 5 minute time
interval.
358 Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3
Rotationally induced luminescence of nanoclusters immersed in superfluid helium
We performed similar investigations for the gas mixture
N2:He = 1:400. Fig. 4 shows the dependence of integrated
intensity of the α-group of N atoms in nanoclusters im-
mersed into He II on the rotation speed of the beaker for
three different gas mixtures used for injection of nano-
clusters. It is clearly seen that increasing the rotational speed
of the beaker led to an increase of the integrated lumines-
cence for each of the gas mixtures used in the experiments.
Also, it was found that increasing the flux of nitrogen clus-
ters into bulk He II resulted in increasing the intensity of the
α-group for each value of rotation speed of the beaker.
The spectra observed in the NIR range by the Avantes
spectrometer show a result similar to that obtained in the
UV–VIS ranges, namely, the emission from the gas-phase
jet was essentially unaltered by the rotation of the beaker
with He II as seen in Fig. 5. The most dramatic effect of
rotating He II was observed for the emission of the δ-group
of N atoms stabilized in the N2 nanoclusters. Figure 6(a)
shows a comparison of the intensities of the overlapping
N atom δ-group and N2 (B3Πg, 30 , 0)uv A v+= → Σ =′ ′′
emissions during the injection of two different gas mixtures
(N2:He = 1:100 and 1:200) for three different rotational
speeds of the beaker. Similar investigations were made for
gas mixture N2:He = 1:400. We performed deconvolution
for these overlapping bands. An example of the analysis is
shown in Fig. 6(b) for the spectra recorded during the injec-
tion of N2:He 1:100 gas mixture into the beaker rotating
with the angular speed 4 rad/s. A similar deconvolution was
made for all spectra shown in Fig. 6(a) to obtain the depend-
ence of the integrated intensity of δ-group emission on the
rotation speed of the beaker. Figure 7 shows the dependence
of the integrated intensity of the N atom δ-group in nano-
clusters immersed in He II on the rotational speed of the
beaker with He II for three different gas mixtures used for
injection of nanoclusters. For gas mixture 1:400 an almost
linear growth of the δ-group intensity with increasing rota-
tional speed of He II was observed. For more concentrated
Fig. 4. (Color online) Dependence of integrated intensity of
N atom α-group observed during the injection of nitrogen-helium
gas mixtures N2:He = 1:100 (black squares), 1:200 (red circles)
and 1:400 (blue triangles) into a rotating beaker with He II on the
rotation speed of the beaker.
Fig. 5. (Color online) Comparison of the spectra in the range
900–1650 nm observed with the Avantes spectrometer during the
injection of nitrogen-helium gas mixture N2:He = 1:100 (solid
line) and 1:200 (dashed line) into a rotating beaker with He II for
different rotational speeds: 3 rad/s (black, 1), 4 rad/s (red, 2),
7.5 rad/s (blue, 3).
Fig. 6. (Color online) (a) Comparison of the spectra of overlapping
N atom δ-group and N2 (B
3Πg, 30 , 0)uv A v+= → Σ =′ ′′ emissions
observed during the injection of nitrogen-helium gas mixtures
N2:He = 1:100 (solid lines) and 1:200 (dashed lines) into rotating
He II for different rotational speeds: 3 rad/s (black, 1), 4 rad/s
(red, 2), 7.5 rad/s (blue, 3). (b) Deconvolution of the overlapping
spectra of δ-group and N2 (B3Πg, 30 , 0)uv A v+= → Σ =′ ′′ emis-
sions. Experimental spectrum of these two bands recorded during
injection of N2:He = 1:100 gas mixture into beaker rotating at
4 rad/s (red, 2), Lorentzian fitting line for δ-group emission (magen-
ta), Lorentzian fitting line for N2 (B3Πg, 30 , 0)uv A v+= → Σ =′ ′′
emission (green, 4), the sum of the fitting lines (blue, 3).
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3 359
P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, and V.V. Khmelenko
gas mixtures N2:He = 1:100 and 1:200 increasing of the
integrated intensity of δ-group was observed only with in-
creasing the rotation speed of the beaker from 3 to 4 rad/s.
Further increase of the rotational speed of the beaker with
He II to 7.5 rad/s resulted in a small decrease of the intensity
of δ-group emission.
4. Discussion
Superfluid helium is characterized by two unique fea-
tures, anomalously high heat conductance and formation of
quantized vortices. The efficient heat removal property of
He II was efficiently used in the method of injection of
products of our discharge in nitrogen-helium gas mixtures
into bulk He II [16]. This approach allows us to achieve
the highest concentrations of stabilized nitrogen atoms
[20–22]. Nitrogen atoms are stabilized on molecular nitro-
gen nanoclusters, which form an aerogel-like porous struc-
ture inside He II [23]. Nanoclusters are formed during the
process of cooling down atoms and molecules entering
from the gas discharge zone by passage through the cold
helium vapors on the way to the surface of He II in the
collection beaker. From x-ray investigations of nano-
clusters collected inside He II an estimate of the average
size of nanoclusters on the order of 5 nm has been made
[24,25]. This allows us to determine the flux of nano-
clusters to be 2·1013 s–1 in the process of condensation of
our nitrogen-helium gas mixture N2:He = 1:100 which has
a flux 1019 s–1. Each nanocluster contains on average 50
nitrogen atoms, which reside mostly on the surfaces of
these nanoclusters [17]. Usually during the process of their
injection into He II, the nanoclusters collide inside super-
fluid helium and nitrogen atoms from the adjacent nano-
cluster strands can meet each other and recombine. This
leads to continuous luminescence from nanoclusters inside
He II. As a result of N atom recombination, the N2 mole-
cules in high vibrational states are formed. The recombina-
tion energy (∼ 9.8 eV) is released rather slowly in the time
scale of a few seconds [26,27]. This time scale allows the
removal of heat released from the nanoclusters during the
process of vibrational relaxation of excited N2 molecules
by the high heat conductance of superfluid helium [28].
Another part of the N2 molecule excitation transfers effi-
ciently to the stabilized atoms and is subsequently released
by light emission. These two processes prevent the thermal
explosions of nanoclusters [29]. As a consequence the en-
sembles of molecular nitrogen nanoclusters with high con-
centrations of nitrogen atoms are stable upon immersion
into superfluid helium. The mechanism of thermolumine-
scence in solid nitrogen containing stabilized nitrogen at-
oms is well understood [30–32]. Two ground state nitrogen
atoms recombine to form metastable nitrogen molecules.
4 4 3
2N( ) N( ) N ( )uS S A ++ → Σ . (1)
Energy from these molecules can be transferred to
ground state nitrogen atoms stabilized in the nanoclusters.
3 4 2 1
2 2N ( ) N( ) N( ) N ( )u uA S D X+ +Σ + → + Σ . (2)
These excited N(2D) nitrogen atoms emit the α-group.
2 4N( ) N( )D S→ + α-group. (3)
Similarly for the δ-group, metastable nitrogen mole-
cules can excite stabilized nitrogen atoms, to the higher
N(2P) metastable state.
3 4 2 1
2 2N ( ) N( ) N( ) N ( )u uA S P X+ +Σ + → + Σ (4)
which emit the δ-group
2 4N( ) N( )P D→ + δ-group. (5)
In this work we studied the influence of the rotation
speed of the beaker with He II on the intensity of lumines-
cence of nitrogen atoms in the process of injecting
nanoclusters into rotating He II. It was found experimentally
(see Figs. 2 and 3) that rotation of the beaker with He II sub-
stantially increases the intensity of luminescence of nitrogen
atoms in molecular nitrogen nanoclusters immersed in He II.
Increasing the rotation speed of the beaker with He II from
3 rad/s to 7 rad/s led to 1.5–6 fold increase of α-group inten-
sity for the gas mixtures studied. When we increased the
flux of nanoclusters by changing gas mixture from N2:He =
= 1:400 to gas mixture N2:He =1:100 the intensity of lumi-
nescence from nanoclusters in rotating He II also increased
for each of the three rotation speeds investigated as seen in
Fig. 7. In our earlier work we found that applying tempera-
ture gradients to the collection of nanoclusters immersed in
He II led to the initiation of chemical reactions of nitrogen
Fig. 7. (Color online) Dependence of integrated intensity of
N atom δ-group observed during the injection of nitrogen-helium
gas mixtures N2 = 1:100 (black squares), 1:200 (red circles),
1:400 (blue triangles) into He II on the rotation speed of the
beaker. Integrated intensities of δ-group lines were obtained from
the deconvolution of the spectra shown in Fig. 6(a).
360 Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3
Rotationally induced luminescence of nanoclusters immersed in superfluid helium
atoms stored on the surfaces of the nanoclusters [15]. The
luminescence of ensembles of nanoclusters immersed in
He II was found to be correlated with the vortex density in
bulk He II. This correlation was explained by using a model,
which suggested that some loose nanoclusters were captured
in the vortex cores in He II. Inside the vortex cores nano-
clusters collide more efficiently and the recombination of
nitrogen atoms residing on surfaces of nanoclusters was
initiated. As a result of nitrogen atom recombination and
other processes described above, nitrogen atom lumines-
cence was observed. The intensity of this luminescence thus
tended to increase with the density of vortices in the He II.
We follow the same model to explain the results ob-
tained in this work, only the method of forming vortices is
more straightforward. By rotating our beaker containing
He II we created an array of quantum vortices, which
aligned parallel to the axis of the beaker corresponding to
the direction of the injected flux of nanoclusters entering
bulk He II. When nanoclusters enter into bulk He II, they
introduce a heat flux, which is compensated by the super-
fluid component of He II. The superfluid component mo-
ves to the location of the entering nanoclusters, while sim-
ultaneously the normal component of helium moves in the
opposite direction. Nanoclusters can move together with
the normal component of helium. Thus nanoclusters can be
captured in vortex cores. Increasing vortex density by rota-
tion of the beaker should increase the efficiency for captur-
ing nanoclusters into the array of vortex cores. Inside the
vortex cores the collision rate of nanoclusters becomes
larger [14]. Collisions of pairs of nanoclusters can lead to
recombination of nitrogen atoms residing on their surfaces.
As a result, rotation of the beaker can initiate chemical
reactions between nitrogen atoms in the vortex cores, lead-
ing to formation of highly excited nitrogen molecules. The
energy from excited nitrogen molecules was efficiently
transferred to stabilized nitrogen atoms, which was respon-
sible for the increased luminescence.
The density of the quantized vortices in He II, L, is giv-
en by the Feynman rules with L = 2000 Ω·cm–2, where Ω
is the angular velocity of the beaker in rad/s. The observed
increase in the intensity of N atom luminescence when
rotation speed of He II was increased from 3 to 7.5 rad/s
can be explained by the proportional increase of the vortex
density from 6000 cm–2 to 15000 cm–2.
The increase in the intensity of luminescence for each ro-
tation speed of the beaker with He II when the content of N2
molecules in the condensed gas mixtures was increased can
be explained by an increase of the flux of nanocluster partic-
ipating in chemical reactions in the vortex cores. The model
works well for explaining the behavior of the α-group emis-
sion of N atoms in nanoclusters injected into a rotating
beaker with He II.
The behavior of δ-group emission of N atoms is similar
at low rotation speeds of He II, but at higher rotation speed
(7.5 rad/s) the intensity of δ-group emission was saturated
(see Fig. 7). To understand the latter result, additional inves-
tigations are needed. It may be that differences in the beha-
vior of α-group and δ-group emissions are somehow con-
nected to differences in the lifetimes of the 2D and 2P states
of nitrogen atoms in the N2 solid matrix, which are equal to
30 s and 1 ms, respectively, or related to differences in the
formation of these metastable states of N atoms.
5. Conclusions
1. We observed direct correlation between the increase
of rotation speed of the beaker with He II and the increase
of luminescence intensity of N atom α-group in molecular
nitrogen nanoclusters during their injection into a rotating
beaker with He II. The increase of the luminescence inten-
sity with increasing He II rotation speed was explained by
the initiation of chemical reactions of N atoms on the sur-
faces of nanoclusters trapped inside vortex cores. Increas-
ing the rotation speed of He II led to an increase of the
vortex density and, correspondingly, an enhancement of
the processes of chemical reactions involving trapped
nanoclusters in the vortex cores.
2. The method of initiation of luminescence of nitrogen
nanoclusters immersed in He II can be used to visualize
vortex cores and to study quantum turbulence in He II.
3. This method opens the possibility of initiating chemi-
cal reactions for a variety of free radicals residing on the
surfaces of nanoclusters immersed in bulk He II. It may also
provide new possibilities for synthesis of exotic new species.
Acknowledgments
This work has been supported by the NSF grant number
# DMR 1707565, the ONR Award N00014-16-1-3054 and
AFOSR grant #FA9550-18-0100.
________
1. G.P Bewley, D.P. Lathrop, and K.R. Sreenivasan, Nature
441, 588 (2006).
2. W.F. Vinen, J. Low Temp. Phys. 145, 7 (2006).
3. C.F. Barenghi, L. Skrbek, and K.R. Sreenivasan, Proc. Natl.
Acad. Sci. USA, (Suppl. 1) 111, 4647 ( 2014).
4. Y.A. Sergeev and C.F. Barenghi, J. Low Temp. Phys. 157,
429 (2009).
5. G.P. Bewley, M.S. Paoletti, K.R. Sreenivasan, and D.P.
Lathrop, Proc. Natl. Acad. Sci. USA 105, 13707 (2008).
6. E. Fonda, D.P. Meichle, N.T. Ouellette, S. Hormoz, and D.P.
Lathrop, Proc. Natl. Acad. Sci. USA, (Suppl. 1) 111, 4707
(2014).
7. M.S. Paoletti, M.E. Fisher, K.R. Sreenivasan, and D.P.
Lathrop, Phys. Rev. Lett. 101, 154501 (2008).
8. M.La Mantia, D. Duda, M. Rotter, and L. Skrbek, J. Fluid
Mech. 717, R9 (2013).
9. W. Guo, J.D. Wright, S.B. Cahn, J.A. Nikkel, and D.N.
McKinsey, Phys. Rev. Lett. 102, 235301 (2009).
10. D.E. Zmeev, F. Pakpour, P.M. Walmsley, A.I. Golov,
W. Guo, D.N. McKinsey, G.G. Ihas, P.V.E. McClintock,
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3 361
https://doi.org/10.1007/s10909-006-9240-6
https://doi.org/10.1073/pnas.1400033111
https://doi.org/10.1073/pnas.1400033111
https://doi.org/10.1007/s10909-009-9994-8
https://doi.org/10.1073/pnas.0806002105
https://doi.org/10.1073/pnas.1312536110
https://doi.org/10.1103/PhysRevLett.101.154501
https://doi.org/10.1017/jfm.2013.31
https://doi.org/10.1017/jfm.2013.31
https://doi.org/10.1103/PhysRevLett.102.235301
P.T. McColgan, S. Sheludiakov, P.M. Rentzepis, D.M. Lee, and V.V. Khmelenko
S.N. Fisher, and W.F. Vinen, Phys. Rev. Lett. 110, 175303
(2013).
11. W. Guo, S.B. Cahn, J.A. Nikkel, W.F. Vinen, and D.N.
McKinsey, Phys. Rev. Lett. 105, 045301 (2010).
12. W. Guo, M. La Mantia, D.P. Lathrop, and S.W. Van Sciver,
Proc. Natl. Acad. Sci. 111, 4653 (2014).
13. E.B. Gordon, A.V. Karabulin, V.I. Matyushenko, V.D.
Sizov, and I.I. Khodos, J. Exp. Theor. Phys. 112, 1061
(2011).
14. E.B. Gordon, A.V. Karabulin, V.I. Matyushenko, V.D.
Sizov, and I.I. Khodos, Chem. Phys. Lett. 519-520, 64
(2012).
15. A. Meraki, P.T. McColgan, P.M. Rentzepis, R.Z. Li, D.M.
Lee, and V.V. Khmelenko, Phys. Rev. B 95, 104502 (2017).
16. E.B. Gordon, L.P. Mezhov-Deglin, and O.F. Pugachev, J.
Exp. Theor. Phys. Lett. 19, 63 (1974).
17. S. Mao, R.E. Boltnev, V.V. Khmelenko, and D.M. Lee, Fiz.
Nizk. Temp. 38, 1313 (2012) [Low Temp. Phys. 38, 1037
(2012)].
18. H.E. Hall and W.F. Vinen. Proc. Roy. Soc. London A 238,
204 (1956).
19. E.B. Gordon, M.I. Kulish, A.V. Karabulin, V.I. Matyushenko,
E.V. Dyatlova, A.S. Gordienko, and M.E. Stepanov, Fiz. Nizk.
Temp. 43, 1316 (2017) [Low Temp. Phys. 43, 1055 (2017)].
20. E.B. Gordon, V.V. Khmelenko, A.A. Pelmenev, E.A. Popov,
and O.F. Pugachev, Chem. Phys. Lett. 155, 301 (1989).
21. R.E. Boltnev, I.N. Krushinskaya, A.A. Pelmenev, E.A.
Popov, D.Yu. Stolyarov, and V.V. Khmelenko, Fiz. Nizk.
Temp. 31, 723 (2005) [Low Temp. Phys. 31, 547 (2005)].
22. E.P. Bernard, R.E. Boltnev, V.V. Khmelenko, and D.M. Lee,
J. Low Temp. Phys. 134, 199 (2004).
23. S.I. Kiselev, V.V. Khmelenko, D.M. Lee, V. Kiryukhin, R.E.
Boltnev, E.B. Gordon, and B. Keimer, Phys. Rev. B 65,
024517 (2001).
24. V. Kiryukhin, B. Keimer, R.E. Boltnev, V.V. Khmelenko,
and E.B. Gordon, Phys. Rev. Lett. 79, 1774 (1997).
25. V. Kiryukhin, E.P. Bernard, V.V. Khmelenko, R.E. Boltnev,
N.V. Krainyukova, and D.M. Lee, Phys. Rev. Lett. 98,
195506 (2007).
26. A.A. Ovchinnikov, Sov. Phys. J. Exp. Teor. Phys. 30, 147
(1970).
27. K. Dressler, O. Oehler, and D.A. Smith, Phys. Rev. Lett. 34,
1364 (1975).
28. V. Arp, Cryogenics 10, 96 (1970).
29. E.B. Gordon, L.P. Mezhov-Deglin, O.F. Pugachev, and V.V.
Khmelenko, Sov. Phys. J. Exp. Teor. Phys. 46, 502 (1977).
30. A.M. Bass and H.P. Broida, Formation and Trapping of
Free Radicals, Academic Press, New York, London (1960).
31. O. Oehler, D. A. Smith, and K. Dressler, J. Chem. Phys. 66,
2097 (1977).
32. A. Meraki, S. Mao, P.T. McColgan, R.E. Boltnev, D.M. Lee,
and V.V. Khmelenko, J. Low Temp. Phys. 185, 269 (2016).
___________________________
Індукована обертанням люмінесценція
нанокластерів, які знаходяться у надплинному гелії
P.T. McColgan, S. Sheludiakov, P.M. Rentzepis,
D.M. Lee, and V.V. Khmelenko
Досліджено вплив швидкості обертання склянки з надплин-
ним гелієм (He II) на інтенсивність люмінесценції нано-
кластерів, які знаходяться всередині He II. Спостерігається
збільшення емісії α-групи атомів азоту (перехід 2D → 4S) в
нанокластерах, яке корелювало зі збільшенням швидкості обер-
тання склянки. Збільшення люмінесценції також спостерігалося
при збільшенні вмісту молекулярного азоту в азотно-гелієвій
газовій суміші, яку використовували для отримання нано-
кластерів молекулярного азоту. Ми припускаємо, що цей ефект
пов'язаний зі зміною щільності квантових вихорів в He II при
зміні швидкості обертання склянки. При збільшенні щільності
вихорів ймовірність захоплення нанокластеров в серцевинах
вихорів також підвищується. Усередині серцевин вихорів
відбувається зіткнення нанокластерів, внаслідок цього від-
бувається рекомбінація атомів азоту, що знаходяться на
поверхні нанокластерів, та їх люмінесценція.
Ключові слова: люмінесценція, квантові вихори, оптична
спектроскопія, нанокластери.
Индуцированная вращением люминесценция
нанокластеров, находящихся в сверхтекучем гелии
P.T. McColgan, S. Sheludiakov, P.M. Rentzepis,
D.M. Lee, and V.V. Khmelenko
Исследовано влияние скорости вращения стакана со
сверхтекучим гелием (He II) на интенсивность люминесцен-
ции нанокластеров, находящихся внутри He II. Наблюдается
увеличение эмиссии α-группы атомов азота (переход 2D→4S)
в нанокластерах, которое коррелировало с увеличением ско-
рости вращения стакана. Увеличение люминесценции также
наблюдалось при повышении содержания молекулярного
азота в азотно-гелиевой газовой смеси, используемой для
получения нанокластеров молекулярного азота. Мы предпо-
лагаем, что этот эффект связан с изменением плотности
квантовых вихрей в He II при изменении скорости вращения
стакана. При увеличении плотности вихрей вероятность за-
хвата нанокластеров в сердцевинах вихрей также увеличи-
вается. Внутри сердцевин вихрей происходит столкновение
нанокластеров, в результате которого происходит рекомби-
нация атомов азота, находящихся на поверхности нанокла-
стеров, и их люминесценция.
Ключевые слова: люминесценция, квантовые вихри, оптиче-
ская спектроскопия, нанокластеры.
362 Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3
https://doi.org/10.1103/PhysRevLett.110.175303
https://doi.org/10.1103/PhysRevLett.105.045301
https://doi.org/10.1073/pnas.1312546111
https://doi.org/10.1134/S1063776111040182
https://doi.org/10.1016/j.cplett.2011.11.020
https://doi.org/10.1103/PhysRevB.95.104502
https://doi.org/10.1063/1.4765092
https://doi.org/10.1063/1.4765092
https://doi.org/10.1063/1.5004447
https://doi.org/10.1016/0009-2614(89)85329-1
https://doi.org/10.1063/1.2001631
https://doi.org/10.1023/B:JOLT.0000012556.69060.eb
https://doi.org/10.1103/PhysRevB.65.024517
https://doi.org/10.1103/PhysRevLett.79.1774
https://doi.org/10.1103/PhysRevLett.98.195506
https://doi.org/10.1103/PhysRevLett.34.1364
https://doi.org/10.1016/0011-2275(70)90078-0
https://doi.org/10.1063/1.434171
https://doi.org/10.1007/s10909-016-1557-1
1. Introduction
2. Experimental setup
3. Experimental results
4. Discussion
5. Conclusions
Acknowledgments
|